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101.
Residual radiation injury was demonstrated in long-term primary cultures of mouse bone marrow. Control cultures underwent three phases of hematopoietic activity as distinguished by initial establishment, steady high (plateau) production of granulocytes, and gradual decline. Irradiation with 50, 300, or 550 rads, given at the end of the initial phase, did not prevent any culture flasks from entering the plateau phase. However, actual production levels and the time they were maintained varied inversely with the radiation dose so that the accumulated postradiation cell production corresponded to an exponential dose-response relationship at any time after treatment. The accumulated cell productions were found to be similar in all groups when expressed by the number of stem cell doublings necessary to produce them. The findings cannot be explained by reproductive cell death and are consistent with the notion of a limited division capacity in hematopoietic stem cells. 相似文献
102.
Ursula Meindl 《Protoplasma》1982,110(2):143-146
Summary Developing cells ofMicrasterias denticulata Bréb. show a characteristic fluorescence of the plasma membrane (or cortical protoplasm) after treatment with chlorotetracycline (CTC), which is known to be an indicator for membrane-bound Ca2+. Depending on the stage of development the fluorescing sites of the young half cell are distributed in a specific pattern which corresponds to cell pattern formation. Therefore growth and thus cytomorphogenesis inMicrasterias seem to be mediated by a patterned accumulation of Ca2+ at the periphery of the differentiating cell. Participation of Ca2+ in a membrane-recognition process responsible for local vesicle incorporation is discussed. 相似文献
103.
Ursula Meindl 《Protoplasma》1982,112(1-2):138-141
Summary During the stage of pore formation developing cells ofMicrasterias denticulata show a patterned distribution of fluorescent dots on the plasma membrane after treatment with chlorotetracycline. The center-to-center spacing of these dots corresponds with the distances between the individual cell wall pores ofMicrasterias. Therefore it is supposed that the patterned distribution of pores and their formation which is mediated by special pore vesicles are related to local accumulations of membrane-associated Ca2+. Membrane-associated Ca2+ seems not only to be functional in tip growth but to be a general mediator for recognition and fusion processes between various vesicles and the plasma membrane. 相似文献
104.
Klaus Lange Konrad Keller Wolf-Dieter Ludwig Ingrid Monden Ingeborg Reinsch Ursula Brandt 《Journal of neurochemistry》1982,39(6):1594-1600
Previous studies have revealed two different kinds of regulation of glucose utilization in cell lines derived from the nervous system (Keller et al., 1981). We found glucose metabolism of C-6 glioma cells to be limited and regulated by membrane transport. In contrast, glucose utilization of C-1300 neuroblastoma (N2A) cells was limited by the known regulatory enzymes of the Embden-Meyerhof pathway. Under the given experimental conditions the "membrane-limited" C-6 glioma cells were characterized by periodically changing glucose transport rates and very low intracellular glucose concentrations, which remained constant in spite of widely differing transport rates. These findings suggest the close functional coupling between transport and phosphorylation required for the regulation of glucose transport by cellular metabolic needs. 相似文献
105.
Unusual behaviour of SPO1 DNA with respect to restriction and modification enzymes recognizing the sequence 5''-G-G-C-C 总被引:7,自引:0,他引:7
John N. Reeve Egon Amann Ravindra Tailor Ursula Günthert Klaus Scholz Thomas A. Trautner 《Molecular & general genetics : MGG》1980,178(1):229-231
Summary SPO1 DNA contains only 5 cleavage sites for restriction enzymes which recognize and cleave the sequence 5-G-G-C-C (HaeIII or BsuR). Fragments of SPO1 DNA cloned in E. coli to substitute 5-hydroxymethyluracil (HMU) by thymine (T) remain resistant to HaeIII indicating that this unexpectedly small number of cleavages by HaeIII is not correlated with the presence of HMU in the normal phage DNA. It was previously shown that SPO1 is neither subject to B. subtilis R restriction (Trautner et al., 1974) nor modification in vivo (Günthert et al., 1975). We now show that SPO1 DNA can however be restricted and modified in vitro. 相似文献
106.
Michael L. McConnell Gerald Rhodes Ursula Watson Milos Novotný 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1979,162(4)
The applicability of threshold logic units, a form of nonparametric pattern recognition, to the processing of metabolic profile data obtained by high-efficiency glass capillary column gas chromatography has been investigated. The test data included profiles of the volatile constituents of urine from normal individuals and from individuals with diabetes mellitus. A feature extraction algorithm allowed for dimensionality reduction and indicated the constituents most important in the normal versus pathological distinction. With an optimum number of dimensions, a normal versus pathological prediction rate of 93.75% was achieved. Gas chromatography—mass spectrometry was utilized to identify important profile constituents. 相似文献
107.
Isolation and Genetic Analysis of Mutant Strains of CHLAMYDOMONAS REINHARDI Defective in Gametic Differentiation 总被引:1,自引:0,他引:1
Impotent mutant strains of Chlamydomonas reinhardi, mating-type (mt) plus, are described that have normal growth and motility but fail to differentiate into normal gametes. Procedures for their isolation and their genetic analysis are described. Five of the imp strains (imp-2, imp-5, imp-l, imp-7, and imp-8) exhibit no flagellar agglutination when mixed with mt- or mt+ gametes and the mutations are shown to be unlinked to the mt locus (with the possible exception of imp-7). Two of the strains (imp-3 and imp-4) carry leaky mutations that affect cell fusion; neither mutation is found by tetrad analysis to be linked to mt or to the other. Cells of the imp-1 strain agglutinate well with mt- gametes and active agglutination continues for up to 48 hours, but cell fusion occurs only very rarely. Analysis of these rare zygotes indicates that imp-1 is closely linked to the mt+ locus, and fine-structural studies reveal that imp-1 gametes produce a mutant mating structure involved in zygotic cell fusion. The development of sexuality in C. reinhardi therefore appears amenable to genetic dissection. 相似文献
108.
109.
Hassan-Fahmi Aly Hans Geiger Ursula Schücker Hugh Waldrum George Vander Velde Tom J. Mabry 《Phytochemistry》1975,14(7):1613-1615
Ten glycosides of kaempferol and quercetin, including the hitherto unknown kaempferol and quercetin 3-rutinoside-7-rhamnosides, have been isolated from Equisetum silvaticum L. 相似文献
110.