Oxygenic Photosynthesis in silico: Ferredoxin and Alternative Electron Transport Pathways

Abstract

The work is devoted to the mathematical analysis of alternative electron transport pathways in chloroplasts related to the functioning of ferredoxin molecules located at the “crossroad” of electron transport pathways on the acceptor side of photosystem I. This study is based on the kinetic model we proposed earlier, which describes the light-induced transformations of the reaction centers of photosystem I and photosystem II, ferredoxin, plastoquinone, and plastocyanin molecules, as well as the processes of trans-thylakoid proton transfer and ATP synthesis. The effect of alternative channels of electron outflow from ferredoxin molecules (reduction of molecular oxygen, cyclic electron transport around photosystem I, and reduction of thioredoxin) on the dynamics of light-induced redox transformations of electron transport chain transporters has been studied. It has been shown that accelerated electron outflow from photosystem I contributes to an increase in the efficiency of the centers of photosystem I, which is especially important at the initial stages of chloroplast illumination when the Calvin–Benson cycle is inactive. Alternative electron fluxes make it possible to maintain a sufficiently high trans-thylakoid pH difference (ΔрН ≈ 1.8), ensuring efficient synthesis of ATP. The results obtained are compared with experimental data in the context of pH-dependent mechanisms of regulation of electron transport and energy metabolism processes associated with the synthesis of ATP in chloroplasts.