Effects of herbicidal carbamates on mitochondria and chloroplasts

At concentrations near 2 × 10^?4M, barban, chlorpropham, and phenmedipham are inhibitors of the electron transfer in potato and mung bean mitochondria. The inhibition seems to be localized in the flavoprotein region. It affects preferentially the exogenous NADH dehydrogenation, in potato mitochondria (I₅₀, 10^?4M). Succinate dehydrogenation is less inhibited. At noninhibiting concentrations, the studied carbamates cannot uncouple the oxidative phosphorylations. Photosynthesis is completely inhibited by 2.10^?7M phenmedipham, 5 × 10^?5M barban, and 2 × 10^?4M chlorpropham. The inhibition takes place at the PS II level. Moreover, barban and chlorpropham are uncouplers of the photophosphorylations for concentrations between 5 × 10^?5 and 5 × 10^?4M. The effects observed on mitochondrial respiration can also be found on respiration of Acer cultured cells. The effects on isolated chloroplast photosynthesis are also observed for slightly higher concentrations on cultured Chlorella and on pea and oat leaf fragments.     

Binding of mercury compounds to the chloroplasts in relation to the inhibition of the Hill reaction

The binding behavior of mercuric chloride (HgCl₂), phenylmercuric acetate (PMA), and ethylmercuric chloride (EMC) to the spinach chloroplasts in relation to the inhibition of the Hill reaction was studied at pH 6.8 and 7.8 using ²⁰³Hg labeled compounds. The pH of the reaction medium did not influence the amount of mercury binding of the chloroplast at various mercurial concentrations, but it altered the inhibition curve of the Hill reaction. Between 0–1 × 10^?5M the binding of Hg²⁺ and EMC were similar and increased linearly with the concentration, while the binding of PMA was similar to the binding of Hg²⁺ only at a concentration below 4 × 10^?6M and was less when the concentration was above 4 × 10^?6M. However, the inhibition of the Hill reaction by these mercury compounds was quite different; at pH 7.8, the I₅₀ values for Hg²⁺, PMA, and EMC were 5 × 10^?6, 2.5 × 10^?6, and 2.5 × 10^?6M, respectively, while at pH 6.8, these values were 4 × 10^?6, 4 × 10^?5, and 2 × 10^?4M, respectively. The differential block of electron flow by the mercury compounds at pH 6.8 and 7.8 was further confirmed by electron spin resonance study.     

Pyrethroid insecticides: Potent,stereospecific enhancers of mouse brain sodium channel activation

Deltamethrin and NRDC 157, pyrethroid insecticides that produce different poisoning syndromes in mammals, enhanced veratridine-dependent, sodium channel-mediated ²²Na⁺ uptake in mouse brain synaptosomes. Concentrations producing half-maximal enhancement were 2.5 × 10^?8M (deltamethrin) and 2.2 × 10^?7M (NRDC 157). This effect was stereospecific: The nontoxic 1S enantiomers had no significant effect on veratridine-dependent activation. At high deltamethrin concentrations, enhancement was maximal at 5 × 10^?5?1 × 10^?4M veratridine. Pyrethroid enhancement was completely blocked by 5 × 10^?6M tetrodotoxin, and neither pyrethroid affected ²²Na⁺ uptake in the absence of veratridine at concentrations up to 1 × 10^?5M. The relative potencies of deltamethrin and NRDC 157 in the synaptosomal sodium channel assay agree well with their relative acute toxicities to mice when administered by intracerebral injection. These findings demonstrate that pyrethroids exemplifying both characteristic poisoning syndromes are potent, stereospecific modifiers of sodium channel function in mammalian brain.     

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.     

The action of insecticides on neurosecretory neurons in the stick insect, Carausius morosus

The action of insecticides on the spontaneous electrical activity of neurohemal tissue in the stick insect, Carausius morosus, has been studied using extracellular electrodes. The pyrethroid, permethrin, causes a massive increase in the frequency of the spontaneously generated action potentials at concentrations between 5 × 10^?5 and 5 × 10^?8M. Concentrations as low as 5 × 10^?11M are still effective in producing bursting activity.DDT, at concentrations between 5 × 10^?5M and 5 × 10^?6M, produces an overall increase in activity although the bursting activity is less violent than that shown with permethrin. DDT, 5 × 10^?7M, is ineffective at altering the resting pattern.Carbaryl and coroxon cause a transitory increase in electrical activity at 1 × 10^?4M, but are ineffective at 1 × 10^?5M.It is concluded that insecticides could have a direct effect upon the neurohormonal balance in insects.     

Trifluralin effects on tobacco callus tissue: Mitosis and selected metabolic effects

Inhibition of growth of pith callus of tobacco (Nicotiana tabacum, var. S-73) by the herbicide trifluralin (α,α,α - trifluoro - 2,6 - dinitro - N,N- dipropyl - p - toluidine) was previously observed. Inhibition of cell division in callus tissue of varying age by this herbicide was investigated using the Feulgen reagent and light microscopy. Upon staining and counting the number of cells in each phase of mitosis, a decrease in the number of cells in metaphase, anaphase, and telophase in the treated tissues was found. In addition to this reduction, arrested metaphases and multinucleated cells were observed. Similar results were observed with 10^?4M colchicine. The effects of trifluralin on incorporation of ¹⁴C-precursors into callus RNA, DNA, and protein were also investigated. Apparent RNA, DNA, and protein synthesis in callus were inhibited by trifluralin (5 × 10^?6M) treatment. The inhibition, however, was not expressed until 5–7 days after initiating treatment. Colchicine also affected apparent RNA, DNA, and protein synthesis; however, these effects were different than those observed with trifluralin. Incorporation of ¹⁴C-amino acids into protein was most severely inhibited by colchicine.     

Potassium uptake in atrazine-treated roots of sensitive and resistan plants

The action of atrazine and its biodegradation products on the membrane transport of potassium in roots was evaluated in both sensitive and resistant plants. Excised roots of maize and oat showed inhibition of potassium uptake efficiency in the presence of 1.4 × 10^?4M atrazine and 1.4 × 10^?4M deethylated atrazine. Other biodegradation products such as 2-chloro-4-amino-6-ethylamino-1,3,5-triazine,2-chloro-4,6-,bisamino-1,3,5-triazine, and 2-chloro-4-amino-1,3,5-triazine showed no inhibitory effect on the K⁺ uptake capacity. Two maize hybrids showing different uptake efficiency were inhibited differently by atrazine. We suggest that atrazine and deethylated atrazine inhibited the K⁺ transport interacting directly with the plant cell membranes without discerning between resistant and sensitive plants.     

Effects of benomyl,carbendazim and thiophanates on respiration and oxidative phosphorylation of Fusarium oxysporum and Saccharomyces cerevisiae

Benomyl [methyl 1-(butylcarbamoyl)-benzimidazol-2-ylcarbamate] (350 × 10^?6 M) decreased the respiration rate of Fusarium oxysporum conidia by 50% during germination. This inhibition was maintained at least 24 h after the treatment had begun. The treatment did not modify the relation between incubation time and respiration rate. Carbendazim [methyl benzimidazol-2-ylcarbamate], thiabendazole[2-(thiazol-4-yl)benzimidazole], thiophanate [1,2-di-(3-ethoxycarbonyl-2-thioureido)benzene] and thiophanate-methyl [1,2-di-(3-methoxycarbonyl-2-thioureido)benzene] were assayed using isolated mitochondria of Saccharomyces cerevisiae. These four compounds decreased mitochondrial respiration and oxidative phosphorylation rates to different extents when they were applied at a concentration of 250 × 10^?6 M . Thiophanate-methyl was the most effective since it completely suppressed the mitochondrial respiratory control at 75 × 10^?6 M .     

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.     

Breakdown rates of dimethoate in fruit and vegetable dips

In order to determine the effect of pH and temperature on post-harvest dip solutions of dimethoate (500 mg litre^?1), the half-lives and pseudo first-order rate constants were calculated from measurements at pH 4, 6, 8, 10, 11.5, and at two temperatures 25 and 52°C. The half-lives ranged from 206 days to 39.3 min at 25°C, and from 5.6 days to 205s at 52°C; the rate constants ranged from 3.9 × 10^?8 s^?1 to 2.9 × 10^?4 s^?1 at 25°C, and from 1.4 × 10^?6 s^?1 to 3.4 × 10^?3 s^?1 at 52°C. The results show that the water used in dips should have a pH≤7. The addition of benomyl to the dip solutions at two concentrations (0.5 and 1.0 g litre^?1) had no effect on the half-lives and rate constants. The use of hard and salted waters in dips also showed no major effect. A formula was developed that gives the half-life of the dimethoate as a function of the pH and temperature.     

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.     

Differential inhibition of potassium ion absorption by difenzoquat in wild oat and cereals

Over a concentration range of 5.0 × 10^?6?7.5 × 10^?4M, the selective herbicide difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium) caused more pronounced inhibition of potassium ion (K⁺) absorption by excised seedling roots of susceptible wild oat (Avena fatua L.) compared to those of tolerant barley (Hordeum vulgare L. cv. Bonanza) or wheat (Triticum aestivum L. cv. Neepawa). At 2.5 × 10^?5M difenzoquat, the relative inhibition of K⁺ (⁸⁶Rb) absorption by wild oat root segments inceased from 30% with a 10-min uptake period to 75% with an uptake period of 90 min, whereas no inhibition at all was evident for wheat root segments even after a 90-min exposure to the herbicide. An ion efflux compartmental analysis procedure demonstrated that difenzoquat did not affect the passive permeability properties of the plasma membrane of wild oat root cells. The experimental findings indicated that difenzoquat interfered directly with the process of active ion transport across the plasma membrane of root cells.     

Effects of chlordimeform on rectus abdominis muscle of frog

The effects of chlordimeform on rectus abdominis muscle of frog were investigated. Chlordimeform (10^?3M) caused a slow contraction, and at lower concentration (10^?5–10^?3M) it inhibited the acetylcholine-induced contraction in noncompetitive manner. When chlordimeform was applied to the muscle of Rana catesbiana, K⁺-induced contraction was also inhibited in noncompetitive manner. Whereas it had no effect on caffeine-induced contraction.Chlordimeform-induced contraction was not affected by respective addition of d-tubocurarine (10^?4M), procaine (10^?3M), or eserine (0.3 mM), which results were same as that of K⁺-induced contraction. Chlordimeform, at lower concentration (10^?5–10^?3M), inhibits the acetylcholine- and K⁺-induced contractions probably owing to depression of not only the sensitivity of endplate but also the excitability of cell membrane.     

The effects of pyrethroids on the electrical activity of neurosecretory cells from the brain of Rhodnius prolixus

The effects of pyrethroids on the on-going electrical activity of the axons of neurosecretory cells from the brain of fifth instar Rhodnius prolixus have been studied using extracellular electrodes. Low concentrations of the pyrethroids decamethrin, bioresmethrin, permethrin, and bioallethrin all produce dramatic increases in the overall frequency and dramatic changes in the pattern of electrical activity when applied directly to the exposed brain and corpora cardiaca in an otherwise intact insect. This change in activity was brought about by a recruitment in active units and the production of phasic acivity. A doubling of frequency over that of controls was brought about by low doses of the pyrethroids, namely decamethrin, 1 × 10^?10M; bioresmethrin, 2 × 10^?10M; permethrin, 1 × 10^?9M; and bioallethrin, 2 × 10^?7M. Similar hyperactivity of this system occurred during intoxication of intact insects following topical application of LD₉₅ bioresmethrin. The enhanced sensitivity shown by neurosecretory cells over that of other cell types is discussed, as is the possibility that the increases in electrical activity of neurosecretory axons may result in massive neurohormonal release and thereby contribute to the eventual poisoning of the insect.     

The inhibition of HEOM epoxide hydrase in mammalian liver microsomes and insect pupal homogenates

A range of compounds were tested as inhibitors of the enzyme epoxide hydrase, using a cyclodiene epoxide (HEOM) as substrate. Rat and rabbit liver microsomes and pupal homogenates of the blowfly (Calliphora erythrocephala) and the yellow mealworm (Tenebrio molitor) were compared as sources of the enzyme. Only minor differences were found between the four enzyme preparations, when considering I₅₀ values and percentage inhibition at standard concentration. The simple epoxide 1,1,1-trichloropropane-2,3-epoxide and two glycidyl ethers p-nitrophenyl glycidyl ether and p-ethylphenyl glycidyl ether tended to have lower I₅₀ values (1.8×10^?6 to 8.0×10^?5M) than triphenyl phosphate and SKF 525A (4.5×10^?5 to 1.4×10^?4M). Triphenyl phosphate and SKF 525A were competitive inhibitors for both the rat and Tenebrio enzymes. The only clear difference found between these two epoxide hydrase preparations was with respect to their inhibition by 1,1,1-trichloropropane-2,3-epoxide, which was an uncompetitive inhibitor with the rat enzyme, but showed kinetics of mixed inhibition with the insect preparation.     

Effects of U-40481 and formetanate on the isolated rabbit central ear artery

Formetanate, a formamidine-type pesticide, and U-40481 (N-methyl-N′-2,4-xylylformamidine), a metabolite of amitraz, also a formamidine pesticide, contract the rabbit central ear artery with their maximal contractions being 22 ± 8% and 49 ± 6% of norepinephrine contractions, respectively. Maximal contractions were obtained with 10^?3M formetanate and 10^?4M U-40481, and cumulatively added higher concentrations caused a decrease in tension from that maximum. Their contractions were antagonized by 10^?6M and 3 × 10^?6M phentolamine. U-40481 reversibly antagonized contractions induced by serotonin, norepinephrine, and histamine, and to some extent potassium. Formetanate had little antagonist activity. Neither compound altered the resting rate of washout of radioactivity from [³H]norepinephrine preloaded strips. Both reduced electrically induced release, which may be related to local anesthetic-like actions on sympathetic neurones. Thus both compounds are partial agonists at the α-adrenergic receptor, and reduce electrically induced norepinephrine release, and U-40481 antagonizes contractions induced by certain other vasoactive agents.     

Effect of alachlor on Avena seedlings: Inhibition of growth and interaction with gibberellic acid and indoleacetic acid

The growth of Avena seedlings grown in sand was found to be inhibited by alachlor with the time of onset of inhibition after treatment being a function of herbicide concentration. There was a 12 hr lag period following a subirrigation with 2.5 × 10^?4M alachlor before growth inhibition could be detected. This lag period may be due to uptake and translocation of alachlor from the roots to the site of inhibition or to the exhaustion of certain growth-limiting substance(s) whose biosynthesis is inhibited by alachlor. Additions of gibberellic acid by subirrigation simultaneously with alachlor or after alachlor treatment did not prevent growth inhibition. However, treatment with 10^?3M gibberellic acid 24 hr prior to alachlor treatment overcame the alachlor inhibition. On the other hand, in contrast to gibberellic acid, indoleacetic acid did not prevent inhibition by alachlor.     

Influence of monuron on photosystem II and light-dependent 14CO2 fixation in isolated cells of C3 and C4 plants

Cells were isolated from the developing leaves of Ipomoea aquatica (water spinach), a C₃ plant, and three kinds of C₄ plants, namely, Digitaria sanguinalis (NADP⁺-specific malate dehydrogenase type), Panicum miliaceum (NAD⁺-specific malic enzyme type), and Panicum texanum (phosphoenopyruvate carboxy kinase type), to study the effect of monuron on light-dependent ¹⁴CO₂ fixation and oxygen evolution. Bundle sheath cells, except for those of D. sanguinalis, and mesophyll cells of all plants fixed approximately the same amount of ¹⁴CO₂. Monuron, at the range used (2 to 10 × 10^?7M), showed strong inhibition in the mesophyll cells of water spinach and in bundle sheath cells of P. miliaceum and P. texanum and moderate inhibition in the mesophyll cells of all C₄ plants. In the bundle sheath cells of D. sanguinalis the low rate of ¹⁴CO₂ fixation was stimulated to some extent by the addition of malate and ribose 5-phosphate. The I₅₀ value was 6 × 10^?7M for the sensitive cells. Monuron inhibited the oxygen evolution of all seven cell types and their I₅₀ values varied between 3 × 10^?7 to 6 × 10^?7M. The differential response of isolated plant cells from different species to light-dependent CO₂ fixation in the presence of monuron may also be involved in urea herbicide selectivity and undoubtedly is due to the differential photosynthetic pathways present nn them.     

DDT and sodium transport in the eel electroplaque

DDT inhibits the ATPase activity of the intact eel electroplaque. At a concentration of 10^?5M, DDT inhibited 46% of the total ATPase activity, and 10^?4M DDT inhibited 62% of the total ATPase activity and 62% of the ouabain-sensitive ATPase activity. The latter concentration of DDT reduced the rate of Na efflux from intact electroplaques and slowed the rate of recovery of the membrane potential following a large depolarization produced by carbamylcholine application. Repetitive direct stimulation of the innervated membrane at 10 Hz during the application of 10^?4M DDT produced a significant irreversible depolarization. Ouabain, 10^?4M, produced similar effects. The possible role of the inhibition of active NaK transport in producing the symptoms of DDT poisoning is discussed.     

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.