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421.
LINDA D. JONES CLIVE R. DAVIES GORDON M. STEEL PATRICIA A. NUTTALL 《Medical and veterinary entomology》1989,3(2):195-202
ABSTRACT. Experimental studies were undertaken to ascertain the vector potential of Rhipicephalus appendiculatus Neumann and Amblyomma variegatum Fabricius for Thogoto (THO) and Dhori (DHO) viruses, candidate members of the Orthomyxoviridae. In the first set of experiments, ticks were infected orally by feeding on viraemic hamsters. THO virus replicated in R.appendiculatus and A.variegatum, persisted trans-stadially in both tick species, and was transmitted to susceptible hosts during feeding. In contrast, both R. appendiculatus and A. variegatum were refractory to per os infection by DHO virus. In the second set of experiments, engorged R. appendiculatus and A. variegatum nymphs were parenterally inoculated with DHO virus. The virus persisted transstadially in both tick species and was transmitted by bite to susceptible hosts. These results indicate that the midgut acts as a barrier to per os infection of R.appendiculatus and A. variegatum by DHO virus. However, when this barrier is bypassed, i.e. by parenteral inoculation, both R.appendiculatus and A.variegatum can serve as efficient vectors of DHO virus. 相似文献
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Aspen (Populus tremuloides Michx.) callus tissue grown on a synthetic medium containing either an auxin (2,4-dichloro-phenoxyacetic acid) or cytokinin [6-(3-methyl-2-butenylamino) purine] differed in growth rate, total peroxidase activity, peroxidase isoenzyme expression, and in lignin, cell wall sugars and extractive content. Tissue treated with auxin increased more rapidly in fresh weight, but stopped growing sooner than did the cytokinin-treated tissues. Lignification also proceeded more rapidly, and lignin formed a greater fraction of the cell wall weight in auxin-treated tissue. For both treatments, peroxidase activity and growth rate were positively related (r = 0.96). Polyacrylamide gel electrophoresis showed some quantitative, but few qualitative, isoenzyme differences with hormonal treatment and growth rate. 相似文献
423.
GORDON J. LEITCH QING HE SARA WALLACE GOVINDA S. VISVESVARA 《The Journal of eukaryotic microbiology》1993,40(6):711-717
Spores of the microsporidian parasitic protozoan Encephalitozoon hellem were purified and incubated at 37° C in a solution with an electrolyte composition similar to that of mammalian extracellular fluid, and in solution in which the calcium had been replaced with 0.2 mM EGTA. Polar filament extrusion (germination) was monitored by both scanning electron microscopy and light microscopy. Germination was pH-dependent, with optima at pH 7.4 and 9.5, and was significantly greater in the presence of medium calcium. Hydrogen peroxide caused a concentration-dependent increase in germination that was also reduced in a calcium-free medium. Four agents were found to inhibit spontaneous and H2O2-stimulated polar filament extrusion: the microfilament disrupter, cytochalasin D; the microtubule disrupter, demecolcine; the calcium channel blocker, nifedipine; and the antifungal agent, itraconazole. These results are consistent with the existence of a calcium-channel-mediated step, and requirements for an F-actin- and for a tubulin-containing element in the germination process of the spore of this parasite. Nifedipine, cytochalasin D and itraconazole all have different sites of action and were therefore able to potentiate one another when used in paired combination to inhibit germination. 相似文献
424.
GAD PERRY GORDON RODDA THOMAS FRITTS & THOMAS SHARP 《Global Ecology and Biogeography》1998,7(5):353-365
We sampled the lizard fauna of twenty-two small islets fringing the Pacific island of Guam and used these data to shed light on the processes responsible for present-day diversity. Habitat diversity, measured by islet area and vegetation complexity, was significantly correlated with the number of species found on an islet. However, islet distance and elevation were not significant predictors of diversity. Distribution patterns were slightly different for the two major families in our sample, Scincidae and Gekkonidae: skinks needed larger islets to maintain a population than did geckos. Presence/absence patterns were highly and significantly nested, and population density was correlated with the number of islets on which a species was found. An area cladogram was poorly supported and showed no faunal similarity between nearby islands. These patterns indicate that extinctions on most islets were due mostly to non-catastrophic, long-acting biological causes. The presence on the islets of species extirpated on Guam and the lack of significant nestedness on islands with greater maximum elevation highlight the impact that predators (primarily brown treesnakes) can have. Our findings also show that small reserves will not suffice to protect endangered lizard faunas, and that the islets may serve as a short-term repository of such species until snake-free areas can be established on Guam 相似文献
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ABSTRACT. Female Acheta domesticus L. were tested for tracking model calling songs with different syllable periods on the Kramer treadmill in the dark, under homogenous light, and in the presence of a visually attractive target (black square) positioned either perpendicular to or in front of the invisible acoustical target. The females exhibited tracking of the two targets by different walking modes. 相似文献
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Isolated cell envelopes from the leaf mesophyll of Italian ryegrass were examined in a transmission electron microscope equippedwith an energy-dispersive X-ray spectrometer. Silicon was detectedin these walls at an estimated concentration of 12 percent. Samples were also subjected to a range of techniques,for the removal of organic matter, which confirmed the presenceof silica throughout the cell walls. Lolium multiflorum Lam, Italian rye grass, cell walls, silica, electron microscopy, X-ray microanalysis 相似文献