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Nitrate supply affects ammonium transport in canola roots

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Babourina, O and Voltchanskii, K and McGann, B and Newman, IA and Rengel, Z (2007) Nitrate supply affects ammonium transport in canola roots. Journal of Experimental Botany, 58 (3). pp. 651-658. ISSN 0022-0957

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Abstract

Plants may suffer from ammonium (NH4
+) toxicity when
NH4
+ is the sole nitrogen source. Nitrate (NO3
–) is known
to alleviate NH4
+ toxicity, but the mechanisms are
unknown. This study has evaluated possible mechanisms
of NO3
– alleviation of NH4
+ toxicity in canola
(Brassica napus L.). Dynamics of net fluxes of NH4
+, H+,
K+ and Ca2+ were assessed, using a non-invasive microelectrode
(MIFE) technique, in plants having different
NO3
– supplies, after single or several subsequent
increases in external NH4Cl concentration. After an
increase in external NH4Cl without NO3
–, NH4
+ net fluxes
demonstrated three distinct stages: release (t1), return
to uptake (t2), and a decrease in uptake rate (t3). The
presence of NO3
– in the bathing medium prevented
the t1 release and also resulted in slower activation of
the t3 stage. Net fluxes of Ca2+ were in the opposite
direction to NH4
+ net fluxes, regardless of NO3
– supply.
In contrast, H+ and K+ net fluxes and change in external
pH were not correlated with NH4
+ net fluxes. It is
concluded that (i) NO3
– primarily affects the NH4
+ lowaffinity
influx system; and (ii) NH4
+ transport is inversely
linked to Ca2+ net flux.

Item Type: Article
Journal or Publication Title: Journal of Experimental Botany
Publisher: Oxford University Press
Page Range: pp. 651-658
ISSN: 0022-0957
Identification Number - DOI: 10.1093/jxb/erl238
Additional Information:

The definitive publisher-authenticated version http://www.oxfordjournals.org/

Copyright © 2007 Oxford University Press

Date Deposited: 07 Apr 2008 14:10
Last Modified: 18 Nov 2014 03:33
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