Biochemical response of inbred and hybrid corn (Zea mays L.) to R-25788 and its distribution with EPTC in corn seedlings

The average endogenous GSH content of eight lines of inbred corn was almost twofold greater than ten varieties of hybrid corn. When inbred and hybrid corn lines were treated with R-25788, the average GSH content increased by 56 and 95%, respectively. R-25788 protected two special inbred corn lines, GT 112 (atrazine susceptible) and GT 112 RfRf (atrazine resistant) from EPTC injury by increasing the GSH content and GSH S-transferase activity in roots. Most of the radiolabel from [¹⁴C]R-25788-treated plants remained in the root tissues whereas the radiolabel in [¹⁴C]EPTC-treated plants was evenly distributed between foliar and root tissues. From radiolabel experiments, hybrid corn seedlings were found to absorb more R-25788 from soil than EPTC. There was no difference between inbred and hybrid corn in the amounts of R-25788 or EPTC taken up or in the enhancement of GSH S-transferase activity caused by R-25788.     

Comparative metabolism of atrazine and EPTC in proso millet (Panicum miliaceum L.) and corn

The purpose of this study was to examine the differential activities of proso millet (Panicum miliaceum L.) and corn (Zea mays L.) with respect to atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-S-triazine] and EPTC (S-ethyldipropyl thiocarbamate) metabolism. GSH-S-transferase was isolated from proso millet shoots and roots. When assayed spectrophotometrically using CDNB (1-chloro 2,4-dinitrobenzene) as a substrate, the shoot enzyme had only 10% of the activity of corn shoot enzyme while the root enzyme had 33% the activity of corn root enzyme. However, when proso millet shoot GSH-S-transferase was assayed in vitro using ¹⁴C-ring-labeled atrazine, it degraded the atrazine to water-soluble products at the same rate as the corn shoot enzyme. Incubation of excised proso millet and corn roots with [¹⁴C]EPTC indicated that uptake of EPTC was similar in both plants. However, proso millet metabolized the EPTC to water-soluble products at only half the rate of corn. Glutathione levels of proso millet roots were 35.9 μg GSH/g fresh wt, compared with 65.4 μg GSH/g fresh wt for corn. However, a 2.5-day pretreatment with R-25788 (N,N-diallyl-2-2-dichloroacetamide) elevated proso millet GSH levels to 62.7 μg GSH/g fresh wt. R-25788 did not elevate the activity of proso millet GSH-S-transferase, in contrast to its effects on corn. We conclude that differences in response to atrazine and EPTC in proso millet and corn are a result of their differential metabolism.     

Gibberellin precursor biosynthesis inhibition by EPTC and reversal by R-25788

S-ethyl dipropylthiocarbamate (EPTC) inhibited gibberellic acid (GA) precursor biosynthesis in a cell-free enzyme preparation from unruptured, etiolated sorghum (Sorghum bicolor L. cv. G522 DR) coleoptiles. EPTC, 1 μM, inhibited incorporation of [¹⁴C]mevalonic acid into kaurene 60%, while 10 μM EPTC inhibited ¹⁴C incorporation into kaurene 90%. The precursor of kaurene cyclization (GGPP) increased in ¹⁴C content at both EPTC concentrations. R-25788 reversed the EPTC inhibition of kaurene synthesis. Kaurene oxidation was modified by both EPTC and R-25788. Hypothesized modes of action for EPTC and R-25788 are (a) inhibition of GA synthesis, (b) increased peroxidase activity resulting in increased lignification, (c) increased detoxification by sulfoxidation and carbamoylation, and (d) inhibition of fatty acid synthesis and/or desaturation. These hypotheses are discussed with three of them being incorporated into one working unit which correlates with EPTC and R-25788 symptom phenology. The fourth hypothesis could also fit into this general pattern.     

The effect of CDAA (N,N,-diallyl-2-chloroacetamide) pretreatments on subsequent CDAA injury to corn (Zea mays L.)

The effects of CDAA (N,N-diallyl-2-chloroacetamide) pretreatment on subsequent CDAA injury to corn were examined and compared with the effects of the herbicide protectant R-25788 (N,N,-diallyl-2,2-dichloroacetamide). In addition, the effects of CDAA pretreatment on subsequent CDAA metabolism were determined. It was found that 5μM CDAA protected corn from injury by 200 μM CDAA when given as a 2.5- or 1-day pretreatment. R-25788 at similar concentrations did not protect corn from subsequent R-25788 injury. Pretreatment with CDAA increased GSH levels of corn roots by 61% within 1 day, and these levels did not increase with a longer 2.5-day pretreatment with CDAA. GSH-S-transferase activity was assayed spectrophotometrically using CDNB (1-chloro-2,4-dinitrobenzene). A 1-day pretreatment with CDAA increased the root GSH-S-transferase activity by 35%, but did not affect shoot GSH-S-transferase activity. A 2.5-day pretreatment resulted in a 50% increase in root GSH-S-transferase activity but no response of the shoot enzyme was observed. Even longer pretreatments with CDAA did not result in any further increases in enzyme activity. When corn roots pretreated with CDAA for 2.5 days were excised and incubated with radiolabeled CDAA, they exhibited greater rates of uptake and metabolism than did nonpretreated roots. With in vitro studies, a fairly high rate of nonenzymatic degradation of CDAA was observed. However, the enzymatic rate was always double that of the nonenzymatic rate under the experimental conditions used. It is concluded that elevations in the GSH levels and GSH-S-transferase activities of corn roots following CDAA pretreatments may be involved in the protection of corn from subsequent CDAA injury.     

Rapid effects of a thiocarbamate herbicide and its dichloroacetamide protectant on macromolecular syntheses and glutathione levels in maize cell cultures

The rapid effects of the thiocarbamate herbicide S-ethyl dipropyl thiocarbamate (EPTC) and the herbicide protectant N,N-diallyl-2,2-dichloroacetamide (DDCA) on macromolecular syntheses and glutathione (GSH) levels in maize cell cultures were studied to determine whether stimulation of GSH could be the primary mechanism of action of DDCA. EPTC (0.5 and 1 mM) reduced incorporation of radioactive precursors within 1 hr after treatment, and affected incorporation of [³H]acetate into lipids more than incorporation of [³H]adenosine into acid-precipitable nucleic acids, or [¹⁴C]protein hydrolysate into protein. [¹⁴C]EPTC was rapidly biotransformed within 8 hr by maize cell suspensions. Measureable decreases in GSH levels following treatment with 1 mM EPTC occurred after 15 hr. DDCA stimulated incorporation of [³H]acetate into lipids within 4 hr but did not affect incorporation of [¹⁴C]protein hydrolysate into protein or [³H]adenosine incorporation into nucleic acids. Measureable increases in GSH following DDCA treatment began after 12 hr. Treatment with EPTC and DDCA in combination inhibited incorporation of [³H]acetate into lipids less than EPTC given alone. Increases in GSH levels could be observed following pretreatments with glutathione precursors, but no protectant activity could be detected, in contrast to treatments with DDCA. It is suggested that DDCA has an initial rapid effect on lipid metabolism followed by a slower effect involving increases in cellular GSH.     

Comparative studies of safeners for the prevention of EPTC injury in maize

The herbicide safener N-dichloroacetyl-1-oxa-4-aza-spiro-4,5-decane (AD-67) is of similar efficiency as the extensively used N.N-diallyl-2,2-dichloroacetamide (R-25788) and the structurally related 3-(dichloroacetyl)-2,2-dimethyl-1,3-oxa-zolidine (AD-2) in reducing EPTC [S-ethyl-N,N-dipropyl (thiocarhamate)] injury to maize (Zea mays L. cv. KSC 360). EPTC treatment produces growth retardation and deformities and inhibits CO₂ fixation. It does not reduce epicuticular lipids appreciably but affects wax arrangement on the leaf surface. When EPTC is applied together with one of these safeners, these injuries are not observed. All three safeners act similarly. Each prevents the herbicide-induced aggregation of epicuticular wax of maize, thereby protecting the plants against the formation of areas where the underlying cuticle layers are exposed and increase in transpiration.     

Potential antidotes against acetanilide herbicide injury to corn (Zea mays)*

R-25788 (2,2-Dichloro-N,N-diallylacetamide) was the most effective of six potential antidotes evaluated to counter corn (Zea mays L.) injury from the acetanilide herbicides alachlor, metolachlor, acetochlor, H-22234 (N-chloroacetyl-N-(2,6-diethylphenyl)glycine ethyl ester), and H-26910 (N-chloroacetyl-N-(2-methyl-6-cthylphenyl)glycine isopropyl ester). The other potential antidotes in order of decreasing effectiveness were: R-29148 (2,2-dimethyl-5-methyl-dichloroacetyloxazolidine), NA (1,8-naphthalic anhydride), CDAA (2-chloro-N,N-diallylacetamide), Carboxin (2,3-dihydro-5-carboxanilido-6-methyl-l,4-oxathiin), and gibberellin (GA₃). GA₃ only partly relieved the stunting of corn caused by EPTC and metolachlor and did not prevent other herbicide injury symptoms, suggesting that the mode of action of EPTC and metolachlor is not to simply block GA₃ synthesis. R-25788 protected corn equally well from acetanilide or EPTC injury. Produits protecteurs du maïs (Zea mays) contre les dommages provoqués par les acétanilides herbicides Le R-25788 (2,2-dichloro-N.N-diallylacétamide) s'est révéléêtre le plus efficace de six produits protecteurs essayés pour préserver le maïs (Zeas mays L.) des dégâts provoqués par des acétanilides herbicides: alachlore, métolachlore, acétochlore, H-22234 (ester éthylique de la N-chloracétyl-N-(2,6-diéthylphényl) glycine) et H-26910 (ester isopropylique de la N-chloroacétyl-N-(2-méthyl-6-éthylphényl) glycine. Les autres produits protecteurs potentiels ont été, dans l'ordre d'efficacité décroissante: le R-29148 (2,2-diméthyl-5-méthyl-dichloroacéthyloxazolidine), l'AN (anhydride 1.8-naphtalique), le CDAA (2-chloro-N-N-diallylacétamide), la carboxyne (2,3-dihydro-5-carboxanilido-6-méthyl-l,4-oxathiine) et la gibbérelline (A₃ G). Cette dernière a seulement atténué le rabou-grissement provoqué par l.EPTC et le métolachlore chez le maïs. Elle n'a pas supprimé les symptômes de dommages provoqués par les autres herbicides, ce qui suggère que le mode d'action de I'EPTC et du métolachlore ne consiste pas seulement en un blocage de la synthèse de la gibbérelline. Le R-25788 a protégé le maïs des dommages provoqués par l'acétanilide ainsi que par I'EPTC. Potentielle Antidots zur Vermeidung von Acetanilid-Herbizid-schäden an Mais (Zea mays) Von sechs potentiellen Antidots, die geprüft wurden, um Schäden an Mais (Zea mays L.) durch Acetanilid-Herbizide zu vermeiden, war R-25788 (2,2-Dichlor-N,N-diallylacetamid) am wirksamsten. Die verwendeten Herbizide waren: Alachlor, Metolachlor, Acetochlor, H-22234 [N-Chloracetyl-N-(2,6- diäthylphenyl) glycin Älhylester] und H-26910 [N-Chloracelyl-N-(2-méthyl-6-äthylphenyl)glycin lsopropylester]. Die weiteren möglichen Antidots, in der Reihenfolge abnehmender Wirksamkeit, waren: R-29148 (2,2-Dimethyl-5-methyldichlorace-toxazolidin), NA (1,8-Naphthalsäureanhydrid), CDAA (2-Chlor-N,N-diallylacetamid), Carboxin (2,3-Dihydro-5-car- boxanilido-6-methyl-l,4-oxathiin) und Gibberellin (GA₃). durch GA₃ wurde die dureh EPTC und Metolachlor verursachte Stauchung des Mais nur teilweise vermieden. Die durch andere Herbizide verusachten Symptome liessen sich durch GA₃ nicht vermeiden, was darauf schliessen lässt, dass die Wirkungsweise von EPTC und Metolachlor nicht einfach mit einer Blockierung der GA₃ -Synthese zu erklären ist. R-25788 schützte Mais gleichermassen vor Acetanilid-, wie vor EPTC-Schäden.     

Competition between a thiocarbamate herbicide and herbicide protectants at the level of uptake into maize cells in culture

The rapid interactions between the herbicide S-ethyl dipropyl thiocarbamate (EPTC) and the structurally similar herbicide protectant N,N-diallyl 2,2-dichloroacetamide (DDCA) at the level of herbicide uptake were examined in maize cell cultures. When the two compounds were given simultaneously, DDCA inhibited uptake of [¹⁴C]EPTC into maize cells measured for 30 min. A Lineweaver-Burk plot indicated this inhibition to be competitive. N,N-Diallyl 2-chloroacetamide (CDAA), a compound similar in structure to DDCA, inhibited uptake to a lesser extent. Other protectants having no similarity in structure to either DDCA or EPTC had no inhibitory effect on the uptake of EPTC. The data suggest that competition between DDCA and EPTC for a site of uptake may be related to their similarity in chemical structure. Experiments with metabolic inhibitors suggested that uptake of EPTC is not via an active transport mechanism. We suggest that competition for uptake between EPTC and DDCA may represent the first step in a complex series of interactions between the herbicide and its protectant that contributes to the protection of maize from herbicide injury.     

Sulfoxidation of thiocarbamate herbicides and metabolism of thiocarbamate sulfoxides in living mice and liver enzyme systems

The microsome-NADPH system of mouse liver oxidizes each of benthiocarb, butylate, cycloate, EPTC, molinate, pebulate, and vernolate herbicide chemicals to the corresponding thiocarbamate sulfoxide which is then cleaved by the liver soluble-glutathione system. These sulfoxides are also detected as transient metabolites in the liver of mice injected with EPTC, molinate, pebulate, and vernolate but not with the other three thiocarbamates. Thiocarbamate sulfones are not detected as metabolites of the thiocarbamates. Studies in vivo and in vitro with [¹⁴C]EPTC and -pebulate or their corresponding sulfoxides and/or sulfones further indicate that sulfoxidation is the initial metabolic step in cleavage of the thiocarbamate ester group. Sulfoxidation appears to be a detoxification mechanism for thiocarbamate herbicides in mammals.     

Dichloroacetamide herbicide antidotes enhance sulfate metabolism in corn roots

The herbicide antidotes N,N-diallyl-2,2-dichloroacetamide (R25788) and 3-dichloroacetyl-2,2,5-trimethyloxazolidine (R29148) at ppm levels slightly enhance the uptake of [³⁵S]sulfate in corn roots and greatly increase its metabolism to “bound sulfide”, cysteine, and glutathione (GSH). The decrease in free sulfate content of the roots with R25788 is closely associated with an increase in GSH level. The sulfate content is decreased with an 8-hr exposure to R25788 and R29148 at 3 ppm and its decline continues through 48 hr to about 5% of the control level. Effects on sulfate content are evident at 24 hr even with 0.3–1 ppm of these antidotes. Several other mono- or dichloroacetamide antidotes at 30 ppm also decrease the free sulfate content of corn roots to about 34–60% of control levels within 24 hr. R25788 at 30 ppm has little or no effect at 24 hr on sulfate levels in corn leaves whether the plants are grown in the light or in the dark. R25788 and R29148 decrease sulfate levels in the leaves of milo and in whole pigweed plants, but not in barley, lambsquarters, water grass, wheat, or wild mustard. In increasing GSH biosynthesis, the antidote acts in corn prior to the reduction step to form bound sulfide; in fact, R25788 increases the specific activity of ATP sulfurylase, the first enzyme involved in sulfate assimilation. Thus, dichloroacetamides such as R25788 and R29148 provide a means to experimentally, and perhaps even practically, manipulate sulfate utilization in corn and some other plants.     

Herbicide antidotes—A review

The history of herbicide antidotes is reviewed, beginning with the exploration of compounds to protect wheat (Triticum aestivum L.) against barban in the early 1960s, and the later introduction of naphthalic anhydride (NA, naphthalene-1, 8-dicarboxy-licanhydride) as a seed dressing for protecting maize (Zea mays L.) against EPTC. This compound was largely replaced by Stauffer's R-25788 (N, N-diallyl-2, 2-dichloroacetamide) which has continued to be widely used in conjunction with EPTC and butylate in maize. This compound is highly specific to maize and can thus be applied in admixture with the herbicide, but has not proved of practical value on other crop species. NA on the other hand is less specific and is of potential value on sorghum [Sorghum bicolor (L.) Moench] and rice (Oryza sativa L.); experimental work continues on these crops. The only other antidote to be marketed so far is cyometrinil as a seed dressing for protecting sorghum against metolachlor and related herbicides. Other compounds are under development. Mode of action and structure-activity relations are discussed, as well as the current and future potential for antidotes in respect of the control of weed species in closely related crops, the increased options for herbicide use in minor crops and the possibility of reduced costs for broad spectrum weed control in major crops.     

Metabolism of EPTC in germinating corn: Sulfone as the true carbamoylating agent

Corn (Zea mays L. single cross hybrid Mv 620) was germinated in a petri dish with addition of carbonyl[¹⁴C]EPTC (S-ethyl-N,N-dipropylthiocarbamate). The shoots and roots of 4-day-old seedlings were crushed and extracted in 80% methanol. On the chromatogram of the extract three radioactive peaks were found. The main peak was identified as S-(N,N-dipropylcarbamoyl)-glutathione. For the comparison of carbamoylating ability [¹⁴C]EPTC, [¹⁴C]EPTC-sulfoxide, and [¹⁴C]EPTC-sulfone were incubated with glutathione. Only EPTC-sulfone reacted in the 10-day incubation time. In aquatic solutions EPTC and EPTC-sulfoxide proved to be stable during the 10 days compared to EPTC-sulfone which quickly degraded, S-(N,N-Dipropylcarbamoyl)-glutathione was converted to S-(N,N-dipropylcarbamoyl)-cysteine in corn shoot homogenate. [¹⁴C]EPTC, [¹⁴C]EPTC-sulfoxide and [¹⁴C]EPTC-sulfone were added to corn shoot homogeneates and each of the three mixtures were analyzed by chromatography after 1 day incubation. EPTC was partly oxidized to EPTC-sulfoxide. EPTC-sulfoxide did not change and EPTC-sulfone produced similar metabolites as had been found in the germination experiment.     

NN-DIALLYL-αα-DICHLOROACETAMIDE AS AN ANTIDOTE FOR EPTC AND OTHER HERBICIDES IN CORN

Summary. The efficacy of NN -diallyl-αα-dichloroacetamide (R-25788) as an antidote for reducing the injury of various herbicides in corn ( Zea mays L.) was tested under controlled conditions in growth rooms. The application of R-25788 to the soil as a pre-plant incorporated treatment to corn significantly reduced the toxicity often out of twenty-two herbicides tested. These ten herbicides were, in order of decreasing effectiveness of the antidote, EPTC, barban, sulfallate, vernolate, molinate, butylate, alachlor, pebulate, linuron and di-allate. In quartz sand nutrient culture, R-25788 was more effective as an antidote for barban applied to the foliage of corn than it was for barban applied to the roots.
Le NN- diallyl-αα-dichloroacétamide comme antidote de I'EPTC et autres herbicides dans le mais .     

Effect of herbicide antidotes on glutathione content and glutathione S-transferase activity of sorghum shoots

The effects of the herbicide antidotes CGA-92194 (α-[(1,3-dioxolan-2-yl-methoxy)-imino]benzeneacetonitrile), flurazole [phenylmethyl 2-chloro-4-(trifluoromethyl)-5-thiazolecarboxylate], dichlormid (2,2-dichloro-N,N-di-2-propenylacetamide), and naphthalic anhydride (1H,3H-naphtho(1,8-cd)-pyran-1,3-dione) on nonprotein thiol content, glutathione content, and glutathione S-transferase (GST) activity in etiolated sorghum (Sorghum bicolor L.) Moench) shoots were examined. CGA-92194 and naphthalic anhydride had no effect on nonprotein thiol or reduced glutathione (GSH) content of sorghum shoots. In contrast, dichlormid and flurazole increased nonprotein thiol content of sorghum shoots by 24 and 48%, respectively. These increases were largely attributable to an increase in GSH. The antidotes increased GST activity less than twofold when using CDNB (1-chloro-2,4-dinitrobenzene) as a substrate. In contrast, when using metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] as a substrate, the increase in GST activity in response to antidote treatment was much greater: flurazole (30-fold), CGA-92194 (20-fold), naphthalic anhydride (17-fold), dichlormid (5-fold). The degree of protection from metolachlor injury conferred by a particular antidote was strongly correlated (R² = 0.95) with its ability to enhance GST activity, as evaluated with metolachlor as substrate. A comparison of GST activity in untreated and CGA-92194-treated seedlings, over a range of metolachlor concentrations (0.5–500 μM), indicated that the relative enhancement of enzyme activity by CGA-92194 was greater at lower metolachlor concentrations. The rate of nonenzymatic conjugation of metolachlor and GSH in vitro was much less (on a gram fresh weight equivalent basis) than the enzymatic rate. These results are consistent with the hypothesis that the above antidotes protect sorghum by enhancing GST activity which results in accelerated detoxification of metolachlor via GSH conjugation.     

Metabolism of EPTC by a pure bacterial culture isolated from thiocarbamate-treated soil

A bacterial strain has been isolated from an enhanced thiocarbamate degradation soil and identified as Corynebacterium sp. The strain was capable of rapidly metabolizing EPTC in a liquid culture where the herbicide was the sole source of carbon. Evolution of high quantities of [¹⁴C]carbon dioxide was coupled with a rapid decline of [¹⁴C]EPTC in the medium; after 12 h incubation these accounted for, respectively, 60% and 0% of the recoverable radioactivity. Radioactivity in the polar extract increased gradually up to 20% after 6 h of incubation and then declined slowly. TLC analysis and identification based on comparison to reference compounds showed that the polar extract consisted of EPTC sulfoxide and two conjugates, EPTC-GSH and EPTC-cysteine (1·8%, 3·4%, and 16%, respectively). Piperonyl butoxide and tetcyclasis, but not tridiphane, were found to be effective inhibitors of EPTC metabolism in the bacterial culture, suggesting that the breakdown of EPTC might be carried out by a cytochrome P-450 monooxygenase-type activity. The thiocarbamate extender, dietholate, also strongly inhibited the metabolism of EPTC in bacterial culture. Based on these results it was postulated that the bacteria metabolize EPTC mainly by hydroxylation of the α-propyl carbon finally to release [¹⁴C]carbon dioxide, while EPTC sulfoxidation appears to be a minor route.     

安全剂R-28725保护玉米免受咪唑乙烟酸药害的机理研究

研究了安全剂R-28725对玉米的保护作用及对咪唑乙烟酸的解毒机理。当咪唑乙烟酸的使用量为20、40、60 g/hm2时,R-28725能够明显提高玉米株高、株鲜重和产量,直接增加植株体内谷胱甘肽(GSH)活性,增加咪唑乙烟酸与谷胱甘肽的轭合,从而达到解毒的目的。     

Inhibition of juvenile hormone biosynthesis in the tobacco hornworm, Manduca sexta, by a bisthiolcarbamate juvenoid and related compounds

Biosynthesis of juvenile hormone in the tobacco hornworm, Manduca sexta, is inhibited by the bisthiolcarbamate juvenoid N-ethyl-1,2-bis(isobutylthiolcarbamoyl)ethane both in vitro and in vivo. In vitro an extremely steep dose-response curve was obtained with an ID₅₀ value of 6 × 10^?6M. However, in vivo topical treatment with the compound resulted in mild JH antagonistic symptoms, suggesting rapid metabolism of the compound. In agreement with results from metabolic studies performed on plants and in mammals, sulfoxidation of the thiocarbamate S-(4-chlorobenzyl)N,N-diethylthiocarbamate resulted in an enhanced inhibitory effect on JH biosynthesis in vitro. This suggests that the corresponding thiocarbamate sulfoxides may act as intermediates in carbomylating critical thiol sites important in the terpenoid biosynthesis pathway. Furthermore, this study shows that these prototype compounds are interesting tools for further investigation of chemical inhibition of JH biosynthesis in insects.     

Effects of the herbicide EPTC and the protectant DDCA on incorporation and distribution of [2-14C]acetate into major lipid fractions of maize cell suspension cultures

The rapid effects of the herbicide EPTC (S-ethyl dipropylthiocarbamate) and the protectant DDCA (N,N-diallyl-2,2-dichloroacetamide) on [2-¹⁴C]acetate incorporation into lipids of maize cell cultures were studied in order to determine whether they act at similar sites of lipid synthesis. DDCA, at 0.05 mM and 0.1 mM, increased the incorporation of [2-¹⁴C]acetate into neutral lipids of a total lipid extract within 2 h. It had very little effect on the major polar lipid constituents. DDCA altered neither the distribution of label within the major lipid classes, nor turnover of the major lipids within 2 h. EPTC (0.1 mM) inhibited overall uptake of [2-¹⁴C]acetate into both neutral and polar lipids by about 30% after a 2-h incubation. The major polar lipid affected was an unidentified glycolipid. In addition to reducing the quantity of lipids synthesized, EPTC changed the lipid profile, altering the distribution of label, mainly within the neutral lipid fraction. A crude membrane fraction from maize cells contained both polar lipids and some neutral lipids. DDCA stimulated [2-¹⁴C]acetate incorporation into different lipid species. EPTC inhibited incorporation of [2-¹⁴C]acetate into both neutral and polar membrane lipids but altered significantly only its distribution into neutral lipids. DDCA (0.1 mM) given together with EPTC (0.2 mM) partially counteracted the effect of EPTC within the neutral lipid fraction. It is suggested that DDCA has a rapid effect on lipid synthesis, but it is probably not sufficient to account for the entire mode of action of the protectant.     

Potential safeners for protecting sorghum (Sorghum bicolor (L.) Moench) against chlorsulfuron,fluazifop-butyl and sethoxydim*

In greenhouse studies, the efficacy of the herbicide safeners NA(1,8-naphthalic anhydride), R-25788 (N,N-diallyl-2,2-dichloroacetamide), cyometrinil and CGA-92194 [N-(1,3-dioxolan-2-yl-methoxy)imino-benzeneaceto-nitrile] in protecting grain sorghum (Sorghum bicolor (L.) Moench, cv. ‘Funk G623’) against injury from pre-emergence or early post-emergence applications of the herbicides chlorsulfuron, fluazifop-butyl and sethoxydim was examined. NA as a seed dressing at 0·5 or 1·0% (w/w) was the most effective of the four safeners and offered partial to good protection to sorghum against injury from the lower rates of pre-emergence applications of all three herbicides. R-25788 was totally ineffective as a sorghum protectant against fluazifop-butyl injury but it did antagonize partially the injurious effects of the lower rates of sethoxydim and chlorsulfuron on sorghum. Cyometrinil and CGA-92194 offered partial protection to sorghum against injury from the lowest rate of all herbicides but their efficacy against higher rates of the three herbicides was very limited. None of the four safeners was effective in protecting grain sorghum against injury from post-emergence applications of the three herbicides tested.     

RESPONSE OF YELLOW NUTSEDGE,FLORIDA PUSLEY,AND PEANUTS TO THIOCARBAMATE HERBICIDES AS AFFECTED BY METHOD OF PLACEMENT IN SOIL*

Summary. Thiocarbamate herbicides were applied with incorporation devices and new subsurface application equipment on loamy sand at Tifton, Georgia, U.S.A. Subsurface-applied ethyl N,N-dipropylthiolcarbamate (EPTC), S-propyl bulylethylthiocarbamate (pebulate), and S-propyl dipropylthiocarbamate (vernolate) generally gave better control of Cyperus esculentus L. and Richardia scabra St Hil, but injured peanuts more than applications made on the soil surface and then incorporated into the soil. For soil incorporation, the power-driven rotary hoe was generally better than a disc harrow. Depth of subsurface placement critically affected herbicidal activity, especially on Cyperus esculentus; placement 1·5 in. below the soil surface gave more effective control than placement at 5·5 in. Réactions de Cyperus esculentus, de Richardia scabra et de l'arachide mix herbicides à base de thiocarbamate, en relation avec la methode de placement dans le sol