Effect of high pH on the plasma membrane potential and conductance in Elodea densa.
In leaves of Elodea densa the membrane potential measured in light equals the equilibrium potential of H+ on the morphological upper plasma membrane. The apoplastic pH on the upper side of the leaf is as high as 10.5-11.0, which indicates that alkaline pH induces an increased H+ permeability of the plasmalemma. To study this hypothesis in more detail we investigated the changes in membrane potential and conductance in response to alterations in the external pH from 7 (= control) to 9 or 11 under both light and dark conditions. Departing from the control pH 7 condition, in light and in dark the application of pH 9 resulted in a depolarization of the membrane potential to the Nernst potential of H+. In the light but not in the dark, this depolarization was followed by a repolarization to about -160 mV. The change to pH 9 induced, in light as well as in dark, an increase in membrane conductance. The application of pH 11, which caused a momentary hyper- or depolarization depending on the value at the time pH 11 was applied, brought the membrane potential to around -160 mV. The membrane conductance also increased, in comparison to its value at pH 7, as a result of the application of pH 11, irrespective of the light conditions.
Miedema
H
H
Department of Plant Biology, University of Groningen, Haren, The Netherlands.
Felle
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Prins
H B
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D002021:Buffers; D002462:Cell Membrane / Q000502:physiology*; D003624:Darkness; D004553:Electric Conductivity; D006863:Hydrogen-Ion Concentration; D008029:Lighting; D008564:Membrane Potentials; D018521:Plant Physiological Phenomena; D010944:Plants / Q000648:ultrastructure; D011188:Potassium / Q000502:physiology; D012996:Solutions
D002021:Buffers; D012996:Solutions; D011188:Potassium