Microfilamentous system and secretion of enzyme in the exocrine pancreas. Effect of cytochalasin B

The microfilaments in the acinar cell of the exocrine pancreas are essentially located in the apical part of the cell: thin microfilaments (50 A), cytochalasin B (CB)-sensitive, form the axis of the microvilli and a network lying beneath the apical membrane; thicker filaments (100 A), at least partly CB-insensitive, form bundles parallel to the plasma cell membrane and the desmosomal links. CB interaction with the acinar cell of the exocrine pancreas involves at least two sites: a membrane site involved in the inhibitory effect of CB on the monosaccharide transport and a less sensitive site at the filamentous level at least partly responsible for the inhibitory effect of CB in the secretion of the exportable enzyme from the pancreatic cell. CB did not alter the energy balance of the acinar cell nor the exchanges of 15-Ca between the extracellular medium and the pancreatic tissue. CB (2 times 10-minus 7 and 2 times 10-minus 6 M) has secretagogue properties whereas CB (2 times 10-minus 5 M) has inhibitory effect on stimulated secretion and secretagogue properties. The mechanism of these secretory effects is not yet explained. The analysis presented in this investigation affords strong evidence for the involvement of the microfilamentous network in the last steps of the secretory cycle in the acinar cell of the exocrine pancreas.     

Studies of mixed anaerobic infections involving Bacteroides gingivalis

The infectiousness of several combinations of bacteria containing Bacteroides gingivalis and other bacteria associated with periodontal diseases was evaluated by subcutaneous injection to guinea pigs. Among the seven mixtures studied, only one permitted the development of an infection easily transmissible to a second guinea pig; this bacterial mixture was composed of B. gingivalis, Fusobacterium nucleatum, Eubacterium saburreum, and Capnocytophaga ochracea (formerly Bacteroides ochraceus). Owing to its ability to synthesize many lytic enzymes and potentially cytotoxic products, B. gingivalis represented the most virulent species of the mixture. Results from in vitro studies suggest that the development of B. gingivalis in the infected animal depends on the growth of C. ochracea. Succinic acid produced in large amount by C. ochracea seems to be one of the growth factors used by B. gingivalis.     

INFLUENCE DU SUPERPARASITISME SUR LA DURÉE DU DÉVELOPPEMENT LARVAIRE ET LE POIDS DU PARASITOÏDE LIXOPHAGA DIATRAEAEÉLEVÉ DANS UN HÔTE DE SUBSTITUTION GALLERIA MELLONELLA

Résumé G. mellonella infestée au dernier stade larvaire avec 1, 2, 3 ou 5 planidia/hôte (ph/H) produit 1 à 5 pupes/hôte (pu/H). La mortalité des chenilles augmente avec le nombre de pl/H. Le poids des pupes et décroît avec un nombre croissant de pu/H (18,2 à 12,9 mg pour les et 12,5 à 9,7 mg pour les ). Le développement larvaire dure 8,7 j. chez les et 8,3 chez les ; il est peu affecté par le superparasitisme. Avec 1, 2, 3 et 5 pl/H nous obtenons 0,84–1,61–2,17 et 3,43 pu/H et 0,81–1,48–2,10 et 3,11 imagos/H. L'optimum est de 3 pl/H ou 1 à 2=pl/H pour obtenir des parasitoïdes plus lourds.

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Summary The influence of superparasitism on larval and pupal development is investigated. Last-larval instar G. mellonella (200±5 mg) were infected with 1, 2, 3 or 5 planidia/host (pl/H) producing 1 to 5 pupae per host (pu/H). Host mortality (8.6–8.3–14.3 and 22.2%) increased with the number of planidia. The planidia may transmit a bacteriosis. Pupal weight ( and ) decreased as number of pu/H increased. pupae were heavier than ones: 12.9 to 18.2 mg for against 9.7 to 12.5 mg for . Larval development lasted slightly longer for (8.7 d.) than for (8.3 d.), and its duration was little affected by superparasitism. 1, 2, 3 or 5 pl/H yielded 0.84–1.61–2.17 and 3.43 pu/H and 0.81–1.48–2.10 and 3.11 adults/H. An optimum was obtained with 3 planidia of L. diatraeae on G. mellonella or 1 to 2 to obtain heavier parasitoids.

     

Accumulation of beta-Fructosidase in the Cell Walls of Tomato Roots following Infection by a Fungal Wilt Pathogen

Active defense in plants is associated with marked metabolic alterations, but little is known about the exact role of the reported changes in specific activity of several enzymes in infected plant tissues. β-Fructosidase (invertase), the enzyme that converts sucrose into glucose and fructose, increases upon infection by fungi and bacteria. To understand the relationship between fungal growth and β-fructosidase accumulation, we used an antiserum raised against a purified deglycosylated carrot cell wall β-fructosidase to study by immunogold labeling the spatial and temporal distribution of the enzyme in susceptible and resistant tomato (Lycopersicon esculentum) root tissues infected with the necrotrophic fungus, Fusarium oxysporum f. sp. racidis-lycopersici. In susceptible plants, the enzyme started to accumulate in host cell walls about 72 hours after inoculation. Accumulation occurred only in colonized cells and was mainly restricted to areas where the walls of both partners contacted each other. In resistant plants, accumulation of β-fructosidase was noticeable as soon as 48 hours after inoculation and appeared to reach an optimum by 72 hours after inoculation. Increase in wall-bound β-fructosidase was not restricted to infected cells but occurred also, to a large extent, in tissues that remained uncolonized during the infection process. The enzyme also accumulated in wall appositions (papillae) and intercellular spaces. This pattern of enzyme distribution suggests that induction of β-fructosidase upon fungal infection is part of the plant's defense response. The possible physiological role(s) of this enzyme in infected tomato plants is discussed in relation to the high demand in energy and carbon sources during pathogenesis.     

Properties of oral asaccharolytic black-pigmented Bacteroides

Bacteroides endodontalis, a newly described asaccharolytic black-pigmented Bacteroides, along with the other two recognized species of this group (B. gingivalis and B. asaccharolyticus) were studied for their susceptibility to various dyes and inhibitory agents and for some of their enzymatic activities to facilitate differentiating between them. Bacteroides endodontalis resembles B. asaccharolyticus physiologically except for the fact that the former cannot grow on media containing methylene blue, neutral red, or 3% sodium chloride, whereas B. asaccharolyticus can. On the other hand, B. endodontalis and B. gingivalis can grow on a medium containing Congo red while B. asaccharolyticus cannot.     

Antifungals: Mold control and safe levels in artificial media forTrichogramma [Hymenoptera: Trichogrammatidae]

Ten chemicals known to be fungicides are tested in artificial media forTrichogramma dendrolimi Matsu. [Hymenoptera: Trichogrammatidae]. Tests are performed in France by using artificial host egg capsules. Most of the fungicides cannot control fungus or are toxic forTrichogramma at effective levels. Geneticin, Amphotericin B and Nystatin, used at proper levels are able to control molds efficiently without modifyingTrichogramma development. These antifungals are also tested in actual conditions of mass production, in Guangzhou (China).      

Enquête sur la répartition des tachninaires [Diptera: Tachnidae] prasitoïdes de la pyrale du maïsOstrinia nubilalis [Lepidoptera: Pyralidae] en France (1985–87)

Résumé Trois annés d'éhantillonnage automnal de pyrale du ma?s dans différentes régions ma?sicoles de France ont permis de déterminer le taux de parasitisme par les Tachinidae. Ce taux varie de 1% à 51% selon les régions et les années. Les tachinaires sont préents dans toutes les zones étudiées.Lydella thompsoni Hert. est l'espèce la plus abondante et la plus répandue.Pseudoperichaeta nigrolineata Walk. se rencontre dans le Sud-Ouest. Les Tachinidae pourraient jouer un r?le important dans la régulation des populations de pyrale.      

Evaluation of new thiadiazoles and benzothiazoles as potential radioprotectors: Free radical scavenging activity in vitro and theoretical studies (QSAR,DFT)

Thiol and aminothiol compounds are among the most efficient chemical radioprotectors. To increase their efficiency, we synthesized two new classes of thiol and aminothiol compounds derived from benzothiazole (T1, T2, AM1, AM2) and thiadiazole (T3, T4, AM3) structures. We examined them for their ability to scavenge free radicals (DPPH^·, ABTS^·+, ^·OH). Thiol derivatives with a thiadiazole structure are the most active compounds scavenging DPPH^· and ABTS^·+ free radicals, with an IC₅₀ of 0.053 ± 0.006 and 0.023 ± 0.002 mM, respectively, for the derivative T3. Moreover, compounds T1, T2, and T3 at 60 μM gave 83% protection against 2-deoxyribose degradation by ^·OH. The ability of these compounds to protect DNA against ^·OH produced by a Fenton reaction and γ-irradiation (15 Gy)-induced strand breaks was also evaluated on pBR322 plasmid DNA. In both tests thiol derivatives were the most efficient compounds. Derivatives T2 and T3 totally inhibit DNA strand breaks at the concentration of 50 μM. The protection afforded by these derivatives was comparatively higher than that of the radioprotectors WR-2721 and WR-1065. Our data indicate that these two compounds are free radical scavengers and potential antioxidant agents. Finally, DFT and QSAR studies were performed to support the experimental observations.     

Mixing characteristics of sludge simulant in a model anaerobic digester

This study aims to investigate the mixing characteristics of a transparent sludge simulant in a mechanically agitated model digester using flow visualisation technique. Video images of the flow patterns were obtained by recording the progress of an acid–base reaction and analysed to determine the active and inactive volumes as a function of time. The doughnut-shaped inactive region formed above and below the impeller in low concentration simulant decreases in size with time and disappears finally. The ‘cavern’ shaped active mixing region formed around the impeller in simulant solutions with higher concentrations increases with increasing agitation time and reaches a steady state equilibrium size, which is a function of specific power input. These results indicate that the active volume is jointly determined by simulant rheology and specific power input. A mathematical correlation is proposed to estimate the active volume as a function of simulant concentration in terms of yield Reynolds number.