Competition between uptake of ammonium and potassium in barley and Arabidopsis roots: molecular mechanisms and physiological consequences

• Published in: Journal of experimental botany Vol. 61; no. 9; pp. 2303 - 2315
• Main Authors: Hoopen, Floor ten, Cuin, Tracey Ann, Pedas, Pai, Hegelund, Josefine N, Shabala, Sergey, Schjoerring, Jan K, Jahn, Thomas P
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 01.05.2010
• Subjects: Ammonium toxicity; Arabidopsis; Arabidopsis - genetics; Arabidopsis - metabolism; Barley; Biological and medical sciences; Biological Transport; Cation Transport Proteins; Cation Transport Proteins - genetics; Cation Transport Proteins - metabolism; cations; cDNA libraries; Cell membranes; clones; competition; complementary DNA; Fundamental and applied biological sciences. Psychology; gadolinium; Gene Expression Regulation, Plant; genetics; Hordeum; Hordeum - genetics; Hordeum - metabolism; Hordeum vulgare; metabolism; mutants; Nitrogen; Plant physiology; Plant Proteins; Plant Proteins - genetics; Plant Proteins - metabolism; Plant Roots; Plant Roots - genetics; Plant Roots - metabolism; Plants; Potassium; Potassium - metabolism; potassium nutrition; Quaternary Ammonium Compounds; Quaternary Ammonium Compounds - metabolism; RESEARCH PAPER; Research Papers; root growth; roots; Seedlings; tetraethyl ammonium; toxicity; transporters; Yeasts; Competition; Monocotyledones; Ammonium; Toxicity; Cereal crop; tetraethyl ammonium; potassium nutrition; Arabidopsis thaliana; Absorption; Cruciferae; Gramineae; Dicotyledones; Angiospermae; Botany; Physiology; Molecular process; Barley; Hordeum vulgare; Nutrition; Root; Arabidopsis; Spermatophyta; Ammonium toxicity; Experimental plant; Potassium; gadolinium
• ISSN: 0022-0957; 1460-2431; 1460-2431
• DOI: 10.1093/jxb/erq057

Plants can use ammonium (NH[Formula: see text]) as the sole nitrogen source, but at high NH[Formula: see text] concentrations in the root medium, particularly in combination with a low availability of K⁺, plants suffer from NH[Formula: see text] toxicity. To understand the role of K⁺ transporters and non-selective cation channels in K⁺/NH[Formula: see text] interactions better, growth, NH[Formula: see text] and K⁺ accumulation and the specific fluxes of NH[Formula: see text], K⁺, and H⁺ were examined in roots of barley (Hordeum vulgare L.) and Arabidopsis seedlings. Net fluxes of K⁺ and NH[Formula: see text] were negatively correlated, as were their tissue concentrations, suggesting that there is direct competition during uptake. Pharmacological treatments with the K⁺ transport inhibitors tetraethyl ammonium (TEA⁺) and gadolinium (Gd³⁺) reduced NH[Formula: see text] influx, and the addition of TEA⁺ alleviated the NH[Formula: see text]-induced depression of root growth in germinating Arabidopsis plants. Screening of a barley root cDNA library in a yeast mutant lacking all NH[Formula: see text] and K⁺ uptake proteins through the deletion of MEP1-3 and TRK1 and TRK2 resulted in the cloning of the barley K⁺ transporter HvHKT2;1. Further analysis in yeast suggested that HvHKT2;1, AtAKT1, and AtHAK5 transported NH[Formula: see text], and that K⁺ supplied at increasing concentrations competed with this NH[Formula: see text] transport. On the other hand, uptake of K⁺ by AtHAK5, and to a lesser extent via HvHKT2;1 and AtAKT1, was inhibited by increasing concentrations of NH[Formula: see text]. Together, the results of this study show that plant K⁺ transporters and channels are able to transport NH[Formula: see text]. Unregulated NH[Formula: see text] uptake via these transporters may contribute to NH[Formula: see text] toxicity at low K⁺ levels, and may explain the alleviation of NH[Formula: see text] toxicity by K⁺.