Energy-Dependent Chlorophyll Fluorescence Quenching in Chloroplasts Correlated with Quantum Yield of Photosynthesis

Chlorophyll a fluorescence quenching was studied in intact, C 0 2 fixing chloroplasts isolated from spinach. Energy-dependent quenching (qE), which is correlated with the light-induced pro­ ton gradient across the thylakoid membrane presumably reflects an increase in the rate-constant of thermal dissipation of excitation energy in the photosynthetic pigment system. The extent of qE was found to be linearly related to the decrease of quantum yield o f photosynthesis. We suggest that this relationship indicates a dynamic property of the membrane to adjust thermal dissipation of absorbed light energy to the energy requirement of photosynthesis.