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  • Electronic Resource  (5)
  • 1995-1999  (5)
  • Genetic variation  (3)
  • Polymer and Materials Science  (2)
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  • Electronic Resource  (5)
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Year
  • 1
    ISSN: 1432-2242
    Keywords: Pinus ; Allozymes ; Chloroplast DNA ; Genetic variation ; Evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We studied allozyme and chloroplast (cp) DNA variation in natural populations of Pinus kesiya and P. merkusii from Thailand and Vietnam. The results showed striking differences between the two species in the amount and distribution of allozyme variation. P. kesiya harboured considerable allozyme variation and showed weak interpopulational differentiation. In contrast, P. merkmii had very low intrapopulational variability but a high level of interpopulational differentiation. The average Nei's genetic distance separating the two species was exceptionally high (0.701) taking into account their close taxonomic placement in the same subsection Sylvestres. The constructed phylogenetic trees revealed very early divergence of P. kesiya and P. merkusii. The present analysis of cpDNA variation also confirmed the dissimilar character of these two species and was compatible with other evidence indicating the outstanding position of P. merkusii as compared to other Asian members of the subsection Sylvestres. Analysis of cpDNA variation in sympatric populations of P. kesiya and P. merkusii revealed that they are pure representatives of the species in question. This result indicates that despite an overlapping distribution P. kesiya and P. merkusii do not hybridise in nature. We suggest that the distinctive character of P. merkusii is a result of an early separation from other Eurasian pines. Despite spatial proximity, P. kesiya and P. merkusii are kept apart by strong reproductive barriers. The low genetic variability of P. merkusii may be explained by previous bottlenecks, reduced gene flow among populations, and an inbreeding due to small population size and asynchronous flowering.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2242
    Keywords: Key words  Pinus ; Allozymes ; Chloroplast DNA ; Genetic variation ; Evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract   We studied allozyme and chloroplast (cp) DNA variation in natural populations of Pinus kesiya and P. merkusii from Thailand and Vietnam. The results showed striking differences between the two species in the amount and distribution of allozyme variation. P. kesiya harboured considerable allozyme variation and showed weak interpopulational differentiation. In contrast, P. merkusii had very low intrapopulational variability but a high level of interpopulational differentiation. The average Nei's genetic distance separating the two species was exceptionally high (0.701) taking into account their close taxonomic placement in the same subsection Sylvestres. The constructed phylogenetic trees revealed very early divergence of P. kesiya and P. merkusii. The present analysis of cpDNA variation also confirmed the dissimilar character of these two species and was compatible with other evidence indicating the outstanding position of P. merkusii as compared to other Asian members of the subsection Sylvestres. Analysis of cpDNA variation in sympatric populations of P. kesiya and P. merkusii revealed that they are pure representatives of the species in question. This result indicates that despite an overlapping distribution P. kesiya and P. merkusii do not hybridise in nature. We suggest that the distinctive character of P. merkusii is a result of an early separation from other Eurasian pines. Despite spatial proximity, P. kesiya and P. merkusii are kept apart by strong reproductive barriers. The low genetic variability of P. merkusii may be explained by previous bottlenecks, reduced gene flow among populations, and an inbreeding due to small population size and asynchronous flowering.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Plant ecology 123 (1996), S. 65-71 
    ISSN: 1573-5052
    Keywords: Ecotype ; Genetic variation ; Plant population ; Reciprocal transplant ; Salt tolerance ; Wild barley
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Tillers and seedlings ofHordeum jubatum L. from three sites with contrasting salinity regimes in central Saskatchewan, Canada were reciprocally transplanted in order to examine the tolerance of populations of this species to salinity and related habitat factors. Survival, growth and fecundity of the three populations were controlled more by transplant site characteristics than by genetic differences, i.e. differences among populations at a site tended to be smaller than differences among sites. Survival, growth and reproduction of all three populations were best at the non-saline site. The population originating at the non-saline site showed the poorest growth in the two saline habitats, but still had substantial salt tolerance. Fecundity was greatest when the populations were grow at their site of origin.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 36 (1997), S. 516-521 
    ISSN: 0021-9304
    Keywords: porous-coated ; titanium ; PLA-PGA ; protein release ; degradation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Tissue ingrowth into porous-coated orthopedic and dental implants is commonly used as a means to achieve long-term fixation of these prostheses. However, the degree of tissue ingrowth is often inadequate and inconsistent. If the pores of these implants are impregnated with a controlled drug release system delivering relevant growth factors, then it might be possible to stimulate more tissue ingrowth. The present study introduces such a system based on biodegradable polymers and investigates its protein release profile and polymer degradation characteristics. Porous coated titanium implants were impregnated with a mixture of a 50%-50% polylactic acid-polyglycolic acid copolymer and a model protein, soybean trypsin inhibitor. Control implants contained only the polymer and no protein. The implants were subjected to hydrolytic degradation in phosphate buffered saline at 37°C for periods of 3, 6, and 11 weeks. The protein release and the mass and molecular weight of the polymer were monitored. The results indicate that the protein is released in three distinct phases and the polymer loses almost all its mass and molecular weight by 11 weeks. There was a significant difference in the polymer degradation characteristics between the control and test implants, which might be the result of some complex polymer-protein interactions. © 1997 John Wiley & Sons, Inc. J Biomed Mater Res, 36, 516-521, 1997.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1040-0397
    Keywords: XPS analysis ; Fluoride ; Ion selective electrode ; Surface analysis ; Hydroxide interference ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Lanthanum fluoride and cerium fluoride single crystals, used as the sensing membranes of the fluoride ion-selective electrode (F-ISE), were investigated for their hydroxide interference and surface reactions with OH- in high pH conditions. While these membranes show fast response and excellent Nernstian behavior over a wide concertration range in buffered F- solutions, they deviate from the theoretical slope at high pH. CeF3, in particular, exhibits a much larger deviation from the Nernstian slope and a substantially slower response to a F- activity change compared to LaF3. This larger deviation is due to more extensive and faster formation of hydroxo-complexes, with the release of a greater amount of the fluoride ion into the hydrated gel layer. The slower response of the CeF3 membrane after contact with OH- is due to the formation of CeIV oxide on the surface, which acts as a blocking layer to the exchange of F-.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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