Primary photochemical reactions in chloroplast photosynthesis

Photosynthesis begins with the absorption of light energy and this absorbed energy is transferred to special sites, termed reaction centres. At these sites, the light energy is transformed into chemical products through an oxidation-reduction reaction that generates the primary reactants, an oxidized pigment molecule (P + ) and a reduced electron acceptor (A – ) (Clayton, 1972). The subsequent reactions of these species in the dark ultimately results in the formation of chemical products required for the fixation of CO 2 . In this essay we will discuss the nature of the primary reactants generated in the light reactions of chloroplast photosynthesis, stressing recent advances in the identification and characterization of such reactants.