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  • 1990-1994  (4)
  • 1991  (4)
  • 1
    Electronic Resource
    Electronic Resource
    Plastid polarity and meiotic spindle development in microsporogenesis ofSelaginella (1991)
    Springer
    Protoplasma 161 (1991), S. 168-180 
    Details
    ISSN: 1615-6102
    Keywords: Microsporogenesis ; Microtubules ; Mitotic apparatus ; Plastid polarity ; Selaginella
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Microsporogenesis inSelaginella was studied by fluorescence light microscopy and transmission electron microscopy. As in other examples of monoplastidic meiosis the plastids are involved in determination of division polarity and organization of microtubules. However, there are important differences: (1) the meiotic spindle develops from a unique prophase microtubule system associated with two plastids rather than from a typical quadripolar microtubule system associated with four plastids; (2) the division axes for first and second meiotic division are established sequentially, whereas as in all other cases the poles of second division are established before those of first division; and (3) the plastids remain in close contact with the nucleus throughout meiotic prophase and provide clues to the early determination of spindle orientation. In early prophase the single plastid divides in the plane of the future division and the two daughter plastids rotate apart until they lie on opposite sides of the nucleus. The procytokinetic plate (PCP) forms in association with the two slender plastids; it consists of two spindle-shaped microtubule arrays focused on the plastid tips with a plate of vesicles at the equatorial region and a picket row of microtubules around one side of the nucleus. Second plastid division occurs just before metaphase and the daughter plastids remain together at the spindle poles during first meiotic division. The meiotic spindle develops from merger of the component arrays of the PCP and additional microtubules emanating from the pair of plastid tips located at the poles. After inframeiotic interphase the plastids migrate to tetrahedral arrangement where they serve as poles of second division.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01322729
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  • 2
    Electronic Resource
    Electronic Resource
    Pollen development in orchids (1991)
    Springer
    Protoplasma 165 (1991), S. 155-166 
    Details
    ISSN: 1615-6102
    Keywords: Cytokinesis ; F-actin ; Microsporogenesis ; Microtubules ; Orchids ; Phragmoplast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cytokinesis in microsporocytes of moth orchids is unusual in that it occurs simultaneously after meiosis, the cytoplasm does not infurrow in the division planes, and cell plates are deposited in association with centrifugal expansion of phragmoplasts. Microtubules radiating from the nuclear envelopes appear to be of fundamental importance in establishment of division planes. Primary interzonal spindles develop between sister nuclei and interaction of radial microtubules triggers development of secondary interzonal spindles between non-sister nuclei. From three to six or more phragmoplasts, depending upon the arrangement of nuclei in the coenocyte, develop from these postmeiotic arrays. The phragmoplasts consist of co-aligned microtubules and F-actin organized into bundles that are broad proximal to the mid-plane and taper distally. Ultrastructure of the phragmoplast/cell plate reveals that abundant ER is associated with vesicle aggregation and coalescence. Cell plates are deposited in association with phragmoplasts as they expand centrifugally to join the parental wall and/or fuse with one another in the interior of the cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01322286
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  • 3
    Electronic Resource
    Electronic Resource
    Pollen development in orchids 1. Cytoskeleton and the control of division plane in irregular patterns of cytokinesis (1991)
    Springer
    Protoplasma 163 (1991), S. 9-18 
    Details
    ISSN: 1615-6102
    Keywords: Meiotic cytokinesis ; Microsporogenesis ; Microtubules ; Orchids ; Phragmoplast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The cytokinetic apparatus in microsporogenesis lacks a preprophase band of microtubules and the selection of cytokinetic planes is dependent upon disposition of nuclei which define cytoplasmic domains via post-meiotic radial systems of microtubules. Meiotic cytokinesis was investigated in hybrid moth orchids (Phalaenopsis) exhibiting irregular patterns of cytokinesis. In these polliniate orchids, spindle orientation is imprecise, and the tetrad nuclei (therefore the microspores) may be in rhomboidal, tetrahedral or linear arrangement. The hybrid “Sabine Queen” (section Phalaenopsis) regularly undergoes simultaneous cytokinesis, as is common in orchids. The hybrid “Vista Rainbow” (section Amboinenses) produces either a complete dyad wall, a partial wall, or no wall after first nuclear division. In all cases, a first division phragmoplast is initiated in the interzonal region and expands centrifugally into the peripheral cytoplasm. Fluorescence microscopy shows that the phragmoplast consists of fusiform bundles of microtubules and Factin bisected by a non-fluorescent zone. If a cell plate fails to form, a band of organelles polarized in the equatorial region effectively divides the cell into two domains. The organelles disperse when a dyad wall is complete, but tend to remain polarized around an incomplete wall. In four-nucleate coenocytes, the usual interzonal microtubules between sister nuclei (primary) form slightly in advance of secondary arrays between non-sister nuclei. Phragmoplasts are initiated in sites defined by the post-meiotic microtubule arrays.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01323402
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  • 4
    Electronic Resource
    Electronic Resource
    Kinetic model of liquid B2O3 gasification in a hydrocarbon combustion environment: I. Heterogeneous surface reactions (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 23 (1991), S. 957-970 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: As part of an ongoing program to model hydrocarbon assisted boron combustion, a kinetic model has been developed to describe gasification of the ubiquitous boron oxide coating that inhibits particulate boron ignition. This model includes homogeneous gas phase oxidation reactions, multi-component gas phase diffusion, heterogeneous surface reactions, and oxide vaporization. The kinetic processes are treated using a generalized kinetics code, with embeded sensitivity analysis, for the combustion of a one-dimensional (particle radius), spherical particle.This article presents the heterogeneous surface reactions used to describe oxide gasification and presents selected model results for a spherical boron oxide droplet which illustrate the dependence of the oxide gasification rates on the ambient temperature and particle diameter.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.550231102
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