18] Functions of carotenoids in photosynthesis

Abstract

Publisher Summary Carotenoids are essential for the survival of photosynthetic organisms. Carotenoids have been shown to have two major functions in photosynthesis. They act as photoprotective agents, preventing the harmful photodynamic reaction, and as accessory light-harvesting pigments, extending the spectral range over which light drives photosynthesis. The first of these two functions depends on the triplet states of the carotenoid, while the second depends on their excited singlet states. The chapter discusses the way carotenoids are organized and arranged within the photosynthetic apparatus. Most common carotenoids found in photosynthetic cells and organelles are rather hydrophobic molecules and are typically located within the photosynthetic membranes. However, they are not usually freely mobile within the lipid interior of these membranes but rather are noncovalently bound to the photosynthetic reaction centers and the light-harvesting complexes. Although carotenoids function just as well in plants and algae as in photosynthetic bacteria, the antenna system of the purple bacteria is an ideal model system in which to demonstrate their functions, because they are spectrally so well defined and have a much simpler organization than those of plants.