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  • 1
    ISSN: 1432-041X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Recent studies on the differentiation of the body wall musculature in a medicinal leech and in the free-living plathelminth Macrostomum hystricinum marinum, Beklemischev 1950 provide the first evidence of a complex developmental signalling pattern, possibly involving stem cells and the nervous system, in the organization of the muscle grid formed by developing myocytes. To enhance further our understanding of the ontogenetic and phylogenetic origin of such muscle grids, which consist of circular, longitudinal and diagonal muscle fibres, we have undertaken a study of muscle development in the polyclad flatworm Hoploplana inquilina Wheeler 1894 in collaboration with the Marine Biological Laboratory, Woods Hole. We have also continued our examination of the development of the body wall musculature in M. hystricinum. Both species were studied using rhodamine-phalloidin staining and transmission electron microscopy. Additional visualization of the fluorescent whole mount preparations was performed with confocal laser microscopy and digital image processing. The results of our investigation suggest that: (1) the mechanism of muscle development in H. inquilina supports the deeply rooted concept of bilateral symmetry (right and left longitudinal founder muscle), and (2) a first circular muscle in this species develops on the border between an anterior body unit and the main body; a caudalmost region is less obvious. The presence of a spiral muscle functioning as a circular muscle system of the “head region” points to a separate developmental mechanism for this region and the trunk. In contrast to H. inquilina, where the larval stage forces an intermediate restructuring of the musculature of the body wall before the adult body shape is finally developed, the formation of the body wall musculature of M. hystricinum already seems constrained by the adult body shape.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In 1974 the authors collected, sorted and enumerated meiofauna from 400, 800 and 4000 m off North Carolina, USA. Samples were replicated respectively with 4 boxcores and 21 subsamples, 2 boxcores and 7 subsamples and 2 boxcores and 8 subsamples. Total meiofaunal numbers were highest in fine silt sediment at 800 m ( $$\bar x$$ =891.9 10 cm−2) and lowest in very fine silt at 4000 m ( $$\bar x$$ =73.5 10 cm−2). Fine sand at 400 m yielded a mean of 442.4 10 cm−2. At all depths, most fauna were located in the upper 3 cm of sediment ( $$\bar x$$ depth distribution=2.2 cm), and typically only nematodes and foraminiferans were found below 4 cm. Total community abundances significantly differed with depth; however, there were no differences among replicate boxcores at particular depths. Since most (85.7%) of the variance was associated with subsamples from a boxcore, it appears that meiofauna densities are homomeneous within large areas at particular depths, and that patchiness is a smallscale phenomenon at the level of the 10 cm2 subsampler. Comparisons of sorting efficiencies of live and preserved samples indicated that to accurately enumerate formainiferans, samples must first be fixed and stained, while turbellarians and oligochaetes must be sorted live.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In enumerating data for systematic and ecological studies on meiofauna, an unfortunate diversification exists in the methods used for observation, identification, preservation and curatorial treatment of various taxa. The application of transmission electron microscopy resin embedment techniques to whole, quantitative, extracted meiofauna samples is described here as a new method, which overcomes most of these problems. Slide-shaped resin blocks are produced by this method; they contain the mass-embedded meiofauna on one side and sand from the sample site on the other side; the latter can be used in studying sand-grain epigrowth of Protista, Fungi and Monera. Examples for the applicability of these slides to various meiobenthic studies are given for most taxa, but especially for Turbellaria, Annelida and Mystacocarida. Using this resin-slide technique, whole quantitative transects can be deposited as “ecotype material” in museums.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. The sensitivity pattern of the Vicia faba main root meristem against the radiomimetic compounds ethanol, myleran and nitrogen-mustard was found to be dependent on root length. In the case of ethanol sensitivity, measured by the percentage of metaphases with chromosome aberrations, it was similar in 2 and 4 cm roots. Further enlargement of roots up to 10 cm length caused a drastic decrease in the number of damaged cells. This decrease was not so striking and happened later when myleran and HN 2 were used. 2. No sensitivity differences between 2 cm long main and lateral roots were found when treated with myleran or HN 2. Contrary to this the lateral rootlets showed practically no aberrations after treatment with ethanol, the percentage of damaged cells in the main root meristem being 44%. 3. Results are discussed in relation to the question whether these sensitivity differences are real or only spurious, e.g. caused by permeation phenomena or alterations in duration of mitosis. It is concluded, that changes in the sensitivity pattern are true and probably caused by metabolic changes in the meristem cells, correlated with growth of the root, and upon which the three radiomimetic compounds reacted differently because of different modes of action.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary N-nitroso-N-methylurea was tested for its ability to induce chromosomal aberrations in root-tip meristems of Vicia faba and in two ascites tumour strains (Ehrlich mouse ascites carcinoma and S2-sarcoma) of the mouse. In all cases the agent was found to be active (Table 1,8). The effectivity of the agent in aberration induction was strikingly different in the two tumour strains and possible reasons for that are discussed. In Vicia the radiomimetic activity of nitrosomethylurea was studied in more detail. The compound had a delayed effect (Table 2) and the aberrations induced were exclusively of the chromatid type. They were preferentially localized in the heterochromatic segments of the chromosomes and unevenly (not length proportional) distributed between the chromosomes. The distribution-ratio of aberrations between the short (5 pairs) and long chromosomes (one pair) was in favour of the short ones and dependent on concentration and duration of treatment (Table 1,2). The distribution of isolocus breaks and chromatid translocations between cells was in accordance with expectation on the basis of a Poisson-distribution (Table 3) and the effectivity of nitrosomethylurea was dependent on the temperature of the treatment solution (Table 4). The agent was almost inactive in the absence of oxygen and its activity was greatly reduced when the meristems were pretreated with the enzymeinhibitor sodium azide. Pretreatments with 2,4-dinitrophenol, KCN, hydroxylamine and chloromycetin did not affect significantly the rate of induced aberrations (Table 5). Pretreatment with the chelator EDTA sensitized to the radiomimetic effects of nitrosomethylurea (Table 6). Breaks induced by the compound stayed open for approximately 4–8 hours (Table 7). The experimental results are discussed and the tentative conclusion as to the mode of action of nitrosomethylurea is, that the aberrations become induced by a breakdown product of the agent the formation of which is dependent on the presence of oxygen and an enzyme containing heavy metal. Probably this decomposition product is not an alkylating agent.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Cold and HCl-acetic acid treatments have been used to study the localization and the visualization frequencies of H sections (H segments of Darlington and La Cour) in metaphase chromosomes of five reconstructed Vicia faba karyotypes. H sections are indicative of the presence of heterochromatin and were found in 14 of the 28 segments into which the chromosome complements had been subdivided. In some cases treatment-specific differences of segment-involvement in H sections have been observed. The visualization frequencies of H sections were found to be characteristic for individual sections and the treatment used to reveal them. The visualization frequencies of the majority of H sections remained unchanged after transposition into new chromosomal positions of the segments harbouring them. Changes of the visualization frequencies of H sections upon segment transposition have been observed in three cases. Possible causes underlying these as well as some correlations between cold-treatment induced chromosome differentiation and the Giemsa banding pattern are discussed.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Biochemical and Biophysical Research Communications 9 (1962), S. 280-284 
    ISSN: 0006-291X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Biochemical and Biophysical Research Communications 7 (1962), S. 331-335 
    ISSN: 0006-291X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Biochemical and Biophysical Research Communications 13 (1963), S. 366-371 
    ISSN: 0006-291X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Biochemical and Biophysical Research Communications 11 (1963), S. 120-124 
    ISSN: 0006-291X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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