[Photo-induced H+ transport in Nitellopsis obtusa cells]. / Fotoindutsirovannyi transport H+ v kletkakh Nitellopsis obtusa.

Light-induced changes of pH in the vacuole as well as changes of the electric potential difference across the plasmalemma and the tonoplast of Nitellopsis obtusa were measured simultaneously by means of conventional and H+-specific glass or antimony microelectrodes. Illumination is found to produce a decrease in pH of the vacuolar sap by 0.1-0.5 units concomitant with cell depolarization. Cells suspended in a medium with pH 9.0 exhibit great (up to 100 mV) light-induced potential changes but only small pH changes of the vacuolar sap. When pH of the external medium (pH0 in shifted from 9.0 to more acid values the amplitude of photoinduced changes of pH in the vacuole rises up to 0,3-0.5 pH units and the amplitude of the potential changes at the plasmalemma gets smaller. At pH0 = 9.0 a transient acidification of the medium is observed upon illumination whereas at lower pH light-induced alkalinization was only seen. Transition of the cells from pH0 9.0 to pH0 7,5 results in cell hyperpolarization by 60-80 mv and a decrease of vacuolar pH by 0.4-0.5 units under light conditions but has no significant effect on the potential and the vacuolar pH in the darkness. It is proposed that mechanisms of active H+ extrusion from the cytoplasm are located both at the plasmalemma and tonoplast. Light-induced depolarization seems to be determined by the increase of H+-conductance of the plasmalemma and by a correspondent decrease in the electrogenic components of the membrane potential. The ratio of light-induced H+-fluxes across the tonoplast and the plasmalemma depends crucially on the level of H+-conductance of the plasmalemma.

Photoinduction kinetics of electrical potential in a single chloroplast as studied with micro-electrode technique.

1. Using single chloroplasts of Peperomia metallica the kinetics of light-induced potential changes were studied. Three kinetic components (the initial fast rise, the decay in the light and the decay in the dark) were found to be characterized by time constants 4, 220 and 60 ms, respectively at light intensity 5000 1x and temperature 18 degrees C. After flash excitation the potential kept on rising for about 10 ms. Cooling of the medium down to 5 degrees C had no effect on the duration of potential rise after the flash. 2. Variations in the medium temperature in the range 2-23 degrees C had little effect on photoresponse magnitude but resulted in significant acceleration of decay in the light. 3. Addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (5-)0(-6) M) resulted in suppression of the magnitude of the photoresponse but was not accompanied by any change in the rate of initial rise of potential. 3-(3,4-Dichlorophenyl)-1,1-dimethylurea-inhibited photoresponse could be restored and even enhanced by subsequent addition of N-methylphenazonium methosulfate (10(-4) M). N-Methylphenazonium methosulfate essentially influenced the time course and light-intensity curves of photoresponse. 4. The chloroplast photoresponses were of different time-courses when elicited by red (640 nm) or far red (712 nm) light. This fact as well as an enhancement effect of combined illumination by two intermittent light beams indicate on the interaction of two photosynthetic pigment systems when the photoelectric response was formed. 5. An imposed electrical field resulted in stimulation or suppression of chloroplast photoresponse depending on the polarity of the field. No indications for the existance of "reversal potential" for photoelectric response were obtained. 6. A kinetic scheme of photoresponse formation is proposed, which includes two sequential photochemical reactions of photosynthesis.