Carotenoid Localization and Biosynthesis in Radish Seedlings (Raphanus Sativus) Grown in the Presence or Absence of Bleaching Herbicides

Abstract

Chloroplasts from almost all higher plant leaves contain the same collection of main carotenoids, i.e. β-carotene (frequently accompanied by some α-carotene) and the xanthophylls lutein, violaxanthin and neoxanthin, usually with smaller amounts of zeaxanthin, antheraxanthin and lutein 5,6-epoxide. These carotenoids are constituents of pigment-protein complexes which are located in highly specific orientations in photosynthetic reaction centres and light-harvesting assemblies in the thylakoid membranes. It has also been reported that, in some plant species, some carotenoid, particularly violaxanthin, may be present in the chloroplast envelope (Jeffrey et al., 1974). The carotenoids are biosynthesized within the chloroplast, and several biosynthetic transformations have been achieved with isolated chloroplasts (see Britton, 1982, for a review of carotenoid biosynthesis in higher plants). The relative contributions of cytoplasm and chloroplast to the synthesis of mevalonate for terpenoid biosynthesis are not clear, but there can be little doubt that the later stages of carotenoid biosynthesis take place in the chloroplast. The actual site or sites of synthesis within the plastid remains unknown.