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AOBPreview published online on December 22, 2005
Annals of Botany, doi:10.1093/aob/mcj605
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© The Author 2005. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
Received August 8, 2005
Revised September 28, 2005
Accepted November 15, 2005

IBC Root Highlight: Article

Influence of Inorganic Nitrogen and pH on the Elongation of Maize Seminal Roots

ARNOLD J. BLOOM 1 *, JÜRGEN FRENSCH 2, and ALISON R. TAYLOR 3

1 Department of Plant Sciences, University of California, Davis, CA 95616, USA
2 Cyberonics Europe S.A./N.V., Belgicastraat 9, 1930 Zaventem, Belgium
3 Marine Biological Association, The Laboratory, Citadel Hill, Plymouth PL1 2PB, UK

* To whom correspondence should be addressed.
ARNOLD J. BLOOM, E-mail: ajbloom{at}ucdavis.edu


  Abstract

• Background and Aims Root absorption and assimilation of inorganic nitrogen usually alters rhizosphere pH, but the immediate influence of such pH changes on root elongation as well as that of exogenous inorganic nitrogen itself has been uncertain.

• Methods A differential extensiometer that monitored on a real-time, continuous basis root elongation in an intact 3-d-old maize plant was developed. Treatments included root media at pH 6·5 or 5·6 that lacked nitrogen and ones at pH 6·5 that contained 100 mmol m-3 NH4+ or NO3-.

• Key Results Acidifying the root medium from pH 6·5 to 5·6 nearly doubled the elasticity of the seminal root, but slightly decreased its elongation. Plasticity of the root apex was not detectable in all treatments. The presence of ammonium or nitrate in the medium stimulated elongation by 29 % or 14 %, respectively. Addition of an osmoticum to the medium had no effect on root elongation in the absence of inorganic nitrogen, but diminished the stimulation of elongation in the presence of ammonium and nitrate. This indicates that these ions or their by-products serve partially as osmolytes.

• Conclusions In nutrient solution, root elongation of a maize seedling--even one with ample nitrogen reserves--depended most strongly on exogenous inorganic nitrogen, and less so, if at all, on either the pH of the bulk nutrient solution or the mechanical properties of cell walls.

Keywords: Nitrate, ammonium, rhizosphere pH, Zea mays, acid growth, cell wall elasticity, root growth, nutrient solution, turgor pressure, osmotic potential.
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T. L. Rost and A. J. Bloom
Preface.
Ann. Bot., May 1, 2006; 97(5): 837 - 838.
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