Multiphasic Uptake of Sulfate by Barley Roots

Uptake of sulfate by excised barley roots increases upon their washing in aerated water or dilute CaCl 2 solutions. Washing increases the values for V max and the sulfate concentrations required for transition between the lower phases, but the K M ‐values remain essentially constant. At low sulfate concentrations, phase transitions do not occur in the absence of calcium or other divalent cations. These ions are about equally effective in enhancing short‐term sulfate uptake. Phase transitions were not principally altered by sulfhydryl or protein reagents. These concentration‐dependent transitions appear unrelated to temperature‐dependent phase transitions as evidenced by similar multiphasic patterns at low and high temperature.