title: A photoprotective role for O(2) as an alternative electron sink in photosynthesis?
abstract: Photoprotection of the photosynthetic apparatus has two essential elements: first, the thermal dissipation of excess excitation energy in the photosystem II antennae (i.e. non-photochemical quenching), and second, the ability of photosystem II to transfer electrons to acceptors within the chloroplast (i.e. photochemical quenching). Recent studies indicate that the proportion of absorbed photons that are thermally dissipated through the non-photochemical pathway often reaches a maximum well before saturating irradiances are reached. Hence, photochemical quenching is crucial for photoprotection at saturating light intensities. When plants are exposed to environmental stresses and the availability of CO(2) within the leaf is restricted, the reduction of oxygen by both the photorespiratory and the Mehler ascorbate peroxidase pathways appears to play a critical photoprotective role, substituting for CO(2) in sustaining electron flow. Induction of high activity of the Mehler ascorbate peroxidase pathway may be associated with acclimation to environmental stress.
authors.affiliation: Photosynthesis Research Unit, USDA/ARS & Department of Plant Biology, University of Illinois, Urbana, Illinois 61801, USA.
authors.forename: Donald R
authors.initials: DR
authors.lastname: Ort
authors.forename: Neil R
authors.initials: NR
authors.lastname: Baker
mesh_terms: D000064:Acclimatization / Q000502:physiology* / Q000528:radiation effects; D060387:Ascorbate Peroxidases; D002736:Chloroplasts / Q000502:physiology / Q000528:radiation effects; D003683:Dehydroascorbic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D004579:Electron Transport / Q000502:physiology / Q000528:radiation effects; D008027:Light; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology / Q000528:radiation effects; D010544:Peroxidases / Q000378:metabolism; D010788:Photosynthesis / Q000502:physiology* / Q000528:radiation effects; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism / Q000528:radiation effects; D045332:Photosystem II Protein Complex; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism; D013482:Superoxide Dismutase / Q000378:metabolism; D014867:Water / Q000378:metabolism
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D014867:Water; C000820:semidehydroascorbic acid; D010544:Peroxidases; D060387:Ascorbate Peroxidases; D013482:Superoxide Dismutase; D012273:Ribulose-Bisphosphate Carboxylase; D010100:Oxygen; D003683:Dehydroascorbic Acid