Abstract

The regulation of photosynthetic electron and proton transport is critical for optimizing energy conversion in chloroplasts, particularly in response to environmental fluctuations. This study investigates the **pH-dependent regulatory mechanisms** governing these processes, utilizing a combined approach of **in situ** measurements and **in silico** mathematical modeling. The research objective was to elucidate how changes in the thylakoid lumen pH ($\Delta$pH) influence the kinetics of electron transfer and the activity of the ATP synthase. The **in silico** component involved developing and applying a comprehensive mathematical model of the thylakoid membrane, which accounts for the pH-dependent regulation of key components, including the cytochrome $b_6f$ complex and the plastoquinone pool. **In situ** experiments, likely involving chlorophyll fluorescence and electrochromic shift measurements in isolated chloroplasts, were used to validate the model's predictions. Key findings indicate that a decrease in lumen pH significantly **decelerates the electron flux** between Photosystem II and Photosystem I, primarily by modulating the rate of plastoquinol oxidation and the activity of the ATP synthase. The model successfully reproduced the complex kinetics observed in metabolic states, confirming the central role of $\Delta$pH in photosynthetic control. This work highlights the sophisticated, short-term regulatory capacity of the photosynthetic apparatus, providing a quantitative framework for understanding how chloroplasts maintain energy balance under varying light conditions.