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  • 1
    Electronic Resource
    Electronic Resource
    An analysis of the role of actin during pollen activation leading to germination in pear (Pyrus communis L.): treatment with cytochalasin D (1990)
    Springer
    Sexual plant reproduction 3 (1990), S. 121-129 
    Details
    ISSN: 1432-2145
    Keywords: Actin ; Cytochalasin D ; Microfilaments ; Pollen (activation, germination, tube growth) ; Pyrus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Major stages of actin organization during activation leading to germination of pear (Pyrus communis L.) pollen were disrupted by treatment with 5 μg/ml cytochalasin D (CD), and the effects of the drug were monitored with rhodamine-phalloidin staining. CD induced the formation of granules or short rods in the place of the filamentous arrays that occur in normally developing pollen. Filamentous arrays, however, returned upon removal of CD. Pollen incubated directly in CD showed a gradual disappearance of circular actin profiles and their replacement by either granules or, less frequently, short rods. These granules and rods initially had a random distribution in the cell, but with time in CD they became localized at one of the three germination apertures. Pollen was also allowed to reach three stages of microfilament (MF) organization (initial fibrillar arrays, interapertural MFs, and MFs confined beneath a single aperture) prior to being continously exposed to CD. After CD treatment, germination was blocked and the number of cells containing short rods increased, but movement of actin to a single aperture continued. Finally, when pollen at different stages of MF organization was treated with a CD pulse and then transferred to drug-free medium, germination was delayed regardless of the stage of MF organization at the time of treatment. The results indicate that an uninterrupted progression of actin organization is essential for pollen germination, but that movement of actin in the cell is CD-insensitive.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00198856
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  • 2
    Electronic Resource
    Electronic Resource
    An intermediate-voltage electron microscopic study of freeze-substituted generative cell in pear (Pyrus communis L.): features with relevance to cell-cell communication between the two cells of a germinating pollen (1994)
    Springer
    Sexual plant reproduction 7 (1994), S. 177-186 
    Details
    ISSN: 1432-2145
    Keywords: Cell-to-cell communication ; Cell shape Generative cell ; Microfilaments ; Pyrus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The ultrastructure of the generative cell (GC) wall complex in germinating pear (Pyrus communis L.) pollen was studied with the aim of identifying features that may shed light on the mechanism of uptake of substances by the GC from its host, the vegetative cell (VC). The techniques of rapid freeze-fixation and freeze-substitution, serial sectioning, and conventional and intermediate-voltage transmission electron microscopy were employed. The wall complex consisted of two plasma membranes (PMs), one derived from the GC and the other from the VC. A nonfibrillar wall material occurred in the space between the two PMs. Plasmodesmata could not be identified in this wall complex. However, in localized areas the wall complex formed processes that protruded into the VC cytoplasm. In other areas, the wall complex showed certain cup-shaped invaginations. Certain double membrane bound multivesicular bodies occurred in the GC cytoplasm; their morphological characteristics indicated that they may have been derived from the GC wall complex. The data indicate that in pear the GC surface is amplified by wall processes, presumably to perform a role analogous to transfer cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00228491
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  • 3
    Electronic Resource
    Electronic Resource
    pH-Dependent solubility and assembly of microtubules in bovine brain extracts (1994)
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 28 (1994), S. 69-78 
    Details
    ISSN: 0886-1544
    Keywords: cytoskeleton ; microtubule-associated protein (MAP) ; marine egg extracts ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Alkaline pH favors the assembly of microtubules (MTs) in marine egg extracts [Suprenant and Marsh, 1987: J. Cell Sci. 184:167-180; Suprenant, 1989: Exp. Cell Res. 184:167-180; 1991: Cell Motil. Cytoskeleton 19:207-220] and mammalian brain extracts [Tiwari and Suprenant, 1993: Anal. Biochem. 215:96-103], even though the assembly of purified microtubule protein (MTP) from both of these sources is favored at slightly acidic pH. The present investigation examines whether alkaline pH has a direct or indirect effect on MT nucleation and growth in soluble brain extracts. Cell-free extracts were prepared from bovine cerebral cortex, and a nucleated assembly assay was used to demonstrate that MT assembly in brain extracts is favored at slightly acidic pH. The increase in MT mass found at alkaline pH is due to an increase in the solubility of tubulin not an increase in the extent of assembly On average, 47.7 ± 11.3% of the total tubulin is soluble at pH 7.2, while only 30.9 ± 8.9% of the tubulin is soluble at pH 6.8. A model is proposed that indicates how microtubule proteins from both mammalian brain and marine eggs may be associated with pH-dependent factors. © 1994 Wiley-Liss, Inc.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cm.970280107
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  • 4
    Electronic Resource
    Electronic Resource
    Spatial and temporal organization of actin during hydration, activation, and germination of pollen inPyrus communis L.: a population study (1988)
    Springer
    Protoplasma 147 (1988), S. 5-15 
    Details
    ISSN: 1615-6102
    Keywords: Actin ; Germinating pollen ; Polarity ; Pyrus communis ; Rhodamine-phalloidin staining
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Dynamics of F-actin organization during activation and germination ofPyrus communis (pear) pollen was examined using rhodaminephalloidin. Prior to activation, the rhodamine-phalloidin labelling pattern appeared as circular profiles in the peripheral cytoplasm of the vegetative cell and as coarse granules around the vegetative nucleus. In activated pollen, parallel arrays of cortical F-actin were aligned circumferentially, along the polar axis in non-apertural areas of the pollen grain, and at 45° to 90° to the polar axis beneath the apertures. Some pollen also showed fluorescent granules or fusiform bodies dispersed throughout the cytoplasm, but as the number of such pollen diminished with prolonged incubation, these are being considered as intermediate patterns. In later stages, the filaments became organized as interapertural bundles traversing the three apertures. However, prior to emergence of the pollen tube, labelling became confined to a single aperture. In germinated pollen grains, actin microfilaments are aligned more or less axially with respect to the axis of the developing pollen tube. The granular labelling pattern seen around the vegetative nucleus prior to pollen activation also became clearly filamentous with pollen activation; this filamentous pattern persisted until germination when it was replaced by cables that aligned longitudinally with respect to the emerging tube axis. The results demonstrate that the organization of actin undergoes considerable changes in the period preceding pollen germination and that microfilament polarization is achieved before pollen germination.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01403873
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  • 5
    Electronic Resource
    Electronic Resource
    Organization of the cytoskeleton in pollen tubes ofPyrus communis: a study employing conventional and freeze-substitution electron microscopy, immunofluorescence, and rhodamine-phalloidin (1988)
    Springer
    Protoplasma 147 (1988), S. 100-112 
    Details
    ISSN: 1615-6102
    Keywords: Cytoskeleton ; Pollen tube ; Pyrus ; Tip growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The structure and organization of the cytoskeleton in the vegetative cell of germinated pollen grains and pollen tubes ofPyrus communis was examined at the ultrastructural level via chemical fixation and freeze substitution, and at the light microscopic level with the aid of immunofluorescence of tubulin and rhodamine-phalloidin. Results indicate that cortical microtubules and microfilaments, together with the plasma membrane, form a structurally integrated cytoskeletal complex. Axially aligned microtubules are present in cortical and cytoplasmic regions of the pollen grain portion of the cell and the distal region of the pollen tube portion. Cytoplasmic bundles of microfilaments are found in association with elements of endoplasmic reticulum and vacuoles. Axially aligned microfilaments are also found in this region, associated with and independent of the microtubules. Microtubules are lacking in the subapical region where short, axially aligned microfilaments are found in the cell cortex. In the apical region, which also lacks microtubules, a 3-dimensional network of short microfilaments occurs. Microfilaments, but not microtubules, appear to be associated with the vegetative nucleus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01403337
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