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Ian D. Hodkinson Jeremy M. Bird Jane K. Hill Robert Baxter . 《Ecological Entomology》2001,26(4):376-387
1. Salix lapponum host plants at an upper altitudinal site differed significantly in size, structural density, phenology, growth performance, and spatial isolation from those growing at a lower site. 2. Plant differences were paralleled by significant differences in psyllid population density and phenology parameters, with psyllid population density, percentage of catkins occupied, and phenological development relatively lower or retarded at the upper site. Population densities at the upper site, nevertheless, remained high. 3. Plant measurements were good predictors of insect density, often explaining up to 73% of the variance in abundance among plants at a given site. 4. Sets of four plant characters identified by best subsets regression were better predictors of psyllid density and development than single factors, although differences were often not great and the combinations of characters selected by multiple regression sometimes differed from the best single predictors. 5. Best single predictors of psyllid density on catkins were measurements of plant size, particularly height, length, and basal stem diameter. Shoot density and catkin phenology were occasionally important but plant isolation and prior growth performance were less important. 6. By contrast with density, age structure of the psyllid population was predicted best from plant phenological measurements, notably catkin phenology. 相似文献
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D. Jane Bower 《Chromosoma》1987,95(1):76-80
At least one-third of mouse trophoblast cells undergo endoreduplication during the first half of gestation. It has been suggested that the endoreduplicated chromosomes may be polytenised. Here it is shown, using in situ hybridisation to the -1 antitrypsin genes, which map at a unique site, that while there is a tendency for duplicated chromosomes to cluster, this does not involve the complete fusion of replicated chromatids found in fully polytene chromosomes, and in a substantial proportion of homologues the sites on the chromosome arms corresponding to these genes are widely separated. The centromeres do not fuse into a single chromocentre but the possibility is not ruled out that individual chromosomes may be polytenised in the centromeric region. Evidence is also presented showing that endoreduplication in trophoblast nuclei is not accompanied by the formation of new prekinetochore structures, in contrast to the situation in polyploid mouse liver and C127 cells. 相似文献
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Summary Calcitonin gene-related peptide-immunoreactive cells were identified within the epithelium of distal conducting airways in the human fetus and infant. Several peptides and amines, including calcitonin, have been identified previously within a specific population of airway epithelial cells. These cells, referred to as pulmonary neuroendocrine cells, are postulated to be airway chemoreceptors responsible for changes in ventilation and perfusion in response to changes in airway gas composition. Calcitonin gene-related peptide immunoreactive cells could be identified throughout the period of development studies (20 weeks gestation to 3 months of age), but were present in only limited numbers in less than 50% of individuals (n=23). In contrast, large numbers of calcitonin gene-related peptide immunoreactive cells were identified in 100% of infants (1–3 months, n=5) with bronchopulmonary dysplasia. The differential processing of mRNA transcribed from the calcitonin gene in neural and non-neural tissue suggests that calcitonin, rather than calcitonin gene-related peptide, is the primary product of translation in pulmonary neuroendocrine cells. However, considering the potent vasodilatory and bronchoconstrictive effects of calcitonin gene-related peptide, its presence in pulmonary neuroendocrine cells, even in small amounts, may be important in controlling pulmonary vaso- and/or bronchomotor tone. The presence of large numbers of calcitonin gene-related peptide immunoreactive cells in infants with bronchopulmonary dysplasia suggests that calcitonin gene-related peptide may be one further agent contributing to the pulmonary pathophysiology seen in this disease. 相似文献
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Jane Dawson 《BMJ (Clinical research ed.)》1987,295(6598):597-598
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This work provides further evidence that plants contain appreciable amounts of inorganic pyrophosphate (PPi), and that breakdown of phosphoribosyl pyrophosphate (PPRibP) does not contribute significantly to the PPi detected in plant extracts. Inorganic pyrophosphate in extracts of the roots of Pisum sativum L., clubs of the spadices of Arum maculatum L., and the developing endosperm of Zea mays L. was assayed with pyrophosphate fructose 6-phosphate 1-phosphotransferase (EC 2.7.1.90), and with sulphate adenyltransferase (EC 2.7.7.4). The two different assays gave the same value for PPi content, and for recovery of added PPi. It was shown that PPRibP is converted to PPi during the extraction of PPi. However, the amounts of PPRibP in clubs of A. maculatum and the developing endosperm of Z. mays were negligible in comparison with the contents of PPi.Abbreviations EDTA
ethylenediaminetetraacetic acid
- PFK(PPi)
pyrophosphate fructose 6-phosphate 1-phosphotransferase
- PPi
inorganic pyrophosphate
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PPRibP
phosphoribosyl pyrophosphate 相似文献
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DNA from 22 strains belonging to the ' Mycoplasma mycoides cluster' was tested for methylation of adenine in GATC sequences by its resistance or susceptibility to digestion by the restriction endonucleases MboI , which is inhibited by the methylation, or DpnI , which requires the methylation. Strains of bovine serogroup 7, M. mycoides subsp. mycoides SC, and some M. mycoides subsp. capri strains plus M. capricolum strain Cal Kid lacked the methylation, whereas other strains of M. mycoides subsp. capri and of M. capricolum , plus the F38-like and M. mycoides subsp. mycoides LC strains, possessed it. We conclude that this simple test could provide a valuable criterion in identifying these mycoplamas. 相似文献
20.
Summary This study demonstrates that endocytosis in the oocyte of Drosophila melanogaster is reversibly blocked at the stage of pit formation by the temperature-sensitive, single-gene mutant, shibire
ts1. Uptake of horseradish peroxidase conjugated with wheat-germ agglutinin was observed to be normal in mutant oocytes at 19°C, but was blocked at 29°C. After 10 min at 29°C, there was a build-up of coated pits along invaginations of the plasma membrane. Also, the endosomal compartment consisting of tubules, bulbs, and small yolk spheres, disappeared. Lowering the temperature to 19°C after 10 min at 29°C released a synchronized wave of endocytosis into a cytoplasm cleared of uptake-related organelles. By observing this synchronized wave after exposure to 19°C for varying durations, we determined that endocytosis proceeds as follows: coated pits/vesiclestubulessmall yolk spheresmature yolk spheres. The observations suggest that these organelles transform one into another within this sequence. 相似文献