Differential response of wheat genotypes to low nitrogen stress: Variation in antioxidant capacity

Two wheat (Triticum aestivum L.) genotypes viz. Uniculm ‘Gigas’ Line 492 and Kalyansona were used to study the development of oxidative stress and antioxidant capacity in fully expanded flag leaves in response to low nitrogen (N). The genotypes differed in terms of metabolic constituents, green leaf area, membrane integrity and activities of antioxidant enzymes. Uniculm maintained photosynthetic rate and metabolic constituents in spite of large reduction in total flag leaf area. Low N resulted in increased formation of hydrogen peroxide (H₂O₂) and accumulation of thiobarbituric acid reactive substances (TBARS) in flag leaves of both the genotypes. However, the activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) were higher in N stressed plants of Uniculm till maturity. In N stressed Kalyansona, activities of SOD and APX declined early as compared to control N plants. The low N induced generation of reactive oxygen species (ROS) was higher in Kalyansona as compared to Uniculm due to lower APX activity and/or the higher SOD/APX or SOD/CAT ratio. Kalyansona was found to be highly sensitive to low N in comparison to Uniculm. The catalase activity did not increase in low N grown plants of Kalyansona leading to increased hydrogen peroxide in this genotype. The study provides evidence that wheat genotypes respond differentially to N supply.