A Weakly Voltage-Dependent, Nonselective Cation Channel Mediates Toxic Sodium Influx in Wheat

• Published in: Plant physiology (Bethesda) Vol. 122; no. 3; pp. 823 - 834
• Main Authors: Romola Jane Davenport, Tester, Mark
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Physiologists 01.03.2000
• Subjects: Absorption. Translocation of ions and substances. Permeability; Agronomy. Soil science and plant productions; Biological and medical sciences; Cations; Cations - metabolism; Cell Membrane - metabolism; Cell membranes; Cell physiology; Economic plant physiology; Electric potential; Environmental and Stress Physiology; Fundamental and applied biological sciences. Psychology; Ion Channels - metabolism; Ion Transport; Lipid Bilayers - metabolism; Membrane Potentials; Nutrition. Photosynthesis. Respiration. Metabolism; Plant physiology and development; Plant roots; Plant Roots - metabolism; Plants; Plasma membrane and permeation; Protoplasts; Rye; Sodium; Sodium - metabolism; Sodium - toxicity; Triticum - drug effects; Triticum - metabolism; Wheat; Monocotyledones; Cell permeability; Electrophysiology; Ionic channel; Cereal crop; Salinity; Phytotoxicity; Ionic selectivity; Sodium; Gramineae; Membrane transport; Angiospermae; Spermatophyta; Carrier protein; Triticum aestivum
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.122.3.823

To determine the transporters responsible for toxic Na+ influx in wheat (Triticum aestivum), root plasma membrane preparations were screened using the planar lipid bilayer technique as an assay for Na+-permeable ion channel activity. The predominant channel in the bilayer was a 44-pS channel that we called the nonselective cation (NSC) channel, which was nonselective for monovalent cations and weakly voltage dependent. Single channel characteristics of the NSC channel were compared with ^{22}\text{Na}^{+}$ influx into excised root segments. Na+ influx through the NSC channel resembled ^{22}\text{Na}^{+}$ influx in its partial sensitivity to inhibition by Ca2+, Mg2+, and Gd3+, and its insensitivity to all other inhibitors tested (tetraethylammonium, quinine, Cs+, tetrodotoxin, verapamil, amiloride, and flufenamate). Na+ influx through the NSC channel also closely resembled an instantaneous current in wheat root protoplasts (S. D. Tyerman, M. Skerrett, A. Garill, G. P. Findlay, R. Leigh [1997] J Exp Bot 48: 459-480) in its permeability sequence, selectivity for K+ over Na+ (approximately 1.25), insensitivity to tetraethylammonium, voltage independence, and partial sensitivity to Ca2+. Comparison of tissue, protoplast (S. D. Tyerman, M. Skerrett, A. Garill, G. P. Findlay, R. Leigh [1997] J Exp Bot 48: 459-480), and single-channel data indicate that toxic Na+ influx is catalyzed by a single transporter, and this is likely to be the NSC channel identified in planar lipid bilayers.