Sodium-Driven Potassium Uptake by the Plant Potassium Transporter HKT1 and Mutations Conferring Salt Tolerance

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Science  08 Dec 1995:
Vol. 270, Issue 5242, pp. 1660-1663
DOI: 10.1126/science.270.5242.1660


Sodium (Na+) at high millimolar concentrations in soils is toxic to most higher plants and severely reduces agricultural production worldwide. However, the molecular mechanisms for plant Na+ uptake remain unknown. Here, the wheat root high-affinity potassium (K+) uptake transporter HKT1 was shown to function as a high-affinity K+-Na+ cotransporter. High-affinity K+ uptake was activated by micromolar Na+ concentrations; moreover, high-affinity Na+ uptake was activated by K+ (half-activation constant, 2.8 μM K+). However, at physiologically detrimental concentrations of Na+, K+ accumulation mediated by HKT1 was blocked and low-affinity Na+ uptake occurred (Michaelis constant, ∼16 mM Na+), which correlated to Na+ toxicity in plants. Point mutations in the sixth putative transmembrane domain of HKT1 that increase Na+ tolerance were isolated with the use of yeast as a screening system. Na+ uptake and Na+ inhibition of K+ accumulation indicate a possible role for HKT1 in physiological Na+ toxicity in plants.