Enhancement of Na⁺ Uptake Currents, Time-Dependent Inward-Rectifying K⁺ Channel Currents, and K⁺ Channel Transcripts by K⁺ Starvation in Wheat Root Cells

• Published in: Plant physiology (Bethesda) Vol. 122; no. 4; pp. 1387 - 1397
• Main Authors: Peter H. Buschmann, Rama Vaidyanathan, Gassmann, Walter, Schroeder, Julian I.
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Physiologists 01.04.2000; American Society of Plant Biologists
• Subjects: Absorption. Translocation of ions and substances. Permeability; Agronomy. Soil science and plant productions; Amino Acid Sequence; Arabidopsis Proteins; Base Sequence; Biological and medical sciences; Cell membranes; Cell physiology; Cloning, Molecular; Complementary DNA; DNA Primers; Economic plant physiology; Environmental and Stress Physiology; Fundamental and applied biological sciences. Psychology; Molecular Sequence Data; Nutrition. Photosynthesis. Respiration. Metabolism; Pipettes; Plant cells; Plant physiology and development; Plant Proteins - genetics; Plant Proteins - metabolism; Plant roots; Plant Roots - cytology; Plant Roots - metabolism; Plants; Plasma membrane and permeation; Polymerase chain reaction; Potassium; Potassium - metabolism; Potassium Channels - genetics; Potassium Channels - metabolism; Protoplasts; RNA, Messenger - genetics; RNA, Messenger - metabolism; Roots; Seedlings; Sodium - metabolism; Starvation; Triticum - genetics; Triticum - metabolism; Up-Regulation; Wheat; Monocotyledones; Starvation; Salt resistance; Cell permeability; Root; Electrophysiology; Ionic channel; Salinity; Absorption; Sodium; Gramineae; Angiospermae; Plasma membrane; Spermatophyta; Experimental plant; Potassium; Triticum aestivum
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.122.4.1387

Excessive low-affinity Na+ uptake is toxic to the growth of glycophytic plants. Recently, several reports have suggested that the interaction between K+ and Na+ uptake might represent a key factor in determining the Na+ tolerance of plants. We investigated the effects of K+ starvation on Na+ and K+ uptake mechanisms in the plasma membrane of wheat (Triticum aestivum L.) root cortex cells using the patch-clamp technique. Unexpectedly, K+ starvation of wheat seedlings was found to enhance the magnitude and frequency of occurrence of time-dependent inward-rectifying K+ channel currents ($\text{I}_{\text{K}}{}^{+}{}_{\text{in}}$). We examined whether the transcription of a wheat root $\text{K}^{+}{}_{\text{in}}$ channel gene is induced by K+ starvation. A cDNA coding for a wheat root K+ channel homolog, TaAKT1 (accession no. AF207745), was isolated. TaAKT1 mRNA levels were up-regulated in roots in response to withdrawal of K+ from the growth medium. Furthermore, K+ starvation caused an enhancement of instantaneous Na+ currents ($\text{I}_{\text{Na}}{}^{+}$). Electrophysiological analyses suggested that $\text{I}_{\text{K}}{}^{+}{}_{\text{in}}$ and $\text{I}_{\text{Na}}{}^{+}$ are not mediated by the same transport protein based on: (a) different activation curves, (b) different time dependencies, (c) different sensitivities to external Ca2+, and (d) different cation selectivities. These data implicate a role for $\text{I}_{\text{Na}}{}^{+}$ in Na+ uptake and stress during K+ starvation, and indicate that $\text{K}^{+}{}_{\text{in}}$ channels may contribute to K+-starvation-induced K+ uptake in wheat roots.