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  • 1
    Electronic Resource
    Electronic Resource
    Meiosis in the leek (Allium porrum L.) revisited I. Prophase I pairing (1995)
    Springer
    Chromosome research 3 (1995), S. 433-439 
    Details
    ISSN: 1573-6849
    Keywords: allium porrum ; meiosis ; polyploid ; synaptonemal complex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Meiotic chromosome pairing of the tetraploid speciesAllium porrum, the cultivated leek, was analysed by electron microscopy of 83 surface-spread nuclei in the late zygotene to early diplotene interval of prophase I, from four different varieties. Prophase I quadrivalent frequency, at 71%, marginally but significantly exceeds the two-thirds expected on a simple random end-pairing model, suggesting that more than two autonomous pairing sites occur, in some tetrasomes at least. This pattern of synaptic behaviour is consistent with an autotetraploid status, but comparison with other tetraploids, including otherAllium species, indicates thatAllium porrum may be a weak segmental allopolyploid displaying limited preferential homologous pairing. The incidence of pairing partner switches (PPSs) in prophase I quadrivalents is relatively low; 90% of all analysed quadrivalents had only one or two PPSs. The positional distribution of PPSs along quadrivalents was distinctly uneven with peaks in mid-chromosome arms and reduced frequencies around centromeres and near the ends. The four different varieties of leek analysed were remarkably similar in their meiotic behaviour despite their diverse breeding history, but individual plants within varieties displayed substantial variation in quadrivalent and PPS frequencies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00713894
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  • 2
    Electronic Resource
    Electronic Resource
    Cytological characterization of four meiotic mutants of Arabidopsis isolated from T-DNA-transformed lines (1997)
    Springer
    Chromosome research 5 (1997), S. 551-559 
    Details
    ISSN: 1573-6849
    Keywords: Arabidopsis ; fertility ; meiosis ; mutants ; T-DNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A secondary screen of the Feldmann collection of T-DNA transformed Arabidopsis lines identified several meiotic mutants. We used a spreading technique combined with DAPI staining in a detailed cytogenetic analysis of meiotic chromosome behaviour in four of these mutants, all of which are putatively T-DNA tagged and therefore candidates for molecular and functional analysis of the mutated genes. Two of them are defined as ‘synaptic’ mutants, showing greatly reduced association of homologous chromosomes at metaphase I: one is asynaptic, showing failure of synapsis during prophase I, whereas the other is desynaptic and is characterized by normal but non-maintained synapsis. Another mutant is defective in meiotic cell cycle control and undergoes a third meiotic division, resembling a second division but without an additional round of chromosome duplication. A further mutant shows meiosis-limited chromosome disruption, resulting in extensive chromosome fragmentation combined with other defects. All four mutants experience very irregular chromosome distribution during the meiotic divisions, resulting in abnormal numbers and/or sizes of microspores, with resulting reduced fertility.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018497804129
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  • 3
    Electronic Resource
    Electronic Resource
    A light microscopic atlas of meiosis inArabidopsis thaliana (1996)
    Springer
    Chromosome research 4 (1996), S. 507-516 
    Details
    ISSN: 1573-6849
    Keywords: Arbidopsis ; cytogenetics ; light microscopy ; meiosis ; chromosomes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An atlas of meiosis inArabidopsis thaliana, encompassing all stages from preleptotene to telophase II and early microspore formation, is presented in detail for the first time. The photomicrographs and descriptions are based on staining with the DNA fluorochrome 4′,6-diamidino-2-phenylindole (DAPI) combined with a spreading procedure, or haematoxylin-iron alum (HIA) staining. Despite previous reservations about the practicality of cytogenetic meiotic analysis inArabidopsis due to its small genome size, good-quality and clearly analysable preparations of all meiotic stages were obtained. This atlas of normal, wild-type meiosis is considered an essential prerequisite to informed analyses of meiotic mutants. Furthermore, extended prophase I chromosomes, particularly at the pachytene stage, offer considerable potential for producing a detailed cytogenetic map (karyotype) ofArabidopsis chromosomes with the additional prospect of high-resolution physical mapping based on fluorescencein situ hybridization (FISH) of defined DNA probes to these extended chromosomes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02261778
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  • 4
    Electronic Resource
    Electronic Resource
    Purification of human granulocytes by centrifugal elutriation and measurement of transmembrane potential (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 104 (1980), S. 425-431 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Viable cell samples containing 93% pure granulocytes were obtained from human blood using the techniques of dextran sedimentation followed by centrifugal elutriation. The resting transmembrane potential (Em) of human granulocytes was estimated using the fluorescent lipophilic cation, Di-S-C3(5), from the null point for potassium - i.e., the external K concentration at which there is no change in Em in response to valinomycin (a K ionophore). The Em of human granulocytes, as calculated from the Nernst potential for K at the null point, is approximately - 100 mV. Data indicate that this large transmembrane potential is due in part to the presence of an electrogenic Na-K pump in human granulocytes which is stimulated by external potassium and inhibited by ouabain.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041040315
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  • 5
    Electronic Resource
    Electronic Resource
    Transmembrane potential changes associated with superoxide release from human granulocytes (1981)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 106 (1981), S. 75-83 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Treatment of human granulocytes with concanavalin A, phorbol myristate acetate (PMA), N-formyl-methionyl-leucyl-phenylalanine (FMLP), and A23187 (a calcium ionophore) stimulates the release of superoxide anion and the generation of chemiluminescence. The fluorescent probe, Di-S-C3(5), has been used to monitor shifts in membrane potential in response to these stimulants which precede the secretion of superoxide. Concanavalin A, PMA, and FMLP induce a biphasic shift in transmembrane potential (Em), i.e., a rapid depolarization followed by a prolonged hyperpolarization. This depolarization is dependent on both external sodium and calcium while the hyperpolarization is inhibited by ouabain which blocks the electrogenic Na-K pump. In contrast, A23187 induces a rapid and prolonged depolarization. This monophasic shift in Em is dependent on external calcium. These results suggest that depolarization acts as a signal to initiate events associated with the “respiratory burst” of these phagocytes.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041060109
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  • 6
    Electronic Resource
    Electronic Resource
    Increase in copy number of an integrated vector during continuous culture of Hansenula polymorpha expressing functional human haemoglobin (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 10 (1994), S. 1569-1580 
    Details
    ISSN: 0749-503X
    Keywords: Hansenula ; haemoglobin ; integration ; continuous culture ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Recombinant human haemoglobin A (rHbA) was produced by a leucine-requiring strain of Hansenula polymorpha which had been transformed with an integration vector containing the Saccharomyces cerevisiae LEU2 gene and cDNAs for the expression of α and β globin each driven by the H. polymorpha MOX promoter. After 40 generations in a chemostat it was found that the integrated vector had become amplified in the host strain. In some cases this led to an increase in LEU2 gene dosage, but a loss of globin expression cassettes. In other cases the globin gene dosage also increased. These changes coincided with an increase in rHbA production in the culture, which was reversed when the dilution rate was increased. Isolates from a chemostat culture producing elevated levels of rHbA were grown in fed-batch fermentations, resulting in higher productivities than when inoculated with the parent strain. The rHbA produced was purified and characterized. Oxygen binding studies and electrospray mass spectrometry showed that the rHbA had been processed and assembled correctly, and behaved as a fully functional co-operative tetramer.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/yea.320101206
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