Pot culture experiments were carried out to investigate the effect of nitrogen source on nitrogen uptake and it's assimilation in three rice genotypes viz. Basmati, Jaya and Pusa-33 at different stages of plant growth. The results indicate that there is no consistant effect of nitrogen source—NH4 or NO3 on the N content of plant tissues. Nitrate reductase activity was higher in NO3-N plants as compared to NH4-N plants. The enzyme activity gradually increased from a very low value to maximum in young plants and declined to the minimum at anthesis. Grain protein was higher in Pusa-33 and Basmati varieties which were having more NR activity at the later stages of growth. GDH activity was higher in plants supplied with NH4-N as compared to nitrate grown plants.
