Planta

, Volume 189, Issue 3, pp 410–419

Comparison of K+-channel activation and deactivation in guard cells from a dicotyledon (Vicia faba L.) and a graminaceous monocotyledon (Zea mays)

  • K. A. Fairley-Grenot
  • S. M. Assmann
Article

Abstract

We describe and compare inward and outward whole-cell K+ currents across the plasma membrane surrounding guard-cell protoplasts from the dicotyledon, Vicia faba, and the graminaceous monocotyledon, Zea mays. Macrosopic whole-cell current is considered in terms of microscopic single-channel activity, which involves discrete steps between conducting (open) and nonconducting (closed) states of the channel protein. Kinetic equations are used to model the number of open and closed states for channels conducting K+ influx (K(in)) and K+ efflux (K(out)) in the two species, and to calculate the rate at which open-closed transitions occur. The opening and closure of K(in) channels in both Vicia and Zea follow single-exponential timecourses, indicating that K(in)-channel proteins in each species simply fluctuate between one open and one closed state. In both species, opening of K(in) channels is voltage-independent, but closure of K(in) channels is faster at more positive membrane potentials. In response to identical voltage stimuli, K(in) channels in Zea open and close approximately three times as fast as in Vicia. In contrast to K(in), K(out) channels in Zea open and close more slowly than in Vicia. The closure of K(out) channels follows a single-exponential timecourse in each species, indicating one open state. The kinetics of K(out)-channel opening are more complicated and indicate the presence of at least two (Vicia) or three (Zea) closed states.

Key words

Guard cell Patch clamp Potassium channel (kinetics) Stomate Vicia Zea 

Abbreviations and Symbols

C, O

closed, open state of channel

EK

equilibrium potential

Iinf

current at infinite time (t)

K(in),K(out)

K+ influx, efflux

P

number of independent membranebound particles that control opening of the channel

τIA, τoa

time constant for activation of inward and outward current

τIDod

time constant for deactivation of inward and outward current

Vm

membrane potential

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Copyright information

© Springer-Verlag 1993

Authors and Affiliations

  • K. A. Fairley-Grenot
    • 1
  • S. M. Assmann
    • 1
  1. 1.Harvard Biological LaboratoriesCambridgeUSA
  2. 2.School of Biological Sciences, A12The University of SydneyAustralia

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