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InCatharanthus roseusL. cells, the study of glyphosate uptake indicates that, at low concentrations, glyphosate is transported against a concentration gradient, reaching an accumulation ratio of about 30, 18 h after the cells are transferred into a fresh medium. Evidence that part of the glyphosate uptake may be carrier mediated was provided by concentration dependence experiments which showed that glyphosate uptake exhibited a saturation phase at low concentrations (up to 50 μM). The role played by a phosphate transporter in this process is demonstrated 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 protoplasts and vacuoles indicated that [14C]glyphosate is distributed between the cytosolic and the vacuolar compartments, but the greater part is localized in the cytosol. Detailed studies carried out to investigate 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+, and the presence of iron. |
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