http://eprints.utas.edu.au/3878/ Nitrate supply affects ammonium transport in canola roots Babourina, O Voltchanskii, K McGann, B Newman, IA Rengel, Z 249901 Biophysics 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. Oxford University Press 2007 Article PeerReviewed application/pdf http://eprints.utas.edu.au/3878/1/3878.pdf http://dx.doi.org/10.1093/jxb/erl238 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 http://eprints.utas.edu.au/3878/http://eprints.utas.edu.au/3878/1/