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  • Pollen tube  (9)
  • Cytoskeleton  (4)
  • Microtubules  (4)
  • Megagametophyte  (2)
  • 1
    ISSN: 1432-2048
    Keywords: Kinesin ; Nicotiana ; Organelle movement ; Pollen tube
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In plant cells, microtubule-based motor proteins have not been characterized to the same degree as in animal cells; therefore, it is not yet clear whether the movement of organelles and vesicles is also dependent on the microtubular cytoskeleton. In this work the kinesinimmunoreactive homologue from pollen tubes of Nicotiana tabacum L. has been purified and biochemically characterized. The protein preparation mainly contained a polypeptide with a relative molecular weight of approx. 100 kDa. This polypeptide bound to animal microtubules in an ATP-dependent manner and it further copurified with an ATPase activity fourfold-stimulated by the presence of microtubules. In addition, the sedimentation coefficient (approx. 9S) was similar to those previously shown for other kinesins. Immunofluorescence analyses revealed a partial co-distribution of the protein with microtubules in the pollen tube. These data clearly indicate that several properties of the kinesin-immunoreactive homologue are similar to those of kinesin proteins, and suggest that molecular mechanisms analogous to those of animal cells may drive the microtubule-based motility of organelles and vesicles in plants.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Sexual plant reproduction 1 (1988), S. 88-96 
    ISSN: 1432-2145
    Keywords: Pollen activation ; Generative cell ; Vegetative cell ; Cytoskeleton
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Both the internal anatomy and the external morphology of the mature pollen grain of Aloe ciliaris have been studied, together with the cytological changes occurring during pollen activation. In mature pollen, the generative cell (GC) and the vegetative nucleus (VN) are closely associated with each other, and both can be found in the central part of the grain. In the generative cytoplasm, some organelles and microtubular bundles are present. In the vegetative cell, dictyosomes, stacks of rough endoplasmic reticulum, mitochondria, plastids, vacuoles, ribosomes, and masses of fibrillar material have been described. During pollen activation, important changes occur in both the generative and vegetative cells (VC). In the GC, the microtubular bundles become clearly visible, and the GC and VC gradually move towards the germ pore. The RER cisterns become free from the stacks, and organelles, such as dictyosomes, become very active. The fibrillar masses gradually decrease in number, and the individual fibrils become more evident and clearer in resolution.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Sexual plant reproduction 12 (1999), S. 67-70 
    ISSN: 1432-2145
    Keywords: Key words Cytoskeleton ; Cytoskeleton proteins ; Cytoskeleton function ; Pollen tube ; Embryo sac
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Sexual reproduction in plants is intimately connected to the activity of the cytoskeletal apparatus in reproductive cells. Because of the ease with which the pollen tube can be studied, it has become a model for studying many aspects of cell physiology related to the cytoskeleton, such as movement of organelles and vesicles and cell division. However, information about cytoskeletal proteins is still insufficient for determining cytoskeletal functions during reproduction, especially in terms of cell-cell interactions. One reason may be that cytological and biochemical research on the cytoskeleton of pollen and the embryo sac has not been complemented by sufficient research activity at genetic and molecular levels, and few laboratories are currently involved in this work. This might be because of problems in identifying appropriate applied applications of the work that might attract more investigation.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Sexual plant reproduction 5 (1992), S. 64-71 
    ISSN: 1432-2145
    Keywords: Generative cell ; Isolation ; Microtubules ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Upon squashing of the pollen grain, the isolated generative cell ofNicotiana tabacum looses its spindle shape to become spherical; this phenomenon is independent of the sucrose concentration used. The time necessary for this change can vary from 1 min (0% sucrose) to 20 min (30% sucrose). The microtubular cytoskeleton was studied by means of immunofluorescence and electron microscopy. Just after isolation, 5 to 15 clearly visible bundles in microtubules organized in a basket-like structure are present. After 15 min in medium with 15% sucrose, the microtubular cytoskeleton disappears, and a diffusely spread tubulin can be observed. Neither the addition of 10–20 μM taxol to the medium, nor the omission of Ca2+ to the medium has any effect on the changes in cell shape and loss of microtubular bundles after isolation.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Sexual plant reproduction 9 (1996), S. 59-64 
    ISSN: 1432-2145
    Keywords: Motor proteins ; Pollen tube ; Tip growth ; Organelle movement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The growth of pollen tubes is characterized by an intense cytoplasmic streaming, during which the movements of smaller organelles (like secretory vesicles) and larger ones (including the generative cell and vegetative nucleus) are precisely coordinated. A well-characterized cytoskeletal apparatus is likely responsible for these intracellular movements. In recent years both microfilament and microtubule-based motor proteins have been identified and assumed to be the translocators of the several organelle categories. Their precise function during pollen tube growth is not yet clear, but apparently an actomyosin-based system is mainly responsible for pollen tube elongation. On the other hand, microtubules and microtubule-based motors have been thought to play a role in the maintenance of cell polarity. Both cytoskeletal systems (and their respective motor activities) could cooperate to ensure a precise regulation of pollen tube growth.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Sexual plant reproduction 1 (1988), S. 208-216 
    ISSN: 1432-2145
    Keywords: Megagametophyte ; Synergids ; Brassica campestris ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In Brassica campestris, both synergids of the ovule degenerate before the arrival of the pollen tube. Synergid degeneration does not depend on pollination. At the non-degenerated stage, the synergids are completely filled with a complexly organized cytoplasm containing numerous mitochondria with many cristae, a large number of dictyosomes with many associated vesicles, and a very extensive rough endoplasmic reticulum. The degenerative changes that occur in the cytoplasm of the synergids are characterized by a loss of visibility of the membranes of the endoplasmic reticulum and the simultaneous formation of dense deposits on the surrounding membranes of the mitochondria. Locally, the plasma membranes of the synergids disappear, and some ground plasma of the synergids penetrates into the space between the plasma membranes of the egg cell and the central cell.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-2145
    Keywords: Female germ unit ; Nicotiana ; Megagametophyte ; Organelle movement ; Video microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Living embryo sacs and megagametophytic cells of Nicotiana alata and Nicotiana tabacum were obtained using enzymatic maceration and microdissection. The yields of isolated embryo sacs, egg apparatus and central cells were up to 35%, 40% and 35%, respectively. Vectorial movement of organelles and undulations of tubular structures, presumably endoplasmic reticulum, were observed in eggs, synergids and central cells using video-enhanced microscopy. Despite evident viability using the fluorochromatic reaction, the egg displays much less organelle movement and therefore appears to be quiescent. The large vacuole of the central cell is traversed by mobile strands of cytoplasm through which organelles migrate. A polygonal network is located at the periphery of the central cell, which may contribute to anchorage of the cell with the embryo-sac wall. The observation of organelle movement provides direct evidence of the condition of the cell and may be a useful approach for assessing cell vigor.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Sexual plant reproduction 8 (1995), S. 223-227 
    ISSN: 1432-2145
    Keywords: Pollen ; Generative cell ; Cytoskeleton ; Motility ; Myosin immunogold labelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In pollen grains of Convallaria majalis the outer membrane of the generative cell (GC) is the inner membrane of the vegetative cell (VC). Striped projections (SP) at the cytoplasmic face of the outer membrane of the GC were revealed by chemical fixation and also by a rapid freeze-fixation and freeze-substitution. The projections, located in groups on the protruding lobes of the GC, were arranged parallel to each other and were equally spaced (40 nm apart). The length of the SP, estimated from grazing sections of GC, was 400 nm. Each projection was composed of T-shaped elements, about 35 nm high, spaced at an average distance of 25 nm. SP were observed in mature, hydrated, activated and germinated pollen grains and seemed to be associated with microtubules and microfilaments of the VC. No evidence exists yet of SP on the sperm cell membrane. Immunogold labelling with anti-myosin antibodies showed many gold particles attached preferentially to the surface of the protruding lobes of the GC in the area of the projections. These results may suggest that the SP of Convallaria GC contain myosin-like protein and play an important role in the motility of the GC during pollen tube growth.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Sexual plant reproduction 9 (1996), S. 59-64 
    ISSN: 1432-2145
    Keywords: Key words Motor proteins ; Pollen tube ; Tip growth ; Organelle movement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The growth of pollen tubes is characterized by an intense cytoplasmic streaming, during which the movements of smaller organelles (like secretory vesicles) and larger ones (including the generative cell and vegetative nucleus) are precisely coordinated. A well-characterized cytoskeletal apparatus is likely responsible for these intracellular movements. In recent years both microfilament- and microtubule-based motor proteins have been identified and assumed to be the translocators of the several organelle categories. Their precise function during pollen tube growth is not yet clear, but apparently an actomyosin-based system is mainly responsible for pollen tube elongation. On the other hand, microtubules and microtubule-based motors have been thought to play a role in the maintenance of cell polarity. Both cytoskeletal systems (and their respective motor activities) could cooperate to ensure a precise regulation of pollen tube growth.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Planta 133 (1976), S. 35-40 
    ISSN: 1432-2048
    Keywords: Pollen tube ; Style ; Callose ; Petunia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In Petunia pollen tubes growing in the style there appear to be two ways of callose deposition. The first one is callose deposition outside the plasma membrane as a distinct layer closely appressed to the cell wall. The second one is callose deposition within the cytoplasm as distinct callose grains, leading to the formation of callose plugs. This second way is accompanied by a characteristic ultrastructure of the cytoplasm, namely strong electron-density of the plasma matrix, partial absence of the plasma membrane and the absence of plastids and dictyosomes. For both ways of callose deposition a mechanism is proposed and the function of callose plugs is discussed.
    Type of Medium: Electronic Resource
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