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  • Embryogenesis  (2)
  • Azadirachta indica  (1)
  • 1995-1999  (3)
  • 1955-1959
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  • 1
    Digitale Medien
    Digitale Medien
    Significance of preprophase bands of microtubules in the induction of microspore embryogenesis of Brassica napus (1999)
    Springer
    Planta 208 (1999), S. 383-391 
    Details
    ISSN: 1432-2048
    Schlagwort(e): Key words: Brassica (microspore embryogenesis) ; Cell wall ; Embryogenesis ; Microspore (division symmetry) ; Microtubule ; Preprophase band
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract. Microspores of Brassica napus L. cv. Topas, undergo embryogenesis when cultured at 32.5 °C for the first 18–24 h and then at 25 °C. The first division in heat-treated microspores is a symmetric division in contrast to the asymmetric division found after the first pollen mitosis in-planta or in microspores cultured continuously at 25 °C. This asymmetric division is unique in higher plants as it results in daughter cells separated by a non-consolidated wall. The cytoskeleton has an important role in such morphological changes. We examined microtubule (MT) organization during the first 24 h of heat induction in the embryogenic B. napus cv. Topas and the non-embryogenic B. napus breeding line 0025. Preprophase bands (PPBs) of MTs appeared in cv. Topas microspores in late uninucleate microspores and in prophase figures after 4–8 h of heat treatment. However, more than 60% of the PPBs were not continuous bands. In contrast, PPBs were never observed in pollen mitosis; MT strands radiated from the surface of the nuclear envelope throughout microspore maturation to the end of prophase of pollen mitosis I, during in-planta development and in microspores cultured at 25 °C. Following 24 h of heat treatment, over 95% of the microspores appeared to have divided symmetrically as indicated by the similar size of the daughter nuclei, but only 7–16% of the microspores eventually formed embryos. Discontinuous walls were observed in more than 50% of the divisions and it is probable that the discontinuous PPBs gave rise to such wall abnormalities which may then obstruct embryo development. Preprophase bands were not formed in heat-treated microspores of the non-embryogenic line 0025 and the ensuing divisions showed discontinuous walls. It is concluded that the appearance of PPBs in heat-induced microspores marks sporophytic development and that continuous PPBs are required for cell wall consolidation and embryogenesis. It follows that induced structures with two equally condensed nuclei, do not necessarily denote symmetric divisions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004250050573
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Cellular changes during heat shock induction and embryo development of cultured microspores ofBrassica napus cv. Topas (1995)
    Springer
    Protoplasma 185 (1995), S. 106-112 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Brassica napus ; Embryogenesis ; Heat shock ; Induction ; Microspore embryogenesis ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Brassica napus cv. Topas microspores, isolated and cultured near the time of the first pollen mitosis and subjected to a heat treatment of 24 h, can be induced to develop into haploid embryos. This is a study of microspore structure during induction and embryo determination. Early during the 32.5 °C incubation period the nucleus moved away from the edge of the cell, and granules, 30 to 60 nm in diameter, appeared in the mitochondria and as a cluster in the cytoplasm. Cells divided symmetrically and at the end of the heat treatment, acquired the features of induced bicellular structures described previously. The features persisted as the cells divided randomly within the exine for 4–7 days following heat induction. Multicellular structures released from the exine underwent periclinal divisions resulting in protoderm differentiation of the globular embryo, thus determining embryo development. The cytoplasm of early heart-stage embryos contains abundant polyribosomes. Non-embryogenic development was indicated by large accumulations of starch and/or lipid and thickened cell walls or an unorganized pattern of cell division following release of the multicellular structures from the exine. Embryogenesis is discussed in terms of induction, embryo determination and development.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01272758
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Photooxidation of Nimbin and Salannin, Tetranortriterpenoids from the Neem Tree (Azadirachta indica) (1997)
    Springer
    Journal of chemical ecology 23 (1997), S. 2841-2860 
    Details
    ISSN: 1573-1561
    Schlagwort(e): Azadirachtin ; nimbin ; salannin ; antifeedant ; growth inhibition ; Azadirachta indica ; Spodoptera littoralis ; Locusta migratoria ; Schistocerca gregaria ; photooxidation ; photoisomerization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract Nimbin and salannin, major triterpenoids accompanying azadirachtin in extracts of neem (Azadirachta indica) seeds, were photooxidized by UV light in the presence of oxygen to more polar, unstable intermediates that rearranged on silica gel to two final products in which the furan ring had been oxidized to isomeric hydroxybutenolides. The isomeric hydroxybutenolides were also readily formed when a crude extract of triterpenoids from neem seeds was irradiated, and both isomers of salannin have been isolated from seeds. Photooxidation of nimbin and salannin proceeded much faster than that of azadirachtin. All photoproducts showed some biological activity againstSpodoptera littoralis, Locusta migratoria, andSchistocerca gregaria. Isonimbinolide was as potent as azadirachtin at inhibiting feeding in all three species, and it also inhibited the growth ofS. littoralis. Isosalanninolide showed potent antifeedant and growth inhibitory activity againstS. littoralis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1022523329255
    Standort Signatur Erwartet Verfügbarkeit
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