Chen, J.; Tan, J.; Fu, L.; Guo, Y.

Photochemical reactions were analyzed and modeled to observe photoenergy regulation mechanisms in PSII from measured chlorophyll fluorescence (ChlF) kinetics. Two pH-driven mechanisms were revealed: One is the PsbS-mediated non-photochemical quenching (NPQ) of activated antennae (A*), as commonly understood, and the other is a disruption of energy transfer from A* to P680. Representing the latter with a conformational change from complex formation of zeaxanthin and lutein with antennae closely described measured ChlF from initially dark-adapted state to light-adapted state and measured NPQ variations. Analysis based on the model indicates that zeaxanthin and lutein lead to slow protracted reductions in P680* and ChlF via the second mechanism without strong influence by pH or PsbS. Protonation of PsbS plays a major role via the first mechanism in responding to fast changes in illumination. The research provides insights into the mechanisms for photoenergy regulation in PSII and a kinetic model with broadened applicability.