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91.
92.
Information on the commercially utilized marine red alga Furcellaria lumbricalis is summarized from published sources. Biological aspects under discussion include: nomenclature, taxonomy, morphology, development and life history, distribution, phenology, ecophysiology, growth and resource management. A brief history of the utilization of this species, and an account of its chemical constituents including the hydrocolloid furcellaran are also presented. 相似文献
93.
Kim B. Saunders Patricia A. D’Amore 《In vitro cellular & developmental biology. Animal》1992,28(7-8):521-528
Summary Heterotypic cell-cell interactions appear to be involved in the control of development and function in a wide variety of tissues.
In the vasculature, endothelial cells and mural cells (smooth muscle cells or pericytes) make frequent contacts, suggesting
a role for intercellular interactions in the regulation of vascular growth and function. We have previously grown endothelial
cells and mural cells together in mixed cultures and found that heterocellular contact led to endothelial growth inhibition.
However, this mixed culture system does not lend itself to the examination of the effects of contact on the phenotype of the
individual cell types. We have therefore developed a co-culture system in which cells can be co-cultured across a porous membrane,
permitting intercellular contact while maintaining pure cell populations. Co-culture of endothelial cells and smooth muscle
cells across membranes with pore sizes of 0.02, 0.4, 0.6, and 0.8μm maintained the two cell types as homogeneous populations, whereas smooth muscle cells migrated across the membrane through
pores of 2.0μm. Vascular cell co-culture across membranes with 0.8-μm pores resulted the inhibition of endothelial cell proliferation and the generation of conditioned media which inhibited
endothelial cell growth. The arrangement of the cells in this co-culture system mimics thein vivo orientation of vascular cells in which mural cells are separated from the abluminal surface of the endothelium by a fenestrated
internal elastic lamina or basement membrane. Because this co-culture system maintains separable populations of cells in contact
or close proximity allowing for biochemical and molecular analyses of pure populations, it should prove useful for the study
of cell-cell interactions in a variety of systems. 相似文献
94.
Diel Nitrogen Fixation by Cyanobacterial Surface Blooms in Sanctuary Lake, Pennsylvania 总被引:2,自引:0,他引:2 下载免费PDF全文
Diel nitrogen fixation studies were conducted with assemblages of cyanobacteria sampled from surface blooms on Sanctuary Lake, Pa. The studies were conducted between July and September of 1982 to 1985 by using the acetylene reduction technique. Assemblages with the lowest cell concentrations (0.9 × 109 to 1.0 × 109 cells per liter) exhibited nitrogen fixation activity throughout the day, with maximum fixation rates occurring in mid to late afternoon; fixation proceeded throughout the night at rates equivalent to 23 to 28% of the afternoon maximum. In studies conducted with the highest cell concentrations (3.7 × 109 to 6.7 × 109 cells per liter), fixation rates reached maximum values in mid to late morning. The rates declined rapidly throughout the midday period and subsequently ceased from late afternoon until sunrise on the following day. The afternoon decline and cessation of fixation exhibited by high cell concentrations correlated with photosynthetically induced low total CO2 and supersaturating O2 concentrations. The midday decline could be prevented and partially reversed by experimentally lowering O2 and increasing total CO2 concentrations. Under experimental conditions which simultaneously prevented supersaturating O2 concentrations and maintained high total CO2 availability, nitrogen fixation continued throughout the solar day, with maximum rates occurring at midday. These observations indicate that temporal changes in photosynthetic activity may affect diel fluctuations in nitrogen fixation. 相似文献
95.
96.
97.
pLE2451, a 24.5 megadalton conjugative plasmid from Neisseria gonorrhoeae, was capable of efficiently mobilizing gonococcal beta-lactamase plasmids between gonococci and from gonococci to Haemophilus influenzae and restriction-deficient Escherichia coli. Donor strains of N. gonorrhoeae carrying pLE2451 were also found to be capable of mobilizing a variety of non-conjugative plasmids originally derived from enteric bacteria or Haemophilus species when such plasmids were resident in E. coli. Nevertheless, pLE2451 was not detected physically in E. coli or H. influenzae transconjugants. This suggests that the plasmid is unstable in these hosts but survives transiently to provide transfer functions for mobilization. The proficiency of pLE2451 in promoting intraspecific and intergeneric mobilization was not paralleled by pUB701, pRI234 and pFR16017, a series of conjugative plasmids derived originally from Haemophilus species. These plasmids were incapable of mobilizing even Haemophilus beta-lactamase plasmids, such as RSF0885, between Haemophilus species. 相似文献
98.
Angie Rizzino Victor Terranova David Rohrbach Craig Crowley Heather Rizzino 《Journal of cellular biochemistry》1980,13(2):243-253
In this paper we have examined the growth and differentiation of the embryonal carcinoma cell line, F9, in the defined medium EM-3 at low density. We show that the growth of F9 and their differentiated cells (F9-diff) in EM-3 is strongly density dependent. At low cell densities the growth of both cell types is severely limited and most of the cells do not survive. Although this poses a problem for working with F9 and F9-diff in EM-3, it provides a convenient assay for identifying molecules that support their growth at low density. Using this assay, we have determined that laminin, a newly isolated glycoprotein of basement membranes, significantly improves the growth and short-term survival of both F9 and F9-diff. However, addition of laminin to EM-3 is insufficient to promote the clonal growth of these cell types. Our findings also indicate that laminin promotes the attachment of F9 and F9-diff in defined media. On the basis of our results, we propose an attachment function for laminin during the early stages of mammalian development. 相似文献
99.
Heather Windle 《BMJ (Clinical research ed.)》1980,280(6229):1425-1426
100.
Pathway of plasmid transformation in Pneumococcus: open circular and linear molecules are active. 总被引:13,自引:7,他引:6 下载免费PDF全文
We have extended the analysis of plasmid transformation in Streptococcus pneumoniae by finding that monomeric and dimeric open circular and linear forms of pMV158 were active in transformation. Their efficiencies were at least 35-fold lower than those of the corresponding closed circular forms. The evidence came largely from analysis of S1 nuclease-digested plasmid deoxyribonucleic acid by combinations of dye-buoyancy, gel electrophoresis, and sedimentation velocity methods. As with closed circular forms, monomer open circular forms gave second-order kinetics and dimer forms gave first-order kinetics. Unique linear products of digestion by either of two restriction enzymes were inactive, but a mixture of the two digests was active, as was the mixture of linear monomer deoxyribonucleic acids produced by S1 nuclease. Absolute efficiencies of transformation were low even for closed circular donors. All of the results, including the low efficiencies, were consistent with the interpretation that plasmid replicons were assembled in the recipient cell by pairing of fragments of single strands that had entered the cell separately from duplex donors that had been cut on the cell surface. 相似文献