INVOLVEMENT OF SULFITE AND SULFATE ANIONS IN THE SO2-INDUCED INHIBITION OF THE OXYGEN EVOLVING ENZYME PHOTOSYSTEM-II IN CHLOROPLASTS - A REVIEW

The oxygen evolving enzyme of chloroplasts (Photosystem II) responsible for reduction of the photosynthetic electron transport carriers has been shown to be sensitive to SO2 absorption by plants. The involvement of SO2-derived anions sulfite and sulfate in inhibition of Photosystem II has been proposed and the direct effects of these anions on PSII investigated by many groups. A survey of recent advances on this subject is presented here, and the relevance of some in vitro studies discussed. From results of in vitro and in vitro experiments, a model is proposed in which sulfate, the product of sulfite oxidation, is responsible for the inhibition of PSII in SO2-exposed leaves. The detection of an increased amount of sulfate in chloroplasts after SO2 treatment and the reversibility and sensitivity to light of PSII inhibition by sulfate support the postulated model.