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Updated: Jul 18, 2026

Measuring Fluxes of Mineral Nutrients and Toxicants in Plants with Radioactive Tracers
Published on: August 22, 2014
Nitrate supply affects ammonium transport in canola roots
Olga Babourina1, Konstantin Voltchanskii, Bart McGann
1School of Earth and Geographical Sciences, M087, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia. olgab@cyllene.uwa.edu.au
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 (tau1), return to uptake (tau2), and a decrease in uptake rate (tau3). The presence of NO3- in the bathing medium prevented the tau1 release and also resulted in slower activation of the tau3 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+ low-affinity influx system; and (ii) NH4+ transport is inversely linked to Ca2+ net flux.
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