Distribution and metabolism of D/L‐, L‐ and D‐glufosinate in transgenic, glufosinate‐tolerant crops of maize (Zea mays L ssp mays) and oilseed rape (Brassica napus L var napus)

Abstract

The aim of the present study was to determine whether post-emergence application of glufosinate to transgenic crops could lead to an increase in residues or to the formation of new, hitherto unknown metabolites. Transgenic oilseed rape and maize plants were treated separately with L-glufosinate, D-glufosinate or the racemic mixture. Whereas about 90% of the applied D-glufosinate was washed off by rain and only 5-6% was metabolised, 13-35% of the applied L-glufosinate remained in the form of metabolites and unchanged herbicide in both transgenic maize and oilseed rape. The main metabolite was N-acetyl-L-glufosinate with total residues of 91% in oilseed rape and 67% in maize, together with small amounts, of 5% in oilseed rape and 28% in maize, of different methylphosphinyl fatty acids. These metabolites were probably formed from L-glufosinate by deamination and subsequent decarboxylation. The residues were distributed in all fractions of the plants, with the highest contents in treated leaves and the lowest in the grains (0.07-0.3% in maize and 0.4-0.6% in oilseed rape). There was no indication of an accumulation of total residues or of residue levels above the official tolerances for glufosinate.

The impact of altered herbicide residues in transgenic herbicide‐resistant crops on standard setting for herbicide residues

“…In line with these findings are other reports in the scientific literature that describe the metabolism of DL ‐glufosinate and/or L ‐glufosinate in experimentally grown crop plantlets, including glufosinate‐resistant brassica (canola), maize, cotton and soybean expressing PAT 49–53. These studies show that, in the treated leaves and other parts of glufosinate‐resistant plants, L ‐glufosinate is metabolised to a significant extent.…”

“…These studies show that, in the treated leaves and other parts of glufosinate‐resistant plants, L ‐glufosinate is metabolised to a significant extent. NAG has been demonstrated to be the main metabolite of the parent compound 49, 52, 53. In glufosinate‐resistant maize and brassica (canola), Ruhland et al 53 also reported the additional presence of MPP and MHB, as well as 2‐methyl‐phosphinico‐acetic acid (MPA) (Fig.…”

Glufosinate Absorption, Translocation, and Metabolic Fingerprint Effects in gdhA‐Transformed Tobacco

“…This research failed to demonstrate any difference in foliar uptake of glufosinate between tobacco genotypes. Translocation rates in glufosinate-resistant crops have been reported below 20% in corn and from 29% in soybean to 68% in oilseed rape (Pline et al, 1999;Ruhland et al, 2004). The greatest total translocation of 14 C from glufosinate out of the treated leaf was evident for the gdhA 9 tobacco line, which has been characterized as the tobacco line exhibiting the least whole-plant sensitivity to glufosinate (Nolte et al, 2004), relative to the other genotypes included in this research.…”

Metabolomics in pesticide research and development: review and future perspectives

“…Two sources of genes have been used in transformations, Streptomyces hygroscopicus (bar gene) and S. viridochromogenes (pat gene). Both genes encode phosphinothricin N-acetyltransferase (PAT) which converts L-glufosinate to the non-phytotoxic metabolite Nacetyl-L-glufosinate (OECD 2002b; Ruhland et al 2004). On the other hand, genetically engineered plants to express insecticidal metabolites have been introduced in order to minimize yield losses caused by insects (Kos et al 2009).…”