Characteristics of light-induced H+ transport in spinach chloroplast at lower temperatures I. Relationship between H+ transport and physical changes of the microenvironment in chloroplast membranes

Light-induced H⁺ transport of spinach chloroplasts was investigatedin the temperature range from 5° to 30°C with a glasselectrode. The rate of H⁺ transport was reduced by lowering the temperature.Addition of 1 µM phenazine methosulfate (PMS) considerablystimulated the H⁺ uptake in chloroplasts. PMS was also effectivein stimulating the H⁺ efflux when the illumination was turnedoff. The latter effect became more marked at lower temperatures.These results indicate that electron transfer reactions in thechloroplast not only drive the forward process of H⁺ gradientformation, but also participate in the backward H⁺ efflux. The Arrhenius plot applied to the first-order rate constantof the H⁺ efflux showed a discontinuity at about 20°C. Nohysteresis was detected with the temperature dependence andits discontinuity in the H⁺ transport. On the other hand, theaddition of PMS abolished the discontinuity and a linear relationshipwas observed in the Arrhenius plot. Probably, temperature-dependentphysical changes in the microenvironment of the chloroplastlamellae are responsible for determining the characteristicsof the H⁺transport. (Received September 11, 1975; )