S-ethyl Dipropylthiocarbamate Research Articles

Evidence of transboundary movement of chemicals from Mexico to the U.S. in Tijuana River Estuary sediments

The Tijuana River Estuary (TRE) has been a public health hazard and point of contention between the United States and Mexico for decades, with sources of pollution on both sides of the border. The goal of our study is to determine the presence and dynamics of chemical contamination in the TRE. We sampled sediment from four TRE locations in the U.S. during stable dry conditions and immediately after a wet weather period. Organic chemicals were initially screened with non-targeted analysis using gas chromatography high-resolution mass spectrometry (GC/HRMS) that tentatively identified 6978 chemicals in the NIST 20 database. These tentative identifications were filtered using the USEPA CompTox database to guide quantitative targeted analysis at detection limits below 1 ng/g dry weight sediment. Quantitative targeted analysis of 152 organic pollutants and 18 inorganic elements via GC/HRMS revealed generally higher concentrations of contaminants in dry weather sediments compared to wet weather sediments. The highest concentrations of all chemical classes were detected at the site closest to the U.S.-Mexico border, followed by an urban area near Imperial Beach, California, U.S. All sites exhibited a mixture of petrogenic and pyrogenic polycyclic aromatic hydrocarbons (PAHs). Current-use pesticides were dominated by pyrethroid insecticides and the thiocarbamate herbicide s-Ethyl dipropylthiocarbamate (EPTC), while the U.S.-banned organochlorine pesticides were dominated by chlordanes, dieldrin, and dichlorodiphenyltrichloroethane (DDT) and its degradation byproducts. Polychlorinated biphenyl (PCB) concentrations were greatest at the site closest to the U.S.-Mexico border but in the low nanogram-per-gram range. Phthalates were only found at the same site, with relatively high concentrations of bis(2-ethylhexyl) phthalate. This study provides positive identification and quantitative concentrations for organic pollutants in TRE sediments. Our data suggest that there are multiple sources of chemical contamination in the estuary, including possible transboundary movement of pollutants from Mexico.

Purple Nutsedge Management in Florida Strawberry with Herbicides and a Modified Florida 3-Way Fumigation Program

The “Florida 3-way” consists of chloropicrin 35% + 1,3-dichloropropene 65% followed by minicoulter application of metam potassium. We evaluated the efficacy of a modified version of the Florida 3-way in which chloropicrin 35% + 1,3-dichloropropene 65% was used as primary bed fumigant and consisted of different drip tape application timings (at the time of bed formation and 2 weeks after bed formation) of metam potassium or the use of herbicides (sulfentrazone and s-ethyl dipropylthiocarbamate) as the supplemental application for the control of purple nutsedge (Cyperus rotundus) in strawberry (Fragaria ×ananassa) fields. Efficacy of modified Florida 3-way was not significantly different from standard Florida 3-way; however, supplemental herbicide such as s-ethyl dipropylthiocarbamate and sulfentrazone provided better purple nutsedge control than supplemental metam potassium application in one of two experimental growing seasons. Addition of metam potassium to the chloropicrin 35% + 1,3-dichloropropene 65% did not result in additional purple nutsedge control in Florida 3-way, which indicates the limitations of this approach.

Effects of Mulching and Preemergence Herbicide Placement on Yellow Nutsedge Control and Ornamental Plant Quality in Landscape Beds

Yellow nutsedge (Cyperus esculentus) is one of the most troublesome and widespread perennial weeds infesting landscape plantings in the United States. Few selective herbicides are available for managing this weed. A combination of organic mulch with preemergence herbicide may improve control efficacy at tuber emergence and reduce the need for subsequent postemergence applications. However, limited information is available on potential interactions between herbicide placement and mulching and their effect on yellow nutsedge control and landscape plant growth and quality. In this study, control efficacy of preemergence herbicide s-ethyl dipropylthiocarbamate (EPTC) applied at 0, 4, or 6 lb/acre above or under pine straw, pine nuggets, or shredded cypress mulches were evaluated in landscape beds infested with yellow nutsedge and planted with ‘Mystery’ gardenia (Gardenia jasminoides), ‘Stella de Oro’ daylily (Hemerocallis), and ‘Big Blue’ liriope (Liriope muscari). Pine nuggets provided greater yellow nutsedge control compared with shredded cypress during the first 6 weeks after treatment (WAT) in mulch-alone plots. All mulch-alone plots had similar yellow nutsedge shoot densities and were 40% to 60% less than untreated bare soil plots from 6 to 12 WAT. Control efficacy was greater when EPTC was applied under mulch compared with above-mulch applications regardless of mulch products. In addition, EPTC at low rate resulted in similar control as high rate when applied under mulch. No injury was observed on any ornamental plants treated with EPTC. Mulching improved growth, flowering, and overall visual quality of gardenia, but reduced number of flowers in daylily and aboveground biomass in liriope at some sample dates though their visual qualities were unaffected. Based on these preliminary data, EPTC applied preemergence before mulching a new landscape bed or replenishing an existing bed can improve yellow nutsedge control without injuring selected ornamental plants.

Characterization of Cupriavidus metallidurans CYP116B1 – A thiocarbamate herbicide oxygenating P450–phthalate dioxygenase reductase fusion protein

The novel cytochrome P450/redox partner fusion enzyme CYP116B1 from Cupriavidus metallidurans was expressed in and purified from Escherichia coli. Isolated CYP116B1 exhibited a characteristic Fe(II)CO complex with Soret maximum at 449 nm. EPR and resonance Raman analyses indicated low-spin, cysteinate-coordinated ferric haem iron at both 10 K and ambient temperature, respectively, for oxidized CYP116B1. The EPR of reduced CYP116B1 demonstrated stoichiometric binding of a 2Fe-2S cluster in the reductase domain. FMN binding in the reductase domain was confirmed by flavin fluorescence studies. Steady-state reduction of cytochrome c and ferricyanide were supported by both NADPH/NADH, with NADPH used more efficiently (K(m[NADPH]) = 0.9 ± 0.5 μM and K(m[NADH]) = 399.1 ± 52.1 μM). Stopped-flow studies of NAD(P)H-dependent electron transfer to the reductase confirmed the preference for NADPH. The reduction potential of the P450 haem iron was -301 ± 7 mV, with retention of haem thiolate ligation in the ferrous enzyme. Redox potentials for the 2Fe-2S and FMN cofactors were more positive than that of the haem iron. Multi-angle laser light scattering demonstrated CYP116B1 to be monomeric. Type I (substrate-like) binding of selected unsaturated fatty acids (myristoleic, palmitoleic and arachidonic acids) was shown, but these substrates were not oxidized by CYP116B1. However, CYP116B1 catalysed hydroxylation (on propyl chains) of the herbicides S-ethyl dipropylthiocarbamate (EPTC) and S-propyl dipropylthiocarbamate (vernolate), and the subsequent N-dealkylation of vernolate. CYP116B1 thus has similar thiocarbamate-oxidizing catalytic properties to Rhodoccocus erythropolis CYP116A1, a P450 involved in the oxidative degradation of EPTC.

Vegetable Crop Response to EPTC Applied Preemergence Under Low-Density Polyethylene and High Barrier Plastic Mulch

The continued phase-out of methyl bromide (MBr) challenges vegetable growers' abilities to control weeds in plasticulture production. Herbicides, such as EPTC (S-ethyl dipropylthiocarbamate), may be needed as part of a MBr alternative system. An experiment was conducted during the springs of 2008 and 2009 in Ty Ty, GA, to determine tomato, pepper, eggplant, and watermelon tolerance to EPTC applied under mulch. Treatments consisted of a factorial arrangement of four rates of EPTC (0, 2, 3, or 4 kg ai ha−1) and two plastic mulch types (low density polyethylene [LDPE] mulch or a high barrier mulch [HBM]). Each crop was planted 28 d after applying herbicides and laying mulch. EPTC, regardless of rate, applied under LDPE mulch did not impact plant growth, fruit number produced, or fruit weights for any crop. Conversely, pepper, tomato, and eggplant heights were reduced 65 to 72%, 30 to 75%, and 9 to 32%, respectively, by EPTC at 2 to 4 kg ai ha−1when applied under HBM. Similar trends were observed for crop yield; fruit number and weight were reduced by 71 to 84% for pepper, 36 to 76% for tomato, and 7 to 15% for eggplant when EPTC was applied at 2 to 4 kg ai ha−1as compared to the no EPTC HBM control. Watermelon stem lengths, fruit number, and fruit weights were not impacted by EPTC applied under HBM mulch. It appears as though HBMs reduce the loss of EPTC through volatilization, thereby increasing the dose present at time of planting. EPTC could be included as part of a MBr alternative system for tomato, pepper, eggplant, and watermelon when applied under LDPE mulch, and may also be applied at labeled rates with the HBM utilized in this experiment for watermelon.

Genetic Variation in Base Excision Repair Pathway Genes, Pesticide Exposure, and Prostate Cancer Risk

Background: Previous research indicates increased prostate cancer risk for pesticide applicators and pesticide manufacturing workers. Although underlying mechanisms are unknown, evidence suggests a role of oxidative DNA damage.Objectives: Because base excision repair (BER) is the predominant pathway involved in repairing oxidative damage, we evaluated interactions between 39 pesticides and 394 tag single-nucleotide polymorphisms (SNPs) for 31 BER genes among 776 prostate cancer cases and 1,444 male controls in a nested case–control study of white Agricultural Health Study (AHS) pesticide applicators.Methods: We used likelihood ratio tests from logistic regression models to determine p-values for interactions between three-level pesticide exposure variables (none/low/high) and SNPs (assuming a dominant model), and the false discovery rate (FDR) multiple comparison adjustment approach.Results: The interaction between fonofos and rs1983132 in NEIL3 [nei endonuclease VIII-like 3 (Escherichia coli)], which encodes a glycosylase that can initiate BER, was the most significant overall [interaction p-value (pinteract) = 9.3 × 10–6; FDR-adjusted p-value = 0.01]. Fonofos exposure was associated with a monotonic increase in prostate cancer risk among men with CT/TT genotypes for rs1983132 [odds ratios (95% confidence intervals) for low and high use compared with no use were 1.65 (0.91, 3.01) and 3.25 (1.78, 5.92), respectively], whereas fonofos was not associated with prostate cancer risk among men with the CC genotype. Carbofuran and S-ethyl dipropylthiocarbamate (EPTC) interacted similarly with rs1983132; however, these interactions did not meet an FDR < 0.2.Conclusions: Our significant finding regarding fonofos is consistent with previous AHS findings of increased prostate cancer risk with fonofos exposure among those with a family history of prostate cancer. Although requiring replication, our findings suggest a role of BER genetic variation in pesticide-associated prostate cancer risk.

UV absorption spectrum and Henry's law constant of EPTC

Both UV–visible absorption spectrum and Henry's law constants H of S-ethyl dipropylthiocarbamate (EPTC) were investigated in this work. Absolute values of molar absorptivity coefficients ɛ of EPTC in methanol were determined using a deuterium lamp over the wavelength range 233–343 nm at room temperature (298 ± 2 K). Absorbances were also measured at 253.7 nm using an Hg-lamp in the concentration range 10–426 mg L −1. The absolute value of ɛ at this wavelength, ɛ = 45 ± 4 M −1 cm −1, was then determined according to the Beer–Lambert's law. The quoted error corresponds to 2 σ obtained from the least square fit analysis and includes an estimated systematic error of 5% due to the uncertainties in aqueous concentrations. The absorbances measured were lower than 1.2 and did not exhibit any deviation from the Beer–Lambert's law. Henry's law constants H of EPTC were determined over the temperature range 278–293 K with a dynamic system based on the existence of an equilibrium at the water/air interface within the length of a microporous tube. The obtained data were used to derive the following Van't Hoff expression: ln H = (9134 ± 1180)/ T − (26.6 ± 3.9) leading to a mean value of 91 ± 22 M atm −1 at 293 K. The quoted errors are given at 2 σ level from the least-squares analysis and include the estimated systematic error of 5%. It is shown that, at a cumulus cloud temperature of 283 K, the fraction of EPTC in the atmospheric aqueous phase is negligible and therefore this compound will be mainly present in the gas phase.

Biological decomposition of herbicides (EPTC) by activated sludge in a slurry bioreactor

Biological treatment of hazardous chemical substances emitted into the environment has been expected to be a desirable treatment method. In this study the biodegradation of an herbicide, S-ethyl dipropylthiocarbamate (EPTC), has been investigated in an airlift bioreactor in batch experiments using waste activated sludge, freely suspended and immobilized, under aerobic conditions. The influence of activated sludge loadings (MLSS = 2000–9000 ppm), EPTC concentrations ( S o = 2–11 ppm) and aeration rates ( Q g = 0.4–3.5 l min −1) on the degradation rate was discussed. The results show that for a constant activated sludge concentration of 4162 ppm, the biological degradation rate of EPTC increased with increasing aeration rate up to 2.5 l min −1. Although the increase of activated sludge concentration enhanced the biological degradation rate, the higher aeration rate was required to suspend activated sludge uniformly through the reactor and supply enough oxygen to the activated sludge. The maximum biodegradation rate was 0.16 h −1 at an activated sludge loading of 6000 ppm and aeration rate of 3.5 l min −1. Also, it was observed that the biodegradation rates for immobilized activated sludge were higher than those for freely suspended activated sludge. Finally a mathematical model was proposed to describe the biodegradation of EPTC in the bioreactor.

Environmental monitoring and ecological risk assessment for pesticide contamination and effects in Lake Pamvotis, northwestern Greece

Monitoring of pesticide residues in water and sediments was conducted as a basis for subsequent ecotoxicological risk assessment for the shallow eutrophic Lake Pamvotis, northwestern Greece. During a one-year study period, atrazine, desethylatrazine (DEA), simazine, diazinon, malathion, oxamyl, carbofuran, and ethion were detected in water and atrazine, desethylatrazine, diazinon, and s-ethyl dipropylthiocarbamate (EPTC) in sediments, all at ppb concentration level. Temporal variation in pesticide concentrations was observed. Highest residue levels for most pesticides in both water and sediment matrices occurred in the May to July period with the exception of atrazine and DEA, which show highest levels in water during the September to November period. The ecological risk associated with pesticide contamination was assessed using two different methods: The toxic unit method, which provides a first indication of the relative contribution of detected pesticides to the total toxicity and a probabilistic approach, and the inverse method of Van Straalen and Denneman, which is used to quantify the ecological risk. The maximum percentage of the ecological risk was 10.3 and 51.8% for water and 17.2 and 70.6% for sediment, based on acute and chronic level, respectively. These results show that pesticides exert a significant pressure on the aquatic system of Lake Pamvotis, especially for the chronic-effect level. Simple quotient methods should be coupled with higher-tier risk assessment, especially if restoration activities on lake ecosystems are to be undertaken for sustainable development.

Agricultural exposure to carbamate pesticides and risk of non-Hodgkin lymphoma.

Recent epidemiological studies have suggested an increased risk of non-Hodgkin lymphoma (NHL) from carbamate insecticide use among farmers. To further explore the possible relationships, we conducted a pooled analysis of three population-based case-control studies conducted in four midwestern states in the United States. A total of 985 white male subjects and 2895 control subjects were included in this analysis. Unconditional logistic regression was used to estimate the association and control for confounding. Compared with nonfarmers, farmers who had ever used carbamate pesticides had a 30% to 50% increased risk of NHL, whereas farmers without carbamate pesticide use showed no increased risk. Analyses for individual carbamate pesticides found a more consistent association with Sevin but not carbofuran, butylate, or S-ethyl dipropylthiocarbamate plus protectant. Among farmers using Sevin, the risk of NHL was limited to those who personally handled the product, those who first used the product for > or = 20 years before their disease diagnosis, and those who used the product for a longer period. These associations persisted after adjusting for other major classes of pesticides. These results suggest an increased risk of NHL associated with carbamate pesticide use, particularly Sevin. Further investigation of the association is warranted.

Oviposition by Plutella xylostella (Lepidoptera: Plutellidae) and effects of phylloplane waxiness.

Three approaches were used to investigate effects of host plant epicuticular waxes on oviposition site selection by Plutella xylostella (L.). In the first approach, oviposition on canola (Brassica napus L.) that had epicuticular wax reduced by application of a carbamate herbicide (S-ethyl dipropylthiocarbamate) was compared with oviposition on untreated control plants. A second approach compared oviposition on sibling strains of B. napus with different wax blooms (glossy and waxy), and a third approach compared oviposition by P. xylostella on parafilm that had been applied to glossy and waxy B. napus strains for transfer of leaf components. Significantly more eggs were deposited on herbicide-treated plants (with reduced epicuticular wax) than on untreated controls. Similarly, more eggs were deposited on glossy than on waxy sibling strains of B. napus. In parafilm assays significantly more eggs were deposited on treated than on untreated parafilm. Several mechanisms could explain the differences in attractiveness of surfaces with varying wax content as oviposition sites for P. xylostella, including visual, chemical, and tactile differences between substrates. These mechanisms are discussed.

Characterization of the expression of the thcB gene, coding for a pesticide-degrading cytochrome P-450 in Rhodococcus strains.

A cytochrome P-450 system in Rhodococcus strains, encoded by thcB, thcC, and thcD, participates in the degradation of thiocarbamates and several other pesticides. The regulation of the system was investigated by fusing a truncated lacZ in frame to thcB, the structural gene for the cytochrome P-450 monooxygenase. Analysis of the thcB-lacZ fusion showed that the expression of thcB was 10-fold higher in the presence of the herbicide EPTC (s-ethyl dipropylthiocarbamate). Similar enhancement of the thcB-lacZ expression was found with other thiocarbamate pesticides. Atrazine, simazine, or carbofuran, although metabolized by the system, had no effect on the thcB-lacZ expression. The presence of glucose slightly increased the expression of thcB-lacZ, indicating no catabolic repression of the thcB-lacZ expression. The expression of thcB-lacZ was decreased more than twofold in Luria-Bertani medium. This was due in part to cysteine, which repressed thcB-lacZ expression. It was confirmed that the thcR gene, which is transcribed divergently from thcB, codes for a positive regulatory protein which is essential for the thcB-lacZ expression. Studies of the thcR-lacZ protein fusion showed that the thcR gene is expressed constitutively.

Specific binding of a dichloroacetamide herbicide safener in maize at a site that also binds thiocarbamate and chloroacetanilide herbicides.

Dichloroacetamide safeners such as N,N-diallyl-2,2-dichloroacetamide and (R,S)-3-dichloroacetyl-2,2,5-trimethyl-1,3-oxazolidine protect maize (Zea mays) against injury from thiocarbamate and chloroacetanilide herbicides. Binding activity of tritium-labeled (R,S)-3-dichloroacetyl-2,2,5-trimethyl-1,3-oxazolidine (15 Ci/mmol; referred to as [3H]Saf) was characterized in extracts of etiolated maize seedlings. The binding is saturable, involves a single class of binding sites (Kd 0.12 microM; maximal binding in coleoptiles 0.53 nmol/g fresh weight, equivalent to 55 pmol/mg protein), and is sensitive to boiling and protease treatment. Binding in etiolated maize seedlings is highest in the coleoptile and lowest in the leaves. Binding of [3H]Saf also occurs in etiolated sorghum (Sorghum bicolor) shoots but not several other cereals. There is a good correlation between known safener effectiveness and the concentration that inhibits [3H]Saf binding half-maximally among 21 dichloroacetamides and related compounds. N,N-Diallyl-2,2-dichloroacetamide had the lowest inhibitor concentration that reduces specific binding by 50% (IC50), 0.01 microM. [3H]Saf binding is inhibited by 4 chloroacetanilide herbicides with IC50 values of 0.07 to 0.48 microM and by 12 thiocarbamate herbicides and analogs with IC50 values of 0.06 to 2.3 microM. The inhibition of [3H]Saf binding by alachlor and S-ethyl dipropylthiocarbamate is competitive.

Cloning of the genes for degradation of the herbicides EPTC (S-ethyl dipropylthiocarbamate) and atrazine from Rhodococcus sp. strain TE1

The degradation of the herbicides EPTC (S-ethyl dipropylthiocarbamate) and atrazine (2-chloro-4-ethyl-amino-6-isopropylamino-1,3,5-triazine) is associated with an indigenous plasmid in Rhodococcus sp. strain TE1. Plasmid DNA libraries of Rhodococcus sp. strain TE1 were constructed in a Rhodococcus-Escherichia coli shuttle vector, pBS305, and transferred into Rhodococcus sp. strain TE3, a derivative of Rhodococcus sp. strain TE1 lacking herbicide degradation activity, to select transformants capable of growing on EPTC as the sole source of carbon (EPTC+). Analysis of plasmids from the EPTC+ transformants indicated that the eptA gene, which codes for the enzyme required for EPTC degradation, residues on a 6.2-kb KpnI fragment. The cloned fragment also harbored the gene required for atrazine N dealkylation (atrA). The plasmid carrying the cloned fragment could be electroporated into a number of other Rhodococcus strains in which both eptA and atrA were fully expressed. No expression of the cloned genes was evident in E. coli strains. Subcloning of the 6.2-kb fragment to distinguish between EPTC- and atrazine-degrading genes was not successful.

A single cytochrome P-450 system is involved in degradation of the herbicides EPTC (S-ethyl dipropylthiocarbamate) and atrazine by Rhodococcus sp. strain NI86/21

During atrazine degradation by Rhodococcus sp. strain N186/21, N-dealkylated metabolites and an hydroxyisopropyl derivative are produced. The cytochrome P-450 system that is involved in degradation of thiocarbamate herbicides by strain N186/21 (I. Nagy, G. Schoofs, F. Compernolle, P. Proost, J. Vanderleyden, and R. De Mot, J. Bacteriol. 177:676-687, 1995) is also required for atrazine degradation. Atrazine-degrading activity was conferred on the atrazine-negative strains, mutant FAJ2027 of Rhodococcus sp. strain N186/21 and Rhodococcus erythropolis SQ1, upon transformation with the genes encoding the cytochrome P-450 system.

Delayed and enhanced biodegradation of soil‐applied diphenamid, carbendazim, and aldicarb

Recent studies have demonstrated that interaction between various agrochemicals and soil microorganisms may either slow down or enhance processes of degradation. Soil disinfestation is employed for the control of soil-borne pathogens and weeds. Soil application of such broad-spectrum biocides, as well as some more selective chemicals, has a strong effect on microbial activity, which may result in drastic reduction in the rate of degradation of pesticides applied to such treated soils. Application of pesticides to previously disinfested soils may extend their biological activity, which in the case of herbicides could cause phytotoxic damage to the next crop. In contrast, repeated application of the same or structurally related pesticides may result in a selective buildup of microbial populations capable of degrading the pesticide at much faster rates. Cases of accelerated degradation were reported for pesticides belonging to various chemical groups. Studies were conducted to evaluate the mechanisms of accelerated degradation. For several pesticides it has been shown that soil fungi are involved in their normal degradation, but not in their accelerated degradation. The shift in the rate of degradation of pesticides such as diphenamid, benomyl, and S-ethyl dipropylthiocarbamate, in soils that have acquired accelerated degradation, seems to be associated with the buildup of populations of bacterial degraders. Moreover, it has been shown that for the herbicide diphenamide, accelerated degradation is apparently linked to the induction of an oxidative demethylation process in soil bacteria, which might be analogous to the development of resistance in pests. Contrary to studies demonstrating accelerated degradation of the systemic insecticide aldicarb and accumulation of aldicarb sulfoxide in non-history soils, our work has shown that repeated application of this carbamate at several locations in Israel over a 10-year period did not induce accelerated degradation. It should be pointed out that in the Israeli soils there was only minimal formation of aldicarb sulfoxide. These studies were performed in soils with a pH ranging from 7.8 to 8.3, which is higher than the pH reported for soils where accelerated degradation was detected.

Inhibitory effect of parathion on the bacterial degradation of EPTC

Effects of organophosphorus insecticides on the degradation of EPTC (S-ethyl dipropylthiocarbamate) by Rhodococcus TE1 isolated from herbicide-exposed soil were studied. Among the insecticides tested, parathion (O,O-diethyl O-p-nitrophenyl phosphorothioate) was found to inhibit EPTC degradation greatly. This effect was mainly due to the inhibition of growth of the bacterial strain TE1 by parathion. Parathion also inhibited the growth of other Rhodococcus strains irrespective of their ability to degrade EPTC. Rhodococcus TE1 was also shown to degrade parathion (...)

Bioactivity of controlled release formulations of starch-encapsulated EPTC

Using a bioassay technique, the biological activities of starch-encapsulated formulations of EPTC (S-ethyl dipropylthiocarbamate) were determined in relationship to their controlled release characteristics. The bioactivity of the highly volatile herbicide EPTC was retained on a wet soil surface for 6 to 8 days by starch encapsulation utilizing several crosslinking processes (both chemical and non-chemical) and starches with different ratios of amylopectin to amylose. The rate of release, a measure of the integrity of the granule, depended on the nature of the starch and the crosslinking process. With the herbicide EPTC, encapsulation with a pearl or high amylose starch utilizing the jet-cooking process produced the best controlled release formulation even under the most adverse conditions.

Herbicidal disruption of proton gradient development and maintenance by plasmalemma and tonoplast vesicles from oat root

Quinacrine fluorescence quenching was used to evaluate the effects of 23 herbicides (100 μ M) on ATP-dependent proton gradient development and maintenance by low-density (tonoplast-enriched) and high-density (plasmalemma-enriched) vesicles from oat ( Avena sativa L.) roots. Naptalam stimulated the rate of proton gradient formation but did not stimulate total ATPase activity of high-density vesicles. Naptalam action was specific for this vesicle type. (2-Methyl-4-chlorophenoxy)acetic acid, dinitramine, chlorpropham, and S-ethyl dipropylthiocarbamate inhibited the initial rate of proton gradient formation and decreased the magnitude of the equilibrium proton gradient formed by low-density vesicles. Dinitramine and chlorpropham were also effective disruptors of proton gradient formation by high-density vesicles. Diclofop-methyl, fluazifop-butyl, and flamprop-isopropyl altered proton gradient generation and/or maintenance across both vesicle types. The free acid forms of these compounds were less effective disruptors than the ester forms. ATPase activity of both high- and low-density vesicles was either unaffected or slightly stimulated by these compounds. Both acifluorfen and alachlor accelerated the rate of decay of proton gradients formed across low-density but not high-density vesicles and stimulated the KCl, Mg 2+-ATPase activity of low-density but not high-density vesicles. Atrazine, metribuzin, dalapon, glyphosate, amitrole, pyrazon, picloram, and bentazon did not affect proton-gradient formation or maintenance by either vesicle type. These results support the hypothesis that some herbicides can have rapid, direct effects on proton gradient maintenance by the plasmalemma and the tonoplast in plant cells.

S-Ethyl dipropylthiocarbamate (EPTC) and 2,2-dichloro- N,N-di-2-propenylacetamide (Dichlormid) inhibitions of synthesis of acetyl-coenzyme A derivatives

[2- 14C]Acetate incorporation into acetyl-coenzyme A (acetyl-CoA) in wheat ( Triticum aestivum L. cv Stacy) chloroplasts was inhibited by S-ethyl dipropylthiocarbamate (EPTC, 0.01 μ M) and the inhibition was reversed by 90 μ M acetate. [2- 14C]Pyruvate was converted to acetyl-CoA by the pyruvate dehydrogenase complex (PDC) in wheat chloroplasts and the conversion was inhibited by EPTC (0.01 μ M). The inhibition was reversed by 90 μ M pyruvate. Production of NADH by wheat (cv. Holly) mitochondrial PDC was inhibited 10% by 3.3 10 −14 M EPTC and 90% by 0.33 μ M EPTC. Mitochondrial 2-oxoglutarate dehydrogenase complex activity was inhibited 65% by 0.033 μ M EPTC. Dichlormid (2,2-dichloro- N,N-di-2-propenylacetamide, 0.01 μ M) inhibited the incorporation of [2- 14C]acetate into wheat chloroplast acetyl-CoA and the inhibition was reversed by 90 μ M acetate. Dichlormid (0.01 μ M) also inhibited the chloroplastic conversion of [2- 14C]pyruvate into acetyl-CoA and partially reversed the inhibition by EPTC (0.1 μ M) of conversion of [2- 14C]pyruvate to acetyl-CoA.