Optimizing Oxygenic Photosynthesis: pH-Regulation of Electron Transport in Chloroplasts In Silico

The work is devoted to the mathematical modeling of the regulation of electron and proton transport in the thylakoid membranes of chloroplasts under different operating conditions of the electron transport chain (ETC). The study is based on the kinetic model that we proposed earlier, which describes the redox transformations of the photosystem 1 (PSI) reaction center and molecules of ferredoxin, plastoocyanin, as well as several forms of plastoquinone molecules (the PSII-related concentrations of PQ_A, PQ_B, and the plastoquinone pool PQ/PQH₂). The induction curve of chlorophyll a fluorescence in the leaves of higher plants adapted to darkness is also modelled. The multiphase kinetic curves, obtained by varying the model parameters reflecting the rate of functioning of the Calvin–Benson cycle and the cyclic electron transport path around PSI, are in satisfactory agreement with the experimental data presented in the literature. The main result of our work is that it mathematically describes how pH-dependent regulatory processes occurring at various sites of ETC of chloroplasts (non-cyclic, cyclic, and pseudocyclic electron transport) are reflected in the kinetics of induction processes (slow induction of chlorophyll a fluorescence and redox transformations of the photoreaction center of PSI in chloroplasts of plants adapted to darkness.