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排序方式: 共有79条查询结果,搜索用时 328 毫秒
71.
Ilina Krasteva Aleksandar Shkondrov Iliana Ionkova Petranka Zdraveva 《Phytochemistry Reviews》2016,15(4):567-590
The genus Astragalus L., Fabaceae (Leguminosae) is presented in Bulgarian flora by 31 species including local endemics, nine of them listed in the Red Data Book. The main biologically active compounds found in the Bulgarian Astragalus plants are saponins and flavonoids with a variety of effects: immunomodulatory, hepatoprotective, cytotoxic, antioxidant, antihypoxic and others. In the recent years volatiles with cytotoxic activity have also been determined. Saponins and flavonoids are still preferably produced by plants due to their complex structures. Variable quantities and qualities of the wild plant material, plants that need to grow several years before they are ready for harvesting and over-collecting of endangered Astragalus species are just a few of the problems connected with the production of these natural products. Therefore, cultured cells are possible alternative for production of high-value secondary metabolites. This review is focused on phytochemical, pharmacological and biotechnological studies of Bulgarian Astragalus plants and includes also results from our investigations. 相似文献
72.
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74.
James W. Petranka 《Evolutionary ecology》2007,21(6):751-764
Current evolutionary models for amphibian life cycles reflect tradeoffs in size-specific growth and mortality rates between
the aquatic and terrestrial stages. A limitation of these models is that they do not incorporate evolutionary phenomena that
are associated with metapopulation structure. In this work I address components of the evolution of complex life cycles (CLCs)
that are tied to the metapopulation dynamics of amphibians that use seasonal wetlands that vary in hydroperiod. In particular,
I describe how selection for the minimum length of the larval period affects metapopulation viability and the selection/migration
equilibrium. Selection to increase the minimum length of the larval period functionally reduces the number of viable breeding
sites on the landscape, increases the average distance between neighboring sites, and increases the risk of metapopulation
extinction. Within a metapopulation, asymmetric gene flow between populations that are adapted to different hydroperiods tends
to swamp local selection for long larval periods at sites with long hydroperiods. The evolutionary stability of CLCs of many
species with metapopulation structure may reflect the fact that extremely small metamorphs cannot survive on land, while lineages
with long larval periods incur a high risk of metapopulation extinction. I encourage theorists to more carefully consider
how life history traits and metapopulation viability are related for these and other taxa. 相似文献
75.
76.
On the origins of esterases 总被引:8,自引:0,他引:8
Comparisons among the primary sequences of five cloned eukaryotic esterases
reveal two distinct lineages, neither bearing any significant overall
sequence similarity to the functionally related serine protease multigene
family. We have not eliminated the possibility that the esterases may have
residual conformational similarities to the serine proteases. However, our
profile analysis and analyses of the predicted conformations of the
esterases reveal little similarity to the serine proteases. Four of the
esterase proteins share 27%-53% overall sequence similarity and evidence of
a catalytic mechanism involving the same Arg- Asp-Ser or His-Asp-Ser charge
relay. We propose that these four esterases, three of them cholinesterases,
form part of a multigene family essentially separate from the serine
proteases.
相似文献
77.
Wetland Restoration for Amphibians: Should Local Sites Be Designed to Support Metapopulations or Patchy Populations? 总被引:1,自引:0,他引:1
Pond-breeding amphibians have been characterized as having metapopulation structure, and a goal of many local restoration projects is to establish viable metapopulations. However, recent studies suggest that metapopulation organization is unlikely at the local level because of high dispersal rates between neighboring ponds. Although many amphibians avoid ovipositing in habitats that pose high predation risk to their offspring, the spatial scale of avoidance is poorly resolved for natural systems and could involve wholesale movements between ponds. To determine the scale of avoidance, we monitored annual habitat use by the Wood frog ( Rana sylvatica ), American toad ( Bufo americanus ), and Spotted salamander ( Ambystoma maculatum ) at a restoration site in western North Carolina, U.S.A. Wood frogs consistently used most fish-free ponds, but rapidly curtailed use following fish invasions. American toads rarely used the same breeding site from year to year, and adults strongly avoided ovipositing in habitats with predatory Wood frog tadpoles. Spotted salamanders exhibited a predator avoidance response to fish that was weaker than the predator avoidance response of anurans. Our data indicate that the spatial scale of predator avoidance by ovipositing amphibians often exceeds that of an individual pond and that the focal species at this site are organized as patchy populations rather than as metapopulations. At local restoration sites, ponds that are placed in spatial arrays to create metapopulations may not accomplish their goal and may limit the extent to which ovipositing adults can express an adaptive antipredator behavior. We discuss an alternative design that is more likely to enhance the long-term persistence of local populations. 相似文献
78.
Nicholas JG Webster Lui-Guojing Evans Matt Caples Laura Erker Shern L Chew 《BMC molecular biology》2004,5(1):7-15
Background
Incorporation of exon 11 of the insulin receptor gene is both developmentally and hormonally-regulated. Previously, we have shown the presence of enhancer and silencer elements that modulate the incorporation of the small 36-nucleotide exon. In this study, we investigated the role of inherent splice site strength in the alternative splicing decision and whether recognition of the splice sites is the major determinant of exon incorporation. 相似文献79.