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

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Abstract
Light-induced H+ transport of spinach chloroplasts was investigated in the temperature range from 5° to 30°C with a glass electrode. The rate of H+ transport was reduced by lowering the temperature. Addition of 1 μM phenazine methosulfate (PMS) considerably stimulated the H+ uptake in chloroplasts. PMS was also effective in stimulating the H+ efflux when the illumination was turned off. The latter effect became more marked at lower temperatures. These results indicate that electron transfer reactions in the chloroplast not only drive the forward process of H+ gradient formation, but also participate in the backward H+ efflux. The Arrhenius plot applied to the first-order rate constant of the H+ efflux showed a discontinuity at about 20°C. No hysteresis was detected with the temperature dependence and its discontinuity in the H+ transport. On the other hand, the addition of PMS abolished the discontinuity and a linear relationship was observed in the Arrhenius plot. Probably, temperature-dependent physical changes in the microenvironment of the chloroplast lamellae are responsible for determining the characteristics of the H+transport.

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