COMPARISON OF THE PRIMARY EVENTS OF PHOTOINHIBITION IN CYANOBACTERIA, GREEN-ALGAE AND THYLAKOIDS OF HIGHER-PLANTS

In whole cells of the wild type of Synechocystis 6714 exposed to high irradiance (HI) the electron transfer to Q(B) was inhibited before the transfer to Q(A). In the mutant AzV with two point mutations in the Q(B) pocket (Ala 251 Val and Phe 211 Ser) the inhibition of electron transport to Q(B) had about the same rate as in the wild type but (the transport to Q(A) was inhibited faster in the mutant. In the mutant also the repair of photosystem 2 (PS 2) reaction centres was slower after a moderate photoinhibitory damage. In contrast degradation of the D1 protein in the course of photoinhibition in vitro was slower with thylakoids from the mutant than with those of the wild type. In Chlamydomonas cells photoinhibited at low temperature (5-degrees-C) and in spinach thylakoids under anaerobic conditions a fast inhibition of electron transfer developed in PS 2 simultaneously with a state characterized by a high level of F(o). This high fluorescent state disappeared and electron transport activity was restored in the dark without protein synthesis when photoinhibited samples were soon transferred to higher temperature (25-degrees-C) or to aerobic conditions, respectively. On the other hand, the irreversible photoinhibitory damage characterized by the decline of F(m) was slowed down by lowering of the temperature in all the objects tested.