CHARACTERIZATION OF PHOSPHATE-UPTAKE BY SUSPENSION CULTURED CATHARANTHUS-ROSEUS CELLS

The mechanism of uptake of inorganic phosphate was studied with suspension cultured Catharanthus roseus cells. The kinetics showed both a low and a high affinity phase with K(m) values in the mu-M and mM range, respectively. Experiments with different inhibitors suggested that the high affinity phosphate transport is driven by the proton motive force at the plasma membrane and probably includes a protonphosphate symport. The low affinity transport revealed properties different from those of the high affinity transport; its relation to phosphate transport at the tonoplast membrane is discussed. The high affinity phase of Pi uptake, studied with cells from different phases of the growth cycle, revealed little changes in the K(m) values, which were between 2 to 5-mu-M, whereas the V(max) values strongly depended on the growth stage with values up to 70 nmol min-1 g-1 FW.