Variability of nitrogen uptake and assimilation among N-efficient and N-inefficient wheat (Triticum aestivum L.) genotypes

Ten genotypes of wheat (Triticum aestivum L.) were grown for 20 days in complete nutrient solution with 1 mM (nitrogen-insufficient), 4 mM (nitrogen-moderate) and 10 mM (nitrogen-sufficient) nitrogen (N) levels, and nitrogen efficiency (NE) was analyzed. Of these 10 genotypes, VL829 was identified as the most N-efficient, while HUW234 the most N-inefficient. To find out the physiological basis of this difference, we investigated the possible role of NO32- influx across the root cell plasma membrane in conferring NE by measuring the short-term NO32- uptake in selected 10 genotypes. Uptake experiments revealed the presence of two separate nitrate transporter systems mediating high-and low-affinity nitrate uptake. Interestingly, the nitrate uptake by the roots of VL829 is mediated by both high-and low-affinity nitrate transporter systems, while that of HUW234 by only low affinity nitrate transporter system. The study suggests that root NO32- uptake rate may play an important role in conferring N-efficiency of wheat genotypes under N-limiting condition. Also the activities and expression levels of nitrate assimilatory enzymes in N-efficient and N-inefficient wheat genotypes showed that nitrate reductase (NR) and glutamine synthetase (GS) play important roles in N assimilation under low-nitrogen conditions.