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JXB Advance Access originally published online on July 24, 2008
Journal of Experimental Botany 2008 59(12):3415-3423; doi:10.1093/jxb/ern190
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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

NH4+-stimulated and -inhibited components of K+ transport in rice (Oryza sativa L.)

Mark W. Szczerba *, Dev T. Britto, Shabana A. Ali, Konstantine D. Balkos and Herbert J. Kronzucker{dagger}

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

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

The disruption of K+ transport and accumulation is symptomatic of NH4+ toxicity in plants. In this study, the influence of K+ supply (0.02–40 mM) and nitrogen source (10 mM NH4+ or NO3–) on root plasma membrane K+ fluxes and cytosolic K+ pools, plant growth, and whole-plant K+ distribution in the NH4+-tolerant plant species rice (Oryza sativa L.) was examined. Using the radiotracer 42K+, tissue mineral analysis, and growth data, it is shown that rice is affected by NH4+ toxicity under high-affinity K+ transport conditions. Substantial recovery of growth was seen as [K+]ext was increased from 0.02 mM to 0.1 mM, and, at 1.5 mM, growth was superior on NH4+. Growth recovery at these concentrations was accompanied by greater influx of K+ into root cells, translocation of K+ to the shoot, and tissue K+. Elevating the K+ supply also resulted in a significant reduction of NH4+ influx, as measured by 13N radiotracing. In the low-affinity K+ transport range, NH4+ stimulated K+ influx relative to NO3– controls. It is concluded that rice, despite its well-known tolerance to NH4+, nevertheless displays considerable growth suppression and disruption of K+ homeostasis under this N regime at low [K+]ext, but displays efficient recovery from NH4+ inhibition, and indeed a stimulation of K+ acquisition, when [K+]ext is increased in the presence of NH4+.

Key words: Ammonium toxicity, influx, ion transport, potassium, rice, translocation

* Present address: Department of Plant Sciences, University of California, Davis, Davis, CA, USA

Received 6 May 2008; Revised 18 June 2008 Accepted 26 June 2008


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