Present address: Department of Biology, 111 Koshland Hall, University of California, Berkeley, Berkeley, CA 94720-3102, USA.
Alkali cation selectivity of the wheat root high-affinity potassium transporter HKT1
Article first published online: 5 MAR 2002
The Plant Journal
Volume 10, Issue 5, pages 869–882, November 1996
How to Cite
Gassmann, W., Rubio, F. and Schroeder, J. I. (1996), Alkali cation selectivity of the wheat root high-affinity potassium transporter HKT1. The Plant Journal, 10: 869–882. doi: 10.1046/j.1365-313X.1996.10050869.x
- Issue published online: 5 MAR 2002
- Article first published online: 5 MAR 2002
- Received 7 May 1996; revised 26 July 1996; accepted 20 August 1996.
- Cited By
The wheat root high-affinity K+ transporter HKT1 functions as a sodium-coupled potassium co-uptake transporter. At toxic millimolar levels of sodium (Na+), HKT1 mediates low-affinity Na+ uptake while potassium (K+) uptake is blocked. In roots, low-affinity Na+ uptake and inhibition of K+ uptake contribute to Na+ toxicity. In the present study, the selectivity among alkali cations of HKT1 expressed in Xenopus oocytes and yeast was investigated under various ionic conditions at steady state. The data show that HKT1 is highly selective for uptake of the two physiologically significant alkali cations, K+ and Na+ over Rb+, Cs+ and Li+. In addition, Rb+ and Cs+, and an excess of extracellular K+ over Na+, are shown to partially reduce or block HKT1-mediated K+-Na+ uptake. Furthermore, K+, Rb+ and Cs+ also effectively reduce outward currents mediated by HKT1, thereby causing depolarizations. In yeast, HKT1 can produce high-affinity Rb+ uptake at approximately 15-fold lower rates than for K+. Rb+ influx in yeast can be mediated by the ability of the yeast plasma membrane proton pump to balance the 35-fold lower HKT1 conductance for Rb+. A model for HKT1 activity is presented involving a high-affinity K+ binding site and a high-affinity Na+ binding site, and competitive interactions of K+, Na+ and other alkali cations for binding to these two sites. Possible implications of the presented results for physiological K+ and Na+ uptake in plants are discussed.