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  • Microtubules  (6)
  • Analytical Chemistry and Spectroscopy  (5)
  • 1990-1994  (10)
  • 1975-1979  (1)
  • 1960-1964
  • 1940-1944
  • 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
    Organisation of microtubules and actin filaments in the cortex of differentiating Selaginella guard cells (1993)
    Springer
    Protoplasma 177 (1993), S. 37-44 
    Details
    ISSN: 1615-6102
    Keywords: Actin ; Confocal microscopy ; Guard cells ; Microtubules ; Selaginella ; Stomata
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Using fluorescent probes and confocal laser scanning microscopy we have examined the organisation of the microtubule and actin components of the cytoskeleton in kidney-shaped guard cells of six species of Selaginella. The stomata of Selaginella exhibit novel cytoskeletal arrangements, and at different developmental stages, display similarities in microtubule organisation to the two major types of stomata: grass (dumbbell-shaped) and non-grass (kidney-shaped). Initially, cortical microtubules and F-actin radiate from the stomatal pore and extend across the external and internal periclinal cell surfaces of the guard cells. As the stomata differentiate, the cytoskeleton reorients only along the internal periclinal walls. Reorganisation is synchronous in guard cells of the same stoma. Microtubules on the inner periclinal walls of the guard cells now emanate from areas of the ventral wall on either side of the pore and form concentric circles around the pore. The rearrangement of F-actin is similar to that of microtubules although F-actin is less well organised. Radial arrays of both microtubules and F-actin are maintained adjacent to the external surfaces. Subsequently, in two of the six species of Selaginella examined, microtubules on both the internal and external walls become oriented longitudinally and exhibit no association with the ventral wall. In the other four species, microtubules adjacent to the internal walls revert to the initial radial alignment. These findings may have implications in the development and evolution of the stomatal complex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01403397
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  • 3
    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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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Polar organizers mark division axis prior to preprophase band formation in mitosis of the hepaticReboulia hemisphaerica (Bryophyta) (1990)
    Springer
    Protoplasma 156 (1990), S. 74-81 
    Details
    ISSN: 1615-6102
    Keywords: Bryophytes ; Preprophase band ; Microtubules ; Mitotic apparatus ; Microtubule organizing center
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Changes in the pattern of microtubules during the cell cycle of the hepaticReboulia hemisphaerica (Bryophyta) were studied by indirect immunofluorescence using conventional and confocal laser scanning microscopy (CLSM). The first indication that a cell is preparing for division is fusiform shaping of the nucleus accompanied by the appearance of well-defined polar organizers (POs) at the future spindle poles. Microtubules emanating from the POs ensheath the nucleus and eventually develop into the half-spindles of mitosis. Some of the microtubules from each PO pass tangential to the nucleus and interact in the region of the future mitotic equator. A preprophase band (PPB) forms in this region later in prophase and coexists with the prophase spindle. Thus, the plane of division appears to be determined by interaction of opposing arrays of microtubules emanating from POs. Prometaphase is marked by disappearance of the POs, loss of astral microtubules, and conversion of the fusiform spindle of prophase to a truncated, barrel-shaped spindle more typical of higher plants. Restoration of cortical microtubules in daughter cell occurs on the cell side distal to the new cell plate, but nucleation of microtubules is associated with the nuclear envelope and not with organized POs. At the next division POs appear at opposite poles of preprophase nuclei with no evidence of division and migration that is characteristic of cells with centriolar centrosomes. These data lend additional support for the view that mitosis in hepatics is transitional between green algae and higher plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01666508
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  • 6
    Electronic Resource
    Electronic Resource
    Pollen development in orchids 4. Cytoskeleton and ultrastructure of the unequal pollen mitosis inPhalaenopsis (1992)
    Springer
    Protoplasma 167 (1992), S. 183-192 
    Details
    ISSN: 1615-6102
    Keywords: Endoplasmic reticulum ; F-actin ; Microtubules ; Orchids ; Pollen ; Mitosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The unequal first mitosis in pollen ofPhalaenopsis results in a small generative cell cut off at the distal surface of the microspore and a large vegetative cell. No preprophase band of microtubules is present, but polarization of the microspore prior to this critical division is well marked. A generative pole microtubule system (GPMS) marks the path of nuclear migration to the distal surface, and the organelles become unequally distributed. Mitochondria, plastids and dictyosomes are concentrated around the vegetative pole in the center of the microspore and are almost totally excluded from the generative pole. The prophase spindle is multipolar with a dominant convergence center at the GPMS site. The metaphase spindle is disc-shaped with numerous “minipoles” terminating in broad polar regions. In anaphase, the spindle becomes cone-shaped as the spindle elongates and the vegetative pole narrows. These changes in spindle architecture are reflected in the initial shaping of the telophase chromosome groups. F-actin is coaligned with microtubules in the spindle and is also seen as a network in the cytoplasm. An outstanding feature of orchid pollen mitosis is the abundance of endoplasmic reticulum (ER) associated with the spindle. ER extends along the kinetochore fibers, and the numerous foci of spindle fibers at the broad poles terminate in a complex of ER.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01403382
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  • 7
    Electronic Resource
    Electronic Resource
    Isotope ratio measurements in lead using three-photon one-colour resonance ionization mass spectrometryBritish Crown Copyright 1993/MOD. Published with the permission of the Controller of Her Britannic Majesty's Stationery Office. (1993)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 7 (1993), S. 524-527 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Resonance effects on measured isotope ratios in lead using three-photon one-colour resonance ionization mass spectrometry are discussed. The shape of the ionization signal is considered for the case of a non-monochromatic laser field. The intensity of the laser radiation is adjusted to be low enough not to cause saturation of the transitions. The variation of the measured isotope ratio as a function of laser frequency is considered. It is shown that the deviation of the measured from the expected isotope ratio, for a Lorentzian laser lineshape equals the ratio of the isotope shift to the laser bandwidth. Unfortunately, the background noise in the experiments makes verification of this behaviour difficult for the isotopes of low abundance.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290070625
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  • 8
    Electronic Resource
    Electronic Resource
    Ion detection limitations to mass resolution in matrix-assisted laser desorption time-of-flight mass spectrometry (1992)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 6 (1992), S. 690-696 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The ion detection process in a discrete-dynode electron multiplier can result in significant mass resolution losses in time-of-flight mass spectrometry (TOF-MS) for higher mass-to-charge (m/z) ion species. This resolution loss is attributed to propagation time delays and signal broadening in the ion detector. This is presumed tobe due to the generation o a distribution of secondary ion species produced initially upon impact of a primary ion with the first ynoe surface of the ion detector. Comparisons are made between the signals produced by a standard discrete dynode ion detector (which amplified the negatively chqrged species produced by impact of a primry ion) and a detector modified to respond to only the positively charged secondary ion species produced by a primary ion impact. Ion signals for higher m/z ions with the standard detector geometry are see to be due to a narrow signal component, most likely due to the generation o secondary electrons and/or very low mass secondary ions (H-), and a broad signal component, apparently due to secondary ions which take signifiant amounts of time to traverse the low potential fields between the first and second detector dynode. This results in ion signal tailing for higher m/z ion species. Numerical subtraction of the ion signal obtained with the standard and modified detector geometries (singly protonated molecular ion species of equine myoglobin) results in an improvement in mass resolution, such that a new adduct ion species (from trifluoroacetic acid) can be resolved.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290061112
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  • 9
    Electronic Resource
    Electronic Resource
    Opimizing signal and mass resolution for matrix-assisted laser desorption utilizing a linear time-of-flight mass spectrometer (1992)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 6 (1992), S. 697-701 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Results are oresented for various instrumental configurations employed for matrix-assisted laser desorption mass spectrometry. Mass resolution is determined for a linear time-of-flight mass spectrometer for various lengths of the field-free region. A wire ion guide is utilized and is shown to improve ion transport efficiencies for longer field-free regions. It is also determined experimentally that a modest mass resolution increase is often obtained in configurations employing the wire ion guide when compared to the mass resolution obtained with the same geometr without the wire ion guide. Optimal applied potentials are determined for the wire ion guide. No mass dependence on the opitmal applied potential (-100 V) for the wire ion guide is observed for samples of equine myoglobin (MW 16 951.5 Da) and a bacterial protease (MW 27 228.4 Da). The optimal applied voltage was also found to b identical (-100 V) for the singly through quadruply charged molecular ion species of rabbit gamma globulin (MW ≍ 150 000 Da). It is shown that a 2 m flight tube with a wire ion guide provides better signal-to-noise mass spectra than a 1 m flight tube without the wire ion guide and can more than double the mass resolution obtainable. Utilization obtainable. Utilization of a 4 m flight tube gives minimal mass resolution enhancement at the expense of signal-to-noise.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290061113
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  • 10
    Electronic Resource
    Electronic Resource
    Low-temperature Raman spectrum of phase V ammonium nitrate (1992)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 23 (1992), S. 697-705 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Raman spectra of polycrystalline normal and three 15N isotopic ammonium nitrates (15NH4NO3, NH4 15NO3 and 15NH4 15NO3) were recorded at various temperatures between 10 and 300 K. Isotopic shifts of both internal and external modes of the ammonium ion relative to isotopic normal NH4NO3 were observed. Various components of the hetero-ionic coupled internal mode (ν3 of the nitrate ion with ν4′ of the ammonium ion) were assigned with more certainty on the basis of the 15N isotopic shifts. Detailed studies of the temperature dependence of one internal mode (ν1) of the NO3 - ion and several external modes were made. The frequency and half band width versus temperature plots for both the internal mode and the external modes of 15NH4NO3 indicate only one crystal structure (phase V) between 10 and 257 K. Comparison of the frequency shifts between various isotopic compounds in the external mode region permitted a more precise assignment of the lattice modes associated with the NH4+ and NO3- ions to be made.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250231207
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