Buxton, LJ, Takahashi, S, Hill, R & Ralph, PJ 2012, 'Variability in the primary site of photosynthetic damage in Symbiodinium sp. (Dinophyceae) exposed to thermal stress', Journal of Phycology, vol. 48, no. 1, pp. 117-126.View/Download from: Publisher's site
Exposure to elevated temperature is known to cause photosynthetic inhibition in the coral symbiont Symbiodinium sp. Through the use of the artificial electron acceptor, methyl viologen, this study identified how reduced photosynthetic capacity occurs as a result of inhibition up- and/or downstream of ferredoxin in Symbiodinium sp. in hospite and in culture. Heterogeneity between coral species and symbiont clades was identified in the thermal sensitivity of photosynthesis in the symbionts of the scleractinian corals Stylophora pistillata and Pocillopora damicornis, as well as among Symbiodinium cultures of clades A, B, and C. The in hospite symbionts of S. pistillata and the cultured clade C Symbiodinium both exhibited similar patterns in that their primary site of thermal inhibition occurred downstream of ferredoxin at 32 degrees C. In contrast, the primary site of thermal inhibition occurred upstream of ferredoxin in clades A and B at 32 degrees C, while at 34 degrees C, all samples showed combined up- and downstream inhibition. Although clade C is common to both P. damicornis and S. pistillata, the manner of thermal inhibition was not consistent when observed in hospite. Results showed that there is heterogeneity in the primal site of thermal damage in Symbiodinium among coral species and symbiont clades.
Buxton, LJ, Badger, M & Ralph, PJ 2009, 'Effects Of Moderate Heat Stress And Dissolved Inorganic Carbon Concentration On Photosynthesis And Respiration Of Symbiodinium Sp (Dinophyceae) In Culture And In Symbiosis', Journal of Phycology, vol. 45, no. 2, pp. 357-365.View/Download from: Publisher's site
The influence of temperature and inorganic carbon (C-i) concentration on photosynthesis was examined in whole corals and samples of cultured symbiotic dinoflagellates (Symbiodinium sp.) using combined measurements from a membrane inlet mass spectrometer and chl a fluorometer. In whole corals, O-2 production at 26 degrees C was significantly limited at C-i concentrations below ambient seawater (similar to 2.2 mM). Further additions of C-i up to similar to 10 mM caused no further stimulation of oxygenic photosynthesis. Following exposure to 30 degrees C (2 d), net oxygen production decreased significantly in whole corals, as a result of reduced production of photosynthetically derived oxygen rather than increased host consumption. Whole corals maintained a rate of oxygen evolution around eight times lower than cultured Symbiodinium sp. at inorganic carbon concentrations < 2 mM, but cultures displayed greater levels of photoinhibition following heat treatment (30 degrees C, 2 d). Whole corals and cultured zooxanthellae differed considerably in their responses to C-i concentration and moderate heat stress, demonstrating that cultured Symbiodinium make an incongruous model for those in hospite. Reduced net oxygen evolution, in whole corals, under conditions of low C-i (< 2 mM) has been interpreted in terms of possible sink limitation leading to increased nonphotochemical energy dissipation. The advantages of combined measurement of net gas exchange and fluorometry offered by this method are discussed.
Trapido-Rosenthal, H, Zielke, S, Owen, R, Buxton, LJ, Boeing, B, Bhagooli, R & Archer, J 2005, 'Increased zooxanthellae nitric oxide synthase activity is associated with coral bleaching', Biological Bulletin, vol. 208, no. 1, pp. 3-6.View/Download from: Publisher's site
Coral bleaching, the breakdown of the symbiotic relationship between host corals and their photosynthetic dinoflagellate endosymbionts, is a phenomenon of major ecological significance. The cellular and molecular mechanisms underlying bleaching are poorl