Formation of superoxide anion and carbon-centered radicals by photosystem II under high light and heat stress—EPR spin-trapping study
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In this study, electron paramagnetic resonance spin-trapping spectroscopy was used to study the light-induced production of superoxide anion (O2•-) and carbon-centered (R•) radicals by Photosystem II (PSII). It is evidenced here that exposure of PSII membranes to high light (2,000 μmol photons m−2 s−1) or heat (47 °C) treatments prior to the illumination suppressed O2•- production, while R• was formed. Formation of R• in the both high light- and heat-treated PSII membranes was enhanced by DCMU. Removal of molecular oxygen by glucose/glucose oxidase/catalase system and O2•- scavenging by exogenous superoxide dismutase completely suppressed carbon-centered radical formation. It is proposed here that the oxidation of polyunsaturated fatty acids and amino acids by O2•- on the electron acceptor side of PSII results in the formation of R•, known to initiate a cascade reaction leading to the lipid peroxidation and protein degradation, respectively.
KeywordsHeat stress Photoinhibition Photosystem II Reactive oxygen species Redox potential
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