[The current concepts of functional role of carotenoids in the eukaryotic chloroplasts]

Current state of knowledge of functional role of carotenoids in algal and higher plant chloroplasts is reviewed. Basic functions of carotenoids are shown to be light-protective, light-absorbing, and structural, as well as participating in photochemical processes of photosystems I and II. Such xanthophylls as neoxanthin, fucoxanthin, peridinin and alloxanthin, which have allenic or acetylenic bond, mostly function as light-absorbers. They transmit absorbed energy to chlorophyll b. Other xanthophylls occupying certain strictly specified loci in light-absorbing chlorophyll-a/b-protein complexes of photosystems have either structural function (lutein) or light-protective function (zeaxanthin, antheraxanthin, violaxanthin). Carotenoids of xanthophyll cycles preserve chlorophylls and lipids of photosynthetic membranes from photodestruction at overlighting in the presence of oxygen. In eukaryotic chloroplasts, three types of xanthophyll cycles were found: violaxanthin, lutein-5,6-epoxide, and diadinoxanthin. The similarities and dissimilarities between epoxidation and de-epoxidation reactions of these cycles are discussed in detail in the present work. The pattern of occurrence of xanthophyll cycles among higher plants and freshwater and marine algae is outlined.