title: Mitochondrial Alternative Pathway-Associated Photoprotection of Photosystem II is Related to the Photorespiratory Pathway.
abstract: Respiratory electron transport has two ubiquinol-oxidizing pathways, the cytochrome pathway (CP) and the alternative pathway (AP). The AP, which is catalyzed by the alternative oxidase (AOX), is energetically wasteful but may alleviate PSII photoinhibition under light conditions excessive for photosynthesis. However, its mechanism remains unknown. We used Arabidopsis aox1a mutants lacking AOX activity and studied the mutation's effects on photoinhibition by measuring the decrease in the maximum quantum yield of PSII (Fv/Fm) after high light exposure. Since the CP compensates for the lack of AOX, we monitored the extent of photoinhibition under conditions where CP activity is partially inhibited by antimycin A. When leaves were exposed to high light at 350 µmol m-2s-1, the decline in Fv/Fmwas significantly faster in the aox1a mutants than in the wild type. However, under conditions where photorespiration was suppressed by high CO2or low O2levels, the decline in Fv/Fmwas suppressed in the aox1a mutants, but not in the wild type, making the difference between the wild type and mutants small. Our results demonstrate that the lack of the AP causes an acceleration of PSII photoinhibition in relation to the photorespiratory pathway, suggesting that the AP can support the activity of the photorespiratory pathway under high light conditions.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan chihiro_watanabe@bs.s.u-tokyo.ac.jp.
authors.forename: Chihiro K A
authors.initials: CK
authors.lastname: Watanabe
authors.affiliation: Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan.|Center for Environment, Health and Field Sciences, Chiba University, Kashiwa, Chiba, 277-0882 Japan.
authors.forename: Wataru
authors.initials: W
authors.lastname: Yamori
authors.affiliation: Division of Plant Sciences, Research School of Biology, The Australian National University, Canberra, Australian Capital Territory, 2601 Australia.|Division of Environmental Photobiology, National Institute for Basic Biology, Okazaki, 444-8585 Japan.
authors.forename: Shunichi
authors.initials: S
authors.lastname: Takahashi
authors.affiliation: Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan.
authors.forename: Ichiro
authors.initials: I
authors.lastname: Terashima
authors.affiliation: School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo, 192-0392 Japan.
authors.forename: Ko
authors.initials: K
authors.lastname: Noguchi
mesh_terms: D000968:Antimycin A / Q000494:pharmacology; D017360:Arabidopsis / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects*; D002245:Carbon Dioxide / Q000494:pharmacology; D019069:Cell Respiration / Q000187:drug effects / Q000528:radiation effects; D002701:Chloramphenicol / Q000494:pharmacology; D008027:Light; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D024101:Mitochondrial Proteins / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D010088:Oxidoreductases / Q000378:metabolism; D010100:Oxygen / Q000494:pharmacology; D055668:Photochemical Processes / Q000187:drug effects / Q000528:radiation effects*; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D018515:Plant Leaves / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D010940:Plant Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000528:radiation effects*; D000099188:Alternative Oxidase
chemical_list: D000968:Antimycin A; D002245:Carbon Dioxide; D002701:Chloramphenicol; D024101:Mitochondrial Proteins; D010088:Oxidoreductases; D010100:Oxygen; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D000099188:Alternative Oxidase
keywords: Alternative oxidase; Alternative pathway; Arabidopsis thaliana; Photoinhibition; Photorespiratory pathway; Respiration