title: Heat Induction of Cyclic Electron Flow around Photosystem I in the Symbiotic Dinoflagellate Symbiodinium.
abstract: Increases in seawater temperature impair photosynthesis (photoinhibition) in the symbiotic dinoflagellate Symbiodinium within cnidarian hosts, such as corals and sea anemones, and may destroy their symbiotic relationship. Although the degree of photoinhibition in Symbiodinium under heat stress differs among strains, the differences in their responses to increased temperatures, including cyclic electron flow (CEF), which sustains photoprotective thermal energy dissipation, have not been investigated. Here, we examined CEF in cultured Symbiodinium cells or those in an endosymbiotic relationship within a cnidarian host. The light-dependent reduction of the primary electron donor photosystem I, i.e. P700(+), was enhanced in any Symbiodinium cell by increasing temperatures, indicating CEF was induced by heat, which was accompanied by thermal energy dissipation activation. The critical temperatures for inducing CEF were different among Symbiodinium strains. The clade A strains with greater susceptibility to photoinhibition, OTcH-1 and Y106, exhibited higher CEF activities under moderate heat stress than a more phototolerant clade B strain Mf1.05b, suggesting that the observed CEF induction was not a preventive measure but a stress response in Symbiodinium.
authors.affiliation: Division of Environmental Photobiology, National Institute for Basic Biology, Nishigonaka 38, Myodaiji, Okazaki 444-8585, Japan (Y.A., S.T., J.M.); andDepartment of Basic Biology, School of Life Science, SOKENDAI (The Graduate University for Advanced Studies), Okazaki 444-8585, Japan (S.T., J.M.).
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Aihara
authors.affiliation: Division of Environmental Photobiology, National Institute for Basic Biology, Nishigonaka 38, Myodaiji, Okazaki 444-8585, Japan (Y.A., S.T., J.M.); andDepartment of Basic Biology, School of Life Science, SOKENDAI (The Graduate University for Advanced Studies), Okazaki 444-8585, Japan (S.T., J.M.).
authors.forename: Shunichi
authors.identifier: 0000-0002-8939-7547
authors.initials: S
authors.lastname: Takahashi
authors.affiliation: Division of Environmental Photobiology, National Institute for Basic Biology, Nishigonaka 38, Myodaiji, Okazaki 444-8585, Japan (Y.A., S.T., J.M.); andDepartment of Basic Biology, School of Life Science, SOKENDAI (The Graduate University for Advanced Studies), Okazaki 444-8585, Japan (S.T., J.M.) minagawa@nibb.ac.jp.
authors.forename: Jun
authors.identifier: 0000-0002-3028-3203
authors.initials: J
authors.lastname: Minagawa
mesh_terms: D004141:Dinoflagellida / Q000378:metabolism* / Q000502:physiology; D004583:Electrons; D018869:Heat-Shock Response; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D013559:Symbiosis; D013696:Temperature
chemical_list: D045331:Photosystem I Protein Complex