Carotenoid binding to photosystems I and II of Chlamydomonas reinhardtii cells grown under weak light or exposed to intense light

Thylakoids, isolated from Chlamydomonas reinhardtii cells which were grown under weak light or exposed to a short period of intense light, were solubi lised with decanoyl-N-methylglucamide (Mega 10) or with a new related deter gent, dodecanoyl-N-hydroxyethylglucamide (DODHEGA) to prepare photosystem I and II complexes or sub-complexes for pigment stoichiometry determination. Loroxanthin was only bound to photosystem II antenna but most of the lutei n, the other main alpha -carotene derived xanthophyll, was also associated with photosystem II antenna, as well as with the photosystem I antenna in w hich it represented the main xanthophyll species. The mean xanthophyll comp osition of the photosystem II antenna, prepared both by partially denaturin g electrophoresis or sucrose gradient sedimentation, showed that more than three molecules (most probably four) were associated with individual light- harvesting complex II (LHCII) polypeptide (on the basis of seven chl a per polypeptide). Intense light exposition of the cells resulted in increased l evels of lutein and of components of the violaxanthin cycle, part of them b eing only loosely bound to pigment protein complexes. The violaxanthin cycl e components were recovered in PSI and PSII whereas the additional level of lutein was restricted to PSII sub-complexes. (C) 2001 Editions scientifiqu es et medicales Elsevier SAS.