title: Evidence for the role of the oxygen-evolving manganese complex in photoinhibition of Photosystem II.
abstract: Photoinhibition of PSII occurs at the same quantum efficiency from very low to very high light, which raises a question about how important is the rate of photosynthetic electron transfer in photoinhibition. We modulated electron transfer rate and light intensity independently of each other in lincomycin-treated pea leaves and in isolated thylakoids, in order to elucidate the specific effects of light and PSII electron transport on photoinhibition. Major changes in the rate of electron transport caused only small changes in the rate of photoinhibition, suggesting the existence of a significant photoinhibitory pathway that contains an electron-transfer-independent phase. We compared the action spectrum of photoinhibition with absorption spectra of PSII components that could function as photoreceptors of the electron-transfer-independent phase of photoinhibition and found that the absorption spectra of Mn(III) and Mn(IV) compounds resemble the action spectrum of photoinhibition, showing a steep decrease from UV-C to blue light and a low visible-light tail. Our results show that the release of a Mn ion to the thylakoid lumen is the earliest detectable step of both UV- and visible-light-induced photoinhibition. After Mn release from the oxygen-evolving complex, oxidative damage to the PSII reaction center occurs because the Mn-depleted oxygen-evolving complex cannot reduce P680+ normally.
authors.affiliation: Department of Biology, Laboratory of Plant Physiology and Molecular Biology, Biocity A, University of Turku, FI-20014 University of Turku, Finland.
authors.forename: Marja
authors.initials: M
authors.lastname: Hakala
authors.forename: Ilona
authors.initials: I
authors.lastname: Tuominen
authors.forename: Mika
authors.initials: M
authors.lastname: Keränen
authors.forename: Taina
authors.initials: T
authors.lastname: Tyystjärvi
authors.forename: Esa
authors.initials: E
authors.lastname: Tyystjärvi
mesh_terms: D028464:Cucurbita / Q000378:metabolism*; D004579:Electron Transport / Q000502:physiology; D005985:Glyceraldehyde; D008027:Light; D017895:Manganese Compounds / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*; D018532:Pisum sativum / Q000378:metabolism*; D010777:Photochemistry; D010788:Photosynthesis / Q000528:radiation effects*; D045332:Photosystem II Protein Complex / Q000378:metabolism* / Q000528:radiation effects; D020524:Thylakoids / Q000378:metabolism
chemical_list: D017895:Manganese Compounds; D045332:Photosystem II Protein Complex; D005985:Glyceraldehyde; D010100:Oxygen