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  • Chemistry  (5)
  • Triticum aestivum  (2)
  • 1995-1999  (3)
  • 1975-1979  (2)
  • 1970-1974  (1)
  • 1965-1969
  • 1945-1949  (1)
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  • 1
    ISSN: 1573-1561
    Keywords: Aphid ; experience ; probing behavior ; sieve elements ; salivation ; cell punctures ; hydroxamic acids ; EPG ; Sitobion fragariae ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract We hypothesized that aphids after previous exposure to hydroxamic acids (Hx), a family of secondary plant compounds deleterious to aphids, are able to reduce their subsequent exposure to them. This hypothesis was tested by evaluating the time to produce salivation into a sieve element (SSE) by the aphid Sitobion fragariae on seedlings of two wheat cultivars of Triticum aestivum differing in their concentration of Hx. The total time to produce a first SSE was significantly longer in the high-Hx cultivar; however, the subsequent, second SSE (first SSE after interruption of probing) in this cultivar was significantly reduced, reaching the level observed in the low-Hx plants. Therefore, a strategy to reduce the exposure to secondary compounds was observed only in the second SSE in high-Hx plants. When the experimental plant was replaced by a new unattacked plant after the first SSE, aphids did not change the behavior described, thus excluding an aphid-induced plant susceptibility. The number of cell punctures and accumulated duration was not affected by previous exposure to Hx, either in low or high Hx cultivars. Total time and pathway time but not cell punctures, seem to be the variables affected by previous exposure to Hx.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1570-7458
    Keywords: sieve element ; salivation ; aphid ; plant resistance ; wheat ; Sitobion fragariae ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Extended sieve element salivation (E1 waveform in the electrical penetration graph) is a characteristic activity during early sieve element punctures, particularly in resistant plants. In order to explore a chemically-mediated mechanism of resistance associated with sieve element salivation, we compared the pattern of feeding behaviour of the aphid, Sitobion fragariae (Walker), on two cultivars of the wheat Triticum aestivum L., with different concentrations of hydroxamic acids (Hx). During 24 h of electronic monitoring, aphids dedicated over 50% of the total time to phloem ingestion from the sieve elements. Total time allocated to E1 in the experiment, time to first E1 within the experiment, time allocated to E1 before a sustained phloem ingestion (E2) and the contribution of sieve element salivation to the phloem phase (E1/[E1+E2]) were significantly higher in the high-Hx cultivar. The increased salivation in plants with higher contents of Hx suggests the existence, at least in this system, of a chemically-mediated sieve element constraint.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 59 (1976), S. 1133-1139 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: CNDO/Z, MINDO/3 and ab initio molecular orbital calculations indicate that C-protonated diazomethane is more stable than N(end)-protonated diazomethane. Extrapolation of these results to solution chemistry as well as the kinetic references of protonation of diazomethane are discussed.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 405 (1974), S. 315-328 
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Catalysis of p-H2 Conversation on Pure and CO-poisoned PlatinumThe reaction has been studied on a Pt foil using u. h. v. cleaning conditions. The rate of the conversion is extremely high on a clean Pt surface, the activation energy being 4.1 kcal/mole. CO/poisons reversibly. After preadsorption of CO on half of the Pt surface the activity descreases to 6% of the original value and the activation energy increases p to 8.4 kcal/mole. In the discussion a direct correlation between the activation energy and the lowest adsorption heats of hydrogen is proposed. The reaction occurs predominantly on centres with lowest bond strength.
    Notes: Die Reaktion wurde an einer Pt-Folie unter UHV-Reinheitsbedingungen untersucht. An reiner Pt-Oberfläche verläuft die Reaktion extrem schnell mit einer Aktivierungsenergie von 4,1 kcal/Mol. CO vergiftet reversibel. Bei Vorbelegung der halben Pt-Oberfläche mit CO fällt die Aktivität auf 6% des Ausgangswertes während die Aktivierungsenergie auf 8,4 kcal/Mol ansteigt. Diskutiert wird ein direkter Zusammenhang der Aktivierungsenergie mit den minimalen Adsorptionswärmen des Wasserstoffs. Die Umwandlung erfolgt bevorzugt an Zentren mit geringster Bindungsfestigkeit.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 60 (1977), S. 1487-1495 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: CNDO/2, MINDO/3 and ab initio molecular orbital calculations are used in a study of conformational isomerism, protonation site and mechanism of protonation of the title compounds.
    Additional Material: 5 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 33 (1999), S. 380-380 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 60 (1948), S. 100-108 
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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