Tissue culture ofKarwinskia humboldtiana—a plant producing toxins with antitumoural effects

Isolated embryos ofKarwinskia humboldtiana were cultured in vitro. The growth of embryos and development to plantlets on woody plant medium supplemented with indole-3-acetic acid 6.10^-2 mol l^–1, gibberellic acid (GA₃) 3.10^-2 mol l^–1, and 6-benzylaminopurine (BA) 2 mol l^–1 was obtained. Multiplication of shoots and rooting of excised shoots has been achieved. Callus formation on modified Murashige-Skoog medium supplemented with 1-naphthaleneacetic acid 10 mol l^–1, GA₃ 14 mol l^–1, and kinetin 5 mol l^–1 on hypocotyls, or on root cultures on medium supplemented with 2.4-dichlorophenoxyacetic acid 10 mol l^–1 and BA 10 mol l^–1 was induced.Abbreviations BA 6-benzylaminopurine - 2,4-d 2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid - IAA indole-3-acetic acid - NAA 1-naphthaleneacetic acid - TEM transmission electron microscopy     

First survey on the natural occurrence of Fusarium mycotoxins in Bulgarian wheat

Wheat for human consumption (140 samples) was collected after harvest from all regions of Bulgaria. The 1995 crop year was characterized by heavy rainfall in the spring and summer months. The internal mycoflora of wheat samples was dominated by Fusarium spp. and Alternaria spp., and storage fungi were rarely present. The samples were analysed for contamination with Fusarium mycotoxins deoxynivalenol (DON), 3-acetyldeoxynivalenol (3-AcDON), 15-acetyldeoxynivalenol (15-AcDON), T-2 Toxin (T-2), diacetoxyscirpenol (DAS), and zearalenone (ZEA), using enzyme immunoassay methods. DON and ZEA were the predominant toxins, with a contamination frequency of 67% and 69%, respectively. The average levels of these toxins in positive samples were 180 g/kg (DON) and 17 g/kg (ZEA), maximum concentrations were 1800 g kg^–1 and 120 g kg^–1, respectively. Acetyl derivatives of DON, namely 3-AcDON and 15-AcDON, were found in 2.1 % and 0.7% of the samples, at at maximum level of about 100 g kg^–1. Only one sample was positive for T-2 (55 g/kg), DAS was not detected. This is the first report about the natural occurrence of a range of Fusarium mycotoxins in wheat for human consumption in Bulgaria.Abbreviations 3-AcDON 3-acetyldeoxynivalenol - 15-AcDON 15-acetyldeoxynivalenol - DAS diacetoxyscirpenol - DON deoxynivalenol - EIA enzyme immunoassay - T-2 T-2 toxin - ZEA zearalenone     

Unexpected effects of chitinases on the peach-potato aphid (Myzus persicae Sulzer) when delivered via transgenic potato plants (Solanum tuberosum Linné) and in vitro

With the aim of producing insect-resistant potato plants, internode explants of Solanum tuberosum L. cv. Désirée were transformed with an Agrobacterium strain C58pMP90 containing an insect (Phaedon cochleariae: Coleoptera, Chrysomelidae) chitinase gene and the neomycin phosphotransferase (nptII) gene as selectable marker, both under the control of the viral CaMV 35S promoter. Three transformed potato lines (CH3, CH5 and CH25) exhibiting the highest chitinolytic activities were selected for feeding experiments with the peach-potato aphid, Myzus persicae (Sulzer), under controlled photoperiod and temperature conditions. Aphids fed on transgenic potato plants showed a reduced pre-reproductive period and an enhanced daily fecundity. Transgenic potato lines did not affect nymphal mortality, but improved several biological parameters related to aphid populations growth. Artificial diets were used to provide active (1, 10, 100 and 500 g ml^–1) and inactive (500 g ml^–1) bacterial (Serratia marcescens) chitinase to M. persicae. These compounds increased nymph survival at all active chitinase doses when compared to the control diet, while inactive chitinase did not. Although the pre-reproductive period was slightly shortened and the daily fecundity slightly higher, active and inactive chitinase provided as food led a reduction from 1 to 1.5 day populations doubling time. Therefore chitinase activity was responsible for the probiotic effects on aphids. Our results question the relevance of a chitinase-based strategy in the context of potato culture protection.     

Effect of zearalenone (F-2) on pea stem,maize root,and rat liver mitochondria

At 5 and 10 g ml^-1 concentration, zearalenone (F-2), a mycotoxin produced by a number of species of the genus Fusarium, causes an inhibition of the oxidative phosphorylation of isolated plant mitochondria, while at 20 and 40 g ml^-1 it causes uncoupling. However, when the mitochondria are pre-incubated for 20 min with F-2, the uncoupling appears to be the prevailing effect. F-2 is also able to inhibit the mitochondrial ATPase activity (Mg²⁺-dependent). Conversely, F-2 (40 g ml^-1) does not alter the ATP level of maize roots and only slightly affects the ATPase activity of pea stem and maize root microsomal fractions. In addition, F-2 (10–40 g ml^-1) inhibits ATP synthesis catalyzed by rat liver mitochondria. It is suggested that the phytotoxicity of F-2, also known for its ability to collapse the transmembrane electric potential of maize roots, may be mainly linked to its ability to increase the proton permeability of the cell, similar to the common uncouplers.Abbreviations F-2 zearalenone - DCCD N,N-dicyclohexylcarbodiimide - PCCP carbonyl cyanide, p-trifluoromethoxiphenylhydrazone - CBT Cerospora beticola toxin     

Antialgal activity of a hepatotoxin-producing cyanobacterium,Microcystis aeruginosa

Antimicrobial activity of toxin produced by a freshwater bloom-forming cyanobacterium Microcystis aeruginosa has been studied. When tested against certain green algae, cyanobacteria, heterotrophic bacteria and fungi, the toxin inhibited growth of only green algae and cyanobacteria. The toxin has been partially purified employing Thin layer chromatography (TLC) and High-performance liquid chromatography (HPLC) techniques and appears to be microcystin-LR (leucine–arginine). Both crude and purified toxins showed toxicity to mice, the clinical symptoms in test mice being similar to those produced by hepatotoxin. Purified toxin at a concentration of 50 g ml^–1 caused complete inhibition of growth followed by cell lysis in Nostoc muscorum and Anabaena BT1 after 6 days of toxin addition. Addition of toxin (25 g ml^–1) to the culture suspensions of the Nostoc and Anabaena strains caused instant and drastic loss of O₂ evolution. Furthermore a marked reduction (about 87%) in the ¹⁴CO₂ uptake was also observed at a concentration of 50 g ml^–1. Besides its inhibitory effects on photosynthetic processes, M. aeruginosa toxin (50 g ml^–1) also caused 90% loss of nitrogenase activity after 8 h of its addition. Experiments performed with ¹⁴C-labelled toxin indicate that the toxin uptake by cyanobacterial cells occurs both in light and dark. These results demonstrate that the toxin is strongly algicidal and point to the possibility that it may have an important role in establishment and maintenance of toxic blooms of M. aeruginosa in freshwater ecosystems. The relative significance of the hepatotoxic effect and the algicidal effect of the toxin is discussed with reference both to survival and dominance of M. aeruginosa in nature.     

Effect of phytotoxic metabolites ofFusarium culmorum on barley root and root-hair development

Summary A mixture of gluconic acid and two unidentified organic acids, isolated from the culture filtrate ofFusarium culmorum, grown in glucose-limited continuous culture, were found to be highly toxic to growth of barley seedlings. A concentration of 900 g ml^–1 of the acid totally inhibited germination of barley seeds, with lower concentrations greatly inhibiting growth and development of germinated seeds. Root extension and root-hair production were inhibited at a concentration of 450 g ml^–1 of the acids, but the number of roots per seedling was increased. Toxicity of the acids was promoted at low pH.     

Feeding rate inhibition in crowded Daphnia pulex

Feeding rates of Daphnia pulex fed a range of levels of the alga Chlamydomonas reinhardi of 15 °C are strongly density-dependent. At lower densities, Daphnia (30 1^–1) fed at higher rates than crowded (270 1^–1) Daphnia which manifest a relatively depressed saturation feeding response. At 30 individuals/liter, Daphnia consumed 8.5 – 15.7 × 10⁴ cells d^–1h^–1 (on a volume basis, 12.1 – 22.2 × 10⁶ m³), at 270 L^–1 3.7 – 3.9 × 10⁴ (5.2 – 5.5 = 10⁶ m³ cells d^–1h^–1 when feeding on algae at 80 000 cells ml^–1 (11.3 × 10⁶ m³ ml^–1). The feeding rate data best fit an Ivlev feeding function. An autoallelopath might be causing the repression. Water preconditioned with crowded Daphnia completely repressed feeding in uncrowded Daphnia after six hours.     

Stimulation of growth and phospholipase A2 by the peptides mastoparan and melittin and by the auxin 2,4-dichlorophenoxyacetic acid

The peptide mastoparan from wasp venom and the peptide melittin from bee venom stimulated growth in etiolated zucchini (Cucurbita pepo L.) hypocotyls. Both peptides were only effective in hypocotyls with abraded cuticles. At concentrations of 2 g ml^–1 peptide growth was stimulated 72% by mastoparan and 50% by melittin after 2 h as compared to the controls. Mastoparan (5 g ml^–1), melittin (10 g l^–1) and 2,4-dichlorophenoxyacetic acid (5×10^–4 M) stimulated accumulation of ¹⁴C-choline-labeled lysophosphatidylcholine in less than 10 min in cultured soybean cells (Glycine max L.), all to about the same extent. The effects of these peptides are among the first to be reported on plant cells and may be related to important events coupled to growth stimulation.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid     

Arsenic concentrations in water and fish from Chautauqua Lake,New York

Synopsis Arsenic persists in Chautauqua Lake, New York waters 13 years after cessation of herbicide (sodium arsenite) application and continues to cycle within the lake. Arsenic concentrations in lake water ranged from 22.4–114.81 g l^–1, = 49.0 ag l^–1. Well water samples generally contained less than 10 g l^–1 arsenic. Arsenic concentrations in lake water exceeded U.S. Public Health Service recommended maximum concentrations (10 g l^–1) and many samples exceeded the maximum permissible limit (50 g l^–1). Fish accumulated arsenic from water but did not magnify it. Fish to water arsenic ratios ranged from 0.4–41.6. Black crappie (Pomoxis nigromaculatus) contained the highest arsenic concentrations (0.14–2.04 g g^–1 ), X = 0.7 g g^–1) while perch (Perca flavescens), muskellunge (Esox masquinongy) and largemouth bass (Micropterus salmoides) contained the lowest concentrations (0.02–0.13 g g^–1). Arsenic concentrations in fish do not appear to pose a health hazard for human consumers.     

Endophytic fungi from Musa acuminata leaves and roots in South China

One hundred and sixty-three endophytic fungal cultures were isolated from 200 leaf samples of Musa acuminata trees, which were soaked in 36% formaldehyde solution for surface sterilization. They belonged to the genera of Gloeosporium musae (45%), Myxosporium spp. (11%), Deightoniella torulosa (8.5%), Alternaria tenuis (7.9%), Sphaceloma spp. (7.4%), Aureobasidium spp. (4.3%), Melida spp. (1.8%), Uncinula spp. (1.8%), Penicillium spp. (1.8%), Aspergillus spp. (1.2%), Sarcinella spp. (1.2%), Cladosporium sp. (0.6%), Cephalosporium sp. (0.6%) and sterile mycelium (6.7%). Sixty-eight endophytic fungal cultures were isolated from 100 root samples. They respectively belonged to the genera of Aspergillus spp. (31%), Paecilomyces spp. (16%), Penicillium spp. (15%), Fusarium spp. (10%), Gloeosporium musae (6%), yeast (3%), Deightoniella torulosa (3%), Spicaria sp. (1.4%), Cephalosporrium sp. (1.4%), Meliola sp. (1.4%) and sterile mycelium (10%). Water agar (containing 50 g chloramphenicol ml^–1 and 50 g streptomycin ml^–1) seemed to be a better medium for isolation of endophytic fungi than potato-dextrose agar (PDA, containing 50 g chloramphenicol ml^–1 and 50 g streptomycin ml^–1).     

In vitro micropropagation of Arctostaphylos uva-ursi (L.) Sprengel.: Comparison between two methodologies

In vitro micropropagation of Arctostaphylos uva-ursi was performed to increase the number of ground cover species able to serve as substitute for members of the Rosaceae susceptible to fire blight. Explants (node segments) excised from plants growing in the greenhouse were established in vitro on a medium containing 10 M -naphthaleneacetic acid (NAA) and activated charcoal (2 g I^-1). Using in vitro grown shoots, two propagation procedures were used:- Culture of nodal fragments with 50 M NAA resulted in the growth of 6 to 7 nodes every 4 weeks, yielding 1 700 almost rootable shoots after 4 subcultures;- Development of axillary shoots obtained with media containing 25 M benzyladenine (BA) and 20 M indoleacetic acid (IAA) yielded almost 500 rootable shoots after 4 subcultures. The rate of propagation decreased after the 3^rd subculture.Percentage of in vitro rooted shoots reached 98% with diluted micronutrients and 10 M NAA but 31% of the plants died during acclimatization.Abbreviations BA benzyladenine - BM basal medium - HID high intensity discharge - IAA indoleacetic acid - IBA indolebutyric acid - NAA -naphthaleneacetic acid - PAR photosynthetic active radiation - 2iP 2-isopentenyladenine     

Antifouling activity of seaweed extracts on the green alga Enteromorpha prolifera and the mussel Mytilus edulis

Twenty-seven species of common seaweeds from the coast of Korea havebeen screened for antifouling activity. The seaweed extracts were tested inlaboratory assays against the marine fouling green alga Enteromorphaprolifera and the blue mussel Mytilus edulis. Tissue growth, sporesettlement, zygote formation and germlings of the E. prolifera wereinhibited by methanol extracts of the seaweed Ishige sinicola (= I. foliacea) and Sargassum horneri. Spore settlement was stronglyinhibited by using extract concentrations as low as 30 g mL^-1with I. sinicola and 120 g mL^-1 with S. horneri. The repulsive activity of the foot of the mussel was completely inhibited bymethanol extracts of I. sinicola and Scytosiphon lomentaria atconcentrations of 40 g per 10 L drop supplied to eachmussel. These extracts also showed strong antifouling activities onlarval settlement with, respectively, no or only 6% of the spat settlingwhen a test concentration of 0.8 mg mL^-1 was used. This work isthe first stage towards the development of novel antifouling agents frommarine macroalgae.     

Influence of inorganic microelements on the production of camptothecin with suspension cultures of <Emphasis Type="Italic">Camptotheca acuminata</Emphasis>

The effects of eight microelements (I^–, BO₃ ^3–, MoO₄ ^2–, Co²⁺, Cu²⁺, Mn²⁺, Fe²⁺, Zn²⁺) on the biosynthesis of camptothecin and the growth of suspension cultures of Camptotheca acuminata were studied. The increase of I^– to 25 M l^–1, Cu²⁺ to 1 M l^–1, Co²⁺ to 2 M l^–1 and MoO₄ ^2– to 10 M l^–1 in Murashige and Skoog (MS) medium resulted in 1.66, 2.84, 2.53 and 2.04 times higher of camptothecin yield than that in standard MS medium respectively. Combined treatment of I^– (25 M l^–1), Cu²⁺ (1 M l^–1), Co²⁺ (2 M l^–1) and MoO₄ ^2– (10 M l^–1) lead to improve cell dry weight, camptothecin content, and camptothecin yield to 30.56 g l^–1, 0.0299%, and 9.15 mg l^–1, respectively, which were 20.2, 208.9 and 273.8% increment respectively when compared with those of control.     

Shoot,root and flower morphogenesis on tomato inflorescence explants

Regeneration of de novo shoots, roots and flowers has been obtained on inflorescence explants of tomato (Lycopersicon esculentum Mill.). Indole-3-acetic acid (IAA), indole-3-butyric acid (IBA) and -naphthaleneacetic acid (NAA) were added in a 3×3×3 factorial combination with kinetin, each at 0.001, 0.1 and 10 M concentrations. Direct shoot formation occurred on media with 10 M kinetin and 0.001 M IAA or NAA. Root formation was observed on media with 0.1–10 M IAA, IBA or NAA. Flower formation occurred on elongated shoots with several leaves on media with 10 M IAA and 0.1 M kinetin. Shoot organogenesis was increased by substituting 10 M zeatin or N⁶-benzyladenine (BA) for kinetin. Eleven tomato cultivars were tested for their ability to undergo de novo shoot regeneration on the improved medium. All tomato cultivars were capable of shoot morphogenesis with a mean number of shoots per explant that ranged from 1.3 (Red Alert) to 5.3 (Large Red Cherry). Histological studies revealed that active cell divisions occurred in subepidermal and cambial tisue during the first week of culture. Meristematic centers of dividing cells were evident by day 14, and well-developed shoot apices and leaf structures were observed on 50% of the explants 28 days after culture initiation.Abbreviations BA N⁶-benzyladenine - IAA Indole-3-acetic acid - IBA Indole-3-butyric acid - 2iP N⁶-[²-isopentyl]adenine - NAA -naphthaleneacetic acid - PGR plant growth regulator     

Some effects of long-term ozone fumigation on Norway spruce

Summary Potted cuttings of a 12-year-old Picea abies tree were fumigated with ozone, 100 or 300 g O₃· m^–3 (50 or 150 ppb O₃) being added to charcoal-filtered air during the 1985 growing season for a total of 1215 h. The wax structure of ozone-fumigated needles was no different from that of controls. Because flattened wax structures and fused wax fibrils also occurred in controls, these phenomena could not serve as bioindications for the ozone concentrations applied. A smooth layer was found beneath the soluble wax layer and covered needle surface and stomatal openings of ozone-fumigated needles to a greater extent than in controls. Wax quantity was considerably reduced by fumigation with 300 g O₃ · m^–3. Leaf pigments (as extracted with the wax) were less abundant in needles treated with 300 gO₃; the smooth layer probably contributed to the impeded extraction of pigments.     

Biosorption and solubilization of copper oxychloride fungicide by Aspergillus niger and the influence of calcium

The biosorption of copper oxychloride fungicide particulates(1 m diameter), at concentrations ranging from 25 to 500 ppm active ingredient (ai), by pelleted mycelium of Aspergillus niger grown on Czapek Dox medium was evaluated. The concentration of the fungicide adsorbed to the mycelium, remaining suspended or solubilized in the medium, was determined by analysis of its copper content (CuF)using atomic absorption spectrophotometry (AAS). 2-day-old pellets exhibited highbiosorption efficiency ranging from 97 ± 1.0 to 88 ± 1.2% of the initially added fungicide concentrations, respectively, within 10 min. However, underthe same conditions, amounts of the removed fungicide by 6-day-old mycelial pellets were significantly lower and ranged from 0.5 ± 0.03 to 0.15 ± 0.01%. Scanning electron microscopy studies of 2-day-old pellets supplemented with thefungicide revealed predominant aggregations of clumps and dense particulates on the hyphal tips. The adsorbed CuF of 125 ppm ai fungicide subsequently decreased from 7.5 ± 0.5 to 2.1 ± 0.1 mol Cu (mg dry wt)^-1 after 12 h incubation. Simultaneously, the soluble portion of CuF remaining in the medium increased from 0.9 ± 0.6 to4.9 ± 0.2 mol Cu ml^-1. The presence of 50 mM CaCl₂ resulted in a decrease of the adsorbed CuF to 3.5 ± 0.5 mol Cu (mg dry wt)^-1 and solubilizedcopper in the medium increased to 5.9 ± 0.8 mol Cu ml^-1. Additionally, the cellular copper contents attained after 2 h were 0.08 ± 0.01 and 0.16 ± 0.007 mol Cu (mg dry wt)^-1 in absence and presence of calcium, respectively. The addition of calcium to glucose-starved pellets greatly increased the medium [H⁺] which was conclusively discussed in relation to Ca²⁺/H⁺ exchangecapacity of the fungal cells. These results are of potential environmental,biotechnological and agricultural importance.     

Ivermectin as a possible control agent for the tsetse fly,Glossina morsitans

Ivermectin produced 100% mortality in adult teneral males, mature males and fertile females ofGlossina morsitans morsitans following a single meal of defibrinated pig blood containing concentrations of 0.1, 1.6 or >1.6 g ml^–1 respectively. The lethal concentration was reduced to <0.04 g ml^–1 for teneral males when fed repeatedly on treated blood. When pregnant females were fed a single blood meal containing ivermectin (0.08 g ml^–1) on the day after their first larviposition, followed by normal blood meals, no offspring were produced in the subsequent reproductive cycle but full recovery occurred thereafter. A dose dependent decline in fecundity was measured and data were subjected to Probit analysis. Thus estimates were made of ivermectin concentrations in the peripheral blood of treated animals by measuring the reduction in fecundity induced in flies fed on such blood. Indications are that with subcutaneous injections at least, amounts greatly in excess of the recommended clinical dose would be required to achieve levels lethal to feeding flies following a single blood meal. Oral treatment of a horse with twice the anthelmintic dose of ivermectin (0.4 mg kg^–1) produced a maximum concentration in the blood of about 0.14 g ml^–1 within 24 h and this was adequate to reduce tsetse fecundity to zero following a single meal. Such levels in a single blood meal were also sufficient to shorten the life expectancy of teneral male flies. The half-life of ivermectin in the horse was approximately 5–6 days with a maximum of 2.4% of ingested material entering the peripheral circulation. A cow treated with injectable ivermectin (0.2 mg kg^–1) produced maximum blood levels of about 0.005 g ml^–1 after one week; this was only 0.17% of the administered dose and sufficient to reduce fecundity in female flies to 50% of normal following a single blood meal. Such levels in a single blood meal had no effect on the longevity of flies. However, at least half the maximum activity was present in the circulation between 3 and 14 days following injection. Repeated feeding on the blood of a treated animal reduced considerably the dose of ivermectin required to produce a given effect. The fecundity of female flies was reduced to zero by repeated feeding on blood taken from the horse 8 days after treatment, and even after 15 days the blood of the horse contained sufficient drug to reduce fly fecundity to 50% of normal. Thus where domestic animals constitute major hosts of tsetse, treatment with ivermectin can be expected to achieve some measure of fly population reduction.

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L'invermectine comme moyen de lutte utilisable contre la mouche tsé-tsé,Glossina morsitans

Résumé Après un repas unique de sang de porc défibrillé contenant 0,1; 1,6 ou plus de 1,6 g ml^–1 d'ivermectine, tous les mâles jeunes non encore alimentes, tous les mâles adultes et toutes les femelles fécondes deGlossina morsitans morsitans sont tués. Les concentrations léthales ont été réduites à moins de 0,04 g ml^–1 pour les jeunes mâles quand on les a alimentés régulièrement sur du sang traité. Quand des femelles en gestation ont été alimentées, le jour après leur première parturition, avec un seul repas de sang contenant 0,08 g ml^–1 d'ivermectine, et ensuite avec des repas de sang normal, il n'y a pas eu production de descendants pendant le cycle suivant, bien qu'une restauration totale ait eu lieu par la suite. Une diminution de la fécondité en relation avec la dose a été enregistrée, et les données soumisses à un test Probit. Ainsi des estimations de la concentration en ivermectine du sang périphérique des animaux traités ont été obtenues en mesurant la réduction de la fécondité induite chez les mouches ayant consommé ce sang. Ceci montre qu'une dose absorbée de 4 mg kg^–1, ou une injection souscutanée de 16 mg kg^–1, seraient nécessaires pour obtenir le seuil létal chez des mouches alimentées après un repas de sang unique, c'est-à-dire 20 fois la dose absorbée et 80 fois la dose subcutanée nécessaires contre les nématodes gastrointestinaux. Le traitement par voie buccale d'un cheval avec 2 fois la dose vermifuge d'ivermectine (0,4 mg kg^–1) provoque dans les 24 heures des taux sanguins suffisants pour réduire la fécondité jusqu'à zéro après un seul repas de sang. La demi-vie dans le cheval a été approximativement de 5 à 6 jours avec une pénétration dans la circulation périphérique d'une quantité maximale de 2,4% de l'ivermectine absorbée. Une vache traitée avec de l'ivermectine injectable (0,2 mg kg^–1) atteint la teneur sanguine maximale au bout d'une semain; celle-ci, correspondant seulement à 0,17% de la quantité administrée, était suffisante pour réduire de 50% la fécondité des mouches après un repas unique de sang. Cependant, entre les 3ème et 14ème jours suivant l'injection, la circulation sanguine présente au moins la moitié de l'activité maximale. Des repas répétés sur le sang des animaux traités réduisent considérablement la dose d'ivermectine nécessaire pour produire un effet donné. La fécondité des mouches devient nulle après des repas répétés sur le sang d'un cheval 8 jours après le traitement; et même après 15 jours, le sang de ce cheval contient suffisamment de produits pour abaisser la fécondité des mouches de 50%. Ainsi, à où les animaux domestiques constituent les principaux hôtes de la mouche tsé-tsé, avec le traitement à l'ivermectine, on peut espérer réduire d'une façon efficace la population de mouches.

     

Polyamines and proline are affected by cadmium stress in nodules and roots of soybean plants

The effect of moderate (50 M) and high (200 M) doses of Cd were studied in relation to polyamine (Pas) metabolism, proline level and the glutamine synthetase/glutamate synthase system (GS/GOGAT) activity in nodules and roots of soybean plants during 6 days of treatment. The lower Cd concentration increased putrescine (Put) in both nodules and roots, while 200 M Cd increased Spm only in nodules and Put in roots. Spermidine (Spd) decreased in roots under both Cd concentrations. Arginine decarboxylase (ADC) and ornithine decarboxylase (ODC) were both involved in Put biosynthesis in roots. In nodules, Put formation could mainly be attributed to ODC activity. Diamine oxidase (DAO) activity was severely reduced by 50 and 200 M Cd either in nodules or roots. The GS/GOGAT system activity was depressed either with 50 or 200 M Cd, but most significantly with the highest metal concentration. Under 200 M Cd, GS activity decayed to 25% or 60% of the control in nodules and roots, respectively, while GOGAT decreased 85% in nodules and 79% in roots by day 4 of treatment. Ammonium increased greatly in nodules (200% over the controls) and roots (100%) under 200 M Cd. Proline concentration increased significantly in nodules and roots under both Cd treatments, more markedly under 200 M Cd. The relationship between Pas and proline accumulation and nitrogen assimilation is discussed.     

Changes in phosphorus concentrations and pH in the rhizosphere of some agroforestry and crop species

The aim of this work was to assess whether agroforestry species have the ability to acquire P from pools unavailable to maize. Tithonia diversifolia(Hemsley) A. Gray, Tephrosia vogelii Hook f., Zea mays and Lupinus albusL. were grown in rhizopots and pH change and depletion of inorganic and organic P pools measured in the rhizosphere. Plants were harvested at the same growth stage, after 56 days for maize and white lupin and 70 days for tithonia and tephrosia, and the rhizosphere sampled. The rhizosphere was acidified by tithonia (pH change –0.3 units to pH 4.8) and lupins (–0.2 units to 4.9), alkalinised by tephrosia (+0.4 units to pH 5.4), and remained unchanged with maize growth. Concurrent with acidification in the rhizosphere of tithonia there was a decline in resin-P (0.8 g P g^–1). However, there was also a decline in NaOH extractable inorganic P (NaOH-P_i) (5.6 g P g^–1 at the root surface) and organic P pools (NaOH-P_o) (15.4 g P g^–1 at 1.5 mm from the root), which would not be expected without specific P acquisition mechanisms. Alkalinisation of tephrosia rhizosphere was accompanied by changes in all measured pools, although the large depletion of organic P (21.6 g P g^–1 at 5 mm from the root) suggests that mineralisation, as well as desorption of organic P, was stimulated. The size of changes of both pH and P pools varied with distance away from the rhizoplane. Decline of more recalcitrant P pools with the growth of the agroforestry species contrasted with the effect of maize growth, which was negligible on resin-P and NaOH-P_i, but led to an accumulation of P as NaOH-P_o (14.2 g P g^–1 at 5 mm from the root). Overall the depletion of recalcitrant P pools, particularly P_o, suggests that the growth of tithonia and tephrosia enhance desorption and dissolution of P, while also enhancing organic P mineralisation. Both species appear to have potential for agroforestry technologies designed to enhance the availability of P to crops, at least in the short term.     

Cadmium-copper antagonism in the activation of periplasmic nitrous oxide reductase of copper-deficient cells fromPseudomonas stutzeri

Summary Copper-deficient cells ofPseudomonas stutzeri strain ZoBell synthesize catalytically inactive nitrous oxide (N₂O) reductase which is activated by added Cu(II) in the absence of de novo protein synthesis. The apparentK _m for the activation process is 0.13 M. Activation is temperature-dependent and is inhibited by Cd(II)(K _i 1.27 M) and less strongly by Zn(II), Ni(II), and Co(II). The same metal ions at 20 M have little or no effect on N₂O reduction of intact cells. Apo-N₂O reductase of transposon Tn5-inducednos ^– mutants with defective Cu-chromophore biosynthesis is not reactivated by Cu(II). N₂O reductase of Cu-sufficient and Cu-deficient wild type, and ofnos ^– mutants is localized in the periplasm, the latter providing the likely site of metal incorporation into the apoenzyme.