GLORIA

GEOMAR Library Ocean Research Information Access

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Male reproductive cell development in Nicotiana tabacum: male germ unit associations and quantitative cytology during sperm maturation (1994)
    Springer
    Sexual plant reproduction 7 (1994), S. 324-332 
    Details
    ISSN: 1432-2145
    Keywords: Generative cell ; Male germ unit Nicotiana tabacum ; Pollen tube ; Sperm cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Generative and sperm cells were examined at four stages of development from generative cell formation to sperm cell maturation using serial transmission electron microscopy. The generative cell and vegetative nucleus are associated in a male germ unit association during pollen maturation and tube elongation, except for generative cell mitosis. At late stages of prophase, this association loosens; the generative cell separates from the vegetative nucleus at metaphase. Slender, unbranched, or occasionally branched projections may be found at one or both ends of the generative cell, or they may be single, blunt, and short. Slender projections are rare during anaphase and telophase. The vegetative nucleus moves back into apposition with one sperm cell at the end of mitosis. During the re-establishment of the association, the vegetative nucleus first touches the end of the leading sperm cell and then moves next to the middle of the sperm nucleus. As the sperm cells enter interphase, a conventional association is re-established between one cell and the vegetative nucleus through one or more long and slender cytoplasmic extensions; these associations are maintained throughout later passage in the pollen tube. During maturation, a significant increase occurs in the surface area of the sperm cells (particularly in the sperm cell in association with the vegetative nucleus), and a lesser increase in nuclear volume and surface area. Other sperm cell parameters, including those of heritable organelles, remain unchanged during sperm cell maturation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00230511
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Populations of plastids and mitochondria during male reproductive cell maturation in Nicotiana tabacum L.: A cytological basis for occasional biparental inheritance (1994)
    Springer
    Planta 193 (1994), S. 115-122 
    Details
    ISSN: 1432-2048
    Keywords: Autophagy ; Cytoplasmic inheritance ; Generative cell ; Nicotiana (reproductive cells) ; Plastid diminution ; Sperm cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The dynamics of plastid and mitochondrial populations in male reproductive cells of tobacco (Nicotiana tabacum L.) were examined during development using serial ultrathin sections and transmission electron microscopy to reconstruct 58 generative cells and 31 sperm cells at selected stages of maturation from generative cell formation through gametic fusion. The first haploid mitosis resulted in incomplete exclusion of plastids providing an average of 2.81 plastids and 82.7 mitochondria for each newly formed generative cell. During generative-cell maturation, plastid content decreased to an average of 0.48 plastids/generative cell at anthesis owing to autophagy of organelles. Plastids were present in low frequency within generative and sperm cells in the pollen tube and appeared to be transmitted, according to observations immediately prior to fertilization. This forms a cytological basis for genetic reports of occasional biparental plastid inheritance. In contrast, mitochondria were transmitted in larger numbers, and approximately 80 mitochondria per generative cell or sperm cell pair were retained throughout development. This provides a potentially stable source for the transmission of male mitochondrial DNA, if present at fertilization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00191614
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Preliminary observations on the formation of the male germ unit in pollen tubes ofCyphomandra betacea sendt. (1988)
    Springer
    Protoplasma 147 (1988), S. 55-63 
    Details
    ISSN: 1615-6102
    Keywords: Generative cell ; Sperm cell ; Treetomato ; Ultrastructure ; Vegetative nucleus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The structure of the generative cell and its association with the vegetative nucleus in the pollen tube ofCyphomandra betacea Sendt. were observed with the electron microscope. The generative cell, bounded by its own plasma membrane and the inner plasma membrane of the vegetative cell, possesses the cytoplasmic extension which lies within the embayments of a vegetative nucleus. The generative cell contains the normal complement of organelles and, especially, microtubules which cluster into several groups adjacent to the plasma membrane, oriented along the longitudinal axis of the cell. In the pollen tube reaching the lower end of the style aftersemivivo pollination, both of the sperm cells are elongated and polyribosomes and microtubules are the outstanding feature in the cytoplasm. The two sperm cells are connected by a common transverse cell wall, while cytoplasmic channels exist in both the periplasm of the two sperm cells and the transverse wall. The leading sperm cell (Svn) is closely associated with the vegetative nucleus. Thus the present study demonstrates the existence of the male germ unit in the pollen tube ofC. betacea. The possible cytoplasmic continuity between the sperm cells and between the gametes and vegetative cell is considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01403877
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Effect of thermal history on crystallization behavior of polyetheretherketone studied by differential scanning calorimetry (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 164 (1988), S. 21-34 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Das Kristallisationsverhalten von Polyetheretherketon (PEEK) wurde mit Hilfe der Differentialkalorimetrie (DSC) untersucht. Mit der Erhöhung der Kristallinität verschiebt sich die Glastemperatur zu höheren Temperaturen. Hitzebehandeltes PEEK zeigt Doppelpeaks in der DSC-Kurve, was für PEEK charakteristisch ist. Diese Doppelpeaks werden, je nach den Bedingungen der Hitzebehandlung, durch die Bildung unvollständiger Kristallstrukturen hervorgerufen.
    Notes: The crystallization behavior of polyetheretherketone (PEEK) was investigated by differential scanning calorimetry (DSC). The glass transition temperature of PEEK shifts to higher temperatures with an increase in crystallinity. Heat-treated PEEK showed double peaks in their DSC curves, which is a characteristic phenomenon of PEEK. These double peaks were caused by the formation of incomplete crystal structures according to the conditions of heat-treatment.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051640102
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Hydrogenation of m-xylene catalyzed by a silica-supported polysilazane-platinum complex (1996)
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 7 (1996), S. 79-83 
    Details
    ISSN: 1042-7147
    Keywords: hydrogenation ; m-xylene ; polysilazane ; stereochemistry ; platinum complex ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A new kind of inorganic polymer, silica-supported polysilazane (Si-N), and its platinum complex (Si-N-Pt) were prepared and characterized by X-ray photoelectron spectroscopy. It was found that Si-N-Pt can catalyze hydrogenation of m-xylene under mild conditions (30-50°C, 1 atm). The products of the reaction were cis- and trans-1,3-dimethylcyclohexane. The formation of trans-1,3-dimethylcyclohexane may be adequately explained according to the “roll-over” model. The stereoselectivity was influenced by temperature and catalyst concentration, the proportion of the cis isomer decreasing with an increase in each of the two factors. The effects of other reaction parameters, such as the N/Pt mole ratio in the complex, solvents and reaction time, etc., on the hydrogenation of m-xylene were also studied. The Si-N-Pt catalyst is very stable in reaction and turnover numbers amount to 520 in 70 hr.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...