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  • 1980-1984  (1)
  • 1975-1979  (1)
Materialart
Erscheinungszeitraum
Jahr
  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Planta 146 (1979), S. 237-241 
    ISSN: 1432-2048
    Schlagwort(e): Asparagine ; Cyanide pathway ; Root (asparagine synthesis) ; Zea
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract An asparagine synthetase which is active with either glutamine or NH 4 + has been found in maize (Zea mays L.) roots. Unlike the enzyme obtained from legume cotyledons, the maize-root enzyme is only slightly more efficient with glutamine (Km, 1.0 mM) than with NH 4 + (Km, 2.0–3.0 mM). The activity of this enzyme is higher in the mature root than in the root-tip region, i.e. root cells develop a capacity to make asparagine from glutamine or NH 4 + as they mature. β-Cyanoalanine synthetase is also present in maize roots. The apparent Km for cysteine is 2.6 mM and for cyanide is 0.57 mM. The enzyme is more active in the root tip than in mature root tissue. Thus, if asparagine were made in the root tip, the cyanide pathway could represent the mechanism of synthesis. It is our contention, however, that this potential is not realized under normal conditions because 14C-experiments performed previously have indicated a limited availability of both CN and cysteine in the maize root.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Planta 151 (1981), S. 457-461 
    ISSN: 1432-2048
    Schlagwort(e): Nitrogen assimilation enzymes ; Organelles, enzyme distribution ; Root
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The cellular distribution of enzymes involved in nitrogen assimilation: nitrate reductase (EC 1.6.6.2), nitrite reductase (EC 1.6.6.4), glutamine synthetase (EC 6.3.1.2), glutamate synthase (EC 2.6.1.53), and glutamate dehydrogenase (EC 1.4.1.3) has been studied in the roots of five plants: maize (Zea mays L. hybrid W 64A x W 182E), rice (Oryza sativa L. cv. Delta), bean (Phaseolus vulgaris L. cv. Contender), pea (Pisum sativum L. cv. Demi-nain), and barley (Hordeum vulgare L.). Initially, cell organelles were separated from soluble proteins by differential centrifugation. Cell organelles were also subjected to sucrose density gradients. The results obtained by these two methods indicate that nitrite reductase and glutamate synthase are localized in plastids, nitrate reductase and glutamine synthetase are present in the cytosol, and glutamate dehydrogenase is a mitochondrial enzyme.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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