Carrier‐mediated uptake of glyphosate in broad bean (Vicia faba) via a phosphate transporter

The possibility that the herbicide glyphosate (N‐phosphonomethylglycine) may be taken up in plant cells via a phosphate transporter of the plasma membrane was investigated using protoplasts of broad bean leaves ( Vicia faba L.). Phosphonoformic acid, a powerful inhibitor of phosphate transport in animal cells, was first demonstrated to be a competitive inhibitor of phosphate uptake inbroad bean protoplasts. Glyphosate was able to inhibit phosphate uptake into the protoplasts, and to protect partially the phosphate transporter from inhibition by phosphonoformic acid. Concentration dependence studies showed that glyphosate uptake exhibited a saturable phase at low glyphosate concentrations (0. 5 to 3 μ M ), superimposed by a linear uptake at higher concentrations (up to 100 μ M ). Inhibition of glyphosate uptake by para ‐chloromercuribenzene sulphonic acid, sodium azide and carbonyl‐cyanide‐ m ‐chlorophenylhydrazone was much stronger at 1 than at 100 μ M glyphosate. Kinetics indicated that the saturable component of glyphosate transport was competitively inhibited by either phosphate or phosphonoformic acid. It is concluded that glyphosate can be absorbed via a phosphate transporter of the plasma membrane