title: PSI Mehler reaction is the main alternative photosynthetic electron pathway in Symbiodinium sp., symbiotic dinoflagellates of cnidarians.
abstract: Photosynthetic organisms have developed various photoprotective mechanisms to cope with exposure to high light intensities. In photosynthetic dinoflagellates that live in symbiosis with cnidarians, the nature and relative amplitude of these regulatory mechanisms are a matter of debate. In our study, the amplitude of photosynthetic alternative electron flows (AEF) to oxygen (chlororespiration, Mehler reaction), the mitochondrial respiration and the Photosystem I (PSI) cyclic electron flow were investigated in strains belonging to three clades (A1, B1 and F1) of Symbiodinium. Cultured Symbiodinium strains were maintained under identical environmental conditions, and measurements of oxygen evolution, fluorescence emission and absorption changes at specific wavelengths were used to evaluate PSI and PSII electron transfer rates (ETR). A light- and O2 -dependent ETR was observed in all strains. This electron transfer chain involves PSII and PSI and is insensitive to inhibitors of mitochondrial activity and carbon fixation. We demonstrate that in all strains, the Mehler reaction responsible for photoreduction of oxygen by the PSI under high light, is the main AEF at the onset and at the steady state of photosynthesis. This sustained photosynthetic AEF under high light intensities acts as a photoprotective mechanism and leads to an increase of the ATP/NADPH ratio.
authors: Laboratoire d'Ecologie Animale et d'Ecotoxicologie, Département de Biologie, Ecologie et Evolution, Université de Liège, 11 Allée du 6 Août, B-4000, Liège, Belgium.|Laboratoire de Bioénergétique, Institut de Botanique, Université de Liège, 27 Bld du Rectorat, B-4000, Liège, Belgium.
authors: Stéphane
authors: S
authors: Roberty
authors: Laboratoire de Génétique et Physiologie des Microalgues, Institut de Botanique, Université de Liège, 27 Bld du Rectorat, B-4000, Liège, Belgium.
authors: Benjamin
authors: B
authors: Bailleul
authors: Laboratoire de Génétique et Physiologie des Microalgues, Institut de Botanique, Université de Liège, 27 Bld du Rectorat, B-4000, Liège, Belgium.
authors: Nicolas
authors: N
authors: Berne
authors: Laboratoire de Bioénergétique, Institut de Botanique, Université de Liège, 27 Bld du Rectorat, B-4000, Liège, Belgium.|PhytoSYSTEMS, Université de Liège, B-4000, Liège, Belgium.
authors: Fabrice
authors: F
authors: Franck
authors: Laboratoire de Génétique et Physiologie des Microalgues, Institut de Botanique, Université de Liège, 27 Bld du Rectorat, B-4000, Liège, Belgium.|PhytoSYSTEMS, Université de Liège, B-4000, Liège, Belgium.
authors: Pierre
authors: P
authors: Cardol
mesh_terms: D000818:Animals; D037421:Anthozoa; D002734:Chlorophyll / Q000378:metabolism; D003063:Cnidaria / Q000378:metabolism*; D004141:Dinoflagellida / Q000378:metabolism* / Q000502:physiology; D004579:Electron Transport; D008027:Light; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis; D045331:Photosystem I Protein Complex / Q000737:chemistry / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D013559:Symbiosis
chemical_list: D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D010100:Oxygen
keywords: Symbiodinium; chlororespiration; coral bleaching; cyclic electron flow; mitochondrial respiration; oxygen uptake; reef-building corals; water-water cycle