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1.
Helge A. Thomsen Kurt R. Buck Susan L. Coale Dave L. Garrison Marcia M. Gowing 《Nordic Journal of Botany》1988,8(4):419-436
The examination of whole mounts prepared for transmission electron microscopy has resulted in the finding of thirteen taxa of nanoplanktonic coccolithophorids from the Weddell Sea, Antarctica. The material was collected as part of the AMERIEZ programme, March 1986. Cold-water adapted nanoplanktonic coccolithophorids have previously been shown to constitute a recurrent plankton element at subarctic and arctic localities. Three of the Weddell Sea species, Wigwamma annulifera, W. arctica , and Papposphaera sagittifera , are conspecific with northern hemisphere material, while two species, Calciarcus alaskensis and Turrisphaera arctica , are possibly identical with previously described arctidsubarctic material. Six taxa new to science have been described from the Weddell Sea, Wigwamma antarctica, W. triradiata, Trigonaspis melvillea, Pappomonas weddellensis, Papposphaera obpyramidalis , and P. simplicissima . The cooccurrence of identical forms at the two poles, and the fact that the species described are allocated to "arctic" genera, indicate a geologically relatively recent exchange of biological material between the poles. 相似文献
2.
Abstract Subinhibitory concentrations of trimethoprim-sulfamethoxazole increased the total yield of Shiga-like toxin (SLT), produced by Shigella dysenteria 1 and by enterophathogenic and enterohemorrhagic strains of Escherichia coli . Stimulation of SLT synthesis by trimethoprim-sulfamethoxazole was demonstrated by an increase in cytotoxic activity for HeLa cells and the diameter of the zone formed around bacterial colonies probed with monoclonal antibodies to SLT. Thus, supplementation of culture media with trimetroprimsulfamethoxazol will facilitate SLT purification and detection of SLT-producing bacteria. 相似文献
3.
Helge Klaus Körner 《Cell and tissue research》1969,100(3):466-473
Summary Two types of bacterial symbionts (a- and t-types) were present intracellularly in embryos of the leafhopperEuscelis plebejus. In the electron microscope, three unit membranes were seen to surround the bacteria; the two inner membranes appeared to originate from the bacteria, the outer — from the host cytoplasm. DNA-structures were not observed in the symbionts. The a-symbionts contained in their cytoplasm crystalloid bodies presumably of protein nature and, during certain stages of embryonic development, tubular membranous bodies. The t-symbionts contained in their cytoplasm chymotrypsin-resistant dense bodies, that probably invade the host cytoplasm.Zusammenfassung Das elektronenmikroskopische Bild der intrazellulären a- und t-Symbionten vonEuscelis plebejus Fall. läßt erkennen, daß die symbiontischen Bakterien von drei Elementarmembranen umgeben sind. Morphologische Gründe sprechen dafür, daß die beiden inneren den Bakterien entstammen, die äußere Hüllmembran aber vom Cytoplasma der Wirtszelle gebildet wird. Bakterien-DNS konnte noch in keinem der beiden Symbiontentypen mit Sicherheit nachgewiesen werden. Die a-Symbionten sind vor Aufnahme in die Mycetocyten reich an tubulären Membrankörpern. Sie enthalten außerdem einen mit Chymotrypsin auflösbaren kristallinen Körper. In den t-Symbionten befinden sich Chymotrypsin-resistente dense bodies, die wahrscheinlich in das Wirtscytoplasma abgegeben werden.
Mit Unterstützung durch Mittel der Deutschen Forschungsgemeinschaft, die Herrn Prof. Dr.K. Sander zur Verfügung standen. 相似文献
Mit Unterstützung durch Mittel der Deutschen Forschungsgemeinschaft, die Herrn Prof. Dr.K. Sander zur Verfügung standen. 相似文献
4.
Transduction of a Plasmid Carrying the Cohesive End Region from Lactococcus lactis Bacteriophage ΦLC3 下载免费PDF全文
Plasmids carrying the cohesive end region from temperate lactococcal bacteriophage ΦLC3 could be packaged in vivo by ΦLC3 and transduced into its host strain, Lactococcus lactis subsp. cremoris NCDO 1201. The transduction frequencies were between 10-4 and 10-3 transducing particles per PFU, depending on the size of the phage DNA insert. This transduction system is limited to only certain lactococcal strains. The ΦLC3 cohesive site region (cos) appears to play an important role in plasmid transduction. 相似文献
5.
Mycorrhizal and nonmycorrhizal roots of Allium schoenoprasum were tested for activities of α-mannosidase, β-glucosidase and arabinosidase. Mannosidase activity was higher by a factor
of two in mycorrhizal than in nonmycorrhizal root extracts. The apparent molecular weight of the enzyme was 152 kDa and its
KM was 1.25 mM in colonized roots and 1.85 mM in uncolonized roots. α-Mannosidase activity was further characterized by an acid
pH optimum and Zn2+ dependency. No significant differences could be found between mycorrhizal and nonmycorrhizal roots for β-glucosidase and
arabinosidase activities.
Accepted: 28 August 1995 相似文献
6.
Summary Single primary cilia are found in developing as well as mature ciliated cells of guinea-pig tracheal epithelium. A few biciliated cells were observed, and in a rare case one cell had developed four such processes. Primary cilia are characterized by a 9 + 0 microtubular arrangement near the base, while a transition to an 8 + 1 pattern occurs at a slightly more distal position. Spokes are lacking, and dynein arms are absent or incompletely developed. The function, if any, of primary cilia remains unknown.In the population of the motile 9 + 2 cilia atypical forms are very rare, i.e. <0.1%. Of the various abnormalities cilia with supernumary microtubules are most common. Only one atypical basal body was observed. Although some of the aberrant forms undoubtedly are non-motile, their very low number suggests that they have no practical influence on the muco-ciliary clearance.Local extrusions of the ciliary membrane, here named ciliary knobs, are believed to be fixation artefacts. It is suggested that they represent circumscribed regions of the ciliary membrane which are sensitive to changes in the environmental osmotic pressure. 相似文献
7.
Summary Under histochemical conditions (fresh frozen sections from liver, kidney and cerebellum of the rat) it was shown that the oxidation of L-glutamic acid was carried out by the NAD-dependent L-glutamate dehydrogenase (E.C. 1.4.1.2) and/or the NAD- or NADP-dependent L-glutamate dehydrogenase (E.C. 1.4.1.3) as well as by an enzyme system which is not dependent on externally added NAD, NADP, FAD, FMN or CoQ10 for activity.This non-pyridine dependent activity was related to the L-glutamate dehydrogenases proper, owing to the following: a) the localization of activity noticed corresponds to that obtained with the NAD- or NADP-containing media, b) the incubation time needed for initial formation of red and blue formazans is similar to that with coenzyme-containing media, c) pre-extraction experiments reveal similarity in enzyme diffusion rates, d) the named activity is influenced by the same agents and to the same extent as the activity obtained by the inclusion of NAD or NADP (e.g. dissociation of the dehydrogenase molecule into subunits due to urea, inhibition of activity due to N-ethyl maleimide and 1.10-phenanthroline, activation due to the allosteric effect of ADP and to high substrate concentration, allosteric inhibition caused by GTP and inhibition caused by -ketoglutaric acid, no inhibitory effect of KCN), and e) the named activity was not affected by added PMS (excluding activity due to L-aminoacid oxidase).In the in situ localization of enzyme activity it was found that L-glutamate dehydrogenases E.C. 1.4.1.2 and E.C. 1.4.1.3 co-exist in the cells of kidney and cerebellum, while the L-glutamate dehydrogenase E.C. 1.4.1.3 only was present in liver cells.Finally, it was stated that incubation time should be kept as short as possible in order to avoid Nothing dehydrogenase reaction as well as inhibition due to accumulation of -ketoglutaric acid. Only gel incubation media should be applied.Recipient of a research grant from the Danish Ministry of Education 相似文献
8.
9.
Syntenic relationships between Medicago truncatula and Arabidopsis reveal extensive divergence of genome organization 总被引:4,自引:0,他引:4 下载免费PDF全文
Zhu H Kim DJ Baek JM Choi HK Ellis LC Küester H McCombie WR Peng HM Cook DR 《Plant physiology》2003,131(3):1018-1026
Arabidopsis and Medicago truncatula represent sister clades within the dicot subclass Rosidae. We used genetic map-based and bacterial artificial chromosome sequence-based approaches to estimate the level of synteny between the genomes of these model plant species. Mapping of 82 tentative orthologous gene pairs reveals a lack of extended macrosynteny between the two genomes, although marker collinearity is frequently observed over small genetic intervals. Divergence estimates based on non-synonymous nucleotide substitutions suggest that a majority of the genes under analysis have experienced duplication in Arabidopsis subsequent to divergence of the two genomes, potentially confounding synteny analysis. Moreover, in cases of localized synteny, genetically linked loci in M. truncatula often share multiple points of synteny with Arabidopsis; this latter observation is consistent with the large number of segmental duplications that compose the Arabidopsis genome. More detailed analysis, based on complete sequencing and annotation of three M. truncatula bacterial artificial chromosome contigs suggests that the two genomes are related by networks of microsynteny that are often highly degenerate. In some cases, the erosion of microsynteny could be ascribed to the selective gene loss from duplicated loci, whereas in other cases, it is due to the absence of close homologs of M. truncatula genes in Arabidopsis. 相似文献
10.
Dawid Brat Christian Weber Wolfram Lorenzen Helge B Bode Eckhard Boles 《Biotechnology for biofuels》2012,5(1):1-16