CAROTENOIDS .3. IN-VIVO FUNCTIONS OF CAROTENOIDS IN HIGHER-PLANTS

The function of the long-chain, highly unsaturated carotenoids of high er plants in photoprotection is becoming increasingly well understood, while at the same time their function in other processes, such as lig ht collection, needs to be reexamined, Recent progress in this area ha s been fueled by more accurate determinations of the photophysical pro perties of these molecules, as well as extensive characterization of t he physiology and ecology of a particular group of carotenoids, those of the xanthophyll cycle, that play a key role in the photoprotection of photosynthesis under environmental stress, The deepoxidized xanthop hylls zeaxanthin and antheraxanthin, together with a low pH within the photosynthetic membrane, facilitate the harmless dissipation of exces s excitation energy directly within the light-collecting chlorophyll a ntennae, Evidence for this function as well as current contrasting hyp otheses concerning its molecular mechanism are reviewed, In addition, the acclimation of the xanthophyll cycle content and composition of le aves to contrasting environments with different demands for photoprote ction is summarized.