3878 11 archive 337 disk0/00/00/38/78 2008-04-07 14:10:56 2008-08-08 02:31:20 2008-07-16 17:02:31 article show Ian.Newman@utas.edu.au Babourina O Voltchanskii K McGann B Newman IA Ian.Newman@utas.edu.au Rengel Z pub 029901 249901 970102 780102 restricted The definitive publisher-authenticated version http://www.oxfordjournals.org/ Copyright © 2007 Oxford University Press category => A1 categoryDesc => Refereed Article in a Scholarly Journal eprintID => 0 field1 => Journal of Experimental Botany field10 => field11 => field12 => field13 => field2 => "Oxford, England" field3 => 58 field4 => 3 field5 => 651-658 field6 => Oxford University Press field7 => 0022-0957 field8 => field9 => funding => Q grant => lastUpdate => 25/07/2007 rfcd => 249901 seo => 780102 themeArea => title => Nitrate supply affects ammonium transport in canola roots tor => SB uid => 45563 update => no 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. 2007 published Journal of Experimental Botany 58 3 Oxford University Press 651-658 10.1093/jxb/erl238 TRUE 0022-0957 http://dx.doi.org/10.1093/jxb/erl238 6199 3 3878 1 application/pdf en staffonly

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