Kinetics of nitrate uptake system in wheat genotypes

The nitrate uptake kinetics (C_min, K_m, and V_max) were studied in two cultivars of wheat differing in the level of activity of enzyme nitrate reductase. The uptake kinetics especially K_m and V_max depend on the concentration of nitrate in rhizosphere. At low range of external nitrate concentration uptake system follows Michaelis-Menten saturation kinetics, while at high external nitrate concentration, the nitrate uptake system follows linear kinetics. The uptake system did not show any saturation at least up to 10mM external nitrate. Lineweaver-Burk plot transformation of the uptake data at low nitrate concentration, the K_m and V of HD 2285 (high nitrate reductase activity-HNR) and HD 1981 (low_max nitrate reductase activity-LNR) were found to be 0.186 and 0.725 mM, and 0.17 and 0.798 mmol g⁻¹ fr. wt. h⁻¹, respectively. The C_min was calculated by estimating the accumulation of tissue nitrate and found to be 0.9 and 1.5 mM. At low range (0.05–0.5), the rate of nitrate uptake was higher in LNR genotype and at high external nitrate concentration, the uptake of nitrate was more in HNR genotype.