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21.
Estimating the rate of plasmid transfer: an end-point method 总被引:5,自引:0,他引:5
We describe a method for determining the rate parameter of conjugative plasmid transfer that is based on single estimates of donor, recipient and transconjugant densities and the growth rate in exponential phase of the mating culture. The formula for estimating the plasmid transfer rate, gamma, was derived from a mathematical model describing cell growth and plasmid transfer in batch culture. Computer simulations were used to explore the sensitivity of this method to the realities of bacterial life, such as growth rate differences, plasmid segregation and transitory derepression of pilus synthesis. As predicted by the theory, mating experiments with the plasmid R1 in Escherichia coli K12 demonstrated that the estimate gamma is unaffected by cell density, donor:recipient ratio and mating time. Unlike previous techniques, our method allows us to investigate the effect of environmental factors on plasmid transfer rates when these factors also influence population growth rates. To illustrate this, we examined the effect of temperature on the rate of plasmid transfer. 相似文献
22.
Growth-associated modifications of low-molecular-weight thiols and protein sulfhydryls in human bronchial fibroblasts 总被引:2,自引:0,他引:2
Luigi Atzori Jeannette M. Dypbukt Kristina Sundqvist Ian Cotgreave Charlotte C. Edman Peter Moldus Roland C. Grafstrm 《Journal of cellular physiology》1990,143(1):165-171
The thiol redox status of cultured human bronchial fibroblasts has been characterized at various growth conditions using thiol-reactive monobromobimane, with or without the combination of dithiotreitol, a strong reducing agent. This procedure has enabled measurement of the cellular content of reduced glutathione (GSH), total glutathione equivalents, cysteine, total cysteine equivalents, protein sulfhydryls, protein disulfides, and mixed disulfides. Passage of cells with trypsin perturbs the cellular thiol homeostasis and causes a 50% decrease in the GSH content, whereas the total cysteine content is subsequently increased severalfold during cell attachment. During subsequent culture, transient severalfold increased levels of GSH, protein-bound thiols, and protein disulfides are reached, whereas the total cysteine content gradually declines. These changes in the redox balance of both low-molecular-weight thiols and protein-bound thiols correlate with cell proliferation and mostly precede the major growth phase. When the onset of proliferation is inhibited by maintenance of cells in medium containing decreased amounts of serum, the GSH content remains significantly increased. Subsequent stimulation of growth by addition of serum results in decreased GSH levels at the onset of proliferation. In thiol-depleted medium, proliferation is also inhibited, whereas GSH levels are increased to a lesser extent than in complete medium. Exposure to buthionine sulfoximine inhibits growth, prevents GSH synthesis, and results in accumulation of total cysteine, protein-bound cysteine, and protein disulfides. For extracellular cystine, variable rates of cellular uptake correlate with the initial increase in the total cysteine content observed following subculture and with the GSH peak that precedes active proliferation. The results strongly suggest that specific fluctuations in the cellular redox balance of both free low-molecular-weight thiols and protein sulfhydryls are involved in growth regulation of normal human fibroblasts. 相似文献
23.
MHC-like molecules in some nonmammalian vertebrates can be detected by some cross-reactive xenoantisera 总被引:3,自引:0,他引:3
J Kaufman K Skjoedt J Salomonsen M Simonsen L Du Pasquier R Parisot P Riegert 《Journal of immunology (Baltimore, Md. : 1950)》1990,144(6):2258-2272
Rabbit antisera raised to human and chicken MHC molecules were used to immunoprecipitate cross-reactive molecules from biosynthetically and cell surface-labeled spleen and/or blood cells of representative vertebrate species. Five major points emerged: 1) There were many nonspecific cross-reactions using these techniques, so various criteria were developed to distinguish these from true MHC-like molecules. 2) Only very small subpopulations of immunogen-specific antibodies cross-reacted with MHC-like molecules in other nonmammalian species. These subpopulations were different for each species and even within a species, sometimes being so limited as to behave like alloantisera. This led to a very scattered pattern of true cross-reactions that sometimes failed to reflect the properties of the bulk antibody population. 3) Antisera containing antibodies to class II beta- and class I alpha-chains cross-reacted better and more widely than those to B-G, class II alpha and, in general, beta 2-microglobulin. 4) Some cross-reactive antibodies were clearly directed to epitopes on the surface of the mature heterodimers, but many seemed to recognize nonlinear cryptic determinants, presumably in the contact regions between the chains. These latter antibodies recognized biosynthetic intermediates and also a variety of unusual cell surface MHC-like molecules present in reptile and amphibian, but absent in the mammal and chicken cells tested. These included E homodimers whose relationship to chicken B-G molecules is unknown. 5) MHC-like molecules were identified in a bird, three reptiles, and two amphibians, but no molecules with the expected properties were found with these reagents in any of the fish tested. 相似文献
24.
Charlotte L. Branchaud Cynthia G. Goodyer Harvey J. Guyda Yves Lefebvre 《In vitro cellular & developmental biology. Plant》1990,26(9):865-870
Summary We have compared hormone production by early gestation and term human placental trophoblasts cultured in Ham's F10 medium
containing 10% fetal bovine serum with that by cells cultured in serum-free HB102 medium. Mean daily production of progesterone
on Days 3 to 7 was approximately 25% less by both early gestation and term cells cultured in HB102 as compared to Ham's F10,
but production was maintained at a stable level for at least 7 d longer than the cells in Ham's. Estradiol production from
10−6
M dehydroepiandrosterone by both early gestation and term cells was comparable in both media. Human placental lactogen production
on Days 3 to 7 was 40% less by cells cultured in HB102. Human chorionic gonadotropin (hCG) output by early gestation cells
was also 50% less in HB102 but term cells in HB102 produced twice as much hCG as those in Ham's F10. 3B-Hydroxysteroid dehydrogenase
(3BHSD) activity in early gestation and term cells and 11B-hydroxysteroid dehydrogenase (11BHSD) activity of early gestation
cultures was comparable in the two media. 11BHSD activity was decreased in the term cultures, and this decrease was more marked
in Ham's than in HB102. Sulfatase and aromatase activities in the early gestation cultures were comparable in both media;
sulfatase activity was comparable and aromatase activity only 20% less in the term cells cultured in HB102. These results
indicate that serum-free HB102 supports differential function of human trophoblast cells and is useful for studies of placental
activity for as long as 14 d in culture. 相似文献
25.
The details of spermatogenesis and spermiogenesis are described forOphryotrocha puerilis. The ultrastructure of mature sperm is shown forO. puerilis, O. hartmanni, O. gracilis, O. diadema, O. labronica, andO. notoglandulata. Clusters of sixteen cells each are proliferated by two stem cells in each setigerous segment ofO. puerilis representing the very early stages of both oogenesis and spermatogenesis. In each spermatocyte-I cluster, the cells are interconnected
by cytoplasmic bridges. Early, clusters are enveloped by peritoneal sheath cells. These transient gonad walls break down prior
to meiosis. The meiotic processes may start in the clusters with the cells still interconnected, or during breakdown of the
original cluster, giving rise to smaller subclusters of both spermatocytes I and spermatocytes II with various numbers of
cells. Finally, spermatid tetrads are present. As spermiogenesis progresses, the tetrads disintegrate. Golgi vesicles in both
spermatocytes and spermatids contain electron-dense material, presumably preacrosomal. The acrosome is formed by such vesicles.
In the six species studied here, the acrosomes appear to be of a similar overall structure but are of different shape. Centrioles
are usually located beneath the acrosome. The distal centriole forms the basal body of a flagellum-like cytoplasmic process.
The microtubules of these flagellar equivalents do not show a normal ciliar arrangement. The flagellar equivalent appears
to be non-motile. InO. hartmanni and inO. notoglandulata, a flagellar equivalent is missing. Microtubules originating from the proximal end of the distal centriole stretch to the
nuclear envelope. This feature appears to be especially conspicuous inO. puerilis and inO. labronica. InO. labronica and inO. notoglandulata, bundles of microtubules paralleling the cell perimeter appear to stabilise the sperm. Various numbers of mitochondria are
either randomly distributed around the nucleus or accumulate on one side, often directly under the acrosome.
Parts of the present paper were presented at the 2nd International Polychaete Conference, Copenhagen 1986 and at the 3rd International Polychaete Conference, Long Beach, Ca. 1989. 相似文献
26.
In this study we describe a novel gene, which was isolated in an attempt to search for specific plant resistance genes of Arabidopsis against isolates of the phytopathogenic bacterium Xanthomonas campestris pv. campestris. The gene was cloned by differential screening of a genomic library of the Xcc 750-resistant ecotype Col-0, using cDNA populations derived from ecotype Col-0 and the Xcc 750-susceptible ecotype Oy-0. The isolated gene, CXc750, is differentially expressed in ecotypes of Arabidopsis thaliana. In addition, although highly expressed in uninfected plants, gene expression increases in response to pathogen attack.
CXc750 potentially codes for a small, basic protein of about 10 kDa. The predicted protein product contains a potential signal leader peptide at the amino-terminal end but no ER retention sequence and no further transmembrane domain. This indicates that the gene product is transported to other compartments or out of the cell.The possible function of CXc750 as a member of the plant defense response system is discussed. 相似文献
27.
Charlotte Poulsen Oscar J. M. Goddijn J. Harry C. Hoge Robert Verpoorte 《Transgenic research》1994,3(1):43-49
TransgenicNicotiana tabacum L. Petit Havana SR1 F1-plants expressing tryptophan decarboxylase cDNA (tdc) fromCatharanthus roseus (L.) G. Don under the control of the CaMV 35S promoter and terminator exhibited tryptophan decarboxylase (TDC) enzyme activity and accumulated tryptamine. The plants with the highest TDC activity contained 19 pkat per mg of protein. The influence of transgenic expression oftdc on the activities of anthranilate synthase (AS) and chorismate mutase (CM) were examined in 10 transgenic tobacco plants. The specific activities of these two chorismate-utilizing enzymes were not significantly affected by expression oftdc, despite their important functions as branch point enzymes in the shikimate pathway. The results indicate that the normal route of tryptophan biosynthesis in plants is sufficient to supply a considerable amount of this essential amino acid for the biosynthesis of secondary metabolites. Despite their increased tryptamine content, the growth and development of the transgenic tobacco plants expressingtdc appeared normal. 相似文献
28.
Marianne Schwartz Maria Anvret Mireille Claustres Hans Geir Eiken Kristin Eiklid Charlotte Schaedel Lisa Stolpe Lisbeth Tranebjærg 《Human genetics》1994,93(2):157-161
In a systematic screening for mutations in the gene encoding the cystic fibrosis transmembrane regulator among Danish cystic fibrosis (CF) patients, we identified a mutation in exon 3 (394delTT); this mutation was found to be relatively common in Denmark. We therefore screened for 394delTT in Sweden and Norway, where it turned out to be the second most frequent mutation, accounting for 4% of all CF mutations. It also occurs with a high frequency in Finland, but has not been found in larger surveys of mutations in the CFTR gene. Thus, 394delTT seems to be a specific Nordic CF mutation. 相似文献
29.
The influence of chromium concentration on ethylene production in bean plants ( Phaseolus vulgaris L. cv. Contender) was investigated. A Cr ion-induced inhibition of ethylene synthesis from endogenous 1-aminocyclopropane-1-carboxylic acid (ACC) was observed within both leaf discs floated on 2 m M CrO2− 4 or Cr3+ and leaf discs from plants cultured in nutrient solutions containing 10, 20 or 40 μ M CrO2− 4 . However, Cr ions supplied either to plants with the nutrient solution or to discs with the incubation medium rather increased the conversion of exogenous ACC to ethylene. Primary leaves of plants exposed to CrO2− 4 -containing nutrient solutions showed a statistically insignificant decrease of ACC-synthase activity. In the trifoliolate leaves of plants exposed to 10 μ M CrO2− 4 , in which a significant decrease of ethylene production from endogenous ACC was observed, a substantial increase of ACC synthase was found. These results indicate that Cr ion-induced inhibition of ethylene production is not due to a breakdown of membrane integrity, which is necessary for ethylene forming enzyme activity, but caused by metabolic alterations leading to decreased ACC availability. Chromium ions may act by inhibiting ACC synthase activity or by diverting a metabolic step prior to the ACC synthase catalyzed reaction. 相似文献
30.
Inger Kirstine Due Tuvesson Rebecka Charlotte Viktoria Öhlund 《Plant Cell, Tissue and Organ Culture》1993,34(2):163-167
Wheat microspores mechanically isolated from the anthers before culture and isolated from the anthers during the hole culture period in a chemically defined medium resulted in proembryos, embryos and finally plants. Of the four genotypes included, all responded with proembryos, and the two spring wheats Ciano and Walter gave rise to macroscopic embryos and plants. The frequency of embryo regeneration and the frequency of albino plants in both Ciano and Walter was in accordance with previously obtained results with anther culture derived material.Abbreviations 2,4-d
2,4-dichlorophenoxy acetic acid
- NAA
1-naphthaleneacetic acid 相似文献