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ARS Home » Research » Publications at this Location » Publication #61098
Title: CYTOCHROME B559 PROTECTS PHOTOSYSTEM II AGAINST PHOTOINHIBITION BY ACCEPTING AN ELECTRON FROM PHEOPHYTIN

Author
item POULSON, MARY - UNIV OF ILLINOIS CHA
item WHITMARSH, CLIFFORD

Submitted to: Photosynthesis International Congress Symposium Proceedings and Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 6/28/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: The capacity of photosystem II (PSII) to evolve oxygen can be impaired when plants are exposed to excess light. Photoinhibition is initiated by electron transport reactions that create damaging redox states within PSII such as the rarely-formed but long-lived state P680/Pheo/Qa. Experiments using thylakoid and PSII- enriched membranes poised at different ambient redox potentials demonstrate that light-induced damage to PSII is controlled by a redox component within the reaction center. We have provided evidence that the redox component is cytochrome b559 (Cyt b559), an intrinsic heme protein within PSII. If the low potential form of the cytochrome (Cyt b559LP) is reduced prior to illumination, the rate of photoinhibition is fast, whereas if it is oxidized the rate of photoinhibition is slow. In continuous light under anaerobic conditions and without added redox mediators, Cyt b559LP accumulates in the reduced state prior to photoaccumulation of reduced pheophytin and loss of oxygen evolution capacity. These results support the proposal that electrons can flow from pheophytin to Cyt b559 and thereby protect PSII against photoinhibition.