Expression and activity analysis of genes/enzymes of nitrate assimilation at low nitrogen level in high and low nitrogen use efficient wheat genotypes at pre and post-flowering stages

High and low nitrogen use efficient wheat genotypes were evaluated for expression analysis and activity of nitrate assimilation enzymes under limiting nitrogen supply to understand the basic differences and to verify any post-translational regulatory mechanism. Even at a limiting nitrogen treatment the high nitrogen use efficient genotypes NIAW-1994 and HD 2781 had significantly higher NR, GS, Fd-GOGAT, and NADH-GOGAT activities. The increased activity of NADH-GOGAT, Fd-GOGAT, and glutamine synthetase during post anthesis suggests that these enzymes are involved in photorespiratory ammonia remobilization. The expression level of the cytosolic isoform of TaGS1 was comparatively higher in high-NUE genotypes at the post-anthesis stage as compared to the pre-anthesis stage is supportive of better nitrogen (N) remobilization efficiency. TaFd-GOGAT expression was higher at the post-anthesis stage as compared to the pre-anthesis stage. The results revealed that the high nitrogen efficient genotypes exhibited increased assimilation ability during the pre-anthesis stage and remobilization ability during the post-anthesis stage. The relative quantification of TaGS1 at pre-anthesis and post-anthesis could be used to breed better NUE genotypes. The activity of in vivo NR and GS1 and Fd GOGAT expression and activity are key so far as response to low nitrogen level is concerned.