Nitrogen availability prevents oxidative effects of salinity on wheat growth and photosynthesis by up-regulating the antioxidants and osmolytes metabolism, and secondary metabolite accumulation

Abstract

Background: Salinity is one of the damaging abiotic stress factor. Proper management techniques have been proposed to considerably lower the intensity of salinity on crop growth and productivity. Therefore experiments were conducted to assess the role of improved nitrogen (N) supplementation on the growth and salinity stress tolerance in wheat by analyzing the antioxidants, osmolytes and secondary metabolites.

Results: Salinity (100 mM NaCl) stress imparted deleterious effects on the chlorophyll and carotenoid synthesis as well as the photosynthetic efficiency. N supplementation resulted in increased photosynthetic rate, stomatal conductance and internal CO₂ concentration with effects being much obvious in seedlings treated with higher N dose. Under non-saline conditions at both N levels, protease and lipoxygenase activity reduced significantly reflecting in reduced oxidative damage. Such effects were accompanied by reduced generation of toxic radicals like hydrogen peroxide and superoxide, and lipid peroxidation in N supplemented seedlings. Antioxidant defence system was up-regulated under saline and non-saline growth conditions due to N supplementation leading to protection of major cellular processes like photosynthesis, membrane structure and function, and mineral assimilation. Increased osmolyte and secondary metabolite accumulation, and redox components in N supplemented plants regulated the ROS metabolism and NaCl tolerance by further strengthening the antioxidant mechanisms.

Conclusions: Findings of present study suggest that N availability regulated the salinity tolerance by reducing Na uptake and strengthening the key tolerance mechanisms.

Keywords: Antioxidants; AsA-GSH cycle; Nitrogen; Oxidative damage; Salinity; Triticum aestivum.

Fig. 1

Effect of nitrogen (50 and 100 mg kg^− 1 soil) supplementation on the content of (a) free sugars, (b) free proline, (c) free amino acids, (d) glycine betaine and (e) relative water content in Triticum aestivum L subjected to salinity stress. Data is mean (±SE) of three replicates, bars denoted by different letters are significantly different at P < 0.05

Fig. 2

Effect of nitrogen (50 and 100 mg kg^− 1 soil) supplementation on the (a) hydrogen peroxide, (b) superoxide and (c) lipid peroxidation in Triticum aestivum L subjected to salinity stress. Data is mean (±SE) of three replicates, bars denoted by different letters are significantly different at P < 0.05

Fig. 3

Effect of nitrogen (50 and 100 mg kg^− 1 soil) supplementation on the (a) protease and (b) lipoxygenase activity in Triticum aestivum L subjected to salinity stress. Data is mean (±SE) of three replicates, bars denoted by different letters are significantly different at P < 0.05

Fig. 4

Effect of nitrogen (50 and 100 mg kg^− 1 soil) supplementation on the (a) superoxide dismutase and (b) catalase activity in Triticum aestivum L subjected to salinity stress. Data is mean (±SE) of three replicates, bars denoted by different letters are significantly different at P < 0.05

Fig. 5

Effect of nitrogen (50 and 100 mg kg^− 1 soil) supplementation on the (a) ascorbate peroxidase, (b) glutathione reductase, (c) dehydroascorbate reductase, (d) monodehydroascorbate reductase activity and content of (e) ascorbate and (f) reduced glutathione in Triticum aestivum L subjected to salinity stress. Data is mean (±SE) of three replicates, bars denoted by different letters are significantly different at P < 0.05

Fig. 6

Effect of nitrogen (50 and 100 mg kg^− 1 soil) supplementation on the tocopherol content in Triticum aestivum L subjected to salinity stress. Data is mean (±SE) of three replicates, bars denoted by different letters are significantly different at P < 0.05

Fig. 7

Effect of nitrogen (50 and 100 mg kg^− 1 soil) supplementation on the content of (a) total phenol and (b) flavonoids, and the activity of (c) phenylalanine ammonia lyase in Triticum aestivum L subjected to salinity stress. Data is mean (±SE) of three replicates, bars denoted by different letters are significantly different at P < 0.05

Fig. 8

Effect of nitrogen (50 and 100 mg kg^− 1 soil) supplementation on the activity of (a) nitrate reductase and (b) nitrogen content in Triticum aestivum L subjected to salinity stress. Data is mean (±SE) of three replicates, bars denoted by different letters are significantly different at P < 0.05