【植物钾离子通道】Devrim Coskun Dev T. Britto Mingyuan Li Saehong Oh and Herbert J. Kronzucker. Capacity and Plasticity of Potassium Channels and High-Affinity Transporters in Roots of Barley and Arabidopsis. Plant Physiology May 2013 vol. 162 no. 1 496-511

Abstract

The role of potassium (K⁺) transporters in high- and low-affinity K⁺ uptake was examined in roots of intact barley (Hordeum vulgare) and Arabidopsis (Arabidopsis thaliana) plants by use of ⁴²K radiotracing electrophysiology pharmacology and mutant analysis. Comparisons were made between results from barley and five genotypes of Arabidopsis including single and double knockout mutants for the high-affinity transporter AtHAK5 and the Shaker-type channel AtAKT1. In Arabidopsis steady-state K⁺ influx at low external K⁺ concentration ([K⁺]_ext = 22.5 µm) was predominantly mediated by AtAKT1 when high-affinity transport was inhibited by ammonium whereas in barley by contrast K⁺ channels could not operate below 100 µm. Withdrawal of ammonium resulted in an immediate and dramatic stimulation of K⁺ influx in barley indicating a shift from active to passive K⁺ uptake at low [K⁺]_ext and yielding fluxes as high as 36 µmol g (root fresh weight)⁻¹ h⁻¹ at 5 mm [K⁺]_ext among the highest transporter-mediated K⁺ fluxes hitherto reported. This ammonium-withdrawal effect was also established in all Arabidopsis lines (the wild types atakt1 athak5 and athak5 atakt1) at low [K⁺]_ext revealing the concerted involvement of several transport systems. The ammonium-withdrawal effect coincided with a suppressio