GLYPHOSATE UPTAKE IN CATHARANTHUS-ROSEUS CELLS - ROLE OF A PHOSPHATE TRANSPORTER

In Catharanthus roseus L. cells, the study of glyphosate uptake indica tes that, at low concentrations, glyphosate is transported against a c oncentration gradient, reaching an accumulation ratio of about 30, 18 h after the cells are transferred into a fresh medium. Evidence that p art of the glyphosate uptake may be carrier mediated was provided by c oncentration dependence experiments which showed that glyphosate uptak e exhibited a saturation phase at low concentrations (up to 50 mu M). The role played by a phosphate transporter in this process is demonstr ated by the existence of a lag period and the inhibition of glyphosate uptake in the presence of high concentrations of sodium phosphate. It is also shown by the effect of PFA, a powerful inhibitor of phosphate transport in animal cells, and also by the action of protein chemical reagents (PCMBS and DCCD). Compartmental analysis with isolated proto plasts and vacuoles indicated that [C-14]glyphosate is distributed bet ween the cytosolic and the vacuolar compartments, but the greater part is localized in the cytosol. Detailed studies carried out to investig ate the requirements of the glyphosate transporter showed that, among the different constituents of the Gamborg's nutrient medium, the major elements increasing the cellular glyphosate uptake were Ca2+, Mg2+, a nd the presence of iron. (C) 1997 Academic Press.