Low Nitrogen Stress Stimulated Nitrate Uptake Rate Modulated by Auxin in Brassica napus L.

In order to investigate the mechanisms of auxin regulation on the stimulation of nitrate uptake rate of Brassica napus L. under low nitrogen stress. Four treatments were applied: (1) 15 M, plants grown in normal nitrogen (N) solution (NO 3 − : 15 mmol/L); (2) 1 M, plants grown in low N stress solution (NO 3 − : 1 mmol/L); (3) 15 M + IAA, the normal N supply solution contain auxin (IAA, 10 −8 mol/L); and (4) 1 M + NPA, plants grown in low N stress solution with 5 μmol/L N-1-naphthylphthalamic acid (NPA, an inhibitor of polar auxin transport) applied to the rootstocks. The contents of auxin, NO 3 − uptake rate, the expression of BnNRT1.1, PM H + -ATPase activity, and the genes expression involved in the auxin synthesis and polar transport were all assayed. The NO 3 − uptake rate, root auxin content, a number of auxin synthesis, and polar transport related genes in 1 M were significantly increased than that of 15 M. The root IAA increment in 1 M compared with 15 M, originated from root synthesis shared with 29.20% and polar transport from shoot shared with 70.80%. The expression of BnNRT1.1 and PM H + -ATPase activity were significantly promoted in 1 M compared with 15 M. In addition, the NO 3 − uptake rate in 15 M + IAA was significantly higher than that of 15 M, and the NO 3 − uptake rate in 1 M + NPA was significantly lower than that of 1 M. Because of low N stress promoted in situ synthesis of auxin in root and its polar transport from shoot, the root auxin content was increased, enhanced the expression of BnNRT1.1 and PM H + -ATPase activity, resulting in higher NO 3 − uptake rate.