BETA-CAROTENE TO ZEAXANTHIN CONVERSION IN THE RAPID TURNOVER OF THE D1 PROTEIN OF PHOTOSYSTEM-II

The carotenoid composition was investigated during enhanced D1 protein turnover in Chlamydomonas reinhardtii exposed to high light. After 2 h of high light there was no loss of the D1 protein yet, However, the beta-carotene content was significantly reduced, In parallel, an incre ase of the zeaxanthin content was found, which was higher than can be accounted for by the light-induced de-epoxidation of violaxanthin in t he xanthophyll cycle reactions, We therefore assume that beta-carotene of photosystem II (PS II) is hydroxylated to zeaxanthin under high li ght stress, Inhibitors of carotene biosynthesis led to the loss of bot h PS II activity and D1 protein, indicating the requirement of beta-ca rotene synthesis for the reassembly of PS II in high light. Diuron blo cked D1 protein as well as beta-carotene turnover, In the presence of chloramphenicol - which allows just one turnover of the D1 protein -15 % of the total beta-carotene was lost, calculated to be two beta-carot ene. (C) 1998 Federation of European Biochemical Societies.