Effects of N deprivation and nitrate pulses on NRT1 and NRT2 transcript levels and nitrate influx rate in Brassica napus L.

Abstract

A model has been proposed by Clarkson (1986) in which nitrate uptake by higher plants is down-regulated under conditions of high internal N. This model was investigated in Brassica napus L. by measuring the activity of low and high affinity transport systems (HATS and LATS) in relation to mRNA abundance of inducible nitrate transporter genes BnNRT1 and BnNRT2 in roots. Induction effects of nitrate were examined by supplying N-deprived plants with nitrate pulses 12 h before measuring influx and 4 h before assaying mRNA levels. N deprivation decreased nitrate influx from both low and high external concentrations with no significant changes in the relative abundance of BnNRT1 and BnNRT2 transcripts. Nitrate pulses increase the NO3? influx of the HATS and the mRNA expression of BnNRT2 gene with the increasing duration of N deprivation but had no effect on LATS activity and BnNRT1 mRNA abundance.