Absorption and efflux of glyphosate by cell suspensions

of controlling both annual and perennial weeds (Grossbard and Atkinson, 1985). Researchers have The absorption and efflux of [14C]-glyphosate (N-[phos- investigated the uptake, translocation and metabolism of phonomethyl]glycine) was studied in maize (Zea mays glyphosate at the whole plant level, revealing gross interL. cv. Aussie) and soybean (Glycine max L. Merr. cv. specific diVerences in its eYcacy (Atkinson, 1985; Terry, Maple Arrow) cell suspensions. Glyphosate absorption 1985; Bovey 1985). Such studies have shown that a was complex: at low external herbicide concentrations variable amount of the glyphosate dose gets absorbed (3‐250 mM) there was evidence for a single active which is often less than 60% (Ahmadi et al., 1980; Devine uptake system with an apparent K m of 31 mM and V max and Bandeen, 1983; Caseley and Coupland, 1985). Also, of 11 nmol g’1 fr. wt. 2 h’1. The system was inhibited only a small fraction of the applied dose (around 5%) by carbonylcyanide m-chlorophenyl hydrazone (CCCP), gets translocated from the treated leaves (Sandberg et al., orthovanadate, diethylstilbestrol (DES), phosphate, 1980). The mode of action of glyphosate is by inhibition and phosphonoformic acid (PFA) suggesting the of the enzyme 5-enolpyruvylshikimate 3-phosphate syn