SINGLET OXYGEN PRODUCTION IN THYLAKOID MEMBRANES DURING PHOTOINHIBITION AS DETECTED BY EPR SPECTROSCOPY

Exposure of isolated spinach thylakoids to high intensity illumination (photoinhibition) results in the well-characterized impairment of Pho tosystem II electron transport, followed by degradation of the 1 react ion centre protein. In the present study we demonstrate that this proc ess is accompanied by singlet oxygen production. Singlet oxygen was de tected by EPR spectroscopy, following the formation of stable nitroxid e radicals from the trapping of singlet oxygen with a sterically hinde red amine TEMP (2,2,6,6-tetramethylpiperidine). There was no detectabl e singlet oxygen production during anaerob photoinhibition or in the p resence of sodium-azide. Comparing the kinetics of the loss of PS II f unction and D1 protein with that of singlet oxygen trapping suggests t hat singlet oxygen itself or its radical product initiates the degrada tion of D1.