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Letters to Nature
Nature 312, 361 - 362 (22 November 1984); doi:10.1038/312361a0

Potassium-selective single channels in guard cell protoplasts of Vicia faba

J. I. Schroeder*, R. Hedrich & J. M. Fernandez*

*Department of Membrane Biophysics, Max–Planck-Institut für biophysikalische Chemie, D-3400 Göttingen, FRG
Pflanzenphysiologisches Institut, Universität Göttingen, D-3400 Göttingen, FRG

In plants, stomata control the gaseous exchange between the intercellular spaces of the leaf and the atmosphere. Fluxes of ions, in particular potassium fluxes, across the membranes of the guard cells produce changes in turgor of the guard cells which in turn result in the opening and closing of the stomatal pore1,2. The molecular mechanisms involved in the uptake or release of ions in guard cells are poorly understood2. Cell-free membrane patches of the plasmalemma, isolated following patch-clamp techniques3–5, allow, for the first time in higher plant cells, the separation of the electrical properties of the plasmalemma from those of the tonoplast. We have applied these techniques to study the properties of single-ion channels in the plasmalemma of guard cell protoplasts of Vicia faba (broad bean). Predominantly a cation-selective channel was observed, which showed a high selectivity for K+, with a permeability ratio P K+/P Na+ of 11:1 and a single-channel conductance of 37 pS(=37 × 10;−12 −1) in symmetrical 225 mM KC1 solutions. We estimate that this K+ channel contributes significantly to the uptake and release of K+ by guard cells during stomatal movement.

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