title: Reduction-Induced Suppression of Electron Flow (RISE) in the Photosynthetic Electron Transport System of Synechococcus elongatus PCC 7942.
abstract: Accumulation of electrons under conditions of environmental stress produces a reduced state in the photosynthetic electron transport (PET) system and causes the reduction of O2by PSI in the thylakoid membranes to produce the reactive oxygen species superoxide radical, which irreversibly inactivates PSI. This study aims to elucidate the molecular mechanism for the oxidation of reaction center Chl of PSI, P700, after saturated pulse (SP) light illumination of the cyanobacterium Synechococcus elongatus PCC 7942 under steady-state photosynthetic conditions. Both P700 and NADPH were transiently oxidized after SP light illumination under CO2-depleted photosynthesis conditions. In contrast, the Chl fluorescence intensity transiently increased. Compared with the wild type, the increase in Chl fluorescence and the oxidations of P700 and NADPH were greatly enhanced in a mutant (Δflv1/3) deficient in the genes encoding FLAVODIIRON 1 (FLV1) and FLV3 proteins even under high photosynthetic conditions. Furthermore, oxidation of Cyt f was also observed in the mutant. After SP light illumination, a transient suppression of O2evolution was also observed in Δflv1/3. From these observations, we propose that the reduction in the plastquinone (PQ) pool suppresses linear electron flow at the Cyt b6/f complex, which we call the reduction-induced suppression of electron flow (RISE) in the PET system. The accumulation of the reduced form of PQ probably suppresses turnover of the Q cycle in the Cyt b6/f complex.
authors.affiliation: Department of Biological and Environmental Science, Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada, Kobe, 657-8501 Japan.
authors.forename: Keiichiro
authors.initials: K
authors.lastname: Shaku
authors.affiliation: Department of Biological and Environmental Science, Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada, Kobe, 657-8501 Japan.
authors.forename: Ginga
authors.initials: G
authors.lastname: Shimakawa
authors.affiliation: Department of Biological and Environmental Science, Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada, Kobe, 657-8501 Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Hashiguchi
authors.affiliation: Department of Biological and Environmental Science, Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada, Kobe, 657-8501 Japan cmiyake@hawk.kobe-u.ac.jp.|Core Research for Environmental Science and Technology, Japan Science and Technology Agency, 7 Gobancho, Chiyoda-ku, Tokyo, 102-0076 Japan.
authors.forename: Chikahiro
authors.initials: C
authors.lastname: Miyake
mesh_terms: D002245:Carbon Dioxide / Q000494:pharmacology; D002734:Chlorophyll / Q000378:metabolism; D004579:Electron Transport / Q000187:drug effects / Q000528:radiation effects; D005453:Fluorescence; D005798:Genes, Bacterial; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction / Q000187:drug effects / Q000528:radiation effects; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis / Q000187:drug effects / Q000528:radiation effects; D045332:Photosystem II Protein Complex / Q000378:metabolism; D046940:Synechococcus / Q000187:drug effects / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects
chemical_list: D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D002245:Carbon Dioxide; D009249:NADP; D010100:Oxygen
keywords: Electron transport; Flavodiiron protein; Oxygen; Photosynthesis; Q cycle; RISE