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排序方式: 共有217条查询结果,搜索用时 31 毫秒
1.
2.
M J Olszewska H Kuran B Damsz K Marciniak 《Folia histochemica et cytobiologica / Polish Academy of Sciences, Polish Histochemical and Cytochemical Society》1987,25(1):69-77
Experimental model consisted in blocking cells in G1 phase by cold treatment (12 h, 10 degrees C); following 3 h of postincubation at 20 degrees C, cells initiated S phase. In the present studies it has been shown that 2 h postincubation at 20 degrees C of cold-treated young seedlings of Helianthus annuus L. results in transformation of inactive meristematic nucleoli, characterized by small sizes, reduced amount of dry mass and granular component and by the presence of few and large fibrillar centres into large active nucleoli displaying high dry mass and granular component contents, numerous and small fibrillar centres. After 3 h of postincubation at 20 degrees C, nucleoli lose their granular component, decrease in size and dry mass content. At this moment cytoplasm enriches in ribosomes and its dry mass increases. Maximum of nucleolar activity is preceded by an accumulation of proteins in nucleoli. It is concluded that an enhanced transport of ribosomes is one of the conditions of S phase initiation. 相似文献
3.
Résumé Les granulations qui constituent les structures les plus primitives de la plaque cellulaire contiennent des enzymes hydrolytiques caractéristiques pour les sphérosomes de la cellule végétale; la plupart de ces enzymes sont présentes dans les lysosomes de la cellule animale. Dans les granulations de la plaque cellulaire nous avons constaté l'activité des enzymes suivantes: estérases non spécifiques, lipases, phosphatases acide et alcaline, aryl-sulfatase, désoxyribonucléase acide et probablement-glucuronidase. Le caractère chimique et morphologique de ces granulations, ainsi que leur équipement enzymatique correspondent aux sphérosomes.Dans la littérature les images de la cytocinèse au microscope électronique étant divergentes, le problème de l'origine et de la nature des granulations en question ne peut pas être pour le moment totalement résolu.
Zusammenfassung Die Körnchen, die die ursprünglichen Strukturen der Zellplatte bilden, enthalten die hydrolytischen Enzyme, die für die Sphärosomen der pflanzlichen Zelle und meistens für die Lysosomen der tierischen Zelle charakteristisch sind. Es sind die folgenden Enzyme: Esterasen (nicht spezifisch), Lipasen, saure Phosphatase, Aryl-sulfatase, saure Desoxyribonuklease und-Glukuronidase. Außerdem enthalten diese Körnchen die alkalische Phosphatase. Der morphologische und chemische Charakter dieser Körnchen und ihr enzymatischer Inhalt entsprechen den Sphärosomen.Wegen großer Unterschiede der in der Literatur vorhandenen Beschreibungen der Zellplatte in elektronenmikroskopischen Bildern kann das Problem der Entstehung und der Natur dieser Körnchen zur Zeit nicht völlig entschieden werden.相似文献
4.
We have broadly defined the DNA regions regulating esterase6 activity in
several life stages and tissue types of D. melanogaster using P-
element-mediated transformation of constructs that contain the esterase6
coding region and deletions or substitutions in 5' or 3' flanking DNA.
Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and
the primary sequences regulating its activity lie between -171 and -25 bp
relative to the translation initiation site: deletion of these sequences
decrease activity approximately 20-fold. Hemolymph activity is also
modulated by four other DNA regions, three of which lie 5' and one of which
lies 3' of the coding region. Of these, two have positive and two have
negative effects, each of approximately twofold. Esterase6 activity is
present also in two male reproductive tract tissues; the ejaculatory bulb,
which is another ancestral activity site, and the ejaculatory duct, which
is a recently acquired site within the melanogaster species subgroup.
Activities in these tissues are at least in part independently regulated:
activity in the ejaculatory bulb is conferred by sequences between -273 and
-172 bp (threefold decrease when deleted), while activity in the
ejaculatory duct is conferred by more distal sequences between -844 and
-614 bp (fourfold decrease when deleted). The reproductive tract activity
is further modulated by two additional DNA regions, one in 5' DNA (-613 to
-284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to
+2731 bp; threefold decrease when deleted) that probably overlaps the
adjacent esteraseP gene. Collating these data with previous studies
suggests that expression of EST6 in the ancestral sites is mainly regulated
by conserved proximal sequences while more variable distal sequences
regulate expression in the acquired ejaculatory duct site.
相似文献
5.
Litman GW; Rast JP; Shamblott MJ; Haire RN; Hulst M; Roess W; Litman RT; Hinds- Frey KR; Zilch A; Amemiya CT 《Molecular biology and evolution》1993,10(1):60-72
Immunoglobulins are encoded by a large multigene system that undergoes
somatic rearrangement and additional genetic change during the development
of immunoglobulin-producing cells. Inducible antibody and antibody-like
responses are found in all vertebrates. However, immunoglobulin possessing
disulfide-bonded heavy and light chains and domain-type organization has
been described only in representatives of the jawed vertebrates. High
degrees of nucleotide and predicted amino acid sequence identity are
evident when the segmental elements that constitute the immunoglobulin gene
loci in phylogenetically divergent vertebrates are compared. However, the
organization of gene loci and the manner in which the independent elements
recombine (and diversify) vary markedly among different taxa. One striking
pattern of gene organization is the "cluster type" that appears to be
restricted to the chondrichthyes (cartilaginous fishes) and limits
segmental rearrangement to closely linked elements. This type of gene
organization is associated with both heavy- and light-chain gene loci. In
some cases, the clusters are "joined" or "partially joined" in the germ
line, in effect predetermining or partially predetermining, respectively,
the encoded specificities (the assumption being that these are expressed)
of the individual loci. By relating the sequences of transcribed gene
products to their respective germ-line genes, it is evident that, in some
cases, joined-type genes are expressed. This raises a question about the
existence and/or nature of allelic exclusion in these species. The
extensive variation in gene organization found throughout the vertebrate
species may relate directly to the role of intersegmental
(V<==>D<==>J) distances in the commitment of the individual
antibody-producing cell to a particular genetic specificity. Thus, the
evolution of this locus, perhaps more so than that of others, may reflect
the interrelationships between genetic organization and function.
相似文献
6.
Summary Chromatin-like structures have been observed in material extracted from the mitochondria of Paramecium aurelia and evidence is presented which establishes that these structures do not originate from nuclear contamination of mitochondrial preparations but are exclusively of mitochondrial origin. Extraction of these chromatin-like structures with dilute acid followed by gel electrophoresis of the extract shows the presence of five major basic proteins which are of similar electrophoretic mobility to histones. Digestion of mitochondrial extracts with endogenous nuclease, followed by electrophoresis of the extracted DNA, demonstrated that the mitochondrial genome is protected from nuclease digestion by regular repeating units very similar to those observed in the nuclease digestion of chromatin.This research was supported by a postgraduate studentship from University of Edinburgh to E. Olszewska and by the Science Research Council. 相似文献
7.
Summary Activities of DNA polymerases and RNA polymerases were studied by autoradiographic methods in growing and differentiating root cortex cells ofZea mays — a species in which endomitosis occurs — andTulipa kaufmanniana — in which this process does not occur. InTulipa kaufmanniana, the highest activity of DNA polymerase appears in the nuclei of meristematic zone during the S phase of the cell cycle. InZea mays, endomitotic replication of DNA occurs in all growth and differentiation zones and the activity of DNA polymerase in the nuclei is similar to that in the meristematic zone. In both species, nuclear RNA synthesis, measured with3H uridine incorporation, is highest in the meristematic zone and declines steadily with development. Activity of nuclear RNA polymerase is present in all developmental zones in both species and is similar to that in the meristematic zone.3H uridine incorporation into nucleoli decreases markedly in both species, whereas the activity of nucleolar RNA polymerase remains at a high level in all root segments inZea mays and decreases slightly inTulipa kaufmanniana.It is argued that the differences between the incorporation of3H uridine and that or3H UMP may be caused by a reduction of the pool of endogenous ribonucleoside triphosphates. Marked activities of DNA polymerase and RNA polymerase in cytoplasm are possibly related to the growth and division of plastids and mitochondria. 相似文献
8.
M J Olszewska A Bilecka H Kuran K Marciniak R Osiecka 《Folia histochemica et cytobiologica / Polish Academy of Sciences, Polish Histochemical and Cytochemical Society》1989,27(2):107-112
In root meristems of 3 species (Secale cereale L., Vicia faba L. subsp. minor, Allium cepa L.) the durations of cell cycles and their phases were calculated using 3H-thymidine labelling. In the above species and in Helianthus annuus L. (parameters of the cell cycle determined earlier) the G1 and G2 phase durations were different: G1 + 1/2 M from 3 h to 6.1 h, G2 + 1/2 M from 1.1. h to 8.3 h, depending on the species. The rate of rRNA transport from nucleoli into cytoplasm during recovery after cold treatment was calculated from our data presented earlier. The results indicate that in 4 species studied there is no correlation (at P = 0.05) between the rate of rRNA transport and the duration of G1 and G2 phases. 相似文献
9.
Schistosomiasis vector snails are subjected to extreme seasonal changes, particularly in ephemeral rivers and lentic waterbodies. In the tropics, aestivation is one of the adaptive strategies for survival and is used by snails in times of extremely high temperatures and desiccation. Aestivation therefore plays an important role in maintaining the transmission of schistosomiasis. This review assesses the possible impacts of climate change on the temporal and spatial distribution of schistosomiasis-transmitting snails with special emphasis on aestivation, and discusses the effect of schistosome infection on aestivation ability. The impacts of parasite development on snails, as well as physiological changes, are discussed with reference to schistosomiasis transmission. This review shows that schistosome-infected snails have lower survival rates during aestivation, and that those that survive manage to get rid of the infection. In general, snail aestivation ability is poor and survival chances diminish with time. Longer dry periods result in fewer, as well as uninfected, snails. However, the ability of the surviving snails to repopulate the habitats is high. 相似文献
10.
Katarzyna Ciach Marek Niedoszytko Anna Abacjew-Chmylko Izabela Pabin Przemyslaw Adamski Katarzyna Leszczynska Krzysztof Preis Hanna Olszewska Dariusz G. Wydra Rita Hansdorfer-Korzon 《PloS one》2016,11(1)