Kinetic analysis of the light-induced fluorescence quenching in light-harvesting chlorophyll a/b pigment-protein complex of photosystem II

We carried out a kinetic analysis of the light-induced fluorescence quenching (Delta F) of the light-harvesting chlorophyll a/b pigment-protein complex of photosystem II (LHCII) that was first observed by Jennings et al, (Photosynth. Res. 27, 57-64, 1991), We show that during a 2 min light, 2 min dark cycle, both the light and dark phases exhibit biexponential kinetics; this is tentatively explained by the presence of two types of light-induced quenchers in different domains of aggregated LHCII, Quantitative analysis could be carried out on the faster kinetic component; the slower component that was not completed during the measurement was not amenable for quantitative analysis. Our analysis revealed that the rate of the light-induced decrease of the fluorescence yield depended linearly on the light intensity, which shows that the generation of the quencher originates from a reaction that is first order with respect to the concentration of the excited domains. As shown by the estimated rate constant, photogeneration of the quencher is a fast reaction that can compete with other excitation-relaxation pathways. Both the decay and the recovery time constants of Delta F depended strongly on the temperature. Thermodynamic analysis showed that the fast light-induced decline in the fluorescence was determined by a low fraction of the excited states. Recovery was associated with large decrease in the entropy of activation that indicated the involvement of large structural rearrangements. Macroaggregated LHCII exhibited larger Delta F than small aggregates, which is consistent with the proposed role of aggregated LHCII in thylakoid membranes in nonphotochemical quenching.