Single guard cell recordings in intact plants: light-induced hyperpolarization of the plasma membrane

Authors

  • M. Rob G. Roelfsema,

    1. Julius-von-Sachs-Institut für Biowissenschaften, Lehrstuhl für Molekulare Pflanzenphysiologie und Biophysik, Universität Würzburg, Julius-von-Sachs-Platz 2, 97082 Würzburg, Germany, and
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  • Ralf Steinmeyer,

    1. Julius-von-Sachs-Institut für Biowissenschaften, Lehrstuhl für Molekulare Pflanzenphysiologie und Biophysik, Universität Würzburg, Julius-von-Sachs-Platz 2, 97082 Würzburg, Germany, and
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  • Marten Staal,

    1. Department of Plant Biology, University of Groningen, PO Box 14, 9750 AA Haren, The Netherlands
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  • Rainer Hedrich

    Corresponding author
    1. Julius-von-Sachs-Institut für Biowissenschaften, Lehrstuhl für Molekulare Pflanzenphysiologie und Biophysik, Universität Würzburg, Julius-von-Sachs-Platz 2, 97082 Würzburg, Germany, and
      For correspondence (fax +49 931 8886157; e-mail hedrich@botanik.uni-wuerzburg.de).
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For correspondence (fax +49 931 8886157; e-mail hedrich@botanik.uni-wuerzburg.de).

Summary

Guard cells are electrically isolated from other plant cells and therefore offer the unique possibility to conduct current- and voltage-clamp recordings on single cells in an intact plant. Guard cells in their natural environment were impaled with double-barreled electrodes and found to exhibit three physiological states. A minority of cells were classified as far-depolarized cells. These cells exhibited positive membrane potentials and were dominated by the activity of voltage-dependent anion channels. All other cells displayed both outward and inward rectifying K+-channel activity. These cells were either depolarized or hyperpolarized, with average membrane potentials of −41 mV (SD 16) and −112 mV (SD 19), respectively. Depolarized guard cells extrude K+ through outward rectifying channels, while K+ is taken up via inward rectifying channels in hyperpolarized cells. Upon a light/dark transition, guard cells that were hyperpolarized in the light switched to the depolarized state. The depolarization was accompanied by a 35 pA decrease in pump current and an increase in the conductance of inward rectifying channels. Both an increase in pump current and a decrease in the conductance of the inward rectifier were triggered by blue light, while red light was ineffective. From these studies we conclude that light modulates plasma membrane transport through large membrane potential changes, reversing the K+-efflux via outward rectifying channels to a K+-influx via inward rectifying channels.

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