Carotenoids in photosynthesis

Abstract

Carotenoids are usually considered to perform two major functions in photosynthesis. They serve as accessory light harvesting pigments, extending the range of wavelengths over which light can drive photosynthesis, and they act to protect the chlorophyllous pigments from the harmful photodestructive reaction which occurs in the presence of oxygen. Drawing upon recent work with photosynthetic bacteria, evidence is presented as to how the carotenoids are organized within both portions of the photosynthetic unit (the light harvesting antenna and the reaction centre) and how they discharge both their functions. The accessory pigment role is a singlet-singlet energy transfer from the carotenoid to the bacteriochlorophyll, while the protective role is a triplet-triplet energy transfer from the bacteriochlorophyll to the carotenoid.