Abstract:

This paper reports the cloning and expression analysis of a high-affinity nitrate transporter in wheat (Triticum aestivum L.). A full-length cDNA, TaNRT2.3 (accession number AY053452), was isolated from NO₃^–-induced roots of wheat. The cDNA encodes a polypeptide with 507 amino acids and 12 transmembrane domains, belongs to nitrate/nitrite porter (NNP) family within the major facilitator superfamily (MFS), and is closely related to other NRT2 proteins from plants. The expressions of TaNRT2 genes in wheat tissues were analyzed using Northern blot, results indicated that TaNRT2 were induced specifically in roots but not in shoots in response to both low (5-200 mmol/L) and high (2.0 mmol/L) concentrations of NO₃^–. TaNRT2 transcripts were undetectable in N-deprived or NH₄⁺-grown plant roots. The significant correlation between the time course of TaNRT2 transcription accumulation in the roots of wheat plants grown in 0.2 mmol/L NO₃^– and the time course of the nitrate uptake rates by wheat plants grown under the same conditions suggested that TaNRT2 played an important role in high-affinity NO₃^– uptake. Using the split root system, we found that supplying NO₃^– to one part of the roots induced the expression of TaNRT2 in the other part not supplied with NO₃^– or supplied with NH₄⁺, which implied that N cycling within plants acted as a regulatory signal for N uptake.

Key words: Triticum aestivum, high-affinity nitrate transporter, nitrate induction, high-affinity nitrate uptake rate