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BACKGROUND Hybrid corn varieties exhibit benefits associated with heterosis and account for most of the corn acreage in the USA. Hybrid seed corn is produced by crossing a female parent which is male-sterile and therefore incapable of self-pollination with a male parent as the pollen donor. The majority of hybrid seed corn is produced by mechanical detasseling which involves physically removing the tassel, a process that is laborious and costly. RESULTS Glyphosate-resistant corn was developed via expression of a glyphosate insensitive 5-enolpyruvyl-shikimate 3-phosphate synthase enzyme (CP4-EPSPS). Experimentation with molecular expression elements resulted in selective reduction of CP4-EPSPS expression in male reproductive tissues. The resulting plant demonstrated sterile tassel following glyphosate application with little to no injury to the rest of the plant. Using 14C-glyphosate as a marker, we also examined the translocation of glyphosate to the tassel via spray application in a track sprayer to simulate field application. The results allowed optimization of spray parameters such as dose, spray timing and target to maximize tassel delivery of glyphosate for efficient sterilization. CONCLUSION The Roundup hybridization system (RHS) is a novel process for hybrid seed production based on glyphosate-mediated male sterility. RHS replaces mechanical detasseling with glyphosate spray and greatly simplifies the process of hybrid seed corn production. © 2013 Society of Chemical Industry

Distribution of [14C]glyphosate was examined in mature glyphosate-resistant cotton plants at the 13-node stage in the absence of phytotoxicity. Initial experiments employed manual application of glyphosate to individual leaves within a relatively immature (Node 9) or mature (Node 5) sympodium (i.e., fruiting node) in the plant. We measured glyphosate export out of the treated leaf to the fruiting structures and foliage in the sympodium as well as out of the sympodium into the plant. Application to the Stem leaf, Leaf 1 or Leaf 2 in Node 9 showed 30–37% glyphosate export by 14 days after treatment. While Stem leaf exported mainly to the plant, Leaves 1 and 2 exported equally between the plant and the sympodium. Within the sympodium, glyphosate was distributed almost entirely to the fruiting structures with Boll 1 containing the highest level irrespective of the treated leaf. In Node 5, application to the Stem leaf or Leaves 1–3 showed overall lower glyphosate export (20–27%) with Stem leaf and Leaf 3 exporting mainly to the plant, and Leaves 1 and 2 exporting mainly to the sympodium. Within Node 5, the subtending boll of the treated leaf was not the main distribution target, but instead the boll at the next higher sympodial position relative to the treated leaf. Subsequent studies were conducted using over-the-top spray application of [14C]glyphosate at field use-rates in mature plants at the 13-node stage. Analysis of open bolls at full maturity showed high residues in seeds and fiber of Bolls 1 and 2 in the mature sympodia. Our results suggest that glyphosate distribution in mature plants was affected by sympodial age, position of the treated leaf, and position and sink strength of the bolls.

The mechanism of glyphosate resistance in horseweed was investigated. Eleven biotypes of putative sensitive (S) and resistant (R) horseweed were obtained from regions across the United States and examined for foliar retention, absorption, translocation, and metabolism of glyphosate. Initial studies used spray application of14C-glyphosate to simulate field application. When S and R biotypes were compared in the absence of toxicity at a sublethal dose, we observed comparable retention and absorption but reduced root translocation in the R biotypes. S and R biotypes from Delaware were further examined at field use rates and results confirmed similar retention and absorption but reduced root translocation in the R biotypes. Application of14C-glyphosate to a single leaf demonstrated reduced export out of the treated leaf and lower glyphosate import into other leaves, the roots, and the crown in R relative to S biotypes. Examination of the treated leaf by autoradiography showed that glyphosate loading into the apoplast and phloem was delayed and reduced in the R biotype. Our results consistently showed a strong correlation between impaired glyphosate translocation and resistance. Tissues from both S and R biotypes showed elevated levels of shikimate suggesting that 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) remained sensitive to glyphosate. Analysis of tissue shikimate levels demonstrated reduced efficiency in EPSPS inhibition in the R biotypes. Our results suggest that resistance is likely due to altered cellular distribution that impaired phloem loading and plastidic import of glyphosate resulting in reduced overall translocation as well as inhibition of EPSPS.

Leaf cytoarchitecture was evaluated by light microscopy and scanning electron microscopy, and cell viability was monitored by fluorescence after treatment of velvetleaf with defined concentrations and droplet sizes of formulated glyphosate and blended tallowamine surfactant. In response to droplets of formulated glyphosate larger than in field sprays but useful for studying structural change, we observe that the leaf epidermis thins and flattens within 1.5 h, the epidermal, mesophyll, and vascular cells at the contact site exhibit localized cytolysis by 6 h, and cytolysis and pycnosis remain restricted to the contact site at 24 h. Using endogeneous fluorescence as a marker for nonviable cells, it was determined that cellular changes are directly correlated with droplet size and that the changes are minimal after exposure to spray sizes and concentrations of formulated glyphosate and blended tallowamine typically used in the field. The results show that, at field use concentrations, the effect of formulated glyphosate and blended tallowamine on leaf cytoarchitecture is modest and localized but sufficient to allow herbicide entry.

Glyphosate efficacy was examined in young velvetleaf plants from the standpoint of its tissue distribution and sensitivity. In whole plant assays, manual application of a sub-lethal dose to the first leaf resulted only in meristem injury while other tissues remained visually healthy. Our studies showed that this differential tissue response was caused by a combination of differential distribution as well as sensitivity to glyphosate. Using [14C]glyphosate, we measured tissue injury and glyphosate residue, and calculated tissue threshold for 50% growth inhibition. Our studies showed that roots and meristem have high glyphosate distribution (45 and 34% of translocated, respectively) and low inhibition thresholds (0.23 and 0.21 ppm, respectively) resulting in tissues that were easily killed by glyphosate. In contrast, the base stem contained a much higher inhibition threshold (8.4 ppm) with only intermediate distribution (10%) resulting in a tissue that was most difficult to kill. We observed a linear relationship between glyphosate dose and tissue concentration; furthermore, tissue distribution pattern was independent of dose or surfactants class. At a sub-lethal dose, sensitive tissues that received a large distribution of glyphosate were preferentially killed. As the dose was increased, more glyphosate was available for distribution, and all tissues received a proportionately greater amount of glyphosate. Plant death occurred when the applied dose was sufficient to attain the lethal threshold in all tissues.

The effect of droplet size on retention, absorption, and translocation of 14C-glyphosate was studied in glyphosate-resistant corn. Fine, medium, and coarse spray droplets were studied using a track-sprayer equipped with commercially available nozzles. Glyphosate-resistant corn was used to obtain measurements at field use rates in the absence of phytotoxicity. Spray retention on corn leaves was calculated based on recovered glyphosate per leaf area, and retention was higher with application of fine droplets (47%) than with application of coarse (38%) and medium (37%) droplets. Absorption in corn leaves was directly correlated with droplet size and reached a plateau 1 d after treatment (DAT) for all droplet sizes. Based on glyphosate recovered 3 DAT, coarse droplets showed the highest absorption (49%), followed by medium (35%) and fine (30%) droplets. Percentage of translocation also increased with droplet size, and translocation was primarily toward strong sink tissues such as roots and young leav...

Three commercial formulations of glyphosate were spiked with 14C-glyphosate and applied via a spray nozzle to velvetleaf plants. The use of 14C-glyphosate as a marker caused minimal alteration to formulation properties, and the use of spray application simulated field practices. Formulation retention, calculated based on maximum plant-leaf area, showed that only 27 to 33% of the available area retained the spray. The small differences in retention among the formulations suggest that they contribute little to differences in efficacy. Following spray application, plants were harvested at various times to measure the levels of glyphosate uptake into the plant and translocation into roots. Significant differences were observed among the formulations in the rate of glyphosate uptake. The most efficient formulation absorbed about one third of the dose by 24 hr after treatment. Root translocation of glyphosate was approximately proportional to uptake and accounted for less than one third of the absorbe...

Experiments were conducted to determine potential mechanisms of glyphosate resistance inLolium rigidumfrom Australia.14C-Glyphosate uptake, translocation, and metabolism were compared between resistant (R) and sensitive (S) biotypes. The R seed (48118a) represented the F1progenies of plants having survived a 1.73-kg ae ha−1(4.8 L ha−1) application of a Roundup®formulation. The S seed was a sensitive biotype ofL. rigidumfrom Australia. Plants (one to four tillers, 2 to 4 wk old) were presprayed with a high (1.26 kg ae ha−1) or a low (0.28 kg ae ha−1) dose of formulated glyphosate. The first leaf of the first tiller, which was shielded from the spray, was immediately treated with a14C-glyphosate solution via manual application to the adaxial surface. Harvest was made 6 days after treatment (DAT), and glyphosate residues in the leaf wash, treated leaf, roots, and shoots were quantified based on radioactivity as percentage of applied dose. The overall radioactivity recoveries were very good (90.2 to 97.3% of applied dose). R and S plants showed comparable uptake at the high (79.2 vs. 78.0%) or the low (64.0 vs. 64.7%) doses of glyphosate. About one-half of the absorbed glyphosate in both R and S (32.9 to 38.3% appl.) was translocated into the plant and distributed almost equally into roots (13.6 to 16.0% appl.) and shoots (18.1 to 22.6% appl.). Autoradiography studies demonstrated no difference in tissue localization of glyphosate between the R and S plants. For metabolism studies, tissues from individual plants were homogenized in water, and extracts were analyzed by anion exchange high-pressure liquid chromatography (HPLC) with radioactivity detection. There was little to no metabolism of glyphosate in extracts from various tissues of either R or S plants. Based on these results, we conclude that neither uptake, translocation, nor metabolism play a major role in glyphosate resistance inL. rigidum.

Rat liver tissue homogenates were utilized for in vitro enzymatic conversion of 2,6-diethylaniline (DEA) to the important alachlor metabolite 4-amino-3,5-diethylphenyl sulfate (ADEPS), which was also generated as a radiolabeled standard for use in metabolism studies. ADEPS formation in rodents is associated with the production of other reactive metabolites implicated in alachlor rodent carcinogenesis, making dependable access to an ADEPS standard highly desirable. 14C-DEA was oxidized by rat liver microsomes to 14C-4-amino-3,5-diethylphenol, which was further converted to ADEPS via addition of the phosphosulfate transferase cofactor adenosine-3‘-phosphate-5‘-phosphosulfate. Microprobe NMR was used in conjunction with high-resolution mass spectrometry to fully characterize the resulting 14C-ADEPS and confirm its structure. Because microgram quantities sufficed for full characterization, the enzymatic transformation provides a viable alternative to radiosynthesis of 14C-ADEPS. Keywords: Alachlor; enyzmes; m...

Uptake and translocation of glyphosate in three commercial formulations were examined in velvetleaf, a dicotyledonous weed that is commonly treated with glyphosate. The formulations included Roundup? (MON 35085), Roundup Ultra, and Touchdown? as sold in Canada. A minimal amount of 14C-glyphosate was spiked into a lethal rate of each formulation, and the short-term (3 to 72 h) uptake into the treated leaf and subsequent translocation into the plant were measured. Time- course studies showed very rapid uptake and translocation of glyphosate in the Ultra formulation. In comparison, the uptake and translocation of glyphosate in Touchdown was much slower but continued throughout the 72-h period. Glyphosate in the Roundup formulation showed intermediate uptake and translocation. Tissue necrosis at the application sites of Ultra and Roundup was visible within 24 h after treatment. Examinations using stereo and fluorescence microscopy revealed exten- sive cell death and tissue disruption. Tissue necrosis from Ultra and Roundup was also observed in blank formulations containing no glyphosate and therefore was likely caused by the surfactants. In contrast, the application sites of Touchdown produced little to no leaf damage. Our results demon- strated a direct correlation between tissue necrosis and rapid rates of glyphosate uptake and trans- location. Nomenclature: Glyphosate, N-(phosphonomethyl)glycine; velvetleaf, Abutilon theophrasti Medik. #3 ABUTH. Additional index words: Uptake, translocation, glyphosate, formulation, surfactant, tissue damage. Abbreviation: HAT, hours after treatment.

Plants were engineered to confer resistance to thiazopyr, a member of the pyridine herbicide family, via an esterase deactivation mechanism. Earlier studies showed that transformation of thiazopyr to its monoacid metabolite resulted in loss of herbicidal activity (P.C.C. Feng et al., 1995, Xenobiotica 35, 27). Based on thiazopyr hydrolytic activity, a 60-kDa esterase was purified from rabbit liver. The N-terminal amino acid sequence of purified pyridine-esterase demonstrated high homology to the published protein sequence of rabbit liver esterase isozyme 1 (RLE1). PCR primers designed based on the amino acid sequence of RLE1 recovered a novel cDNA (RLE3) whose derived amino acid sequence was 95% homologous to RLE1. Baculovirus-mediated expression of RLE3 cDNA in insect cells detected the 60-kDa esterase as well as activity against thiazopyr. Stable plant transformation of RLE3 cDNA was conducted in tomato and tobacco under a constitutive expression promotor. R 0 plants demonstrated wild-type phenotype, and analysis of leaf tissues confirmed the presence of the 60-kDa esterase. Transgenic seedlings demonstrated both in vitro and in vivo deactivation of thiazopyr to the monoacid. In growth chamber and greenhouse tests, R 1 seedlings from transgenic tomato and tobacco demonstrated enhanced resistance to thiazopyr. Resistance was directly correlated to the level of pyridine-esterase expression. A field study was conducted with transgenic tomato seedlings which further confirmed resistance to thiazopyr.

Hybrid corn varieties exhibit benefits associated with heterosis and account for most of the corn acreage in the USA. Hybrid seed corn is produced by crossing a female parent which is male-sterile and therefore incapable of self-pollination with a male parent as the pollen donor. The majority of hybrid seed corn is produced by mechanical detasseling which involves physically removing the tassel, a process that is laborious and costly.Glyphosate-resistant corn was developed via expression of a glyphosate insensitive 5-enolpyruvyl-shikimate 3-phosphate synthase enzyme (CP4-EPSPS). Experimentation with molecular expression elements resulted in selective reduction of CP4-EPSPS expression in male reproductive tissues. The resulting plant demonstrated sterile tassel following glyphosate application with little to no injury to the rest of the plant. Using (14)C-glyphosate as a marker, we also examined the translocation of glyphosate to the tassel via spray application in a track sprayer to simulate field application. The results allowed optimization of spray parameters such as dose, spray timing and target to maximize tassel delivery of glyphosate for efficient sterilization.The Roundup hybridization system (RHS) is a novel process for hybrid seed production based on glyphosate-mediated male sterility. RHS replaces mechanical detasseling with glyphosate spray and greatly simplifies the process of hybrid seed corn production.

Metabolism of the herbicide thiazopyr [methyl 2-(difluoromethyl)-5-(4,5-dihydro-2-thiazolyl)-4-(2-methylpropyl)-6-(trifluoromethyl)-3-pyridinecarboxylate] was examined in young seedlings of redroot pigweed, grain sorghum, sunflower, corn and soybean. As previously observed with rat liver microsomes plants predominantly metabolized thiazopyr via oxidation reactions. Sulfur and carbon atoms in the thiazoline ring were the primary sites of plant oxygenases. De-esterification was also identified as an important pathway of transformations in plants. Although similar pathways of thiazopyr metabolism were observed among plants, our data indicated species differences in rates of thiazopyr degradation. Among species examined, pigweed (Amaranthus retroflexus L.) showed the fastest metabolism. Thiazopyr metabolism in pigweed was significantly inhibited by several cytochrome P450 monooxygenase inhibitors, among which tetcyclacis (TET) and piperonyl butoxide (PBO) were the most inhibitory. Thiazopyr metabolism in pigweed was not inhibited by organophosphates, known inhibitors of esterases. The results suggest that thiazopyr metabolism in plants is predominantly mediated via plant monooxygenases.

The preceding paper described inhibition of thiazopyr metabolism in plant seedlings by inhibitors of cytochrome P450 monooxygenases, and the lack of inhibition by esterase inhibitors. We now describe greenhouse evaluation of the effects of these metabolic inhibitors on the bioefficacy of thiazopyr. Inhibitors of cytochrome P450 monooxygenases, piperonyl butoxide (PBO), 1-aminobenzotriazole (ABT), metyrapone (MET) and tetcyclacis (TET), all enhanced the bioefficacy of thiazopyr against pigweed and other plant species. In contrast, inhibitors of esterases, tributyl phosphate (TBP) and triphenyl phosphate (TPP), produced only slight enhancement of thiazopyr activity. The effect of PBO was dose-dependent and was demonstrated against barnyardgrass, grain sorghum, redroot pigweed, seedling johnsongrass, and giant foxtail. PBO demonstrated no enhancement of thiazopyr activity in velvetleaf, tall morningglory, cotton, or soybeans. Bioefficacy was most enhanced via exposure of seedling shoots to PBO and thiazopyr. The combination of results from the present and the preceding papers suggests that PBO enhances thiazopyr bioefficacy by effectively inhibiting thiazopyr metabolism in plants.

Thiazopyr [methyl 2-(difluoromethyl)-5-(4,5-dihydro-2-thiazolyl)-4-(2-methylpropyl)-6-(trifluoromethyl)-3-pyridinecarboxylate] is an experimental herbicide being developed for weed control in cotton, citrus, and other crops. The in vitro metabolic fate of key thiazopyr crop metabolites in animals was investigated using rat liver homogenates. The thiazopyr crop metabolites studied were sulfoxide ester, sulfone ester, nitrile ester, amide acid, and sulfonic diacid. Our results showed that the ester crop metabolites were extensively metabolized by rat liver homogenates to products previously observed during in vivo rat metabolism studies. Metabolites were identified using several techniques including high-performance liquid chromatography coelution with standards, direct identification by mass spectrometry and comparison with standards, and derivatization followed by mass spectrometry. In contrast, the acidic crop metabolites (amide acid and sulfonic diacid) were not metabolized, likely due to their water solubility and high polarity. Our study showed that these crop metabolites, if absorbed by rats, are further transformed to polar products that are likely to be eliminated rapidly from the body.

Thiazopyr is an experimental herbicide from the pyridine family that shows excellent preemergent activity against narrow-leafed weeds. Biotransformation of thiazopyr was examined in vitro using rat liver microsomes to assess the extent of its metabolism in vivo . Thiazopyr was rapidly and extensively oxidized exclusively in the thiazoline ring. The sulfur atom in the thiazoline ring was sequentially oxidized to the corresponding sulfoxide and sulfone metabolites. Oxidation of the carbon atoms in the thiazoline ring produced carbinolimine intermediates, which underwent dehydration or arrangements leading to the opening of thiazoline ring. A total of six metabolites were identified based on electrospray LC/MS and/or cochromatography with standards.

Various fluorescent stains and vital dyes have been used to identify dead cells in animal tissues and celi lines. In plants, fluorescein diacetate and propidium iodide have been used to label nuclei and to identify necrotic cells in plant protoplasts and 4,6-diamidino-2-phenylindole (DAPI) has been used to mark senescing cells in sections of roots. However, these dyes may be problematic when used with intact plant tissue with well-developed cells walls which may impede dye penetration. Endogenous fluorescence has been used to identify dead cells in intact and sectioned plant tissues. Published procedures typically employ ultraviolet (UV) excitation wavelengths of 340-380 nm and emission wavelengths of 400- 425 nm, thus requiring a UV filter set.

Using in vitro assays, this study was undertaken to determine whether the components of Lasso herbicide formulation had an effect on the human immune system. Mononuclear cells from human peripheral blood were exposed to analytical alachlor, alachlor conjugated to human serum albumin or Lasso formulation over a concentration range from .01 microM-1.0 microM. The effects of the test materials on the following immunological functions were determined: lymphocyte proliferation induced by mitogen or antigen; antibody synthesis of IgG and IgM isotypes in pokeweed stimulated mononuclear cell cultures; cytotoxic T cell proliferation; lysis of target cells by natural killer cells and lymphokine activated killer cells. The data demonstrated that the test compounds had no significant, dose related effect on the function of immunocompetent cells. Hence, the data suggest that the components of the Lasso formulation have no effect on the human immune system.

Acetochlor and acetochlor S -glutathione conjugate were degraded in soil with respective half-lives of 7 days and 30 min to a similar distribution of identical metabolites. Degradation of acetochlor-glutathione conjugate appears to be initiated by γ-glutamyl transpeptidase, and the addition of γ-glutamyl transpeptidase inhibitors effectively retarded the soil degradation of both acetochlor and its glutathione conjugate. The addition of a γ-glutamyl transpeptidase inhibitor to the soil caused the accumulation of acetochlor-glutathione conjugate as a transient metabolite of acetochlor and thereby facilitated its detection. These results suggested that conjugation of acetochlor with glutathione is an initial pathway of metabolism in soil. Acetochlor-glutathione conjugate was further degraded in soil to acetochlor S -cysteine conjugate, which was shown to be a key intermediate in the formation of the major acidic metabolites of acetochlor in soil.

(...) Cross-reactivity studies showed that these antibodies were capable of distinguishing alachlor from other structurally similar chloroacetanilide herbicides, including metolachlor, and that they showed little cross-reactivity toward the major soil metabolites of alachlor. (...) The concentration of alachlor in environmental water samples was measured by ELISA, and the results were compared with those obtained by a GC/MS method

BACKGROUND: Glyphosate is a widely used broad-spectrum herbicide. Recent studies in glyphosate-resistant (GR) crops have shown that, in addition to its herbicidal activity, glyphosate exhibits activity against fungi, thereby providing disease control benefits. In GR wheat, glyphosate has shown both preventive and curative activities against Puccinia striiformis f. sp. tritici (Erikss) CO Johnston and Puccinia triticina Erikss, which cause stripe and leaf rusts respectively. RESULTS: Laboratory studies confirmed earlier observations that glyphosate has activity against Phakopsora pachyrhizi Syd & P Syd which causes Asian soybean rust (ASR) in GR soybeans. The results showed that glyphosate at rates between 0.84 and 1.68 kg ha−1 delayed the onset of ASR in GR soybeans. However, field trials conducted in Argentina and Brazil under natural infestations showed variable ASR control from application of glyphosate in GR soybeans. Further field studies are ongoing to define the activity of glyphosate against ASR. CONCLUSIONS: These results demonstrate the disease control activities of glyphosate against rust diseases in GR wheat and GR soybeans. Copyright © 2007 Society of Chemical Industry

Glyphosate is a broad-spectrum herbicide used for the control of weeds in glyphosate-resistant crops. Glyphosate inhibits 5-enolpyruvyl shikimate 3-phosphate synthase, a key enzyme in the synthesis of aromatic amino acids in plants, fungi, and bacteria. Studies with glyphosate-resistant wheat have shown that glyphosate provided both preventive and curative activities against Puccinia striiformis f. sp. tritici and Puccinia triticina , which cause stripe and leaf rusts, respectively, in wheat. Growth-chamber studies demonstrated wheat rust control at multiple plant growth stages with a glyphosate spray dose typically recommended for weed control. Rust control was absent in formulation controls without glyphosate, dependent on systemic glyphosate concentrations in leaf tissues, and not mediated through induction of four common systemic acquired resistance genes. A field test with endemic stripe rust inoculum confirmed the activities of glyphosate pre- and postinfestation. Preliminary greenhouse studies also demonstrated that application of glyphosate in glyphosate-resistant soybeans suppressed Asian soybean rust, caused by Phakopsora pachyrhizi .

Crop resistance can be generated through a selection process or the introduction of a gene via transformation. We will refer to the latter as engineered herbicide resistance. The literature contains numerous studies on engineered plant resistance to various herbicide classes. There is a large distinction between demonstrating a resistance phenotype in plants versus developing a commercial resistant crop that requires consistent performance under varying environmental conditions. Creating an herbicide resistant crop must successfully navigate a maze of key technical issues while satisfying the practical product goals of agronomic equivalence, weed management, economic feasibility, governmental regulatory compliance and public acceptance. Most of our experience has been derived from developing crop resistance to glyphosate. In this review, we will utilise these experiences to describe the essential studies required for the development of a commercial herbicide-resistant crop with emphasis on the development of glyphosate resistance. Keywords: commercialised; experimental; herbicide-resistance strategy

1. Triple Resonance Isotope EDited nmr spectroscopy (TRIED) has been developed to detect and examine minute levels of glyphosate metabolites in microbial soil isolates. Using stable isotopic labelling (13C and 15N), TRIED allows the simultaneous detection of multiple metabolites in crude matrices at submicrogram levels. An improvement over earlier techniques where milligrams are needed, TRIED can detect 500 ng of triply labelled compound in a crude sample (1:14,000 mass ratio) in just hours. 2. TRIED is used here to compare the kinetics and metabolic pathways of glyphosate metabolism by two strains of Ochrobactrum anthropi, LBAA and S5. Both LBAA and S5 appear to metabolize glyphosate primarily via the aminomethylphosphonate (AMPA) pathway, since no detectable levels of glycine or sarcosine are observed in the media or lysates of either microbe. The formation of N-methylAMPA is common to the metabolism of both microorganisms, but N-acetylAMPA is observed only in LBAA. N-methylacetamide is detected predominantly in media and lysates of S5, although some evidence also points to the formation of this metabolite in LBAA. 3. Results are consistent with conventional radioactive tracer studies. TRIED nmr provides more specific structural information complementary to radiolabel methods. Both nmr and radioactivity studies show S5 glyphosate metabolism to be much slower than that of LBAA.

Commercial formulations of glyphosate were compared for surfactant leaf damage and glyphosate uptake. The formulations (Roundup™ Ultra, Roundup™, and Touchdown™ were diluted with water to 12.5 g AI litre−1 and applied as 1-μl drops to the first leaf adaxial surface. Tissues at application sites were examined by light, fluorescence and scanning electron microscopy. At 24 h after treatment, tissue necrosis was clearly visible with Ultra and Roundup™, but not with Touchdown™. The application sites of Ultra and Roundup™, but not with Touchdown™. The application sites of Ultra and Roundup™ demonstrated a well-demarcated zone of injury showing extensive rupturing of cell membranes in both epidermal and mesophyll cells. Studies using blank formulations without glyphosate confirmed that tissue damage was caused by the surfactant formulants. Diluted formulations (12.5 g AI litre−1) spiked with a minimum of [14C-glyphosate were applied similarly. Time-course studies showed the fastest uptake with Ultra, followed by Roundup™ and Touchdown™. Mobilization of glyphosate away from the treated leaf was proportional to uptake. The use of a deuterium NMR method demonstrated that pretreatment of leaves with glyphosate formulations facilitated subsequent leaf loading of deuterium oxide. The extent of the latter correlated with leaf loading of glyphosate in formulations. These results indicate that the role of the surfactant is to overcome the leaf cuticle and membrane barriers to facilitate glyphosate entry into the leaf. © 1999 Society of Chemical Industry

Incubation of alachlor with microsomal enzyme preparations from rats, mice, and monkeys produced four major metabolites. These metabolites arose from benzylic hydroxylation(s) at one or both arylethyl side chains and N -dealkylation of alachlor. Kinetic studies demonstrated similar rates of alachlor oxidation by liver microsomal enzymes of mice, monkeys, and male rats. The rate of oxidation by female rat liver microsomes was significantly less than that observed by male rats. A slight induction of liver microsomal oxygenase activity was observed after chronic oral dosing of male rats with alachlor.