EXPOSURE OF A PHOTOSYSTEM-II COMPLEX TO CHEMICALLY GENERATED SINGLET OXYGEN RESULTS IN D1 FRAGMENTS SIMILAR TO THE ONES OBSERVED DURING AEROBIC PHOTOINHIBITION

Exposure of a PS II core complex to singlet oxygen, generated either c hemically in the dark or through the photodynamic action of rose benga l, caused a rapid degradation of D1 protein. Photoinhibitory illuminat ion of the PS II complex, either at 25 degrees C or at 4 degrees C, re sulted in D1 protein fragments similar to those observed upon exposure of the PS II complex to singlet oxygen. Histidine, a singlet oxygen s cavenger, provided a significant protection of D1 protein against degr adation. We therefore suggest that singlet oxygen, which is generated during acceptor-side induced photoinhibition, is responsible for the i n vitro fragmentation of D1 protein.