title: The role of inactive photosystem-II-mediated quenching in a last-ditch community defence against high light stress in vivo.
abstract: Photoinactivation of photosystem II (PSII), the light-induced loss of ability to evolve oxygen, is an inevitable event during normal photosynthesis, exacerbated by saturating light but counteracted by repair via new protein synthesis. The photoinactivation of PSII is dependent on the dosage of light: in the absence of repair, typically one PSII is photoinactivated per 10(7) photons, although the exact quantum yield of photoinactivation is modulated by a number of factors, and decreases as fewer active PSII targets are available. PSII complexes initially appear to be photoinactivated independently; however, when less than 30% functional PSII complexes remain, they seem to be protected by strongly dissipative PSII reaction centres in several plant species examined so far, a mechanism which we term 'inactive PSII-mediated quenching'. This mechanism appears to require a pH gradient across the photosynthetic membrane for its optimal operation. The residual fraction of functional PSII complexes may, in turn, aid in the recovery of photoinactivated PSII complexes when conditions become less severe. This mechanism may be important for the photosynthetic apparatus in extreme environments such as those experienced by over-wintering evergreen plants, desert plants exposed to drought and full sunlight and shade plants in sustained sunlight.
authors.affiliation: Photobioenergetics Group, Research School of Biological Sciences, Australian National University, GPO Box 475, Canberra, ACT 2601, Australia. chow@rsbs.anu.edu.au
authors.forename: Wah Soon
authors.initials: WS
authors.lastname: Chow
authors.forename: Hae-Youn
authors.initials: HY
authors.lastname: Lee
authors.forename: Youn-Il
authors.initials: YI
authors.lastname: Park
authors.forename: Yong-Mok
authors.initials: YM
authors.lastname: Park
authors.forename: Yong-Nam
authors.initials: YN
authors.lastname: Hong
authors.forename: Jan M
authors.initials: JM
authors.lastname: Anderson
mesh_terms: D004735:Energy Transfer; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008027:Light; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism* / Q000528:radiation effects*; D045332:Photosystem II Protein Complex; D010935:Plant Diseases; D018521:Plant Physiological Phenomena
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex