title: Chloroplast Cu/Zn-superoxide dismutase is a highly sensitive site in cucumber leaves chilled in the light.
abstract: Light-chilling stress, the combination of low-light illumination and low temperature, preferentially inactivated photosystem I (PSI) of cucumber (Cucumis sativus L.) leaves, resulting in the photoinhibition of photosynthesis. The extent of PSI photoinhibition, determined in vivo by monitoring absorption changes around 810 nm (induced by far-red light), was closely correlated with the redox state of the PSII electron acceptor Q(A), measured as the chlorophyll fluorescence parameter, 1-qP, where qP is a photochemical quenching coefficient. In contrast, the decrease in the far-red-induced leaf absorptance signal was not well correlated with the limited fragmentation of the PsaA/B gene products in the PSI reaction center after the light-chilling stress. Amongst various enzymes involved in the photooxidative damage such as superoxide dismutase (SOD), ascorbate peroxidase, and NAD(P)H dehydrogenase, only SOD was inhibited by light-chilling treatment. Further, an approximately 3-fold increase in the leaf content of H(2)O(2), a potent inhibitor of Cu/Zn-SOD, was observed after light-chilling stress. From these results, we suggest that Cu/Zn-SOD is the primary target of the light-chilling stress, followed by subsequent inactivation of PSI by reactive oxygen species.
authors.affiliation: Department of Biology, Chungnam National University, Daejeon 305-764, Korea.
authors.forename: Sun Mi
authors.initials: SM
authors.lastname: Choi
authors.forename: Suk Won
authors.initials: SW
authors.lastname: Jeong
authors.forename: Won Joong
authors.initials: WJ
authors.lastname: Jeong
authors.forename: Suk Youn
authors.initials: SY
authors.lastname: Kwon
authors.forename: Wah Soon
authors.initials: WS
authors.lastname: Chow
authors.forename: Youn-Il
authors.initials: YI
authors.lastname: Park
mesh_terms: D000222:Adaptation, Physiological / Q000528:radiation effects; D060387:Ascorbate Peroxidases; D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000201:enzymology* / Q000528:radiation effects; D003080:Cold Temperature; D018553:Cucumis sativus / Q000201:enzymology* / Q000502:physiology / Q000528:radiation effects; D004579:Electron Transport / Q000502:physiology / Q000528:radiation effects; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008027:Light; D045342:Light-Harvesting Protein Complexes; D009252:NADPH Dehydrogenase / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D010544:Peroxidases / Q000378:metabolism; D010788:Photosynthesis / Q000502:physiology / Q000528:radiation effects; D045322:Photosynthetic Reaction Center Complex Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000528:radiation effects; D045331:Photosystem I Protein Complex; D018515:Plant Leaves / Q000201:enzymology* / Q000502:physiology / Q000528:radiation effects; D017382:Reactive Oxygen Species / Q000378:metabolism; D013482:Superoxide Dismutase / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D017382:Reactive Oxygen Species; D002734:Chlorophyll; D006861:Hydrogen Peroxide; D010544:Peroxidases; D060387:Ascorbate Peroxidases; D013482:Superoxide Dismutase; D009252:NADPH Dehydrogenase; D010100:Oxygen