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51.
Mavis Hendson Lizzie Askjaer Jennifer A. Thomson Marc van Montagu 《Applied microbiology》1983,45(5):1526-1532
Eighteen strains of Agrobacterium tumefaciens isolated from crown galls were tested for agrocin production. Of six agrocin-producing strains, one (D286) produced a broad-host-range agrocin active against strains carrying nopaline, octopine, and agropine type Ti plasmids. Sensitivity to agrocin D286 was found to map in the 11- to 18-megadalton region of the nopaline Ti plasmid pTiC58. The agrocin was partially purified, and its physical characteristics were consistent with its being a nucleotide, as is agrocin 84. Agrocin D286 was shown to inhibit DNA, RNA, and protein syntheses. Strain D286 spontaneously lost its pathogenicity, and its potential for use in the biological control of crown gall is discussed. 相似文献
52.
1. Mycophenolic acid, an antibiotic of some antiquity that more recently has been found to have marked activity against a range of tumours in mice and rats, strongly inhibits DNA synthesis in the L strain of fibroblasts in vitro. 2. The extent of the inhibition of DNA synthesis is markedly increased by preincubation of the cells with mycophenolic acid before the addition of [(14)C]thymidine. 3. The inhibition of DNA synthesis by mycophenolic acid in L cells in vitro is reversed by guanine in a non-competitive manner, but not by hypoxanthine, xanthine or adenine. 4. The reversal of inhibition by guanine can be suppressed by hypoxanthine, 6-mercaptopurine and adenine. 5. Mycophenolic acid does not inhibit the incorporation of [(14)C]thymidine into DNA in suspensions of Landschütz and Yoshida ascites cells in vitro. 6. Mycophenolic acid inhibits the conversion of [(14)C]hypoxanthine into cold-acid-soluble and -insoluble guanine nucleotides in Landschütz and Yoshida ascites cells and also in L cells in vitro. There is some increase in the radioactivity of the adenine fraction in the presence of the antibiotic. 7. Mycophenolic acid inhibits the conversion of [(14)C]hypoxanthine into xanthine and guanine fractions in a cell-free system from Landschütz cells capable of converting hypoxanthine into IMP, XMP and GMP. 8. Preparations of IMP dehydrogenase from Landschütz ascites cells, calf thymus and LS cells are strongly inhibited by mycophenolic acid. The inhibition showed mixed type kinetics with K(i) values of between 3.03x10(-8) and 4.5x10(-8)m. 9. Evidence was also obtained for a partial, possibly indirect, inhibition by mycophenolic acid of an early stage of biosynthesis of purine nucleotides as indicated by a decrease in the accumulation of formylglycine amide ribonucleotide induced by the antibiotic azaserine in suspensions of Landschütz and Yoshida ascites cells and L cells in vitro. 相似文献
53.
Summary The ultrastructure of the haematopoietic cells in the polychaetes Neoamphitrite figulus Dalyell, Lanice conchilega (Pallas), Arenicola marina (L.), Myxicola infundibulum Renier, Megalomma vesiculusom (Montagu), Sabella penicillus L., are compared: all show similarities in having well developed Golgi, granular endoplasmic reticulum and haemoglobin or chlorocruorin in vesicles, and numerous mitochondria. The porphyrin byproducts of synthesis are combined with iron as haematins within electrondense granules built up from multi-lamellar organelles. The structure of the basal lamina which alone separates the cells from the lumen of the vessels is described and evidence is presented for the method of release of the haem into the plasma by reverse pinocytosis. The cycle of synthesis within the cell is discussed and the process of haem synthesis in annelids is reviewed. The structure of the haemoglobin-containing coelomocytes of Neoamphitrite figulus is briefly described.This work was made possible by an award from the Science Research Council. We would also like to thank the Director and Staff of the Plymouth Laboratory, where some of the work was done, for their hospitality and facilities. 相似文献
54.
55.
Hillary A. Hahm Margot M. Ip Kathleen Darcy Jennifer D. Black Wendy K. Shea Suzanne Forczek Masami Yoshimura Takami Oka 《In vitro cellular & developmental biology. Plant》1990,26(8):803-814
Summary A serum-free primary culture system is described which allows normal rat mammary epithelial cells (RMECs) embedded within
a reconstituted basement membrane to undergo extensive growth and functional differentiation as detected by synthesis and
secretion of the milk products casein and lipid. RMECs isolated from mammary glands of immature virgin rats were seeded within
an extracellular matrix preparation derived from the Engelbreth-Holm-Swarm sarcoma and cultured in a serum-free medium consisting
of Dulbecco's modified Eagle's medium-F12 containing insulin, prolactin, progesterone, hydrocortisone, epidermal growth factor,
bovine serum albumin, transferrin, and ascorbic acid. Casein synthesis and secretion were documented at the electron microscopic
level as well as by an enzyme-linked immunosorbent assay (ELISA) assay using a polyclonal antibody against total rat caseins.
Numerous secretory vesicles with casein micelles were noted near the apical surface of the RMECs, and secreted casein was
observed in the lumen. These ultrastructural data were confirmed by the ELISA assay which showed that microgram amounts of
casein per well were synthesized by the RMECs and that the amount of casein increased with time in culture. Using immunoblot
analysis it was demonstrated that the full complement of casein proteins was synthesized. In addition to casein protein, β-casein
mRNA levels were shown to increase with time. Synthesized lipid was detected at both the light and electron microscopic levels.
Phase contrast photomicrographs demonstrated extensive intracellular lipid accumulation within the ductal and lobuloalveolarlike
colonies, and at the electron micrograph level, lipid droplets were predominantly localized near the apical surface of the
RMECs. The lipid nature of these droplets was verified by oil red O staining. Results from this study demonstrate that RMECs
from immature virgin rats proliferate extensively and rapidly develop the capacity to synthesize and secrete casein and lipid
when grown within a reconstituted basement membrane under defined serum-free conditions. This unique system should thus serve
as an excellent model in which the regulation of mammary development and gene expression can be investigated.
This work was supported by grants CA 33240 and CA 35641 and by core grant CA 24538 from the National Institutes of Health,
Bethesda, MD. 相似文献
56.
Michael A. Bowers Stephen F. Matter James L. Dooley Jr. Jennifer L. Dauten John A. Simkins 《Oecologia》1996,108(1):182-191
Habitat fragmentation involves a reduction in the effective area available to a population and the imposition of hard patch edges. Studies seeking to measure effects of habitat fragmentation have compared populations in fragments of different size to estimate and area effect but few have examined the effect of converting open populations to closed ones (an effect of edges). To do so requires a shift in spatial scope-from comparison of individual fragments to that of fragmented versus unfragmented landscapes. Here we note that large-scale, controlled studies of habitat fragmentation have rarely been performed and are needed. In making our case we develop a simple computer simulation model based on how individual animals with home ranges are affected by the imposition of habitat edges, and use it to predict population-level responses to habitat fragmentation. We then compare predictions of the model with results from a field experiment on Peromyscus and Microtus. Our model treats the case where home ranges/territories fall entirely within or partially overlap with that of sample areas in continuous landscapes, but are restricted to areas within habitat fragments in impacted landscapes. Results of the simulations demonstrate that the imposition of hard edges can produce different population abundances for similar-sized areas in continuous and fragmented landscapes. This edge effect is disproportionately greater in small than large fragments and for species with larger than smaller home ranges. These predictions were generally supported by our field experiment. We argue that large-scale studies of habitat fragmentation are sorely needed, and that control-experiment contrasts of fragmented and unfragmented microlandscapes provide a logical starting point. 相似文献
57.
58.
Patricia L. Stranahan Jennifer Laroe Ronda McCombs Alex Goldsmith Iffat Rahim Mark Overland David E. Pettijohn 《Glycoconjugate journal》1996,13(5):741-747
Intratumoral phenotypic diversity is well documented with regard to tumor associated carbohydrate antigens (TACA). The factors which control the expression of these cell-surface oligosaccharides on different cells of the same tumor are not understood. We investigated the expression of a panel of mucin associated oligosaccharides in cell lines growing at different surface densities (number of cells per cm2 of growth flask). Results show that the apparent expression of extended Lea-Lex, Lea and Lex, sialyl Lea, Tn and sialyl Tn varies with density of growth by an invasive human squamous cell lung carcinoma cell line (NU6-1), a benign variant (NE-18) and the human lung epithelial cell line BEAS-2B. The results indicate that one of the factors influencing the apparent expression of mucin-associated oligosaccharides is cell-cell interactions.Abbreviations Mab
monoclonal antibody
- FIT
fluorescein isothiocyanate
- TACA
tumor associated carbohydrate antigen 相似文献
59.
Physiological aspects of Taxus brevifolia seeds in relation to seed storage characteristics 总被引:1,自引:0,他引:1
Water relations, desiccation tolerance and longevity of Taxus brevifolia (Nutt.) seeds were studied to determine the optimal stage of development and storage conditions for seeds of this species. Seeds equilibrated to a range of relative humidities (RHs) had unusually low water contents which can be accounted for by the high lipid content of gametophyte tissues (71% of the dry mass). Water relations of embryonic tissue were more typical of those reported for other seed species. The water content below which freezing transitions were not observable in the embryo was ca 0.24 g H2 O (g dry weight)−1 (g g−1 ) for all maturity classes studied. Embryos did not achieve significant levels of desiccation tolerance (survival to water contents less than 0.5 g g−1 ) until the latter stages of development when dry matter was maximal. Mature embryos could be dried to 0.025 g g−1 (seed water content of 0.010 g g−1 ) with no loss of viability. Thus, at the latter stages of development, embryo water content could be optimized to avoid both desiccation and freezing damage. Survival of mature seeds declined over a 2-year period when seeds were stored at temperatures between 5 and 35°C and RHs between 14 and 75%, corresponding to seed water contents between 0.015 and 0.07 g g−1 . The deterioration rate was slowest for seeds stored at the lowest RH and temperature. Our data indicate that seeds of Taxus brevifolia show orthodox rather than recalcitrant storage characteristics, but that the optimum water content for storage was extremely low. The results suggest that even if stored at optimal water contents and low temperatures, T. brevifolia seeds will be relatively short lived. The high quantity of lipids or reducing sugars may be contributing factors in the poor storage characteristics. 相似文献
60.
Induction of leaf senescence in Arabidopsis thaliana by long days through a light-dosage effect 总被引:2,自引:0,他引:2
Larry D. Nooden Jennifer W. Hillsberg Michael J. Schneider 《Physiologia plantarum》1996,96(3):491-495
Given the influence of photoperiod on reproductive development and whole-plant senescence in monocarpic plants, one would suspect that leaf senescence in these plants might be under photoperiodic control. In Arabidopsis thaliana , which is monocarpic and also a nonobligate long-day (LD) plant, LDs (16 h, 300 μmol m−2 s−1 ) caused leaves to die earlier than did short days (SDs, 10 h). Since leaf longevity was not paralleled by the reproductive development in the present study, the reproductive structures did not seem to be the primary controls of leaf senescence. The LD effect appeared to depend on the amount of light rather than on day length, for leaves given LDs at reduced light intensity (180 μmol m−2 s−1 ) lived longer than those in LDs with full light. In addition, the higher light intensity promoted chlorophyll loss and anthocyanin accumulation in LDs. Thus, senescence of these leaves seems to be governed by light dosage rather than photoperiod. Light may play a natural role in promoting the senescence of A. thaliana leaves. 相似文献