Temperature dependence (25-50 °C) of chlorophyll (Chl) fluorescence induction, far-red radiation (FR)-induced relaxation of the post-irradiation transient increase in apparent F0, and the trans-thylakoid proton gradients (ΔpH) was examined in maize leaves. Temperatures above 30 °C caused an elevation of F0 level and an enhancement of F0 quenching during actinic irradiation. Millisecond delayed light emission (ms-DLE), which reflects the magnitude of ΔpH, decreased strikingly above 35 °C, and almost disappeared at 50 °C. It indicates that the heat-enhanced quenching of F0 under actinic irradiation could not be attributed mainly to the mechanism of ΔpH-dependent quenching. The relaxation of the post-irradiation transient increase in apparent F0 upon FR irradiation could be decomposed into two exponential components (τ1 = 0.7-1.8 s, τ2 = 2.0-9.9 s). Decay times of both components increased with temperature increasing from 25 to 40-45 °C. The bi-phasic kinetics of FR-induced relaxation of the post-irradiation transient increase in apparent F0 and its temperature dependence may be related to plastoquinone (PQ) compartmentation in the thylakoid membranes and its re-organisation at elevated temperature. and Ming-Xian Jin, De-Yao Li, Hualing Mi.