Biosynthesis of carotenoids in the chloroplasts of algae and higher plants.

Abstract

Physiological, biochemical, and genetic aspects of carotenoid biosynthesis in the chloroplast membranes of green algae and higher plants are discussed starting from the earliest stages of biosynthesis of key C5-isoprene units. The latter are synthesized either from acetate (C2) to mevalonic acid (C6) or from glucose (C6) by forming glyceraldehyde 3-phosphate (C3) and pyruvate decarboxylation product (C2) through intermediate compounds to isopentenyl diphosphate (C5). In all organisms, the further carotenoid synthesis from isopentenyl diphosphate and its isomer dimethylallyl diphosphate (C5) proceeds through their transformation into geranyl diphosphate (C10), farnesyl diphosphate (C15), geranylgeranyl diphosphate (C20) and phytoene (C40). Phytoene desaturation (dehydrogenation) to carotene, neurosporene, and lycopene, and all steps of their cyclization to α, β and e carotenes are discussed in detail. The synthesis of xanthophylls in chloroplasts is presented as the sequential formation of hydroxy-, epoxy- and oxo- groups. Genetic control of biosynthesis, as well as the localization and functional role of carotenoids in the chloroplast membranes of plants and algae are briefly discussed.