Effects of light-induced changes in pH of stroma and lumen on the kinetics of electron transport in chloroplasts. A mathematical model

A mathematical model for the description of electron and proton transport in chloroplasts of higher plants has been developed. The model takes into account the light-induced changes in the pH values of stroma (pH(o)) and intrathylakoid lumen (pH(i)), electron transport from photosystem 2 (PS2) to NADP+, a terminal electron acceptor of photosystem 1 (PS1), ATP synthesis from ADP and P(i) coupled to the transmembrane proton flow, and the consumption of NADPH and ATP in the Calvin cycle reactions. The effects of the light-induced changes in the values of pH(i) and pH(o) on the rates of electron flow on the plastoquinone segment of electron transport chain and on the acceptor side of PS1 allowed us to describe some peculiarities of the complex kinetics of electron transport in intact chloroplasts. According to computer experiments, the acceleration of electron efflux from PS1 due to the activation of Calvin cycle reactions in response to the light-induced rise of pH(o) may be one of the reasons for the non-monotonous kinetics of P700 redox transients, which is typical of dark-adapted cyanobacteria, algae, and intact chloroplasts of higher plants.