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 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.     

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.     

The effect of phosphine on electron transport in mitochondria

The effects of phosphine on electron transport and on some partial reactions of oxidative phosphorylation of mitochondria from mouse liver, housefly flight muscles and granary weevils has been studied. Phosphine was a strong inhibitor of respiration of mitochondria in the “active” state (state 3), uncoupled state, and ion-pumping state on glutamate, pyruvate plus malate, succinate, α-glycerophosphate, and ascorbate-cytochrome c as substrates. Respiration of mitochondria in state 3 was completely inhibited by about 250 μM phosphine. By contrast, the respiration of mitochondria in state 4 was much less sensitive. This inhibition could not be released by uncouplers suggesting that it is due to a direct effect on electron transport. Only site III was inhibited to any significant extent. Kinetic studies show that the inhibition was noncompetitive with Ki ranging from 1.6×10^?5 to 7.2×10^?5 depending on the source and purity of cytochrome oxidase. The inhibition of site III was also more pronounced in sonicated particles than in intact mitochrondria. The significance of this is discussed in relation to membrane sideness and topology of the components of the respiratory chain.Phosphine was unable to activate the “latent” ATPase nor did it have any inhibition of the Mg²⁺-simulated ATPase and only high levels (1.1 mM) showed modest inhibition (41%) of uncoupler-stimulated ATPase. Phosphine had no effect on the ATP-Pi exchange and on the ATP-ADP exchange reaction at concentrations causing strong respiratory inhibition.     

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.     

Mitochondrial changes during storage of untreated or CIPC-treated potatoes

During storage of potato tubers (Solanum tuberosum L., var. Bintje), important changes appear which affect respiratory control, $\text{ADP}\text{O}$, intensity of O₂ consumption in the presence of different substrates, and NAD⁺ dependence, In mitochondria extracted under strictly similar conditions, from patato tubers stored at 4°C, the respiratory control (RC) maintains a value near 4 for 4 to 5 months. It then declines progressively to low values. At 20°C, a stable RC of 4 can be observed for several months, which then decreases at the end of dormancy. Then, the RC increases sharply; at this stage, $\text{ADP}\text{O}$ are abnormally low, and, some time later, NAD⁺ dependence disappears. Mitochondria treated with 250 μM chlorpropham show a 50% inhibition of the electron transfer with exogenous NADH as substrate. After tuber treatment with 1% chlorpropham, sprouting is inhibited for several months. The activities of mitochondria extracted from such tubers remain unaffected by the treatment. The use of this phenylcarbamate for potato tuber treatment permits obtaining functional mitochondria from tubers after a slightly longer period of storage.     

Effects of certain herbicides on the oxidative decarboxylation of tryptophan by peroxidase

Non-enzymic and peroxidase-catalysed oxidative decarboxylations of tryptophan (TPP) were studied. The in-vitro rate of enzymic reaction was affected by various herbicides at low concentrations (10^?5?10^?4_M): dinoseb, 2,4-D, dichlobenil and benazolin acted as inhibitors; on the other hand, chlorpropham, bromacil, diphenamid and 4-ethylamino-6-isopropylamino-1,3,5-triazin-2-ol (hydroxyatrazine) were stimulatory. The results of in-vivo experiments showed that chlorpropham and 2,4-D changed the activity of peroxidase from Brassica germinated seeds in vivo, as they do in vttro. Determinations of consumed TPP were carried out either by spectro-photometry or by chromatography.     

The effect of DDT and its analogs on the fragility of human erythrocytes

The antihemolytic actions of DDT and eight analogs were examined with human erythrocytes. Apparent aqueous concentrations to produce 60% of control hemolysis ranged from 3.7 × 10^?4 to 2.4 × 10^?6M, with DDT being one of the least active. No correlation was found between antihemolytic potency and neurotoxicity, and it was concluded that the findings did not illuminate the toxic or neural actions of these compounds.     

The mechanism of fungistatic action of sec-butylamine: II. The effect of sec-butylamine on pyruvate oxidation by mitochondria of Penicillium digitatum and on the pyruvate dehydrogenase complex

sec-Butylamine at 5 mM inhibited the oxidation of pyruvate by mitochondria isolated from hyphae of Penicillium digitalum, but had little effect on the oxidation of citrate, isocitrate, succinate, malate, acetyl-coenzyme A, or reduced nicotinamide adenine dinucleotide. sec-Butylamine did not interfere with oxidative phosphorylation, as evidenced by similar $\text{P}\text{O}$ ratios in treated and control mitochondria. The pyruvate dehydrogenase complex (EC 1.2.4.1) isolated from young hyphae of P. digitatum was inhibited strongly by 20 mM sec-butylamine, whereas other tricarboxylic acid cycle enzymes were only slightly affected at most. Inhibition of the pyruvate dehydrogenase complex by sec-butylamine was competitive with respect to pyruvate. The K_i for sec-butylamine in the reaction was 1.38 × 10^?2M, and the K_m for pyruvate was 2.28 × 10^?4M. These observations and other evidence derived from studies with intact hyphae support the hypothesis that the pyruvate dehydrogenase complex is the primary site of the fungistatic action of sec-butylamine.     

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.     

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.     

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 .     

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.     

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.     

Trifluralin effects on carrot callus tissue

The effect of trifluralin on the growth, oxygen uptake, and adenosine phosphates level of carrot (Daucus carota L.) callus tissue was determined over a period of 18 days after subculture. The herbicide (10^?4 and 10^?5M) reduced fresh weight gain significantly; the reduction was less with lower trifluralin concentrations. Dry weight accumulation was not inhibited until after Day 6 of the test period and thereafter was reduced by all concentrations tested. Oxygen consumption was inhibited by trifluralin (10^?4 and 10^?5M) throughout the test period. Concentrations of 10^?6.10^?7, and 10^?8M produced variable effects. The response profile of O₂ consumption in the presence of dinitrophenol was different from that of trifluralin. Analysis of adenosine phosphates level gave no clear response trend. Energy charge values of 0.7 to 0.85 were obtained for untreated tissue. Trifluralin had no effect on energy charge until Day 9 (10^?4M) and after Day 15 (all concentrations).     

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.     

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.     

Modification of frescon action in Lymnaea stagnalis smooth and cross-striated muscles by agents that alter potential-dependent or receptor-operated calcium permeability

The calcium entry blockers sodium nitroprusside (10^?2M) and sodium pentobarbital (5 × 10^?3M) had different effects on high-potassium-induced and Frescon-induced contractures in a smooth and a cross-striated muscle of the snail Lymnaea stagnalis. This suggests that Frescon causes an increase in sarcolemmal calcium permeability by a mechanism which is different from that utilized by high extracellular potassium.     

Determination of sugarbeet herbicides in soil samples by hplc

Determination of sugarbeet herbicides such as chloridazon, metamitron and phenmedipham in soil samples is described. After extraction with acetone, pesticides were determined by HPLC on an RP-18 column using methanol/water as mobile phase. Average recoveries were 82% for chloridazon, 93% for metamitron and 77% for phenmedipham. Quantification limits were 3·5 μg kg^?1 for chloridazon, 6·3 μg kg^?1 for metamitron and 3·6 μg kg^?1 for phenmedipham.     

Complex formation of picloram and related chemicals with metal lons

The complex formation of metal ions with pyridine carboxylic acids was estimated with polarography and spectrophotometry. Picloram (4-amino-3,5,6-trichloropicolinic acid), α-picolinic acid, fusaric acid, dipicolinic acid, and quinolinic acid formed complexes with Fe(III) or Cu(II) whose coordination involves, most probably, a lone pair of electrons of pyridine nitrogen and a carboxylic group. Picloram-metal complexes were, however, estimated to be relatively unstable compared to other pyridine-α-carboxylic acids tested. Effects of pyridine carboxylic acids on oxidation of indole-3-acetic acid (IAA) were tested in vitro in a horseradish protoheme peroxidase system. No significant effect of the pyridine carboxylic acids was observed at 2 × 10^?4M. Also, no concentration effect of picloram (10^?5 to 3 × 10^?3M) was obtained. These results suggest that the phytotoxic action of picloram may not result from the depletion of free metal ions in plants nor inhibition of activity of metal-containing enzymes through strong chelation as hypothesized. Thus, auxin activity of picloram should be explained in other wasy.