Studies on the mechanism of photosystem II photoinhibition II. The involvement of toxic oxygen species |
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Authors: | Michael Richter Wolfgang Rühle Aloysius Wild |
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Institution: | (1) Institute of General Botany of the Johannes Gutenberg University, Saarstr. 21, D-6500 Mainz, FRG |
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Abstract: | In a previous paper it was shown that photoinhibition of reaction centre II of spinach thylakoids was predominantly caused by the degradation of D1-protein. An initial inactivation step at the QB-site was distinguished from its breakdown. The present paper deals with the question as to whether this loss of QB-function is caused by oxygen radical attack. For this purpose the photoinhibition of thylakoids was induced at 20°C in the presence of either superoxide dismutase and catalase or the antioxidants glutathione and ascorbic acid. This resulted in comparable though not total protection of D1-protein, photochemistry and fluorescence from photoinhibition. The combined action of both the enzymatic and the non-enzymatic radical scavenging systems brought about an even more pronounced protective effect against photoinhibition than did either of the two systems singularly at saturating concentrations. The results signify a major contribution of activated oxygen species to the degradation process of D1-protein and the related phenomena of photoinhibition. Thylakoids treated with hydroxyl radicals generated through a Fenton reaction showed a loss of atrazine binding sites, electron transport capacity and variable fluorescence in a similar manner, though not to the same extent, as usually observed following photoinhibitory treatment.Abbreviations Asc
ascorbate
- Fecy
ferricyanide
- GSH
reduced glutathione
- PQ
plastoquinone
- QA
primary quinone acceptor of PS II
- QB
secondary quinone acceptor of PS II
- SOD
superoxide dismutase |
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Keywords: | activated oxygen species D1-protein photoinhibition spinach thylakoids |
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