title: Environmental stress inhibits the synthesis de novo of proteins involved in the photodamage-repair cycle of Photosystem II in Synechocystis sp. PCC 6803.
abstract: The Photosystem II complex (PSII) is susceptible to inactivation by strong light, and the inactivation caused by strong light is referred to as photoinactivation or photoinhibition. In photosynthetic organisms, photoinactivated PSII is rapidly repaired and the extent of photoinactivation reflects the balance between the light-induced damage (photodamage) to PSII and the repair of PSII. In this study, we examined these two processes separately and quantitatively under stress conditions in the cyanobacterium Synechocystis sp. PCC 6803. The rate of photodamage was proportional to light intensity over a range of light intensities from 0 to 2000 microE m(-2) s(-1), and this relationship was not affected by environmental factors, such as salt stress, oxidative stress due to H2O2, and low temperature. The rate of repair also depended on light intensity. It was high under weak light and reached a maximum of 0.1 min(-1) at 300 microE m(-2) s(-1). By contrast to the rate of photodamage, the rate of repair was significantly reduced by the above-mentioned environmental factors. Pulse-labeling experiments with radiolabeled methionine revealed that these environmental factors inhibited the synthesis de novo of proteins. Such proteins included the D1 protein which plays an important role in the photodamage-repair cycle. These observations suggest that the repair of PSII under environmental stress might be the critical step that determines the outcome of the photodamage-repair cycle.
authors.affiliation: Department of Regulation Biology, National Institute for Basic Biology, Okazaki, Japan.
authors.forename: Suleyman I
authors.initials: SI
authors.lastname: Allakhverdiev
authors.forename: Norio
authors.initials: N
authors.lastname: Murata
mesh_terms: D000222:Adaptation, Physiological / Q000528:radiation effects; D001426:Bacterial Proteins / Q000378:metabolism*; D000458:Cyanobacteria / Q000145:classification / Q000502:physiology* / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D004777:Environment; D008027:Light / Q000009:adverse effects*; D045332:Photosystem II Protein Complex / Q000378:metabolism / Q000502:physiology* / Q000528:radiation effects*; D011522:Protons; D013045:Species Specificity; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D045332:Photosystem II Protein Complex; D011522:Protons; C422369:photosystem II, psbA subunit