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

Abstract

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 pore^1,2. 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 techniques^3–5, 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 $P_{{\text{K}}^{+}}$/$P_{{\text{Na}}^{+}}$ of 11:1 and a single-channel conductance of 37 pS(=37 × 10;⁻¹² Ω⁻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.