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  • dormancy  (2)
  • 25.40.-h  (1)
  • Chemoreceptor  (1)
  • Seed coat structure  (1)
  • Chemistry
  • Springer  (4)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 183 (1998), S. 361-366 
    ISSN: 1432-1351
    Keywords: Key wordsParamecium ; Chemoattractant ; Biotin ; Chemoreceptor ; Chemokinesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Paramecium tetraurelia locate their␣foodsource by detecting bacterial metabolites and altering swimming behavior to congregate near bacterial populations on which they feed. Several attractants, such as folate, glutamate, cAMP and acetate have been identified and various aspects of chemoreception, signal transduction and effector mechanisms have been described. Here we characterize the Paramecium chemoresponse to biotin. An essential enzymatic cofactor in all cells, biotin is secreted by a large number of bacterial species during growth phase. P. tetraurelia are strongly attracted to biotin with a half-maximal behavioral response at 0.3 mmol · 1−1 in T-maze assays. Physiological recordings from whole cells show that cells hyperpolarize in a concentration-dependent manner in biotin. Whole-cell binding assays utilizing 3H-biotin identify a saturable and specific binding site with an apparent dissociation constant of 0.4 mmol · l−1. The biotin analogs desthiobiotin and biotin methyl ester are also strong attractants. Diaminobiotin fails to attract P. tetraurelia at 1 mmol · l−1, but does interfere with the biotin chemoresponse and displaces 3H-biotin from whole cells. We hypothesize that the keto group and/or fidelity of the ureido ring of biotin are necessary for biotin chemoresponse.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Plant growth regulation 11 (1992), S. 201-209 
    ISSN: 1573-5087
    Keywords: Seed coat structure ; dormancy ; permeability ; Dichrostachys cinerea ; natural dormancy-breaking factors ; inhibitors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract An understanding of dormancy mechanisms is of ecological and economic importance. Identification of the level at which dormancy is imposed appears to be species specific. The variation brought about by this therefore requires that developmental studies be included in seed coat dormancy experiments. In most cases, a site of permeability can be identified during the developmental process, and this information can be utilized later to remove dormancy. Under natural conditions, the removal of seed coat dormancy requires the interaction of a number of ecological and physiological dormancy-breaking cues.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1434-601X
    Keywords: 25.40.-h ; 25.30.+ S ; 13.85.-t
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have investigated kinematical correlations between the outgoing beam proton and the proton emerging from the fragmentingα-particle inpα collisions at $$\sqrt {s_{p\alpha } } = 88GeV$$ . Strong correlations are seen, indicating the dominance of quasi-elasticpp scattering in the fragmentation channelp+α→p+pX, for the ¦t¦ range 0.05–1.00 (GeV/c)2. A Monte Carlo simulation of this process can explain the observed correlation spectra assuming an admixture of about 16% spectator protons.
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  • 4
    ISSN: 1573-5087
    Keywords: bush encroachment ; Dichrostachys cinerea ; dormancy ; germination ; impermeability ; natural factors ; seed
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstracts Dichrostachys cinerea seeds are impermeable to water and do not germinate readily. The plant, however, contributes to a bush encroachment problem, minimising visibility in wildlife reserves and reducing the area available for grazing. Natural dormancy-breaking conditions must therefore exist, promoting the germinability of these normally dormant seeds. Diurnal temperature fluctuations (50°C/15°C), especially when combined with moisture were found to break dormancy. High temperatures, such as those generated by fire, destroyed seeds. Seeds ingested by herbivorous browsers such as nyala, became permeable. Seed burial for 48 weeks, was a more effective treatment than storage in promoting permeability. Distribution of D. cinerea will therefore be restricted to areas in which these conditions or factors occur. Seeds germinated optimally at 30δC in the laboratory.
    Type of Medium: Electronic Resource
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