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  • 1
    Electronic Resource
    Electronic Resource
    Adaptive significance of furanocoumarin diversity inPastinaca sativa (Apiaceae) (1991)
    Springer
    Journal of chemical ecology 17 (1991), S. 207-215 
    Details
    ISSN: 1573-1561
    Keywords: Heliothis zea ; corn earworm ; Lepidoptera ; Noctuidae ; Pastinaca sativa ; wild parsnip ; Apiaceae ; furanocoumarins ; defense ; xanthotoxin ; photoactivation ; bioassay
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Fruits ofPastinaca sativa (Apiaceae), the edible parsnip, contain six different furanocoumarins that are differentially capable of ultraviolet-mediated cross-linkage of DNA and inhibition of DNA transcription. Individually, none of the other furanocoumarins present in parsnip seeds is as toxic as the photosensitizer xanthotoxin. Nevertheless, the natural mixture of compounds is toxicologically more effective againstHeliothis zea (Lepidoptera: Noctuidae), both in the presence and absence of UV light, than is an equimolar amount of xanthotoxin. The difference in toxicity diminishes with increasing light levels. Thus, a series of structurally related natural products can display toxicity lacking in individual compounds and may represent an adaptive compromise to varying environmental conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00994434
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  • 2
    Electronic Resource
    Electronic Resource
    Parthenocarpic fruits in wild parsnip: Decoy defence against a specialist herbivore (1991)
    Springer
    Evolutionary ecology 5 (1991), S. 136-145 
    Details
    ISSN: 1573-8477
    Keywords: Parthenocarpy ; fruits ; defence ; wild parsnip ; Pastinaca sativa ; parsnip webworm ; Depressaria pastinacella ; furanocoumarins ; decoys
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Parthenocarpy, the production of fruits without viable seeds, is a widespread phenomenon in plants. While failure to effect pollination or fertilization is often cited as the cause of parthenocarpy, this explanation alone is inadequate to explain why plants produce, maintain and further develop fruits. Wild parsnips (Pastinaca sativa) frequently produce parthenocarpic fruit. When parsnip webworms (Depressaria pastinacella), specialist feeders on wild parsnip, were given choices between normal fruit and parthenocarpic fruit, they exhibited a strong preference for parthenocarpic fruit. However, on parthenocarpic fruit, insects fed less efficiently and grew more slowly than insects fed normal fruit. Parthenocarpic fruits, then, may act as decoys that divert herbivores away from fruits that contain plant offspring.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02270830
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  • 3
    Electronic Resource
    Electronic Resource
    Observations of hamster sperm-egg fusion in freeze-fracture replicas including the use of filipin as a sterol marker (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 27 (1990), S. 351-365 
    Details
    ISSN: 1040-452X
    Keywords: Electron microscopy ; Sperm-egg interactions ; Polyspermic conditions ; Filipin ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: We have extended the observations of previous transmission electron microscopy studies of sperm-egg fusion to include those of freeze-fracture replicas showing sperm-egg interactions before, during, and following sperm head fusion with the egg membrane. Hamster eggs were incubated with hamster sperm under polyspermic conditions and were observed after a period of 5-30 minutes. After fixation, the eggs and sperm were exposed to filipin, which binds β-OH-sterols to form visible complexes in freeze-fracture replicas. Filipin can act as a marker for egg plasma membrane wherein it is abundant, while filipin is relatively scarce in the acrosome-reacted hamster sperm membrane, found only in the plasma membrane of the equatorial segment. The earliest sperm-egg interactions are observed between the egg microvilli and the perforatorium and the equatorial segment of the sperm, and the initial fusion between egg and sperm occurs in the vicinity of the equatorial segment. At later stages of fusion involving the postacrosomal segment, a clear line of demarcation is observed between the filipin-rich egg membrane and the filipin-poor sperm postacrosomal segment, suggesting that filipin binding lipids from the egg intercalate into the sperm membrane following membrane fusion. The anterior segment of the sperm does not fuse with the egg but is instead incorporated into a cytoplasmic vesicle derived from both sperm and egg membranes. In this latter step, filipin-sterol complexes are not found in sperm-derived membranes suggesting that there may be barriers to the movement of filipin binding lipids from the egg into these sperm membranes.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrd.1080270410
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  • 4
    Electronic Resource
    Electronic Resource
    Further observations on the phagocytosis of Candida albicans by Hamster and Human Oocytes (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 28 (1991), S. 79-84 
    Details
    ISSN: 1040-452X
    Keywords: Yeast ; Ultrastructure ; Oocyte infection ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Pathogenic yeast, Candida albicans, were incubated with hamster and human oocytes for up to 21 hours in order to determine the nature and time course of phagocytosis of these organisms. Aliquotes of the interacting cells were taken at various time intervals for electron microscopic examination. Some specimens had their zona pellucidae enzymatically removed prior to incubation with yeast, and these specimens showed the most extensive interaction and phagocytosis of Candida. The zona pellucida appears to be an effective barrier to yeast, at least over the time span studied. The observations are consistent with the hypothesis of an initial attachment of yeast via a surface component to oocyte microvilli followed by phagocytic uptake into an endosome. There is no compelling evidence of lysosomal degradation of the yeast over the time course of this study; however, the oocytes appear to undergo some degenerative changes at long incubation times.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrd.1080280113
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  • 5
    Electronic Resource
    Electronic Resource
    Spermophagy in semen in the red wolf, Canis rufus (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 37 (1994), S. 457-461 
    Details
    ISSN: 1040-452X
    Keywords: Canine sperm ; Pyospermia ; Ultrastructure ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The red wolf (Canis rufus) is an endangered species with 194 individuals remaining in the wild and in various captive facilities. Breeding efforts at the Graham, WA site (Point Defiance Zoo and Aquarium) have involved artificial insemination with fresh or frozen semen in an effort to increase population and maximize the genetic potential of the stock. Electron microscopic observations were made in semen specimens obtained by electroejaculation from mature males prior to their use in an effort to determine semen parameters that might be useful in guiding breeding procedures. Sperm samples were either fixed immediately or treated with capacitating media and fixed after 4 to 7 hr of incubation. Many of the specimens examined were pyospermic (white cell in semen) and showed evidence of spermophagy, primarily by neutrophils. Of the six animals surveyed, only one showed little evidence of spermophagy, and three had extensive pyospermia and spermophagy but this finding was not correlated with fertility. Samples fixed immediately as well as those incubated for several hours showed evidence of spermophagy, indicating that the phagocytosis was not the result of culture. Gene pool restriction and/or captive stress may be contributing factors of reduced semen quality. © 1994 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrd.1080370413
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  • 6
    Electronic Resource
    Electronic Resource
    Temperature-dependent sex determination in reptiles: Proximate mechanisms, ultimate outcomes, and practical applications (1994)
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 15 (1994), S. 297-312 
    Details
    ISSN: 0192-253X
    Keywords: Sex determination ; sexual differentiation ; reptiles ; temperature-dependent sex determination ; behavior ; steroidogenic enzymes ; aromatase ; reductase ; estrogen ; androgen ; steroid hormone receptors ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: In many egg-laying reptiles, the incubation temperature of the egg determines the sex of the offspring, a process known as temperature-dependent sex determination (TSD). In TSD sex determination is an “all or none” process and intersexes are rarely formed. How is the external signal of temperature transduced into a genetic signal that determines gonadal sex and channels sexual development? Studies with the red-eared slider turtle have focused on the physiological, biochemical, and molecular cascades initiated by the temperature signal. Both male and female development are active processes - rather than the crganized/default system characteristic of vertebrates with genotypic sex determination - that require simultaneous activation and suppression of testis- and ovary-determining cascades for normal sex determination. It appears that temperature accomplishes this end by acting on genes encoaing for steroidogenic enzymes and steroid hormone receptors and modifying the endocrine microenvironment in the embryo. The temperature experienced in development also has long-term functional outcomes in addition to sex determination. Research with the leopard gecko indicates that incubation temperature as well as steroid hormones serve as organizers in shaping the adult phenotype, with temperature modulating sex hormone action in sexual differentiation. Finally, practical applications of this research have emerged for the conservation and restoration of endangered egg-laying reptiles as well as the embryonic development of reptiles as biomarkers to monitor the estrogenic effects of common environmental contaminants. © 1994 Wiley-Liss, Inc.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/dvg.1020150310
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  • 7
    Electronic Resource
    Electronic Resource
    Comparisons of the low-resolution structures of ornithine decarboxylase by electron microscopy and X-ray crystallography: The utility of methylamine tungstate stain and butvar support film in the study of macromolecules by transmission electron microscopy (1991)
    New York, NY : Wiley-Blackwell
    Journal of Electron Microscopy Technique 18 (1991), S. 157-166 
    Details
    ISSN: 0741-0581
    Keywords: Proteins ; Molecular structure ; Negative-stain electron microscopy ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: The structure of ornithine decarboxylase (Mr ≍ 1.04 × 106) from Lactobacillus 30a was investigated by electron microscopy and x-ray crystallography. Electron micrographs showed the structure to be well preserved in methylamine tungstate stain. The molecules interacted little with the Butvar support film, yielding three unique projections: a hexagonal ring (front view) and two rod-shaped projections (edge views). Stereo pairs revealed a novel feature of the Butvar film in that some molecules were suspended in the stain in random orientations. Consequently, the relatedness of the hexagonal ring and the rod-shaped particles could be demonstrated since some particle shapes interconverted when the stage was tilted ± 45°. The two edge views were related by a 30° rotation about the sixfold axis. Image averaging of the three primary views suggested a dodecamer (point group symmetry 622) composed of two hexameric rings, apparently in an eclipsed configuration. To investigate the structural organization of the complex, the dissociation of the enzyme was studied by electron microscopy. The dissociation process involved the initial breakage of the ring followed by separation of dimers from the ring (one subunit from each of the two hexamers). Thus, the dodecamer forms as a hexamer of dimers rather than a dimer of hexamers. These structural studies were confirmed and extended by x-ray crystallographic analysis. A 4.0-Å resolution electron density map revealed two hexameric rings, consisting of six closely associated dimers, tilted approximately 10° with respect to the molecular twofold axis. Electron density projections of the three primary views of the molecule derived from the x-ray data corresponded closely to those obtained from image averaging of the electron microscopy data, thereby establishing in a novel way the reliability of the electron microscopy studies. Methylamine tungstate stain and Butvar support film therefore offer unique advantages for investigating protein structures by electron microscopy.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jemt.1060180210
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