Skip Navigation


JXB Advance Access originally published online on January 17, 2008
Journal of Experimental Botany 2008 59(2):303-313; doi:10.1093/jxb/erm309
This Article
Right arrow Full Text Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrowOA All Versions of this Article:
59/2/303    most recent
erm309v1
Right arrow E-letters: Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when E-letters are posted
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrow Disclaimer
Google Scholar
Right arrow Articles by Szczerba, M. W.
Right arrow Articles by Kronzucker, H. J.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Szczerba, M. W.
Right arrow Articles by Kronzucker, H. J.
Agricola
Right arrow Articles by Szczerba, M. W.
Right arrow Articles by Kronzucker, H. J.
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?

© 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

Alleviation of rapid, futile ammonium cycling at the plasma membrane by potassium reveals K+-sensitive and -insensitive components of NH4+ transport

Mark W. Szczerba, Dev T. Britto, Konstantine D. Balkos and Herbert J. Kronzucker*

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

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

Futile plasma membrane cycling of ammonium (NH4+) is characteristic of low-affinity NH4+ transport, and has been proposed to be a critical factor in NH4+ toxicity. Using unidirectional flux analysis with the positron-emitting tracer 13N in intact seedlings of barley (Hordeum vulgare L.), it is shown that rapid, futile NH4+ cycling is alleviated by elevated K+ supply, and that low-affinity NH4+ transport is mediated by a K+-sensitive component, and by a second component that is independent of K+. At low external [K+] (0.1 mM), NH4+ influx (at an external [NH4+] of 10 mM) of 92 µmol g–1 h–1 was observed, with an efflux:influx ratio of 0.75, indicative of rapid, futile NH4+ cycling. Elevating K+ supply into the low-affinity K+ transport range (1.5–40 mM) reduced both influx and efflux of NH4+ by as much as 75%, and substantially reduced the efflux:influx ratio. The reduction of NH4+ fluxes was achieved rapidly upon exposure to elevated K+, within 1 min for influx and within 5 min for efflux. The channel inhibitor La3+ decreased high-capacity NH4+ influx only at low K+ concentrations, suggesting that the K+-sensitive component of NH4+ influx may be mediated by non-selective cation channels. Using respiratory measurements and current models of ion flux energetics, the energy cost of concomitant NH4+ and K+ transport at the root plasma membrane, and its consequences for plant growth are discussed. The study presents the first demonstration of the parallel operation of K+-sensitive and -insensitive NH4+ flux mechanisms in plants.

Key words: Ammonium, barley, efflux, influx, nitrogen-13, non-selective cation channels, potassium

Received 8 August 2007; Revised 8 November 2007 Accepted 12 November 2007


Add to CiteULike CiteULike   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us    What's this?


This article has been cited by other articles:


Home page
 J Exp BotHome page
M. W. Szczerba, D. T. Britto, S. A. Ali, K. D. Balkos, and H. J. Kronzucker
NH4+-stimulated and -inhibited components of K+ transport in rice (Oryza sativa L.)
J. Exp. Bot., September 1, 2008; 59(12): 3415 - 3423.
[Abstract] [Full Text] [PDF]


Disclaimer:
Please note that abstracts for content published before 1996 were created through digital scanning and may therefore not exactly replicate the text of the original print issues. All efforts have been made to ensure accuracy, but the Publisher will not be held responsible for any remaining inaccuracies. If you require any further clarification, please contact our Customer Services Department.