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Emeritus Professor Anthony Larkum

Biography

My early work was concerned with the processes of ion uptake in roots and giant algal cells. However, my interest in sub-aquatic physiology led increasingly to programs involving algae and seagrasses.

More recently, much of my research effort in this area has been devoted to photoinhibition and UV inhibition of algae and corals including algae in coral reefs and coral bleaching mechanisms and since 1997 my major work has been devoted to understanding the phenomenon of mass coral bleaching, which has been linked to increase in surface sea temperatures and thus to global warming.

In addition I have been interested in novel cyanobacteria, such as Acaryochloris, which have novel chlorophylls capable of absorbing near infra-red light.

A further interest has been the choice and use of microalgae for biofuel research and at UTS I will be working with the C3 Aquatic Processes Group in the Algal Biofuels Research program..

Professional

EDITORIAL BOARDS

  • Trends in Plant Science
  • Limnology and Oceanography
  • Phycologia

Image of Anthony Larkum
Adjunct Professor, Climate Change Cluster
Associate Member, Climate Change Cluster
 
Phone
+61 2 9514 7533

Research Interests

Books

Larkum, A.W.D., Orth, R.J. & Duarte, C.M. 2006, Seagrasses: Biology, ecology and conservation.
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Seagrasses are unique plants; the only group of flowering plants to recolonise the sea. They occur on every continental margin, except Antarctica, and form ecosystems which have important roles in fisheries, fish nursery grounds, prawn fisheries, habitat diversity and sediment stabilisation. Over the last two decades there has been an explosion of research and information on all aspects of seagrass biology. However the compilation of all this work into one book has not been attempted previously. In this book experts in 26 areas of seagrass biology present their work in chapters which are state-of-the-art and designed to be useful to students and researchers alike. The book not only focuses on what has been discovered but what exciting areas are left to discover. The book is divided into sections on taxonomy, anatomy, reproduction, ecology, physiology, fisheries, management, conservation and landscape ecology. It is destined to become the chosen text on seagrasses for any marine biology course. © 2006/2007 Springer. All Rights Reserved.
King, R.J., Hutchings, P.A., Larkum, A.W.D. & West, R.J. 1991, Southeastern Australia.
Outlines the major environmental features of the littoral zone and introduces the characteristic biota of the major habitats: rocky shores, sandy beaches and coastal lagoons, estuaries and embayments. Comments are made on biogeography. The biota is particularly rich and diverse. Resumes are provided of the nature of: macroalgae, seagrasses, fishes, echinoderms, molluscs, Crustacea and polychaetes. Plant biomass and annual productivity are noted for algae and seagrasses, and decomposition and nutrients are discussed. -P.J.Jarvis

Chapters

Li, Y., Larkum, A., Schliep, M.T., Kuhl, M., Neilan, B. & Chen, M. 2013, 'Newly isolated Chl d-containing cyanobacteria' in Kuang, T., Lu, C. & Zhang, L. (eds), Photosynthesis Research for Food, Fuel and the Future - 15th International Conference on Photosynthesis, Springer-Verlag GmbH, Beijing, pp. 686-690.
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Stromatolites are sedimentary structures formed by microbial mats that are typically found in limestone-or dolostone-rich environments. Shark Bay, Australia, has abundant examples of living marine stromatolites. Although the stromatolites from Shark Bay are only about 20003000 years old, they are similar to fossilized evidence of life found on Earth up to 3.5 billion years ago. Using infra-red light centred at 720 nm, new chlorophyll d-containing microorganisms were isolated from the living stromatolites (collected from Shark Bay, Western Australia) and red algae on mangrove pneumatophores (collected from the Georges River, Sydney, Australia) and enriched in KES+ seawater medium. Microscopic examination of the red-light enriched cultures confirmed that they are Acaryochloris-like cyanobacteria. Using cyanobacterial-specific 16S rRNA gene primers, we obtained almost full length sequences of 16S rDNA from the newly isolated Chl d-containing cyanobacteria. The sequences shared 98% identity with Acaryochloris marina MBIC11017. Interestingly, the strain isolated from stromatolites (designated as ssball1 strain) was more similar to Acaryochloris sp CR111A while the strain isolated from Georges River (designated as Mangrove1 strain) was more closely related to Acaryochloris sp CCMEE 5401, which was isolated from an inland lake, Salton Sea in California,. Pigment composition of the newly isolated strains were determined using HPLC, However, no obvious differences were noted. Chl d was the major photopigment while Chl a was present as a minor photopigment, about 2%3.5 % of the total chlorophyll.
Larkum, A. 2012, 'Harvesting solar energy through natural or artificial photosynthesis: Scientific, social, political and economic implications' in Wydrzynski, T.J. & Hillier, W. (eds), Molecular Solar Fuels, Royal Society of Chemistry, United Kingdom, pp. 1-19.
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Natural photosynthesis is an inherently inefficient process that developed millions or even billions of years ago. Thus present systems for harvesting solar energy in the form of organic carbon are inefficient compared with solar photovoltaic cells. The highest productivities are about 1% compared with ~10% for solar cells. Somewhat higher rates can be envisaged in the future but only through the use of a high solar footprint (the area of the Earth's surface needed to sustain a certain energy output), i.e. by using extra energy, which in a long-term sustainable world can come only from solar energy. While bioenergy production from algae may be lead to even greater efficiencies in the future it seems that this will only come about by an even higher solar footprint. Additionally, while bioenergy production may seem to be favourable in terms of carbon footprint, in practice there are several unfavourable outcomes. Further, bioenergy production immediately conflicts with use of the Earth's surface for food production and/or the need to maintain biodiversity. Thus artificial photosynthesis with very much higher expected efficiencies than natural photosynthesis is a worthwhile goal, in that it could potentially compete in efficiency with energy production by photovoltaic cells.
Chen, M., Donohoe, K., Crossett, B., Schliep, M.T. & Larkum, A. 2008, 'Molecular bases of antenna systems adaptation in a Chl d- containing organism' in Allen, J.F., Ganntt, E., Golbeck, J. & Osmond, B. (eds), Photosynthesis: Energy from the Sun, Springer.
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Kuhl, M., Chen, M. & Larkum, A. 2007, 'Biology of the Chlorophyll D-Containing Cyanobacterium Acaryochloris Marina' in Seckbach, J. (ed), Algae and Cyanobacteria in Extreme Environments, Springer, Netherlands, pp. 101-123.
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Oxygenic phototrophs (cyanobacteria, algae and higher plants) primarily absorb solar energy in the visible spectral (400700 nm) region by use of various chlorophylls, while anoxygenic phototrophs are bacteria, which can absorb infrared wavelengths (>7001100 nm) by use of different bacteriochlorophylls (Overmann and Garcia-Pichel, 2004). Each of the groups also has a variety of characteristic antenna pigments and other accessory pigments that can enhance light capture and/or provide protection against excess actinic light and UV-radiation in specific habitats. However, amongst these broadly defined groups there are outlier organisms exhibiting atypical photopigmentation
Larkum, A., Drew, E. & Ralph, P.J. 2006, 'Photosynthesis and Metabolism in Seagrasses at the Cellular Level' in Larkum, A.W.D., Orth, R.J. & Dyarte, C.M. (eds), Seagrasses:Biology, Ecology and Conservation, Springer, Dordrecht, The Netherlands, pp. 323-345.
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Kuhl, M. & Larkum, A. 2002, 'The microenvironment and photosynthetic performance of Prochloron sp. in symbiosis with didemnid ascidians' in Cellular Origin, Life in Extreme Habitats and Astrobiology, Springer, Netherlands, pp. 273-290.

Conferences

Hsu, S., Paoletti, C., Torres, M., Ritchie, R.J., Larkum, A. & Grillet, C. 2012, 'Light transmission of the marine diatom Coscinodiscus wailesii', Proceedings of SPIE vol 8339: Bioinspiration, Biomimetics, and Bioreplication 2012, Bioinspiration, Biomimetics, and Bioreplication 2012, SPIE, San Diego, United States, pp. 1-8.
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The results of a detailed investigation of light transmission behavior of a centric marine diatom species Coscinodiscus wailesii are reported. We measured 3-dimentional intensity distributions of both broadband and monochromatic light transmitted through individual valves of the diatom in air and water. Cross-sectional intensity profiles of transmitted light indicates valves of C. wailesii can concentrate light into certain regions. At a distance from the valve shorter than its diameter, light intensities close to the optical axis are relatively higher than those in the surrounds; at a longer distance, transmitted light intensities display ring-shaped profiles. The distance showing this light concentration characteristic becomes shorter as the wavelength of incoming light goes up. These results may offer insight into the understanding of biological functions of diatom frustules' intricate structures and inspire new optical biomimetic applications.
Schliep, M.T., Chen, M., Larkum, A. & Quinnell, R. 2007, 'The function of MgDVP in a chlorophyll d-containing organism', Photosynthesis. Energy from the Sun 14th International Congress on Photosynthesis, 14th International Congress on Photosynthesis, Springer, Glasgow, pp. 1125-1128.
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Chen, M., Donohoe, K., Crossett, B., Schliep, M.T. & Larkum, A. 2007, 'Molecular basis of antenna system adaptation in a Chl d- containing organism', Photosynthesis. Energy from the Sun: 14th International Congress on Photosynthesis, 14th International Congress on Photosynthesis, Springer, Glasgow, pp. 243-246.
Salih, A., Wiedenmann, J., Matz, M., Larkum, A.W. & Cox, G. 2006, 'Photoinduced activation of GFP-like proteins in tissues of REEF corals', Progress in Biomedical Optics and Imaging - Proceedings of SPIE.
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A variety of fluorescent and chromophoric proteins homologous to the green fluorescent protein (GFP) has been recently discovered and cloned from non-bioluminescent marine animals, such as corals, and now provide a multitude of colors for use in fluorescence imaging applications. Recently, a novel fluorescence imaging methodology has emerged that utilizes the unique photoactivatory property of several GFP-like proteins, which respond to irradiation by altering their optical properties, thereby providing a new spatio-temporal capability to the GFP-based imaging applications. During our studies of GFP-like proteins from the Great Barrier Reef corals, several novel photoactivatable (PA) GFP-like proteins have been discovered. These include fluorescence photo-amplifiers and reversible photoswitchers, similar to PA jelly-fish derived PA-GFP and Dronpa, that greatly increase their emissions following ultraviolet-A (UVA) irradiation; the red-to-green (R-to-G) converters, similar to DsRed, that rapidly change to green color following single- or 2-photon irradiation; the green-to-red (G-to-R) converters, that acquire bright red fluorescence following UV-violet irradiation, similar to Kaede-like proteins; and the kindling GFP-like proteins, that are non fluorescent, but rapidly acquire bright fluorescence after green light irradiation. We report on the various optical characteristics of these coral PA proteins that may be used to expand the scope of the available fluorescence bio-imaging technologies.
Salih, A., Larkum, A., Cronin, T., Wiedenmann, J., Szymczak, R., Cox, G. & 2004, 'Biological properties of coral GFP-type proteins provide clues for engineering novel optical probes and biosensors.', GENETICALLY ENGINEERED AND OPTICAL PROBES FOR BIOMEDICAL APPLICATIONS II, pp. 61-72.
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Salih, A., Cox, G. & Larkum, A.W. 2003, 'Cellular organization & spectral diversity of GFP-like proteins in live coral cells studied by single & multi-photon imaging & microspectroscopy', Proceedings of SPIE - The International Society for Optical Engineering, pp. 194-200.
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Tissues of many marine invertebrates of class Anthozoa contain intensely fluorescent or brightly coloured pigments. These pigments belong to a family of photoactive proteins closely related to Green Fluorescent Protein (GFP), and their emissions range from blue to red wavelengths. The great diversity of these pigments has only recently been realised. To investigate the role of these proteins in corals, we have performed an in vivo fluorescent pigment (FP) spectral and cellular distribution analyses in live coral cells using single and multi-photon laser scanning imaging and microspectroscopy. These analyses revealed that even single colour corals contain spectroscopically heterogeneous pigment mixtures, with 2-5 major colour types in the same area of tissue. They were typically arranged in step-wise light emission energy gradients (e.g. blue, green, yellow, red). The successive overlapping emission-excitation spectral profiles of differently coloured FPs suggested that they were suited for sequential energy coupling. Traces of red FPs (emission = 570-660 nm) were present, even in non-red corals. We confirmed that radiative energy transfer could occur between separate granules of blue and green FPs and that energy transfer was inversely proportional to the square of the distance between them. Multi-photon micro-spectrofluorometric analysis gave significantly improved spectral resolution by restricting FP excitation to a single point in the focal plane of the sample. Pigment heterogeneity at small scales within granules suggested that fluorescence resonance energy transfer (FRET) might be occurring, and we confirmed that this was the case. Thus, energy transfer can take place both radiatively and by FRET, probably functioning in photoprotection by dissipation of excessive solar radiation.
Wolterding, M. & Larkum, A.W.D. 2002, 'Post-wildfire leaf production in the Australian seagrass Posidonia australis', Bulletin of Marine Science, pp. 1207-1214.
The effect of a nearby wildfire on Posidonia australis leaf production was examined through comparison with pre-fire values recorded the previous year and with control groups growing some distance from the fire. Post-fire leaf growth, leaf area and leaf width increased significantly over pre-fire levels measured the year before. Control groups showed no significant increases in these variables over the same time interval. The rapid, significant increase in post-fire leaf production suggests that, wildfires can have a major impact on summer P. australis growth, most likely through increasing nutrient availability.

Journal articles

Del Campo, J., Pombert, J.F., Šlapeta, J., Larkum, A. & Keeling, P.J. 2017, 'The 'other' coral symbiont: Ostreobium diversity and distribution.', The ISME journal, vol. 11, pp. 296-299.
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Ostreobium is an endolithic algal genus thought to be an early-diverging lineage of the Bryopsidales (Ulvophyceae, Chlorophyta). Ostreobium can live in low-light conditions on calcium carbonate substrata in tropical conditions. It is best known as a symbiont of corals, where it lives deep within the animal skeleton and exchanges nitrogen and carbon, as well as providing nutrients and photoassimilates. In contrast to the relatively well-studied role of the photosynthetic zooxanthellae symbionts in coral (Symbiodinium), Ostreobium phylogeny, diversity and distribution are all poorly understood. Here, we describe the phylogenetic position and diversity of Ostreobium based on plastid 16S ribosomal DNA (rDNA), 18S rDNA and rbcL genes from a nuclear genome survey and complete plastid genome, and determined its environmental diversity and distribution by screening the publicly available environmental data for those genes. The results shed light on the phylogeny and the ecology of the 'other' coral symbiont.The ISME Journal advance online publication, 15 July 2016; doi:10.1038/ismej.2016.101.
Najafpour, M.M., Heidari, S., Balaghi, S.E., Hołyńska, M., Sadr, M.H., Soltani, B., Khatamian, M., Larkum, A.W. & Allakhverdiev, S.I. 2017, 'Proposed mechanisms for water oxidation by Photosystem II and nanosized manganese oxides.', Biochim Biophys Acta, vol. 1858, no. 2, pp. 156-174.
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Plants, algae and cyanobacteria capture sunlight, extracting electrons from H2O to reduce CO2 into sugars while releasing O2 in the oxygenic photosynthetic process. Because of the important role of water oxidation in artificial photosynthesis and many solar fuel systems, understanding the structure and function of this unique biological catalyst forms a requisite research field. Herein the structure of the water-oxidizing complex and its ligand environment are described with reference to the 1.9Å resolution X-ray-derived crystallographic model of the water-oxidizing complex from the cyanobacterium Thermosynechococcus vulcanus. Proposed mechanisms for water oxidation by Photosystem II and nanosized manganese oxides are also reviewed and discussed in the paper.
Wangpraseurt, D., Holm, J.B., Larkum, A.W.D., Pernice, M., Ralph, P.J., Suggett, D.J. & Kühl, M. 2017, 'In vivo Microscale Measurements of Light and Photosynthesis during Coral Bleaching: Evidence for the Optical Feedback Loop?', Front Microbiol, vol. 8, p. 59.
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Climate change-related coral bleaching, i.e., the visible loss of zooxanthellae from the coral host, is increasing in frequency and extent and presents a major threat to coral reefs globally. Coral bleaching has been proposed to involve accelerating light stress of their microalgal endosymbionts via a positive feedback loop of photodamage, symbiont expulsion and excess in vivo light exposure. To test this hypothesis, we used light and O2 microsensors to characterize in vivo light exposure and photosynthesis of Symbiodinium during a thermal stress experiment. We created tissue areas with different densities of Symbiodinium cells in order to understand the optical properties and light microenvironment of corals during bleaching. Our results showed that in bleached Pocillopora damicornis corals, Symbiodinium light exposure was up to fivefold enhanced relative to healthy corals, and the relationship between symbiont loss and light enhancement was well-described by a power-law function. Cell-specific rates of Symbiodinium gross photosynthesis and light respiration were enhanced in bleached P. damicornis compared to healthy corals, while areal rates of net photosynthesis decreased. Symbiodinium light exposure in Favites sp. revealed the presence of low light microniches in bleached coral tissues, suggesting that light scattering in thick coral tissues can enable photoprotection of cryptic symbionts. Our study provides evidence for the acceleration of in vivo light exposure during coral bleaching but this optical feedback mechanism differs between coral hosts. Enhanced photosynthesis in relation to accelerating light exposure shows that coral microscale optics exerts a key role on coral photophysiology and the subsequent degree of radiative stress during coral bleaching.
Slavov, C., Schrameyer, V., Reus, M., Ralph, P.J., Hill, R., Büchel, C., Larkum, A.W. & Holzwarth, A.R. 2016, '"Super-quenching" state protects Symbiodinium from thermal stress - Implications for coral bleaching.', Biochimica et biophysica acta, vol. 1857, no. 6, pp. 840-847.
The global rise in sea surface temperatures causes regular exposure of corals to high temperature and high light stress, leading to worldwide disastrous coral bleaching events (loss of symbiotic dinoflagellates (Symbiodinium) from reef-building corals). Our picosecond chlorophyll fluorescence experiments on cultured Symbiodinium clade C cells exposed to coral bleaching conditions uncovered the transformations of the alga's photosynthetic apparatus (PSA) that activate an extremely efficient non-photochemical "super-quenching" mechanism. The mechanism is associated with a transition from an initially heterogeneous photosystem II (PSII) pool to a homogeneous "spillover" pool, where nearly all excitation energy is transferred to photosystem I (PSI). There, the inherently higher stability of PSI and high quenching efficiency of P(700)(+) allow dumping of PSII excess excitation energy into heat, resulting in almost complete cessation of photosynthetic electron transport (PET). This potentially reversible "super-quenching" mechanism protects the PSA against destruction at the cost of a loss of photosynthetic activity. We suggest that the inhibition of PET and the consequent inhibition of organic carbon production (e.g. sugars) in the symbiotic Symbiodinium provide a trigger for the symbiont expulsion, i.e. bleaching.
Lichtenberg, M., Larkum, A.W.D. & Kuehl, M. 2016, 'Photosynthetic Acclimation of Symbiodinium in hospite Depends on Vertical Position in the Tissue of the Scleractinian Coral Montastrea curta', FRONTIERS IN MICROBIOLOGY, vol. 7.
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Rehman, A.U., Szabó, M., Deák, Z., Sass, L., Larkum, A., Ralph, P. & Vass, I. 2016, 'Symbiodinium sp. cells produce light-induced intra- and extracellular singlet oxygen, which mediates photodamage of the photosynthetic apparatus and has the potential to interact with the animal host in coral symbiosis.', The New phytologist, vol. 212, pp. 472-484.
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Coral bleaching is an important environmental phenomenon, whose mechanism has not yet been clarified. The involvement of reactive oxygen species (ROS) has been implicated, but direct evidence of what species are involved, their location and their mechanisms of production remains unknown. Histidine-mediated chemical trapping and singlet oxygen sensor green (SOSG) were used to detect intra- and extracellular singlet oxygen ((1) O2 ) in Symbiodinium cultures. Inhibition of the Calvin-Benson cycle by thermal stress or high light promotes intracellular (1) O2 formation. Histidine addition, which decreases the amount of intracellular (1) O2 , provides partial protection against photosystem II photoinactivation and chlorophyll (Chl) bleaching. (1) O2 production also occurs in cell-free medium of Symbiodinium cultures, an effect that is enhanced under heat and light stress and can be attributed to the excretion of (1) O2 -sensitizing metabolites from the cells. Confocal microscopy imaging using SOSG showed most extracellular (1) O2 around the cell surface, but it is also produced across the medium distant from the cells. We demonstrate, for the first time, both intra- and extracellular (1) O2 production in Symbiodinium cultures. Intracellular (1) O2 is associated with photosystem II photodamage and pigment bleaching, whereas extracellular (1) O2 has the potential to mediate the breakdown of symbiotic interaction between zooxanthellae and their animal host during coral bleaching.
Schrameyer, V., Krämer, W., Hill, R., Jeans, J., Larkum, A.W.D., Bischof, K., Campbell, D.A. & Ralph, P.J. 2016, 'Under high light stress two Indo-Pacific coral species display differential photodamage and photorepair dynamics', Marine Biology, vol. 163, no. 8.
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© 2016, Springer-Verlag Berlin Heidelberg.The in hospite Symbiodinium symbiont of corals on shallow reefs relies on photoprotection and photorepair during periods of exposure to short-term high light and/or temperature stress. A coral's susceptibility to bleaching is species specific and determined not only by Symbiodinium type, size and physiology, but also by coral host features. Here, photoprotective, photorepair, photochemical and non-photochemical efficiency parameters of Symbiodinium harboured in two morphologically different coral species were examined on Heron Island (23.4420°S, 151.9140°E) in July 2011. The two coral species were exposed to high light stress for 96 h, with or without inhibition of photosystem (PS) II repair by lincomycin. Symbiodinium harboured in Pocillopora damicornis showed an increase in xanthophyll de-epoxidation under high light exposure, whereas algal symbionts in Pavona decussata showed constant levels of xanthophyll de-epoxidation. High light-treated specimens of P. damicornis maintained steady PsbA protein (D1 protein) content throughout the experiment, but P. decussata showed a peak in PsbA protein content after 48 h of exposure. In hospiteSymbiodinium in P. damicornis had greater content of PsbA protein fragments, suggesting higher accumulation of photodamaged products, compared to Symbiodinium in P. decussata, where both maintained steady PSII photochemical capacity over 96 h of exposure. Under inhibition of PSII repair, both species lost PsbA protein content and PSII photochemical capacity. Both species showed increased heat dissipation under inhibition of PSII repair, but differed in photoprotective strategies and photorepair activity. Our results suggest that, as well as any differences in the symbiont, characteristics of the coral host can alter important physiological responses in Symbiodinium.
Davey, P.A., Pernice, M., Sablok, G., Larkum, A., Lee, H.T., Golicz, A., Edwards, D., Dolferus, R. & Ralph, P. 2016, 'The emergence of molecular profiling and omics techniques in seagrass biology; furthering our understanding of seagrasses.', Functional & Integrative Genomics, vol. 16, no. 5, pp. 465-480.
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Seagrass meadows are disappearing at alarming rates as a result of increasing coastal development and climate change. The emergence of omics and molecular profiling techniques in seagrass research is timely, providing a new opportunity to address such global issues. Whilst these applications have transformed terrestrial plant research, they have only emerged in seagrass research within the past decade; In this time frame we have observed a significant increase in the number of publications in this nascent field, and as of this year the first genome of a seagrass species has been sequenced. In this review, we focus on the development of omics and molecular profiling and the utilization of molecular markers in the field of seagrass biology. We highlight the advances, merits and pitfalls associated with such technology, and importantly we identify and address the knowledge gaps, which to this day prevent us from understanding seagrasses in a holistic manner. By utilizing the powers of omics and molecular profiling technologies in integrated strategies, we will gain a better understanding of how these unique plants function at the molecular level and how they respond to on-going disturbance and climate change events.
Marcelino, V.R., Cremen, M.C., Jackson, C.J., Larkum, A. & Verbruggen, H. 2016, 'Evolutionary dynamics of chloroplast genomes in low light: a case study of the endolithic green alga Ostreobium quekettii.', Genome biology and evolution.
Some photosynthetic organisms live in extremely low light environments. Light limitation is associated with selective forces as well as reduced exposure to mutagens, and over evolutionary timescales it can leave a footprint on species' genomes. Here we present the chloroplast genomes of four green algae (Bryopsidales, Ulvophyceae), including the endolithic (limestone-boring) alga Ostreobium quekettii, which is a low light specialist. We use phylogenetic models and comparative genomic tools to investigate whether the chloroplast genome of Ostreobium corresponds to our expectations of how low light would affect genome evolution. Ostreobium has the smallest and most gene-dense chloroplast genome among Ulvophyceae reported to date, matching our expectation that light limitation would impose resource constraints reflected in the chloroplast genome architecture. Rates of molecular evolution are significantly slower along the phylogenetic branch leading to Ostreobium, in agreement with the expected effects of low light and energy levels on molecular evolution. We expected the ability of Ostreobium to perform photosynthesis in very low light to be associated with positive selection in genes related to the photosynthetic machinery, but instead, we observed that these genes may be under stronger purifying selection. Besides shedding light on the genome dynamics associated with a low light lifestyle, this study helps to resolve the role of environmental factors in shaping the diversity of genome architectures observed in nature.
Lee, H., Golicz, A.A., Bayer, P.E., Jiao, Y., Tang, H., Paterson, A.H., Sablok, G., Krishnaraj, R.R., Chan, C.K., Batley, J., Kendrick, G.A., Larkum, A.W., Ralph, P.J. & Edwards, D. 2016, 'The Genome of a Southern Hemisphere Seagrass Species (Zostera muelleri).', Plant physiology, vol. 172, no. 1, pp. 272-283.
Seagrasses are marine angiosperms that evolved from land plants but returned to the sea around 140 million years ago during the early evolution of monocotyledonous plants. They successfully adapted to abiotic stresses associated with growth in the marine environment, and today, seagrasses are distributed in coastal waters worldwide. Seagrass meadows are an important oceanic carbon sink and provide food and breeding grounds for diverse marine species. Here, we report the assembly and characterization of the Zostera muelleri genome, a southern hemisphere temperate species. Multiple genes were lost or modified in Z. muelleri compared with terrestrial or floating aquatic plants that are associated with their adaptation to life in the ocean. These include genes for hormone biosynthesis and signaling and cell wall catabolism. There is evidence of whole-genome duplication in Z. muelleri; however, an ancient pan-commelinid duplication event is absent, highlighting the early divergence of this species from the main monocot lineages.
Gardner, S.G., Nielsen, D.A., Petrou, K., Larkum, A.W.D. & Ralph, P.J. 2015, 'Characterisation of coral explants: a model organism for cnidarian-dinoflagellate studies', CORAL REEFS, vol. 34, no. 1, pp. 133-142.
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Golicz, A.A., Schliep, M., Lee, H.T., Larkum, A.W.D., Dolferus, R., Batley, J., Chan, C.-.K.K., Sablok, G., Ralph, P.J. & Edwards, D. 2015, 'Genome-wide survey of the seagrass Zostera muelleri suggests modification of the ethylene signalling network', JOURNAL OF EXPERIMENTAL BOTANY, vol. 66, no. 5, pp. 1489-1498.
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Behrendt, L., Brejnrod, A., Schliep, M., Sorensen, S.J., Larkum, A.W.D. & Kuhl, M. 2015, 'Chlorophyll f-driven photosynthesis in a cavernous cyanobacterium', ISME JOURNAL, vol. 9, no. 9, pp. 2108-2111.
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Nielsen, D.A., Pernice, M., Schliep, M., Sablok, G., Jeffries, T.C., Kuehl, M., Wangpraseurt, D., Ralph, P.J. & Larkum, A.W.D. 2015, 'Microenvironment and phylogenetic diversity of Prochloron inhabiting the surface of crustose didemnid ascidians', ENVIRONMENTAL MICROBIOLOGY, vol. 17, no. 10, pp. 4121-4132.
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Tamburic, B., Evenhuis, C.R., Suggett, D.J., Larkum, A.W.D., Raven, J.A. & Ralph, P.J. 2015, 'Gas Transfer Controls Carbon Limitation During Biomass Production by Marine Microalgae', CHEMSUSCHEM, vol. 8, no. 16, pp. 2727-2736.
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Najafpour, M.M., Ghobadi, M.Z., Larkum, A.W., Shen, J.-.R. & Allakhverdiev, S.I. 2015, 'The biological water-oxidizing complex at the nano-bio interface.', Trends in plant science, vol. 20, no. 9, pp. 559-568.
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Photosynthesis is one of the most important processes on our planet, providing food and oxygen for the majority of living organisms on Earth. Over the past 30 years scientists have made great strides in understanding the central photosynthetic process of oxygenic photosynthesis, whereby water is used to provide the hydrogen and reducing equivalents vital to CO2 reduction and sugar formation. A recent crystal structure at 1.9-1.95Å has made possible an unparalleled map of the structure of photosystem II (PSII) and particularly the manganese-calcium (Mn-Ca) cluster, which is responsible for splitting water. Here we review how knowledge of the water-splitting site provides important criteria for the design of artificial Mn-based water-oxidizing catalysts, allowing the development of clean and sustainable solar energy technologies.
Chan, Y.-.W., Millard, A.D., Wheatley, P.J., Holmes, A.B., Mohr, R., Whitworth, A.L., Mann, N.H., Larkum, A.W.D., Hess, W.R., Scanlan, D.J. & Clokie, M.R.J. 2015, 'Genomic and proteomic characterization of two novel siphovirus infecting the sedentary facultative epibiont cyanobacterium Acaryochloris marina.', Environmental microbiology, vol. 17, no. 11, pp. 4239-4252.
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Acaryochloris marina is a symbiotic species of cyanobacteria that is capable of utilizing far-red light. We report the characterization of the phages A-HIS1 and A-HIS2, capable of infecting Acaryochloris. Morphological characterization of these phages places them in the family Siphoviridae. However, molecular characterization reveals that they do not show genetic similarity with any known siphoviruses. While the phages do show synteny between each other, the nucleotide identity between the phages is low at 45-67%, suggesting they diverged from each other some time ago. The greatest number of genes shared with another phage (a myovirus infecting marine Synechococcus) was four. Unlike most other cyanophages and in common with the Siphoviridae infecting Synechococcus, no photosynthesis-related genes were found in the genome. CRISPR (clustered regularly interspaced short palindromic repeats) spacers from the host Acaryochloris had partial matches to sequences found within the phages, which is the first time CRISPRs have been reported in a cyanobacterial/cyanophage system. The phages also encode a homologue of the proteobacterial RNase T. The potential function of RNase T in the mark-up or digestion of crRNA hints at a novel mechanism for evading the host CRISPR system.
Tamburic, B., Guruprasad, S., Radford, D.T., Szabo, M., Lilley, R., Larkum, A., Franklin, J., Kramer, D., Blackburn, S., Raven, J., Schliep, M.T. & Ralph, P.J. 2014, 'The effect of diel temperature and light cycles on the growth of Nannochloropsis oculata in a photobioreactor matrix', PLoS One, vol. 9, no. 1, p. e86047.
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Macreadie, P.I., Baird, M.E., Trevathan-Tackett, S.M., Larkum, A. & Ralph, P.J. 2014, 'Quantifying and modelling the carbon sequestration capacity of seagrass meadows - A critical assessment', Marine Pollution Bulletin, vol. 83, pp. 430-439.
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Seagrasses are among the planets most effective natural ecosystems for sequestering (capturing and storing) carbon (C); but if degraded, they could leak stored C into the atmosphere and accelerate global warming. Quantifying and modelling the C sequestration capacity is therefore critical for successfully managing seagrass ecosystems to maintain their substantial abatement potential. At present, there is no mechanism to support carbon financing linked to seagrass. For seagrasses to be recognised by the IPCC and the voluntary C market, standard stock assessment methodologies and inventories of seagrass C stocks are required. Developing accurate C budgets for seagrass meadows is indeed complex; we discuss these complexities, and, in addition, we review techniques and methodologies that will aid development of C budgets. We also consider a simple process-based data assimilation model for predicting how seagrasses will respond to future change, accompanied by a practical list of research priorities.
Jeans, J., Szabo, M., Campbell, D.A., Larkum, A., Ralph, P.J. & Hill, R. 2014, 'Thermal bleaching induced changes in photosystem II function not reflected by changes in photosystem II protein content of Stylophora pistillata', Coral Reefs, vol. 33, pp. 131-139.
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Wangpraseurt, D., Larkum, A., Franklin, J., Szabo, M., Ralph, P.J. & Kuhl, M. 2014, 'Lateral light transfer ensures efficient resource distribution in symbiont-bearing corals', Journal of Experimental Biology, vol. 217, pp. 489-498.
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Coral tissue optics has received very little attention in the past, although the interaction between tissue and light is central to our basic understanding of coral physiology. Here we used fibre-optic and electrochemical microsensors along with variable chlorophyll fluorescence imaging to directly measure lateral light propagation within living coral tissues. Our results show that corals can transfer light laterally within their tissues to a distance of ~2 cm. Such light transport stimulates O2 evolution and photosystem II operating efficiency in areas >0.51 cm away from direct illumination. Light is scattered strongly in both coral tissue and skeleton, leading to photon trapping and lateral redistribution within the tissue. Lateral light transfer in coral tissue is a new mechanism by which light is redistributed over the coral colony and we argue that tissue optical properties are one of the key factors in explaining the high photosynthetic efficiency of corals.
Wangpraseurt, D., Polerecky, L., Larkum, A., Ralph, P.J., Nielsen, D.A., Pernice, M. & Kuhl, M. 2014, 'The in situ light microenvironment of corals', Limnology and Oceanography, vol. 59, no. 3, pp. 917-926.
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We used a novel diver-operated microsensor system to collect in situ spectrally resolved light fields on corals with a micrometer spatial resolution. The light microenvironment differed between polyp and coenosarc tissues with scalar irradiance (400700 nm) over polyp tissue, attenuating between 5.1- and 7.8-fold from top to base of small hemispherical coral colonies, whereas attenuation was at most 1.5-fold for coenosarc tissue. Fluctuations in ambient solar irradiance induced changes in light and oxygen microenvironments, which were more pronounced and faster in coenosarc compared with polyp tissue. Backscattered light from the surrounding benthos contributed . 20% of total scalar irradiance at the coral tissue surface and enhanced symbiont photosynthesis and the local O2 concentration, indicating an important role of benthos optics for coral ecophysiology. Light fields on corals are species and tissue specific and exhibit pronounced variation on scales from micrometers to decimeters. Consequently, the distribution, genetic diversity, and physiology of coral symbionts must be coupled with the measurements of their actual light microenvironment to achieve a more comprehensive understanding of coral ecophysiology.
Behrendt, L., Nielsen, J., Sorensen, S.J., Larkum, A., Winther, J.R. & Kuhl, M. 2014, 'Rapid TaqMan-based quantification of chlorophyll d-containing cyanobacteria in the genus Acaryochloris', Applied and Environmental Microbiology, vol. 80, no. 10, pp. 3244-3249.
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Reports of the chlorophyll (Chl) d-containing cyanobacterium Acaryochloris have accumulated since its initial discovery in 1996. The majority of this evidence is based on amplification of the gene coding for the 16S rRNA, and due to the wide geographical distribution of these sequences, a global distribution of Acaryochloris species was suggested. Here, we present a rapid, reliable, and cost-effective TaqMan-based quantitative PCR (qPCR) assay that was developed for the specific detection of Acaryochloris species in complex environmental samples. The TaqMan probe showed detection limits of ~10 16S rRNA gene copy numbers based on standard curves consisting of plasmid inserts. DNA from five Acaryochloris strains, i.e., MBIC11017, CCMEE5410, HICR111A, CRS, and Awaji-1, exhibited amplification efficiencies of >94% when tested in the TaqMan assay. When used on complex natural communities, the TaqMan assay detected the presence of Acaryochloris species in four out of eight samples of crustose coralline algae (CCA), collected from temperate and tropical regions. In three out of these TaqMan-positive samples, the presence of Chl d was confirmed via high-performance liquid chromatography (HPLC), and corresponding cell estimates of Acaryochloris species amounted to 7.6 101 to 3.0 103 per mg of CCA. These numbers indicate a substantial contribution of Chl d-containing cyanobacteria to primary productivity in endolithic niches. The new TaqMan assay allows quick and easy screening of environmental samples for the presence of Acaryochloris species and is an important tool to further resolve the global distribution and significance of this unique oxyphototroph.
Hill, R., Szabo, M., Rehman, A., Vass, I., Ralph, P.J. & Larkum, A. 2014, 'Inhibition of photosynthetic CO2 fixation in the coral Pocillopora damicornis and its relationship to thermal bleaching', Journal of Experimental Biology, vol. 217, pp. 2150-2162.
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Two inhibitors of the CalvinBenson cycle [glycolaldehyde (GA) and potassium cyanide (KCN)] were used in cultured Symbiodinium cells and in nubbins of the coral Pocillopora damicornis to test the hypothesis that inhibition of the CalvinBenson cycle triggers coral bleaching. Inhibitor concentration range-finding trials aimed to determine the appropriate concentration to generate inhibition of the CalvinBenson cycle, but avoid other metabolic impacts to the symbiont and the animal host. Both 3 mmol l-1 GA and 20 µmol l-1 KCN caused minimal inhibition of host respiration, but did induce photosynthetic impairment, measured by a loss of photosystem II function and oxygen production. GA did not affect the severity of bleaching, nor induce bleaching in the absence of thermal stress, suggesting inhibition of the CalvinBenson cycle by GA does not initiate bleaching in P. damicornis. In contrast, KCN did activate a bleaching response through symbiont expulsion, which occurred in the presence and absence of thermal stress. While KCN is an inhibitor of the CalvinBenson cycle, it also promotes reactive oxygen species formation, and it is likely that this was the principal agent in the coral bleaching process. These findings do not support the hypothesis that temperature-induced inhibition of the CalvinBenson cycle alone induces coral bleaching.
Szabo, M., Parker, K.B., Guruprasad, S., Kuzhiumparambil, U., Lilley, R.M., Tamburic, B., Schliep, M.T., Larkum, A., Schreiber, U., Raven, J. & Ralph, P.J. 2014, 'Photosynthetic acclimation of Nannochloropsis oculata investigated by multi-wavelength chlorophyll fluorescence analysis', Bioresource Technology, vol. 167, pp. 521-529.
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Multi-wavelength chlorophyll fluorescence analysis was utilised to examine the photosynthetic efficiency of the biofuel-producing alga Nannochloropsis oculata, grown under two light regimes; low (LL) and high (HL) irradiance levels. Wavelength dependency was evident in the functional absorption cross-section of Photosystem II (sII (?)), absolute electron transfer rates (ETR(II)), and non-photochemical quenching (NPQ) of chlorophyll fluorescence in both HL and LL cells. While sII(?) was not significantly different between the two growth conditions, HL cells upregulated ETR(II) 1.6 to 1.8-fold compared to LL cells, most significantly in the wavelength range of 440-540 nm. This indicates preferential utilisation of blue-green light, a highly relevant spectral region for visible light in algal pond conditions. Under these conditions, the HL cells accumulated saturated fatty acids, whereas polyunsaturated fatty acids were more abundant in LL cells. This knowledge is of importance for the use of N. oculata for fatty acid production in the biofuel industry.
Tamburic, B., Szabo, M., Tran, A., Larkum, A., Suggett, D.J. & Ralph, P.J. 2014, 'Action spectra of oxygen production and chlorophyll a fluorescence in the green microalga Nannochloropsis oculata', Bioresource Technology, vol. 169, pp. 320-327.
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The first complete action spectrum of oxygen evolution and chlorophyll a fluorescence was measured for the biofuel candidate alga Nannochloropsis oculata. A novel analytical procedure was used to generate a representative and reproducible action spectrum for microalgal cultures. The action spectrum was measured at 14 discrete wavelengths across the visible spectrum, at an equivalent photon flux density of 60 µmol photons m-2 s-1. Blue light (~414 nm) was absorbed more efficiently and directed to photosystem II more effectively than red light (~679 nm) at light intensities below the photosaturation limit. Conversion of absorbed photons into photosynthetic oxygen evolution was maximised at 625 nm; however, this maximum is unstable since neighbouring wavelengths (646 nm) resulted in the lowest photosystem II operating efficiency. Identifying the wavelength-dependence of photosynthesis has clear implications to optimising growth efficiency and hence important economic implications to the algal biofuels and bioproducts industries.
Szabo, M., Wangpraseurt, D., Tamburic, B., Larkum, A., Schreiber, U., Suggett, D.J., Kühl, M. & Ralph, P.J. 2014, 'Effective light absorption and absolute electron transport rates in the coral Pocillopora damicornis', Plant Physiology and Biochemistry, vol. 83, pp. 159-167.
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Pulse Amplitude Modulation (PAM) fluorometry has been widely used to estimate the relative photosynthetic efficiency of corals. However, both the optical properties of intact corals as well as past technical constrains to PAM fluorometers have prevented calculations of the electron turnover rate of PSII. We used a new Multi-colour PAM (MC-PAM) in parallel with light microsensors to determine for the first time the wavelength-specific effective absorption cross-section of PSII photochemistry, sII(?), and thus PAM-based absolute electron transport rates of the coral photosymbiont Symbiodinium both in culture and in hospite in the coral Pocillopora damicornis. In both cases, sII of Symbiodinium was highest in the blue spectral region and showed a progressive decrease towards red wavelengths. Absolute values for sII at 440 nm were up to 1.5-times higher in culture than in hospite. Scalar irradiance within the living coral tissue was reduced by 20% in the blue when compared to the incident downwelling irradiance. Absolute electron transport rates of P. damicornis at 440 nm revealed a maximum PSII turnover rate of ca. 250 electrons PSII-1 s-1, consistent with one PSII turnover for every 4 photons absorbed by PSII; this likely reflects the limiting steps in electron transfer between PSII and PSI. Our results show that optical properties of the coral host strongly affect light use efficiency of Symbiodinium. Therefore, relative electron transport rates do not reflect the productivity rates (or indeed how the photosynthesis-light response is parameterised). Here we provide a non-invasive approach to estimate absolute electron transport rates in corals.
Schrameyer, V., Wangpraseurt, D., Hill, R., Kuehl, M., Larkum, A.W.D. & Ralph, P.J. 2014, 'Light Respiratory Processes and Gross Photosynthesis in Two Scleractinian Corals', PLOS ONE, vol. 9, no. 10.
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Torres, M.A., Ritchie, R.J., Lilley, R., Grillet, C. & Larkum, A.W.D. 2014, 'Measurement of photosynthesis and photosynthetic efficiency in two diatoms', New Zealand Journal of Botany, vol. 52, no. 1, pp. 6-27.
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Lockhart, P.J., Larkum, A.W.D., Becker, M. & Penny, D. 2014, 'We are Still Learning About the Nature of Species and Their Evolutionary Relationships', Annals of the Missouri Botanical Garden, vol. 100, no. 1-2, pp. 6-13.
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Schliep, M.T., Cavigliasso, G., Quinnell, R.G., Stranger, R. & Larkum, A. 2013, 'Formyl group modification of chlorophyll a: a major evolutionary mechanism in oxygenic photosynthesis', Plant Cell and Environment, vol. 36, pp. 521-527.
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We discuss recent advances in chlorophyll research in the context of chlorophyll evolution and conclude that some derivations of the formyl side chain arrangement of the porphyrin ring from that of the Chl a macrocycle can extend the photosynthetic active radiation (PAR) of these molecules, for example, Chl d and Chl f absorb light in the near-infrared region, up to ~750 nm. Derivations such as this confer a selective advantage in particular niches and may, therefore, be beneficial for photosynthetic organisms thriving in light environments with particular light signatures, such as red- and near-far-red light-enriched niches. Modelling of formyl side chain substitutions of Chl a revealed yet unidentified but theoretically possible Chls with a distinct shift of light absorption properties when compared to Chl a.
Raven, J., Beardall, J., Larkum, A. & Sanchez-baracaldo, P. 2013, 'Interactions of photosynthesis with genome size and function', Philosophical Transactions of the Royal Society B, vol. 368, no. 1622, pp. 1-11.
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Photolithotrophs are divided between those that use water as their electron donor (Cyanobacteria and the photosynthetic eukaryotes) and those that use a different electron donor (the anoxygenic photolithotrophs, all of them Bacteria). Photolithotrophs wi
Garby, T., Walter, M., Larkum, A. & Neilan, B.A. 2013, 'Diversity Of Cyanobacterial Biomarker Genes From The Stromatolites Of Shark Bay, Western Australia', Environmental Microbiology, vol. 15, no. 5, pp. 1464-1475.
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Families of closely related chemical compounds, which are relatively resistant to degradation, are often used as biomarkers to help trace the evolutionary history of early groups of organisms and the environments in which they lived. Biomarkers derived from hopanoid variations are particularly useful in determining bacterial community compositions. 2-Methylhopananoids have been thought to be diagnostic for cyanobacteria, and 2-methylhopanes in the geological record are taken as evidence for the presence of cyanobacteria-containing communities at the time of sediment deposition. Recently, however, doubt has been cast on the validity of 2-methylhopanes as cyanobacterial biomarkers, since non-cyanobacterial species have been shown to produce significant amounts of 2-methylhopanoids. This study examines the diversity of hpnP, the hopanoid biosynthesis gene coding for the enzyme that methylates hopanoids at the C2 position. Genomic DNA isolated from stromatolite-associated pustular and smooth microbial mat samples from Shark Bay, Western Australia, was analysed for bacterial diversity, and used to construct an hpnP clone library. A total of 117 partial hpnP clones were sequenced, representing 12 operational taxonomic units (OTUs). Phylogenetic analysis showed that 11 of these OTUs, representing 115 sequences, cluster within the cyanobacterial clade. We conclude that the dominant types of microorganisms with the detected capability of producing 2-methylhopanoids within pustular and smooth microbial mats in Shark Bay are cyanobacteria.
Gleason, F.H., van Ogtrop, F., Lilje, O. & Larkum, A. 2013, 'Ecological roles of zoosporic parasites in blue carbon ecosystems', Fungal Ecology, vol. 6, no. 5, pp. 319-327.
Pathosystems describe the relationships between parasites, hosts and the environment. Generally these systems remain in a dynamic equilibrium over time. In this review we examine some of the evidence for the potential impacts of change in dynamic equilibrium in blue carbon ecosystems and the relationships to the amount of stored carbon. Blue carbon ecosystems are marine and estuarine ecosystems along the coasts. Virulent pathogens can be introduced into ecosystems along with non-native hosts. Alteration of environmental conditions, such as temperature, pH and salinity, may cause parasites to dominate the pathosystems resulting in significant decreases in productivity and population sizes of producer hosts and in changes in the overall species composition and function in these ecosystems. Such changes in blue carbon ecosystems may result in accelerated release of carbon dioxide back into the ocean and atmosphere, which could then drive further changes in the global climate. The resiliency of these ecosystems is not known. However, recent evidence suggests that significant proportions of blue carbon ecosystems have already disappeared.
Behrendt, L., Staal, M., Cristescu, S.M., Harren, F.J., Schliep, M., Larkum, A.W. & Kühl, M. 2013, 'Reactive oxygen production induced by near-infrared radiation in three strains of the Chl d-containing cyanobacterium Acaryochloris marina.', F1000Research, vol. 2, p. 44.
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Cyanobacteria in the genus Acaryochloris have largely exchanged Chl a with Chl d, enabling them to harvest near-infrared-radiation (NIR) for oxygenic photosynthesis, a biochemical pathway prone to generate reactive oxygen species (ROS). In this study, ROS production under different light conditions was quantified in three Acaryochloris strains (MBIC11017, HICR111A and the novel strain CRS) using a real-time ethylene detector in conjunction with addition of 2-keto-4-thiomethylbutyric acid, a substrate that is converted to ethylene when reacting with certain types of ROS. In all strains, NIR was found to generate less ROS than visible light (VIS). More ROS was generated if strains MBIC11017 and HICR111A were adapted to NIR and then exposed to VIS, while strain CRS demonstrated the opposite behavior. This is the very first study of ROS generation and suggests that Acaryochloris can avoid a considerable amount of light-induced stress by using NIR instead of VIS for its photosynthesis, adding further evolutionary arguments to their widespread appearance.
Raven, J.A., Beardall, J., Larkum, A.W.D. & Sánchez-Baracaldo, P. 2013, 'Interactions of photosynthesis with genome size and function.', Philosophical transactions of the Royal Society of London. Series B, Biological sciences, vol. 368, no. 1622, p. 20120264.
Photolithotrophs are divided between those that use water as their electron donor (Cyanobacteria and the photosynthetic eukaryotes) and those that use a different electron donor (the anoxygenic photolithotrophs, all of them Bacteria). Photolithotrophs with the most reduced genomes have more genes than do the corresponding chemoorganotrophs, and the fastest-growing photolithotrophs have significantly lower specific growth rates than the fastest-growing chemoorganotrophs. Slower growth results from diversion of resources into the photosynthetic apparatus, which accounts for about half of the cell protein. There are inherent dangers in (especially oxygenic) photosynthesis, including the formation of reactive oxygen species (ROS) and blue light sensitivity of the water spitting apparatus. The extent to which photolithotrophs incur greater DNA damage and repair, and faster protein turnover with increased rRNA requirement, needs further investigation. A related source of environmental damage is ultraviolet B (UVB) radiation (280-320 nm), whose flux at the Earth's surface decreased as oxygen (and ozone) increased in the atmosphere. This oxygenation led to the requirements of defence against ROS, and decreasing availability to organisms of combined (non-dinitrogen) nitrogen and ferrous iron, and (indirectly) phosphorus, in the oxygenated biosphere. Differential codon usage in the genome and, especially, the proteome can lead to economies in the use of potentially growth-limiting elements.
Larkum, A., Ross, I.L., Kruse, O. & Hankamer, B. 2012, 'Selection, breeding and engineering of microalgae for bioenergy and biofuel production', Trends In Biotechnology, vol. 30, no. 4, pp. 198-205.
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Microalgal production technologies are seen as increasingly attractive for bioenergy production to improve fuel security and reduce CO2 emissions. Photosynthetically derived fuels are a renewable, potentially carbon-neutral and scalable alternative reserve. Microalgae have particular promise because they can be produced on non-arable land and utilize saline and wastewater streams. Furthermore, emerging microalgal technologies can be used to produce a range of products such as biofuels, protein-rich animal feeds, chemical feedstocks (e.g. bio-plastic precursors) and higher-value products. This review focuses on the selection, breeding and engineering of microalgae for improved biomass and biofuel conversion efficiencies.
Behrendt, L., Schrameyer, V., Qvortrup, K., Lundin, L., Sørensen, S., Larkum, A. & Kuhl, M. 2012, 'Biofilm growth and near-infrared radiation-driven photosynthesis of the chlorophyll d-containing cyanobacterium Acaryochloris marina', Applied and Environmental Microbiology, vol. 78, no. 11, pp. 3896-3904.
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The cyanobacterium Acaryochloris marina is the only known phototroph harboring chlorophyll (Chl) d. It is easy to cultivate it in a planktonic growth mode, and A. marina cultures have been subject to detailed biochemical and biophysical characterization. In natural situations, A. marina is mainly found associated with surfaces, but this growth mode has not been studied yet. Here, we show that the A. marina type strain MBIC11017 inoculated into alginate beads forms dense biofilm-like cell clusters, as in natural A. marina biofilms, characterized by strong O-2 concentration gradients that change with irradiance. Biofilm growth under both visible radiation (VIS, 400 to 700 nm) and near-infrared radiation (NIR, similar to 700 to 730 nm) yielded maximal cell-specific growth rates of 0.38 per day and 0.64 per day, respectively. The population doubling times were 1.09 and 1.82 days for NIR and visible light, respectively. The photosynthesis versus irradiance curves showed saturation at a photon irradiance of E-k (saturating irradiance) >250 mu mol photons m(-2) s(-1) for blue light but no clear saturation at 365 mu mol photons m(-2) s(-1) for NIR. The maximal gross photosynthesis rates in the aggregates were similar to 1,272 mu mol O-2 mg Chl d(-1) h(-1) (NIR) and similar to 1,128 mu mol O-2 mg Chl d(-1) h(-1) (VIS). The photosynthetic efficiency (alpha) values were higher in NIR-irradiated cells [(268 +/- 0.29) x 10(-6) m(2) mg Chl d(-1) (mean +/- standard deviation)] than under blue light [(231 +/- 0.22) x 10(-6) m(2) mg Chl d(-1)]. A. marina is well adapted to a biofilm growth mode under both visible and NIR irradiance and under O-2 conditions ranging from anoxia to hyperoxia, explaining its presence in natural niches with similar environmental conditions.
Jimenez Denness, I.M., Larkum, A., Ralph, P.J. & Kuhl, M. 2012, 'In situ thermal dynamics of shallow water corals is affected by tidal patterns and irradiance', Marine Biology, vol. 159, pp. 1773-1782.
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We studied the diel variation of in situ coral temperature, irradiance and photosynthetic performance of hemispherical colonies of Porites lobata and branching colonies of Porites cylindrica during different bulk water temperature and tidal scenarios on the shallow reef flat of Heron Island, Great Barrier Reef, Australia. Our study presents in situ evidence that coral tissue surface temperatures can exceed that of the surrounding water under environmental conditions typically occurring during low tide in shallow reef or lagoon environments. Such heating may be a regular occurrence on shallow reef flats, triggered by the combined effects of high irradiance and low water flow characteristic of low Spring tides. At these times, solar heating of corals coincides with times of maximum water temperature and high irradiance, where the slow flow and consequent thick boundary layers impede heat exchange between corals and the surrounding water. Despite similar light-absorbing properties, the heating effect was more pronounced for the hemispherical P. lobata than for the branching P. cylindrica. This is consistent with previous laboratory experiments showing the evidence of interspecific variation in coral thermal environment and may result from morphologically influenced variation in convective heat transfer and/or thermal properties of the skeleton. Maximum coral surface warming did not coincide with maximum irradiance, but with maximum water temperature, well into the low-tide period with extremely low water flow in the partially drained reef flat, just prior to flushing by the rising tide. The timing of low tide thus influences the thermal exposure and photophysiological performance of corals, and the timing of tidally driven coral surface warming could potentially have different physiological impacts in the morning or in the afternoon.
Behrendt, L., Larkum, A., Trampe, E., Norman, A., Sørensen, S. & Kuhl, M. 2012, 'Microbial diversity of biofilm communities in microniches associated with the didemnid ascidian Lissoclinum patella', ISME Journal, vol. 6, no. 6, pp. 1222-1237.
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We assessed the microbial diversity and microenvironmental niche characteristics in the didemnid ascidian Lissoclinum patella using 16S rRNA gene sequencing, microsensor and imaging techniques. L. patella harbors three distinct microbial communities spatially separated by few millimeters of tunic tissue: (i) a biofilm on its upper surface exposed to high irradiance and O-2 levels, (ii) a cloacal cavity dominated by the prochlorophyte Prochloron spp. characterized by strong depletion of visible light and a dynamic chemical microenvironment ranging from hyperoxia in light to anoxia in darkness and (iii) a biofilm covering the underside of the animal, where light is depleted of visible wavelengths and enriched in near-infrared radiation (NIR). Variable chlorophyll fluorescence imaging demonstrated photosynthetic activity, and hyperspectral imaging revealed a diversity of photopigments in all microhabitats. Amplicon sequencing revealed the dominance of cyanobacteria in all three layers. Sequences representing the chlorophyll d containing cyanobacterium Acaryochloris marina and anoxygenic phototrophs were abundant on the underside of the ascidian in shallow waters but declined in deeper waters. This depth dependency was supported by a negative correlation between A. marina abundance and collection depth, explained by the increased attenuation of NIR as a function of water depth. The combination of microenvironmental analysis and fine-scale sampling techniques used in this investigation gives valuable first insights into the distribution, abundance and diversity of bacterial communities associated with tropical ascidians. In particular, we show that microenvironments and microbial diversity can vary significantly over scales of a few millimeters in such habitats; which is information easily lost by bulk sampling
Wangpraseurt, D., Larkum, A., Ralph, P.J. & Kuhl, M. 2012, 'Light gradients and optical microniches in coral tissues', Frontiers in Microbiology, vol. 3, no. 316, pp. 1-9.
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Light quantity and quality are among the most important factors determining the physiology and stress response of zooxanthellate corals. Yet, almost nothing is known about the light ?eld that Symbiodinium experiences within their coral host, and the basic optical properties of coral tissue are unknown. We used scalar irradiance microprobes to characterize vertical and lateral light gradients within and across tissues of several coral species. Our results revealed the presence of steep light gradients with photosynthetically available radiation decreasing by about one order of magnitude from the tissue surface to the coral skeleton. Surface scalar irradiance was consistently higher over polyp tissue than over coenosarc tissue in faviid corals. Coral bleaching increased surface scalar irradiance by ~150% (between 500 and 700 nm) relative to a healthy coral. Photosynthesis peaked around 300 µm within the tissue, which corresponded to a zone exhibiting strongest depletion of scalar irradiance. Deeper coral tissue layers, e.g., ~1000 µm into aboral polyp tissues, harbor optical microniches, where only ~10% of the incident irradiance remains. We conclude that the optical microenvironment of corals exhibits strong lateral and vertical gradients of scalar irradiance, which are affected by both tissue and skeleton optical properties. Our results imply that zooxanthellae populations inhabit a strongly heterogeneous light environment and highlight the presence of different optical microniches in corals; an important ?nding for understanding the photobiology, stress response, as well as the phenotypic and genotypic plasticity of coral symbionts.
Jimenez Denness, I.M., Larkum, A., Ralph, P.J. & Kuhl, M. 2012, 'Thermal effects of tissue optics in symbiont-bearing reef-building corals', Limnology and Oceanography, vol. 57, no. 6, pp. 1816-1825.
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Reflectance spectroscopy and microscale temperature measurements were used to investigate links between optical and thermal properties of corals. Coral tissue heating showed a species-specific linear correlation to the absorptance of incident irradiance. Heat budgets estimated from absorptance and thermal boundary layer measurements indicated differences in the relative contribution of convection and conduction to heat loss in Porites lobata and Stylophora pistillata, and a higher heat conduction into the skeleton of the thin-tissued branching S. pistillata as compared to the massive thick-tissued P. lobata. Decreasing absorptance associated with bleaching resulted in decreased surface warming of coral tissue. Action spectra of coral tissue heating showed elevated efficiency of heating at wavelengths corresponding to absorption maxima of major zooxanthellae photopigments. Generally, energy-rich radiation (, 500 nm) showed the highest heating efficiency. Speciesspecific relationships between coral tissue heating and absorptance can be strongly affected by differences in the thermal properties of the skeleton and/or tissue arrangement within the skeletal matrix, indicating a yet unresolved potential for coral shape, size, and tissue thickness to affect heat dissipation and especially the conduction of heat into the coral skeleton.
Larkum, A., Chen, M., Li, Y., Schliep, M.T., Trampe, E., West, J., Salih, A. & Kuhl, M. 2012, 'A novel epiphytic chlorophyll d-containing cyanobacterium isolated from a mangrove-associated red alga', Journal of Phycology, vol. 48, no. 6, pp. 1320-1327.
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A new habitat and a new chlorophyll (Chl) d-containing cyanobacterium belonging to the genus Acaryochloris are reported in this study. Hyperspectral microscopy showed the presence of Chl d-containing microorganisms in epiphytic biofilms on a red alga (Gelidium caulacantheum) colonizing the pneumato-phores of a temperate mangrove (Avicennia marina). The presence of Chl d was further proven by high performance liquid chromatography (HPLC)-based pigment analysis and by confocal imaging of cultured cells. Enrichment of mangrove biofilm samples under near-infrared radiation (NIR) yielded the new Acaryochloris sp. MPGRS1, which was closely related in terms of 16S rRNA gene sequence to an isolate from the hypertrophic Salton Sea, USA. The new isolate used Chl d as its major photopigment; Chl d and Chl a contents were ~98% and 1%2% of total cellular chlorophyll, respectively. These findings expand the variety of ecological niches known to harbor Chl d-containing cyanobacteria and support our working hypothesis that such oxyphototrophs may be ubiquitous in habitats depleted of visible light, but with sufficient NIR exposure
Hill, R., Larkum, A., Prasil, O., Kramer, D.M., Szabo, M., Kumar, V. & Ralph, P.J. 2012, 'Light-induced dissociation of antenna complexes in the symbionts of scleractinian corals correlates with sensitivity to coral bleaching', Coral Reefs, vol. 31, pp. 963-975.
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Elevated temperatures in combination with moderate to high irradiance are known to cause bleaching events in scleractinian corals, characterised by damage to photosystem II (PSII). Photoprotective mechanisms of the symbiont can reduce the excitation pressure impinging upon PSII. In the bleaching sensitive species, Acropora millepora and Pocillopora damicornis, high light alone induced photoprotection through the xanthophyll cycle, increased content of the antioxidant carotenoid, -carotene, as well as the dissociation of the light-harvesting chlorophyll complexes. The evidence is compatible with either the membrane-bound chlorophyll a-chlorophyll c 2-peridinin-protein (acpPC) complex or the peripheral peridinin-chlorophyll-protein complex, or both, disconnecting from PSII under high light. The acpPC complex potentially showed a state transition response with redistribution towards photosystem I to reduce PSII over-excitation. This apparent acpPC dissociation/reassociation was promoted by the addition of the xanthophyll cycle inhibitor, dithiothreitol, under high irradiance. Exposure to thermal stress as well as high light promoted xanthophyll de-epoxidation and increased -carotene content, although it did not influence light-harvesting chlorophyll complex (LHC) dissociation, indicating light, rather than temperature, controls LHC dissociation. Photoinhibition was avoided in the bleaching tolerant species, Pavona decussata, suggesting xanthophyll cycling along with LHC dissociation may have been sufficient to prevent photodamage to PSII. Symbionts of P. decussata also displayed the greatest detachment of antenna complexes, while the more thermally sensitive species, Pocillopora damicornis and A. millepora, showed less LHC dissociation, suggesting antenna movement influences bleaching susceptibility.
Kuhl, M., Behrendt, L., Trampe, E., Qvortrup, K., Schreiber, U., Borisov, S.M., Klimant, I. & Larkum, A. 2012, 'Microenvironmental ecology of the chlorophyll b-containing symbiotic cyanobacterium Prochloron in the didemnid ascidian Lissoclinum patella', Frontiers in Microbiology, vol. 3, pp. 1-18.
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The discovery of the cyanobacterium Prochloron was the first finding of a bacterial oxyphototroph with chlorophyll (Chl) b, in addition to Chl a. It was first described as Prochloron didemni but a number of clades have since been described. Prochloron is a conspicuously large (7â25mm) unicellular cyanobacterium living in a symbiotic relationship, primarily with (sub-) tropical didemnid ascidians; it has resisted numerous cultivation attempts and appears truly obligatory symbiotic. Recently, a Prochloron draft genome was published, revealing no lack of metabolic genes that could explain the apparent inability to reproduce and sustain photosynthesis in a free-living stage. Possibly, the unsuccessful cultivation is partly due to a lack of knowledge about the microenvironmental conditions and ecophysiology of Prochloron in its natural habitat.We used microsensors, variable chlorophyll fluorescence imaging and imaging of O2 and pH to obtain a detailed insight to the microenvironmental ecology and photobiology of Prochloron in hospite in the didemnid ascidian Lissoclinum patella. The microenvironment within ascidians is characterized by steep gradients of light and chemical parameters that change rapidly with varying irradiances. The interior zone of the ascidians harboring Prochloron thus became anoxic and acidic within a few minutes of darkness, while the same zone exhibited O2 super-saturation and strongly alkaline pH after a few minutes of illumination. Photosynthesis showed lack of photoinhibition even at high irradiances equivalent to full sunlight, and photosynthesis recovered rapidly after periods of anoxia.We discuss these new insights on the ecological niche of Prochloron and possible interactions with its host and other microbes in light of its recently published genome and a recent study of the overall microbial diversity and metagenome of L. patella.
Ritchie, R.J. & Larkum, A. 2012, 'Modelling Photosynthesis In Shallow Algal Production Ponds', Photosynthetica, vol. 50, no. 4, pp. 481-500.
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Shallow ponds with rapidly photosynthesising cyanobacteria or eukaryotic algae are used for growing biotechnology feedstock and have been proposed for biofuel production but a credible model to predict the productivity of a column of phytoplankton in suc
Behrendt, L., Larkum, A., Norman, A., Qvortrup, K., Chen, M., Ralph, P.J., Sorensen, S.J., Trampe, E. & Kuhl, M. 2011, 'Endolithic chlorophyll d-containing phototrophs', ISME Journal, vol. 5, no. 6, pp. 1072-1076.
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Cyanobacteria in the genus Acaryochloris are the only known oxyphototrophs that have exchanged chlorophyll a (Chl a) with Chl d as their primary photopigment, facilitating oxygenic photosynthesis with near infrared (NIR) light. Yet their ecology and natural habitats are largely unknown. We used hyperspectral and variable chlorophyll fluorescence imaging, scanning electron microscopy, photopigment analysis and DNA sequencing to show that Acaryochloris-like cyanobacteria thrive underneath crustose coralline algae in a widespread endolithic habitat on coral reefs. This finding suggests an important role of Chl d-containing cyanobacteria in a range of hitherto unexplored endolithic habitats, where NIR light-driven oxygenic photosynthesis may be significant.
Jimenez Denness, I.M., Kuhl, M., Larkum, A. & Ralph, P.J. 2011, 'Effects of flow and colony morphology on the thermal boundary layer of corals', Journal of the Royal Society Interface, vol. 8, no. 65, pp. 1785-1795.
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The thermal microenvironment of corals and the thermal effects of changing flow and radiation are critical to understanding heat-induced coral bleaching, a stress response resulting from the destruction of the symbiosis between corals and their photosynt
Larkum, A., Salih, A. & Kuhl, M. 2011, 'Rapid Mass Movement of Chloroplasts during Segment Formation of the Calcifying Siphonalean Green Alga, Halimeda macroloba', PLoS One, vol. 6, no. 7, pp. 1-9.
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Background: The calcifying siphonalean green alga, Halimeda macroloba is abundant on coral reefs and is important in the production of calcium carbonate sediments. The process by which new green segments are formed over-night is revealed here for the first time. Methodology/Principal Findings: Growth of new segments was visualised by epifluorescence and confocal microscopy and by pulse amplitude modulation (PAM) fluorimetry. Apical colourless proto-segments were initiated on day 1, and formed a loose network of non-calcified, non-septate filaments, containing no chloroplasts. Rapid greening was initiated at dusk by i) the mass movement of chloroplasts into these filaments from the parent segment and ii) the growth of new filaments containing chloroplasts. Greening was usually complete in 3-5 h and certainly before dawn on day 2 when the first signs of calcification were apparent. Mass chloroplast movement took place at a rate of 0.65 mm/s. Photosynthetic yield and rate remained low for a period of 1 to several hours, indicating that the chloroplasts were made de novo. Use of the inhibitors colchicine and cytochalasin d indicated that the movement process is dependent on both microtubules and microfilaments. Significance: This unusual process involves the mass movement of chloroplasts at a high rate into new segments during the night and rapid calcification on the following day and may be an adaptation to minimise the impact of herbivorous activity.
Chan, Y.-.W., Mohr, R., Millard, A.D., Holmes, A.B., Larkum, A.W., Whitworth, A.L., Mann, N.H., Scanlan, D.J., Hess, W.R. & Clokie, M.R.J. 2011, 'Discovery of cyanophage genomes which contain mitochondrial DNA polymerase.', Molecular biology and evolution, vol. 28, no. 8, pp. 2269-2274.
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DNA polymerase is a family A DNA polymerase responsible for the replication of mitochondrial DNA in eukaryotes. The origins of DNA polymerase have remained elusive because it is not present in any known bacterium, though it has been hypothesized that mitochondria may have inherited the enzyme by phage-mediated nonorthologous displacement. Here, we present an analysis of two full-length homologues of this gene, which were found in the genomes of two bacteriophages, which infect the chlorophyll-d containing cyanobacterium Acaryochloris marina. Phylogenetic analyses of these phage DNA polymerase proteins show that they branch deeply within the DNA polymerase clade and therefore share a common origin with their eukaryotic homologues. We also found homologues of these phage polymerases in the environmental Community Cyberinfrastructure for Advanced Microbial Ecology Research and Analysis (CAMERA) database, which fell in the same clade. An analysis of the CAMERA assemblies containing the environmental homologues together with the filter fraction metadata indicated some of these assemblies may be of bacterial origin. We also show that the phage-encoded DNA polymerase is highly transcribed as the phage genomes are replicated. These findings provide data that may assist in reconstructing the evolution of mitochondria.
Lilley, R., Ralph, P.J. & Larkum, A. 2010, 'The determination of activity of the enzyme Rubisco in cell extracts of the dinoflagellate alga Symbiodinium sp. by manganese chemiluminescence and its response to short-term thermal stress of the alga', Plant Cell and Environment, vol. 33, no. 6, pp. 995-1004.
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The dinoflagellate alga Symbiodinium sp., living in symbiosis with corals, clams and other invertebrates, is a primary producer in coral reefs and other marine ecosystems. The function of the carbon-fixing enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) in dinoflagellates is difficult to study because its activity is rapidly lost after extraction from the cell. We report procedures for the extraction of Rubisco from Symbiodinium cells and for stable storage. We describe a continuous assay for Rubisco activity in these crude cell extracts using the Mn2+ chemiluminescence of Rubisco oxygenase. Chemiluminescence time courses exhibited initial transients resembling bacterial Form II Rubisco, followed by several minutes of linearly decreasing activity. The initial activity was determined from extrapolation of this linear section of the time course. The activity of fast-frozen cell extracts was stable at -80 °C and, after thawing and storage on ice, remained stable for up to 1 h before declining non-linearly. Crude cell extracts bound [14C] 2-carboxy-D-arabitinol 1,5-bisphosphate to a high molecular mass fraction separable by gel filtration chromatography. After pre-treatment of Symbiodinium cell cultures in darkness at temperatures above 30 °C, the extracted Rubisco activities decreased, with almost complete loss of activity above 36 °C. The implications for the sensitivity to elevated temperature of Symbiodinium photosynthesis are assessed.
Amoroso, S., Clarke, R.J., Larkum, A. & Quinnell, R. 2010, 'Electrogenic plasma membrane H+-ATPase activity using voltage sensitive dyes', JOURNAL OF BIOENERGETICS AND BIOMEMBRANES, vol. 42, no. 5, pp. 387-393.
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Zhang, Y., Chen, M., Church, W.B., Lau, K.W., Larkum, A.W.D. & Jermiin, L.S. 2010, 'The molecular structure of the IsiA-Photosystem I supercomplex, modelled from high-resolution, crystal structures of Photosystem I and the CP43 protein.', Biochimica et biophysica acta, vol. 1797, no. 4, pp. 457-465.
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We present the molecular structure of the IsiA-Photosystem I (PSI) supercomplex, inferred from high-resolution, crystal structures of PSI and the CP43 protein. The structure of iron-stress-induced A protein (IsiA) is similar to that of CP43, albeit with the difference that IsiA is associated with 15 chlorophylls (Chls), one more than previously assumed. The membrane-spanning helices of IsiA contain hydrophilic residues many of which bind Chl. The optimal structure of the IsiA-PSI supercomplex was inferred by systematically rearranging the IsiA monomers and PSI trimer in relation to each other. For each of the 6,969,600 structural configurations considered, we counted the number of optimal Chl-Chl connections (i.e., cases where Chl-bound Mg atoms are <or=25A apart). Fifty of these configurations were found to have optimal energy-transfer potential. The 50 configurations could be divided into three variants; one of these, comprising 36 similar configurations, was found to be superior to the other configurations in terms of its potential to transfer excitation energy to the reaction centres under low-light conditions and its potential to dissipate excess energy under high-light conditions. Compared to the assumed model [Biochemistry 42 (2003) 3180-3188], the new Chl increases by 7% the ability of IsiA to harvest sunlight while the rearrangement of the constituent components of the IsiA-PSI supercomplex increases by 228% the energy-transfer potential. In conclusion, our model allows us to explain how the IsiA-PSI supercomplex may act as an efficient light-harvesting structure under low-light conditions and as an efficient dissipater of excess energy under high-light conditions.
Larkum, A.W.D. 2010, 'Limitations and prospects of natural photosynthesis for bioenergy production', CURRENT OPINION IN BIOTECHNOLOGY, vol. 21, no. 3, pp. 271-276.
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Chaloub, R.M., Reinert, F., Nassar, C.A.G., Fleury, B.G., Mantuano, D.G. & Larkum, A.W.D. 2010, 'Photosynthetic properties of three Brazilian seaweeds', Revista Brasileira de Botanica, vol. 33, no. 2, pp. 371-374.
Photosynthetic performance of distinct marine macroalgae, Ulva fasciata Delile (green alga), Lobophora variegata (J. V. Lamouroux) Womersley ex E. C. Oliveira (brown alga), and Plocamium brasiliensis (Greville) M. A. Howe & W. R. Taylor (red alga), were compared using a pulse amplitude-modulated fluorometer. The maximum quantum yield (Fv/Fm) ranged from 0.80 to 0.51, and the lowest value was found in P. brasiliensis. Under 400 mol photons m-2 s-1 irradiance, the highest value of photochemical quenching (qP = 0.92 &plusmn; 0.13) was observed for U. fasciata. The red alga P. brasiliensis dissipated high amounts of excitation energy (qN = 0.56 &plusmn; 0.09), resulting in relatively low values for the effective quantum yield of PS-II (0.23 &plusmn; 0.04), as well as for the relative electron transport rate (3.3 &plusmn; 0.7). The high photosynthetic potential found for U. fasciata partially explains the species ability for rapid growth and high productivity.
Mohr, R., Voss, B., Schliep, M.T., Kurz, T., Maldener, I., Adams, D.G., Larkum, A., Chen, M. & Hess, W.R. 2009, 'A new chlorophyll d-containing cyanobacterium: evidence for niche adaptation in the genus Acaryochloris', ISME Journal, vol. 4, no. 11, pp. 1456-1469.
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Chlorophyll d is a photosynthetic pigment that, based on chemical analyses, has only recently been recognized to be widespread in oceanic and lacustrine environments. However, the diversity of organisms harbouring this pigment is not known. Until now, the unicellular cyanobacterium Acaryochloris marina is the only characterized organism that uses chlorophyll d as a major photopigment. In this study we describe a new cyanobacterium possessing a high amount of chlorophyll d, which was isolated from waters around Heron Island, Great Barrier Reef (23 degrees 26' 31.2 '' S, 151 degrees 54' 50.4 '' E). The 16S ribosomal RNA is 2% divergent from the two previously described isolates of A. marina, which were isolated from waters around the Palau islands (Pacific Ocean) and the Salton Sea lake (California), suggesting that it belongs to a different clade within the genus Acaryochloris. An overview sequence analysis of its genome based on Illumina technology yielded 871 contigs with an accumulated length of 8 371 965 nt. Their analysis revealed typical features associated with Acaryochloris, such as an extended gene family for chlorophyll-binding proteins. However, compared with A. marina MBIC11017, distinct genetic, morphological and physiological differences were observed. Light saturation is reached at lower light intensities, Chl d/a ratios are less variable with light intensity and the phycobiliprotein phycocyanin is lacking, suggesting that cyanobacteria of the genus Acaryochloris occur in distinct ecotypes. These data characterize Acaryochloris as a niche-adapted cyanobacterium and show that more rigorous attempts are worthwhile to isolate, cultivate and analyse chlorophyll d-containing cyanobacteria for understanding the ecophysiology of these organisms.
Duxbury, Z., Schliep, M.T., Ritchie, R.J., Larkum, A. & Chen, M. 2009, 'Chromatic photoacclimation extends utilisable photosynthetically active radiation in the chlorophyll d-containing cyanobacterium, Acaryochloris marina', Photosynthesis Research, vol. 101, no. 1, pp. 69-75.
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Chromatic photoacclimation and photosynthesis were examined in two strains of Acaryochloris marina (MBIC11017 and CCMEE5410) and in Synechococcus PCC7942. Acaryochloris contains Chl d, which has an absorption peak at ca 710 nm in vivo. Cultures were grown in one of the three wavelengths (525 nm, 625 nm and 720 nm) of light from narrow-band photodiodes to determine the effects on pigment composition, growth rate and photosynthesis: no growth occurred in 525 nm light. Synechococcus did not grow in 720 nm light because Chl a does not absorb effectively at this long wavelength. Acaryochloris did grow in 720 nm light, although strain MBIC11017 showed a decrease in phycobilins over time. Both Synechococcus and Acaryochloris MBIC11017 showed a dramatic increase in phycobilin content when grown in 625 nm light. Acaryochloris CCMEE5410, which lacks phycobilins, would not grow satisfactorily under 625 nm light. The cells adjusted their pigment composition in response to the light spectral conditions under which they were grown. Photoacclimation and the Q (y) peak of Chl d could be understood in terms of the ecological niche of Acaryochloris, i.e. habitats enriched in near infrared radiation.
Kuhl, M., Holst, G., Larkum, A. & Ralph, P.J. 2008, 'Imaging of oxygen dynamics within the endolithic algal community of the massive coral porites lobata', Journal of Phycology, vol. 44, no. 3, pp. 541-550.
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We used transparent planar oxygen optodes and a luminescence lifetime imaging system to map (at a pixel resolution of <200 ?m) the two-dimensional distribution of O<sub>2</sub> within the skeleton of a Porites lobata colony. The O<sub>2</sub> distribution was closely correlated to the distribution of the predominant endolithic microalga, Ostreobium quekettii Bornet et Flahault that formed a distinct green band inside the skeleton. Oxygen production followed the outline of the Ostreobium band, and photosynthetic O<sub>2</sub> production was detected at only 0.2 ?mol photons m<sup>-2</sup> s<sup>-1</sup>, while saturation occurred at ?37 ?mol photons m<sup>-2</sup> s<sup>-1</sup>. Oxygen levels varied from ?60% to 0% air saturation in the illuminated section of the coral skeleton in comparison to the darkened section. The O<sub>2</sub> production within the Ostreobium band was lower in the region below the upward facing surface of the coral and elevated on the sides. Oxygen consumption in darkness was also greatest within the Ostreobium zone, as well as in the white skeleton zone immediately below the corallites. The rate of O<sub>2</sub> depletion was not constant within zones and between zones, showing pronounced heterogeneity in endolithic respiration. When the coral was placed in darkness after a period of illumination, O<sub>2</sub> levels declined by 50% within 20 min and approached steady-state after 4050 min in darkness. Our study demonstrates the use of an important new tool in endolith photobiology and presents the first data of spatially resolved O<sub>2</sub> concentration and its correlation to the physical structures and specific zones responsible for O<sub>2</sub> production and consumption within the coral skeleton.
Ulstrup, K., Hill, R., van Oppen, M.J., Larkum, A. & Ralph, P.J. 2008, 'Seasonal variation in the photo-physiology of homogeneous and heterogeneous Symbiodinium consortia in two scleractinian corals', Marine Ecology Progress Series, vol. 361, pp. 139-150.
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Seasonal variation in the composition of the algal endosymbiont community and photophysiology was determined in the corals Pocillopora damicornis,w hich show high local fidelity to one symbiont type (Symbiodinium C1) and Acropora valida, with a mixed Symbiodinium synbiont community, compromising members of both clades A and C. The relative abundances of Symbiodinium types varied overtime. A significant decline in symbiont densities in both coral species during the summer of 2005 coincided with a NOAA 'hotspot' warning for Heron Island. This also coincided with a relayiove increase in the presence and dominance of clade A in A. valida particularl in sun-adapted surfaces.
Jimenez Denness, I.M., Kuhl, M., Larkum, A. & Ralph, P.J. 2008, 'Heat budget and thermal microenvironment of shallow-water corals: Do massive corals get warmer than branching corals?', Limnology And Oceanography, vol. 53, no. 4, pp. 1548-1561.
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Coral surface temperature was investigated with multiple temperature sensors mounted on hemispherical and branching corals under (a) artificial lighting and controlled flow; (b) natural sunlight and controlled flow; and (c) in situ conditions in a shallo
Howe, C.J., Barbrook, A.C., Nisbet, R.E.R., Lockhart, P.J. & Larkum, A.W.D. 2008, 'The origin of plastids', PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, vol. 363, no. 1504, pp. 2675-2685.
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Martyn, A.J., Larkum, A.W.D., McConchie, R. & Offord, C.A. 2008, 'Photoinhibition and changes in pigments associated with bract browning in waratahs (Telopea spp., Proteaceae)', JOURNAL OF HORTICULTURAL SCIENCE & BIOTECHNOLOGY, vol. 83, no. 3, pp. 367-373.
Kazandjian, A., Shepherd, V.A., Rodriguez-Lanetty, M., Nordemeier, W., Larkum, A.W.D. & Quinnell, R.G. 2008, 'Isolation of symbiosomes and the symbiosome membrane complex from the zoanthid Zoanthus robustus', Phycologia, vol. 47, no. 3, pp. 294-306.
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The zoanthid Zoanthus robustus was used as a model organism to develop procedures for isolating pure symbiosomes and symbiosome membranes. The symbiosome is comprised of a zooxanthella (Symbiodinium sp.) cell that divides rarely and is separated from the host gastrodermal cytoplasm by a symbiosome multimembrane complex. Devising a method to isolate membranes at the interface between the symbiotic partners is a critical first step in characterising the molecular components involved in the metabolic trafficking necessary to sustain an effective symbiosis. After zoanthid gastrodermal cells were extracted, symbiosomes were released by mechanical disruption, recovered by centrifugation, and then purified using discontinuous sucrose gradient centrifugation. The material forming the membrane complex around symbiosomes proved highly resistant to disruption. Methods used to dissociate this interface from symbionts included (1) Triton X-100 detergent solubilisation, (2) osmotic shock with mechanical disruption, and (3) vigorous mechanical disruptions, where powerful shearing forces were used, combined with a series of sucrose density gradient centrifugation steps. The lipophilic styryl fluorochrome FM 1-43, at a concentration of 30 M, selectively labelled the symbiosome membrane complex, both for isolated symbiosomes and those in hospite. Other cell membranes, including plasma membranes, endoplasmic reticulum, tonoplast, and organelle membranes, were not visibly labelled at this concentration. The selective labelling of the symbiosome membrane complex remained stable even after long exposure times (3 h). At 30 M concentration, FM 1-43 also labelled symbiosome membrane fragments isolated using methods (1), (2) and (3). Method (3) proved to be the most effective in producing a fraction enriched in FM-143-labelled membrane material, which we call a symbiosome membrane complex. Transmission electron microscopy, together with confocal and conventional epifluorescence microsco...
Ralph, P.J., Larkum, A. & Kuhl, M. 2007, 'Photobiology of endolithic microorganisms in living coral skeletons: 1. Pigmentation, spectral reflectance and variable chlorophyll fluorescence analysis of endoliths in the massive corals Cyphastrea serailia, Porites lutea and Goniastrea australensi', Marine Biology, vol. 152, no. 2, pp. 395-404.
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We used microscopy, reflectance spectroscopy, pigment analysis, and photosynthesis-irradiance curves measured with variable fluorescence techniques to characterise the endolithic communities of phototrophic microorganisms in the skeleton of three massive
Raven, J.A. & Larkum, A.W.D. 2007, 'Are there ecological implications for the proposed energetic restrictions on photosynthetic oxygen evolution at high oxygen concentrations?', PHOTOSYNTHESIS RESEARCH, vol. 94, no. 1, pp. 31-42.
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Larkum, A.W.D., Lockhart, P.J. & Howe, C.J. 2007, 'Shopping for plastids.', Trends in plant science, vol. 12, no. 5, pp. 189-195.
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Recent suggestions that endosymbionts in a diatom and an amoeba represent independent origins of plastids from those in plants and algae raise again the question of how many times plastids have evolved. In this Opinion article, we review the evidence for a single origin or multiple origins of primary plastids. Although the data are widely taken as supporting a single origin, we stress the assumptions underlying that view, and argue for a more cautious interpretation. We also suggest that the implicit view of plastids being acquired from single ancestors at a single point (or points) in time is an over-simplification.
Santabarbara, S., Chen, M., Larkum, A.W.D. & Evans, M.C.W. 2007, 'An electron paramagnetic resonance investigation of the electron transfer reactions in the chlorophyll d containing photosystem I of Acaryochloris marina.', FEBS letters, vol. 581, no. 8, pp. 1567-1571.
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Electron paramagnetic resonance (EPR) spectroscopy reveals functional and structural similarities between the reaction centres of the chlorophyll d-binding photosystem I (PS I) and chlorophyll a-binding PS I. Continuous wave EPR spectrometry at 12K identifies iron-sulphur centres as terminal electron acceptors of chlorophyll d-binding PS I. A transient light-induced electron spin echo (ESE) signal indicates the presence of a quinone as the secondary electron acceptor (Q) between P(740)(+) and the iron-sulphur centres. The distance between P(740)(+) and Q(-) was estimated within point-dipole approximation as 25.23+/-0.05A, by the analysis of the electron spin echo envelope modulation.
Gloag, R.S., Ritchie, R.J., Chen, M., Larkum, A.W.D. & Quinnell, R.G. 2007, 'Chromatic photoacclimation, photosynthetic electron transport and oxygen evolution in the chlorophyll d-containing oxyphotobacterium Acaryochloris marina.', Biochimica et biophysica acta, vol. 1767, no. 2, pp. 127-135.
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Changes in photosynthetic pigment ratios showed that the Chlorophyll d-dominated oxyphotobacterium Acaryochloris marina was able to photoacclimate to different light regimes. Chl d per cell were higher in cultures grown under low irradiance and red or green light compared to those found when grown under high white light, but phycocyanin/Chl d and carotenoid/Chl d indices under the corresponding conditions were lower. Chl a, considered an accessory pigment in this organism, decreased respective to Chl d in low irradiance and low intensity non-white light sources. Blue diode PAM (Pulse Amplitude Modulation) fluorometry was able to be used to measure photosynthesis in Acaryochloris. Light response curves for Acaryochloris were created using both PAM and O(2) electrode. A linear relationship was found between electron transport rate (ETR), measured using a PAM fluorometer, and oxygen evolution (net and gross photosynthesis). Gross photosynthesis and ETR were directly proportional to one another. The optimum light for white light (quartz halogen) was about 206+/-51 micromol m(-2) s(-1) (PAR) (Photosynthetically Active Radiation), whereas for red light (red diodes) the optimum light was lower (109+/-27 micromol m(-2) s(-1) (PAR)). The maximum mean gross photosynthetic rate of Acaryochloris was 73+/-7 micromol mg Chl d(-1) h(-1). The gross photosynthesis/respiration ratio (P(g)/R) of Acaryochloris under optimum conditions was about 4.02+/-1.69. The implications of our findings will be discussed in relation to how photosynthesis is regulated in Acaryochloris.
Larkum, A., Zhang, Y., Churdh, B. & Jermiin, L. 2007, 'Modelling the IsiA-PSI supermolecular complex of cyanobacteria', PHOTOSYNTHESIS RESEARCH, vol. 91, no. 2-3, pp. 172-172.
Larkum, A., Lockhart, P. & Howe, C. 2007, 'The origin of plastids: A shopping bag model', PHOTOSYNTHESIS RESEARCH, vol. 91, no. 2-3, pp. 272-272.
Larkum, A., Ip, C., Chen, M. & Jermiin, L. 2007, 'Phylogeny of Prochlorococcus marinus: how is this species related to the rest of the Cyanobacteria?', PHOTOSYNTHESIS RESEARCH, vol. 91, no. 2-3, pp. 272-273.
Zhang, Y., Chen, M., Zhou, B.B., Jermiin, L.S. & Larkum, A.W.D. 2007, 'Evolution of the inner light-harvesting antenna protein family of cyanobacteria, algae, and plants.', Journal of molecular evolution, vol. 64, no. 3, pp. 321-331.
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Two hypotheses account for the evolution of the inner antenna light-harvesting proteins of oxygenic photosynthesis in cyanobacteria, algae, and plants: one in which the CP43 protein of photosytem II gave rise to the extrinsic CP43-like antennas of cyanobacteria (i.e. IsiA and Pcb proteins), as a late development, and the other in which CP43 and CP43-like proteins derive from an ancestral protein. In order to determine which of these hypotheses is most likely, we analyzed the family of antenna proteins by a variety of phylogenetic techniques, using alignments of the six common membrane-spanning helices, constructed using information on the antenna proteins' three-dimensional structure, and surveyed for evidence of factors that might confound inference of a correct phylogeny. The first hypothesis was strongly supported. As a consequence, we conclude that the ancestral photosynthetic apparatus, with 11 membrane-spanning helices, split at an early stage during evolution to form, on the one hand, the reaction center of photosystem II and, on the other hand, the ancestor of inner antenna proteins, CP43 (PsbC) and CP47 (PsbB). Only much later in evolution did the CP43 lineage give rise to the CP43' proteins (IsiA and Pcb) of cyanobacteria.
Ulstrup, K., Ralph, P.J., Larkum, A. & Kuhl, M. 2006, 'Intra-colonial variability in light acclimation of zooxanthellae in coral tissues of Pocillopora damicornis Received:', Marine Biology, vol. 149, pp. 1325-1335.
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Ralph, P.J., Larkum, A. & Kuehl, M. 2005, 'Temporal patterns in effective quantum yield of individual zooxanthellae expelled during bleaching', Journal Of Experimental Marine Biology And Ecology, vol. 316, no. 1, pp. 17-28.
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Bleaching is a worldwide phenomenon affecting coral reefs. During elevated temperature and light conditions (bleaching), expelled zooxanthellae show distinct patterns in photosynthetic health. An innovative new device was used to collect individual expel
Kuehl, M., Chen, M., Ralph, P.J., Schreiber, U. & Larkum, A. 2005, 'A niche for cyanobacteria containing chlorophyll d', Nature, vol. 433, no. 1, pp. 820-820.
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The cyanobacterium known as Acaryochloris marina is a unique phototroph that uses chlorophyll d as its principal light-harvesting pigment instead of chlorophyll a, the form commonly found in plants, algae and other cyanobacteria; this means that it depends on far-red light for photosynthesis. Here we demonstrate photosynthetic activity in Acaryochloris-like phototrophs that live underneath minute coral-reef invertebrates (didemnid ascidians) in a shaded niche enriched in near-infrared light. This discovery clarifies how these cyanobacteria are able to thrive as free-living organisms in their natural habitat.
Ralph, P.J., Schreiber, U., Gademann, R., Kuehl, M. & Larkum, A. 2005, 'Coral photobiology studied with a new imaging pulse amplitude modulated fluorometer', Journal Of Phycology, vol. 41, no. 2, pp. 335-342.
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A new high-resolution imaging fluorometer (Imaging-PAM) was used to identify heterogeneity of photosynthetic activity across the surface of corals. Three species were examined: Acropora nobilis Dana (branching), Goniastrea australiensis Edwards A Haime (
Larkum, A. & Kuhl, M. 2005, 'Chlorophyll d: the puzzle resolved', Trends in Plant Science, vol. 10, no. 8, pp. 355-357.
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Chlorophyll a (Chl a) has always been regarded as the sole chlorophyll with a role in photochemical conversion in oxygen-evolving phototrophs, whereas chlorophyll d (Chl d), discovered in small quantities in red algae in 1943, was often regarded as an artefact of isolation. Now, as a result of discoveries over the past year, it has become clear that Chl d is the major chlorophyll of a freeliving and widely distributed cyanobacterium that lives in light environments depleted in visible light and enhanced in infrared radiation. Moreover, Chl d not only has a light-harvesting role but might also replace Chl a in the special pair of chlorophylls in both reactions centers of photosynthesis.
Petrasek, Z., Schmitt, F.J., Theiss, C., Huyer, J., Chen, M., Larkum, A., Eichler, H.J., Kemnitz, K. & Eckert, H.J. 2005, 'Excitation energy transfer from phycobiliprotein to chlorophyll d in intact cells of Acaryochloris marina studied by time- and wavelength-resolved fluorescence spectroscopy', PHOTOCHEMICAL & PHOTOBIOLOGICAL SCIENCES, vol. 4, no. 12, pp. 1016-1022.
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Chen, M., Bibby, T.S., Nield, J., Larkum, A. & Barber, J. 2005, 'Iron deficiency induces a chlorophyll d-binding Pcb antenna system around Photosystem I in Acaryochloris marina', BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS, vol. 1708, no. 3, pp. 367-374.
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Chen, M., Telfer, A., Lin, S., Pascal, A., Larkum, A.W.D., Barber, J. & Blankenship, R.E. 2005, 'The nature of the photosystem II reaction centre in the chlorophyll d-containing prokaryote, Acaryochloris marina.', Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology, vol. 4, no. 12, pp. 1060-1064.
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Pigment-protein complexes enriched in photosystem II (PS II) have been isolated from the chlorophyll (Chl) d containing cyanobacterium, Acaryochloris marina. A small PS II-enriched particle, we call 'crude reaction centre', contained 20 Chl d, 0.5 Chl a and 1 redox active cytochrome b-559 per 2 pheophytin a, plus the D1 and D2 proteins. A larger PS II-enriched particle, we call 'core', additionally bound the antenna complexes, CP47 and CP43, and had a higher chlorophyll per pheophytin ratio. Pheophytin a could be photoreduced in the presence of a strong reductant, indicating that it is the primary electron acceptor in photosystem II of A. marina. A substoichiometric amount of Chl a (less than one chlorophyll a per 2 pheophytin a) strongly suggests that Chl a does not have an essential role in the photochemistry of PS II in this organism. We conclude that PS II, in A. marina, utilizes Chl d and not Chl a as primary electron donor and that the primary electron acceptor is one of two molecules of pheophytin a.
Chen, M., Bibby, T.S., Nield, J., Larkum, A.W.D. & Barber, J. 2005, 'Structure of a large photosystem II supercomplex from Acaryochloris marina.', FEBS letters, vol. 579, no. 5, pp. 1306-1310.
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Acaryochloris marina is a prochlorophyte-like cyanobacterium containing both phycobilins and chlorophyll d as light harvesting pigments. We show that the chlorophyll d light harvesting system, composed of Pcb proteins, functionally associates with the photosystem II (PSII) reaction center (RC) core to form a giant supercomplex. This supercomplex has a molecular mass of about 2300 kDa and dimensions of 385 A x 240 A. It is composed of two PSII-RC core dimers arranged end-to-end, flanked by eight symmetrically related Pcb proteins on each side. Thus each PSII-RC monomer has four Pcb subunits acting as a light harvesting system which increases the absorption cross section of the PSII-RC core by almost 200%.
Chen, M., Hiller, R.G., Howe, C.J. & Larkum, A.W.D. 2005, 'Unique origin and lateral transfer of prokaryotic chlorophyll-b and chlorophyll-d light-harvesting systems.', Molecular biology and evolution, vol. 22, no. 1, pp. 21-28.
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pcb genes, encoding proteins binding light-harvesting chlorophylls, were cloned and sequenced from the Chl d-containing cyanobacterium, Acaryochloris marina, and the Chl b-containing cyanobacterium, Prochloron didemni. Both organisms contained two tandem pcb genes. Peptide fingerprinting confirmed the expression of one of the A. marina pcb genes. Phylogenetic tree reconstruction using distance-matrix and maximum-likelihood methods indicated a single origin of the pcb gene family, whether occurring in Chl b-containing or Chl d-containing organisms. This may indicate widespread lateral transfer of the Pcb protein-based light-harvesting system.
Chen, M., Eggink, L.L., Hoober, J.K. & Larkum, A.W.D. 2005, 'Influence of structure on binding of chlorophylls to peptide ligands.', Journal of the American Chemical Society, vol. 127, no. 7, pp. 2052-2053.
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Four classes of chlorophyll (Chl), a, b, c, and d, are involved in photosynthesis within cyanobacteria, algae, and plants. These classes have different evolutionary origins, chemical properties, and biological functions. Our results demonstrate that peptide-bound ligands provided by the imidazole group of histidine and the charge-compensated glutamate-arginine ion pair readily form coordination bonds with Chls a and d but do not interact significantly with Chls b and c. These ligands are apparently not sufficiently strong Lewis bases to displace strongly coordinated water from Chls b and c. These differences determine specificity of binding of Chls in light-harvesting complexes and play an important role in assembly of stable Chl-protein complexes, which has had a profound impact on the evolution of photosynthetic organisms.
Rodriguez-Lanetty, M., Scaramuzzi, C., Quinnell, R.G. & Larkum, A.W.D. 2005, 'Transport of symbiotic zooxanthellae in mesogleal canals of Zoanthus robustus?', Coral Reefs, vol. 24, no. 2, pp. 195-196.
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Charpy-Roubaud, C. & Larkum, A.W.D. 2005, 'Dinitrogen fixation by exposed communities on the rim of Tikehau atoll (Tuamotu Archipelago, French Polynesia)', Coral Reefs, vol. 24, no. 4, pp. 622-628.
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Various types of sub-aerially exposed microbial mats, including emergent mats, beach sand, beach rock and Kopara mats, are widespread on the 78 km (25 km2) of rim surrounding the Tikehau atoll lagoon. These mats form laminated accretions or diffuse microbial communities growing under high insolation and temperatures, and are therefore subject to desiccation. Both heterocystous and non-heterocystous cyanobacteria occur in these mats. Using acetylene reduction techniques, nitrogenase activity was observed at all sites over a period of 5 years and was 3-17 times higher during daylight than at night in all communities except for beach rock. 15N2 measurements indicated a molar ratio of acetylene reduction to N2 fixed of 1.6 for all exposed communities. Estimated N2 fixation ranged from 1.44 to 8.0 mg N m-2 day-1 in these exposed communities (mean of 4.66 mg N m-2 day-1) with beachrock showing the highest rates. For the whole reef rim, daily N2 fixation amounted to 98.42 kg N day-1 which represents 28% of the rate of fixation in the entire lagoon (area 400 km2). &copy; Springer-Verlag 2005.
Hill, R., Larkum, A., Frankart, C., Kuehl, M. & Ralph, P.J. 2004, 'Loss of functional Photosystem II reaction centres in zooxanthellae of corals exposed to bleaching conditions: using fluorescence rise kinetics', Photosynthesis Research, vol. 82, pp. 59-72.
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Hill, R., Schreiber, U., Gademann, R., Larkum, A., Kuehl, M. & Ralph, P.J. 2004, 'Spatial heterogeneity of photosynthesis and the effect of temperature-induced bleaching condition in three species of corals', Marine Biology, vol. 144, pp. 633-640.
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Runcie, J., Larkum, A. & Ritchie, R.J. 2004, 'Uptake kinetics and assimilation of phosphorus by Catenella nipae and Ulva lactuca can be used to indicate ambient phosphate availability', Journal of Applied Phycology, vol. 16, no. 3, pp. 181-194.
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Uptake, assimilation and compartmentation of phosphate were studied in the opportunist green macroalgaUlva lactucaand the estuarine red algal epiphyteCatenella nipae. The MichaelisMenten model was used to describe uptake rates of inorganic phosphate (Pi) at different concentrations. Maximum uptake rates (V max) of P-starved material exceededV maxof P-enriched material; this difference was greater forC. nipae. Uptake and allocation of phosphorus (P) to internal pools was measured using trichloroacetic acid (TCA) extracts and32P. Both species demonstrated similar assimilation paths: when P-enriched, most32P accumulated as free phosphate. When unenriched,32P was rapidly assimilated into the TCA-insoluble pool.C. nipaeconsistently assimilated more32P into this pool thanU. lactuca, indicatingC. nipaehas a greater P-storage capacity. In both species,32P release data showed two internal compartments with very different biological half-lives.
Chen, M., Zeng, H., Larkum, A.W.D. & Cai, Z.-.L. 2004, 'Raman properties of chlorophyll d, the major pigment of Acaryochloris marina: studies using both Raman spectroscopy and density functional theory.', Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy, vol. 60, no. 3, pp. 527-534.
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The Raman spectroscopy of purified chlorophyll (Chl) d extracted from Acaryochloris marina has been measured over the wide region of 250-3200 cm(-1) at 77 K following excitation of its Soret band at 488 nm and analyzed with the aid of hybrid density-functional vibrational analyses. A Raman peak specific to Chl d, which arises from the formyl group 3(1) C=O stretching, was clearly observed at 1659 cm(-1) with medium intensity. Peaks due to other C=O stretching vibrations of the 13(1) keto-, 13(3) ester- and 17(3) groups were also observed. Four very strong peaks were observed in the range of 1000-1600 cm(-1), assigned to the CC stretching and mixtures of the CH3 bend and CN stretching. CCC and NCC bending contribute to medium intensity peaks at 986 and 915 cm(-1). Out-of-plane CH bending at Chl d methine sites 10, 5 and 20 contribute to observed peaks at 885, 864 and 853 cm(-1), respectively. A few modes involving the MgN stretching and MgNC bending motions were observed in the very low frequency range. Density functional theory (DFT) calculations have been used to make assignments on the observed Raman spectrum and the DFT results have been found to be in good agreement with the experimental results.
Jermiin, L., Ho, S.Y., Ababneh, F., Robinson, J. & Larkum, A.W. 2004, 'The biasing effect of compositional heterogeneity on phylogenetic estimates may be underestimated.', Systematic biology, vol. 53, no. 4, pp. 638-643.
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Larkum, A., Koch, E.W. & Kuhl, M. 2003, 'Diffusive boundary layers and photosynthesis of the epilithic algal community of coral reefs', Marine Biology, vol. 142, no. 5, pp. 1073-1082.
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The effects of mass transfer resistance due to the presence of a diffusive boundary layer on the photosynthesis of the epilithic algal community (EAC) of a coral reef were studied. Photosynthesis and respiration of the EAC of dead coral surfaces were investigated for samples from two locations: the Gulf of Aqaba, Eilat (Israel), and One Tree Reef on the Great Barrier Reef (Australia). Microsensors were used to measure O2 and pH at the EAC surface and above. Oxygen profiles in the light and dark indicated a diffusive boundary layer (DBL) thickness of 180590 ?m under moderate flow (~0.08 m s-1) and >2,000 ?m under quasi-stagnant conditions. Under light saturation the oxygen concentration at the EAC surface rose within a few minutes to 200550% air saturation levels under moderate flow and to 600700% under quasi-stagnant conditions. High maximal rates of net photosynthesis of 825 mmol O2 m-2 h-1 were calculated from measured O2 concentration gradients, and dark respiration was 1.33.3 mmol O2 m-2 h-1. From lightdark shifts, the maximal rates of gross photosynthesis at the EAC surface were calculated to be 16.5 nmol O2 cm-3 s-1. Irradiance at the onset of saturation of photosynthesis, Ek, was <100 &micro;mol photons m-2 s-1, indicating that the EAC is a shade-adapted community. The pH increased from 8.2 in the bulk seawater to 8.9 at the EAC surface, suggesting that very little carbon in the form of CO2 occurs at the EAC surface. Thus the major source of dissolved inorganic carbon (DIC) must be in the form of HCO3-. Estimates of DIC fluxes across the DBL indicate that, throughout most of the daytime under in situ conditions, DIC is likely to be a major limiting factor for photosynthesis and therefore also for primary production and growth of the EAC.
Nieuwenburg, P., Clarke, R., Cai, Z., Chen, M., Larkum, A., Cabral, N., Ghiggino, K. & Reimers, J.R. 2003, 'Examination Of The Photophysical Processes Of Chlorophyll D Leading To A Clarification Of Proposed Uphill Energy Transfer Processes In Cells Of Acaryochloris Marina', Photochemistry And Photobiology, vol. 77, no. 6, pp. 628-637.
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Larkum, A.W.D., Koch, E.M.W. & Kuhl, M. 2003, 'Diffusive boundary layers and photosynthesis of the epilithic algal community of coral reefs', MARINE BIOLOGY, vol. 142, no. 6, pp. 1073-1082.
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Larkum, A.W.D. 2003, 'Contributions of henrik lundegardh.', Photosynthesis research, vol. 76, no. 1-3, pp. 105-110.
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Henrik Lundeg&aring;rdh made major contributions in the field of ecology and plant physiology from 1912 to 1969. His early work at Hallands V&auml;der&ouml; in the Kattegat pioneered quantitative approaches to plant ecology and laid the understanding of carbon dioxide exchange in natural communities which is still useful today in global carbon accounting. Very early on in this work he invented the flame photometer. In trying to understand salt respiration of plants, he started to formulate hypotheses for the relationship between respiration and ion movement, including protons, hypotheses that were forerunners to the Chemiosmotic Hypothesis of Peter Mitchell. Necessarily, this involved work on plant cytochromes. He invented several early recording spectrophotometers and made many early discoveries in the field of plant cytochromes, including the photo-oxidation of cytochrome f in photosynthesis.
Bibby, T.S., Nield, J., Chen, M., Larkum, A.W.D. & Barber, J. 2003, 'Structure of a photosystem II supercomplex isolated from Prochloron didemni retaining its chlorophyll a/b light-harvesting system.', Proceedings of the National Academy of Sciences of the United States of America, vol. 100, no. 15, pp. 9050-9054.
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Prochlorophytes are a class of cyanobacteria that do not use phycobiliproteins as light-harvesting systems, but contain chlorophyll (Chl) a/b-binding Pcb proteins. Recently it was shown that Pcb proteins form an 18-subunit light-harvesting antenna ring around the photosystem I (PSI) trimeric reaction center complex of the prochlorophyte Prochlorococcus marinus SS120. Here we have investigated whether the symbiotic prochlorophyte Prochloron didemni also contains the same supermolecular complex. Using cells isolated directly from its ascidian host, we found no evidence for the presence of the Pcb-PSI supercomplex. Instead we have identified and characterized a supercomplex composed of photosystem II (PSII) and Pcb proteins. We show that 10-Pcb subunits associate with the PSII dimeric reaction center core to form a giant complex having an estimated Mr of 1,500 kDa with dimensions of 210 x 290 A. Five-Pcb subunits flank each long side of the dimer and assuming each binds 13 Chl molecules, increase the antenna size of PSII by approximately 200%. Fluorescence emission studies indicate that energy transfer occurs efficiently from the Pcb antenna. Modeling using the x-ray structure of cyanobacterial PSII suggests that energy transfer to the PSII reaction center is via the Chls bound to the CP47 and CP43 proteins.
Gilmore, A.M., Larkum, A.W.D., Salih, A., Itoh, S., Shibata, Y., Bena, C., Yamasaki, H., Papina, M. & Van Woesik, R. 2003, 'Simultaneous time resolution of the emission spectra of fluorescent proteins and zooxanthellar chlorophyll in reef-building corals.', Photochemistry and photobiology, vol. 77, no. 5, pp. 515-523.
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Light is absorbed by photosynthetic algal symbionts (i.e. zooxanthellae) and by chromophoric fluorescent proteins (FP) in reef-building coral tissue. We used a streak-camera spectrograph equipped with a pulsed, blue laser diode (50 ps, 405 nm) to simultaneously resolve the fluorescence spectra and kinetics for both the FP and the zooxanthellae. Shallow water (<9 m)-dwelling Acropora spp. and Plesiastrea versipora specimens were collected from Okinawa, Japan, and Sydney, Australia, respectively. The main FP emitted light in the blue, blue-green and green emission regions with each species exhibiting distinct color morphs and spectra. All corals showed rapidly decaying species and reciprocal rises in greener emission components indicating F&ouml;rster resonance energy transfer (FRET) between FP populations. The energy transfer modes were around 250 ps, and the main decay modes of the acceptor FP were typically 1900-2800 ps. All zooxanthellae emitted similar spectra and kinetics with peak emission (approximately 683 nm) mainly from photosystem II (PSII) chlorophyll (chl) a. Compared with the FP, the PSII emission exhibited similar rise times but much faster decay times, typically around 640-760 ps. The fluorescence kinetics and excitation versus emission mapping indicated that the FP emission played only a minor role, if any, in chl excitation. We thus suggest the FP could only indirectly act to absorb, screen and scatter light to protect PSII and underlying and surrounding animal tissue from excess visible and UV light. We conclude that our time-resolved spectral analysis and simulation revealed new FP emission components that would not be easily resolved at steady state because of their relatively rapid decays due to efficient FRET. We believe the methods show promise for future studies of coral bleaching and for potentially identifying FP species for use as genetic markers and FRET partners, like the related green FP from Aequorea spp.
Mi, D., Chen, M., Lin, S., Lince, M., Larkum, A.W.D. & Blankenship, R.E. 2003, 'Excitation dynamics in the core antenna in the photosystem I reaction center of the chlorophyll d-containing photosynthetic prokaryote acaryochloris marina', Journal of Physical Chemistry B, vol. 107, no. 6, pp. 1452-1457.
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Transient absorption difference spectroscopy on the picosecond time scale was used to study the ultrafast excitation dynamics in the photosystem I core antenna in Acaryochloris marina, a newly discovered marine oxygenic photosynthetic prokaryote that contains chlorophyll d as its major photopigment. Photosystem I particles were isolated using a detergent treatment of the thylakoid membranes and sucrose gradient ultracentrifugation. Steady-state fluorescence measurements at both room temperature and 77 K as well as ultrafast transient absorbance and fluorescence measurements were carried out on photosystem I. For ultrafast transient absorbance measurements, the sample was excited at 720, 740, and 75 nm with either high or low excitation energy. In each case, after a rapid (subpicosecond) energy transfer, the excitation energy resided on pigments absorbing at 710 nm. A kinetic component of about 40 ps and a nondecaying component on the order of nanoseconds were resolved. The 40-ps component was assigned to the trapping of excitation energy into the reaction center. The trapping time was confirmed by time-resolved fluorescence measurements. The 40-ps trapping time, because of the formation of a charge-separated state in the reaction center, is nearly excitation wavelength-independent. Narrow spectral-band excitations (5-nm fwhm) at 690, 720, 730, and 740 nm were used to excite different pools of the photosystem I core antenna selectivity. The initial special changes show a strong excitation wavelength dependence. An exceptionally broad, prompt bleaching, spanning from 700 to 740 nm, was induced when excitation was directly into the primary electron donor, P740, suggesting the existence of an excitonic coupling between a group of pigments, most likely the reaction center cofactors. A 2-3-ps energy equilibration process was also observed, similar to that observed in other cyanobacterial photosystem I. No evidence was found for a pool of long-wavelength antenna pigment...
Jermiin, L.S., Ho, S.Y.W., Ababneh, F., Robinson, J. & Larkum, A.W.D. 2003, 'Hetero: a program to simulate the evolution of DNA on a four-taxon tree.', Applied bioinformatics, vol. 2, no. 3, pp. 159-163.
We present a computer program to simulate the evolution of a nucleotide sequence on a phylogenetic tree with four tips. The program, Hetero, allows users to assign lineage-specific differences in the rate matrices used to describe the evolutionary process. It has a simple user interface and output, making it equally useful in the teaching and research of phylogenetics.
Helfrich, M., Bommer, B., Oster, U., Klement, H., Mayer, K., Larkum, A.W.D. & Rüdiger, W. 2003, 'Chlorophylls of the c family: absolute configuration and inhibition of NADPH:protochlorophyllide oxidoreductase.', Biochimica et biophysica acta, vol. 1605, no. 1-3, pp. 97-103.
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Using circular dichroism (CD) spectroscopy, the stereochemistry at C-13(2) of members of the chlorophyll (Chl) c family, namely Chls c(1), c(2), c(3) and [8-vinyl]-protochlorophyllide a (Pchlide a) was determined. By comparison with spectra of known enantiomers, all Chl c members turned out to have the (R) configuration, which is in agreement with considerations drawn from chlorophyll biosynthesis. Except for a double bond in the side chain at C-17, the chemical structure of Chl c(1) is identical with Pchlide a, the natural substrate of the light-dependent NADPH:protochlorophyllide oxidoreductase (POR). Thus, lack of binding to the active site due to the wrong configuration at C-13(2), which had been proposed previously, cannot be an explanation for inactivity of Chl c in this enzymic reaction. Our results show rather that Chl c(1) is a competitive inhibitor for this enzyme, tested with Pchlide a and Zn-protopheophorbide a (Zn-Ppheide a) as substrates.
Runcie, J.W., Ritchie, R.J. & Larkum, A.W.D. 2003, 'Uptake kinetics and assimilation of inorganic nitrogen by Catenella nipae and Ulva lactuca', Aquatic Botany, vol. 76, no. 2, pp. 155-174.
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The kinetics of NH4+, the assimilation of NH4+ and nitrate uptake by Catenella nipae (Rhodophyta) were compared with Ulva lactuca (Chlorophyta). Both algal species demonstrated saturable NH4+ and nitrate uptake kinetics. Uptake of NH3 by simple diffusion across the plasmalemma could not account for the observed saturation uptake kinetics of ammonia-N (NH3 + NH4+), so NH4+ was the chemical form being taken up by the transport systems of the cells. Although the Vmax of NH4+ uptake by C. nipae and U. lactuca was high (550 and 450 mol g-1 DW h-1, respectively), the Km for U. lactuca (85 M) was much lower than that for C. nipae (692 M). The Km and Vmax values for nitrate uptake were much lower than for NH4+ for both C. nipae (Km 5 M; Vmax 8.3 mol g-1 DW h-1) and U. lactuca (Km 34 M; Vmax 116 -mol g-1 DW h-1). Over the incubation times used (up to 28 min) there was no apparent induction of nitrate transport in either species. There was no evidence for induction of NH4+ transport in C. nipae but incubation time did affect the kinetics of NH4+ uptake in U. lactuca. At high concentrations of NH4+, U. lactuca rapidly assimilated it into organic N with limited build-up of intracellular NH4+ whereas C. nipae accumulated large amounts of NH4+ because uptake of NH4+ overtook the rate of assimilation. The effects of species-specific differences and experimental design on uptake-kinetic estimates are discussed in the light of the results of this other comparable studies. C. nipae is promising as a bioindicator species of the N-status of estuaries but U. lactuca changes its N-status too quickly for it to be a useful bioindicator of environmental conditions. &copy; 2003 Elsevier Science B.V. All rights reserved.
Ralph, P.J., Gademann, R., Larkum, A. & Kuehl, M. 2002, 'Spatial heterogeneity in active chlorophyll fluorescence and PSII activity of coral tissues', Marine Biology, vol. 141, no. N/A, pp. 639-646.
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Schreiber, U., Gademann, R., Bird, P., Ralph, P.J., Larkum, A. & Kuehl, M. 2002, 'Apparent light requirement for activation of photosynthesis upon rehydration of desicated beachrock microbial mats', Journal of Phycology, vol. 38, no. N/A, pp. 125-134.
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Longstaff, B.J., Kildea, T., Runcie, J.W., Cheshire, A., Dennison, W.C., Hurd, C., Kana, T., Raven, J.A. & Larkum, A.W.D. 2002, 'An in situ study of photosynthetic oxygen exchange and electron transport rate in the marine macroalga Ulva lactuca (Chlorophyta).', Photosynthesis research, vol. 74, no. 3, pp. 281-293.
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Direct comparisons between photosynthetic O(2) evolution rate and electron transport rate (ETR) were made in situ over 24 h using the benthic macroalga Ulva lactuca (Chlorophyta), growing and measured at a depth of 1.8 m, where the midday irradiance rose to 400-600 mumol photons m(-2) s(-1). O(2) exchange was measured with a 5-chamber data-logging apparatus and ETR with a submersible pulse amplitude modulated (PAM) fluorometer (Diving-PAM). Steady-state quantum yield ((F(m)'-F(t))/F(m)') decreased from 0.7 during the morning to 0.45 at midday, followed by some recovery in the late afternoon. At low to medium irradiances (0-300 mumol photons m(-2) s(-1)), there was a significant correlation between O(2) evolution and ETR, but at higher irradiances, ETR continued to increase steadily, while O(2) evolution tended towards an asymptote. However at high irradiance levels (600-1200 mumol photons m(-2) s(-1)) ETR was significantly lowered. Two methods of measuring ETR, based on either diel ambient light levels and fluorescence yields or rapid light curves, gave similar results at low to moderate irradiance levels. Nutrient enrichment (increases in [NO(3) (-)], [NH(4) (+)] and [HPO(4) (2-)] of 5- to 15-fold over ambient concentrations) resulted in an increase, within hours, in photosynthetic rates measured by both ETR and O(2) evolution techniques. At low irradiances, approximately 6.5 to 8.2 electrons passed through PS II during the evolution of one molecule of O(2), i.e., up to twice the theoretical minimum number of four. However, in nutrient-enriched treatments this ratio dropped to 5.1. The results indicate that PAM fluorescence can be used as a good indication of the photosynthetic rate only at low to medium irradiances.
Chen, M., Quinnell, R.G. & Larkum, A.W.D. 2002, 'The major light-harvesting pigment protein of Acaryochloris marina.', FEBS letters, vol. 514, no. 2-3, pp. 149-152.
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The major light-harvesting protein complex containing chlorophyll (Chl) d was isolated from Acaryochloris marina thylakoid membranes. Isolation was achieved by detergent solubilisation followed by separation on 6-40% sucrose gradients using ultracentrifugation. The best Chl d yield (70%) used 0.3% dodecyl maltoside, 0.15% octyl glucoside, 0.05% zwittergent 3-14 with the detergent:total Chl d ratio around 10:1 (w/w). Characterisation of the light-harvesting pigment protein complex (lhc) involved non-denaturing electrophoresis, SDS-PAGE, absorbance and fluorescence spectroscopy. The main polypeptide in the lhc was shown to be ca. 34 kDa and to contain Chl d and Chl a, indicating that the Acaryochloris lhc is similar to that of prochlorophytes. The Chl a level varied with the culture conditions, which is consistent with previous findings.
Cai, Z.-.L., Zeng, H., Chen, M. & Larkum, A.W.D. 2002, 'Raman spectroscopy of chlorophyll d from Acaryochloris marina.', Biochimica et biophysica acta, vol. 1556, no. 2-3, pp. 89-91.
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The Raman spectroscopy of chlorophyll (Chl) d isolated from Acaryochloris marina has been measured in the range of 250-3200 cm(-1) at 77 K following excitation of its B(x) band at 488 nm. A peak at 1659 cm(-1) of medium intensity arising from Cz=O stretching vibration in the formyl group 3(1) specific to Chl d was observed clearly. Peaks due to other Cz=O stretching vibrations of the 13(1) keto-, 13(3) ester- and 17(3) groups have also been observed with much weaker intensities. Intense Raman peaks in the range of 1000-1800 cm(-1) are reported and homologous comparison with corresponding Raman shifts of Chl a, Chl b and BChl a are presented.
Chen, M., Quinnell, R.G. & Larkum, A.W.D. 2002, 'Chlorophyll d as the major photopigment in Acaryochloris marina', Journal of Porphyrins and Phthalocyanines, vol. 6, no. 11-12, pp. 763-773.
Chlorophyll (Chl) d is the major pigment in the photosystems (PS) and light-harvesting complex(es) of Acaryochloris marina. Chl a is present in small and variable amounts in PSII and in the light-harvesting complex(es). Isolated PSII complex showed a major fluorescence emission peak at 725 nm and a smaller emission peak due to Chl d at 701 nm, while the PSI complex showed two pools of Chl d, one with emission at 730 nm and the other at 709 nm at 77 K. In PSI and PSII of classical cyanobacteria and of higher plants, where Chl a is the predominant pigment rather than Chl d, these differences are not as pronounced. Light energy absorbed by phycobiliproteins was also active in these Chl d emissions. The major light-harvesting pigment protein is similar to the prochlorophyte Chl-binding protein (pcb) and had a major emission peak at 711 nm. In Cyanobacteria an iron-stress induced Chl-binding protein (isiA) forms a polymeric ring around PSI, and so the effect(s) of iron stress on A. marina where investigated. No clear evidence could be deduced for the formation of an isiA protein under iron stress and no clear changes in the proportion of Chl d:Chl a could be discerned although phycobilins showed a decreased under iron-stress conditions, That Chl d replaces Chl a in all its functions in A. marina is clear; the advantage of this evolutionary development appears to be to enable A. marina to absorb far-red light which occurs in environments where red light is filtered out by other photosynthetic organisms. Copyright &copy; 2002 Society of Porphyrins & Phthalocyanines.
Ralph, P.J., Gademann, R. & Larkum, A. 2001, 'Zooxanthellae Expelled from Bleached Corals at 33°C Are Photosynthetically Competent', Marine Ecology Progress Series, vol. 220, pp. 163-168.
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Koop, K., Booth, D.J., Broadbent, A., Brodie, J., Bucher, D., Capone, D., Coll, J., Dennison, W.C., Erdmann, M.V., Harrison, P., Hoegh-Guldberg, O., Hutchings, P., Jones, G., Larkum, A., O'Neill, J., Steven, A., Tentori, E., Ward, S., Williamson, J. & Yellowlees, D. 2001, 'Encore: The Effect of Nutrient Enrichment on Coral Reefs. Synthesis of Results and conclusions', Marine Pollution Bulletin, vol. 42, pp. 91-120.
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Barbrook, A.C., Symington, H., Nisbet, R.E.R., Larkum, A. & Howe, C.J. 2001, 'Organisation and expression of the plastid genome of the dinoflagellate Amphidinium operculatum', MOLECULAR GENETICS AND GENOMICS, vol. 266, no. 4, pp. 632-638.
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Larkum, A.W., Karge, M., Reifarth, F., Eckert, H.J., Post, A. & Renger, G. 2001, 'Effect of monochromatic UV-B radiation on electron transfer reactions of Photosystem II.', Photosynthesis research, vol. 68, no. 1, pp. 49-60.
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The adverse effect of low intensity, small band UV-B irradiation (lambda = 305 +/- 5 nm, I = 300 mW m(-2)) on PS II has been studied by comparative measurements of laser flash-induced changes of the absorption at 325 nm, DeltaA(325)(t), as an indicator of redox changes in Q(A), and of the relative fluorescence quantum yield, F(t)/F(o), in PS II membrane fragments. The properties of untreated control were compared with those of samples where the oxygen evolution rate under illumination with continuous saturating light was inhibited by up to 95%. The following results were obtained: a) the detectable initial amplitude (at a time resolution of 30 mus) of the 325 nm absorption changes, DeltaA(325), remained virtually invariant whereas the relaxation kinetics exhibit significant changes, b) the 300 mus kinetics of DeltaA(325) dominating the relaxation in UV-B treated samples was largely replaced by a 1.3 ms kinetics after addition of MnCl(2), c) the extent of the flash induced rise of the relative fluorescence quantum yield was severely diminished in UV-B treated PS II membrane fragments but the relaxation kinetics remain virtually unaffected. Based on these results the water oxidizing complex (WOC) is inferred to be the primary target of UV-B impairment of PS II while the formation of the 'stable' radical pair P680(+*)Q(A) (-) (*) is almost invariant to this UV-B treatment.
Runcie, J.W. & Larkum, A.W. 2001, 'Estimating internal phosphorus pools in macroalgae using radioactive phosphorus and trichloroacetic acid extracts.', Analytical biochemistry, vol. 297, no. 2, pp. 191-192.
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Charpy-Roubaud, C., Charpy, L. & Larkum, A. 2001, 'Atmospheric dinitrogen fixation by benthic communities of Tikehau lagoon (Tuamotu Archipelago, French Polynesia) and its contribution to benthic primary production', Marine Biology, vol. 139, no. 5, pp. 991-997.
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Acetylene reduction rates were measured in lagoonal sediments, cyanobacterial mats and limestone surfaces between 1991 and 1995 at many sites, depths and seasons; all the studied substrata contained cyanobacteria. The acetylene reduction/15N2 fixation ratio was measured for the different communities and varied between 1.8 and 4.8, depending on substratum. Fixation rates were 1.7 to 7 times higher during daylight compared to night-time rates. N2 fixation rates ranged from 0.4 to 3.9 mg N m-2 day-1 for the lagoonal sediment/mat communities, and the rate was about 2 mg N m-2 day-1 for the lagoonal limestone substrata. Total lagoonal benthic N2 fixation contributed 24.4% of the total nitrogen requirement for the benthic primary production of benthic communities of the lagoon. The input of N2 fixation by the microbial planktonic communities (including cyanobacteria) of the lagoon, which are highly productive, is unquantified but is likely to be large.
De Beer, D. & Larkum, A.W.D. 2001, 'Photosynthesis and calcification in the calcifying algae Halimeda discoidea studied with microsensors', Plant, Cell and Environment, vol. 24, no. 11, pp. 1209-1217.
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With microsensors, we measured the steady-state microprofiles of O2, pH and Ca2+ on the topside of young segments of Halimeda discoidea, as well as the surface dynamics upon light-dark shifts. The effect of several inhibitors was studied. The steady-state measurements showed that under high light intensity, calcium and protons were taken up, while O2 was produced. In the dark, O2 was consumed, the pH decreased to below seawater level and Ca2+ uptake was reduced to 50%. At low light intensity (12 mol photons m-2 s-1), Ca2+ efflux was observed. Upon light-dark shifts, a complicated pattern of both the pH and calcium surface dynamics was observed. Illumination caused an initial pH decrease, followed by a gradual pH increase: this indicated that the surface pH of H. discoidea is determined by more than one light-induced process. When photosynthesis was inhibited by dichlorophenyl dimethyl urea (DCMU), a strong acidification was observed upon illumination. The nature and physiological function of this putative pump is not known. The calcium dynamics followed all pH dynamics closely, both in the presence and absence of DCMU. The Ca-channel blockers verapamil and nifedipine had no effect on the Ca2+ dynamics and steady-state profiles. Thus, in H. discoidea, calcification is not regulated by the alga, but is a consequence of pH increase during photosynthesis. Acetazolamide had no effect on photosynthesis, whereas ethoxyzolamide inhibited photosynthesis at higher light intensities. Therefore, all carbonic anhydrase activity is intracellular. Carbonic anhydrase is required to alleviate the CO2 limitation. Calcification cannot supply sufficient protons and CO2 to sustain photosynthesis.
Ritchie, J., Trautman, D.A. & Larkum, A.W.D. 2001, 'Phosphate limited cultures of the cyanobacterium Synechococcus are capable of very rapid, opportunistic uptake of phosphate', New Phytologist, vol. 152, no. 2, pp. 189-201.
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Phosphate uptake rates were measured in Synechococcus R-2 incubated in artificial secondary- and tertiary-treated sewage. Phosphate uptake was measured using chemical assay and 32P incorporation. Intracellular pH was measured using accumulation of 14C-labelled weak acids and bases and membrane potentials using 86Rb+/valinomycin. Synechococcus cells are capable of very rapid, opportunistic uptake of phosphate (10-30 nmol m-2s-1) even though net uptake by growing cultures was 0.5 nmol m-2 s-1. Km and Vmax in the light were not significantly different at pH0 7.5 and 10. The mean Km values were 1.91 &plusmn; 0.41 mmol m-3 and 0.304 &plusmn; 0.055 mmol m-3 for P-sufficient (secondary-treated sewage) and P-deficient (tertiary-treated sewage) cells, respectively. The transport systems probably recognize both H2PO4- and HPO42-. Intracellular inorganic phosphate is +28 to +56 kJ mol-1 from electrochemical equilibrium. In P-sufficient cells uptake is very slow in the dark (c. 0.1 nmol m-2 s-1) but phosphate-starved cells can opportunistically take up P about 100 times faster. Two separate ATP-driven phosphate uptake mechanisms (1 PO4 in per ATP) appear to be responsible for phosphate uptake by the cells. They have different Km values, different light/dark responses and electrical behaviour.
Salih, A., Larkum, A., Cox, G., Kuhl, M. & Hoegh-Guldberg, O. 2000, 'Fluorescent pigments in corals are photoprotective', Nature, vol. 408, pp. 850-853.
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All reef-forming corals depend on the photosynthesis performed by their algal symbiont, and such corals are therefore restricted to the photic zone. The intensity of light in this zone declines over several orders of magnitudefrom high and damaging levels at the surface to extreme shade conditions at the lower limit1. The ability of corals to tolerate this range implies effective mechanisms for light acclimation and adaptation2. Here we show that the fluorescent pigments3, 4, 5, 6, 7, 8, 9 (FPs) of corals provide a photobiological system for regulating the light environment of coral host tissue. Previous studies have suggested that under low light, FPs may enhance light availability4, 5. We now report that in excessive sunlight FPs are photoprotective; they achieve this by dissipating excess energy at wavelengths of low photosynthetic activity, as well as by reflecting of visible and infrared light by FP-containing chromatophores. We also show that FPs enhance the resistance to mass bleaching of corals during periods of heat stress, which has implications for the effect of environmental stress on the diversity of reef-building corals, such as enhanced survival of a broad range of corals allowing maintenance of habitat diversity.
Ralph, P.J., Gademann, R., Larkum, A. & Schreiber, U. 1999, 'In situ underwater measurements of photosynthetic activity of coral zooxanthellae and other reef-dwelling dinoflagellate endosymbionts', Marine Ecology-Progress Series, vol. 180, pp. 139-147.
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Chlorophyll fluorescence was used to assess the iu situ photosynthesis of a range of reef-dwelling endosymbionts. Such non-intrusive in situ measurements became possible after the recent development of a submersible pulse modulated fluorometer (DIVING-PA
Christen, G., Stevens, G., Lukins, P.B., Renger, G. & Larkum, A.W. 1999, 'Isolation and characterisation of oxygen evolving thylakoids from the marine prokaryote Prochloron didemni.', FEBS letters, vol. 449, no. 2-3, pp. 264-268.
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The present study describes the first successful attempt to isolate oxygen evolving thylakoids and thylakoid fragments from the marine prokaryote Prochloron didemni, a member of the recently discovered group of prochlorophytes. Oxygen evolving thylakoid membranes and fragments were isolated from seawater suspended cells of Prochloron didemni by passage of the cells through a Yeda press and subsequent differential centrifugation of the broken material. Three fractions were collected at 1000 x g, 5000 x g, and 3000 x g and identified by light microscopy as cells (and their fragments), thylakoids and membrane fragments, respectively. Pigment content, oxygen evolution rate and 77 K fluorescence spectra of these fractions were virtually identical. This finding indicates that the membrane fragments obtained are not enriched in photosystem II. The P680+* reduction kinetics of thylakoid membrane fragments were determined by monitoring flash induced absorption changes at 830 nm and analysing the time course of their decay. The multiphasic relaxation kinetics and their modification by NH2OH were found to be similar to those observed in cyanobacteria and plants. These findings provide an independent line of evidence for the idea of a high conservation of the basic structural and functional pattern of the water oxidising complex in all organisms that perform oxygenic photosynthesis.
Lockhart, P.J., Howe, C.J., Barbrook, A.C., Larkum, A.W.D. & Penny, D. 1999, 'Spectral analysis, systematic bias, and the evolution of chloroplasts [3]', Molecular Biology and Evolution, vol. 16, no. 4, pp. 573-576.
Helfrich, M., Ross, A., King, G.C., Turner, A.G. & Larkum, A.W.D. 1999, 'Identification of [8-vinyl]-protochlorophyllide a in phototrophic prokaryotes and algae: Chemical and spectroscopic properties', Biochimica et Biophysica Acta - Bioenergetics, vol. 1410, no. 3, pp. 262-272.
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[8-vinyl]-Protochlorophyllide a1 was isolated from a Prochloron sp. associated with the host ascidian, Lissoclinum patella. To obtain sufficient amounts for identification of the purified pigment, suitable extraction procedures and HPLC systems were developed. The structure was finally elucidated by UV-VIS and fluorescence spectroscopy, mass spectrometry and NMR (rotating-frame Overhauser enhancement spectroscopy). [8-vinyl]-Protochlorophyllide a was originally detected only as an intermediate in chlorophyll biosynthesis. Although its presence as a light-harvesting pigment was previously suggested in some prochlorophytes and eukaryotic algae, this is the first unequivocal demonstration of [8-vinyl]-protochlorophyllide a in an oxygenic phototroph. We also show that [8-vinyl]-protochlorophyllide a occurs in Prochloron species of four other ascidians as well as in Micromonas pusilla and Prochlorococcus marinus. The possible role of this pigment in photosynthesis is discussed. Copyright (C) 1999 Elsevier Science B.V.
Ritchie, R.J. & Larkum, A.W.D. 1998, 'Uptake of Thallium, a Toxic Heavy-Metal, in the Cyanobacterium Synechococcus R-2 (Anacystis nidulans, S. Leopoliensis) PCC 7942', Plant and Cell Physiology, vol. 39, no. 11, pp. 1156-1168.
Uptake of the toxic heavy-metal, thallium, was studied in the cyanobacterium Synechococcus R-2 (PCC 7942) using clinically available 201Tl+. Thallium was found to distribute across the plasmalemma passively, and so the accumulation ratio of the ion ([TI+]i/[Tl+]o) could be used to calculate the apparent membrane potential (i,o) of the cells (ETli,o+=i,o). The permeability of the plasmalemma to Tl+ (PTl+1 to 5 nm s-1) is higher than that of K+. Valinomycin does not increase the permeability of Tl+. Transient changes in the i,o of cells, because of electrogenic transport of ions, could be detected from its effects upon the uptake rate of Tl+. HCO3- hyperpolarized Synechococcus cells, whereas NH4+, CH3NH3+, and K+ led to depolarization. The use of Tl+ as a reporter of i,o has some inherent limitations. Tl+ is toxic at very low concentrations (inhibitory effects are apparent after about 6 h at concentrations as low as 1 mmol m-3). The rate of equilibration is slow (t1/25 to 20 min). Equilibration of Tl+ takes about 2 h, which limits its value as a membrane potential probe. Large amounts of Tl+ bind to the surface of the cells making the method impracticable for measuring accumulation ratios of less than about 10 (i,o values smaller than about -60 mV). Cultures continuously exposed to Tl+ (10 mmol m-3) eventually become Tl+ resistant by actively extruding Tl+ (Tli,o+=-3&plusmn;0.2 kJ mol-1) and so thallium cannot be used as a i,o probe in such cells.
Jones, R.J., Hoegh-Guldberg, O., Larkum, A.W.D. & Schreiber, U. 1998, 'Temperature-induced bleaching of corals begins with impairment of the CO2 fixation mechanism in zooxanthellae', Plant, Cell and Environment, vol. 21, no. 12, pp. 1219-1230.
The early effects of heat stress on the photosynthesis of symbiotic dinoflagellates (zooxanthellae) within the tissues of a reef-building coral were examined using pulse-amplitude-modulated (PAM) chlorophyll fluorescence and photorespirometry. Exposure of Stylophora pistillata to 33 and 34 &deg;C for 4 h resulted in (1) the development of strong non-photochemical quenching (qN) of the chlorophyll fluorescence signal, (2) marked decreases in photosynthetic oxygen evolution, and (3) decreases in optimal quantum yield (F(v)/F(m)) of photosystem II (PSII). Quantum yield decreased to a greater extent on the illuminated surfaces of coral branches than on lower (shaded) surfaces, and also when high irradiance intensities were combined with elevated temperature (33 &deg;C as opposed to 28 &deg;C). qN collapsed in heat-stressed samples when quenching analysis was conducted in the absence of oxygen. Collectively, these observations are interpreted as the initiation of photoprotective dissipation of excess absorbed energy as heat (qN) and O2-dependent electron flow through the Mehler-Ascorbate-Peroxidase cycle (MAP-cycle) following the point at which the rate of light-driven electron transport exceeds the capacity of the Calvin cycle. A model for coral bleaching is proposed whereby the primary site of heat damage in S. pistillata is carboxylation within the Calvin cycle, as has been observed during heat damage in higher plants. Damage to PSII and a reduction in F(v)/F(m) (i.e. photoinhibition) are secondary effects following the overwhelming of photoprotective mechanisms by light. This secondary factor increases the effect of the primary variable, temperature. Potential restrictions of electron flow in heat-stressed zooxanthellae are discussed with respect to Calvin cycle enzymes and the unusual status of the dinoflagellate Rubisco. Significant features of our model are that (1) damage to PSII is not the initial step in the sequence of heat stress in zooxanthellae, and (2) light plays ...
Schreiber, U., Gademann, R., Ralph, P.J. & Larkum, A. 1997, 'Assessment of photosynthetic performance of Prochloron in Lissoclinum patella in hospite by chlorophyll fluorescence measurements', Plant And Cell Physiology, vol. 38, no. 8, pp. 945-951.
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Two new PAM fluorometers (pulse amplitude modulated) were used in an investigation of photosynthetic performance of Prochloron resident as a symbiont in the ascidian Lissoclinum patella, growing in a coral reef of Heron Island on the Great Barrier Reef.
Franklin, L.A. & Larkum, A.W.D. 1997, 'Multiple strategies for a high light existence in a tropical marine macroalga', Photosynthesis Research, vol. 53, no. 2-3, pp. 149-159.
Acclimation to high light conditions on the top of coral reefs was examined in the coenocytic, filamentous green macroalga Chlorodesmis fastigiata (C. Ag.) Ducker. Despite having a pool of violaxanthin, high light does not induce formation of zeaxanthin in this macroalga. Exposure to 11 and 33% of surface irradiance resulted in parallel, reversible declines in F(v)/F(m) and in the number of functional PSII centers. The quantum requirement for PSII inactivation was calculated to be approx. 2 x 107 photons. Recovery of PSII activity after low photon exposures did not depend on protein synthesis, unlike at higher photon exposures, where recovery was inhibited by 50% in the presence of lincomycin. Accumulation of inactive, quenching PSII centers is proposed as a mechanism of energy dissipation; only some of these centers require protein synthesis for reactivation. In natural-sized populations, midday photoinhibition was greater in filament tips than in bases, but the number of inactive PSII centers within entire filaments did not significantly change over the course of the day. It is proposed that the higher chlorophyll concentration in the tips provides protective shading to chloroplasts in lower regions, and that cytoplasmic streaming of chloroplasts within this siphonous alga limits the cumulative exposure to high light, thereby providing another level of protection from high light stress.
La Roche, J., Van Der Staay, G.W.M., Partensky, F., Ducret, A., Aebersold, R., Li, R., Golden, S.S., Hiller, R.G., Wrench, P.M., Larkum, A.W.D. & Green, B.R. 1997, 'Evolution of chlorophyll-binding proteins', Trends in Plant Science, vol. 2, no. 4, p. 123.
Ritchie, R.J., Trautman, D.A. & Larkum, A.W.D. 1997, 'Phosphate Uptake in the Cyanobacterium Synechococcus R-2 PCC 7942', Plant and Cell Physiology, vol. 38, no. 11, pp. 1232-1241.
Phosphate uptake rates in Synechococcus R-2 in BG-11 media (a nitrate-based medium, not phosphate limited) were measured using cells grown semi-continuously and in continuous culture. Net uptake of phosphate is proportional to external concentration. Growing cells at pHo 10 have a net uptake rate of about 600 pmol m-2s-1 phosphate, but the isotopic flux for 32P phosphate was about 4 nmol m-2 s-1. There appears to be a constitutive over-capacity for phosphate uptake. The Km and Vmax of the saturable component were not significantly different at pHo 7.5 and 10, hence the transport system probably recognizes both H2PO4- and HPO42-. The intracellular inorganic phosphate concentration is about 3 to 10 mol m-3, but there is an intracellular polyphosphate store of about 400 mol m-3. Intracellular inorganic phosphate is 25 to 50 kJ mol-1 from electrochemical equilibrium in both the light and dark and at pHo 7.5 and 10. Phosphate uptake is very slow in the dark (100 pmol m-2s-1) and is light-activated (pHo 7.5 1.3 nmol m-2 s-1, PHo 10600 pmol m-2S-1). Uptake has an irreversible requirement for Mg2+ in the medium. Uptake in the light is strongly Na+-dependent. Phosphate uptake was negatively electrogenic (net negative charge taken up when transporting phosphate) at pHo 7.5, but positively electrogenic at pHo 10. This seems to exclude a sodium motive force driven mechanism. An ATP-driven phosphate uptake mechanism needs to have a stoichiometry of one phosphate taken up per ATP (1 PO4 in /ATP) to be thermodynamically possible under all the conditions tested in the present study.
Ritchie, R.J., Nadolny, C. & Larkum, A. 1996, 'Driving Forces for Bicarbonate Transport in the Cyanobacterium Synechococcus R-2 (PCC 7942).', Plant physiology, vol. 112, no. 4, pp. 1573-1584.
Air-grown Synechococcus R-2 (PCC 7942) cultures grown in BG-11 medium are very alkaline (outside pH is 10.0) and use HCO3- as their inorganic carbon source. The cells showed a dependence on Na+ for photosynthesis, but low Na+ conditions (1 mol m-3) were sufficient to support saturating photosynthesis. The intracellular dissolved inorganic carbon in the light was greater than 20 mol m-3 in both low-Na+ conditions and in BG-11 medium containing the usual [Na+] (24 mol m-3, designated high-Na+ conditions). The electrochemical potential for HCO3- in the light was in excess of 25 kJ mol-1, even in high-Na+ conditions. The Na+-motive force was greater than -12 kJ mol-1 under both Na+ conditions. On thermodynamic grounds, an Na+-driven co-port process would need to have a stoichiometry of 2 or greater ([greater than or equal to]2Na+ in/HCO3-1 in), but we show that Na+ or K+ fluxes cannot be linked to HCO3- transport. Na+ and K+ fluxes were unaffected by the presence or absence of dissolved inorganic carbon. In low-Na+ conditions, Na+ fluxes are too low to support the observed net 14C-carbon fixation rate. Active transport of HCO3- hyperpolarizes (not depolarizes) the membrane potential.
La Roche, J., van der Staay, G.W., Partensky, F., Ducret, A., Aebersold, R., Li, R., Golden, S.S., Hiller, R.G., Wrench, P.M., Larkum, A.W. & Green, B.R. 1996, 'Independent evolution of the prochlorophyte and green plant chlorophyll a/b light-harvesting proteins.', Proceedings of the National Academy of Sciences of the United States of America, vol. 93, no. 26, pp. 15244-15248.
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The prochlorophytes are oxygenic prokaryotes differing from other cyanobacteria by the presence of a light-harvesting system containing both chlorophylls (Chls) a and b and by the absence of phycobilins. We demonstrate here that the Chl a/b binding proteins from all three known prochlorophyte genera are closely related to IsiA, a cyanobacterial Chl a-binding protein induced by iron starvation, and to CP43, a constitutively expressed Chl a antenna protein of photosystem II. The prochlorophyte Chl a/b protein (pcb) genes do not belong to the extended gene family encoding eukaryotic Chl a/b and Chl a/c light-harvesting proteins. Although higher plants and prochlorophytes share common pigment complements, their light-harvesting systems have evolved independently.
Lockhart, P.J., Larkum, A.W., Steel, M., Waddell, P.J. & Penny, D. 1996, 'Evolution of chlorophyll and bacteriochlorophyll: the problem of invariant sites in sequence analysis.', Proceedings of the National Academy of Sciences of the United States of America, vol. 93, no. 5, pp. 1930-1934.
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Competing hypotheses seek to explain the evolution of oxygenic and anoxygenic processes of photosynthesis. Since chlorophyll is less reduced and precedes bacteriochlorophyll on the modern biosynthetic pathway, it has been proposed that chlorophyll preceded bacteriochlorophyll in its evolution. However, recent analyses of nucleotide sequences that encode chlorophyll and bacteriochlorophyll biosynthetic enzymes appear to provide support for an alternative hypothesis. This is that the evolution of bacteriochlorophyll occurred earlier than the evolution of chlorophyll. Here we demonstrate that the presence of invariant sites in sequence datasets leads to inconsistency in tree building (including maximum-likelihood methods). Homologous sequences with different biological functions often share invariant sites at the same nucleotide positions. However, different constraints can also result in additional invariant sites unique to the genes, which have specific and different biological functions. Consequently, the distribution of these sites can be uneven between the different types of homologous genes. The presence of invariant sites, shared by related biosynthetic genes as well as those unique to only some of these genes, has misled the recent evolutionary analysis of oxygenic and anoxygenic photosynthetic pigments. We evaluate an alternative scheme for the evolution of chlorophyll and bacteriochlorophyll.
Lukins, P.B., Post, A., Walker, P.J. & Larkum, A.W. 1996, 'P680(+) reduction in oxygen-evolving Photosystem II core complexes.', Photosynthesis research, vol. 49, no. 3, pp. 209-221.
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The kinetics of P680(+) reduction in oxygen-evolving spinach Photosystem II (PS II) core particles were studied using both repetitive and single-flash 830 nm transient absorption. From measurements on samples in which PS II turnover is blocked, we estimate radical-pair lifetimes of 2 ns and 19 ns. Nanosecond single-flash measurements indicate decay times of 7 ns, 40 ns and 95 ns. Both the longer 40 ns and 95 ns components relate to the normal S-state controlled Yz P680(+) electron transfer dynamics. Our analysis indicates the existence of a 7 ns component which provides evidence for an additional process associated with modified interactions involving the water-splitting catalytic site. Corresponding microsecond measurements show decay times of 4 s and 90 s with the possibility of a small component with a decay time of 20-40 s. The precise origin of the 4 s component remains uncertain but appears to be associated with the water-splitting center or its binding site while the 90 s component is assigned to P680(+)-QA (-) recombination. An amplitude and kinetic analysis of the flash dependence data gives results that are consistent with the current model of the oxygen-evolving complex.
Franklin, L.A., Seaton, G.G.R., Lovelock, C.E. & Larkum, A.W.D. 1996, 'Photoinhibition of photosynthesis on a coral reef', Plant, Cell and Environment, vol. 19, no. 7, pp. 825-836.
Photoinhibition of macroalgae in the epilithic algal community (EAC) of coral reefs was studied using chlorophyll fluorescence techniques at One Tree Island, Great Barrier Reef, Australia. Fv/Fm (variable to maximum fluorescence, darkened samples) of shallow macroalgae declined by 50% on fine summer and winter days, recovering in late afternoon. Within a species, thalli from low-light habitats were more photoinhibited (2h at 1400mol m-2 s-1) than those from high-light habitats. The sensitivity of Lobophora variegata (Phaeophyta) and Chlorodesmis fastigiata (Chlorophyta) increased with depth (1 versus 20 m). However, shallow Halimeda tuna (Chlorophyta) plants growing between corals were more photoinhibited than those from deep, open areas. Photoinhibition and recovery were depth- and species-specific. Shallow Lobophora and Chlorodesmis maintained a greater degree of QA oxidation during photoinhibition. In deep thalli, reduced effective quantum yield of open photosystem II centres reflected lower proportions and excitation capture efficiencies of open centres. In Lobophora, zeaxanthin formation accompanied non-photochemical fluorescence quenching (NPQ), but in Chlorodesmis NPQ was limited and no zeaxanthin or antherxanthin formed. Higher photosynthetic efficiency in the lower storey of the EAC may compensate for photoinhibition in the upper storey, thereby reconciling photoinhibition of individual thalli with previous observations of no net inhibition of community productivity.
Lockhart, P.J., Steel, M.A. & Larkum, A.W. 1996, 'Gene duplication and the evolution of photosynthetic reaction center proteins.', FEBS letters, vol. 385, no. 3, pp. 193-196.
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We investigate the evolutionary relationships between photosynthetic reaction center proteins (D1, D2, L and M) and demonstrate that the pattern of nucleotide substitution in these is more complicated than has been assumed in previous phylogenetic analyses. We show that there are serious violations of methodological assumptions in previous published studies. We conclude that there is equal support for hypotheses indicating (i) a single gene duplication of an ancestral reaction center protein followed by diversification and (ii) two independent gene duplications giving rise to proteins in oxygenic and anoxygenic systems.
Post, A., Lukins, P.B., Walker, P.J. & Larkum, A.W. 1996, 'The effects of ultraviolet irradiation on P680(+) reduction in PS II core complexes measured for individual S-states and during repetitive cycling of the oxygen-evolving complex.', Photosynthesis research, vol. 49, no. 1, pp. 21-27.
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Flash-induced absorbance measurements at 830 nm on both nanosecond and microsecond timescales have been used to characterise the effect of ultraviolet light on Photosystem II core particles. A combination of UV-A and UV-B, closely simulating the spectrum of sunlight below 350 nm, was found to have a primary effect on the donor side of P680. Repetitive measurements indicated reductions in the nanosecond components of the absorbance decay with a concomitant appearance and increase in the amplitude of a component with a 10 s time constant attributed to slow reduction of P680(+) by Tyrz when the function of the oxygen evolving complex is inhibited. Single-flash measurements show that the nanosecond components have amplitudes which vary with S-state. Increasing UV irradiation inhibited the amplitude of these components without changing their S-state dependence. In addition, UV irradiation resulted in a reduction in the total amplitude, with no change in the proportion of the 10 s contribution.
Lockhart, P.J., Steel, M.A. & Larkum, A.W.D. 1996, 'Erratum: Gene duplication and the evolution of photosynthetic reaction center proteins (FEBS 16994) (FEBS Letters 385 (1996) 193-196)', FEBS Letters, vol. 390, no. 2, p. 242.
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James, P.L. & Larkum, A.W.D. 1996, 'Photosynthetic inorganic carbon acquisition of Posidonia australis', Aquatic Botany, vol. 55, no. 3, pp. 149-157.
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Oxygen exchange of leaf segments of the seagrass Posidonia australis Hook, F. was used to assess the sources of inorganic carbon (C(i)) available to photosynthesis. Under light saturation (500 mol m-1 s-1) net photosynthesis varied from 953 nmol m-2 s-1 at pH 7.5 to 82 nmol m-2 s-1 at pH 9.0. There was no affect of pH on respiration. Only at pH 9.0 was it necessary to invoke an uptake of HCO3/- based on an unstirred layer of 50 mol. A model is discussed in which the state of equilibrium between the four forms of C(i) in and around the cell wall is determined by the rate of OH production from the dehydration of HCO3/- and the rate of OH efflux away from the leaf surface.
Larkum, A.W.D. 1995, 'Halophila capricorni (Hydrocharitaceae): a new species of seagrass from the Coral Sea', Aquatic Botany, vol. 51, no. 3-4, pp. 319-328.
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A new seagrass species, Halophila capricorni Larkum, is described in the section Halophila. This species differs from Halophila decipiens Ostenfeld in (i) its generally larger size, (ii) the pattern of large hairs on the proximal region of the abaxial leaf surface, (iii) the presence of male and female flowers in separate axils of the same plant, (iv) styles 15-25 mm long, and (v) dispersal by floating fruits. Halophila capricorni is found on sand in deep water in coral environments on the Great Barrier Reef and in New Caledonia. It may also be present in the Philippines and adjoining regions. &copy; 1995.
Larkum, A.W., Scaramuzzi, C., Cox, G.C., Hiller, R.G. & Turner, A.G. 1994, 'Light-harvesting chlorophyll c-like pigment in Prochloron.', Proceedings of the National Academy of Sciences of the United States of America, vol. 91, no. 2, pp. 679-683.
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A chlorophyll c-like pigment, similar to magnesium-3,8-divinyl pheoporphyrin a5 monomethyl ester, has been isolated from Prochloron sp. obtained from five species of didemnid ascidians from the Great Barrier Reef, Australia, and from Palau, Micronesia. The pigment represents 4-15% of the total chlorophyll content and is shown to function in a light-harvesting pigment protein complex of Prochloron. The observation that all of the major chlorophylls (a+b+c) function in a light-harvesting role in Prochloron and possibly in other prochlorophytes is discussed in terms of the phylogeny of the prochlorophytes.
Larkum, A.W.D. & Steven, A.D.L. 1994, 'ENCORE: The effect of nutrient enrichment on coral reefs. 1. Experimental design and research programme', Marine Pollution Bulletin, vol. 29, no. 1-3, pp. 112-120.
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An in situ reef fertilization experiment is being undertaken on the Australian Great Barrier Reef, to investigate the response of coral reefs to nutrient enrichment. This experiment, known as ENCORE, is designed to quantify the fate of nitrogen and phosphorus within a coral reef, and compare their impact on a variety of coral reef organisms. Co-ordinated by the Great Barrier Reef Marine Park Authority (GBRMPA), 30 scientists from eight Australian and three overseas organizations are undertaking research encompassing cellular through to community level responses. This research will provide a scientific basis for developing appropriate water quality management strategies in coral reef environments, and may identify a number of sub-lethal indicators of nutrient stress. &copy; 1994.
Lockhart, P.J., Penny, D., Hendy, M.D. & Larkum, A.D. 1993, 'IsProchlorothrix hollandica the best choice as a prokaryotic model for higher plant Chla/b photosynthesis?', Photosynthesis research, vol. 37, no. 1, pp. 61-68.
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We examine the issue of prochlorophyte origins and provide analyses which highlight the limitations of inferring evolutionary trees from anciently diverged sequences that have markedly different GC contents. Under these conditions we have found that current tree reconstruction methods strongly group together sequences with similar GC contents, whether or not the sequences share a common ancestor. We provide 3'psbA termini sequence forProchloron didemni and find it does not have the 7 amino acid deletion that occurs in Chla/b chloroplasts andProchlorothrix hollandica. This is consistent with the recent findings of a Chlc like pigment in the light harvesting system in other prochlorophytes but apparently absent inP. hollandica. From these observations we suggest thatP. hollandica is the prochlorophyte most closely related to Chla/b containing chloroplasts and hence the most appropriate prokaryotic model for higher plant Chla/b photosynthesis.
Post, A. & Larkum, A.W.D. 1993, 'UV-absorbing pigments, photosynthesis and UV exposure in Antarctica: comparison of terrestrial and marine algae', Aquatic Botany, vol. 45, no. 2-3, pp. 231-243.
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Since Antarctic plants experience a wide range of ultraviolet (UV) exposure, the pigment content of Antarctic algae (Palmaria decipiens (Reinsch) Ricker, Enteromorpha bulbosa (Suhr) Montagne, Prasiola crispa (Lightf.) K&uuml;tz. sp. antarctica (K&uuml;tzing) Knebel) was monitored over a year. In summer the mature form of the marine rhodophyte Palmaria contains a range of UV-absorbing pigments in high concentration providing a broad absorbance with a maximum at 337 nm. Juvenile fronds develop through winter with smaller absorbance maxima at 322 nm, 309 nm and 295 nm. The terrestrial chlorophyte Prasiola crispa contains a single UV-absorbing pigment with a maximum at 325 nm. Compared with other green algae, including the marine Enteromorpha, the UV-absorbing pigment in Prasiola is present in high concentrations. Variations in the level of UV-absorbance relative to chlorophyll in Prasiola, appear to correspond with varying UV exposure. To test this, Prasiola was maintained with an enhanced ratio of UV-B to visible light to simulate the effects of stratospheric ozone depletion. After 4 weeks the chlorophyll content and photosynthetic rates were reduced in the presence of enhanced UV-B light, but the ratio of UV-absorbing pigments to chlorophyll was unchanged. This suggests that even for Antarctic algae, that contain high levels of UV-absorbing pigments, exposure to sunlight with an increased ratio of UV-B to visible light is stressful. &copy; 1993.
Larkum, A.W. & Wood, W.F. 1993, 'The effect of UV-B radiation on photosynthesis and respiration of phytoplankton, benthic macroalgae and seagrasses.', Photosynthesis research, vol. 36, no. 1, pp. 17-23.
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Several species of marine benthic algae, four species of phytoplankton and two species of seagrass have been subjected to ultraviolet B irradiation for varying lengths of time and the effects on respiration, photosynthesis and fluorescence rise kinetics studied. No effect on respiration was found. Photosynthesis was inhibited to a variable degree in all groups of plants after irradiation over periods of up to 1 h and variable fluorescence was also inhibited in a similar way. The most sensitive plants were phytoplankton and deep-water benthic algae. Intertidal benthic algae were the least sensitive to UV-B irradiation and this may be related to adaptation, through the accumulation of UV-B screening compounds, to high light/high UV-B levels. Inhibition of variable fluorescence (Fv) of the fluorescence rise curve was a fast and sensitive indicator of UV-B damage. Two plants studied, a brown alga and a seagrass, showed very poor recovery of Fv over a period of 32 h.
Lockhart, P.J., Penny, D., Hendy, M.D., Howe, C.J., Beanland, T.J. & Larkum, A.W. 1992, 'Controversy on chloroplast origins.', FEBS letters, vol. 301, no. 2, pp. 127-131.
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Controversy exists over the origins of photosynthetic organelles in that contradictory trees arise from different sequence, biochemical and ultrastructural data sets. We propose a testable hypothesis which explains this inconsistency as a result of the differing GC contents of sequences. We report that current methods of tree reconstruction tend to group sequences with similar GC contents irrespective of whether the similar GC content is due to common ancestry or is independently acquired. Nuclear encoded sequences (high GC) give different trees from chloroplast encoded sequences (low GC). We find that current data is consistent with the hypothesis of multiple origins for photosynthetic organelles and single origins for each type of light harvesting complex.
Lockhart, P.J., Beanland, T.J., Howe, C.J. & Larkum, A.W. 1992, 'Sequence of Prochloron didemni atpBE and the inference of chloroplast origins.', Proceedings of the National Academy of Sciences of the United States of America, vol. 89, no. 7, pp. 2742-2746.
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The prochlorophytes, oxygenic photosynthetic prokaryotes containing chlorophylls a and b, have been put forward as descended from the organisms that gave rise to chloroplasts of green plants and algae by endosymbiosis, although this has always been controversial. To assess the phylogenetic position of the prochlorophyte Prochloron didemni, we have cloned and sequenced its atpBE genes. Phylogenetic inference under a range of models gives moderate to strong support for a cyanobacterial grouping rather than a chloroplast one. Possible systematic errors in this and previous analyses of prochlorophyte sequences are discussed.
Howe, C.J., Beanland, T.J., Larkum, A.W.D. & Lockhart, P.J. 1992, 'Plastid origins', Trends in Ecology and Evolution, vol. 7, no. 11, pp. 378-383.
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There has long been controversy over whether the plastids of green plants and algae, rhodophytes and chromophytes arose from a single primary endosymbiotic event or independently from several. DNA sequences from plastid genes are rapidly becoming available, but limitations of current phylogenetic inference techniques make it difficult to draw firm conclusions at present. However, it is clear that the endosymbiotic uptake of photosynthetic prokaryotes or eukaryotes has been far from unique. &copy; 1992.
Murray, D.R. & Larkum, A.W.D. 1992, 'Nitrogen content of seeds of Zostera capricorni and Zostera marina', Aquatic Botany, vol. 43, no. 1, pp. 87-91.
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The nitrogen (N) content of mature seeds of Zostera capricorni Aschers, was found by Kjeldahl analysis to be 1.70% of dry matter. The larger seeds of Zostera marina L. were analysed individually by the more sensitive Heraeus procedure. The mean seed N content of these seeds was 1.37% of dry matter (range 1.20-1.56%, standard deviation (SD) 0.13). Seed water contents were similar for both species, 34.7% and 32.3% of seed mass, respectively. The ecological, physiological and evolutionary significance of these observations is discussed. &copy; 1992.
Lockhart, P.J., Howe, C.J., Bryant, D.A., Beanland, T.J. & Larkum, A.W. 1992, 'Substitutional bias confounds inference of cyanelle origins from sequence data.', Journal of molecular evolution, vol. 34, no. 2, pp. 153-162.
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Available molecular and biochemical data offer conflicting evidence for the origin of the cyanelle of Cyanophora paradoxa. We show that the similarity of cyanelle and green chloroplast sequences is probably a result of these two lineages independently developing the same pattern of directional nucleotide change (substitutional bias). This finding suggests caution should be exercised in the interpretation of nucleotide sequence analyses that appear to favor the view of a common endosymbiont for the cyanelle and chlorophyll-b-containing chloroplasts. The data and approaches needed to resolve the issue of cyanelle origins are discussed. Our findings also have general implications for phylogenetic inference under conditions where the base compositions (compositional bias) of the sequences analyzed differ.
Murray, D.R. & Larkum, A.W.D. 1991, 'Seed proteins of the seagrass Zostera capricorni', Aquatic Botany, vol. 40, no. 2, pp. 101-108.
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Proteins were extracted from the seeds of the seagrass Zostera capricorni Aschers. and analysed by polyacrylamide gel electrophoresis. Pore-gradient gel electrophoresis revealed a predominant storage protein of estimated Mr 340 000, which we have termed 'zosterin'. This protein accounted for about 80% of extractable protein. Dissociation of proteins by the anionic detergent, sodium dodecylsulphate (SDS), in the absence and presence of 2-mercaptoethanol confirmed that disulphide-linked subunits associate to form zosterin. On electrophoresis in uniform-pore gels set from 10% acrylamide, five major subunits were resolved (polypeptides I-V), of estimated Mr 30 000, 27 500, 24 000, 22 000 and 20 500, respectively. These subunits associate to form disulphide-bridged constituents of two size classes, Mr 54 000 and 46 000, with the former predominating ( 2:1). Zosterin is clearly a counterpart of legumin, one of the major storage proteins of legume seeds. &copy; 1991.
Larkum, A.W.D. & West, R.J. 1990, 'Long-term changes of seagrass meadows in Botany Bay, Australia', Aquatic Botany, vol. 37, no. 1, pp. 55-70.
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Long-term changes of seagrass meadows (Posidonia australis Hook. f. and Zostera capricorni Aschers.) in Botany Bay, Australia, were investigated using historical aerial photography (1930-1985), field observations (1970-1987) and in situ sediment coring for fibrous remains of Posidonia. Aerial photography and field observations indicated that P. australis had undergone a steady decline in distribution in Botany Bay over the past 40 years. Between 1942 and 1984, 58% (257 ha) of Posidonia was lost from the bay's southern foreshores. By 1987, the once continuous meadow of Posidonia consisted of a number of fragmented beds. The decline occurred during a period of industrial and residential development in the catchment, which included the dredging of the bay's entrance to allow passage of large container ships. The dredging caused an increased wave height in many parts of the bay, and resulted in deterioration and erosion of seagrass beds, particularly during storm events. As an example of this process, the effect of minor storms in reducing leaf biomass of Posidonia by 70% is reported. Grazing by the sea urchin, Heliocideras erythrogramma (Valenc.), between 1980 and 1986 was responsible for smaller losses of Posidonia. The existence of fibrous remains in sediment cores offered circumstantial evidence that Posidonia had a much wider distribution in Botany Bay prior to the earliest aerial photography. A history of poor catchment management, uncontrolled effluent disposal and widespread dredging is suggested as the cause for these earlier, unquantified losses. Over the same period (1930-1987), Z. capricorni was found to have undergone cyclical fluctuations in area throughout the bay, and had colonised many sites that were previously vegetated with Posidonia. &copy; 1990.
Fork, D.C. & Larkum, A.W.D. 1989, 'Light harvesting in the green alga Ostreobium sp., a coral symbiont adapted to extreme shade', Marine Biology, vol. 103, no. 3, pp. 381-385.
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Ostreobium sp. (Chlorophyta: Siphonales) can be found as green bands within the skeletal material of a number of stony corals in the Indo-Pacific and Caribbean regions. Many of these corals also contain symbiotic dinoflagellates in the overlaying coral polyps that effectively screen out all the typical photosynthetically active radiation from the algae in the green bands below. Ostreobium sp., nevertheless, grows photosynthetically. Its action spectrum and absorption spectrum have been shown to extend much further into the near infra-red compared to other green algae. In the present study, carried out in 1987, fluorescence excitation and emission spectra were measured in Ostreobium sp. and compared to spectra obtained from the green alga Ulva sp. and the brown alga Endarachne sp. Xanthophylls, probably siphonein and an unidentified xanthophyll probably related to siphonaxanthin, are photosynthetically active in Ostreobium sp., and can sensitize Photosystem II fluorescence at 688 nm and Photosystem I (PS I) fluorescence at 718 nm. The fluorescence emission spectra of Ostreobium sp. measured at 25&deg; C and 77 K were not remarkably different from those of the green alga Ulva sp. Absorbance changes induced by light were measured in Ostreobium sp. from 670 to 750 nm and were like those normally seen in green plants except that, in addition to the minimum expected for the reaction-center chlorophyll of PS I (P700) at 703 nm, another minimum was seen at 730 nm. It is possible that this spectrumreflects the functioning of a reaction center of Photosystem I that has adapted to function in light highly enriched in far-red wavelengths. &copy; 1989 Springer-Verlag.
Lockhart, P.J., Larkum, A.W.D., Beanland, T.J. & Howe, C.J. 1989, 'The isolation of high molecular mass DNA from the prochlorophyte Prochloron didemni', FEBS Letters, vol. 248, no. 1-2, pp. 127-130.
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Using a protocol known to inactivate endogenous nucleases in other organisms we have been able to isolate high molecular mass DNA from Prochloron didemni. This DNA is shown to be suitable for restriction endonuclease analysis and the generation of genomic libraries in the cloning vector EMBL3. &copy; 1989.
Chrystal, J. & Larkum, A.W.D. 1988, 'Preservation of long-wavelength fluorescence in the isolated thylakoids of two phytoplanktonic algae at 77 K', BBA - Bioenergetics, vol. 932, no. C, pp. 189-194.
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Loss of long-wavelength fluorescence upon isolation of chloroplasts or thylakoids has long been a problem in studies of the chromophyte algae, that is, algae possessing chlorophyll c and related algae. We now report the preservation of long-wavelength fluorescence, using two such algae, Phaeodactylum tricornutum (Bacillariophyta) and Vischeria helvetica (Eusigmatophyta). Preservation was achieved using an isolation buffer of high osmotic and ionic strength. Anions high on the Hofmeister series were more efficient than anions low on the Hofmeister series. The most efficient buffer was one high in phosphate (0.5 M) and citrate (0.3 M) combined with 0.3 M sucrose. The results indicate that there are basic differences at the molecular level between the arrangement in the thylakoid membrane of chlorophyll-protein complexes of the chromophyte and related algae compared to green algae and higher plants. &copy; 1988.
Hiller, R.G., Larkum, A.W.D. & Wrench, P.M. 1988, 'Chlorophyll proteins of the prymnesiophyte Pavlova lutherii (Droop) comb. nov.: Identification of the major light-harvesting complex', BBA - Bioenergetics, vol. 932, no. C, pp. 223-231.
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A chlorophyll ac-fucoxanthin light-harvesting protein has been separated by SDS-polyacrylamide gel electrophoresis and by digitonin-sucrose density centrifigation from thylakoids of Pavlova lutherii. It contains a single major polypeptide of 21 kDa, comprises 69% of the total chlorophyll a and is enriched in chlorophyll c compared to the thylakoids. Energy transfer from chlorophyll c and fucoxanthin to chlorophyll a was demonstrated within the protein complex. Antibodies to the 21 kDa apoprotein showed cross-reactivity with the 26-28 kDa apoproteins of higher plant light-harvesting chlorophyll a b protein and with the 19 kDa apoprotein of the light-harvesting complex of diatoms, but much reduced or no cross-reactivity with the major thylakoid polypeptides of dinoflagellates and cryptophytes. &copy; 1988.
Larkum, A.W.D., Kennedy, I.R. & Muller, W.J. 1988, 'Nitrogen fixation on a coral reef', Marine Biology, vol. 98, no. 1, pp. 143-155.
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Acetylene reduction was used to assess nitrogen fixation on all major substrates at all major areas over a period of 1 to 6 yr (1980-1986) at One Tree Reef (southern Great Barrier Reef). Experiments using 15N2 gave a ratio of 3.45:1.0 for C2H2 reduced:N2 fixed. Acetylene reduction was largely light-dependent, saturated at 0.15 ml C2H2 per ml seawater, and linear over 6 h. High fixation was associated with two emergent cyanophyte associations, Calothrix crustacea and Scytonema hofmannii, of limited distribution. Subtidally, the major contribution to nitrogen fixation came from well-grazed limestone substrates with an epilithic algal community in the reef flat and patch reefs (3 to 15 nmol C2H4 cm-2 h-1). Similar substrates from the outer reef slope showed lower rates. Nitrogen fixation on beach rock, intertidal coral rubble, reef crest and lagoon sand was relatively small (0.3 to 1.0 nmol C2H4 cm-2 h-1). Seasonal changes in light-saturated rates were small, with slight reduction only in winter. Rates are also reported for experimental coral blocks (13 to 39 nmol cm-2 h-1) and for branching coral inside and outside territories of gardening damselfish (3 to 28 nmol cm-2 h-1). This work supports the hypothesis that the high nitrogen fixation on the reef flat and patch reefs of the lagoon (34 to 68 kg N ha-1 yr-1) is because these subtidal areas support highly disturbed communities with the greatest abundance of nitrogen-fixing cyanophyte algae. It is calculated from a budget of all areas that One Tree Reef has an annual nitrogen fixation rate of 8 to 16 kg N ha-1 yr-1. &copy; 1988 Springer-Verlag.
Larkum, A.W.D. 1988, 'High rates of nitrogen fixation on coral skeletons after predation by the crown of thorns starfish Acanthaster planci', Marine Biology, vol. 97, no. 4, pp. 503-506.
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At One Tree Reef, Great Barrier Reef, Australia, between 1983 and 1985, corals killed by the crown of thorns seastar Acanthaster planci L. gave rise to skeletons which were colonised rapidly by blue-green and other algae. For the next 3 to 9 mo these coral skeletons showed over three times more nitrogen fixation (acetylene reduction) than control substratum rates (9 to 32 nmol vs 3 to 10 nmol C2H2 cm-2 h-1, over all seasons). These values convert to relatively high annual fixation rates of 37 to 127 kg N ha-1 yr-1 but, at the low densities of A. planci on One Tree Reef (ca. 0.65 ha-1), this has little impact on the total nitrogen fixation rate and, as a result, on the level of organic nitrogen in the system. However, it is suggested that on reefs subjected to high aggregations of a. planci such an effect would enhance the level of organic nitrogen and lead to greater primary and secondary production throughout the reef system. &copy; 1988 Springer-Verlag.
Koop, K. & Larkum, A.W.D. 1987, 'Deposition of organic material in a coral reef lagoon, One Tree Island, Great Barrier Reef', Estuarine, Coastal and Shelf Science, vol. 25, no. 1, pp. 1-9.
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Deposition of organic material was measured at four sites on One Tree Island coral reef using fixed sediment traps. Although no reliable data were obtained for the reef crest area because of problems of resuspension, mean deposition in the backreef area amounted to some 4 g organic C m-2 day-1 whereas in the lagoon it was about 15 g C m-2 day-1. This amounted to mean nitrogen deposition rates of 160 and 95 mg N m-2 day-1, respectively. As primary production by turf algae, the principal producers at One Tree Island, has been estimated at about 23 g C m-2 day-1 for the whole reef system and the weighted mean carbon deposition is estimated at 22 g C m-2 day-1, it is clear that the carbon produced by plants is largely retained in the system. Nitrogen deposition, on the other hand, amounted to only about 60% of that produced by turf algae and it must be assumed that much of this leached into the water during sedimentation. Losses of nitrogen may be minimized by incorporation of dissolved nitrogen by pelagic microheterotrophs which may in turn be consumed by filter feeders before they leave the reef. &copy; 1987.
Larkum, A.W.D., Cox, G.C., Hiller, R.G., Parry, D.L. & Dibbayawan, T.P. 1987, 'Filamentous cyanophytes containing phycourobilin and in symbiosis with sponges and an ascidian of coral reefs', Marine Biology, vol. 95, no. 1, pp. 1-13.
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A study was made of the ultrastructure and pigment composition of filamentous cyanophytes living in symbiosis with several sponges and a colonial didemnid ascidian collected from the southern end of the Great Barrier Reef, Australia, between 1983 and 1986. The sponges were Dysidea herbacea Keller and several other encrusting sponges which have not been identified; the ascidian was Trididemnum miniatum Kott (1977). The cyanophyte Oscillatoria spongeliae (Shultz) Hauck was identified as the symbiont of several of the sponges, including D. herbacea. Two other unidentified Oscillatoria species were found in a bristly papillate sponge and in T. miniatum. Chlorophyll a, alone, was present in all the symbionts with the exception of T. miniatum, which contained the cosymbiont Prochloron and where chlorophyll b was also present. Two phycoerythrins were isolated by chromatography and chromatofocusing. Both resembled C-phycoerythrin, but one of the two carried the chromophore phycourobilin as well as phycoerythrobilin possibly on both the and subunits, which had apparent molecular masses of 18 and 20 kdaltons. No subunit was present. Ultrastructurally, the three Oscillatoria species were distinguished by an unusual type of parallel, longitudinal, thylakoid organisation; the arrangement was different in detail in each species. &copy; 1987 Springer-Verlag.
Larkum, A.W.D. 1986, 'A study of growth and primary production in Ecklonia radiat (C.Ag.) J. Agardh (Laminariales) at a sheltered site in Port Jackson, New South Wales', Journal of Experimental Marine Biology and Ecology, vol. 96, no. 2, pp. 177-190.
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A mature closed-canopy forest of Ecklonia radiata (C. Ag.) J. Agardh at a depth of 1.5 m was studied over a period of 18 months. Growth of the primary frond was assayed using a punched-hole technique, with bimonthly sampling. Tagged plants were harvested and measurements made on age, growth, size, and dry weight (DW) of stipe and frond. Each frond was cut into 5-cm strips and the dry weight obtained. Surface area measurements were obtained in the late autumn and late spring. Extension growth of the primary frond was lowest in summer (7.6 mm day-1) and showed a period of high activity from July (17.1 mm day-1) to September (19.6 mm day-1). The size and mass of the whole frond lagged behind the growth of the primary frond reaching a maximum in November or December (mean dry wt 99 g; length 46.3 cm; surface area, 7216 cm2). It is possible, therefore, that growth of lateral meristems continued after the period of maximum growth of the primary meristem. Disregarding this possibility of error in mean growth rate and using the data on extension of the primary frond and the mean biomass of the mature regions of the frond, production varied from a minimum in May (0.27 g DW plant-1 day-1) to a maximum in September (0.50 g DW plant-1 day-1). For a mean density of mature plants in the community of 22.5 m-2, these values lead to a primary production rate of 3.1 kg DW m-2 yr-1 which is similar to values found in other kelps. A second method for measuring production is suggested, which takes into account the lag in growth of secondary fronds. This method yields a similar annual mean primary production rate of 2.9 kg DW m-2 yr-1 but leads to higher values in spring and lower values in autumn than the first method. &copy; 1986.
BOROWITZKA, M.A. & LARKUM, A.W.D. 1986, 'REEF ALGAE', OCEANUS, vol. 29, no. 2, pp. 49-54.
Ritchie, R.J. & Larkum, A.W.D. 1985, 'Potassium transport in Enteromorpha intestinalis (L.) link: II. Effects of medium composition and metabolic inhibitors', Journal of Experimental Botany, vol. 36, no. 3, pp. 394-412.
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In springwater (25.5 mol m-3 Cl-, 20.4 mol m-3 Na+, 0.14 mol m-3 K+) Enteromorpha intestinalis could not survive for more than a few weeks unless provided with 0.5 mol m-3 K+ in the medium or alternatively exposed to seawater for 1 day per week. Maintenance of a cytoplasmic K+ level of about 200 mol m-3 is critical for the maintenance of normal metabolic activity. Net gains of intracellular K+ occurred when the plants were transferred from low-salinity to seawater; conversely large net losses occurred when plants were transferred from seawater to springwater. These two processes were not simply the reverse of one another; net gain of K+ involved a large increase in the tracer flux both into and out of the cell but net loss of K+ virtually halted the tracer flux into the cell. Any injury incurred by rapid salinity changes was short-lived; plants were rapidly able to adjust intracellular [K1.K+). K+(or to some extent Rb+) was found to be necessary in the efflux medium for 42K+ exchange to occur. The osmotic concentration of the medium was also important but extracellular Na+ and Cl-concentrations were not critical. K+ influx and efflux in both springwater and seawater were largely independent of light and were sensitive in varying degrees to a range of common metabolic inhibitors and uncouplers. The results are best explained by the presence of an active K+ influx, generated by an ATP-dependent K+ pump at the plasmalemma. &copy; 1985 Oxford University Press.
Hiller, R.G. & Larkum, A.W.D. 1985, 'The chlorophyll-protein complexes of Prochloron sp. (Prochlorophyta)', BBA - Bioenergetics, vol. 806, no. 1, pp. 107-115.
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Chlorophyll-protein complexes have been isolated from Prochloron sp. by SDS-polyacrylamide gel electrophoresis and SDS-sucrose-gradient centrifugation. Complexes associated with Photosystem I have significant amounts of chlorophyll b and a principle polypeptide of 70 kDa. The largest Photosystem I complex had an Mr of more than 300 000 kDa, a chlorophyll a b ratio of 3.8 and a chlorophyll/P-700 ratio of approx. 100. Complexes enriched in chlorophyll b showed reduced electrophoretic mobility compared to spinach LHCP3, a higher Chl a b ratio (approx. 2.4) and had a principle polypeptide of 34 kDa. Neither the 34 kDa or any other polypeptide showed cross-reactivity with antibodies to spinach light-harvesting chlorophyll a b protein in a Western blot test. &copy; 1985.
Cox, G.C., Hiller, R.G. & Larkum, A.W.D. 1985, 'An unusual cyanophyte, containing phycourobilin and symbiotic with ascidians and sponges', Marine Biology, vol. 89, no. 2, pp. 149-163.
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A study was made of the pigment composition and ultrastructure of a unicellular cyanophyte living in symbiosis with colonial didemnid ascidians and encrusting sponges collected from the southern end of the Great Barrier Reef, Australia, in 1981-1984. The ascidians were Trididemnum tegulum Kott and T. clinides. Kott; the sponges were Prianos aff. melanos de Laubenfels, Spirastrella aff. decumbens Ridley and an unidentified brown fleshy sponge (BFS). This cyanophyte seems to be identical with Synechocystis trididemni Lafargue et Duclaux. A phycoerythrin containing both phycourobilin and phycoerythrobilin chromophores was shown to be present; the urobilin was carried on and subunits, no subunit was found. A second phycoerythrin possessing only erythrobilin chromophores was also present. In thin-sections the cells showed no central DNA-containing nucleoid, and an unusual thylakoid arrangement with some thylakoids having greatly expanded lumens forming pseudo-vacuoles in the centre of the cell. Freeze-fracture showed 11 to 12 nm particles on both PF (protoplasmic face) and EF (exoplasmic face) faces of thylakoids. In many ways, the ultrastructure resembled that of the chlorophyll-b containing prokaryote Prochloron spp. &copy; 1985 Springer-Verlag.
Ritchie, R.J. & Larkum, A.W.D. 1985, 'Potassium transport in Enteromorpha intestinalis (L.) link: Measurement OF intracellular k+, EXCHANGE fluxes AND thermodynamic analysis', Journal of Experimental Botany, vol. 36, no. 1, pp. 63-78.
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Potassium transport has been studied in the marine euryhaline alga, Enteromorpha intestimlis cultured in seawater and in low-salinity medium (Artificial Cape Banks Spring Water, ACBSW; 255 mol m-3 Cl-, 204 mol m-3 Na+, 05 mol m-3 K+). K+ fluxes were measured using 42K+ and 86Rb+ although 86Rb+ does not act as an efficient K+ analogue in this plant. 42K+ experiments on seawater plants typically exhibited a single protoplasmic exchange phase whereas 86Rb+ exhibited two exchange phases. Compartmental analysis of 86Rb+ efflux experiments on seawater-grown Enteromorpha plants were used to deduce the intracellular partition of K+ between the cytoplasm (279&plusmn;38 mMolal) and vacuole (405&plusmn;68 mMolal). The plasmalemma K+ flux in plants in seawater was greater in the light than in the dark (563&plusmn;108 nmol m-2 s-1 versus 389&plusmn;667 nmol m-2 s-1). In low-salinity plants, separate cytoplasmic and vacuolar exchange phases were apparent. Analysis of 42K+ efflux experiments on low-salinity plants yielded a cytoplasmic K+ of 222&plusmn;38 mMolal and a vacuolar K+ of 82&plusmn;11 mMolal. The plasmalemma and tonoplast flux was 23&plusmn;45 nmol m-2 s-1.The Nernst equation showed that, although K+ was close to electrochemical equilibrium, active accumulation of K+ across the plasmalemma occurred in plants in seawater and ACBSW both in the light and dark. K+ was also actively transported inwards across the tonoplast in low-salinity plants. The electrochemical potential for K+ across the plasmalemma ranged from 241&plusmn;060 kJ mol-1 in plants grown in seawater in the light to 579&plusmn;087 kJ mol-1 for plants in ACBSW in the light. Although K+ is close to electrochemical equilibrium, the flux of K+ in plants in both seawater and ACBSW media is high, hence the power consumption of K+ transport is high. The permeability of K+ (PK+) was significantly higher in the light than in the dark in plants in seawater (about 70 versus 25 nm s-1) but in plants in low-salinity (ACBSW) medium the permeability was independent of l...
Tyerman, S.D., Hatcher, A.I., West, R.J. & Larkum, A.W.D. 1984, 'Posidonia australis growing in altered salinities: leaf growth, regulation of turgor and the development of osmotic gradients.', Australian Journal of Plant Physiology, vol. 11, no. 1-2, pp. 35-47.
Leaf growth was unaffected by salinities from 13-57per mille and net photosynthesis was unaffected by reduction in salinity from 34per mille to 19per mille. The cells of the leaves and rhizome adjusted their osmotic pressure by changes in Na+, K+ and Cl- concentrations such that turgor varied only between 0.67-1.52MPa over a range in external osmotic pressures from 0.83-3.89MPa. The tolerance of P. australis to changes in salinity in the absence of severe physical disturbance is largely due to the sheath and to the osmotic pressure gradient. -from Authors
Larkum, A.W.D., Collett, L.C. & Williams, R.J. 1984, 'The standing stock, growth and shoot production of Zostera capricorni aschers. in Botany Bay, New South Wales, Australia', Aquatic Botany, vol. 19, no. 3-4, pp. 307-327.
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Zostera capricorni Aschers. occurs at many shallow sites in Botany Bay, with the exception of one 5-km section of exposed sandy beach; however, bed distribution is very patchy. Details are given for shoot and underground biomass (g fresh weight), shoot density, leaf length and leaf width at 20 representative sites around the Bay. Z. capricorni was found to grow best between -0.2 and -1.0 m, with a lower limit between -2.0 m (northern side) and -3.2 m (southern side). The mean percentage cover was determined for six large areas in the bay. Shoot biomass (g dry weight) was found to be logarithmically related to percentage cover, whereas shoot density (numbers m-2) was linearly related to percentage cover. Large seasonal changes occurred, with a winter die-back characterised by a 4-fold reduction in shoot biomass and a 2-fold reduction in shoot numbers. Flowering occurred from September to April. An equation is presented for determining the total above-ground stock for an area. The total summer above-ground stock of the bay was estimated at 18 &plusmn; 8.1 tonnes for a total area of beds of 309 ha. Mean annual leaf production was estimated to be 5.22 &plusmn; 0.52 gDW m-2 day-1 for a representative healthy bed at 0.3 m depth, and leaf plus flower production was 5.86 &plusmn; 0.59 gDW m-2 day-1. The total above-ground production for all the beds of the bay was estimated to be 512.7 &plusmn; 51.3 tonnes year-1, i.e. 1.66 &plusmn; 0.17 tonnes ha-1 year-1. &copy; 1984.
RITCHIE, R.J. & LARKUM, A.W.D. 1984, 'SODIUM TRANSPORT IN ENTEROMORPHA INTESTINALIS (L.) LINK', New Phytologist, vol. 97, no. 3, pp. 347-362.
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Sodium transport was studied in the marine euryhaline alga, Enteromorpha intestinalis in seawater (465 mM Na+ and in low salinity medium [Artificial Cape Banks Spring Water (ACBSW), 25.5 mM Cr, 20.4 mM Na+, 0.5 mM K+]. The intracellular Na+ concentration ([Na+1]) of E. intestinalis was so low that it was difficult to detect using chemical and 22Na+ methods. Consequently, intracellular Na+ fluxes were also difficult to measure. Most of the Na+of the Enteromorpha tissue was bound to the fixed negative charges of the cell wall and this binding has, in previous studies, led to great overestimates of the intracellular Na+ of this plantData of 22Na+ labelling gave lower estimates of the Na+1] than a rinsing technique using isotonic Ca(NO3)2. The overall mean [Na+1] of seawater plants was only 5.5 &plusmn; 1.4 mM, with a value of 0.623 &plusmn; 0.163 mM Na+ in ACBSW plants. With one exception, all the seawater 22Na+ experiments indicated a single intracellular exchange phase, i.e. a separate vacuolar phase could not be detected. The data on plants grown at low salinity could be interpreted as having either a single intracellular phase or two intracellular phases because of the problem of cell wall Na+ exchange. No significant difference was found in total 22Na+ uptake or exchange fluxes in the light and dark in seawatergrown plants but there may have been a light effect on low salinity plants. The Na+ flux in Enteromorpha plants in seawater was about 3 nmol m2 s1 and in low salinity plants was about 0.2 nmol m2 s1. Sodium in Enteromorpha is far from electrochemical equilibrium (more than &#8211;100 mV) in plants in both seawater and ACBSW medium so that Na+ is actively excluded from the cells. The plasmalemma has a very low Na+ permeability (seawater, 3 pm s1; ACBSW plants, either 3 or 100 pm s1 depending on which compartmentation model is accepted). Copyright &copy; 1984, Wiley Blackwell. All rights reserved
RITCHIE, R.J. & LARKUM, A.W.D. 1984, 'CHLORIDE TRANSPORT IN ENTEROMORPHA INTESTINALIS (L.) LINK', New Phytologist, vol. 97, no. 3, pp. 319-345.
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Rates of 36Cl labelling, efflux and uptake were measured on Enteromorpha plants grown in seawater (547 mM Cl), and also in brackish water medium [Artificial Cape Banks Spring Water (ACBSW), 25.5 mM Cl, 20.4 mM Na+ and 0.5 mM K+]. Efflux experiments showed that, in Enteromorpha plants grown in seawater, light did not affect Cl fluxes at the plasmalemma and tonoplast. Typical experiments exhibited two exchanged phases but a significant number (8/32) exhibited a single exchange phase; this was more likely to occur in darkness. Influx experiments also showed no effect of light on the tonoplast flux. Transfer of plants grown and labelled in seawater to low salinity medium caused a rapid loss of 36C1 label; however, this was related to the change in osmotic potential of the medium rather than to changes in [Clo] or [K+0]. Exchange of 36Cl did not depend on [K+o] in seawater. Cyanide decreased 36Cl uptake in the dark but not in the light. In low salinity medium (ACBSW), 36Cl labelling and the plasmalemma flux in Enteromorpha plants were independent of light; however, the intracellular compartmentation of Cl differed between light and dark. The tonoplast flux was also greater in the light. Intracellular Cl was about 300 mmol kg1 in seawater plants and about 159 mmolkg1 in ACBSW plants. The cytoplasmic Cl concentration ([CI0]) based on compartmental analysis was about 200 mM in Enteromorpha plants in seawater and ACBSW medium. Use of this [Cl0] value and the Nernst equation suggests active Cl uptake in plants in both seawater and ACBSW. However it is unlikely that the cytoplasmic [Cl] is above about 70 to 100 mM since many cytoplasmic enzymes are inhibited by high [Cl0]. Taking this lower estimate of [C10], the Nernst criterion suggests passive accumulation of Cl across the plasmalemma in seawater but active transport would be likely in plants in ACBSW medium. Where separate plasmalemma and tonoplast fluxes were detectable, plasmalemma fluxes were hi...
Stewart, A.C. & Larkum, A.W. 1983, 'Photosynthetic electron transport in thylakoid preparations from two marine red algae (Rhodophyta).', The Biochemical journal, vol. 210, no. 2, pp. 583-589.
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Thylakoid membrane preparations active in photosynthetic electron transport have been obtained from two marine red algae, Griffithsia monilis and Anotrichium tenue. High concentrations (0.5-1.0 M) of salts such as phosphate, citrate, succinate and tartrate stabilized functional binding of phycobilisomes to the membrane and also stabilized Photosystem II-catalysed electron-transport activity. High concentrations (1.0 M) of chloride and nitrate, or 30 mM-Tricine/NaOH buffer (pH 7.2) in the absence of salts, detached phycobilisomes and inhibited electron transport through Photosystem II. The O2-evolving system was identified as the electron-transport chain component that was inhibited under these conditions. Washing membranes with buffers containing 1.0-1.5 M-sorbitol and 5-50 mM concentrations of various salts removed the outer part of the phycobilisome but retained 30-70% of the allophycocyanin 'core' of the phycobilisome. These preparations were 30-70% active in O2 evolution compared with unwashed membranes. In the sensitivity of their O2-evolving apparatus to the composition of the medium in vitro, the red algae resembled blue-green algae and differed from other eukaryotic algae and higher plants. It is suggested that an environment of structured water may be essential for the functional integrity of Photosystem II in biliprotein-containing algae.
Kennelly, S.J. & Larkum, A.W.D. 1983, 'A preliminary study of temporal variation in the colonization of subtidal algae in an Ecklonia radiata community', Aquatic Botany, vol. 17, no. 3-4, pp. 275-282.
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Temporal changes in the colonization of settlement plates by algae were determined for an Ecklonia radiata (C. Ag.) J. Ac community. Relative covers of individual algal types were recorded on plates that were exposed for short periods (2 weeks) and then taken to the laboratory. Sets of plates were examined each month from April 1981 to March 1982. Marked seasonal changes were detected in the total cover of algae, the relative covers of individual algal types and the diversity of the colonizing community (as measured by the Shannon-Weaver diversity index and the number of algal types). Advantages and disadvantages of this method and other methods to determine the structure of the colonizing community are discussed. It is concluded that, in addition to examining subsequent biological processes, future studies on the dynamics of kelp communities should also estimate temporal variation in the settlement of algae. &copy; 1983.
Hatcher, B.G. & Larkum, A.W.D. 1983, 'An experimental analysis of factors controlling the standing crop of the epilithic algal community on a coral reef', Journal of Experimental Marine Biology and Ecology, vol. 69, no. 1, pp. 61-84.
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The hypotheses that grazing losses and/or ambient inorganic nitrogen concentrations control the standing crop of the epilithic algal community were tested in two habitats at One Tree Reef (Great Barrier Reef, Australia). Short (12-15 days) and long (167-306 days) multifactorial experiments using grazer exclusion and nitrogen fertilization treatments were used to partition variance in algal community biomass on portable segments of natural reef substratum during 1980. On outer reef slopes, inorganic nitrogen limited algal community growth, but the standing crop was determined by grazing losses. In the subtidal lagoon inorganic nitrogen and grazing alternated seasonally in controlling standing crop. The recolonization of cleared natural substratum was followed at two additional sites. The algal standing crop in subtidal habitats reached control levels within 4 months, while that in an intertidal reef habitat took up to 14 months. The standing crop of benthic algae on natural reef substrata was monitored in all habitats over 2 yr. In shallow and intertidal habitats, the standing crop was three to five times higher than in deeper areas, and showed a spatial and seasonal variation apparently controlled by factors other than grazing intensity, despite high levels of yield to grazers. Seasonal variation was much less in subtidal habitats. It is concluded that only within limited temporal and spatial scales is grazing intensity alone an adequate predictor of benthic algal standing crop. &copy; 1983.
Larkum, A.W.D. & Barrett, J. 1983, 'Light-harvesting Processes in Algae', Advances in Botanical Research, vol. 10, no. C, pp. 1-219.
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Ritchie, R.J. & Larkum, A.W.D. 1982, 'Ion exchange fluxes of the cell walls of Enteromorpha intestinalis (L. ) link (ulvales, chlorophyta)', Journal of Experimental Botany, vol. 33, no. 1, pp. 140-153.
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The 22Na+ and 36CI- exchange properties of the cell walls of Enteromorpha intestinalis (L. ) Link in simple monovalent salt systems have been shown to be similar to a 'leaky' cation exchange membrane rather than a homogeneous membrane. The ion exchange properties of the cation and anion cell wall contents are what would be expected of a cation exchange membrane i. e. anion exchange is strongly dependent on the bathing electrolyte concentration and becomes very slow in dilute salt. This would lead to the cell wall becoming a barrier to anions in dilute salt. However, measurements of the anion flux across cell walls in living and dead tissues show that anion exchange across cell walls is facilitated by pores. The exchange kinetics of the bulk of the cell wall anions does not limit the anion flux across cell walls of this plant. It is concluded that the cell wall is not a critical limitation to plasmalemma fluxes of the living plant and that unstirred layers are more important than cell walls in the measurement of anion flux rates. &copy; 1982 Oxford University Press.
Ritchie, R.J. & Larkum, A.W.D. 1982, 'Cation exchange properties of the cell walls of Enteromorpha intestinalis (L.) link. (ulvales, chlorophyta', Journal of Experimental Botany, vol. 33, no. 1, pp. 125-139.
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The cell wall of Enteromorpha intestinalis (a marine alga) has been found to behave as a weakly cross-linked cation exchanger in NaCl solutions from 0.1-1020 mMolal (0.1-1000 mMolar). Anion adsorption could be described by Freundlich isotherms over this concentration range. The large anion, inulin carboxylate, was found to be a tracer of the anion free space of plant tissues only in salt solutions above 10 mMolal. The cell wall of Enteromorpha has a cation exchange capacity of about 2500 mol g-1 dry wt. (Na+ form). The cell wallvolume is a complex function of pH and the NaCl concentration. As a result, the cation exchange capacity is only predictable on a dry weight basis. The fixed negative charges of the cell wall have a pKa of2 in situ and 1.75 in vitro, and seem to be a mixture of sulphate and carboxyl sugar esters.The applicability of the Donnan equation to plant cell walls is discussed. Interpretation of the cell wall as a single thermodynamic phase is shown to be inappropriate. A large proportion of the cell wall solution is unaffected by the fixed anions. &copy; 1982 Oxford University Press.
Larkum, A.W.D. & Anderson, J.M. 1982, 'The reconstitution of a Photosystem II protein complex, P-700-chlorophyll a-protein complex and light-harvesting chlorophyll a b-protein', BBA - Bioenergetics, vol. 679, no. 3, pp. 410-421.
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A Photosystem II reaction centre protein complex was extracted from spinach chloroplasts using digitonin. This complex showed (i) high rates of dichloroindophenol and ferricyanide reduction in the presence of suitable donors, (ii) low-temperature fluorescence at 685 nm with a variable shoulder at 695 nm which increased as the complex aggregated due to depletion of digitonin and (iii) four major polypeptides of 47, 39, 31 and 6 kDa on dissociating polyacrylamide gels. The Photosystem II protein complex, together woth the P-700-chlorophylla protein complex and light-harvesting chlorophyll a b-protein complex (LHCP) also isolated using digitonin, were reconstituted with lipids from spinach chloroplasts to form proteoliposomes. The low-temperature (77 K) fluorescence properties of the various proteoliposomes were analysed. The F685 F695 ratios of the Photosystem II reaction centre protein complex-liposomes decreased as the lipid to protein ratios were increased. The F681 F697 ratios of LHCP-liposomes were found to behave similarly. Light excitation of chlorophyll b at 475 nm stimulated emission from both the Photosystem II protein complex (F685 and F695) and the P-700-chlorophyll a-protein complex (F735) when LHCP was reconstituted with either of these complexes, demonstrating energy transfer between LHCP and PS I or II complexes in liposomes. No evidence was found for energy transfer from the PS II complex to the P-700-chlorophyll a-protein complex reconstituted in the same proteoliposome preparation. Proteoliposome preparations containing all three chlorophyll-protein complexes showed fluorescence emission at 685, 700 and 735 nm. &copy; 1982.
Hatcher, A.I. & Larkum, A.W.D. 1982, 'The effects of short term exposure to bass strait crude oil and corexit 8667 on benthic community metabolism in Posidonia australis Hook.f. dominated microcosms', Aquatic Botany, vol. 12, no. C, pp. 219-227.
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Microcosms consisting of a sublittoral seagrass meadow from Botany Bay, N.S.W. were maintained in aquaria in a controlled environment room from March to August 1979. Oxygen production and consumption in the microcosms and leaf turnover of the seagrass, Posidonia australis Hook.f. were measured before, during and after a 7-day treatment in June with Bass Strait crude oil and the dispersant Corexit 8667. Four microcosms received oil and two of these received dispersant. The leaf turnover of P. australis was not significantly affected by the addition of oil and dispersant. Photosynthetic oxygen production decreased and respiration incresed in the microcosms during treatment. In August, 40 days after treatment, oxygen production rates and P/R ratios in the oil-treated microcosms were higher thatn rates measured before treatment. The oil-and-dispersant-treated microcosms did not show this trend. The results of this study indicate that a more severe stress is placed on the P. australis dominated benthic community by oil and dispersant than by oil alone. &copy; 1982.
LILLEY, R.M. & LARKUM, A.W.D. 1981, 'ISOLATION OF FUNCTIONALLY INTACT RHODOPLASTS FROM GRIFFITHSIA-MONILIS (CERAMIACEAE, RHODOPHYTA)', PLANT PHYSIOLOGY, vol. 67, no. 1, pp. 5-8.
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MAY, V. & LARKUM, A.W.D. 1981, 'A subtidal transect in Jervis Bay, New South Wales', Australian Journal of Ecology, vol. 6, no. 4, pp. 439-457.
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Longterm variations in the intertidal algal flora of the entire rock platform at Plantation Point, Jervis Bay, are described by May (1981). The study now reported presents similar longterm changes in the flora of a subtidal region of the same headland, observed within the same period of time. This first detailed report of subtidal macroalgal communities in New South Wales describes a severalyear study of the benthic communities along a transect in the upper sublittoral region of a rocky headland at Plantation Point, Jervis Bay. Eightynine species of algae were recorded, five of which were previously unrecorded for New South Wales. The area studied is dominated by the large brown algae Ecklonia radiata and Phyllospora comosa, large areas of which were cleared periodically by storms. Turf, shade and crustose coralline algal communities also were present. Storms, seasonal variation and longer term changes all affected the abundance and distribution of the algal species growing along the transect and hence the floristic composition of the area. Copyright &copy; 1981, Wiley Blackwell. All rights reserved
West, R.J. & Larkum, A.W.D. 1979, 'Leaf productivity of the seagrass, Posidonia australis, in eastern Australian waters', Aquatic Botany, vol. 7, no. C, pp. 57-65.
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Leaf blade production rates of Posidonia australis Hook. f. have been found to range from 0.7 to 5.5 g dry wt. m-2 day-1, depending on site and season. Leaf-blade production (m-2) was significantly higher in Jervis Bay (New South Wales) compared to Botany Bay (New South Wales) and summer and winter values from a Spencer Gulf (South Australia) site were higher than those of Jervis Bay. In Botany Bay, the average turnover rate of Posidonia leaves is about 0.8-1.1% of leaf biomass per day (i.e. three to four crops of leaves produced per year). Biomass, shoot density and some leaf characteristics are also presented for each site. The contribution of seagrass communities to total primary production in the waters of Botany Bay is estimated to be of major importance, and the continued reduction in this contribution, due to urban development, is a matter of concern. &copy; 1979.
Larkum, A.W. & Wyn Jones, R.G. 1979, 'Carbon dioxide fixation by chloroplasts isolated in glycinebetaine : A putative cytoplasmic osmoticum.', Planta, vol. 145, no. 4, pp. 393-394.
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Spinach chloroplasts capable of high rates of CO2 fixation have been isolated in glycinebetaine as an alternative osmoticum to sorbitol and found to be very stable. Proline was a less satisfactory alternatine. The possible significance of the use of glycinebetaine is discussed as this solute may be the physiological cytoplasmic osmoticum in members of the Chenopodiaceae.
Conacher, M.J., Lanzing, W.J.R. & Larkum, A.W.D. 1979, 'Ecology of botany bay. II: Aspects of the feeding ecology of the fanbellied leatherjacket, monacanthus chinensis (pisces: Monacanthidae), in posidonia australis seagrass beds in quibray bay, botany bay, new south wales', Marine and Freshwater Research, vol. 30, no. 3, pp. 387-400.
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The fanbellied leatherjacket, M. chinensis, was found to ingest fresh seagrass as a major part of its diet. Other important food items were gammarid amphipods, carid shrimps and several species of epiphytic algae. All food items were of seagrass bed origin. Microscopic examination of gut contents suggested that seagrass and algae did not appear to be digested by the fish, but14C-labelling of the plants showed that significant amounts of the labile carbon compounds were removed and assimilated during digestion. The fanbellied leatherjacket was found to feed in the seagrass beds during the day, probably relying on eyesight for detecting food. Variations in tide height did not seem to affect their feeding pattern. The amounts of seagrass, algae, amphipods and shrimps removed by M. chinensis in Quibray Bay were calculated and compared with the availability of each of these foods. Grazing by M. chinensis had little effect on seagrass and algae production rates and standing crops, but probably had a significant influence on carid shrimp and amphipod populations. &copy; 1979 ASEG.
Borowitzka, M.A., Larkum, A.W.D. & Borowitzka, L.J. 1978, 'A preliminary study of algal turf communities of a shallow coral reef lagoon using an artificial substratum', Aquatic Botany, vol. 5, no. C, pp. 365-381.
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The growth, productivity and species composition of algal turf communities growing on glass microscope slides at various sites in the lagoon of One Tree Island,Capricorn Group, Great Barrier Reef, Australia (23&deg; 30 S, 152&deg; 06 E) were measured, and the possible use of algal communities growing on artificial substrates for ecological studies was assessed. Colonization of the bare glass slides by bacteria, green and blue-green algae was rapid. After 3 months, the slides had become covered by filamentous and crustose algae [e.g. Sphacelaria tribuloides Meneghini, Herposiphonia tenella (C. Agardh) Naegeli, Tenarea sp. etc.] and invertebrates (e.g. Spirorbis sp.). Crustose coralline algae settled evenly over the surface of the slide but were soon removed from the slide centre by grazing fish. Eventually, thicker crustose corallines [e.g. Porolithon onkodes (Heydrich) Foslie] from the less grazed edges of these slides began to overgrow the slides, providing a different substrate for growth of algal species such as Lophosiphonia spp. and Laurencia papillosa (Forssk&aring;l) Greville, etc. Various differences in species composition were observed between the different sites and depths. In general, the glass slide communities were less diverse than those on nearby natural substrates, presumably due to the hardness of the glass slides. &copy; 1978.
Borowitzka, M.A. & Larkum, A.W.D. 1977, 'CALCIFICATION IN THE GREEN ALGA HALIMEDA. I. AN ULTRASTRUCTURE STUDY OF THALLUS DEVELOPMENT', Journal of Phycology, vol. 13, no. 1, pp. 6-16.
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The ultrastructure of 4 species of the calcareous, siphonaceous alga Halimeda (H. cylindracea Decaisne, H. discoidea Decaisne, H. macroloba Decaisne and H. tuna (Ellis & Solander) Lamour) has been studied, and the observed changes during growth and development are related to changes in the degree of calcification. A distinct gradient in the types and quantities of cell organelles exists in a growing apical filament. As these filaments grow, branch, and eventually develop into a mature segment, changes in the organization of organelles such as mitochondria and chloroplasts are observed. Calcification begins when the chloroplasts reach structural maturity and when the peripheral utricles adhere (fuse). This adhesion of the peripheral utricles isolates the intercellular space (ICS) in which calcification occurs from the external seawater. Calcification begins in the outermost (pilose) cell wall layer of the walls facing into the ICS. The cell walls at the thallus exterior undergo extensive changes after utricular fusion; the pilose layer is lost, the cuticles of adjacent utricles fuse forming a ridge at their junction, and multiple cuticles are formed. The aragonite (CaCO3) crystals which are initially precipitated within the pilose wall layer, rapidly increase in size and number, eventually filling much of the ICS. Only the initial nucleation of aragonite is associated with the pilose wall layer, the later precipitation of aragonite is totally independent of the pilose layer. In older segments secondary deposition of CaCO3 also occurs around existing aragonite needles. Copyright &copy; 1977, Wiley Blackwell. All rights reserved
Larkum, A.W.D. & Weyrauch, S.K. 1977, 'PHOTOSYNTHETIC ACTION SPECTRA AND LIGHTHARVESTING IN GRIFFITHSIA MONILIS (RHODOPHYTA)', Photochemistry and Photobiology, vol. 25, no. 1, pp. 65-72.
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Abstract&#8212; In cells of the red alga Griffithsia monilis the action spectrum of photosynthetic oxygen production at low light intensity shows that the phycobilins (including allophycocyanin) are the major lightharvesting pigments. As the light intensity is increased carotenoids and chlorophyll a contribute proportionately more to the spectrum, since the phycobilin activity becomes lightsaturated. When action spectra are performed against a background light of various monochromatic wavelengths it can be shown that chlorophyll a increases in its lightharvesting activity. Nevertheless light absorbed at a single wavelength (487 nm) by phycoerythrin (and possibly a carotenoid) still shows the highest photosynthetic activity. Fluorescence measurements at 77K indicate that a chlorophyll a fluorescence is small and that the amount of chlorophyll all (f 693) is very low. A model is proposed in which the phycobilins, in phycobilisomes, pass on absorbed light energy to either photosystem, whereas light absorbed by chlorophyll is passed on mainly to photosystem I. Copyright &copy; 1977, Wiley Blackwell. All rights reserved
LARKUM, A.W.D. & BOROWITZKA, M.A. 1977, 'DEEP-WATER RED ALGAE OF SOUTHERN GREAT BARRIER REEF', JOURNAL OF PHYCOLOGY, vol. 13, pp. 38-38.
BOROWITZKA, M.A. & LARKUM, A.W.D. 1977, 'CALCIFICATION IN GREEN-ALGA HALIMEDA .1. ULTRASTRUCTURE STUDY OF THALLUS DEVELOPMENT', JOURNAL OF PHYCOLOGY, vol. 13, no. 1, pp. 6-16.
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BOROWITZKA, M.A., LARKUM, A.W.D. & DAY, R. 1977, 'SEASONAL ASPECTS OF PRODUCTIVITY OF CORAL-REEF ALGAL TURF COMMUNITIES', JOURNAL OF PHYCOLOGY, vol. 13, pp. 8-8.
Borowitzka, M.A. & Larkum, A.W.D. 1976, 'Calcification in the green alga Halimeda: III. The sources of inorganic carbon for photosynthesis and calcification and a model of the mechanism of calcification', Journal of Experimental Botany, vol. 27, no. 5, pp. 879-893.
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Calcification and photosynthetic rates in Halimeda tuna were measured by the 14C method under conditions of differing pH and total inorganic carbon (CO2) concentrations. The effects of pH and CO2 on photosynthesis and respiration were also monitored with a polarographic O2 electrode. The results obtained indicate that the intercellular pH and CO2 differ from those of the external medium.Experiments carried out over a range of pH values show that Halimeda can use HCO3- for photosynthesis. Photosynthesis appears to stimulate calcification by removing CO2 from the intercellular spaces. As these spaces are isolated from the external sea water by the layer of cell wall of the adpressed peripheral utricles, the removal of CO2 results in a rise in [CO32-] and a rise in pH. This results in an increased rate of CaCO3 precipitation. Respiratory CO2 evolution has an inhibitory effect on calcification by decreasing the pH and [CO32-].A model for calcification in Halimeda is proposed based on the results of this and previous papers. Calcification in Halimeda is seen to be a result of the anatomy of the thallus in which the sites of calcification are within a semi-isolated chamber where removal or addition of CO2 due to photosynthesis or respiration can effectively change [COCO32-] thereby resulting in precipitation of CaCO3. In the Appendix to this paper theoretical calculations illustrate the effects of CO2, HCO3-, and CO32- removal or addition in a closed system on the relative concentrations of the other inorganic carbon species. &copy; 1976 Oxford University Press.
Borowitzka, M.A. & Larkum, A.W.D. 1976, 'Calcification in the green alga Halimeda: II. THE exchange OF ca2+ AND the OCCURRENCE of AGE gradients IN calcification AND photosynthesis', Journal of Experimental Botany, vol. 27, no. 5, pp. 864-878.
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In Halimeda cylindracea and H. tuna segments, the concentration of CaCO3, MgCO3, protein, and chlorophyll, as well as segment volume and wet and dry weight, increase with 'age' i.e. from the apex of a branch downwards. Photosynthetic and calcification rates decrease with age as does the degree of light stimulation of calcification.Studies of the exchange of 45Ca between the Halimeda thallus and the sea water under various conditions showed that most of the Ca exchange is between the cell walls, the aragonite crystals, and the intercellular space. The cell wall has two distinguishable phases with half-times (t05) of 200 and 35 min while the CaCO3 has a rapidly exchanging phase with a t05 of approximately 6 min. The t05 of the exchange of Ca between the intercellular space and the external medium is estimated at about 6 min, on the basis of uptake studies. If the integrity of the barrier between the intercellular space and the external sea water, created by the adpressed peripheral utricles is destroyed the t05 is smaller (3 min).These kinetic studies as well as comparative measurements of calcification rates by both isotopic and chemical methods show that the 45Ca method for measuring calcification rates overestimates the calcification rate, due to binding of 45Ca in the cell walls and retention of 45Ca in the intercellular space. The 14C method gives more accurate results and has the further advantage of allowing simultaneous measurement of the photosynthetic and calcification rate on the same segment. &copy; 1976 Oxford University Press.
Borowitzka, M.A. & Larkum, A.W.D. 1976, 'Calcification in the green alga Halimeda: IV. The action of metabolic inhibitors on photosynthesis and calcification', Journal of Experimental Botany, vol. 27, no. 5, pp. 894-907.
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The effects of a number of metabolic inhibitors on calcification and photosynthesis in Halimeda tuna, H. discoidea, and H. macroloba are described. The inhibitors used are CCCP, DNP, DCMU, azide, cyanide, chloramphenicol, cycloheximide, and Diamox. The effects of these inhibitors, although complex, are consistent with our model of calcification in Halimeda. Inhibition of photosynthetic CO2 uptake inhibits calcification as does stimulation of respiratory CO2 evolution (i.e. uncoupling). There is also indirect evidence for the presence of a possible light stimulated H+ efflux which inhibits calcification. The observed calcification rate is therefore the result of a number of factors which affect the concentration of CO3-Feb-and the pH in the intercellular space of the Halimeda thallus.The results obtained with the carbonic anhydrase inhibitor Diamox provide further evidence for the effective separation of the intercellular space from the external medium by the appressed peripheral utricles. &copy; 1976 Oxford University Press.
Larkum, A.W.D. 1976, 'Ecology of Botany Bay. I. Growth of Posidonia Australis (Brown) Hook. F. In Botany Bay and Other Bays of the Sydney Basin', Marine and Freshwater Research, vol. 27, no. 1, pp. 117-127.
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The distribution, biomass and density of various beds of P. australis have been determined for Botany Bay (N.S.W.). Comparisons have been made with sites at Broken Bay, Port Hacking and Jervis Bay and these include observations of other seagrass beds (Zostera capricorni, Heterozostera tasmanica, Halophila ovalis and Halophila decipiens). The P. australis plants observed were all of the broad-leaved (1.0-1.2 cm) variety. The length of leaves appears to be correlated with depth and with degree of exposure to wave action. The distribution of P. australis in Botany Bay is almost entirely restricted to the southern side and is limited to a maximum depth of 3 m compared with 7 to 9 m at other sites. The growth of plants in well-established beds seems to be as vigorous in Botany Bay as elsewhere but flowering is poor and infrequent and the overgrowth of epiphytes is very great at certain seasons. Clearing experiments in Botany Bay indicate that recolonization by surrounding plants or seedlings is extremely slow. Transplant experiments indicate that mature plants will survive transplanting to cleared sites on both the northern and southern sides of the Bay. Evidence for a much more extensive distribution of P. australis in Botany Bay in times past and the possible effects of pollution are discussed. &copy; 1976 ASEG.
Larkum, A.W. & Boardman, N.K. 1974, 'The effect of nigericin and valinomycin on CO2 fixation electron transport and P518 in intact spinach chloroplasts.', FEBS letters, vol. 40, no. 1, pp. 229-232.
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Borowitzka, M.A. & Larkum, A.W.D. 1974, 'Chloroplast development in the caulerpalean alga Halimeda', Protoplasma, vol. 81, no. 2-3, pp. 131-144.
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The development of the chloroplast in the caulerpalean algae Halimeda cylindracea, H. discoidea and H. macroloba has been studied by electron microscopy. The chloroplast develops from a proplastid via a starch containing young plastid. This young plastid may also develop into an amyloplast. The plastids contain a unique concentric lamellar system at one end. This has been called the thylakoid organising body (TOB) as it is at the base of this body that thylakoid formation is initiated. The TOB persists throughout the life of the chloroplast. &copy; 1974 Springer-Verlag.
Larkum, A.W. & Bonner, W.D. 1972, 'Light-induced absorbance changes of cytochromes and other pigments in pea chloroplasts and chloroplast fragments. II. The effect of inhibitors, uncouplers and ionophores.', Archives of biochemistry and biophysics, vol. 153, no. 1, pp. 249-257.
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Larkum, A.W. & Bonner, W.D. 1972, 'Light-induced oxidation of cytochrome f in isolated chloroplasts of Pisum sativum.', Biochimica et biophysica acta, vol. 256, no. 2, pp. 385-395.
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Larkum, A.W. & Bonner, W.D. 1972, 'The effect of artificial electron donor and acceptor systems on light-induced absorbance responses of cytochromes f and other pigments in intact chloroplasts.', Biochimica et biophysica acta, vol. 267, no. 1, pp. 149-159.
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Larkum, A.W. & Bonner, W.D. 1972, 'Light-induced absorbance changes of P518 in intact chloroplasts.', Biochimica et biophysica acta, vol. 256, no. 2, pp. 396-408.
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Larkum, A.W. & Bonner, W.D. 1972, 'Light-induced absorbance changes of cytochromes and other pigments in pea chloroplasts and chloroplast fragments. I. The effect of red and near far-red actinic light and of ruby laser flashes.', Archives of biochemistry and biophysics, vol. 153, no. 1, pp. 241-248.
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Larkum, A.W.D. 1972, 'Frond structure and growth in laminaria hyperborea', Journal of the Marine Biological Association of the United Kingdom, vol. 52, no. 2, pp. 405-418.
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Age, frond weight, frond area, stipe length and other data have been recorded for plants of Laminaria hyperborea growing off the coast of south-west England and south-west Ireland. The ratio of total frond weight to total frond area (unit frond weight) has been found to be related to age, depth, type of community, and water turbulence. Decrease in unit frond weight appears to result from a decrease in the number of cell layers of the frond, which is most marked at the frond tip. At the frond tip differences between the thickest and thinnest fronds may be fivefold or more. It is concluded that water turbulence, particularly wave-action, is an important factor influencing the changes in frond structure. The importance of submarine irradiance as a factor is not clear from the present evidence. An intrinsic factor affecting frond structure may be the age of plants. &copy; 1972, Marine Biological Association of the United Kingdom. All rights reserved.
Larkum, A.W. & Hill, A.E. 1970, 'Ion and water transport in Limonium. V. The ionic status of chloroplasts in the leaf of Limonium vulgare in relation to the activity of the salt glands.', Biochimica et biophysica acta, vol. 203, no. 1, pp. 133-138.
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Larkum, A.W.D. & Loughman, B.C. 1969, 'Anaerobic phosphate uptake by barley plants', Journal of Experimental Botany, vol. 20, no. 1, pp. 12-24.
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Considerable uptake of phosphate by both the shoot and root has been demonstrated for young barley plants with their roots in anoxic culture solution at concentrations of 1 to 10 M orthophosphate. Consideration of the free space and passive transpirational uptake indicates an accumulatory process, and the immediate efflux caused by respiratory inhibitors supports this. Shoot uptake is much less at higher external concentrations of phosphate and at o.I mM was only 14 per cent of the control. The root accumulation process was unimpaired at an external concentration of 1 M phosphate when the whole plant was subjected to anaerobic conditions (shoot illuminated) but under similar conditions at a concentration of 100 M a considerable efflux of phosphate occurred. Analysis of the fate of phosphate taken up from anoxic solution of phosphate (10 M) indicated that there was a reduction in the level of inorganic phosphate after 4.5 h and steady rise in sugar phosphates up to 6 h with a marked increase in the levels of glucose-6-phosphate, fructose-6-phosphate, and the phosphoglycerate fraction. &copy; 1962 Oxford University Press.
Larkum, A.W.D. 1969, 'Some observations with a new potometer on the absorption of water by young barley plants', Journal of Experimental Botany, vol. 20, no. 1, pp. 25-33.
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A potometer, working on a syphon principle, is described for use with single, small plants where it is undesirable to flood the stem base. It has been shown that anoxia has very little effect on the water absorption of roots of intact barley plants, apart from an initial inhibition of short duration. The action of 1 10-5 M dinitrophenol (pH 6.0) is similar. Neither treatment kills the roots. It is possible that permeability is maintained by fermentation reactions &copy; 1962 Oxford University Press.
Larkum, A.W.D. 1968, 'Ionic relations of chloroplasts in vivo', Nature, vol. 218, no. 5140, pp. 447-449.
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The salt content of the chloroplasts of Tolypella intricata has been found to be very high. To maintain this it seems that there must be some form of ionic control at the outer boundary of the chloroplasts. &copy; 1968 Nature Publishing Group.
LARKUM, A.W. 1965, 'THE ACTION OF IONIZING RADIATION ON THE RESPIRATORY MECHANISM OF BAKER'S YEAST.', Biochimica et biophysica acta, vol. 97, pp. 422-433.
Crossett, R.N., Drew, E.A. & Larkum, A.W.D. 1965, 'Chromatic adaptation in benthic marine algae [41]', Nature, vol. 207, no. 4996, pp. 547-548.
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