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  • 1990-1994  (2)
  • Aphididae  (1)
  • Human plasma  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Chromium (VI) reducing capacity of ascorbic acid and of human plasma in vitro (1992)
    Springer
    Archives of toxicology 66 (1992), S. 45-50 
    Details
    ISSN: 1432-0738
    Keywords: Chromium(VI) ; Ascorbic acid ; Human plasma ; Reduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In the metabolism of chromium(VI) its reduction in human plasma is of importance; an extracellular reduction of Cr(VI) is regarded as a detoxification step. Ascorbic acid has been suggested to represent the majority of the Cr(VI)-reducing capacity of human plasma. Therefore the kinetics of the reaction of Cr(VI) with ascorbic acid, at biologically realistic concentrations were studied. Ascorbic acid, in 0.2 M HEPES buffer and at concentrations ranging from 14.2 to 113.6 nmol ml−1 (2.5–20.0 μg ml−1), was mixed with Cr(VI) (0.4–1.5 nmol ml−1) and incubated at pH 7.4 and 37° C. In addition, chromate solutions at different concentrations [1.5–100 nmol ml−1 Cr(VI)], were incubated at 37° C with freshly drawn blood. From these incubates, ascorbic acid and its oxidized form, dehydroascorbic acid, were simultaneously analyzed by HPLC and post-column derivatization. Chromate was determined by flow injection analysis. The reaction kinetics of ascorbic acid in HEPES buffer with Cr(VI) is of pseudofirst order at higher concentrations, whilst apparently at lower concentrations kinetics are consistent with an autocatalyzed reaction. Results obtained after spiking human plasma are similar. However, when Cr(VI) was reacted with human plasma, no changes in the intrinsic contents of ascorbic acid of the plasma samples occurred. Also, comparing different plasma samples the intrinsic plasma contents of ascorbic acid and the reduction capacities for Cr(VI) [ranging between 0.48 and 0.63 nmol ml−1 Cr(VI) to be reduced] did not correlate. This shows that the reduction of Cr(VI) in native human plasma is complex and is not only determined by the plasma ascorbic acid levels. This is in contrast to the situation in lung lavage fluids (Suzuki 1988; Suzuki and Fukuda 1990) where the concentrations of ascorbic acid are much higher than in blood.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02307269
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of DIMBOA, an aphid resistance factor in wheat, on the aphid predatorEriopis connexa Germar (Coleoptera: Coccinellidae) (1992)
    Springer
    Journal of chemical ecology 18 (1992), S. 469-479 
    Details
    ISSN: 1573-1561
    Keywords: Wheat ; hydroxamic acids ; DIMBOA ; plant resistance ; cereal aphids ; Homoptera ; Aphididae ; aphid predators ; Eriopis connexa ; Coleoptera ; Coccinellidae ; tritrophic interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one), a secondary metabolite found in cereal extracts, confers resistance in wheat to aphids. Its effect on beneficial organisms was tested on larvae of the aphid predatorEriopis connexa Germar. Larvae were fed until pupation on artificial diets to which different concentrations of DIMBOA (2–200μg/g diet) were added, as well as on aphids that had been feeding on wheat seedlings with different DIMBOA levels (140–440 μg/g fresh tissue). In diets, the effect of DIMBOA was greatest on survival of third-instar larvae and on the duration of the second and fourth instars. When aphids were provided as food, those that had fed on a wheat cultivar with an intermediate DIMBOA level led to a significantly longer larval duration in the predator than did those that fed on either low or high DIMBOA cultivars. Shortest predator development times were obtained with aphid prey that had fed on high DIMBOA seedlings. Higher DIMBOA levels in the plant appear to reduce aphid feeding rates (and rates of DIMBOA ingestion), decreasing aphid survival and minimizing the effect of the toxin on the predator.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00994245
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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