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JXB Advance Access published online on June 18, 2008
Journal of Experimental Botany, doi:10.1093/jxb/ern139
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© 2008 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

RESEARCH PAPER

Non-reciprocal interactions between K+ and Na+ ions in barley (Hordeum vulgare L.)

Herbert J. Kronzucker*, Mark W. Szczerba, Lasse M. Schulze and Dev T. Britto

Department of Biological Sciences, University of Toronto, 1265 Military Trail, Ontario, Canada M1C 1A4

* To whom correspondence should be addressed. E-mail: herbertk{at}utsc.utoronto.ca

The interaction of sodium and potassium ions in the context of the primary entry of Na+ into plant cells, and the subsequent development of sodium toxicity, has been the subject of much recent attention. In the present study, the technique of compartmental analysis with the radiotracers 42K+ and 24Na+ was applied in intact seedlings of barley (Hordeum vulgare L.) to test the hypothesis that elevated levels of K+ in the growth medium will reduce both rapid, futile Na+ cycling at the plasma membrane, and Na+ build-up in the cytosol of root cells, under saline conditions (100 mM NaCl). We reject this hypothesis, showing that, over a wide (400-fold) range of K+ supply, K+ neither reduces the primary fluxes of Na+ at the root plasma membrane nor suppresses Na+ accumulation in the cytosol. By contrast, 100 mM NaCl suppressed the cytosolic K+ pool by 47–73%, and also substantially decreased low-affinity K+ transport across the plasma membrane. We confirm that the cytosolic [K+]:[Na+] ratio is a poor predictor of growth performance under saline conditions, while a good correlation is seen between growth and the tissue ratios of the two ions. The data provide insight into the mechanisms that mediate the toxic influx of sodium across the root plasma membrane under salinity stress, demonstrating that, in the glycophyte barley, K+ and Na+ are unlikely to share a common low-affinity pathway for entry into the plant cell.

Key words: Barley, compartmental analysis, cytosol, influx, efflux, potassium, radiotracers, salinity, salt stress, sodium

Received 5 February 2008; Revised 18 April 2008 Accepted 22 April 2008


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