Oxygenic Photosynthesis in silico: Ferredoxin and Alternative Electronic Transport Pathways

The paper is devoted to the mathematical analysis of alternative electron transport routes in chloroplasts related to the functioning of ferredoxin molecules located at the “fork” of electron transport pathways on the acceptor side of photosystem I. This study is based on the kinetic model proposed by us earlier, which describes the phototransformation 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, reduction of thioredoxin) on the dynamics of light-induced redox transformations of electron transport chain carriers has been studied. It has been shown that increased electron outflow from photosystem I contributes to an increase in the efficiency of photosystem I centers, 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 (ΔpH ≈ 1.8), ensuring efficient synthesis of ATP molecules.