Abstract

The interplay between plasma membrane electrical activity and chloroplast photochemistry is a critical, yet complex, aspect of cellular regulation in photosynthetic organisms. This study investigates the **Effect of Plasma Membrane Ion Currents on Chlorophyll Fluorescence and Excitation Quenching in Chara Chloroplasts**, aiming to elucidate the regulatory mechanisms linking cellular bioelectricity to photosynthetic efficiency. Using the giant algal cell *Chara corallina* as a model, we employed simultaneous measurements of plasma membrane ion currents via voltage-clamp techniques and *in vivo* chlorophyll fluorescence kinetics, including non-photochemical quenching (NPQ). Our findings reveal a direct, rapid correlation where changes in the plasma membrane potential, specifically those induced by modulating proton or chloride channel activity, significantly alter the efficiency of photosystem II (PSII) and the magnitude of NPQ. We propose that the plasma membrane ion fluxes act as a rapid signaling pathway, potentially by altering the stromal pH or the concentration of key ions, which in turn influences the thylakoid lumen pH gradient and the activation of photoprotective mechanisms. This work highlights a novel, electrophysiological regulatory layer in photosynthesis, suggesting that the cell's electrical state is a key determinant of light-harvesting and energy dissipation strategies in plant cells.