TY - JOUR
T1 - Nitrate supply affects ammonium transport in canola roots
AU - Babourina, Olga
AU - Voltchanskii, K.
AU - Mcgann, B.
AU - Newman, I.
AU - Rengel, Zed
PY - 2007
Y1 - 2007
N2 - 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 (tau(1)), return to uptake (tau(2)), and a decrease in uptake rate (tau(3)). The presence of NO3- in the bathing medium prevented the tau(1) release and also resulted in slower activation of the tau(3) 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.
AB - 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 (tau(1)), return to uptake (tau(2)), and a decrease in uptake rate (tau(3)). The presence of NO3- in the bathing medium prevented the tau(1) release and also resulted in slower activation of the tau(3) 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.
U2 - 10.1093/jxb/erl238
DO - 10.1093/jxb/erl238
M3 - Article
C2 - 17175549
SN - 0022-0957
VL - 58
SP - 651
EP - 658
JO - Journal of Experimental Botany
JF - Journal of Experimental Botany
IS - 3
ER -