植物細胞における膜電位の発生機構と制御

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Department of Botany, Faculty of Science, University of Tokyo, Hongo, Tokyo 113To study the electrogenic mechanism of the plant plasma membrane, intracellular chemical composition of Chara australis, a Characeae, was modified by the intracellular perfusion. It was suggested that the H+-extruding pump which is fueled by Mg·EATP is operating in the electrogenesis. Activity of the H+-pump was maximum at pHo 5.4-8.4 and at pHi 7. Light activates H+-pump and hyperpolarizes the membrane (light-induced potential change; LPC). Since LPC was not elicited in chloroplast-free Spirogyra cell which was prepared by cell-centrifugation, involvement of photosynthesis in LPC was concluded. Importance of electron transport in photosynthesis was suggested. There is another mechanism of electrogenesis in Chara cells. When internal ATP or Mg2+ concentration was lowared greatly, the plasma membrane depolarized. When such a cell was stained with neutral red, a rapid light-induced potential change (rLPC) was observed. On illumination the membrane potential approached K+-equilibrium potential across th e plasma membrane and K+-channel inhibitors suppressed rLPC, evidence that rLPC is caused by activation of K+-channel. When the cell was made chloroplast-free by the centrifugation, rLPC was removed, and it was recovered by introducing spinach chloroplasts into the chloroplast-free Chara cell. Involvement of electron transport in rLPC was also suggested.
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植物細胞における膜電位の発生機構と制御

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