In our study, EPR spin-trapping technique was employed to study dark production of two reactive oxygen species, hydroxyl radicals (OH.) and singlet oxygen ((1)O2), in spinach photosystem II (PSII) membrane particles exposed to elevated temperature (47 degrees C). Production of OH., evaluated as EMPO-OH adduct EPR signal, was suppressed by the enzymatic removal of hydrogen peroxide and by the addition of iron chelator desferal, whereas externally added hydrogen peroxide enhanced OH. production. These observations reveal that OH. is presumably produced by metal-mediated reduction of hydrogen peroxide in a Fenton-type reaction. Increase in pH above physiological values significantly stimulated the formation of OH., whereas the presence of chloride and calcium ions had the opposite effect. Based on our results it is proposed that the formation of OH. is linked to the thermal disassembly of water-splitting manganese complex on PSII donor side. Singlet oxygen production, followed as the formation of nitroxyl radical TEMPO, was not affected by OH. scavengers. This finding indicates that the production of these two species was independent and that the production of (1)O2 is not closely linked to PSII donor side.

Laboratory of Biophysics Department of Experimental Physics Faculty of Science Palacký University tr Svobody 26 771 46 Olomouc Czech Republic

References provided by Crossref.org

Reactive oxygen species in photosystem II: relevance for oxidative signaling

Amino acid oxidation of the D1 and D2 proteins by oxygen radicals during photoinhibition of Photosystem II

Production of Reactive Oxygen Species by Photosystem II as a Response to Light and Temperature Stress

Singlet oxygen production in Chlamydomonas reinhardtii under heat stress

Role of chloride ion in hydroxyl radical production in photosystem II under heat stress: electron paramagnetic resonance spin-trapping study