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91.
ANNE F. O'MELIA 《Development, growth & differentiation》1979,21(1):99-108
De novo synthesis of 5S RNA and of transfer RNA (tRNA) has been demonstrated previously to occur by mid-cleavage (128-cell stage) in sea urchin embryos (24). The present study focused on determining more precisely the time of onset of activity of the genes for 5S RNA and for tRNA during sea urchin embryogenesis by preloading the GTP precursor pools of unfertilized eggs. The results showed that newly-made 5S RNA and tRNA could be detected as early as the 32-cell stage. In order to determine whether newly-synthesized 5S RNA accumulates coordinately during development with newly-made 26S (34) and 18S ribosomal RNAs (rRNAs), the relative rates of accumulation of these three RNA molecules were measured and compared at each of several stages of sea urchin embryogenesis. In contrast to the coordinated accumulation of newly-synthesized 26S and 18S rRNAs, newly-made 5S RNA accumulated in excess at the mesenchyme blastula (9-fold excess), midgastrula (5-fold excess) and prism (3-fold excess) stages. The 5S RNA/26S RNA molar ratios only approached unity in advanced (48 hr) plutei. The non-coordinated accumulation of newly-made 5S RNA with that of 26S and 18S rRNAs suggests that the accumulation of these newly-synthesized RNAs is differentially regulated during early sea urchin development. 相似文献
92.
Electron probe X-ray microanalysis has been used for the last 25 years by biologists to obtain information about the distribution of elements at the cell and tissue level. During this period, progress has mainly been made through the development of more adequate techniques for specimen preparation (mainly low temperature techniques) and quantitative analysis, so that accurate analysis of the physiologically important cellular ions can be carried out. Use ofin vitrosystems and cell cultures may further increase the number of problems to which X-ray microanalysis can be applied. Among the numerous applications of X-ray microanalysis in cell biology and cell pathology, applications in the areas of epithelial ion transport, the role of calcium in secretory and contractile cells, and the role of ions in cell proliferation and cancer are discussed in more detail. 相似文献
93.
THE OBSTETRICS GYNECOLOGY RISK RESEARCH GROUP: REBECCA KUKLA MIRIAM KUPPERMANN MARGARET LITTLE ANNE DRAPKIN LYERLY LISA M. MITCHELL ELIZABETH M. ARMSTRONG LISA HARRIS 《Bioethics》2009,23(1):1-8
Over the last several years, as cesarean deliveries have grown increasingly common, there has been a great deal of public and professional interest in the phenomenon of women 'choosing' to deliver by cesarean section in the absence of any specific medical indication. The issue has sparked intense conversation, as it raises questions about the nature of autonomy in birth. Whereas mainstream bioethical discourse is used to associating autonomy with having a large array of choices, this conception of autonomy does not seem adequate to capture concerns and intuitions that have a strong grip outside this discourse. An empirical and conceptual exploration of how delivery decisions ought to be negotiated must be guided by a rich understanding of women's agency and its placement within a complicated set of cultural meanings and pressures surrounding birth. It is too early to be 'for' or 'against' women's access to cesarean delivery in the absence of traditional medical indications – and indeed, a simple pro- or con- position is never going to do justice to the subtlety of the issue. The right question is not whether women ought to be allowed to choose their delivery approach but, rather, taking the value of women's autonomy in decision-making around birth as a given, what sorts of guidelines, practices, and social conditions will best promote and protect women's full inclusion in a safe and positive birth process. 相似文献
94.
Measurements of electrical potential difference (PD) and potassiumactivity were carried out on the intact leaf of Tradescantiavirginiana. PD gradients across the stomatal complex were observedwith both open and closed stomata. The guard cell PD appearedto be linearly related to stomatal aperture. With the stomataopen a gradient of potassium activity across the stomatal complexwas observed which became reversed on stomatal closure. Calculationof the driving forces on potassium suggested that it was distributedpassively between the vacuoles of the cells of the stomatalcomplex. The electrophysiological data obtained from this investigationenabled potassium activity in the apoplast to be calculated.The results showed that on stomatal closure there was a massiveincrease in the potassium activity in the guard cell wall. Key words: Stomata, Ionic gradients, Electrical potentials 相似文献
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A scheme for speciating and biotyping enterococcal isolates from chickens is described. All tests are performed using solid media inoculated with a multipoint inoculator and can be done in conjunction with an antibiotic sensitivity test in which the agents are also incorporated into agar. 相似文献
98.
The Entry of Ammonia into Fungal Cells 总被引:2,自引:0,他引:2
When Scopulariopsis brevicaulis grown on an ammonia-free mediumis supplied with an ammonium salt ammonia enters the cells morerapidly than it is removed by assimilation, until an equilibriumlevel of ammonia is reached in the cells. The equilibrium concentrationin the cells is independent of metabolism and depends on theexternal concentration over a wide range. The internal concentra--tionof ammonia can be higher than the external under suitable conditionsof pH. The cells are shown to be permeable to ammonia also inthe outward direction, and the rate of entry or loss dependson the concentration difference between external and internalenvironment. The results support the view that ammonia enters the cells mainlyby the free diffusion of the undissociated molecule. 相似文献
99.
VARTIKA MATHUR ROEL WAGENAAR JEAN‐CLAUDE CAISSARD A. SANKARA REDDY LOUISE E. M. VET ANNE‐MARIE CORTESERO NICOLE M. VAN DAM 《Plant, cell & environment》2013,36(3):528-541
While nectaries are commonly found in flowers, some plants also form extrafloral nectaries on stems or leaves. For the first time in the family Brassicaceae, here we report extrafloral nectaries in Brassica juncea. The extrafloral nectar (EFN) was secreted from previously amorphic sites on stems, flowering stalks and leaf axils from the onset of flowering until silique formation. Transverse sections at the point of nectar secretion revealed a pocket‐like structure whose opening was surrounded by modified stomatal guard cells. The EFN droplets were viscous and up to 50% of the total weight was sugars, 97% of which was sucrose in the five varieties of B. juncea examined. Threonine, glutamine, arginine and glutamate were the most abundant amino acids. EFN droplets also contained glucosinolates, mainly gluconapin and sinigrin. Nectar secretion was increased when the plants were damaged by chewing above‐ and belowground herbivores and sap‐sucking aphids. Parasitoids of each herbivore species were tested for their preference, of which three parasitoids preferred EFN and sucrose solutions over water. Moreover, the survival and fecundity of parasitoids were positively affected by feeding on EFN. We conclude that EFN production in B. juncea may contribute to the indirect defence of this plant species. 相似文献
100.
ANNE MENELEY 《American anthropologist》2007,109(4):678-687
In this article, I track the contemporary possibilities for the global circulation of extravirgin olive oil. Recent technoscientific discoveries about the health benefits of extravirgin olive oil combine with narratives about olive oil's "ancientness" and "naturalness" to make it a very successful food commodity in an era of global concern about the risks of "industrial" food. "The Mediterranean" has emerged as a culture area that is defined by food in two realms: in a scientific register ("the Mediterranean Diet") and in contemporary gustatory discourses of distinction that imagine "the Mediterranean" as a site of delicious, "real" food as opposed to the industrial, processed food of the North Atlantic. 相似文献