Effect of potassium on root influx parameters of wheat at different growth stages

Root influx parameters (V_max and K_m) of wheat (var. HD 2285) were determined at different stages of crop growth, viz., crown root initiation stage (CRIS), maximum tillering stage (MTS), flag leaf stage (FLS) and dough formation stage (DFS). Wheat was grown in sand medium with Hoagland nutrient solution (all nutrients except potassium). Plants were taken out from sand culture at 22, 41, 69, and 87 days after germination and placed in a specially designed assembly of flowing solution in greenhouse. The nutrient solution was allowed to flow into the culture vessel in a regulated manner by means of a separating funnel. Fresh Hoagland solutions having five different concentration of K (2, 6, 10, 13, and 16 mg L⁻¹) were added drop-wise on the funnels at the rate of about 3000 mL day⁻¹ and continuously supplied in five different assemblies. Root influx parameters (V_max and K_m) were determined employing a simple solution culture technique, by measuring the depletion of potassium (input minus output concentration) by wheat roots in five nutrient media differing in potassium concentration only. V_max and K_m were calculated with the help of coefficients obtained by fitting the solution K concentration and K uptake rate data on the Michaelis-Menten equation. The V_max and K_m values decreased with the age of crop. The V_max was 48.7 nmol m⁻² s⁻¹ at 22 days after germination (DAG) and decreased to 4.21 nmo1 m⁻² s⁻¹ at 87 days of crop growth; corresponding K_m values were 299 and 146 μM, respectively.