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

Animal Bioavailability of Defined Xenobiotic Lignin Metabolites.

Lignin has been recognized as a major component of bound pesticide residues in plants and is thought to be undigestible in animals. Two defined ring-U-14C-labeled chloroaniline/lignin metabolites have now been fed to rats, where a release of ∼66% of the bound xenobiotic occurred in the form of simple chloroaniline derivatives. The observed high degree of bioavailability indicates that bound pesticidal residues may possess ecotoxicological significance. In parallel studies, the white-rot fungus Phanerochaete chrysosporium was more efficient, and a soil system was much less efficient, in the degradation of the [ring-U-14C]chloroaniline/lignin metabolites