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Plant and Cell Physiology, 1984, Vol. 25, No. 7 1115-1122
© 1984

Article

Respiration-Dependent H+ Efflux from Intact Cells of Cyanidium caldarium1

Mariko Kura-Hotta2 and Isao Enami

Department of Biology, Faculty of Science, Science University of Tokyo Kagurazaka, Shinjuku-ku, Tokyo 162, Japan
2Department of Pure and Applied Sciences, College of Arts and Sciences, University of Tokyo Present address: Komaba, Meguro-ku, Tokyo 153, Japan

An active H+ efflux depending on respiration was found in an acidophilic unicellular alga, Cyanidium caldarium. Alkalization of the medium due to passive H+ transport into the cells was observed when the respiratory activity was inhibited by adding respiratory poisons, such as rotenone or antimycin A, or by introducing pure nitrogen into the cell suspension. The extent of the H+ influx increased as the pH of the medium was lowered to 2.9, indicating that H+ leaks into the cells according to the pH gradient across the plasma membrane. The medium pH which had increased under anaerobic condition returned to the original level with aeration of the cell suspension. This suggests that an active H+ transport, related to respiration, pumps out the excess H+ accumulated in the cells during anaerobic preincubation. The pH changes in the cell suspension were related to the intracellular ATP level. From these results it was concluded that active H+ efflux dependent upon oxidative phosphorylation functions in the dark to maintain a constant intracellular pH against passive H+ leakage through the plasma membrane.

The light-induced H+ efflux and the respiration-dependent H+ efflux were also compared in relation to the physiological role of the active H+ efflux, especially with respect to the intracellular pH regulation in this alga.

1The data in this paper are included in the Ph. D. dissertation submitted by M. Kura-Hotta to Tokyo Metropolitan University.

(Received February 3, 1984; Accepted June 14, 1984)
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