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  • 1
    Electronic Resource
    Electronic Resource
    Influence of long-term conservation tillage on soil and rhizosphere microorganisms (1999)
    Springer
    Biology and fertility of soils 29 (1999), S. 81-86 
    Details
    ISSN: 1432-0789
    Keywords: Key words Soil tillage ; Rhizosphere microorganisms ; Cereals ; Nitrogen fixation ; Gaeumanomyces graminis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  In long-term field experiments on sandy loam and loamy sand soils, the influence of conservation and conventional tillage on soil and rhizosphere microorganisms was studied. Conservation tillage stimulated rhizosphere bacteria on winter wheat, winter barley, winter rye and maize in different soil layers. Particularly the populations of Agrobacterium spp. and Pseudomonas spp. were increased. On the sandy loam, N2 fixation and nodulation of pea plants were significantly increased. No influence of different soil tillage was determined on the colonization of the rhizosphere by mycorrhiza and saprophytic fungi. Stubble residues infected with Gaeumanomyces graminis were infectious for a longer time on the soil surface than after incorporation into the soil.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003740050528
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  • 2
    Electronic Resource
    Electronic Resource
    Quantitative evaluation of DNA binding data for risk estimation and for classification of direct and indirect carcinogens (1986)
    Springer
    Journal of cancer research and clinical oncology 112 (1986), S. 85-91 
    Details
    ISSN: 1432-1335
    Keywords: Chemical carcinogenesis ; Mechanism of action ; Quantitative risk assessment ; Genotoxicity ; Dose-response relationship ; Aflatoxin B1 ; Formaldehyde ; Vinyl chloride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Investigation of covalent DNA binding in vivo provided evidence for whether a test substance can be activated to metabolites able to reach and react with DNA in an intact organism. For a comparison of DNA binding potencies of various compounds tested under different conditions, a normalization of the DNA lesion with respect to the dose is useful. A covalent binding index, CBI=(μmol chemical bound per mol DNA nucleotide)/(mmol chemical administered per kg body weight) can be determined for each compound. Whether covalent DNA binding results in tumor formation is dependent upon additional factors specific to the cell type. Thus far, all compounds which bind covalently to liver DNA in vivo have also proven to be carcinogenic in a long-term study, although the liver was not necessarily the target organ for tumor growth. With appropriate techniques, DNA binding can be determined in a dose range which may be many orders of magnitude below the dose levels required for significant tumor induction in a long-term bioassay. Rat liver DNA binding was proportional to the dose of aflatoxin B1 after oral administration of a dose between 100 μg/kg and 1 ng/kg. The lowest dose was in the range of general human daily exposures. Demonstration of a lack of liver DNA binding (CBI〈0.1) in vivo for a carcinogenic, nonmutagenic compound is a strong indication for an indirect mechanism of carcinogenic action. Carcinogens of this class do not directly produce a change in gene structure or function but disturb a critical biochemical control mechanism, such as protection from oxygen radicals, control of cell division, etc. Ultimately, genetic changes are produced indirectly or accumulate from endogenous genotoxic agents. The question of why compounds which act via indirect mechanisms are more likely to exhibit a nonlinear range in the dose-response curve as opposed to the directly genotoxic agents or processes is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00404387
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    Paper (German National Licenses)
    Fulltext
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