Regulation of the high-affinity ammonium transporter (BnAMT1;2) in the leaves of Brassica napus by nitrogen status.
Substantial concentrations of NH4+ are found in the apoplast of the leaves of Brassica napus. Physiological studies on isolated mesophyll protoplasts with 15NH4+ revealed the presence of a high-affinity ammonium transporter that shared physiological similarity to the high-affinity NH4+ transporters in Arabidopsis thaliana (AtAMT1;3). PCR techniques were used to isolate a full-length clone of a B. napus homologue of AMT1 from shoot mRNA which showed 97% similarity to AtAMT1;3. The full-length cDNA when cloned into the yeast expression vector pFL61 was able to complement a yeast mutant unable to grow on media with NH4+ as the sole nitrogen source. Regulatory studies with detached leaves revealed a stimulation of both NH4+ uptake and expression of mRNA when the leaves were supplied with increasing concentrations of NH4+. Withdrawal of NH4+ supply for up to 96 h had little effect on mRNA expression or NH4+ uptake; however, plants grown continuously at high NH4+ levels exhibited decreased mRNA expression. BnAMT1;2 mRNA expression was highest when NH4+ was supplied directly to the leaf and lowest when either glutamine or glutamate was supplied to the leaves, which directly paralleled chloroplastic glutamine synthetase ( GS2) activity in the same leaves. These results provide tentative evidence that BnAMT1;2 may be regulated by similar mechanisms to GS2 in leaves.[1]References
- Regulation of the high-affinity ammonium transporter (BnAMT1;2) in the leaves of Brassica napus by nitrogen status. Pearson, J.N., Finnemann, J., Schjoerring, J.K. Plant Mol. Biol. (2002) [Pubmed]
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