Effect of cationic plastoquinone SkQ1 on electron transfer reactions in chloroplasts and mitochondria from pea seedlings

Plastoquinone bound with decyltriphenylphosphonium cation (SkQ1) penetrating through the membrane in nanomolar concentrations inhibited H 2 O 2 generation in cells of epidermis of pea seedling leaves that was detected by the fluorescence of 2′,7′-dichlorofluorescein. Photosynthetic electron transfer in chloroplasts isolated from pea leaves is suppressed by SkQ1 at micromolar concentrations: the electron transfer in chloroplasts under the action of photosystem II or I (with silicomolybdate or methyl viologen as electron acceptors, respectively) is more sensitive to SkQ1 than under the action of photosystem II + I (with ferricyanide or p -benzoquinone as electron acceptors). SkQ1 reduced by borohydride is oxidized by ferricyanide, p -benzoquinone, and, to a lesser extent, by silicomolybdate, but not by methyl viologen. SkQ1 is not effective as an electron acceptor supporting O 2 evolution from water in illuminated chloroplasts. The data on suppression of photosynthetic O 2 evolution or consumption show that SkQ1, similarly to phenazine methosulfate, causes conversion of the chloroplast redox-chain from non-cyclic electron transfer mode to the cyclic mode without O 2 evolution. Oxidation of NADH or succinate in mitochondria isolated from pea roots is stimulated by SkQ1.