scholarly journals The mechanics of mitosis in the pollen-tube of Tulipa

1936 ◽  
Vol 121 (822) ◽  
pp. 207-220 ◽  
Keyword(s):  
Pollen Tube ◽  
Higher Plants ◽  
Generative Cell ◽  
Metaphase Plate ◽  
Cell Plate ◽  
Usual Method ◽  
Generative Nucleus ◽  
A Cell ◽  
Marked Cell

The division of the generative nucleus in the pollen-tube of the higher plants has been studied by several authors, with results differing widely from one another even when concerned with the same genus. For example, Koernicke (1906), Welsford (1914), and O’Mara (1933) have investigated various species of Lilium . Koernicke and Welsford describe the formation of a definite though narrow metaphase plate, while O’Mara, in spite of his illustration (fig. 9), is of the opinion that there is no such regular congression owing to the narrowness of the tube. Trankowsky (1930) finds a metaphase plate in Hemerocallis , the pollen-tube of which is wide in comparison with the size of the spindle, but not in Galanthus or Convallaria . Wulff’s (1933) observations are weakened by his confusing anaphase with pro-metaphase, and centric with nucleolar constrictions. A further point at issue is whether the generative cell divides by constriction or by the formation of a cell-plate, the more usual method in the higher plants. Koernicke illustrates a well marked cell-plate, but Wulff and others are of the opinion that division is by constriction.

scholarly journals Tradescantia bracteata pollen in vitro: pollen tubes development and mitosis

2015 ◽  
Vol 46 (4) ◽  
pp. 587-598 ◽  
Author(s):  
E. Lewandowska ◽  
M. Charzyńska
Keyword(s):  
Pollen Tube ◽  
Generative Cell ◽  
Metaphase Plate ◽  
Pollen Grains ◽  
Neutral Red ◽  
Generative Nucleus ◽  
Mitotic Spindles ◽  
Germinating Pollen ◽  
Vacuolar System

About 90 per cent of <i>Tradescantia bracteata</i> pollen germinates <i>in vitro</i> after 15 min. Mitosis starts in the pollen tube after about 3 h. The mitotic trans-formations of chromosomes within the generative nucleus are not synchronized. They involve succesively the linearly arranged chromosomes in the elongated generative nucleus. In metaphase the chromosomes are arranged tandem-like linearly along the pollen tube. The chromatides translocate in anaphase from various distances to the poles in a plane parallel to the metaphase plate. This suggests that chromosomes have individual mitotic spindles and that coordination of the chromosome transformations in the generative cell is much less strict than in a typical somatic mitosis. Starch is the storage material of pollen grains. In the vegetative cytoplasm of mature pollen grains minute reddish-orange vesicular structures are visible after staining with neutral red. They do not fuse with the vacuoles proper arising in germinating pollen grains to form the vacuolar system of the pollen tube.

The Formation of the Generative Cell in the Pollen Grain of Endymion Non-Scriptus (L)

1968 ◽  
Vol 3 (4) ◽  
pp. 573-578
Author(s):  
R. E. ANGOLD
Keyword(s):  
Cell Wall ◽  
Somatic Cells ◽  
Generative Cell ◽  
Cell Plate ◽  
Pollen Grain ◽  
Generative Nucleus ◽  
A Cell ◽  
Generative Nuclei

The generative cell wall in the pollen grain of Endymion non-scriptus is formed, as in somatic cells, from a cell plate between the vegetative and generative nuclei. This wall curves around the generative nucleus, and fuses with the intine to enclose the generative cell. The generative cell is subsequently freed from the intine by the constriction of the generative cell wall between the generative nucleus and the intine.

Generative cell mitosis in pollen tubes of Nicotiana tabacum: Ultrastructure and 3-D reconstruction

1992 ◽  
Vol 50 (1) ◽  
pp. 848-849
Author(s):  
Hong-Shi Yu ◽  
S. D. Russell
Keyword(s):  
Pollen Tube ◽  
Generative Cell ◽  
Three Dimensional ◽  
Metaphase Plate ◽  
Preprophase Band ◽  
Mitotic Division ◽  
Mitotic Apparatus ◽  
Cell Mitosis

In bicellular pollen, the two sperm cells are formed by mitotic division of the generative cell (GC) in the pollen tube. This division is characterized by several unique features, including: lack of a preprophase band (PPB), absence of a metaphase plate, absence of normal spindle formation, and irregular patterns of cytokinesis. Purportedly, this is the result of spatial constraints within the pollen tube, which in vivo may be as narrow as 3 μm (as in Nicotiana) and slightly wider in vitro.Immunofluorescence studies of GC mitosis have been published in the last five years2−7, but only one incomplete ultrastructural report on GC division in vitro is available. This study is the first using three-dimensional (3-D) techniques to reconstruct the mitotic apparatus of the GC in vivo.

scholarly journals Pollen Development in Orchids. 5. A Generative Cell Domain Involved in Spatial Control of the Hemispherical Cell Plate

1991 ◽  
Vol 100 (3) ◽  
pp. 559-565
Author(s):  
R. C. BROWN ◽  
B. E. LEMMON
Keyword(s):  
Generative Cell ◽  
Preprophase Band ◽  
Cell Plate ◽  
Generative Nucleus ◽  
Pollen Mitosis ◽  
Spatial Control ◽  
Division Plane ◽  
Radial System ◽  
Vegetative Pole ◽  
First Pollen Mitosis

The unequal first pollen mitosis in moth orchids (Phalaenopsis) is followed by an unusual form of cytokinesis that isolates a small lens-shaped generative cell from a large vegetative cell. No preprophase band of microtubules predicts the division plane and the new cell plate grows completely around the generative cell rather than fusing with the parental wall. Development of the phragmoplast cytoskeleton consisting of fusiform bundles of microtubules and F-actin occurs in three major stages: (1) the initial asymmetrical phragmoplast conforming to the shape of the interzonal region, which tapers from the broad mass of chromosomes at the generative pole to the rounded mass at the vegetative pole; (2) the symmetrical plate-like phragmoplast; and (3) the hemispherical phragmoplast, which curves around the generative nucleus. Microtubules of the generative half of the hemispherical phragmoplast are nuclearbased, while those on the vegetative side terminate in endoplasmic reticulum. The path of the phragmoplast appears to outline a cytoplasmic domain denned by a radial system of microtubules emanating from the generative nucleus.

A gamma-tubulin-related protein associated with the microtubule arrays of higher plants in a cell cycle-dependent manner

1993 ◽  
Vol 104 (4) ◽  
pp. 1217-1228 ◽  
Author(s):  
B. Liu ◽  
J. Marc ◽  
H.C. Joshi ◽  
B.A. Palevitz
Keyword(s):  
Cell Cycle ◽  
Mammalian Cells ◽  
Higher Plants ◽  
Cortical Microtubule ◽  
Metaphase Plate ◽  
Preprophase Band ◽  
Cell Plate ◽  
Dependent Manner ◽  
Gamma Tubulin ◽  
Cycle Dependent

An antibody specific for a conserved gamma-tubulin peptide identifies a plant polypeptide of 58 kDa. gamma-Tubulin antibody affinity purified from this polypeptide recognizes the centrosome in mammalian cells. Using immunofluorescence microscopy, we determined the distribution of this gamma-tubulin-related polypeptide during the complex changes in microtubule arrays that occur throughout the plant cell cycle. We report a punctate association of gamma-tubulin-related polypeptide with the cortical microtubule array and the preprophase band. As cells enter prophase, gamma-tubulin-related polypeptide accumulates around the nucleus and forms a polar cap from which early spindle microtubules radiate. During metaphase and anaphase, gamma-tubulin-related polypeptide preferentially associates with kinetochore fibers and eventually accumulates at the poles. In telophase, localization occurs over the phragmoplast. gamma-Tubulin-related polypeptide appears to be excluded from the plus ends of microtubules at the metaphase plate and cell plate. Its distribution during the cell cycle may be significant in light of differences in the behavior and organization of plant microtubules. The identification of gamma-tubulin-related polypeptide could help characterize microtubule organizing centers in these organisms.

scholarly journals Localization of actin in pollen tubes of Ornithogalum virens L.

2014 ◽  
Vol 68 (2) ◽  
pp. 97-102
Author(s):  
Małgorzata Stępka ◽  
Fabricio Ciampolini ◽  
Mauro Cresti ◽  
Maria Charzyńska
Keyword(s):  
Pollen Tube ◽  
Actin Filaments ◽  
Laser Scanning ◽  
Higher Plants ◽  
Generative Cell ◽  
Pollen Tubes ◽  
Confocal Laser ◽  
Vegetative Nucleus ◽  
Ornithogalum Virens

The germinating pollen grain (in vivo on the stigma or in vitro in germination medium) forms a pollen tube which transports the vegetative nucleus and generative cell/two sperm cells participating in the process of double fertilization. The growth of the tube and the transport of organelles and the cells occur due to two major motor systems existing in the pollen tubes of higher plants: the tubuline-dynein/kinesin and the actin-myosin system. In pollen tubes of <em>Ornithogalum virens</em> the actin filaments were labelled with TRITC-phalloidin (2 µg/ml) in the PIPES buffer and the 10% sucrose, without the fixative and DMSO. Omission of the fixative and permeabilizing agent (DMSO) allowed better preservation of the structure, and the "fluorescence" of actin was observed in living pollen tubes. Observations in CLSM (confocal laser scanning microscope) showed that actin is distributed in the vicinity of the cell membrane. This could support the view that actin filaments and the plasmalemma form the pollen tube cortex along which the cytoplasmic movement of organelles, and cell transport occurs.

Freezing

2017 ◽  
Author(s):  
Andrew Clarke
Keyword(s):  
Thermal Hysteresis ◽  
Higher Plants ◽  
Terrestrial Environment ◽  
Cold Temperatures ◽  
Cellular Dehydration ◽  
A Cell ◽  
Unicellular Organisms ◽  
Cell Cytosol ◽  
Freezing Temperatures ◽  
Multicellular Organisms

Freezing is a widespread ecological challenge, affecting organisms in over half the terrestrial environment as well as both polar seas. With very few exceptions, if a cell freezes internally, it dies. Polar teleost fish in shallow waters avoid freezing by synthesising a range of protein or glycoprotein antifreezes. Terrestrial organisms are faced with a far greater thermal challenge, and exhibit a more complex array of responses. Unicellular organisms survive freezing temperatures by preventing ice nucleating within the cytosol, and tolerating the cellular dehydration and membrane disruption that follows from ice forming in the external environment. Multicellular organisms survive freezing temperatures by manipulating the composition of the extracellular body fluids. Terrestrial organisms may freeze at high subzero temperatures, often promoted by ice nucleating proteins, and small molecular mass cryoprotectants (often sugars and polyols) moderate the osmotic stress on cells. A range of chaperone proteins (dehydrins, LEA proteins) help maintain the integrity of membranes and macromolecules. Thermal hysteresis (antifreeze) proteins prevent damaging recrystallisation of ice. In some cases arthropods and higher plants prevent freezing in their extracellular fluids and survive by supercooling. Vitrification of extracellular water, or of the cell cytosol, may be a more widespread response to very cold temperatures than recognised to date.

The development of the male gametophyte and spermatogenesis in Taxus baccata L

1986 ◽  
Vol 228 (1250) ◽  
pp. 85-96 ◽  
Keyword(s):  
Pollen Tube ◽  
De Novo ◽  
Male Gametophyte ◽  
Generative Cell ◽  
Equal Size ◽  
Taxus Baccata ◽  
Transverse Wall ◽  
Proximal Pole ◽  
Spermatogenous Cell ◽  
Tube Cell

The development of the male gametophyte of Taxus baccata has been studied over a period of 20 weeks, from germination of the microspore in February to spermatogenesis in July. A few days after germination the microspore nucleus divides and a transverse wall forms at the equator cutting off the small generative cell and a large tube cell. The latter immediately begins to expand to form the pollen tube. The first division thus establishes the polarity of the gametophyte and the generative cell is regarded as proximal. The transverse wall is ephemeral, and within six weeks it has disappeared. The nucleus of the generative cell divides while still at the proximal pole. The two daughter nuclei are unequal in size, but they remain associated and together move distally. The larger nucleus eventually becomes the nucleus of the spermatogenous cell, and the smaller the sterile nucleus. The spermatogenous cell acquires a distinctive cytoplasm and becomes surrounded by a wall which arises de novo . The nucleus of the spermatogenous cell enlarges, but always remains towards one side of the cell so that at mitosis the spindle is contained within one hemisphere. After division the wall of the spermatogenous cell is ruptured and the two sperms are released as naked nuclei of equal size. The cytoplasm of the spermatogenous cell degenerates as it enters the tube, but remains recognizable until fertilization.

scholarly journals Immunochemical and immunocytochemical identification of a myosin heavy chain polypeptide in Nicotiana pollen tubes

1989 ◽  
Vol 92 (4) ◽  
pp. 569-574
Author(s):  
X.J. Tang ◽  
P.K. Hepler ◽  
S.P. Scordilis
Keyword(s):  
Pollen Tube ◽  
Nuclear Envelope ◽  
Myosin Heavy Chain ◽  
Heavy Chain ◽  
Immunofluorescence Microscopy ◽  
Generative Cell ◽  
Pollen Tubes ◽  
Nuclear Surface ◽  
Common Pattern ◽  
Western Blots

A myosin heavy chain polypeptide has been identified and localized in Nicotiana pollen tubes using monoclonal anti-myosin antibodies. The epitopes of these antibodies were found to reside on the myosin heavy chain head and rod portion and were, therefore, designated anti-S-1 (myosin S-1) and anti-LMM (light meromyosin). On Western blots of the total soluble pollen tube proteins, both anti-S-1 and anti-LMM label a polypeptide of approximately 175,000 Mr. Immunofluorescence microscopy shows that both antibodies yield numerous fluorescent spots throughout the whole length of the tube, often with an enrichment in the tube tip. These fluorescent spots are thought to represent vesicles and/or organelles in the pollen tubes. In addition to this common pattern, anti-S-1 stains both the generative cell and the vegetative nuclear envelope. The different staining patterns of the nucleus between anti-S-1 and anti-LMM may be caused by some organization and/or anchorage state of the myosin molecules on the nuclear surface that differs from those on the vesicles and/or organelles.

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