Herbicidal interference with the photochemical activities of chloroplasts (in vivo and in vitro) of certain crop and weed species

The independent modes of action of diuron and atrazine on the photochemical activities of chloroplasts (In vivo and in vitro) from the leaves of crop plants Pisum sativum and Pennisetum typhoides and the weeds Amaranthus viridis and Cyperus rotundus were investigated. Hill reaction activity (DCPIP photoreduction) of in vivo chloroplasts (chloroplasts isolated from herbicide-sprayed plants) was unaffected by treatment at sublethal or intermediate levels of diuron or atrazine while that of in vitro chloroplasts (chloroplasts incubated in the required herbicidal concentration) was severely inhibited. The ferricyanide catalyzed noncyclic photophosphorylation was markedly reduced in both the in vivo and in vitro chloroplast systems. N-Methyl phenozonium sulfate (PMS)-mediated cyclic photophosphorylation was inhibited in the in vivo system while a pronounced enhancement of activity was noticed in the in vitro chloroplasts. The rate of NADP⁺ photoreduction was severely inhibited in the in vitro chloroplasts. The unaffected in the in vivo system. The herbicidal effects on the photoreactions of isolated chloroplasts were compared with chloroplasts isolated from herbicide-sprayed plants.     

Effect of phytoplasmal infection on photosystem II efficiency and thylakoid membrane protein changes in field grown apple (Malus pumila) leaves

We have studied the effect of the apple proliferation phytoplasmal infection on some features of the thylakoids from field grown apple (Malus pumila) leaves. Changes in photosynthetic pigments, soluble proteins, ribulose-1,5-bisphosphate carboxylase, nitrate reductase, photosynthetic activities and thylakoid membrane proteins were investigated. The level of total chlorophyll and carotenoids were reduced in phytoplasma-infected leaves. Similar results were also observed for soluble proteins and ribulose- 1,5-bisphosphate carboxylase activity. The in vivo nitrate reductase activity was significantly reduced in infected leaves. When various photosynthetic activities were followed in isolated thylakoids, phytoplasmal infection caused marked inhibition of whole chain and photosystem II activity while the inhibition of photosystem I activity was only marginal. The artificial exogenous electron donors, diphenyl carbazide and hydroxylamine significantly restored the loss of photosystem II activity in infected leaves. The same results were obtained when F_v/F_m was evaluated by chlorophyll fluorescence measurements. The marked loss of photosystem II activity in infected leaves could be due to the loss of 47, 33, 28–25, 23 and 17 kDa polypeptides. It is concluded that phytoplasmal infection inactivates the donor side of photosystem II. This conclusion was confirmed by immunological studies showing that the content of the 33 kDa protein of the water-splitting complex was diminished significantly in infected leaves.     

Acetylcholinesterase of Aphis citricola: Properties and significance in determining toxicity of systemic organophosphorus and carbamate compounds

In apterous adults of the spirea aphid, Aphis citricola van der Goot, the optimum conditions for determining acetylcholinesterase (AChE) activity consist of reaction mixture of 0.1 M phosphate buffer (pH 7.5), 10^?3M acetylthiocholine (ASCh), and enzyme extract equivalent to 80 ± 3 μg protein incubated for 15 min at 30°C. The K_m value for ASCh (6.7 × 10^?5M) was much lower than that of butyrylthiocholine (BuSCh) (1.25 × 10^?2M). The enzyme activity was almost completely inhibited by 10^?6M paraoxon or 10^?5M eserine and was 84% inhibited by 10^?5M BW284C51 (a specific AChE inhibitor). DTNB was found to inhibit the enzyme activity and was therefore added at the end of the reaction. AChE activity of A. citricola was inhibited in vitro and in vivo by dimethoxon > dimethoate, and aldicarb sulfoxide > aldicarb > aldicarb sulfone. The in vivo effect correlates well with the toxicity level of the various toxicants. A neurotoxicity index which combines both mortality and in vivo inhibition of the aphid AChE activity is suggested as a measure for determining the toxicity of organophosphorus and carbamate compounds toward aphids.     

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.     

The biochemical and physiological effects and mode of action of AC 222,293 against Alopecurus myosuroides Huds. and Avena fatua L

AC 222,293 was found to exert its mode of action through inhibition of acetolactate synthase, the first enzyme in the biosynthetic pathway of the branched chain amino acids. In vitro AC 222,293 was found to be only a very weak inhibitor of the enzyme, in contrast to the potent inhibition by the free acid, suggesting that action of the herbicide in vivo is dependent on deesterification. Enzyme preparations from susceptible Avena fatua and Alopecurus myosuroides and tolerant wheat (cultivar Fenman) were all equally sensitive with an I₅₀ of approximately 5 · 10⁻⁷ M. Inhibition of treated plants is prevented when valine, leucine, and isoleucine are supplied via the nutrient solution. Prominent secondary effects are inhibition of DNA synthesis and cell division and the action of the herbicide is characterised by cessation of leaf growth.     

Effects of the herbicide methabenzthiazuron on the physiology of wheat plants

Spring wheat (Triticum aestivum L. “Caribo”) was grown in vermiculite containing methabenzthiazuron (N-(benzothiazol-2yl)-NN′-dimethylurea) presowing. Effects of the herbicide on plant development and plant composition were analysed up to an age of 4 weeks. Inhibition of photosynthetic oxygen evolution represented the primary effect induced by the herbicidal treatment and led to a decreased concentration of soluble reducing sugars. Photosynthetic activity however recovered after 3 weeks and even increased above control values. Secondary effects following methabenzthiazuron treatment included a delayed chlorophyll breakdown, a decreased chlorophyll a/b ratio, enlarged chloroplasts, an increased concentration of soluble amino acids and of soluble protein, and an increased in vitro nitrate reductase activity. These responses are taken to indicate an increased photosynthetic and metabolic capacity in methabenzthiazuron treated wheat plants. Comparable results can be obtained with plants grown at low light intensities. It is concluded that the “physiological effects” observed in wheat plants after treatment with methabenzthiazuron are similar to a natural adaptation reaction to low light intensities. It is assumed that this adaptation reaction is caused by a low concentration of soluble reducing sugars. Experiments with plants growing at different light intensities indicated that effects due to herbicidal action were more pronounced at high light intensities. Measurements on daily fluctuations revealed a peak around noon for the sugar content and the nitrate reductase activities measured in vivo as well as in vitro. In vivo nitrate reductase activity in plants treated with 5 parts/million methabenzthiazuron was very low, presumably because of lack of sugars for the production of NADH. The protein concentration was increasing and the amino acids were decreasing during the day in herbicide treated plants, possibly indicating increased protein synthesis in the light in plants treated with methabenzthiazuron.     

Paraoxon-induced release of β-glucuronidase from rat hepatocytes in vitro

A suspension culture of isolated rat hepatocytes was used to reproduce in vitro the paraoxon-induced release of hepatic β-glucuronidase observed in vivo. After a short latent period, exposure of hepatocytes to paraoxon at 10^?7 to 10^?4M resulted in a typical dose-dependent response, with highest release occurring at 10^?4M paraoxon. With 10^?3M paraoxon, however, response was anomalous with a much-decreased enzyme release. As expected from earlier results in vivo, SV₁-oxon exhibited less effect than paraoxon.     

Interaction of some unsubstituted phosphoramidate analogs of methamidophos (O,S-dimethyl phosphorothioamidate) with acetylcholinesterase and neuropathy target esterase of hen brain

At 37°C and pH 7.4–8.0, five higher O-alkyl analogs of methamidophos and four O-alkyl O-2,5-dichlorophenyl phosphoramidates all were more potent progressive inhibitors of hen brain AChE and neuropathy target esterase (NTE) than was methamidophos itself. For AChE, k_a increased from 7.2 × 10² to 1.0 × 10⁵ M⁻¹ min⁻¹ between methyl and n-hexyl S-methyl esters and from 9.3 × 10³ to 8.9 × 10⁵ M⁻¹ min⁻¹ between ethyl and n-hexyl dichlorophenyl analogs. For NTE, the ranges were from 16 to 7.9 × 10⁴ for S-methyl esters, and were 9.7 × 10⁴ to 7.8 × 10⁶ M⁻¹ min⁻¹ for dichlorophenyl. S-methyl esters were more active against AChE than against NTE and all the dichlorophenyl esters were more active against NTE than against AChE. Spontaneous reactivation of 75–100% activity without aging of AChE was found after 19 hr incubation at 37°C after inhibition by all nine straight-chain alkyl analogs. After inhibition by O-isopropyl S-methyl phosphorothioamidate, some spontaneous reactivation with complete aging of all remaining inhibited AChE occurred during 19 hr. No spontaneous reactivation or aging of inhibited NTE was detected. It was concluded that the molecular structures of the inhibited enzymes obtained from equivalent compounds in the two series of inhibitors were identical and that the leaving groups were, therefore, S-methyl and O-2,5-dichlorophenyl, respectively. Although hen brain NTE inhibited by methamidophos in vitro did not age, cases of delayed neuropathy in man have been reported and, presumably, require aging as well as inhibition of NTE. Possible explanations of this apparent discrepancy include (i) the fact that methamidophos consists of two chiral forms and that the form seen to be active in vitro may be disposed of preferentially in vivo, (ii) the possibility of activation in vivo to a different inhibitor, (iii) differences between conformation and ease of aging of inhibited NTE in vitro and in vivo, and (iv) species differences.     

Metabolism of cisanilide (Cis-2,5-dimethyl-1-pyrrolidinecarboxanilide) by rat liver microsomes

Metabolism of [phenyl-¹⁴C] and [(2,5) pyrrolidine-¹⁴C] cisanilide was investigated in vitro with microsomal preparations from rat liver. Microsomal activity was associated with a mixed-function oxidase system that required O₂ and NADPH and was inhibited by CO. Two major ether-soluble metabolites were isolated. They were identified as primary oxidation products: 2-hydroxy-2,5-dimethyl-1-pyrrolidinecarboxanilide (A) and 4′-hydroxy-2,5-dimethyl-1-pyrrolidinecarboxanilide (B). Minor ether-soluble metabolites were also isolated. Precursor product studies and qualitative thin layer chromatography analysis of [pyrrolidine-¹⁴C] and methylated [phenyl-¹⁴C] hydrolysis products suggested that these metabolites were secondary oxidation products formed from metabolites A or B. One of these metabolites appeared to be the dihydroxy product 2,4′-dihydroxy-2,5-dimethyl-1-pyrrolidinecarboxanilide. Crude microsomal preparations (postmitochondrial supernatant fractions) also formed small quantities (<10%) of polar metabolites. Enzyme hydrolysis with β-glucuronidase (Escherichia coli) indicated that approximately 50% of these metabolites were glucuronides. Similarities and differences in cisanilide oxidation in vivo in plants and in vitro with rat liver microsomal preparations were discussed.     

Tridiphane [2-(3,5-dichlorophenyl)-2-(2,2,2-trichloroethyl)oxirane] an atrazine synergist: Enzymatic conversion to a potent glutathione S-transferase inhibitor

Glutathione S-transferases (GST) from corn, giant foxtail, onion, pea, house fly, and equine liver catalyzed conjugation of tridiphane with glutathione (GSH). The conjugate was characterized by soft ionization mass spectral methods. Tridiphane and the GSH conjugate of tridiphane both inhibited GSH conjugation of atrazine in vitro (corn and giant foxtail). Tridiphane did not inhibit GSH conjugation of 1-chloro-2,4-dinitrobenzene (CDNB) in corn or giant foxtail; however, the GSH conjugate of tridiphane was a competitive inhibitor with respect to GSH and was four times more effective with extracts from giant foxtail (K_i = 2 μM) than from corn (K_i = 8 μM). The GSH conjugate of tridiphane inhibited a variety of GST enzymes with several different substrates. When compared to other inhibitors of GST, only triphenyl tin chloride was more effective than the GSH conjugate of tridiphane in inhibition of GST from giant foxtail. Both GST and GSH decreased in corn and increased in giant foxtail as tissues matured. The catabolism of the GSH conjugate of tridiphane was compared in crude enzyme systems from corn, giant foxtail, and onion. The rate of catabolism was much greater in extracts from corn leaves than from giant foxtail leaves. Inhibition of GSH conjugation of CDNB was reversed as the GSH conjugate of tridiphane was catabolized. The possibility that synergism of atrazine toxicity by tridiphane is mediated by conversion of tridiphane to a GSH conjugate is discussed in relationship to the relative rates of GSH conjugation of tridiphane and atrazine, concentrations of GSH, K_i values, tissue age, and stability of the conjugate in different tissues.     

Physiological response of yellow vein mosaic virus-infected bhendi [Abelmoschus esculentus] leaves

The effect of okra yellow vein mosaic virus infection on PS II efficiency and thylakoid membrane protein changes in field-grown bhendi (Abelmoschus esculentus) leaves was studied. The degree of virus infection was determined by means of the ratio of variable to maximum chlorophyll fluorescence (F_v/F_m). Changes in photosynthetic pigments, soluble proteins, nitrate reductase, photosynthetic activities and thylakoid membrane proteins were investigated. Okra yellow vein mosaic virus infection resulted in the reduction of photosynthetic pigments, soluble proteins, ribulose-1, 5-bisphosphate carboxylase activity and nitrate reductase activity. Virus infection caused marked inhibition of PS II activity. The artificial electron donors, diphenyl carbazide and hydroxylamine significantly restored the loss of PS II activity in infected leaves. The marked loss of PS II activity in infected leaves may be due to the loss of 47, 33, 28–25, 17 and 15 kDa polypeptides. It is concluded that the yellow vein mosaic virus infection inactivates the donor side of PS II.     

铵态氮和硝态氮对香蕉枯萎病发生的比较研究

 为寻找降低香蕉枯萎病发生的防治措施,通过室内盆栽接种试验,研究了铵态氮(NH₄⁺-N)和硝态氮(NO₃^--N)对香蕉枯萎病发生及其植株叶绿素含量、气体交换参数、病原菌在植物体内的数量分布和植物钙(Ca)、镁(Mg)、铁(Fe)、钼(Mo)、可溶性糖和木质素含量的效应。结果表明:不接种病原菌的条件下,不同氮素处理对香蕉幼苗生长影响无差异;接菌情况下,与NH₄⁺-N处理相比,NO₃^--N处理显著降低植株各器官的病原菌数量、发病率和发病严重程度。病原菌侵染后,不同氮素处理下植株光合作用均显著下降:NO₃^--N处理香蕉苗保持比NH₄⁺-N处理更高的光合速率;病原菌侵染后NH₄⁺-N处理的植株Ca、Mg、Fe和Mo含量相对于侵染前没有显著差异,但NO₃^--N处理下此4种元素含量均显著升高。病原菌侵染后的植株叶片可溶性糖含量在不同氮素处理中都没有显著变化,但在根系中,NO₃^--N处理的侵染植株可溶性糖含量显著降低。与此同时,病原菌侵染后,木质素含量在NH₄⁺-N处理植株中变化不显著,但其含量在NO₃^--N处理侵染后显著上升。综上所述,NO₃^--N处理可增加植株抗病相关矿质元素的吸收,诱导香蕉苗木质素形成,使其木质化程度增加,从而维持较高的光合作用,保持较高的抗病水平。     

The biochemical basis of malathion resistance in the sheep blowfly,Lucilia cuprina

The in vivo and in vitro metabolism of [¹⁴C]malathion was studied in susceptible (LS) and malathion resistant (RM) strains of the sheep blowfly, Lucilia cuprina (Wiedemann). No difference was found between strains in the penetration, excretion, storage, or inhibitory potency of the insecticide. However, RM degraded malathion to its α- and β-monocarboxylic acid metabolites more rapidly than LS, both in vivo and in vitro. This enhanced degradation of [¹⁴C]malathion occurred in vitro in both mitochondrial and microsomal fractions of resistant flies. Kinetic analysis revealed that these fractions degraded malathion by discrete mechanisms. The enzymes from the mitochondria of both strains had the same K_m, whereas the microsomal enzyme from the RM strain had a fivefold higher K_m than that from the LS strain. Studies of esterase activities and the effect of enzyme inhibitors showed that both the mitochondrial and microsomal resistance mechanisms were the result of enhanced carboxylesterase activity. It was concluded that increased carboxylesterase detoxification of malathion adequately explained the high level of malathion resistance in RM if rate-limiting factors such as cuticular penetration were taken into account.     

In vitro and in vivo analyses of the mechanism of action of SWEP

In vitro experiments with intact chloroplasts from hydroponically grown spinach (Spinacia oleracea L. var. Winter Giant) plants, have shown an I₅₀ value for SWEP (methyl N-3,4-dichlorophenyl) carbamate) of 0.1 μM in PS I and II-linked electron transport H₂0 → NADP⁺. With thylakoid membranes the I₅₀ values for PS II-linked Hill reactions H₂O → [Fe(CN)₆]³⁻ and H₂O → dichlorophenolindophenol are in the range 0.05-0.1 μM, whereas the I₅₀ shifts to 0.45 μM in short PS II-linked transport chain diphenylcarbazide → dichlorophenolindophenol. Trypsination of PS II-enriched particles produces a negligible increase of the I₅₀ value in diphenylcarbazide → dichlorophenolindophenol electron transport, a much smaller increase than occurs with diuron- or atrazine-type inhibitors. All these data show SWEP as a strong inhibitor of electron transport in the Q-B region of the PS II-reducing side. However, it appears to have a different binding site than that of urea and triazine herbicides, either on a trypsin resistant or on a non-surface cluster. As a consequence of the NADPH shortage, SWEP brings about a strong inhibition of CO₂ assimilation, with an I₅₀ of 0.04 μM, and a lower percentage of trioses-P among the intermediates of the Calvin cycle. In vivo experiments have shown a three to five times higher inhibition of PS II-linked electron transport, when SWEP was supplied through the roots than when it was applied to the leaves. We have found I₅₀ values of CO₂ assimilation by isolated chloroplasts of foliar disks of 3 and 5 μM, respectively, when the herbicide was root supplied, as opposed to 10 and 25 μM after leaf application.     

Effect of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) on photosynthesis and respiration of Nitella dactyl cells

Long-term experiments with dactyl cells of Nitella flexilis showed that the herbicide 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) at a concentration of 1 × 10^?5M affected not only O₂ evolution in the light but also O₂ uptake in the dark. The inhibition of O₂ production was transitory, but dark respiration did not recover. DCMU induced the formation of giant mitochondria which disappeared before cell death. It was concluded that the algicidic effect of 1 × 10^?5M DCMU on N. flexilis, but not necessarily the elongation of mitochondria, was due to the inhibition of mitochondrial respiration and not of photosynthesis.     

The inhibition of nuclear DNA polymerizing activity by captan

A study was conducted concerning the inhibition of calf thymus nuclear DNA synthesis by captan. Captan was shown to be toxic to the in vitro incorporation of [³H]dTTP into calf thymus DNA, with an ID₅₀ value of 0.16 mM being measured. This inhibition was determined to be independent of Mg²⁺ concentration. Although intact nuclear activities were affected, the soluble DNA polymerizing activity isolated from calf thymus nuclei exhibited no inhibition when exposed to captan. Treatment of purified calf thymus DNA with 10^?5 and 10^?4M captan caused an elevation of the T_m by 2 and 6°C, respectively. The inhibitory characteristic of captan on DNA polymerizing activities and the influence of this compound on the thermostability of DNA indicate a mechanism of inhibition which is located in the nucleus and is possibly related to the template function of DNA and/or with the nuclear DNA polymerizing enzymes.     

Laboratory studies on the influence of the earthworm Eukerria saltensis (Beddard) (Oligochaeta: Ocnerodrilidae) on overlying water quality and rice plant establishment

Dense infestations of a peregrine oligochaete worm, Eukerria saltensis (Beddard), have been linked to rice crop failures in southern New South Wales, Australia. The influence of E. saltensis on water quality and rice plant establishment was investigated in a series of laboratory experiments using a flooded Riverina clay soil. Worm densities of 20 and 40 per container (2548 and 5096 worms/m², respectively) significantly increased water turbidity after 7 days incubation. Longer incubation periods led to turbidity levels of over 500 NTU being achieved (40 worms per container, 21 days incubation). Water pH was significantly reduced by densities of 10, 20, and 40 worms per container after 7 days under cyclical illumination, however in continuous darkness significant changes in pH related to worm density were only found after 21 days incubation. Nitrogen as NH₄+ and total phosphorus increased significantly in the overlying water in response to increasing worm densities after 21 days incubation, however nitrogen as nitrate/nitrite and soluble phosphorus did not. Algal production (measured as extracted chlorophyll a concentration) was unaffected by the worms, reflecting the low concentrations of available phosphorus in all treatments. Rice plants grown in containers with worms produced significantly longer and heavier shoots than control plants. Root systems were unaffected, and there was no evidence of root abrasion. Evaluation of rice seed stratification in the soil profile indicates that rice seeds can be passively transported below the soil surface by the feeding and tunnelling activity of E. saltensis. Our results suggest that E. saltensis impedes the establishment of aerially-sown rice crops primarily by increasing water turbidity. Plants respond to high turbidity by partitioning more of their growth into shoot production, and consequently become vulnerable touprooting through wave action, particularly as the soil loses compaction because of worm activity. Maintaining the lowest possible water levels during rice crop establishment has helped farmers to minimize these effects.     

Effect of organophosphates in vivo upon acetylcholinesterase isozymes from housefly head and thorax

Four soluble acetylcholinesterase isozymes of head and three from the thorax of housefly (Musca domestica L.) were separated by polyacrylamide gel electrophoresis. Their inhibition in vivo was studied after poisoning with an LD₅₀ of four organophosphates: malaoxon, paraoxon, diazinon and dichlorvos. The isozymes differed greatly in their degree of inhibition. Thoracic isozymes were found to be more sensitive to inhibition than head isozymes. In surviving flies, the recovery rates of head isozymes were much faster than thoracic isozymes. In vitro studies showed that thoracic isozymes differed 4.1- and 2.9-fold in their K_m and V_max.     

Actions of formamidines,local anesthetics,octopamine and related compounds upon the electrical activity of neurohaemal organs of the stick insect (Carausius morosus) and sense organs of fly larvae (Musca domestica; Calliphora erythrocephala)

The pesticides, chlordimeform and amitraz, and their metabolites, demethylchlordimeform, N¹-(2,4-dimethylphenyl)-N-methylformamidine, and 2,4-dimethylformanilide, are effective at concentrations as low as 3 μM in raising the firing rate of endogenously active neurosecretory fibres in the isolated neurohaemal organs of Carausius morosus. Molecules such as bunamidine and cetrimide, with cationic detergent properties, produced sporadic bursting which did not elevate the overall firing rate to any great extent. Indeed, bunamidine could induce complete block of action potentials at concentrations as low as 30 μM. The local anesthetics, procaine, lidocaine, and benzocaine, do not induce block of activity at least up to a level of 1 mM. They have no effect at concentrations lower than 100 μM. Between 100 μM and 1 mM lidocaine and benzocaine produce a small increase in firing rate. Procaine produced a pronounced increase in the frequency of firing. The phenolic amines, octopamine, synephrine, and tyramine, markedly increased electrical activity. The catecholamines, dopamine, noradrenaline, and adrenaline, by contrast, only produced a weak excitation. Neither α- nor β-adrenergic blocking agents were effective in antagonizing the electrical activity induced by chlordimeform or phenolic amines until relatively high concentrations of about 1 mM were used. Chlordimeform was able to induce high-frequency bursts from sense organs associated with the epidermis and body-wall musculature in larvae of Musca domestica and Calliphora erythocephala. Octopamine did not induce any similar bursting activity in these sense organs. These results are discussed in relationship to current views on the mode of action of the N-aryl amidines. It is concluded that the excitatory effects of these compounds upon neurohaemal organs and sense organs are more likely to result from a direct action upon voltage sensitive channels of the nerve membranes, rather than by an effect mediated by interactions with octopamine receptors.     

Metabolism of 2-[methoxy(methylthio)phosphinylimino]-3-ethyl-5-methyl-1,3-oxazolidine in the cotton plant and houseflies

The metabolism of 2-[methoxy(methylthio)phosphinylimino]-3-ethyl-5-methyl-1,3-oxazolidine (Stauffer R-16,661), a new experimental insecticide, was investigated in the cotton plant, houseflies, and in in vitro enzymatic and model oxidation systems. The principal metabolite isolated both in vivo and in vitro proved to be the 4-keto derivative of R-16,661. The structure of this metabolite was confirmed by PMR and mass spectral analysis. Toxicological examination showed that the 4-keto metabolite was approximately equal to R-16,661 in toxicity to the white mouse but was substantially less toxic to the housefly.