Demonstration of Voltage Dependency of Light-induced Potential Change in Chara |
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Authors: | Shimmen Teruo; Tazawa Masashi |
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Institution: | Department of Botany, Faculty of Science, University of Tokyo Hongo, Tokyo 113, Japan |
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Abstract: | The electromotive force (Em) of the plasma membrane of the tonoplast-freecell of Chara australis decreased when the electrogenic pumpwas stopped by removing ATP or Mg2+ from the cell. Such a cellshowed a rapid light-induced potential change (rLPC). Threefactors were considered to be responsible for the generationof rLPC; removal of Mg-ATP, stoppage of the electrogenic pumpand membrane depolarization per se. Tonoplast-free cells having enough Mg-ATP occasionally showedsmall Em (87 116 mV) due to stoppage ofthe electrogenic pump. Since the rLPC was induced in such cells,removal of Mg-ATP cannot be the factor. Cells having large Emdue to active pump activity also showed rLPC when the potentialdifference across the plasma membrane (Vm) was depolarized byan outward electric current; evidence that not the stoppageof the pump but membrane depolarization is a necessary conditionfor the generation of rLPC. In the rLPC Vm always changed in the negative direction. However,calculation of Em revealed the existence of a reversal potential (Em)rev] toward which Em converged from either more negativeor more positive values. The (Em)rev approximately coincidedwith the equilibrium potential for K+ across the plasma membrane.Intracellular anions occupying lower positions in the lyotropicseries inhibited rLPC. (Received February 9, 1981; Accepted May 16, 1981) |
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