Characteristics of Aluminum-Phosphate-Adapted Carrot Cells: Uptake and Utilization of the Phosphate

To elucidate the mechanism responsible for the superior growthof a selected line of carrot cells (Daucus carota L. cv MS Yonsun)in medium that contained AIPO₄, kinetic studies of the uptakeof phosphate and the efficiency of utilization of phosphatewere performed with the selected cells and the wild-type cells.When the two cell lines were grown in a medium with adequatesoluble phosphate (2 mM), there was no difference between theirgrowth rates. Rates of increase in fresh weight as a functionof increasing concentration of phosphate in the medium werealso identical between the cell lines, indicating that the efficiencyof utilization of phosphate by the selected cell line was similarto that by the wild-type cells. However, rate of uptake of phosphateby the selected cells under phosphate limited conditions (20µMNaH₂PO₄ at pH 5.6) was about 5-fold higher than that by thewild-type cells. Apparent K_m values for the uptake of phosphatewere calculated to be 13.6 and 9.1 µM for the selectedand the wild-type cells, respectively. The V_max valuewas estimatedto be 88.8 nmol per g fresh weight per min for the selectedcells and 28.2 for thewild-type cells. Thus, the selected cellshas an enhanced system for uptake of phosphate wherebytherewas an increase in the rate of the uptake without any dramaticchange in the affinity for phosphateions. (Received September 21, 1991; Accepted December 25, 1991)