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991.
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
992.
Kirstin Schultze Klaus Janke Andreas Krüß Wolfgang Weidemann 《Helgoland Marine Research》1990,44(1):39-51
This paper describes the macroflora and macrofauna associated with two bull kelp species,Laminaria hyperborea andL. digitata, at the island of Helgoland, North Sea. During a study period of seven months (March–September 1987), 29 macroflora species
and 125 macrofauna species were found. The dominant taxonomic groups were Polychaeta (25 species), Bryozoa (17), Amphipoda
(14), Hydrozoa (10) and Ascidiae (8). The species maximum was in July. In general,L. hyperborea was preferred as a substrate for settlement toL. digitata. Composition of the communities associated with kelp changed during the season according to exposure to wave action, and
according to location on the kelp thallus. The rhizoid community of both kelps bore more species at exposed locations. Wave-exposedL. digitata lacked obvious faunal settlement on both phylloid and cauloid. Phylloid and cauloid ofL. hyperborea were chosen as an attractive substrate at both sheltered and wave-exposed locations, showing an association of encrusting
bryozoan and hydrozoan colonies. 相似文献
993.
Malamoeba scolyti (Purrini), ein Parasit im Verdauungstrakt des BorkenkäfersDryocoetes autographus (Ratz.), schmarotzt intrazellulär in bestimmten Abschnitten des Mitteldarmepithels und im Epithel der Malpighischen Gefä\e. Sie zerstört die befallenen Epithelzellen, wobei sie sich bis zum zystenstadium entwickeln kann. in umfangreichen Infektionsexperimenten wird gezeigt, daß die Infektion in den vordersten Krypten des Mitteldarms beginnt und sich in mehreren Infecktionswellen bis zu den hintersten Darmdivertikeln und den Malpighischen Gefäßen ausbreitet. Bei 20° Dauertemperatur nimmt die Erstinfektion etwa 6 Tage, der gesamte Krankheitsverlauf bis zum Exitus des Wirtes 5 bis 7 Wochen in Anspruch. Im Gegensatz zu anderen Beschreibungen konnte nur eine einzige Form von Trophozoiten beobachtet werden. Auf die mögliche Bedeutung dieses Umstandes für die taxonomische Identität der Amöbe wird hingewiesen. 相似文献
994.
995.
The complete larval development of the porcellanid crabNeopisosoma negluctum Werding, 1986, was studied under laboratory conditions. At 27°C, the megalopa appeared after 9 days. The development consists
of a transitory prezoea, two zoeal stages and a megalopa stage. The larvae exhibit telsonal features which places them in
thePetrolisthes-group of porcellanid larvae. Larval morphology gives no additional support for the status ofNeopisosoma as an independent genus. 相似文献
996.
Alexandra Marinets Miklós Müller Patricia J. Johnson Jaroslav Kulda Otto Scheiner Gerhard Wiedermann Michael Duchêne 《Journal of molecular evolution》1996,43(6):563-571
Among the unicellular protists, several of which are parasitic, some of the most divergent eukaryotic species are found. The evolutionary distances between protists are so large that even slowly evolving proteins like histones are strongly divergent. In this study we isolated cDNA and genomic histone H3 and H4 clones fromTrichomonas vaginalis. Two histone H3 and three histone H4 genes were detected on three genomic clones with one complete H3 and two complete H4 sequences. H3 and H4 genes were divergently transcribed with very short intergenic regions of only 194 bp, which containedT. vaginalis-specific as well as histone-specific putative promoter elements. Southern blot analysis showed that there may be several more histone gene pairs. The two complete histone H4 genes were different on the nucleotide level but encoded the same amino acid sequence. Comparison of the amino acid sequences of theT. vaginalis H3 and H4 histones with sequences from animals, fungi, and plants as well as other protists revealed a significant divergence not only from the sequences in multicellular organisms but especially from the sequences in other protists likeEntamoeba histolytica, Trypanosoma cruzi, andLeishmania infantum. 相似文献
997.
DNA encapsidation by viruslike particles assembled in insect cells from the major capsid protein VP1 of B-lymphotropic papovavirus. 总被引:5,自引:2,他引:3
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Capsids of polyomaviruses--small, nonenveloped DNA viruses--consist of the major structural protein VP1 and the minor structural proteins VP2 and VP3. The contributions of the individual capsid proteins to functions of the viral particle, such as DNA encapsidation, cell receptor attachment, entry, and uncoating, are still not clear. Here we show that viruslike particles assembled in nuclei of insect cells from VP1 of the monkey B-lymphotropic papovavirus (LPV) are sufficient to unspecifically encapsidate DNA. LPV VP1 expressed in large amounts in insect cells by a baculovirus vector assembled spontaneously in the nuclei to form viruslike particles. After metrizamide equilibrium density gradient purification and nuclease digestion, a fraction of these particles was shown to contain VP1-associated linear, double-stranded DNA with a predominant size of 4.5 kb. The fraction of DNA-containing VP1 particles increased with time and dose of baculovirus vector infection. The DNA-containing particles, further purified by sucrose gradient centrifugation, appeared as "full" particles in negative-staining electron microscopy. As shown by DNA hybridization, the encapsidated DNA consisted of insect cell and baculoviral sequences with no apparent strong homology to LPV sequences. Three non-LPV VP1-derived host proteins with apparent molecular masses of approximately 14, 15, and 16 kDa copurified with the DNA-containing particles and may represent insect cell histones encapsidated together with the DNA. A similar species of host DNA was also found in purified LPV wild-type virions. These data suggest that LPV VP1 alone can be sufficient to encapsidate linear DNA in a sequence-independent manner. 相似文献
998.
Our cytological analysis revealed high proportions of XX males in some housefly populations of Turkey. In contrast to earlier findings in Europe, on the British Islands, and in Japan, the XX male frequency in Turkey was not correlated to the geographical latitude. In general, the frequency of XX males was lower in populations from the central and eastern Anatolian highlands than from coastal regions, demonstrating a correlation of the sex-determining mechanisms to geographical altitude and perhaps other geographical characteristics. 相似文献
999.
This paper summarizes the processing of small enchytraeid species for cinematographic documentation and covers the main details of a film on their locomotion, food uptake, anatomy and reproductive biology. This includes copulation, shedding of the cocoon and hatching of the young, characteristic reproductive patterns for all clitellate worms. 相似文献
1000.
Maleylacetate reductases in chloroaromatic-degrading bacteria using the modified ortho pathway: comparison of catalytic properties. 总被引:1,自引:1,他引:0
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The maleylacetate reductases from Pseudomonas aeruginosa RHO1 and Alcaligenes eutrophus JMP134 were tested for activity and affinity to various maleylacetates as well as dechlorinating properties. The dechlorinating activity and the kcat/Km values revealed high-level similarity of these reductases to that of Pseudomonas sp. strain B13. 相似文献