Alteration in the acceptor side of photosystem II of chloroplast by high light.

ABSTRACT

The effect of high light on the acceptor side of photosystem II of chloroplasts and core particles of spinach was studied. Both Vmax and apparent Km for DCIP were altered in photoinhibited photosystem II core particles. The double reciprocal plot analysis as a function of actinic light showed increased slope in chloroplasts photoinhibited in the presence of DCMU. Exposure of chloroplasts to high light in the presence of DCMU did not protect the chloroplast against high light induced decrease in Fm, level. Further the high light stress induced decrease in Fm level was not restored by the addition of DCMU. These results suggest that the high light stress induced damage to chloroplast involves alteration in the binding site for QB on the DI protein on the acceptor side of photosystem II.