Potassium uptake by wheat roots at low potassium concentrations in ambient solution

Potassium uptake in the roots of intact 6-day-old wheat seedlings (Triticum aestivum L,.) grown on low-salt solutions was investigated; the depletion of potassium in the solution was measured by flame photometry. The kinetics of potassium uptake depended on the initial K+ concentration in the solution. When the potassium concentration exceeded 34 mu M, a gradual acceleration of K+ uptake was recorded at the first stage (20-75 min). This stage became longer at higher initial concentrations of potassium in the nutrient solution. The period of initial acceleration of potassium uptake was almost indistinguishable at 16 mu M K+. At low K+ concentrations (below 30-34 mu M), the kinetic curves were adequately approximated by the equation for first-order reactions. At higher concentrations (30-190 mu M), the isotherm for potassium uptake was more precisely approximated by a linear equation. With some limitations, the isotherm might be approximated by a hyperbola basing on Michaelis-Menten equation with a high K-M Of about 650 mu M. The high value of K-M and initial acceleration of potassium uptake suggest an induction or activation of potassium-transport systems at the first stage by ambient potassium, when its concentration exceeds 30-34 mu M.