EXISTENCE OF A HIGH PHOTOCHEMICAL TURNOVER RATE AT REACTION CENTERS OF SYSTEM -2 IN TRIS-WASHED CHLOROPLASTS

In Tris-washed chloroplasts the kinetics of the primary electron acceptor X 320 of reaction center II was investigated by fast repetitive flash spectroscopy with a time resolution of .apprxeq. 1 .mu.s. X 320 is reduced by a flash in .ltoreq. 1 .mu.s. The subsequent reoxidation in the dark occurs mainly by a reaction with a 100-200 .mu.s kinetics. The light-induced difference spectrum confirms X 320 to be the reactive species. In Tris-washed chloroplasts the reaction centers of System II are characterized by a high photochemical turnover rate mediated either via rapid direct charge recombination or via fast cyclic electron flow.