ROLE OF CAROTENE IN THE RAPID TURNOVER AND ASSEMBLY OF PHOTOSYSTEM-IIIN CHLAMYDOMONAS-REINHARDTII

Inhibitors of the phytoene desaturase in carotene biosynthesis were te sted in the enhanced rapid turnover of the D1 protein of photosystem I I in high light exposure of Chlamydomonas reinhardtii cells. After 1 h high light on heterotrophically grown cells in the presence of norflu razon or fluridone, photosynthesis activity in vivo and PS II activity in vitro is lost. The D1 protein has disappeared, PS I activity is no t affected, nor is the D2 protein. It is concluded that beta-carotene is essential for the assembly of the D1 protein into functional photos ystem II. It is suspected that bleaching of beta-carotene in the react ion center of PS II by high light destabilizes the structure and trigg ers the degradation of the D1 protein.