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  • Springer  (405)
  • 2005-2009  (122)
  • 1990-1994  (283)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Sexual plant reproduction 3 (1990), S. 187-194 
    ISSN: 1432-2145
    Keywords: Pollen tube apical zonation ; Actin cytoskeleton ; Organelle movement ; Tip growth mechanism ; Epilobium angustifolium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In the apical 10–20 μm of actively extending pollen tubes of Epilobium angustifolium, in a zone where the polysaccharide-containing wall precursor bodies (P-particles) dominate and where their movements on superficial observation seem to be random, there is in fact a concerted flux, acropetal movement taking place along the flanks of the tip zone, with a basipetal return flow along the centre. Detailed tracking of individuals shows that lipid globuli (diameters up to 1.5 μm) and amyloplasts (dimensions up to 5.5 × 2.5 μm) follow similar patterns of movement, but are sorted out in the sub-apical region, the smaller bodies penetrating further towards the apex. The findings are interpreted as indicating that the well-documented apical zonation of the pollen tube is maintained in the fluid circumstances of the growing tube by the filtering of cytoplasmic inclusions through the actin cytoskeleton, which, in conformity with recent fine-structural and other observations, is envisaged as consisting of a network of cross-linked microfilaments and microfilament aggregates at the tube tip giving place progressively to a system of more ordered, longitudinally oriented fibrils in the older parts of the tube. The implications for the operation of the actomyosin motility system and the tip growth mechanism are discussed.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2145
    Keywords: Pollen tube apical zonation ; Actin cytoskeleton ; TRITC-staining ; Microwave stabilisation ; Narcissus pseudonarcissus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The disposition of the actin cytoskeleton in pollen tubes of Narcissus pseudonarcissus has been investigated using microwave-accelerated DMSO-permeabilisation and TRITC-phalloidin (Tr-Ph) staining. Extending tubes were transferred from growth medium into a calcium-free medium containing 1 μg ml−1 Tr-Ph and 5% DMSO. After 10 s irradiation in a 500 W microwave oven, when the temperature in the sample was estimated at 52° C, some two-thirds of the tubes retained essentially normal apical zonation; in the remainder the cytoplasm was coarsely granular, and the zonation had been lost. Optimal Tr-Ph staining of the actin cytoskeleton was obtained about 1 h after irradiation. In the most favourable cases, the transition from a longitudinally oriented system of fine fibrils in the sub-apical region to a mass of shorter fibrils in the centre of the apex could be traced, with a peripheral population of more extended fibrils continuing further along the forming wall towards the growing point. This organisation can be reconciled with that revealed in recent fine-structural studies of the microfilament system of the pollen tube apex using freeze-substitution. The relationship of the system with the pattern of movement observed in the apical region of the living tube and with the probable mechanism of tip growth is briefly discussed.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2145
    Keywords: Pollen-tube structure ; Intracellular movement ; Tip-growth mechanism ; Cytochalasin effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The cytochalasins, known as inhibitors of various processes involving motility in plant and animal cells, induce far-reaching structural changes in the cytoplasm and walls of pollen tubes without destroying the capacity for subsequent growth in normal media. The fine structure of tubes of Endymion non-scriptus modified by cytochalasin D suggests that the changes all stem directly or indirectly from the interruption of the longrange cyclosis along the tube axis, which is sustained throughout the period of normal growth. The elimination of this movement breaks down the the pattern of flow responsible for the sorting-out process that maintains the characteristic zonation of organelles and other inclusions at the apex of the extending tube, and leads gradually to re-distribution of the vacuoles and membranes in the vegetative cell, the disposition of which is normally correlated with the longitudinally oriented flow pathways. Random local migrations of organelles and other inclusions of greater amplitude than is to be expected from Brownian movement continue in the tubes in the presence of cytochalasin D, indicating that the motility system is not wholly destroyed. Following the interruption of concerted axial movement, the polysaccharide wall-precursor bodies (P-particles), normally inserted into the wall mainly in the apical part of the tube during tip growth, gradually become dispersed throughout the tube and are incorporated in the wall at random, entering even into the intine of the parent pollen grain.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Sexual plant reproduction 5 (1992), S. 247-255 
    ISSN: 1432-2145
    Keywords: Wheat ; Triticum aestivum ; Pollen germinability ; Intracellular movement ; Actin cytoskeleton ; Effects of dehydration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The tricellular pollen of wheat germinates rapidly on a receptive stigma without the often protracted activation period characteristic of bicellular pollens. This is associated with a high level of hydration in the mature pollen and the absence of a dormancy period. Intracellular movement of organelles continues throughout development; in the mature pollen along pathways related both to the aperture site and the distribution of the amyloplasts in the vegetative cell. The movement pathways reflect the organisation of the actin cytoskeleton, elements of which are already focused upon the germination site at the time of dispersal, a disposition only achieved during rehydration and activation in bicellular pollens. Dehydration after dispersal rapidly arrests movement, disrupts the actin cytoskeleton and leads to loss of germinability. These effects are irreversible, again in contrast to the situation found in bicellular pollens such as those of the Liliaceae, species of which have been shown to be capable of withstanding several cycles of hydration and dehydration while still retaining some capacity for germination.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of sol gel science and technology 2 (1994), S. 295-299 
    ISSN: 1573-4846
    Keywords: indium oxide ; particle morphology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract This paper discusses the formation of colloidal metal oxide modifications from indium aqueous salt solutions. The preparation of spheres (ca. 1 µm), rectangular plates (ca. 20 to 1000×103 nm2), and monodispersed primary particles (ca. 2–5nm) of indium (III) oxide are described. Colloidal materials such as these have potential application as pigments, catalysts, catalyst supports, coatings and fillers etc. An understanding of the factors which control particle morphology and surface chemistry will enable the development of indium oxide technology.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-2242
    Keywords: Genomic probing ; In situ hybridization ; Interphase cytogenetics ; Physical mapping ; Triticum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Genomic in situ hybridization was used to identify alien chromatin in chromosome spreads of wheat, Triticum aestivum L., lines incorporating chromosomes from Leymus multicaulis (Kar. and Kir.) Tzvelev and Thinopyrum bessarabicum (Savul. and Rayss) Löve, and chromosome arms from Hordeum chilense Roem. and Schult, H. vulgare L. and Secale cereale L. Total genomic DNA from the introgressed alien species was used as a probe, together with excess amounts of unlabelled blocking DNA from wheat, for DNA:DNA in-situ hybridization. The method labelled the alien chromatin yellow-green, while the wheat chromosomes showed only the orange-red fluorescence of the DNA counterstain. Nuclei were screened from seedling root-tips (including those from half-grains) and anther wall tissue. The genomic probing method identified alien chromosomes and chromosome arms and allowed counting in nuclei at all stages of the cell cycle, so complete metaphases were not needed. At prophase or interphase, two labelled domains were visible in most nuclei from disomic lines, while only one labelled domain was visible in monosomic lines. At metaphase, direct visualization of the morphology of the alien chromosome or chromosome segment was possible and allowed identification of the relationship of the alien chromatin to the wheat chromosomes. The genomic in-situ hybridization method is fast, sensitive, accurate and informative. Hence it is likely to be of great value for both cytogenetic analysis and in plant breeding programmes.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Optical and quantum electronics 22 (1990), S. 89-94 
    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The use of cavity length control to obtain multiline emission from a hybrid CO2 laser has been investigated. We have obtained simultaneous laser oscillation on up to four lines in the P and R branches of the 10 μm band by operating the c.w. section above the lasing threshold. For sub-threshold operation of the c.w. section the hybrid laser emission is restricted to the stronger 10P lines.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Optical and quantum electronics 23 (1991), S. S813 
    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Diffusion and heat treatment experiments in closed ampoules were carried out on two different molecular beam epitaxy-grown GaAs-AlAs superlattice wafers. All of the diffusion experiments were undertaken at 1000° C. The effects of varying the As and S vapour pressures as well as the diffusion time were investigated. Angle-lapping, transmission electron microscopy, X-ray photoelectron spectroscopy and secondary-ion mass spectroscopy were the techniques employed to analyse the samples. It was demonstrated that the diffusion of S enhances the group III interdiffusion or ‘intermixing’ compared with the effect of plain heat treatment. It was also shown that S-induced intermixing has two origins, one being the diffusion of S and its effects on the concentration of native defects and the other being a mechanism related to the formation of a coating on the semiconductor surface during the diffusion.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Formal methods in system design 5 (1994), S. 35-59 
    ISSN: 1572-8102
    Keywords: Mathematical logic ; deduction and theorem proving
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract This paper describes a construction of the real numbers in the HOL theorem-prover by strictly definitional means using a version of Dedekind's method. It also outlines the theory of mathematical analysis that has been built on top of it and discusses current and potential applications in verification and computer algebra.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1572-8854
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Compounds, Ph3SnCH2OAr, are available from Ph3SnCH2I and NaOAr in EtOH. The crystal and molecular structure of Ph3SnCH2OC6H4Me-p (II) has been determined by X-ray crystallography. The molecule in the crystal contains a slightly distorted tetrahedral tin atom [C-Sn-C valency angles varying from 106.9(5) to 114.1(6)°] with an intramolecular Sn---O distance of 2.900(11) Å. NMR spectral data for (II) and for Ph3SnCH2OC6H3Br2-2,4 are reported.
    Type of Medium: Electronic Resource
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