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  • 1
    ISSN: 1615-6102
    Keywords: Carrot hypocotyl explant ; Flow cytometry ; Somatic embryogenesis ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The cellular events occurring in carrot hypocotyl explants during long-term and pulse treatment with 2,4-D were followed using different techniques (light and transmission electron microscopy, flow cytometry, PCNA staining). Different morphogenetic pathways were induced under the various experimental conditions. Nevertheless, in the explants the activated cells were the same (provascular cells) and they showed very similar structural and ultrastructural changes. The long-term treatment with 2,4-D induced rapid re-activation of the cell cycle.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2048
    Keywords: Key words: Chitinase ; Daucus ; Plant development ; Secretion ; Somatic embryogenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The carrot cell variant ts11 is unable to form somatic embryos at the non-permissive temperature of 32 °C, but the block can be overcome by the addition of a 32-kDa acidic endochitinase to the medium. In this work we conducted a cyto-histological analysis of the blocked embryo forms. The morphology of the endomembrane system is altered; in particular, the ER is dilated and may show electron-dense precipitates and continuity with the plasma membrane. These morphological alterations do not occur in the presence of externally-added endochitinase. We also noticed modifications of the culture medium that are probably related to the morphological observations: the total amount of secreted proteins is reduced and pulse-chase experiments revealed that, compared with wild-type cells, the secretion of major polypeptides is reduced while new minor polypeptides are secreted. Western blot analysis revealed the presence of the binding protein BiP, a resident of the ER and of glutamine synthase, a cytosolic protein, in the medium of ts11 but not wild-type cells. These results indicate that ts11 is altered in the secretory pathway but do not clarify the role of endochitinase.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0263-6484
    Keywords: Priming ; desensitization ; chemotaxis ; superoxide anion ; neutrophil modulation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The kinetics and dose-dependence of activation of human neutrophils exposed to sequential additions of the chemotactic peptide n-formyl-methionyl-leucyl-phenylalanine (fMLP) have been investigated by multiwell microplate assays. Treatment of neutrophils with medium-high doses (from 10-8 to 5 × 10-7 M) of fMLP caused activation of superoxide anion (O2-) production, but prevented further activation by a subsequent addition of an optimal dose (from 10-7 M to 5 × 10-7 M) of fMLP. These findings represent an example of cell desensitization, or adaptation. However, neutrophils treated with low, sub-stimulatory doses (from 10-10 to 5 × 10-9 M) of the peptide and then treated with optimal doses of fMLP exhibited an O2- production that was two to three-fold higher than that induced by the same optimal doses on untreated cells. A similar phenomenon of homologous priming of the oxidative metabolism of neutrophil has not previously been described or characterized. Priming was maximal after about 30 min of incubation with fMLP, which differed from desensitization, which required only a few minutes. Homologous priming was not confined to O2- production, but was also observed with the release of the granule enzyme, lysozyme. Low doses of fMLP were also capable of triggering an increase of intracellular free Ca2+ and of fMLP membrane receptors, which are possible mechanisms responsible for priming.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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