Xantophyll-Zyklus in Chlamydomonas reinhardii

Abstract

During the xanthophyll cycle, which occurs upon illumination in thylakoid membranes of chloroplasts, violaxanthin is transformed via antheraxanthin into zeaxanthin. Not all of the violaxanthin, which seems to be present in a loosely and a more tightly bound form in pigment-protein complexes, participates in the cycle. Here we study the xanthophyll cycle of two pigment deficient mutants of Chlamydomonas reinhardii in order to get some information on the role and organization of the pigments in photosynthetic membranes. The mutant pg-113 has almost no chlorophyll b and is reduced in neoxanthin, whereas mutant pg-10l contains no loroxanthin and normally only traces of lutein. After dark incubation, both mutants contain more violaxanthin per chlorophyll a than the parent strain, from which the mutants have been derived. Upon illumination, in pg-113 violaxanthin is transformed into antheraxanthin and zeaxanthin, while in pg-101 taraxanthin and lutein might be produced. Since the amounts of transformed violaxanthin are higher in the mutants than in the parent strain, during illumination more NADPH (and ascorbate) is consumed in the mutants. We infer that in the mutants the pool of loosely bound violaxanthin as well as the ratio of loosely to tightly-bound pigment are higher than in the parent strain.