Near Infra-Red Flash Absorption: A Tool for Studying Photosynthesis

Abstract

Among photobiological processes, photosynthesis occupies a unique position because it is responsible for the conversion and storage of light energy in the biosphere on a massive scale. The process can be roughly divided into primary reactions, which take place in the photosynthetic membrane, and secondary reactions which occur in a more liquid-like cellular compartment. In the membrane, light is absorbed by pigment-protein complexes which make up the so-called antenna, from which excitation energy is transferred to the reaction centers. These reaction centers are complex proteins where excitation energy induces charge separation (Fig. 1). The initial step of charge separation is followed by a series of electron transfer reactions, which are sometimes coupled to transmembrane proton transfer, and which have three basic functions: i) to decrease the probability of wasteful charge recombination; ii) to achieve the final steps of redox reactions, i.e. to create a useful reductant, such as NADPH, and oxidize a terminal electron donor, which is water in plants; iii) to create a gradient of H+ concentration, which provides the free energy for ATP synthesis by the ATP-synthase. For general reviews and collective books see Clayton, 1970; Amesz, 1987; Barber, 1987; Hatch and Boardman, 1981.