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  • Geophysics  (2)
  • Life and Medical Sciences  (2)
  • Pisum (stem growth)  (2)
  • 1
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    Particle Size Distributions Obtained Through Unfolding 2D Sections: Towards Accurate Distributions of Nebular Solids in the Allende Meteorite (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Size distributions of nebular solids in chondrites suggest an efficient sorting of these early forming objects within the protoplanetary disk. The effect of this sorting has been documented by investigations of modal abundances of CAIs (e.g., [1-4]) and chondrules (e.g., [5-8]). Evidence for aerodynamic sorting in the disk is largely qualitative, and needs to be carefully assessed. It may be a way of concentrating these materials into planetesimal-mass clumps, perhaps 100 fs of ka after they formed. A key parameter is size/density distributions of particles (i.e., chondrules, CAIs, and metal grains), and in particular, whether the radius-density product (rxp) is a better metric for defining the distribution than r alone [9]. There is no consensus between r versus rxp based models. Here we report our initial tests and preliminary results, which when expanded will be used to test the accuracy of current dynamical disk models.
    Keywords: Geophysics
    Type: JSC-CN-25638 , 43rd Lunar aud Plauetary Science Conference; Mar 19, 2012 - Mar 23, 2012; The Woodlands, TX; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Mineralogy of the Almahata Sitta Ureilite (2009)
    In:  Other Sources
    Details
    Publication Date: 2019-07-19
    Description: Mineralogy & Petrography: Almahata Sitta, deriving from the asteroid 2008 TC3, is a coarse-grained- to porous, fine-grained, fragmental breccia with subrounded mineral fragments and olivine aggregates embedded in a cataclastic matrix of ureilitic material. Mineral fragments include polycrystalline olivine, low-calcium, pigeonite, and augite. Abundant carbonaceous aggregates containing graphite, microdiamonds and aliphatics. Kamacite, Cr-rich troilite, silica and schreibersite are abundant. The compositional range of the silicates is characteristic of the ureilites as a group, but unusually broad for an individual ureilite. The dense lithology is typical for ureilites, but the porous lithology is anomalous. In the porous lithology pore walls are largely coated by crystals of olivine. Classification: Almahata Sitta is an anomalous, polymict eucrite. Anomalous features include large compositional range of silicates, high abundance and large size of pores, crystalline pore wall linings, and fine-grained texture. Tomography reveals that the pores define thin, discontinuous "sheets" connected in three dimensions, suggesting that they outline grains that have been incompletely welded together. The crystals lining the pore walls are probably vapor phase deposits. Therefore Almahata Sitta may represent an agglomeration of coarse- to fine-grained, incompletely reduced pellets formed during impact, and subsequently welded together at high temperature.
    Keywords: Geophysics
    Type: JSC-CN-18802 , 41st Annual Meeting of the Division for Planetary Sciences of the American Astronomical Society; Oct 04, 2009 - Oct 09, 2009; Fajardo; Puerto Rico
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
    Electronic Resource
    Electronic Resource
    Indole-3-acetic acid levels after phytochrome-mediated changes in the stem elongation rate of dark- and light-grown Pisum seedlings (1992)
    Springer
    Planta 188 (1992), S. 85-92 
    Details
    ISSN: 1432-2048
    Keywords: Auxin and stem growth ; Epidermis and stem growth ; Pisum (stem growth) ; Phytochrome stem growth ; Stem elongation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effect of red (R) and far-red (FR) light on stem elongation and indole-3-acetic acid (IAA) levels was examined in dwarf and tall Pisum sativum L. seedlings. Red light reduced the extension-growth rate of etiolated seedlings by 70–90% after 3 h, and this inhibition was reversible by FR. Inhibition occurred throughout the growing zone. After 3 h of R, the level of extractable IAA in whole stem sections from the growing zone of etiolated plants either increased or showed no change. By contrast, extractable IAA from epidermal peels consistently decreased 3 h after R treatments. Decreases of 40% were observed for epidermal peels from the top 1 cm of tall plants receiving 3 h R. Brief R treatments resulted in smaller decreases in epidermal IAA levels and these decreases were not as great when FR followed R. In lightgrown plants, end-of-day FR stimulated growth during the following dark period in a photoreversible manner. The uppermost 1 cm of expanding third internodes was most responsive to the FR. Extractable IAA from epidermal peels from the upper 1 cm of third internodes increased by 30% or more 5 h after FR. When R followed the FR the increases were smaller. Levels of IAA in whole stem sections did not change and were twofold greater than in dark-grown plants. In both dark- and light-grown tall plants, IAA levels were lower in epidermal peels than in whole stem segments. These results provide evidence that IAA is compartmentalized at the tissue level within the growing stem and that phytochrome regulation of stem elongation rates may be partly based on modulating the level of IAA within the epidermis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00198943
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Indole-3-acetic acid levels after phytochrome-mediated changes in the stem elongation rate of dark- and light-grownPisum seedlings (1992)
    Springer
    Planta 188 (1992), S. 85-92 
    Details
    ISSN: 1432-2048
    Keywords: Auxin and stem growth ; Epidermis and stem growth ; Pisum (stem growth) ; Phytochrome stem growth ; Stem elongation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effect of red (R) and far-red (FR) light on stem elongation and indole-3-acetic acid (IAA) levels was examined in dwarf and tallPisum sativum L. seedlings. Red light reduced the extension-growth rate of etiolated seedlings by 70–90% after 3 h, and this inhibition was reversible by FR. Inhibition occurred throughout the growing zone. After 3 h of R, the level of extractable IAA in whole stem sections from the growing zone of etiolated plants either increased or showed no change. By contrast, extractable IAA from epidermal peels consistently decreased 3 h after R treatments. Decreases of 40% were observed for epidermal peels from the top 1 cm of tall plants receiving 3 h R. Brief R treatments resulted in smaller decreases in epidermal IAA levels and these decreases were not as great when FR followed R. In lightgrown plants, end-of-day FR stimulated growth during the following dark period in a photoreversible manner. The uppermost 1 cm of expanding third internodes was most responsive to the FR. Extractable IAA from epidermal peels from the upper 1 cm of third internodes increased by 30% or more 5 h after FR. When R followed the FR the increases were smaller. Levels of IAA in whole stem sections did not change and were twofold greater than in dark-grown plants. In both dark- and light-grown tall plants, IAA levels were lower in epidermal peels than in whole stem segments. These results provide evidence that IAA is compartmentalized at the tissue level within the growing stem and that phytochrome regulation of stem elongation rates may be partly based on modulating the level of IAA within the epidermis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01160716
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Genetische Ressourcen von Wildpflanzenarten beleben die Kulturpflanzenzüchtung (1998)
    Weinheim : Wiley-Blackwell
    Biologie in unserer Zeit 28 (1998), S. 371-380 
    Details
    ISSN: 0045-205X
    Keywords: Life and Medical Sciences
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Die Entwicklung der heute in der Landwirtschaft und im Gartenbau genutzten Kulturpflanzen ist eine der wichtigsten Leistungen in der Geschichte der Menschheit. Züchterische Maßlig;nahmen des Menschen haben zum Ziel, Pflanzen so zu verändern, daßlig; sie besser an seine Bedürfnisse angepaßlig;t sind. Die Eingriffe durch Züchtung nennt man „gelenkte Evolution“. Ausgehend von wild vorkommenden Arten hat der Mensch Nutzpflanzen geschaffen, die ohne seine Hilfe in der freien Natur auf Dauer nur geringe überlebenschancen hätten. Neben den Nutzpflanzen findet man in der Natur noch viele wilde Arten, die mit den Kulturpflanzen verwandt sind und sich häufig mit ihnen kreuzen lassen. Die wilden Arten verfügen über ein genetisches Potential, auf das in den letzten Jahren immer häufiger zurückgegriffen worden ist, um Zuchtziele des Menschen zu verwirklichen. Vor allem müssen ständig neue Resistenzen gegen Krankheiten und Schädlinge gefunden werden, um dem Infektionsdruck der Krankheitserreger zu widerstehen. Aber auch Gene für Toleranz gegenüber abiotischem Streßlig;, wie Kälte, Dürre, Salz oder Aluminiumtoxizität, sind in den Wildarten vorhanden. Sie können in die Kulturpflanzen eingekreuzt werden, um sie gegen diese Streßlig;faktoren widerstandsfähiger zu machen.Voraussetzung für den Gentransfer von einer Wildart in eine Kulturart ist ihre Kreuzbarkeit. Darüber hinaus mußlig; im Kreuzungsbastard crossing over zwischen homologen Chromosomen gewährleistet sein. Wenn die Chromosomen nicht zu natürlichem crossing over in der Lage sind, können genetische Paarungsmechanismen in der Meiose eingesetzt werden, die zu dem gewünschten Gentransfer führen.Im folgenden soll anhand von drei Beispielen die Bedeutung des genetischen Potentials wilder und verwandter Pflanzenarten für die Verbesserung der Krankheitsresistenz und Inhaltsstoffe sowie Toleranz gegen abiotischen Streßlig; bei Kulturpflanzen demonstriert werden.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/biuz.960280606
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  • 6
    Electronic Resource
    Electronic Resource
    Evolution und Züchtung des Saatweizens (Triticum aestivum L.) (1991)
    Weinheim : Wiley-Blackwell
    Biologie in unserer Zeit 21 (1991), S. 248-254 
    Details
    ISSN: 0045-205X
    Keywords: Life and Medical Sciences
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Seitdem der abendländische Mensch erkannt hatte, daß sich Getreidekörner, besonders die des Weizens, zur Mehl- und Brotherstellung eignen, ist er auf Gedeih und Verderb mit dieser Pflanzenart verbunden. Ohne den Einfluß des Menschen wären die Kulturformen von Weizen, Reis, Gerste, Hafer und Mais nicht denkbar. War er es doch, der entscheidend dazu beigetragen hat, daß sich im Laufe von Jahrtausenden unsere wichtigsten Getreidearten von ehemals spindelbrüchigen Gräsern, deren Samen nach der Reife auf den Boden fielen, Schrittweise zu zähspindeligen, nichtährenbrüchigen Hochleistungs-Nutzpflanzen umwandelten.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/biuz.19910210509
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