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Gassmann W, Schroeder JI. Inward-Rectifying K+ Channels in Root Hairs of Wheat (A Mechanism for Aluminum-Sensitive Low-Affinity K+ Uptake and Membrane Potential Control). Plant Physiol. 1994;105(4):1399-1408doi: 10.1104/pp.105.4.1399.
Gassmann, W., & Schroeder, J. I. (1994). Inward-Rectifying K+ Channels in Root Hairs of Wheat (A Mechanism for Aluminum-Sensitive Low-Affinity K+ Uptake and Membrane Potential Control). Plant physiology, 105(4), 1399-1408. https://doi.org/10.1104/pp.105.4.1399
Gassmann, W., and Schroeder, J. I.. "Inward-Rectifying K+ Channels in Root Hairs of Wheat (A Mechanism for Aluminum-Sensitive Low-Affinity K+ Uptake and Membrane Potential Control)." Plant physiology vol. 105,4 (1994): 1399-1408. doi: https://doi.org/10.1104/pp.105.4.1399
Gassmann W, Schroeder JI. Inward-Rectifying K+ Channels in Root Hairs of Wheat (A Mechanism for Aluminum-Sensitive Low-Affinity K+ Uptake and Membrane Potential Control). Plant Physiol. 1994 Aug;105(4):1399-1408. doi: 10.1104/pp.105.4.1399. PMID: 12232295; PMCID: PMC159473.
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Plant Physiol. 1994 Aug;105(4):1399-1408. doi: 10.1104/pp.105.4.1399.

Inward-Rectifying K+ Channels in Root Hairs of Wheat (A Mechanism for Aluminum-Sensitive Low-Affinity K+ Uptake and Membrane Potential Control).

Plant physiology

W. Gassmann, J. I. Schroeder

Affiliations

  1. Department of Biology and Center for Molecular Genetics, University of California, San Diego, La Jolla, California 92093-0116.

PMID: 12232295 PMCID: PMC159473 DOI: 10.1104/pp.105.4.1399

Abstract

K+ is the most abundant cation in cells of higher plants, and it plays vital roles in plant growth and development. Extensive studies on the kinetics of K+ uptake in roots have shown that K+ uptake is mediated by at least two transport mechanisms, one with a high and one with a low affinity for K+. However, the precise molecular mechanisms of K+ uptake from soils into root epidermal cells remain unknown. In the present study we have pursued the biophysical identification and characterization of mechanisms of K+ uptake into single root hairs of wheat (Triticum aestivum L.), since root hairs constitute an important site of nutrient uptake from the soil. These patch-clamp studies showed activation of a large inward current carried by K+ ions into root hairs at membrane potentials more negative than -75 mV. This K+ influx current was mediated by hyperpolarization-activated K+-selective ion channels, with a selectivity sequence for monovalent cations of K+ > Rb+ [almost equal to] NH4+ >> Na+ [almost equal to] Li+ > Cs+. Kinetic analysis of K+ channel currents yielded an apparent K+ equilibrium dissociation constant (Km) of [almost equal to]8.8 mM, which closely correlates to the major component of low-affinity K+ uptake. These channels did not inactivate during prolonged stimulation and would thus enable long-term K+ uptake driven by the plasma membrane proton-extruding pump. Aluminum, which is known to inhibit cation uptake at the root epidermis, blocked these inward-rectifying K+ channels with half-maximal current inhibition at [almost equal to]8 [mu]M free Al3+. Aluminum block of K+ channels at these Al3+ concentrations correlates closely to Al3+ phytotoxicity. It is concluded that inward-rectifying K+ channels in root hairs can function as both a physiologically important mechanism for low-affinity K+ uptake and as regulators of membrane potential. The identification of this mechanism is a major step toward a detailed molecular characterization of the multiple components involved in K+ uptake, transport, and membrane potential control in root epidermal cells.

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