%A O Babourina
%A K Voltchanskii
%A B McGann
%A IA Newman
%A Z Rengel
%O The definitive publisher-authenticated version  http://www.oxfordjournals.org/

Copyright ? 2007 Oxford University Press

%J Journal of Experimental Botany
%T Nitrate supply affects ammonium transport in canola roots
%X 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.
%N 3
%P 651-658
%V 58
%D 2007
%I Oxford University Press
%R 10.1093/jxb/erl238
%L epprod3878