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1.
The vast majority of flowering plants rely solely on insects for pollination. A number of pathogens have evolved mechanisms to exploit these close associations and use pollinators as vectors of infective propagules. Factors that affect pollinator movements and successful pollination may in turn also influence successful transmission of fungal spores. Here we investigate the effect of host density and the frequency of diseased Oxalis lanata individuals infected by the anther-smut fungus, Thecaphora capensis, on the likelihood of receiving pollen and fungal spores. Specifically, we determined the numbers of spores and pollen grains deposited on stigmatic surfaces of selected flowers under natural and standardized conditions where host density and disease frequency varied. The effect of host flower density and diseased flower frequency on pollen and spore transfer was variable under natural conditions and these factors interacted significantly. However, an increase in host density and disease frequency significantly influenced pollen and spore deposits under standardized conditions. The effect of host density was, however, not linear and an optimal flower density for pollen and fungal spore transmission was found. Similar to other systems of vector-borne disease, the transmission of anther-smut of Oxalis lanata is more frequency-dependent than density-dependent. This study represents a first step towards understanding the disease transmission process of T. capensis on Oxalis and lays the foundation for future comparative studies between this and other systems to develop and test general hypotheses of disease dynamics in vector-borne disease transmission systems. 相似文献
2.
Various 2-nitronaphthofuran derivatives (related to each other by simple structural modifications) were tested for 2 different effects in CV-1 monkey kidney cell cultures: the immediate inhibition of normal DNA synthesis and the capacity of pretreated cultures (40 h of contact) to support the replication of UV-damaged Herpes simplex virus (HSV). For all compounds tested, a fair correlation was found between their efficiencies to inhibit cellular DNA synthesis and to provoke an increase in UV-HSV production (virus reactivation). Virus reactivation was due to an increase in both the number of virus-producing cells and the amount of infectious particles produced per cell. The most efficient 2-nitronaphthofurans (particularly 2-nitro-7-methoxy-naphtho[2,1-b]furan-R 7000) were at least as potent as aflatoxin B1 in inducing virus reactivation. 相似文献
3.
Loss of integrity of the basal forebrain cholinergic neurons is a consistent feature of Alzheimer’s disease, and measurement of basal forebrain degeneration by magnetic resonance imaging is emerging as a sensitive diagnostic marker for prodromal disease. It is also known that Alzheimer’s disease patients perform poorly on both real space and computerized cued (allothetic) or uncued (idiothetic) recall navigation tasks. Although the hippocampus is required for allothetic navigation, lesions of this region only mildly affect idiothetic navigation. Here we tested the hypothesis that the cholinergic medial septo-hippocampal circuit is important for idiothetic navigation. Basal forebrain cholinergic neurons were selectively lesioned in mice using the toxin saporin conjugated to a basal forebrain cholinergic neuronal marker, the p75 neurotrophin receptor. Control animals were able to learn and remember spatial information when tested on a modified version of the passive place avoidance test where all extramaze cues were removed, and animals had to rely on idiothetic signals. However, the exploratory behaviour of mice with cholinergic basal forebrain lesions was highly disorganized during this test. By contrast, the lesioned animals performed no differently from controls in tasks involving contextual fear conditioning and spatial working memory (Y maze), and displayed no deficits in potentially confounding behaviours such as motor performance, anxiety, or disturbed sleep/wake cycles. These data suggest that the basal forebrain cholinergic system plays a specific role in idiothetic navigation, a modality that is impaired early in Alzheimer’s disease. 相似文献
4.
Maria A. Papathanasopoulos Francois Krier Anne-Marie Revol-Junelles Gerard Lefebvre Jean Pierre Le Caer Alexander von Holy John W. Hastings 《Current microbiology》1997,35(6):331-335
Leuconostoc (Lc.) mesenteroides TA33a produced three bacteriocins with different inhibitory activity spectra. Bacteriocins were purified by adsorption/desorption
from producer cells and reverse phase high-performance liquid chromatography. Leucocin C-TA33a, a novel bacteriocin with a
predicted molecular mass of 4598 Da, inhibited Listeria and other lactic acid bacteria (LAB). Leucocin B-TA33a has a predicted molecular mass of 3466 Da, with activity against Leuconostoc/Weissella (W.) strains, and appears similar to mesenterocin 52B and dextranicin 24, while leucocin A-TA33a, which also inhibited Listeria and other LAB strains, is identical to leucocin A-UAL 187. A survey of other known bacteriocin-producing Leuconostoc/Weissella strains for the presence of the three different bacteriocins revealed that production of leucocin A-, B- and C-type bacteriocins
was widespread. Lc. carnosum LA54a, W. paramesenteroides LA7a, and Lc. gelidum UAL 187-22 produced all three bacteriocins, whereas W. paramesenteroides OX and Lc. carnosum TA11a produced only leucocin A- and B-type bacteriocins.
Received: 11 April 1997 / Accepted: 10 June 1997 相似文献
5.
6.
Arie H. Mulder Francois Hogenboom George Wardeh Anton N. M. Schoffelmeer 《Journal of neurochemistry》1987,48(4):1043-1047
Synaptosomes prepared from rat cerebral cortex and labeled with [3H]noradrenaline (NA) were superfused with calcium-free Krebs-Ringer-bicarbonate medium and exposed to 10 mM K+ plus 0.1 mM Ca2+ so that [3H]NA release was induced. 6,7-Dihydroxy-N,N-dimethyl-2-aminotetralin (TL-99) strongly inhibited synaptosomal K+-induced [3H]NA release (EC50 = 5-10 nM) by activating alpha 2-adrenoceptors. Release was also inhibited (maximally by 40-50%) by morphine (EC50 = 5-10 nM), [Leu5]enkephalin (EC50 = approximately 300 nM), [D-Ala2,D-Leu5]enkephalin (DADLE), and Tyr-D-Ala-Gly-(NMe)Phe-Gly-ol (DAGO) (EC50 values = approximately 30 nM). In contrast to the mu-selective opioid receptor agonists morphine and DAGO, the highly delta-selective agonist [D-Pen2,D-Pen5]enkephalin (1 microM) did not affect [3H]-NA release. Furthermore, the inhibitory effect of DADLE, an agonist with affinity for both delta- and mu-opioid receptors, was antagonized by low concentrations of naloxone. The findings strongly support the view that, like alpha 2-adrenoceptors, mu-opioid receptors mediating inhibition of NA release in the rat cerebral cortex are localized on noradrenergic nerve terminals. 相似文献
7.
Nicole Basset-Séguin Jean Francois Culard Cécile Kerai Fredéric Bernard Annette Watrin Jacques Demaille Jean Jacques Guilhou 《Differentiation; research in biological diversity》1990,44(3):232-238
Human skin is a unique organ, which can be reconstituted in vitro and represents an interesting system for studying cell proliferation and differentiation. A simple technique for producing reconstituted skin with optimal epidermal differentiation is described and characterized. A 4-mm punch biopsy of normal human skin is deposited on the epidermal side of mortified de-epidermized human dermis maintained at the air-liquid interface with a metallic support. The culture medium contains insulin, epidermal growth factor (EGF), cholera toxin, hydrocortisone, penicillin/streptomycin and fungizone. A well-differentiated epidermis develops within 15 days. Morphological and ultrastructural studies show a neoepidermis resembling normal skin. Differentiation markers such as involucrin, filaggrin, and various cytokeratins detected with pancytokeratin antibody are present and confirm this resemblance. The keratin profile is comparable to that observed in other skin culture models. A basement-membrane-like structure is reconstituted with hemidesmosomes and anchoring-filament formation. Bullous pemphigoid (BP) antigen is observed at the dermo-epidermal junction after 21 days of culture. Moreover, both dermal substrates and punch biopsies can be kept frozen for long-term storage, with little or no loss of epidermal growth kinetics and morphology. This skin culture technique is rapid, simple, economical and reproducible. Characterization has here shown high-quality epidermal differentiation. Scientists interested in epidermal in vitro studies should take interest in all these advantages. 相似文献
8.
9.
David H. Sachs Chief Sharon Germana Mona El-Gamil Kenth Gustafsson Francois Hirsch Karen Pratt 《Immunogenetics》1988,28(1):22-29
Class II genes of miniature swine have been characterized by restriction fragment length polymorphism (RFLP) analysis and by analysis of a series of clones isolated from a lymphocyte genomic library. For RFLP analysis, DNA samples from three independent major histocompatibility complex homozygous lines and three intra-MHC recombinant lines were digested with a variety of restriction enzymes and analyzed in Southern blots using human cDNA probes for DP, DQ, DR, and DZ alpha genes, and DP, DQ, DR, and DO beta genes. One, or at most two, unique fragments were detected by hybridization with each of the human probes tested. In contrast, multiple bands (five to six for most enzymes examined) were detected by each of the human probes tested, the majority of which were found to cross-react with at least three of these probes under conditions of moderate stringency. Genomic DNA from the SLA
c
haplotype was cloned into an EMBL-3 bacteriophage vector, and the corresponding genomic library was screened with each of these human cDNA probes. The class II genes thereby isolated from this library showed characteristics consistent with those anticipated from the RFLP analysis. Thus, unique genes were obtained which showed no evidence of cross-hybridization, while genes showed extensive cross-hybridization and were frequently detected in the library by more than one human gene probe. These data are consistent with early evolutionary divergence of a genes, prior to mammalian speciation, and with continuing evolution of genes, with possible shared usage of these genes by different a loci. The data also imply that genes can readily be assigned to loci homologous to their human counterparts, but that genes will require further mapping and/or sequence analysis to confirm assignments. 相似文献
10.
We measured the genotoxic activities in two bacterial tests, the Salmonella/histidine assay (a reverse mutation assay) and the SOS chromotest (an assay for SOS induction in E. coli), of three 2-nitroanthrafurans: 2-nitroanthra[1,2-b]furan (R-7688), the isomeric compound 2-nitroanthra[2,1-b]furan (R-7686) and its 8-methoxylated derivative (R-7707). Their genotoxic activities were compared to that of 7-methoxy-2-nitronaphtho[2,1-b]furan (R-7000) which has been studied in previous works (Arnaise et al., 1986). We found that: (1) for all three 2-nitroanthrafurans, as generally observed for other 2-nitrofuran derivatives, the responses were correlated in the 2 tests and were decreased in the presence of an 'activating mixture' and in nitroreductase-deficient strains; (2) in contrast to what is usually observed with other 2-nitrofuran derivatives for which methoxylation increases genotoxic activity, the genotoxic activity of the methoxylated 2-nitroanthrafuran (R-7707) was comparable and may be even lower than that of the unsubstituted 2-nitroanthrafuran (R-7686); (3) the addition of a third ring that leads from 2-nitronaphthofurans to 2-nitroanthrafurans increased slightly the genotoxic activity of these compounds; (4) compounds with the oxygen heteroatom outside the 'bay region', R-7686 and R-7707, gave higher responses than their isomers with the oxygen heteroatom within the 'bay region', R-7688. 相似文献