Alachlor inhibition

Absorbed alachlor inhibits the growth of the shoots and roots and lateral root development of sensitive plants (Keeley et al., 1972). 

The acetanilides (propachlor, butachlor, alachlor and metolachlor) are used as preemergence herbicides against annual broad-leaved weeds and grasses. The acetanilides owe their herbicidal activity to the inhibition of photosynthetic electron transport and energy production. See Table 5.10. 

Alachlor or 2-chloro-2, 6 -diethyl-N-methoxymethyl-acetanilide Substituted amide Inhibits protein synthesis and root elongation Preemergence-control of annual weeds in cotton, brassicas, peanuts, soy beans, etc. 11-14... 

Alachlor (Figure 1) is the active ingredient of Lasso herbicide and several other herbicide products, and is one of the most widely used of the chloroacetanilide herbicides. We have recently developed effective methods for covalent conjugation of alachlor to protein carriers ( ), and will describe the application of this methodology to the development of antibodies to alachlor. We report herein on the development of an inhibition ELISA technique for detecting... 

Serum previously stored at -80 °C was freshly thawed and diluted 3,500 fold using PBS-T (0.02% Tween 20 in PBS). An aqueous alachlor standard or unknown sample was preincubated with an equal volume of diluted serum at 22 °C for 1 hour. This mixture (0.1 mL/well) was then dispensed into six replicate wells on the plate, which was then covered and incubated at 22 °C for 1.5 hours. After triplicate washes of the wells with PBS-T, each well was treated with 0.1 mL of GAR-HRP (freshly thawed and diluted 4,000 fold with 1.0% powdered milk in PBS). After a final cycle of four washes with PBS-T, 0.2 mL of freshly prepared PDA substrate solution (0.4 mg/mL PDA and 0.01% H2O2 in 0.05 M citric acid containing 0.15 M sodium dibasic phosphate, pH 5.0) was dispensed into each of the wells and incubated in the dark at 22 °C for 30-60 minutes. Sulfuric acid (4 N, 0.05 mL/well) was added to stop the reaction, and the final absorbance of each well (490 nm) was recorded. The presence of free alachlor in samples inhibited the binding of the antibody to alachlor-BSA, resulting in an inhibition of the development of absorbance at 490 nm. The amount of free alachlor was thus inversely proportional to the intensity of color produced. The level of alachlor in unknown water samples was calculated based on alachlor standards which had been analyzed simultaneously on each plate. Alachlor standards (0, 0.2, 0.5, 1.0, 3.0, 5.0, and 8.0 ppb in deionized water) were stored at -20 °C in 1 mL portions, and were freshly thawed for each assay. 

Cross-Reactivitv Studies. The reactivity of the antibodies with a series of alachlor analogues was examined. The concentration of an analyte producing a 50% inhibition in absorbance in the ELISA was defined as its IC50 value (50% inhibition concentration). The IC50 value of alachlor in picomoles per mL was divided by the corresponding value from the analyte and multiplied by 100 to produce the percentage cross-reactivity values. The percentage crossreactivity of the antibodies to alachlor calculated in this way was 100%. 

Figure 2. Inhibition ELISA analysis of alachlor in deionized water. Means and standard deviations were calculated from 20 separate analyses.

Inhibition of the incorporation of uridine into RNA is caused by the herbicides referred to as the chloroacetanilides (e.g., acetochlor, alachlor, butachlor, and several others) and a group of fungicides referred to as phe-nylamides (metalaxyl, ofurace, and oxadixyl). They have similar structure and mode of action ... 

The activity of soil dehydrogenase at the beginning of the soil dilution experiment in 0, 10, 50, and 90% diluted waste-pile soil was 18, 0, 65, and 138%, respectively, of the activity in CHECK soil. After 21 days, soil dehydrogenase was still inhibited in the 0 and 10% diluted waste-pile soil. The inhibition of enzyme activity suggests that high concentrations of alachlor may be toxic, but microbial bioactivity can be restored if contaminated soil is diluted enough. 

It is interesting that although alachlor is closely related to acylanilides, it does not inhibit the Hill reaction (Chandler et al., 1972). 

On the bais of information presently available, the biological mode of action of alachlor is probably the inhibition of protein synthesis. 

Herbicides have been reported to inhibit cell division. Alachlor and metolachlor at 1 yM significantly reduced the frequency of cell division in oat root tips after 30 h (19). 

The action of the tested herbicides was classified as follows (a) growth inhibition in the light without rapid phytotoxicity (metribuzin), (b) bleaching of the cells without rapid phytotoxicity (fluridone), (c) rapid phytotoxicity in the light (nitrofen, paraquat), (d) rapid phytotoxicity in the dark (PCP), (e) direct and rapid inhibition of cell division but not of cell growth (amiprophos -methyl, chlorpropham, trifluralin) and (f) indirect (delayed) inhibition of cell division and growth (alachlor). 

In the case of alachlor, interesting new information has been obtained. The inhibition by alachlor is reversible and concerns a metabolic reaction or process that is required for normal cell division. The herbicide alachlor might specifically interfere with the regulation of cell division. 

Cross-reactivity is expressed as the ratio of the concentration of alachlor to each test compound at level that gives 50% inhibition of the immunoassay maximal binding level. 

These findings were in contrast to a report of competitive binding of the triti-ated dichloroacetamide safener R-29148 and the herbicides EPTC or alachlor at a proteinaceous component of maize seedling extracts. In addition, a good correlation was observed between competitive inhibition of [ H] R-29148 binding by other dichloroacetamide compounds and their effectiveness as safeners. This was taken as support for the hypothesis that dichloroacetamide safeners act as receptor antagonists for the herbicides EPTC and alachlor [24],... 

In the green alga Scenedesmus acutus the uptake of 2- C) acetate, a precursor of fatty acid synthesis, is inhibited with 100 pM alachlor and 100 pM metazachlor within an incubation time of 4 h (1). There is also shown that the incorporation of the labeled acetate in acyl lipids is inhibited. After 16 h and 40 h incubation with a herbicide concentration of 5 yM the fatty acid content of the green alga changed, as shown in the table. 

In the presence of metazachlor, alachlor or dimethenamid (5 pM) fatty acid desaturation in S, acutus was strongly inhibited after 40 h. Under these conditions the relative amounts of polyunsaturated fatty acids decreased while palmitic and oleic acids accumulated (Table 1). In an in-vitro assay, desaturation of oleoyl-CoA by microsomes was also decreased by chloroacetamides, suggesting a direct influence of the herbicides on oleic acid desaturation, although 25 pM were necessary for a significant inhibition (Table 2). l C-oleic acid fed to the algae was rapidly incorporated into the lipids and further desaturated. It was also incorporated into a precipitate obtained after saponification of the cells or lipid extraction. Radioactivity in that fraction was dramatically reduced by metazachlor, a concentration between 10 nM and 100 nM was sufficient for a 50% inhibition [3]. This effect was correlated with... 

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