Light-induced Changes of the Electrical Potential in Chloroplasts Associated with the Activity of Photosystem I and Photosystem II

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Abstract
The electric potential changes induced by flashing and continuous light were measured with microcapillary electrodes in isolated whole chloroplasts of Peperomia inetallica. In continuous light the chloroplast electrical potential rose in two phases. The initial rapid phase coincided in extent with the flash-induced potential and was insensitive to the electron transfer inhibitor DBMIB. The subsequent phase was relatively slow (20–30 ms) and was inhibited by DBMIB. Electron acceptors of photosystem II (p-phenylendiamine, p-benzoquinone) added to DBMIB-treated chloroplasts produced a suppression of the flash-induced response and a considerable increase in the steady level of the potential in the light. The electrical potential associated with the activity of photosystem II rose in continuous light much more slowly than that associated with the activity of photosystem I alone or the activities of both photosystems. Illumination of chloroplasts with successive flashes at a repetition rate 5 Hz in the presence of oxaloacetate, a terminal acceptor of photosystem I, was accompanied with a gradual decline of the flash-induced potential. The specific role of two photosystems in the light-induced H+ transport and the electrogenesis across the chloroplast thylakoid membranes is discussed.