[Reduction paths of reaction centers of photosystem I of photosynthesis].

The behaviour of ESR signal I in blue-green algae and chloroplasts is considered under various illumination and with various previous treatment. It is shown that the main process determining the kinetics of P700 plus reduction is the reaction with reduced components of the electron transfer chain between the two photosystems. If the accumulation of the products is inhibited by any way, then the reduction rate depends on the reactions with reducing agents in the incubation medium accumulated under irradiation before experiment. These exogenic reducing agents may be removed from the chloroplasts with repeated washings, and from algae-by means of the dark incubation for a long time. The relation of cyclic and noncyclic electron transfer is considered with and without artificial cyclic flow mediator.