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101.
Richard I. Samuels Stuart E. Reynolds 《Archives of insect biochemistry and physiology》1993,24(1):33-44
Developmental profiles for a number of molting fluid (MF) enzyme activities were established and related to the progress of pupal cuticle degradation during the four days that precede the eclosion of adult tobacco hornworms. Cuticle degrading activity, molting fluid protease 1 (MFP-1), and molting fluid protease 2 (MFP-2) all increased in activity at the time that loss of material from the old cuticle occurred. In contrast, chitinase and β-acetylglucosaminidase activities did not parallel weight loss from the old cuticle. These results are consistent with the hypothesis that proteolytic activity is a prerequisite for the action of chitinase on cuticle chitin. © 1993 Wiley-Liss, Inc. 相似文献
102.
Luisa F. Gómez-Correa Camila Jaramillo-Hernández Alvaro Duque Raquel Fernandes Araujo Gabriel Arellano Stuart J. Davies Nicolas Castaño Jörg Haarpaintner Fabian Enßle Daniel Zuleta 《Biotropica》2023,55(6):1136-1147
Understanding what drives changes in tree mortality as well as the covariates influencing trees' response is a research priority to predict forest responses to global change. Here, we combined drone photogrammetry and ground-based data to assess the influence of crown exposure to light (relative to total crown area), growth deviations (relative to conspecifics), tree size, and species' wood density (as a surrogate for light-demanding and shade-tolerant life-history strategies) on the mortality of 984 canopy trees in an Amazon terra firme forest. Trees with lower wood density were less prone to die when their proportion of crown was more exposed to sunlight, but this relationship with relative crown exposure weakened and slightly reversed as wood density increased. Trees growing less than their species average had higher mortality, especially when the species' wood density decreased. The role of wood density in determining the survival of canopy trees under varying light conditions indicates differential responses of light-demanding versus shade-tolerant species. Our results highlight the importance of accounting for life-history strategies, via plant functional types, in vegetation dynamic models aiming to predict forest demography under a rapidly changing climate. Abstract in Spanish is available with online material. 相似文献
103.
104.
Stuart P. Hardegree 《American journal of botany》1989,76(3):356-360
The pressure chamber and the thermocouple psychrometer often provide different values when used to estimate plant water potential. One hypothesis to explain the discrepancy between instruments is that water movement between the xylem and symplast occurs during pressurization in the pressure chamber. Pressure chamber and thermocouple psychrometer measurements of Pinus ponderosa (Laws.) seedling shoots and mature Quercus agrifolia (Nee) shoots showed that the discrepancy is greater for Quercus. It was hypothesized that the xylem water content-water potential relationship of these species would explain the magnitude of the discrepancy between instruments. The xylem water holding capacity alone, however, does not explain the difference between species. The larger discrepancy in Quercus is likely due to a greater volume of water held in the xylem relative to the volume held in the symplast. 相似文献
105.
106.
Yu-Sen Wang Anne F. Frederick Mary M. Senior Barbara A. Lyons Stuart Black Paul Kirschmeier Louise M. Perkins Oswald Wilson 《Journal of biomolecular NMR》1996,7(2):89-98
Summary The growth factor receptor-bound protein-2 (Grb2) is an adaptor protein that mediates signal transduction pathways. Chemical shift assignments were obtained for the SH2 domain of Grb2 by heteronuclear NMR spectroscopy, employing the uniformly 13C-/15N-enriched protein as well as the protein containing selectively 15N-enriched amino acids. Using the Chemical Shift Index (CSI) method, the chemical shift indices of four nuclei, 1H, 13C, 13C and 13CO, were used to derive the secondary structure of the protein. Nuclear Overhauser enhancements (NOEs) were then employed to confirm the secondary structure. The CSI results were compared to the secondary structural elements predicted for the Grb2 SH2 domain from a sequence alignment [Lee et al. (1994) Structure, 2, 423–438]. The core structure of the SH2 domain contains an antiparallel -sheet and two -helices. In general, the secondary structural elements determined from the CSI method agree well with those predicted from the sequence alignment.Abbreviations crk
viral p47gag-crk
- EGF
epidermal growth factor
- GAP
GTPase-activating protein
- PI3K
phosphatidylinositol-3-kinase
- PLC-
phospholipase-C-, shc, src homologous and collagen
- src
sarcoma family of nonreceptor tyrosine kinase 相似文献
107.
108.
Stuart L. Pimm 《Biodiversity and Conservation》1996,5(9):1059-1067
During their colonization by Polynesians and later by Europeans, the Hawaiian islands suffered a massive loss of species. All the extinctions are indirectly attributable to human impact. Nonetheless, it has proved extremely difficult to specify which of several possible mechanisms caused each particular extinction. This seems to admit defeat in the battle to understand past extinctions. Such understanding could guide our efforts to protect species that are now threatened with extinction. Will it be easier to understand the causes of future extinctions? Surveys of future extinctions stress habitat destruction as the simple and dominant mechanism. This contrasts to its secondary (and generally confused) role in past extinctions. I argue that this contrast between the complexity of the past and the apparent simplicity of the future arises because extinction mechanisms are inherently synergistic. Once extensive species losses begin, it may be impossible to separate the mechanisms and thus manage an individual species as if its decline had a single cause. 相似文献
109.
James B. Hoying Carl A. Boswell Stuart K. Williams 《In vitro cellular & developmental biology. Animal》1996,32(7):409-419
Summary During angiogenesis, the microvasculature displays both vessel remodeling and expansion under the control of both cellular
and extracellular influences. We have evaluated the role of angiogenic and angiostatic molecules on angiogenesis in anin vitro model that more appropriately duplicates the cellular and extracellular components of this process. Freshly isolated microvessel
fragments from rat adipose tissue (RFMF) were cultured within three-dimensional collagen I gels. These fragments were characterized
at the time of isolation and were composed of vessel segments observed in the microvasculature of fatin situ (i.e., arterioles, venules, and capillaries). Fragments also exhibited characteristic ablumenally associated cells including
smooth muscle cells and pericytes. Finally, fragments were encased in an extracellular matrix composed of collagen type IV
and collagen type I/III. The elongation of microvascular elements was subsequently evaluated using morphologic and immunocytochemical
techniques. The proliferation, migration, and elongation of cellular elements in microvessel fragments from rat adipose tissue
was dependent on initial fragment density, matrix density, and required serum. Inclusion of endothelial cell growth factors
to microvessel fragments from rat adipose tissue 3-D cultures resulted in the accelerated elongation of tube structures and
the expression of von Willebrand factor in cells constituting these tubes. Molecules with reported angiostatic capacity (e.g.,
transforming growth factor and hydrocortisone) inhibited vessel tube elongation.
In vitro methods have been developed to evaluate numerous mechanisms associated with angiogenesis, including endothelial cell proliferation,
migration, and phenotypic modulation. Microvascular endothelial cell fragments described in this study represent anin vitro population of cells that accurately duplicate thein vivo microcirculatory elements of fat. The proliferation of cells and elongation of microvascular elements subsequently observed
in three-dimensional cultures provides anin vitro model of angiogenesis. Microvascular formation in this system results from pre-existing microvessel fragments unlike tube
formation observed when cultured endothelial cells are placed in three-dimensional gels. This form of tube formation from
cultured endothelium is more characteristic of vasculogenesis. Thus, the formation of microvascular elements from microvessel
fragments provides the opportunity to examine the mechanisms regulating angiogenesis in anin vitro system amenable to precise experimental manipulation. 相似文献
110.
Stuart Knutton 《Bioscience reports》1995,15(6):469-479
EnteropathogenicEscherichia coli (EPEC), first described in the 1940's and 1950's, remain an important cause of severe infantile diarrhoea in many parts of the developing world. EPEC do not produce enterotoxins and are not invasive; instead their virulence depends upon exploitation of host cell signalling pathways and the host cell cytoskeleton both as a means of colonizing mucosal surfaces of the small intestine and causing diarrhoea. Following initial mucosal attachment, EPEC secrete signalling proteins and expresss a surface adhesin, intimin, to produce attaching & effacing lesions in the enterocyte brush border membrane characterised by localised destruction of brush border microvilli, intimate bacterial adhesion and cytoskeletal reorganisation and accretion beneath attached bacteria. The pathophysiology of EPEC diarrhoea is also complex and probably results from a combination of epithelial cell responses including both electrolyte secretion and structural damage. 相似文献