Uncoupler Titrations of Energy-Dependent Quenching of Chlorophyll Fluorescence in Chloroplasts

Light-dependent quenching of room-temperature chlorophyll fluorescence associated with the “energisation” of the thylakoid membrane is usually referred to as qE; improvements in the analysis of chlorophyll fluorescence yield (1,2) allow its quantification. qE is generally taken to reflect an increase in energy dissipation by non-radiative pathways (heat) at Photosystem 2. This increased dissipation has been implicated in the control of electron transport through PS2 (3,4) and in protection of PS2 reaction centres against photoinhibition (5). However, the mechanistic links between the onset of ΔpH and the increased energy dissipation remain obscure.