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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
Authors/Creators:	Babourina, O and Voltchanskii, K and McGann, B and Newman, IA and Rengel, Z
Journal or Publication Title:	Journal of Experimental Botany
Publisher:	Oxford University Press
ISSN:	0022-0957
DOI / ID Number:	10.1093/jxb/erl238
Additional Information:	The definitive publisher-authenticated version http://www.oxfordjournals.org/ Copyright © 2007 Oxford University Press
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