Non-photochemical quenching speeds up with increasing temperatures.

Photosynthesis constantly adapts to fluctuating light and temperature. Under high light, non-photochemical quenching (NPQ) protects the photosynthetic machinery by dissipating excess excitation energy as heat. With rising global temperatures and more frequent heat events, understanding how photosynthesis responds to combined light and temperature stress is critical. In vascular plants, NPQ is regulated by the protonation of Photosystem II subunit S (PsbS) and the enzymatic formation of zeaxanthin, but it remains unclear how temperature influences the complete NPQ response and the roles of these molecular components. Here, we analyzed NPQ in Arabidopsis thaliana WT and mutant genotypes affecting PsbS, zeaxanthin, or thylakoid membrane fluidity: npq1 (no zeaxanthin), npq2 (constitutive zeaxanthin), npq4 (no PsbS), PsbS-OE (overexpressed PsbS), and fad7fad8 (more rigid membranes). Plants were acclimated to 10 °C, 20 °C, 30 °C, or 40 °C for 30 min before measuring NPQ induction and relaxation. NPQ kinetics generally accelerated with increasing temperature, enabling faster responses to fluctuating light, and more absorbed energy was allocated to photochemistry rather than dissipation. Our results suggest that the concentration of PsbS is important to regulate this balance between photochemistry and NPQ. Full NPQ development and its temperature dependence required both PsbS and zeaxanthin. Arrhenius analysis of the NPQ induction and relaxation rates revealed that NPQ induction could be hindered by a rigid thylakoid membrane. These results demonstrate that NPQ is modulated by temperature, highlighting the importance of considering thermal effects on photoprotection when predicting plant performance under future climates.