Plant metabolism of herbicides with C-P bonds: Phosphinothricin.

Plants have been reported not to metabolize phosphinothricin. In order to reexamine these literature findings, cell suspension cultures of soybean (Glycine max L.), wheat (Triticum aestivum L.), and maize (Zea mays L.) were incubated with L,-[3,4-14C]phosphinothricin. In maize cells which took up up to 50% of the applied radioactivity four different metabolites were detected. They were identified as 4-methylphosphinico-2-oxo-butyric acid, 4-methylphosphinico-2-hydroxybutyric acid, 4-methylphosphinico-butyric acid, and 3-methylphosphinico-propionic acid, respectively. A new HPLC separation method was developed in order to identify these unusually polar metabolites. In soybean and wheat cultures, 10 and 6%, respectively, of the applied radioactivity was taken up. In soybean only one metabolite, 3-methylphosphinico-propionic acid, could be detected whereas in wheat 4-methylphosphinico-butyric acid was additionally present. Radioactivity in the culture media could be attributed to unchanged herbicide in all cases. 14CO2-evolution from soybean and maize cultures was very low (<0.1% of the applied radioactivity within 4 days). Incorporation of radioactivity from applied [14C]phosphinothricin into bound residues also reached only small amounts (<0.1%). A metabolism scheme for phosphinothricin is proposed

Plant metabolism of herbicides with C-P bonds: Glyphosate.

Plants have been reported not to metabolize glyphosate. In order to reexamine these literature findings, cell suspension cultures of wheat (Triticum aestivum L.), soybean (Glycine max L.), and maize (Zea mays L.) as well as whole-plant samples of spruce (Picea abies L. Karst), tobacco (Nicotiana tabacum sp.), wheat, soybean, and maize have now been incubated with [3-14C]glyphosate. Appreciable uptake of glyphosate was observed with seedlings and leaves and to a lesser extent with cultured cells. The cell extracts contained most of the radioactivity in the form of nonmetabolized glyphosate with aminomethylphosphonic acid (AMPA) as the only detectable metabolite. The ratio of both compounds varied between the different plant species. The highest percentages of AMPA (49.7% of applied radioactivity) were present in soybean cell cultures. In soybean cell cultures 14CO2-evolution of about 1% of the applied radioactivity occurred within 4 days. A low incorporation into the polar group region of soybean phospholipids also occurred. Incorporation into the insoluble residue fraction was more significant (up to 27% in soybean leaves). These bound residues consisted largely of cell wall material and were sequentially solubilized. The incorporated radioactivity was associated with all solubilized residue fractions. In the case of soybean cell cultures it could be shown that the bound radioactivity in the amylase, pronase, and pectinase solubilized fractions was to ≥90% due to AMPA