Abstract: Cytochrome b-559, a heme protein composed of α-and β-subunits encoded by chloroplast genomes, is an integral component of the PSII reaction center. It was indicated that cytochrome b_559 could control PSII photoinhibitional sensitivity through redox conversion and protect against photoinhibition in acceptor and donor side with the research on chloroplasts, but these were not proven in whole plants under physiological conditions.Therefore,it just should be studied in future.