[Effect of illumination prehistory on P700 redox transition kinetics in bean leaves]

The state I in equilibrium state II transients in bean leaves were studied by ESR method at various temperatures. P700 photooxidation induced by far-red light after leaf adaptation to darkness demonstrated two phases. This kinetics correlated with two overshuts in the kinetics of P700+ reduction observed after additional switching on the light exciting Photosystem II. In the atmosphere of gaseous nitrogen P700 behaviour was reversibly modified. Multiphase character of P700 kinetics correlated with the state I in equilibrium state II phenomenon as measured by chlorophyll a fluorescence from Photosystem II. The rate-limiting step at the acceptor side of Photosystem I electron transport chain may be considered as a point controlling the state of intact chloroplasts.