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.     

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 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.     

Is sulfotep a proctolin receptor antagonist?

Proctolin-induced, dose-dependent (10^?8-2 × 10^?6 M) contraction of the isolated foregut of Schistocerca gregaria was antagonised non-competitively by sulfotep (2 × 10^?6-10^?5 M). A higher dose of sulfotep (5 × 10^?5 M) caused restoration of the proctolin dose-response curve to its control value. Neostigmine (10^?5 M) caused non-competitive inhibition of proctolininduced tissue contraction. Increasing the dose of neostigmine to 10^?4 M restored the proctolin response to control values. Sulfotep (10^?5 M) and neostigmine (10^?4 M) caused inhibition of acetylcholinesterase (AChE) activity in tissue homogenates obtained from guts pretreated with either drug for 20 min. The stimulatory effect of sulfotep (5 × 10^?5 M) on proctolin-induced gut contraction was abolished by pretreatment of tissues with atropine (10^?6 M). Under these conditions, 5 × 10^?5 M sulfotep caused further antagonism of the action of proctolin. The results suggest that sulfotep is a proctolin receptor antagonist in the locust foregut. However, higher concentrations inhibit tissue AChE activity, thereby allowing endogenous acetylcholine to activate muscarinic receptors. This leads to enhanced tissue contractility which masks the antagonistic effect of sulfotep on proctolin-induced contraction.     

Studies into primary and secondary infection processes by Plasmodiophora brassicae on canola

The early stages of infection of canola roots by the clubroot pathogen Plasmodiophora brassicae were investigated. Inoculation with 1 × 10⁵ resting spores mL^?1 resulted in primary (root hair) infection at 12 h after inoculation (hai). Secondary (cortical) infection began to be observed at 72 hai. When inoculated onto plants at a concentration of 1 × 10⁴ mL^?1, secondary zoospores produced primary infections similar to those obtained with resting spores at a concentration of 1 × 10⁵ mL^?1. Secondary zoospores caused secondary infections earlier than resting spores. When the plants were inoculated with 1 × 10⁷ resting spores mL^?1, 2 days after being challenged with 1 × 10⁴ or 1 × 10⁵ resting spores mL^?1, secondary infections were observed on the very next day, which was earlier than the secondary infections resulting from inoculation with 1 × 10⁷ resting spores mL^?1 alone and more severe than those produced by inoculation with 1 × 10⁴ or 1 × 10⁵ resting spores mL^?1 alone. Compared with the single inoculations, secondary infections on plants that had received both inoculations remained at higher levels throughout a 7‐day time course. These data indicate that primary zoospores can directly cause secondary infection when the host is under primary infection, helping to understand the relationship and relative importance of the two infection stages of P. brassicae.     

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.     

Challenging the larvae of <Emphasis Type="Italic">Helicoverpa armigera</Emphasis> and assessing the immune responses to nematode-bacterium complex

Helicoverpa armigera is a strong insecticidal resistance developed insect pest. The understanding of its innate immune responses to emerging biocontrol agent entomopathogenic nematode-bacterial complex can provide an opportunity to control this insect in an environmentally benign manner. Study was focused on role of hemocytes changes and PO activity in Steinernema abbasi-Xenorhabdus indica challenged larvae of H. armigera over the time. Total cell count changed effectively from 10.2?±?1.81?×?10⁵ to 15.5?±?3.3?×?10⁵ cells/mm³ upto 9 h and reduced distinctly up to 8.0?±?2.49?×?10⁵ cells/ mm³ in 24 h. PO activity inclined significantly and was recorded highest at 9 h (24.67?±?1.08?×?10² units) and lowest at 24 h (14.34?±?0.74?×?10² units) in total hemolymph with a similar pattern in plasma and the cellular fraction. Phenoloxidase activity in total and cellular component of hemolymph was positively correlated with prohemocytes, granulocytes and oenocytoids. Study showed the hemocytes and PO accounted as active immune responses against nematode infection. The results provide the first insight to understand the hemolytic activity, quick immunosuppression responses of S. abbasi-X. indica and vulnerability of H. armigera.     

In vitro effects of flutriafol and azoxystrobin on Beauvaria bassiana and its efficacy against Tetranychus urticae

BACKGROUND: Testing the compatibility of chemical pesticides and fungal biocontrol agents is necessary if these two agents are to be applied together in the integrated management of plant pests and diseases. In this study, the fungicides azoxystrobin (a strobilurin) and flutriafol (a triazole) were tested in vitro for their effects on germination of conidia and mycelial growth of Beauveria bassiana (Bals.) Vuill. and in bioassay for their effect on fungal activity against Tetranychus urticae Koch. The fungicides were tested at three different concentrations [recommended rate for field use (1 × X) and the dilutions 10^?1× X and 10^?2× X]. RESULTS: Flutriafol inhibited growth of mycelia and germination of the fungal conidia at all concentrations tested in vitro, and also reduced the efficacy of B. bassiana in bioassays against mites. The inhibitive effect of azoxystrobin in vitro varied with the concentration applied. A significant effect was observed at 1 × X and 10^?1× X concentrations on both the germination of conidia and mycelia growth. At 10^?2× X concentration, azoxystrobin showed little effect on B. bassiana. However, when this fungicide was tested in bioassays, none of the concentrations reduced B. bassiana activity against mites. CONCLUSION: Azoxystrobin was most compatible with B. bassiana, while flutriafol was the most harmful. Further studies are required to confirm the negative effect of flutriafol on B. bassiana activity. Copyright © 2010 Society of Chemical Industry     

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.     

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.     

Effect of 2,4,5-T and picloram on the regeneration of blackberry (Rubus procerus P.J. Muell) from root segments

The formation of roots and shoots on root segments of Rubus procerus P.J. Muell was prevented by soaking the segments for 24 h in a 10^?4M solution of 2,4,5-T or a 10^?5M solution of picloram. Shoot numbers were significantly increased after treatment with 10^?9M and 10^?10M 2,4,5-T, but picloram did not cause a significant increase in shoot numbers. Measurement of the concentration of 2,4,5-T in the extracambial tissue showed that roots treated with 10^?4M 2,4,5-T contained 5× 10^?8 mmole 2,4,5-T per mg dry weight, and by extrapolation, roots treated with 10^?9M 2,4,5-T contained 2× 10^?10 mmole/mg dry weight. Action du 2,4,5-T et du piclorame sur la régénération de la ronce (Rubus procerus P.J. Muell) è partir de fragments de racines La formation de racines et de tiges è partir de fragments de racines dc Ruhus procerus P.J. Muell a été supprimée par trempage des fragmenls pendant 24 heures dans une solution a 10^?4M et de 2.4,5-T, ou dans une solution 10^?5M de piclorame. Le nombre de pousses s'est accru significativement après traitement avec le 2,4,5.-T è 10^?9M et 10^?10M, mais le piclorame n'a pas provoqué d'accroissemcnt significatif du nombre de pousses. La mesure de la concentration de 2,4,5-T dans le tissu extra-cambial a montré que les racines trailées avec du 2,4,5-T è 10^?4M contenaient 5×10^?8 mmole de 2.4,5-T par mg de poids sec et par extrapolation, quc les racines traitées avec du 2,4,5-T k 10^?9M devaient contenir 2 × 10^?12 mmole/mg de poids sec. Die Wirkiing von 2,4,5-T und Picloram auf den Wuchs der Wurzehegmenten von Bromheeren (Rubus procerus P.J. Muell). Die Bildung von Wurzeln und Sprossen aus Wurzelsegmen-ten von Ruhu.i procerus P.J. Muell wurde durch 24-stündiges Einlegen der Wurzelstücke in 10^?4M 2,4,5-T bzw 10^?5M Picloram verhindert. Die Anzahl neugebiideter Sprosse wurde nach Einlegen in 10^?9M und 10^?10M 2,4,5-T, nicht jedoch durch Picloram, signifikant erhöht. Im extracambialen Gewebe von Wurzeln, die mit 10^?4M 2,4,5-T behand-elt worden waren, wurden 5×10^?8mMol 2,4,5-T je mg Trockengewiclu bestimmt. Durch Extrapolation wurde ermittclt. dass mit 10^?9M 2,4,5-T behandelte Wurzeln 2× 10^?12mMol/mg Trockengewicht cnthielten.     

Increased activity and reduced sensitivity of glutamine synthetase in glufosinate‐resistant vetiver (Vetiveria zizanioides Nash) cells

Vetiver (Vetiveria zizanioides Nash) cells derived from an inflorescence were cultured in a modified N6 liquid medium supplemented with 10 µm 2,4‐D and 10 mm proline. Exponentially growing cell suspensions were subcultured with a selection medium containing glufosinate (ammonium dl ‐homoalanin‐4‐yl(methyl)phosphinate). The glufosinate‐resistant cells which can grow in a medium containing 5 × 10^?5 M glufosinate was selected by a stepwise selection, and its I₅₀ value was determined to be 4.2 × 10^?5 M. The growth of susceptible cells was inhibited by lower concentrations of glufosinate and its I₅₀ value was 2.5 × 10^?7 M. This indicated that the selected cells were 170‐fold resistant compared with the susceptible cells. Glutamine synthetase (GS) activity of the resistant cells was twice as high as that of the susceptible cells. The I₅₀ values of glufosinate were 3.2 × 10^?5 M and 9.0 × 10^?7 M for GS from the resistant and susceptible cells, respectively. The accumulation of ammonia caused by GS inhibition was higher in the susceptible cells. Absorption of [3,4–¹⁴C]glufosinate was not significantly different between the resistant and susceptible cells. Both cell types did not metabolize glufosinate. These results suggest that the resistance of the selected vetiver cell suspension to glufosinate is mainly due to increased GS activity and its decreased sensitivity to the herbicide.     

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.     

A novel strategy to reduce overwintering inoculum of Monilinia laxa

Brown rot on cherry and plum, caused by Monilinia laxa, is an important disease, for which overwintered mummified fruit is a significant inoculum source for infection of flowers and fruit in the spring. Experiments were conducted to assess the potential of applying plant protection products in winter and/or early spring to suppress sporulation on mummified fruit. Products tested included Indar 5 EW (a commercial fungicide, a.i. fenbuconazole), Aureobasidium pullulans Y126 [a candidate biocontrol agent (BCA)]), Bacillus sp. B91 (a candidate BCA) and Serenade (a commercially formulated BCA of Bacillus subtilis strain QST 713) in addition to control treated with tap water. Indar and A. pullulans Y126 significantly reduced sporulation when applied once in winter. Overall, a single treatment in early spring (February) was slightly more effective than single treatment in winter (November). Application of all products in both winter and early spring led to significant reduction in sporulation. Indar had the highest efficacy, reducing the number of spores from 9?×?10⁵ to 5?×?10³ per mummified plum when applied twice. Of the three BCAs applied on both occasions, A. pullulans Y126 had the highest efficacy, reducing the number of spores from 9?×?10⁵ to 5?×?10⁴ per mummified plum. There were no synergistic but additive effects between the two applications in winter and early spring based on the Bliss independence test. These results suggest that reducing overwintering inoculum in dormant season is effective and may be part of an integrated management strategy for brown rot on stone fruit.     

Response of maize (Zea mays L.) inbred lines and hybrids to chlorsulfuron

Twenty inbred maize lines, raised in a growth chamber, were treated with 0 or 1 ng g^?1 of chlorsulfuron which caused a variable reduction in root-length. In a second experiment, all crosses (reciprocals included) among two tolerant lines (T: Va85 and Mes44) and two susceptible lines (S: B73 and B79) were raised in a growth chamber together with the parental lines and exposed to 0,0×5 or 1 ng g^?1, The interaction of reciprocal effects x rates was not significant for all traits, The T × S hybrids showed an intermediate response between the T × T and S × S responses for root-length and dry weight. Interaction (hybrids vs. parental lines) × rates was not significant for all traits. These results indicate that susceptibility to chlorsulfuron is not controlled by extra-nuclear factors and that additive gene actions prevail. Four crosses (one T × T, two T × S and one S × S) were further investigated at nine rates from 0 to 1 ng g^?1. The responses confirmed the intermediate behaviour of T×S hybrids, resulting in a GR₂₀ of 0×07, 0×55 and 0×94 ng g^?1 for S × S, T × S and T × T, respectively. In a third experiment, the four crosses previously considered were grown in the field with parental lines and treated at five rates from 0 to 1·12 g a.i. ha^?1. Effects on shoot height and dry weight were consistent with root effects found in growth chamber experiments.     

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 .     

Mobilities of organic compounds in reconstituted cuticular wax of barley leaves: Determination of diffusion coefficients

Isolated cuticular wax, obtained from barley leaves, was mixed with ¹⁴Clabelled organic chemicals including aromatic pesticides and long-chain linear alkanes, alcohols and acids. These mixtures were reconstituted from the melt and labelled chemicals were desorbed from the wax by immersing the wax samples in aqueous phospholipid suspensions. Diffusion coefficients (D) of radiolabelled test compounds in the wax were derived from desorption kinetics. Diffusion coefficients ranged from 10^?17 to 10^?22 m² s^?1 and decreased rapidly with increasing molar volumes of solutes. However, size selectivity of D was much more pronounced with the linear, long-chain molecules than with the aromatic compounds. It is argued that the two different groups of chemicals (compounds occurring naturally in cuticular waxes vs pesticide molecules) were trapped in different fractions of wax during crystallization from the melt. The normal long-chain aliphatic compounds appear to be incorporated into the crystalline fraction of the wax, while the cyclic pesticide molecules are confined to the solid amorphous regions. Our data indicate that constituents of cuticular waxes are not immobile. In fact, relatively small linear aliphatic molecules have mobilities that do not differ too much from those of cyclic pesticides. However, the pronounced size selectivity of diffusivities of long-chain aliphatic compounds causes a rapid decrease in D with increasing chain length. The value of D of hexadecanoic acid was 3.81 × 10^?18 m² s^?1 while that of dotriacontane was only 4.07 × 10^?22 m² s^?1. Thus, increasing the carbon number by a factor of two resulted in a decrease in mobility by almost four orders of magnitude. Diffusivities of selected pesticide molecules in reconstituted wax were compared with permeances measured using intact barley leaves and were found to be in satisfactory agreement.     

DIFFUSION COEFFICIENTS FOR TWO TRIAZINE HERBICIDES IN SIX SOILS

Summary. Diffusion of the triazine herbicides propazine and prometryne was studied in six soils. Apparent diffusion coefficients were calculated from the distribution of herbicide in a column of soil after diffusion from one half of the column for a known time. The magnitude of the diffusion coefficients varied from 1·5 × 10^?9 cm² sec^?1 for propazine in a sandy soil to 3·1 × 10^?9 cm² sec^?1 for prometryne in an organic soil. Under the conditions of measurement, the diffusion coefficients decreased in proportion to the extent of adsorption. Calculations were made to determine over what distances diffusion could be of importance in the movement of these herbicides. Coefficients de diffusion de deux triazines herbicides dans six sols Résumé. La diffusion de deux triazines herbicides, la propazine et la prometryne a étéétudiée dans six sols. Les coefficients de diffusion apparente furent calculés selon la distribution de I'herbicide dans une colonne de sol, aprés diffusion à partir de la moitié de la colonne pendant un temps connu. Les coefficients de diffusion variérent de 1,5 × 10^?7cm² see^?1 pour la propazine dans un sol sableux, á 3,1 × 10^?9 cm² sec^?2 pour la prométryne dans un sol organique. Dans les conditions oú les mesures furent effectuées, les coefficients de diffusion diminuérent en proportion de 1′étendue de l'adsorption. Des calculs ont été effectués pour detérminer au-delá de quelles distances la diffusion pouvait presenter une importance dans le mouvement de ces herbicides. Difftisions-KoeffizienUnfur zwei Trtazin-Deriaate in sechs Böden Zusammenfassung. Die Diffusion der beiden Triazin-Derivate Propazin und Prometryn wurde in sechs Böden untersucht. Die Diffusions-Koeffizienten wurden aus der Verteilung des Herbizids in einer Bodensaule nach Diffusion aus der einen Säulenhalfte in einer bestimmten Zeit errechnet. Die Grösse der Diffusions-Koeffizienten variierte von 1,5 × 10^?7 cm²× sec^?1 bei Propazin in einem Sandboden bis 3,1 × 10^?9 cm²× sec^?1 bei Prometryn in einem Humus-Boden. Unter den gegebenen Versuchsbedingungen nahmen die Diffusions-Koeffizienten in Abhángigkeit von der Stärke der Adsorption ab, Es wurden Berechnungen darüber angestellt, über welche Entfernungcn die Diffusion dieser Herbizide im Boden eine Rolle spielen könnte.     

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.