ANTIOXIDANT ACTIVITY OF REDUCED PLASTOQUINONE IN CHLOROPLAST THYLAKOID MEMBRANES

The antioxidant effect of reduced plastoquinone was studied in chlorop last membranes, Isolated spinach thylakoid membranes were subjected to strong illumination followed by analysis of pigment bleaching and lip id peroxidation, The plastoquinone pool was kept in the reduced or oxi dized state during the light stress by the addition of the electron tr ansport inhibitors 2,5-dibromo-3 -methyl-6-isopropyl-p-benzoquinone an d o-phenanthroline, respectively, In the absence of inhibitors there o ccurred a bleaching of carotenoids and chlorophyll a, while chlorophyl l b was unchanged, Formation of thiobarbituric acid reactive substance s, used as a measure of lipid peroxidation, was negligible during the first hour of strong illumination, but during the second hour there wa s a marked increase in the rate of lipid peroxidation, Reduction of th e plastoquinone pool resulted in a virtually complete inhibition of li pid peroxidation and pigment bleaching, In contrast, conditions of an oxidized plastoquinone pool markedly enhanced lipid peroxidation and p igment bleaching, It is argued that the reduced form of plastoquinone can act as a scavenger of toxic oxygen species generated in the thylak oid membranes during strong illumination, (C) 1995 Academic Press, Inc .