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

The effect of high light on the acceptor side of photosystem II of chloroplasts and core particles of spinach mas studied. Both V-max and apparent K-m 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 F-m level. Further the high light stress induced decrease in F-m 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 Q(B) on the D1 protein on the acceptor side of photosystem II.