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  • Ephemeral plants  (1)
  • Nitrogen fixation mutants  (1)
  • Oligonychus gossypii  (1)
  • 1995-1999  (3)
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  • 1995-1999  (3)
Year
  • 1
    Electronic Resource
    Electronic Resource
    Comparison of biological and demographic parameters forMononychellus progresivus andOligonychus gossypii on cassava: influence of temperature (1995)
    Springer
    Entomologia experimentalis et applicata 75 (1995), S. 119-125 
    Details
    ISSN: 1570-7458
    Keywords: Acaru ; Tetranychidae ; Mononychellus progresivus ; Oligonychus gossypii ; biological ; demographic parameters ; cassava
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effect of five constant temperatures (16, 22, 26, 31 and 36°C) on biological (survival and duration of developmental stages, fecundity and longevity of females, sex-ratio) and demographic parameters (R o , G, r m and λ) of the two main phytophagous mites that attack cassava in Africa,Mononychellus progresivus Doreste andOligonychus gossypii (Zacher), was studied in the laboratory. Experiments were performed simultaneously on the two mite species reared on the same cassava variety (1M20) under controlled conditions: 70±10% r.h. and 12L∶12D. The lower thermal threshold was 13°C forM. progresivus and 11°C forO. gossypii. Both species developed in the range from 22 to 36°C. The shortest development time was obtained at 31°C for both species; it was 7.2 days forM. progresivus and 8.2 days forO. gossypii. Maximum fecundity of both species was recorded at 26°C with 42.1 eggs forM. progresivus and 36.3 eggs forO. gossypii The highest intrinsic rate of increase (r m ) was obtained at 31°C for both species with 0.289 and 0.214 forM. progresivus andO. gossypii, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02382170
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of small mammals and vertebrate predators on vegetation in the Chilean semiarid zone (1997)
    Springer
    Oecologia 109 (1997), S. 398-406 
    Details
    ISSN: 1432-1939
    Keywords: Key words Herbivory ; Predation ; Tritrophic effects ; Ephemeral plants ; Chilean semiarid zone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  We monitored the cover and seed bank response of shrubs, perennial herbs, and ephemeral plants to experimental exclusion of both the principal rodent herbivore, Octodon degus, and its vertebrate predators from 1989 to 1994 in a semiarid Chilean mediterranean site. Although both richness and species composition of the plant community at the study site were largely determined by abiotic factors (mainly rainfall and soil nutrients), predator and herbivore exclusion had significant effects on the relative abundance of several plant species. Experimental exclusion of herbivores was associated with increased cover of some shrubs and a perennial grass, and decreased cover and seed densities of several ephemerals, especially those exotic or restricted to areas underneath shrubs. Herbivores apparently reduced shrubs through browsing and indirectly affected herb cover and seed densities by opening up areas under shrubs and/or modifying physical and chemical conditions of the soil. Plant responses to predator exclusion were less clear. Nevertheless, higher cover of some shrubs and ephemerals in the presence of predators suggests tritrophic effects through changes in small mammal densities and/or foraging behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050099
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  • 3
    Electronic Resource
    Electronic Resource
    Ammonium repression of the nitrite-nitrate (nasAB) assimilatory operon of Azotobacter vinelandii is enhanced in mutants expressing the nifO gene at high levels (1997)
    Springer
    Molecular genetics and genomics 255 (1997), S. 172-179 
    Details
    ISSN: 1617-4623
    Keywords: Key wordsnasAB ; Chlorate-resistant mutants ; nifO ; Nitrogen fixation mutants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A number of Tn5 mutants were isolated which were unable to fix nitrogen and showed enhanced ammonium repression of the nitrate/nitrite assimilation genes. They also had reduced nitrate reductase activity under fully inducing conditions. Insertions were localized within the nifB gene, and inability to fix nitrogen was shown to be due to disruption of the nifB gene. However, enhanced ammonium repression proved to be the result of constitutive expression of the downstream nifO gene from an `out' promoter present in Tn5. Our results suggest that molybdenum metabolism might function as a regulatory factor that acts through the nitrate reductase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004380050486
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