Nitrogen-Metabolizing Enzymes: Effect of Nitrogen Sources and Saline Irrigation

Abstract

Indian mustard (Brassica juncea L. cv. was grown under different types and levels of nitrogen (N) sources, i.e. nitrate, ammonical, and nitrate plus ammonical, at 40, 80, and 120 kg ha −1 under green house conditions. The plants were salinized with 8 and 12 dSm −1 at 35 and 55 days after sowing. A progressive inhibition of the activity of enzymes of N metabolism, i.e., nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthase (GOGAT), and glutamate dehydrogenase (GDH), was observed with increasing level of salinity. However, the magnitude of such reductions was lowest at the highest level of N (120 kg ha −1 ) as compared with the lowest level (40 kg ha −1 ) irrespective of N source. The activity of nitrate-assimilating enzymes (NR and NiR) was maximum with nitrate fertilizer, and minimum with the ammonical form. The alleviation of detrimental effects of salinity on NR and NiR was better with the highest level of N (120 kg ha −1 ) in nitrate form as compared with the lowest level of N (40 kg ha −1 ). In contrast, the maximum activity of ammonium-assimilating enzymes (GS, GOGAT, and GDH) was observed with the highest level of N (120 kg ha −1 ) and the minimum with the nitrate form of N under salinity. These results indicate that despite the high salinity, an increase in the concentration and uptake of N stimulates the activities of nitrate-assimilating enzymes (NR and NiR) as well as of the ammonia-assimilating enzymes (GS, GOGAT, and GDH).

Salicylic acid mitigates salinity stress by improving antioxidant defence system and enhances vincristine and vinblastine alkaloids production in periwinkle [Catharanthus roseus (L.) G. Don]

“…Nitrate reductase is the rate-limiting enzyme in nitrogen assimilation and a key enzyme for the regulation of N metabolism, and estimating NR in SA-treated saltaffected plants could indicate the role of SA in this regard. Our results strengthen the findings of Nathawat et al (2005) who reported a salinity-causes decrease in N uptake as well as in the activity of nitrogen assimilation enzymes. An important consequence of salinity stress in plants is the excessive generation of ROS such as superoxide anion, H 2 O 2 and the hydroxyl radicals, particularly in chloroplast and mitochondria, that cause rapid cell damage by triggering a chain reaction (Neill et al 2002).…”

Calcium chloride and gibberellic acid protect linseed (Linum usitatissimum L.) from NaCl stress by inducing antioxidative defence system and osmoprotectant accumulation

“…1c). This result strengthens the findings of Garg et al (1997), Gratten and Grieve (1994), Nathawat et al (2005) and Siddiqui et al (2009), who reported that salinity causes decrease in N uptake and in the activity of nitrogen assimilation enzymes. It was noted that combined application of CaCl 2 and GA 3 mitigated the adverse effect of salt stress and enhanced the NR activity.…”

Role of Nitrogen and Gibberellin (GA3) in the Regulation of Enzyme Activities and in Osmoprotectant Accumulation in Brassica juncea L. under Salt Stress

“…This result is consistent with those of Garg et al. (1993), Grattan and Grieve (1994), Nathawat et al. (2005) where the disruption of N metabolism by salinity has been attributed to decreased N uptake, decreased nitrate and ammonia‐assimilating enzymes, altered amino acid synthesis, increased activity of hydrolyzing enzymes such as RNase, DNase, protease and several others, leading to the degradation of micromolecules.…”