Biochemical Insights into Nitrogen Assimilation and Associated Enzyme Activities in Wheat under Foliar Application of Liquid Nanofertilizer

Abstract

Nitrogen (N) availability strongly influences wheat growth through its role in nitrate assimilation, amino acid formation, chlorophyll biosynthesis, and photosynthetic metabolism. This study evaluated the physicochemical characteristics of liquid Nano-Urea and its short-term biochemical effects on N assimilation in wheat seedlings after foliar application. Wheat seedlings were grown under controlled conditions and treated with Nano-Urea at 2, 4 and 6 mL/L, conventional urea at 2%, and a water control. The formulation was characterised by dynamic light scattering and related physicochemical measurements. The mean hydrodynamic diameter was 145.17 nm, with 95% of particles distributed within the 24–58 nm range. The formulation showed a polydispersity index of 0.765, zeta potential of −9.73 mV, conductivity of 4.57 mS/cm, and viscosity of 5.68 cP at 30°C. Foliar application caused temporal changes in leaf nitrate concentration, with a marked increase at 6 h after treatment and a subsequent decline by 12 h, suggesting rapid nitrate utilisation after foliar supply. The highest nitrate concentration recorded at 6 h was 5300 ppm under 6 mL/L Nano-Urea, whereas nitrate reductase and glutamine synthetase activities were highest under the 4 mL/L treatment, reaching 5.21 µg/min/g fresh weight and 0.21 mg/min/g fresh weight, respectively. Free amino acid content remained lower than the control across treatments, whereas total chlorophyll content increased, with the maximum value of 1.99 mg/g fresh weight recorded under 6 mL/L Nano-Urea. These findings indicate that foliar-applied Nano-Urea can influence short-term nitrate dynamics, N-assimilation enzyme activity, and chlorophyll accumulation in wheat seedlings.