[Light-induced generation of membrane potential in intact chloroplasts suspended in H2O or D2O media]

The membrane potential changes induced by short flashes and continuous light were investigated in isolated chloroplasts of Peperomia metallica suspended in H2O- or D2O media. The potential generated in H2O-suspended chloroplasts by a single turnover flash is approximately two times lower than the maximal level of potential induced by continuous light. The photoelectric response of D2O-suspended chloroplasts differs from that of H2O-suspended chloroplasts by an increased amplitude and a prolonged phase of the potential rise. Te dark decay of the potential proceeds 2-3 times slower in the D2O-suspended chloroplasts as compared to the H2O-suspended chloroplasts. The magnitude of the flash-induced potential is somewhat lower for the chloroplasts in D2O than for the chloroplasts in the H2O medium. The results obtained suggest that the substitution of H2O for D2O results in a decrease of the ionic conductance and an increase of stability of thylakoid membranes. It was shown that the rise of electrical potential under continuous illumination proceeds in two stages. The difference kinetics of membrane potential changes are observed under conditions of separate activity of two systems of photosynthesis.