Abstract
In this study, the regulation and possible functions of energy-dependent quenching (quenching coefficient, qE), have been investigated through a series of experiments on isolated pea chloroplasts. The results presented here suggest that this type of quenching provides some protection against photoinhibition, but is of little or no importance in the regulation of the intrinsic yield of Photosystem II ( Ф p ), which is, instead, controlled directly by the proton gradient. The relationship between qE and the transthylakoid proton gradient, as measured by 9-aminoacridine fluorescence quenching ( q9-AA), showed an apparent redox-state dependency, this being reflected in higher qE:q9-AA ratios under oxidised conditions. A simple model is presented to explain these observations.
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