Electro-induced changes of chlorophyll fluorescence in individual intact chloroplasts

Abstract

The intensity of chlorophyll fluorescence in isolated chloroplasts of Peperomia metallica and in situ chloroplasts of Anthoceros sp. was found to change by 5–10% on passing the electric current through the microelectrode inserted in the intrathylakoid space. The dependence of fluorescence deflections on the direction of a current flow and the absence of electro-induced fluorescence changes in chloroplasts made ion-permeable with gramicidin indicate that the emission was affected by the membrane potential created during the passage of current. A hyperpolarizing displacement of the membrane potential, positive on the inside, produced an increase in the emission in the absence of inhibitors, but has no effect on the fluorescence in chloroplasts treated with DCMU. A stimulation of a variable fluorescence by a positive membrane potential was interpreted as due to slowing down of charge separations and a respective decrease of excitation trapping in Photosystem II. A displacement of the membrane potential to the negative direction resulted in a decrease of chlorophyll fluorescence in both the absence and presence of DCMU. The fluorescence emission seems to be sensitive to variations of the membrane potential of about 100 mV or even less. Possible effects of the light-induced membrane potential on charge separations and the fluorescence emission in Photosystem II are discussed.