NADP+ reduction by a methanogen using HCOOH or H2 as electron donor

Summary The resting cells of methanogen strain HU could be used as biocatalyser for converting exoge nous NADP⁺ into NADPH, using either formate or hydrogen as electron donor. To enhance the conversion efficiency of NADPH from NADP⁺, several inhibitors of methylcoenzyme M reductase were used in order to avoid further oxidation of NADPH to CH₄. When methyl viologen (7.5 mol ml^-1) was added to the reaction mixture (17 mg of dry cells, 2 mg Triton X-100, 294 mol of Na-formate and 12 mol of NADP⁺ per ml reaction mixture), 9.6 mol ml^-1 NADPH (80% yield) could be produced in a 2-h reaction, compared with 7.2 mol ml^-1 NADPH (60% yield) in a 6-h reaction in the absence of methyl viologen. Molecular hydrogen istead of formate also served as electron donor to convert NADP⁺ into NADPH. A gas mixture of H₂/N₂ (75/25) yielded 9.8 mol ml^-1 NADPH (82% yield) in a 3-h reaction in the absence of formate, suggesting that H₂ might be a promising, inexpensive electron donor for this reaction system.     

Bacterial feeding by the rotifer Brachionus calyciflorus: Clearance and ingestion rates,behavior and population dynamics

Summary The rotifer Brachionus calyciflorus is capable of collecting and ingesting cells or short chains of a laboratory-grown bacterium Aerobacter aerogenes. Clearance rate, the volume of water effectively processed animal ^-1h^-1, does not vary systematically with bacterial density between 0.01 and 100 g dry weight ml^-1. Consequently, ingestion rates are strongly density-dependent, reaching maximal values at the highest food densities tested. Bacterial feeding rates are consistently lower than those determined with larger food types, except in very dense cell suspensions. A. aerogenes in high concentration (100 g ml^-1) induces Brachionus to orient their pseudotrochal cirri to form screens over the buccal funnel; this behavior is at least four times less frequently observed at low (10 g ml^-1) food density. Despite its occurrence, pseudotrochal screening appears ineffective in regulating bacterial ingestion rate. B. calyciflorus can be cultured xenically for greater than 40 generations fed A. aerogenes alone, with no diminution in net reproductive rate or intrinsic rate of natural increase, and no lengthening in cohort generation time.     

Effects of GNA and other mannose binding lectins on development and fecundity of the peach-potato aphid Myzus persicae

Three mannose-binding lectins were assayed in artificial diets for their toxic and growth-inhibitory effects on nymphal development of the peach-potato aphid Myzus persicae. The snowdrop (Galanthus nivalis) lectin GNA was the most toxic, with an induced nymphal mortality of 42% at 1500 g ml^–1 (30 M) and an IC₅₀ (50% growth inhibition) of 630 g ml^–1 (13 M). The daffodil (Narcissus pseudonarcissus) lectin NPA and a garlic (Allium sativum) lectin ASA induced no significant mortality in the range 10–1500 g ml^–1, but did result in growth inhibition of 59% (NPA) and 26% (ASA) at 1500 g ml^–1 (40 M for NPA, 63 M for ASA). All three lectins were responsible for a slight but significant growth stimulation when ingested at 10 g ml^–1, reaching +26%, +18% and +11% over the control values for the garlic lectin, the daffodil lectin and the snowdrop lectin, respectively. GNA, as well as the glucose/mannose binding lectin Concanavalin A, were also provided at sublethal doses throughout the life cycle of the aphids, and effects on adult performance were monitored. Adult survival was not significantly altered, but both lectins adversely affected total fecundity and the dynamics of reproduction, resulting in significant reduction in calculated r _ms (population intrinsic rate of natural increase) on lectin-containing diets. These effects are discussed in relation to the use of transgenic plants expressing these toxic lectins for potential control of aphid populations.     

Isolation and culture of Lens culinaris Medik. cv. Eston epicotyl protoplasts to calli

Protoplasts of Lens culinaris Medik. cv. Eston were isolated from epicotyl tissues of seedlings grown on Murashige & Skoog basal medium. For isolating the protoplasts, epicotyl tissues were digested for 12–14 h at 25°C in an isolation mixture (pH 5.7) containing 1% Cellulase RS, 0.5% Driselase, 0.25% Pectolyase Y23, 0.2M calcium chloride, 10 mM mannitol and 10 mM MES. Protoplasts were purified by flotation over 20% sucrose and washed with 0.2 M calcium chloride solution supplemented with 10 mM mannitol. Purified protoplasts were cultured at a density of 10⁵ ml^-1 in agarose (Seaplaque, 0.6%) blocks which were suspended in an identical but liquid KM8P culture medium lacking amino acids, ammonium nitrate, and coconut water but containing 0.35 M glucose and a growth regulator complement of either 2.2 M 2,4-dichlorophenoxyacetic acid (2,4-D), 2.7 M naphthaleneacetic acid (NAA), 2.3 M N-(2-furanylmethyl)-1H-purine-6-amine (kinetin), 2.2 M benzylamino purine (BAP), 2.3 M 2-methyl-4-(1H-purine-6-ylamino)-2-buten-1-ol (zeatin), and 1.4 M gibberellic acid (GA₃), or 5.4 M NAA and 2.2 M each of 2,4-D and BAP. The osmotic potential of the liquid culture medium was gradually reduced over a period of 3 weeks by replacing the spent medium with a fresh medium containing 0.25, 0.1 and 0 M glucose at weekly intervals. About 6% of the dividing protoplasts developed into cell colonies after 3 weeks of culture at 25°C in diffuse light (10 E m^-2s^-1). In 35–42 days the microcolonies were about 1 mm in diameter and developed into calli on transfer to agar-solidified B5 medium supplemented with growth regulators used in the protoplast culture medium and 5 mM glutamine. Attempts to regenerate plants from protoplast-derived calli have so far been unsuccessful.Department of Applied Microbiology and Food Science, University of Saskatchewan     

Production of hydrogen peroxide by Lactobacillus hilgardii and its effect on Leuconostoc oenos growth

In mixed culture of Lactobacillus hilgardii X₁B and Leuconostoc oenos X₂L, isolated from Argentinian wines, an amensalistic growth response was observed: Leuconostoc oenos did not grow, and after 24 h of incubation at 30°C no viable cells were detected. In pure and mixed cultures, Lactobacillus hilgardii produced hydrogen peroxide early in the growth cycle, reaching the maximum at 24 h. The values of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) for the action of hydrogen peroxide on the growth of Leuconostoc oenos were: 4.08g ml^-1 and 17.00 g ml^-1 respectively.     

Induced accumulation of triterpenoids in Scutellaria baicalensis suspension cultures using a yeast elicitor

When growth-phase cell suspension cultures of Scutellaria baicalensis were treated with 50 g of yeast elicitor preparation ml^–1, both oleanolic acid and ursolic acid transiently increased in the culture medium rather than in the cells. The maximal triterpenoid concentration was 13.7 mg l^–1 media approx. 35 h after treatment, whereas the maximum concentration was 2.1 mg l^–1 media after about 20 h following treatment with methyl jasmonate. Elicitor treatment also doubled phospholipase A₂ activity (25 pmol mg^–1 min) and the simultaneous treatment of aristolochic acid, a phospholipase A₂ inhibitor, inhibited triterpenoids accumulation as well as phospholipase A₂ activity.     

Cadmium interferes with steroid biosynthesis in rat granulosa and luteal cellsin vitro

Recently, cadmium has been described to disturb ovarian function in rats. In this paper the direct influence of cadmium on steroid production of ovarian cellsin vitro has been studied. Granulosa and luteal cells were obtained from proestrous and pregnant rats, and incubated with 0, 5, 10, 20 or 40 g ml^–1 CdCl₂ in the presence or absence of 0.1–1000 ng ml^–1 follicle stimulating hormone (FSH) or luteinizing hormone (LH) for 24 or 48 h. Production of progesterone (P) and 17-estradiol (E₂) by granulosa and that of P by luteal cells were measured by radioimmunoassay. In FSH-stimulated granulosa cell cultures, 5 and 40 g ml^–1 CdCl₂ suppressed P accumulation to 65 and 10%, respectively; accumulation of E₂ (at 5 g ml^–1 CdCl₂) decreased to 44%. P production of LH-supported luteal cells dropped to 86 and 66%, respectively, when 5 and 40 g ml^–1 CdCl₂ was added to the medium. No alteration in basal P accumulation occurred in granulosa and luteal cell cultures following incubations with 20 and 40 g ml^–1 CdCl₂, whereas basal E₂ production of granulosa cells was markedly diminished. It is concluded that CdCl₂ suppressing steroid synthesisin vitro exerts a direct influence on granulosa and luteal cell function.     

Analysis of gas exchange in seedlings of Acer saccharum: integration of field and laboratory studies

In the field, photosynthesis of Acer saccharum seedlings was rarely light saturated, even though light saturation occurs at about 100 mol quanta m^-2 s^-1 photosynthetic photon flux density (PPFD). PPFD during more than 75% of the daylight period was 50 mol m^-2 s^-1 or less. At these low PPFD's there is a marked interaction of PPFD with the initial slope (CE) of the CO₂ response. At PPFD-saturation CE was 0.018 mol m^-2 s^-1/(l/l). The apparent quantum efficiency (incident PPFD) at saturating CO₂ was 0.05–0.08 mol/mol. and PPFD-saturated CO₂ exchange was 6–8 mol m^-2 s^-1. The ratio of internal CO₂ concentration to external (C _i /C _a ) was 0.7 to 0.8 except during sunflecks when it decreased to 0.5. The decrease in C _i /C _a during sunflecks was the result of the slow response of stomates to increased PPFD compared to the response of net photosynthesis. An empirical model, which included the above parameters was used to simulate the measured CO₂ exchange rate for portions of two days. Parameter values for the model were determined in experiments separate from the daily time courses being sumulated. Analysis of the field data, partly through the use of simulations, indicate that the elimination of sunflecks would reduce net carbon gain by 5–10%.List of symbols A measured photosynthetic rate under any set of conditions (mol m^-2 s^-1) - A _m (atm) measured photosynthetic rate at saturating PPFD, 350 l/l CO₂ and 21% (v/v) O₂ (mol m^-2 s^-1) - C constant in equation of Smith (1937, 1938) - C _a CO₂ concentration in the air (l/l) - C _i CO₂ concentration in the intercellular air space (l/l) - C _i ^/* C _i corrected for CO₂ compensation point, i.e., C _i -I ^*, (l/l) - CE initial slope of the CO₂ response of photosynthesis (mol m^-2 s^-1/(l/l)) - CEM CE at PPFD saturation - E transpiration rate (mmol m^-2 s^-1) - F predicted photosynthetic rate (mol m^-2 s^-1) - G leaf conductance to H₂O (mol m^-2 s^-1) - I photosynthetic photon flux density (mol m^-2 s^-1) - N number of data points - P _m predicted photosynthetic rate at saturating CO₂ and given PPFD (mol m^-2 s^-1) - P _ml predicted photosynthetic rate at saturating CO₂ and PPFD (mol m^-2 s^-1) - R _d residual respiratory rate (mol m^-2 s^-1) - T _a air temperature (°C) - T _l leaf temperature (°C) - V reaction velocity in equation of Smith (1937, 1938) - V _max saturated reaction velocity in equation of Smith (1937, 1938) - VPA vapor pressure of water in the air (mbar/bar) - VPD vapor pressure difference between leaf and air (mbar/bar) - X substrate concentration in equation of Smith (1937, 1938) - initial slope of the PPFD response of photosynthesis at saturating CO₂ (mol CO₂/mol quanta) - (atm) initial slope of the PPFD response of photosynthesis at 340 l/l CO₂ and 21% (v/v) O₂ (mol CO₂/mol quanta) - I ^* CO₂ compensation point after correction for residual respiration (l/l) - PPFD compensation point (mol m^-2 s^-1)     

Insecticidal activity of avidin and streptavidin against four species of pest Lepidoptera

Two biotin-binding proteins, avidin and streptavidin, were found to be insecticidal to the larvae of four species of Lepidoptera – light brown apple moth, Epiphyas postvittana (Walker) (fam. Tortricidae), green-headed leaf-roller, Planotortrix octo (Dugdale) (fam. Tortricidae), brown-headed leaf-roller, Ctenopseustis obliquana (Walker) (fam. Tortricidae) and potato tuber moth, Phthorimaea operculella (Zeller) (fam. Gelechiidae). Mortality occurred in all species, but there was a wide range in susceptibility. P. operculella larvae were the most susceptible with an LC₅₀ of respectively, 2.3 g ml^–1 for avidin and 1.4 g ml^–1 for streptavidin after 9 days. E. postvittana larvae had an LC₅₀ of 43.4 g ml^–1 for avidin after 21 days, and C. obliquana larvae of 45.7 g ml^–1 for avidin after 28 days. Although significant mortality occurred in P.octo at the highest doses of avidin, there was no sufficient dose-mortality response to calculate an LC₅₀ for this species. For all species mortality curves were steep over a close range of doses followed by a plateau where mortality did not increase significantly with dose and did not reach 100%. Mortality was significantly affected by the amount of biotin in the diet on which the parental generation had been reared. Where this was rich in biotin, significant mortality of the offspring was much lower: larval offspring of a colony of E. postvittana, reared for five generations on a biotin-free diet had an LC₅₀ of 5.1 g ml^–1 after 14 days compared with 76.7 g ml^–1 for larvae from a colony reared on general purpose diet. The implications for use of these proteins to confer insect resistance on transgenic plants are discussed.     

The effects of aflatoxin B1 on immature germinating maize (Zea mays) embryos

Immature maize (Zea mays L.) embryos were treated with aflatoxin B₁ concentrations, ranging from 0.1 g ml^–1 to 25 g ml^–1. Below 5 g ml^–1 aflatoxin B₁, root and shoot elongation was not significantly inhibited. Ultrastructurally, root tip cells showed little deterioration, except a possible diffused clearing in mitochondria and plastids. As the toxin concentration was increased above 5 gml^–1, shoot, and particularly root elongation, was progressively inhibited. Associated with this, there was an apparent decrease in the ribosome population. Furthermore, membranes, particularly the vacuolar membrane, became abnormal and vacuolar distension occurred. At 20 and 25 g ml^–1, these effects were exacerbated, and mitochondria and plastid structure was disrupted. At these concentrations, there was evidence of a disruption in lipid metabolism. The results are discussed in the context of known aflatoxin effects on cellular control mechanisms and ultrastructure in animal systems.     

Feeding in the rotifer Brachionus calyciflorus

Summary The laboratory feeding behavior of Brachionus calyciflorus varies depending upon the type of food cell available in suspension. When feeding on the yeast Rhodotorula glutinis, rotifers show a continuous increase in ingestion with increased cell density between 0.01 and 1000 g dry weight ml^-1. Effective clearance rates drop from ca. 50 l animal^-1 h^-1 to less than 0.5 l animal^-1 h^-1 over this food density range. When feeding on Englena gracilis, B. calyciflorus ingestion rates are constant between 1.0 and 100 g ml^-1 of available food, averaging close to 25 ng animal^-1 h^-1. The decrease in clearance rate is more striking than with R. glutinis, dropping from 45 l animal^-1 h^-1 at 0.1 g ml^-1 to 0.13 l animal^-1 h^-1 at 100 g ml^-1. Differences between the patterns obtained with the two food types indicate fundamental dissimilarities in the feeding behavior of this rotifer species when presented with these different foods.     

Hormone studies inMyxine glutinosa: effects of the eicosanoids arachidonic acid,prostaglandin E1, E2, A2, F2α, thromboxane B2 and of indomethacin on plasma cortisol,blood pressure,urine flow and electrolyte balance

Summary Hagfish,Myxine glutinosa, were used in an investigation of the possible effects of various eicosanoids and the prostaglandin synthetase inhibitor indomethacin, on cortisol production, blood pressure control, urine flow and electrolyte balance.Cortisol levels in plasma of untreated control animals and plasma from animals 1 h following injection of 50 g kg^–1 prostaglandin E₁, E₂, A₂, F₂ TXB₂ and indomethacin were not detectable. However, plasma cortisol levels rose to between 10 and 26 pg ml^–1 1 h following injection of either 50 g kg^–1 arachidonic acid or prostaglandin E₂. This rise was similar in magnitude to that produced 1 h following administration of 50 g kg^–1 porcine ACTH.The resting dorsal aortic blood pressure of between 3.50 and 3.75 mmHg was reduced on average by 50% for 12–15 min when animals received 10 g kg^–1 arachidonic acid, prostaglandin E₁, E₂, A₂, and TXB₂ and was effectively reduced to zero for 20 min or more following 50 g kg^–1 of these eicosanoids. Similar doses of prostaglandin F₂, however, evoked an increase in blood pressure (19–33%) whilst indomethacin was without effect.Control measurements of urine flow inMyxine were estimated to be between 540 and 660 l h^–1 kg^–1. There was a marked reduction in urine output following the arterial vasodepression induced by arachidonic acid, prostaglandin E₁, E₂, A₂ and TXB₂ in doses of 10 g kg^–1, an effect which became even more pronouced following injection of 50 g kg^–1 quantities, leading in some cases to complete anuria. There was no significant change in urine volume following either the vasopressor action of prostaglandin F₂ or following indomethacin.None of the compounds tested in this study significantly influenced the plasma or urine electrolyte status ofMyxine.     

Binding of [3H]muscimol to calf cerebrocortical synaptic membranes and the effects of sulphur-containing convulsant and non-convulsant compounds

Endogenous and xenobiotic sulphur-containing convulsant and non-convulsant compounds containing structural moieties of, or bearing a structural resemblance to, GABA and homocysteine were tested in binding studies for their potency in displacing the GABA-mimetic [³H]muscimol from specific, high-affinity sites (K _d=3.6 nM;B _max=3.94 pmol/mg protein) on freeze-thawed, Triton-treated calf-brain synaptic membranes. The xenobiotic convulsants, 4-mercaptobutyric acid (MBA), 3-mercaptopropionic acid (3-MPA) and 2-mercaptopropionic acid (2-MPA) were found to be two-site competitive inhibitors exhibiting apparent inhibition affinity constants (K _i ^app ) of 5000 M, 3750 M, and 4800 M, respectively; while homocysteic acid (K _i ^app =4800 M) was shown to be a one-site partial competitive inhibitor. Intermediary metabolites of methionine: S-adenosyl-l-homocysteine,l-cysteine, the convulsantl-homocysteine, and its non-convulsant disulphide oxidation product, homocystine, were found to be one-site partial competitive inhibitors exhibitingK _i ^app values of 5750 M, 8350 M, 5000 M, and 510 M, respectively. The endogenous anticonvulsant neuroeffector, taurine, and the tripeptide, reduced glutathione (GSH) were shown to be, respectively, one-site (K _i=20 M) and two-site (K _i ^app =4300 M) competitive inhibitors of [³H]muscimol binding. These findings are discussed with regard to a previously proposed mechanism for the convulsant action of homocysteine.     

Phenotypic expression of Vogesella indigofera upon exposure to hexavalent chromium,Cr6+

A eubacterium producing a blue pigment was isolated from a drinking water filter, and subsequently identified as Vogesella indigofera. This bacterium was further investigated for its morphological and biochemical characteristics after exposure to hexavalent chromium, Cr⁶⁺. The threshold Cr⁶⁺ concentration inhibiting the pigment production by V. indigofera was 200–300 g ml^–1 in liquid cultures of nutrient broth and 100–150 g ml^–1 on nutrient agar plates. The Cr⁶⁺ concentration preventing V. indigofera growth was 300–400 g ml^–1 in liquid cultures, but greater than 150 g ml^–1 on agar plates. Moreover, rugose colonies without the blue pigmentation were observed on agar plates amended with 150 (g Cr⁶⁺) ml^–1. The biochemical utilization profiles of the colonies without pigmentation did not differ from the original pigment-producing ones, indicating phenotypic plasticity of this bacterium. The difference of phenotypic expression of V. indigofera under various Cr⁶⁺ concentrations might have potential application as a pollution bioindicator for heavy metals.     

Growth effects of nagilactone E on cultured cells of lettuce

Nagilactone E, a norditerpene dilactone isolated from a gymnosperm, Podocarpus nagi (Podocarpaceae), was able to stimulate the growth of cultured cells of Lactuca sativa cv. Grand Rapids at 0.1 g ml^-1 but not at 0.01 or 1 g ml^-1. Cell wet weight/unit time and cell number/unit wet weight were increased when they were recorded at the end of the 14-day incubation period. Also, the population of cells treated with that concentration of nagilactone E had a higher percentage of cells with shorter cell length compared to the control (untreated).     

Potassium modulation of methionine uptake in astrocytes in vitro

Methionine participates in a large variety of metabolic pathways in brain, and its transport may play an important regulatory role. The properties of methionine uptake were examined in a preparation of neonatal rat brain astrocytes. Uptake is linear for 15 minutes, up to 2.5 M. At steady state conditions, methionine is concentrated 30–50-fold. Measured methionine homoexchange accounts for a significant fraction of uptake at concentrations greater than 10 M. We recently reported that methionine uptake is decreased by elevations in extracellular K⁺. Potassium induced efflux cannot account for this apparent effect; and thus for concentrations less than 2.5M, and for short times of incubation, measured rates of methionine uptake represent unidirectional flux. At extracellular concentrations of K⁺ equal to 6.9 mM, the apparentV _max of methionine transport is 182 pmol/min/mg protein, and theK _m is 1.3 M. Where K⁺ is shifted to 11.9 mM, theK _m remains unchanged, and theV _max is reduced by half.     

Respiration rates of two species of Gnathostomulids

Summary Respiration rates for two species of Gnathostomulida from poorly oxygenated subtidal sands of Bermuda were measured using Cartesian diver respirometers.ForHaplognathia cf.ruberrima a respiration-body weight regression gaveR=0.790·W ^0,649 (in l·10^-3O₂/h and g wet weight). Respiration rates for adult animals ofGnathostomula sp. of a mean weight of 1.3 g ranged between 0.25 and 0.63 l·10^-3 O₂/h. These rates are low when compared with literature data on meiobenthic species from a wider habitat range but similar to respiration rates of marine and limnic nematodes living in sediments with strongly reducing capacity.     

Parameters influencing transient and stable transformation of barley (Hordeum vulgare L.) protoplasts

Cat gene expression has been investigated following PEG-mediated plasmid uptake into barley protoplasts. The uptake conditions optimised for transient expression were employed for stable transformation. Transformed protoplast-derived calli of the cvs. Dissa and Igri, were selected on medium containing G418 at 40 g ml^–1 or kanamycin sulphate at 250 g ml^–1. Absolute transformation frequencies of 28.9×10^–5 and 21.3×10^–5 were recorded for Dissa with kanamycin sulphate and G418 selection, respectively. The frequency for Igri was 11.5×10^–5 with G418 selection. Antibiotic resistant protoplast-derived colonies expressed NPTII activity; Southern hybridisation confirmed integration of the nptII gene into barley genomic DNA.Abbreviations ABA abscisic acid - AC-CAP acetylated chloramphenicol - BAP 6-benzylaminopurine - cat chloramphenicol acetyltransferase gene - CAT chloramphenicol acetyltransferase activity - CaMV cauliflower mosaic virus - CAP chloramphenicol, 2,4-d-2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid - G418 Geneticin - gus -glucuronidase gene - HEPES (N[2-hydroxyethyl] piperazine-N-[2-ethanesulphonic acid]) - IAA indole acetic acid - MES 2-N-morpholinoethane sulphonic acid - NAA -naphthaleneacetic acid - npt II neomycin phosphotransferase gene - NPTH neomycin phosphotransferase activity - PEG polyethylene glycol - SCV settled cell volume     

Factors affecting chloride conductance in apical membrane vesicles from human placenta

Summary Apical membrane vesicles from human term placenta were isolated using a magnesium precipitation technique, and the purity of the vesicles was assessed morphologically using scanning and transmission electron microscopy, and biochemically, using marker enzymes. The vesicles were found to be morphologically intact and significantly enriched in enzymes associated with apical membranes. ³⁶Cl^– uptake into these vesicles was studied in the presence of an outwardly directed Cl^– gradient. This uptake was found to be time dependent, with an initial rapid uptake tending to peak between 10 and 20 min and thereafter decline. Uptake was found to be voltage dependent since 5 m valinomycin caused a decrease in uptake. The effects of N-phenylanthranilic acid (NPA) and 4,4-diisothiocyanostilbene-2,2-disulphonic acid (DIDS) and bumetanide on the initial rate of Cl^– were examined in the presence and absence of 5 m valinomycin. NPA and DIDS inhibited isotope uptake strongly with IC₅₀ values of 0.83±0.35 m and 3.43±0.37 m, respectively, in the absence of valinomycin. Although valinomycin reduced ³⁶Cl^– uptake by about 80% when added before the isotope, DIDS reduced the uptake which remained in a concentration-dependent fashion with an IC₅₀ of 5.6±2.1 m. Under these conditions, NPA was without effect at concentrations below 100 m. Bumetanide was without effect at the concentrations used in the absence of valinomycin. However, following valinomycin pretreatment, bumetanide reduced ³⁶Cl^– uptake significantly at 100 m concentration. Vesicle diameter, as assessed by flow cytometry, did not change under the conditions employed.The effects of some fatty acids were also investigated. Arachidonic acid and linoleic acid inhibited Cl^– uptake with IC₅₀ values of 37.6±14.9 m and 4.59±0.51 m, respectively. Arachidonyl alcohol and elaidic acid were found to be without effect. These studies show that human placental brush border membrane vesicles possess a chloride conductance channel, the activity of which can be measured in the presence of an outwardly directed Cl^– gradient and this channel is sensitive to Cl^– channel inhibitors, especially N-phenylanthranilic acid, and can be inhibited by unsaturated fatty acids such as arachidonic acid and linoleic acid.This work was supported in part by the Cystic Fibrosis Association of Ireland and Eolas, The Irish Science and Technology Agency. The technical assistance of Mr. Cormac O' Connell in the preparation of the electron micrographs and of Mr. Roddy Monks in the flow cytometric analysis is gratefully acknowledged.     

Accelerated degradation of <Emphasis Type="Italic">N,N′</Emphasis> (DBU) upon repeated application

In a recent study on the degradation of N,N-dibutylurea (DBU), a breakdown product of benomyl [methyl 1-(butylcarbamoyl)-2-benzimidazole carbamate], the active ingredient in Benlate^® fungicides, degradation half-lives of 1.4–46.5days were observed across several soils incubated at various combinations of soil moisture potential (–0.03 and –0.1MPa) and temperature (23, 33, and 44°C) for a single DBU application of 0.08 and 0.8 g g^–1 (Lee et al. 2004). However, Benlate^® can be applied as often as every 7days resulting in the repeated application of DBU likely to be present in the Benlate^® over a growing season. In this study, the effect of seven repeated DBU applications on mineralization rate was investigated in two soils, which encompass the range in rates previously observed. For the slower degrading soil, repeated DBU application increased mineralization from 0.029 to 0.99day^–1 at the 0.08 g g^–1 rate, and 0.037 to 0.89day^–1 at the 0.8 g g^–1 rate. For the faster degrading soil, effects on mineralization of repeated DBU applications were small to negligible. For the latter soil, the effect on mineralization of applied DBU concentrations from 0.0008 to 80 g g^–1 was also investigated. Mineralization rates decreased from 0.43 to 0.019day^–1 with increasing DBU concentrations. However, the amount of DBU mineralized by day 70 was similar across concentrations and averaged 83% of applied. Microbial respiration was not affected by increasing DBU concentrations. These findings support the supposition that DBU is readily degraded by soil microorganisms, thus unlikely to accumulate in agricultural soils.