title: Superoxide anion radicals generated by methylviologen in photosystem I damage photosystem II.
abstract: The effect of superoxide anion radicals on the photosynthetic electron transport chain was studied in leaves and isolated thylakoids from tobacco. Superoxide was generated by methylviologen (MV) in the light at the acceptor side of photosystem I (PSI). In isolated thylakoids, the largest damage was observed at the level of the water-splitting activity in photosystem II (PSII), whereas PSI was hardly affected at the light intensities used. Addition of reactive oxygen scavengers protected PSII against damage. In leaves in the presence of MV, the quantum yield of PSII decreased during illumination whereas the size of the P(700) signal remained constant. There was no D1 protein loss in leaves illuminated in the presence of MV and lincomycin, but a modification to a slightly higher molecular mass was observed. These data show that PSII is more sensitive to superoxide or superoxide-derived reactive oxygen species (ROS) than PSI. In our experiments, this susceptibility was not because of any action of the ROS on the translation of the D1 protein or on the repair cycle of photosystem.
authors.affiliation: Commissariat à l'Energie Atomique (CEA), iBiTec-S, CNRS URA 2096, Service de Bioénergétique Biologie Structurale et Mécanisme, 91191 Gif-sur-Yvette, France.
authors.forename: Anja
authors.initials: A
authors.lastname: Krieger-Liszkay
authors.forename: Péter B
authors.initials: PB
authors.lastname: Kós
authors.forename: Eva
authors.initials: E
authors.lastname: Hideg
mesh_terms: D015151:Immunoblotting; D008027:Light; D010084:Oxidation-Reduction / Q000187:drug effects / Q000528:radiation effects; D010269:Paraquat / Q000494:pharmacology*; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D011789:Quantum Theory; D013312:Stress, Physiological / Q000187:drug effects / Q000528:radiation effects; D013481:Superoxides / Q000378:metabolism*; D020524:Thylakoids / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D014026:Nicotiana / Q000187:drug effects* / Q000378:metabolism* / Q000528:radiation effects
chemical_list: D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D013481:Superoxides; D010269:Paraquat