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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 351 (1995), S. 345-351 
    ISSN: 1434-601X
    Keywords: 12.38.-t ; 12.38.Lg ; 14.65.-q
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The concept of QCD sum rules is extended to bound states composed of particles with finite mass such as scalar quarks or strange quarks. It turns out that mass corrections become important in this context. The number of relevant corrections is analyzed in a systematic discussion of the IR- and UV-divergencies, leading in general to a finite number of corrections. The results are demonstrated for a system of two massless quarks and two heavy scalar quarks.
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  • 2
    ISSN: 1573-5060
    Keywords: aphids ; cereal breeding ; DIBOA ; Diuraphis noxia ; hydroxamic acids ; pest resistance ; Poaceae ; Schizaphis graminum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Hydroxamic acids are secondary metabolites typical of Poaceae that play a role in cereal resistance against pests and pathogens. The content of the hydroxamic acid aglucones DIBOA (2,4-dihydroxy-1,4-benzoxazin-3-one) and DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one) was evaluated in wild Poaceae belonging to the tribes Triticeae (genera Hordeum and Elymus) and Aveneae (genera Deschampsia and Phalaris). The concentration of DIBOA in seedling extracts of the wild barleys Hordeum chilense, H. brevisubulatum subsp. violaceum and H. bulbosum was negatively correlated with parameters related to performance of the cereal aphids Schizaphis graminum and Diuraphis noxia. The relevance of the results obtained for breeding programs aimed at increasing cereal resistance against aphids is discussed.
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  • 3
    ISSN: 1573-5060
    Keywords: Oxalis tuberosa ; oca ; reproductive biology ; breeding system ; tristyly ; genetic resources
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Seven clonal accessions representing all three stylar morphs of tristylous oca were intercrossed and selfed in a complete diallelic crossing design. The four traits total capsule production, total number of seeds/capsule, total number of seeds containing an embryo/capsule, and percent seeds containing an embryo of all seeds per capsule were recorded. Both capsule and seed production were highest in the legitimate pollinations (in which styles are pollinated with pollen of the corresponding anther level), but also in illegitimate pollinations of mid-styled seed parents with long-level anther pollen of short-styled accessions. All 18 types of pollination, consisting of 6 legitimate, 6 illegitimate intermorph, and 6 illegitimate intramorph pollinations, expressed gradually different levels of capsule and seed production. Intramorph pollinations and selfs of mid-styled seed parents were less incompatible than intramorph pollinations and selfs of the long- and short-styled morphs. All accessions studied expressed an intact system of heteromorphic stylar incompatibility despite their exclusive clonal propagation for millennia. A maximum of 16,3 seeds/capsule containing an embryo was obtained in an individual legitimate cross of two accessions, although an average of 25 ovules are present in a flower of O. tuberosa. The results are discussed in relation to the establishment of a genebank based on botanical seed of this clonally propagated, valuable Andean tuber crop.
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  • 4
    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.
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  • 5
    ISSN: 1573-1561
    Keywords: Defense ; herbivory ; aphids ; wheat ; Gramineae ; hydroxamic acids ; Defense theory ; Carbon/Nutrient theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Hydroxamic acids (Hx) are natural products of Gramineae that are associated with cereal resistance to pests. We aimed at characterizing the induction of Hx accumulation in seedlings of wheat,Triticum aestivum, by short-term infestation of the cereal aphid,Rhopalosiphum padi. A load of 25 aphids increased significantly the Hx levels in the infested primary leaf in comparison with control levels. Lower loads did not increase Hx concentration. Aphid infestation lasting 16 hr did not elicit induction of Hx, even after a time-lag of 32 hr to allow the expression of any induced response. Forty-eight hours was the minimum duration of aphid infestation required to trigger Hx induction. The age of the infested tissue (the primary leaf) did not affect induction. Similar increases of Hx were found in unfolding, expanding, and totally expanded primary leaves. It was determined that the regime of nutrient supply (N-intensive nutritive solutions at low and high concentration) to wheat seedlings had no effect on the magnitude of the aphid-induced Hx (N-based secondary metabolites). Results obtained are discussed in the framework of general theories of plant defense allocation.
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  • 6
    ISSN: 1573-1561
    Keywords: Defoliation ; regrowth ; induced responses ; chemical defense ; hydroxamic acids ; rye ; Secale cereale ; Poaceae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The effect of defoliation and consecutive defoliation (condefoliation) of rye seedlings on the allocation patterns of biomass and hydroxamic acids (Hx) was evaluated five days after treatment. Growth of condefoliated seedlings was lower than that of defoliated and nondefoliated ones. Concentration of Hx decreased in shoots of condefoliated seedlings compared to nondefoliated ones, while concentration of Hx in root exudates increased. Allocation of Hx to roots and root exudates increased at the expense of allocation to the shoots in condefoliated seedlings. The ratio of Hx-aglucone to Hx-glucoside was higher in shoots of defoliated and condefoliated seedlings. The decrease in quantity of defense in shoots was accompanied by an increase in its quality, given that aglucones are more toxic than glucosides. The increase in concentration of Hx—an allelopathic compound also involved in mineral uptake by roots—in root exudates of condefoliated seedlings was suggested to lead to an advantage in the acquisition of resources for the regeneration of lost biomass.
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  • 7
    ISSN: 1573-1561
    Keywords: Nothofagus ; Neuquenaphis ; volatiles ; olfactometry ; α-agarofuran
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Extractable metabolites from leaves (EM) and volatiles released from six Nothofagus species were analyzed by TLC and GC-MS, respectively. Aphids of the genus Neuquenaphis, closely associated to Nothofagus, were sampled on each Nathofagus species. Cluster analyses of Nothofagus species were performed based on the presence or absence of EM and volatiles. Dissimilarity distances, from the cluster analyses of EM and volatiles, were used to evaluate their association with the aphid distribution. A major component identified from EM and volatiles of three species of Nothofagus, α-agarofuran, was attractive to alates of the oligophagous Neuquenaphis sensoriata, which use them as hosts. These results suggest that chemicals play a significant role in the host-plant associations between Neuquenaphis and Nothofagus.
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  • 8
    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.
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  • 9
    ISSN: 1573-1561
    Keywords: Temperature ; photoperiod ; hydroxamic acids ; growth ; defense ; secondary metabolites ; wheat ; Gramineae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The effects of temperature and photoperiod on accumulation of hydroxamic acids (Hx) in wheat (Triticum aestivum L.) seedlings were evaluated under laboratory conditions. Hx concentrations were significantly higher at higher temperatures. No such clear trend was found for the photoperiod effect. The significant effect of temperature and photoperiod on growth rate of seedlings and the significant positive correlation between growth rate prior to analysis and levels of Hx, suggested that environmental effects on Hx accumulation were at least partially mediated through their effect on plant growth rate. After uncoupling the effect of environmental conditions from the effect of plant growth rate by statistical means the effect of temperature on Hx was no longer significant. Therefore, temperature effect was fully mediated by plant growth rate. Implications of the patterns found are discussed in issues of plant-defense general theories.
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  • 10
    ISSN: 1573-1561
    Keywords: Aphids ; Sitobion avenae ; feeding deterrents ; antibiotics ; DIMBOA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract A total of 25 compounds including benzoxazinones, benzoxazolinones, and N-glyoxylamide derivatives were tested as antifeedants and antibiotics towards the aphid Sitobion avenae in diet bioassays. The antifeedant and mortality indexes increased with the presence of electron-donating groups in the 7 position of the benzoxazinone moiety, the replacement of the oxygen atom by sulfur in the heterocyclic ring, the presence of a hemiacetal instead of an acetal at C-2 of the benzoxazine moiety (and hence the possibility of ring opening), and the presence of a hydroxyl group at C-4 of the benzoxazine moiety (hydroxamic acid) instead of a hydrogen atom (lactam). The results support earlier hypotheses on the chemical bases for the mode of action of these compounds.
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