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Plant and Cell Physiology, 1985, Vol. 26, No. 2 351-359
© 1985

Article

Homeostatic Regulation of Membrane Potential by an Electrogenic Ion Pump against Change in the K+ Concentration of the Extra- and Intra-Organ Perfusion Solutions

Hiroshi Kojima, Kiyoshi Katou and Hisashi Okamoto

Laboratory of Plant Physiology, Biological Institute, Faculty of Science, Nagoya University Furo-cho, Chikusa-ku, Nagoya 464, Japan

The dependence of membrane potentials on changes in the extra-cellular K+ concentration [K+]e was investigated in potato tuber slices with dripping perfusion, and in growing Vigna hypocotyl segments with pressurized intra-organ perfusion methods. Only under anoxia were the membrane potential of potato tuber slices and the electric potential difference between the parenchyma symplast and xylem (Vpx) of Vigna hypocotyl segments depolarized markedly (46 mV and 42 mV/log[K+]e unit, respectively) with increasing [K+]e above the critical values. The electric potential difference between the parenchyma symplast and organ surface (Vps of the hypocotyl segments remained nearly unchanged up to 30 mEq [K+]e. Under highly aerobic conditions the membrane potentials were relatively independent of [K+]e except at very high K+ concentrations. Vps showed even hyperpolarization with the increasing KCl concentration in the perfusion solution that is not in direct contact with the surface membrane of the parenchyma symplast. The respiration-dependent electrogenic components of the membrane potentials regularly increased with the increasing [K+]e. A voltage-dependent homeostatic control of membrane potential is discussed.

(Received August 13, 1984; Accepted December 21, 1984)
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