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1.
Summary Mitotic divisions during sporangiogenous plasmodial cleavage in Woronina pythii were studied with transmission electron microscopy. We conclude that these nuclear divisions ( e.g., transitional nuclear division, and sporangial mitoses) share basic similarities with the cruciform nuclear divisions in W. pythii and other plasmo-diophoraceous taxa. The major distinction appeared to be the absence of nucleoli during sporangial mitosis and the presence of nucleoli during cruciform nuclear division. The similarities were especially evident with regard to nuclear envelope breakdown and reformation. The mitotic divisions during formation of sporangia were centric, and closed with polar fenestrae, and characterized by the formation of intranuclear membranous vesicles. During metaphase, anaphase, and telophase, these vesicles appeard to bleb from the inner membrane of the original nuclear envelope and appeared to coalesce on the surface of the separating chromatin masses. By late telophase, the formation of new daughter nuclear envelopes was complete, and original nuclear envelope was fragmented. New observation pertinent to the mechanisms of mitosis in the Plasmodiophoromycetes include a evidence for the incorporation of membrane fragments of the original nuclear envelope into new daughter nuclear envelopes, and b the change in orientation of paired centrioles during sporangial mitosis. 相似文献
2.
Vegetative nuclear division in Ceratocystis fagacearum (Bretz) Hunt was found to differ from classical mitosis in that: (1) division always occurs perpendicular to the longitudinal axis of the cell, (2) anaphase movement is unilateral and unsynchronized, (3) a spindle occurs only between separating chromatids. Interphase and prophase nuclei and nucleoli are morphologically similar to those in higher plants. At metaphase the associated chromosomes form a bar of chromatin and lie against the hyphal wall. Spindle fibers appear between separating chromatids, perhaps pushing them apart. When nuclear division is complete the nuclei become attenuated and migrate. Vegetative nuclear division in C. fagacearum may be an evolutionary form of classical mitosis. 相似文献
3.
During conjugation of Paramecium caudatum, there are two well-known stages when nuclear migration occurs. What happens to the nuclei is closely related to their localisations in cells. The first of these stages is the entrance of one meiotic product into the paroral region. This nucleus survives, while the remaining three outside this area degenerate. The second stage is the antero-posterior localisation of eight synkaryon division products. Four posterior nuclei are differentiated into macronuclear anlagen, whereas four anterior nuclei remain as the presumptive micronuclei. In this experiment, the process of the third prezygotic division of P. caudatum was studied with the help of protargol staining. Here, a third nuclear migration was discovered. By two spindle turnings and two spindle elongations, stationary pronuclei were positioned near migratory pronuclei. This positioning of stationary pronuclei could shorten the distance for transferred migratory pronuclei to recognise and reach the stationary pronuclei. This fosters the synkaryon formation of P. caudatum. 相似文献
4.
This paper reports new observations obtained from a study of macronuclear fine structure throughout various stages of the cell division cycle of Euplotes. Study of the ultrastructural organization of the macronuclear chromatin indicates that much of the chromatin is organized into continuous masses, portions of which appear to be attached to the nuclear envelope. The macronuclear envelope appears unchanged in the region of a replication band, and apparent attachments of the chromatin to the inner membrane of the nuclear envelope are maintained in the reticular and diffuse zones. Intranuclear helices were never observed in the diffuse zone. During macronuclear division, linear elements (fibrils or microtubules) were observed in close association with both chromatin bodies and nucleoli. The ultrastructural data suggest that the intranuclear linear fibrils have two functions: elongation of the dividing nucleus, and attachment of chromatin bodies and nucleoli to the envelope. The significance of these observations for macronuclear division and chromatin segregation is considered. 相似文献
5.
Summary In gemmae of Vittaria graminifolia and prothallia of Onoclea sensibilis, cell differentiation is initiated by nuclear migration and geometrically asymmetric cell division. The small daughter cells in Vittaria develop into antheridia in the presence of gibberellic acid or into rhizoids or new prothallia in its absence. Antheridial differentiation from asymmetric division is induced in Onoclea by Pteridium antheridiogen, whereas rhizoid or vegetative cell formation occurs in its absence. Although asymmetric cytokinesis initiates differentiation, it does not in itself determine the developmental fate of the smaller cell. Several histochemical techniques demonstrate that prior to nuclear migration and cell division, Ca 2+ accumulates in the cytoplasm and wall of the cell at the site where asymmetric division will occur, regardless of the developmental fate of the small cell. The cytoplasmic localization of Ca 2+ appears to reflect a mobilization of Ca 2+ from within the cell that eventually moves into the cell wall. We propose that this internal accumulation of Ca 2+ leads to a localized decrease in cytosolic [Ca 2+] which in turn may regulate developmental events such as nuclear migration.Publishing prior to 1984 as Alix R. Bassel. 相似文献
6.
Summary At concentrations that did not affect growth, hydroxyurea and 2 1-deoxyadenosine inhibited DNA synthesis in Chlamydomonas. Evidence that initiation of mitosis is dependent upon completion of DNA replication was provided by the arrest of inhibited cells with undivided nuclei containing undispersed nucleoli. Initiation of cytokinesis is not dependent upon progress of nuclear division since, in arrested cells, cleavage microtubules became deployed in a phycoplast and a cleavage furrow developed fully, until obstructed by the undivided nucleus. Chloroplast constriction and division also continued independently of nuclear division. It is concluded that nuclear division, cytoplasmic cleavage and chloroplast division are in separate sequences of dependent events. This is supported by flexibility of their relative timing in successive divisions, since after the first commitment to divide nuclear division is followed by initiation of cleavage and then chloroplast division, whereas following subsequent commitments these events occur in reverse time order. This flexibility of order indicates changing rates of progress through separate sequences of events.Deposition of wall material was dependent upon the completion of cytokinesis, but this inhibition of wall deposition by incomplete cytokinesis did not extend to other daughters within the same mother cell.These observations are correlated with our earlier data concerning the rate-limiting control points for division and a model for the coordination of division events is presented. The relationships between different plant cell cycles is discussed in view of the findings presented. 相似文献
7.
Centrifugation of living Amoeba proteus labeled with 3H-thymidine permits the identification by electron microscopic radioautography of chromatin in the interphase nucleus by segregating (through centrifugation-induced stratification) the relatively dilute chromatin from the remainder of the nuclear contents. This procedure reveals that the bulk of the chromatin is in the form of a network of 800 to 900 Å fibrils that are moved by centrifugation to a region just centripetal to the rapidly sedimenting nucleoli. — There is a surprising absence of 3H-thymidine labeling associated with the numerous A. proteus nucleoli, raising the possibility that in this organism the genes specifying ribosomal RNA are non-nucleolar. 3H-thymidine label also is absent from nuclear helixes, membranes, and all other recognizable nuclear regions. 相似文献
9.
The nuclear cytology of 9 strains of Sirogonium is described. The interphase nucleus contains 1–3 nucleoli, a nucleolar-organizing track, and many (>100) chromocenters. During the division cycle the nucleoli are transformed into a nucleolar substance which becomes associated with the chromosome and is transported through mitosis on the chromosomes. All strains possess minute dot chromosomes varying in length at metaphase from 0.5 to 1.5 μ; satellite chromosomes are 2.5–3.5 μ long. The number of chromosomes varies from 48 ± 2 to 100 ± 2. No evidence of centromeric activity was observed. 相似文献
10.
Immunofluorescence staining with antisera raised against p35, a basic nuclear protein that accumulates in the pollen nuclei
of Lilium longiflorum, specifically stained the nucleoli in interphase nuclei of somatic tissues, including root and leaf, and in pachytene nuclei
during meiotic division, whereas antisera raised against histone H1 uniformly stained the entire chromatin domain with the
exception of the nucleoli in these nuclei. Further, p35-specific antisera stained the nucleoli in root and leaf nuclei of
the monocotyledonous plants Tulipa gesneriana, Allium cepa and Triticum aestivum and of the dicotyledonous plants Vicia faba and Nicotiana tabacum. Thus, these novel antisera stained the nucleoli in cells of all higher plants examined, although the staining patterns within
nucleoli were somewhat different among plant species and tissues. The full-length cDNA of p35 was cloned on the basis of the
partial amino acid sequence. The deduced amino acid composition and amino acid sequence of p35 indicate that this nucleolar
protein is a novel variant of histone Hl. Further, p35 was strongly bound to ribosomal DNA in vitro. The results of immunoblotting
of histones extracted from each tissue of the various plant species with the nucleolus-specific antibodies also suggested
the conservation of similar epitope(s) in both mono- and dicotyledonous plants. From these results, it is suggested that similar
variants of histone Hl are specifically distributed in the nucleoli of all plant species and help to organize the nucleolar
chromatin.
Received: 25 November 1998; in revised form: 31 January 1999 / Accepted: 10 February 1999 相似文献
11.
Cell division in the marine red algae Polysiphonia harveyi Bailey and P. denudata (Dillwyn) Kutzing was studied with the electron microscope. Cells comprising the compact spermatangial branches of male plants were used exclusively because of their small size, large numbers and the ease with which the division planes can be predetermined. Some features characterizing mitosis in Polysiphonia confirm earlier electron microscope observations in Membranoptera, the only other florideophycean algae in which mitosis has been studied in detail. Common to both genera are a closed, fenestrated spindle, perinuclear endoplasmic reticulum, a typical metaphase plate arrangement of chromosomes, conspicuous, layered kinetochores, chromosomal and non-chromosomal microtubules, and nucleus associated organelles (NAOs) known as polar rings (PRs) located singly in large ribosome-free zones of exclusion at division poles in late prophase. However, other features, unreported in Membranoptera, were observed consistently in Polysiphonia. These include the presence of PR pairs in interphase-early prophase cells, the attachment of PRs to the nuclear envelope during all mitotic stages, the migration of a single PR to establish the division axis, a prominent, nuclear envelope protrusion (NEP) at both division poles at late prophase, the prometaphase splitting of PRs into proximal and distal portions, and the reformation of post-mitotic nuclei by the separation of an elongated interzonal nuclear midpiece at telophase. During cytokinesis, cleavage furrows impinge upon a central vacuolar region located between the two nuclei and eventually pit connections are formed in a manner basically similar to that reported for other red algae. Diagrammatic sequences of proposed PR behavior during mitosis are presented which can account for events known to occur during cell division in Polysiphonia. Mitosis is compared with that reported in several other lower plants and it is suggested that features of cell division are useful criteria to aid in the assessment of phylogenetic relationships of red algae. 相似文献
12.
The calmodulin-binding protein nucleomorphin isoform NumA1 is a nuclear number regulator in Dictyostelium that localizes to intra-nuclear patches adjacent to the nuclear envelope and to a lesser extent the nucleoplasm. Earlier
studies have shown similar patches to be nucleoli but only three nucleolar proteins have been identified in Dictyostelium. Here, actinomycin-D treatment caused the loss of NumA1 localization, while calcium and calmodulin antagonists had no effect.
In keeping with a nucleolar function, NumA1 moved out of the presumptive nucleoli during mitosis redistributing to areas within
the nucleus, the spindle fibers, and centrosomal region before re-accumulating in the presumptive nucleoli at telophase. Together,
these data verify NumA1 as a true nucleolar protein. Prior to this study, the dynamics of specific nucleolar proteins had
not been determined during mitosis in Dictyostelium. FITC-conjugated peptides equivalent to presumptive nuclear localization signals within NumA1 localized to nucleoli indicating
that they also act as nucleolar localization signals. To our knowledge, these represent the first precisely defined nucleolar
localization signals as well as the first nuclear/nucleolar localization signals identified in Dictyostelium. Together, these results reveal that NumA1 is a true nucleolar protein and the only nucleolar calmodulin-binding protein
identified in Dictyostelium. The possible use of nuclear/nucleolar localization signal-mediated drug targeting to nucleoli is discussed. 相似文献
13.
Knox- Davies , P. S., and J. G. Dickson . (U. Wisconsin, Madison.) Cytology of Helmintho sporium turcicum and its ascigerous stage, Trichometasphaeria turcica . Amer. Jour. Bot. 47(5) : 328—339. Illus. 1960.–The cells of the vegetative hyphae were generally multinucleate. Interphase nuclei resembled those of higher organisms, with a matrix of thread-like chromatin material surrounding a spherical nucleolus. “Beaked” nuclei frequently associated with anastomosing hyphae were interpreted as migrating nuclei. Nuclear division in the vegetative hyphae was rapid. Various division stages were distinguished but it was difficult to make accurate chromosome counts. The nucleoli were discarded at prophase or prometaphase and were reorganized in daughter nuclei at telophase. An outstanding feature of nuclear division was that all the nuclei in a cell divided simultaneously. Conidiophores and conidia were occasionally joined by wide cytoplasmic connections. They were multinucleate throughout their development. Mechanisms therefore exist for the perpetuation of heterokaryons through the conidium. Ascus development was studied in a hybrid between a dark and an albino isolate. Crozier formation was typical and nuclear fusion occurred in the young ascus. Four nuclear divisions were completed in the ascus before there was evidence of ascospore delimitation. Further nuclear division took place in the ascospores whose cells were multinucleate. The occurrence of less than 8 ascospores in an ascus appeared to follow degeneration of nuclei rather than the incorporation of a number of division-Ill nuclei in a single ascopore. Chromosome counts and irregularities in the appearance and behavior of nuclei and chromosomes in the asci indicate that aneuploidy occurs in Trichometasphaeria turcica. It is suggested that aneuploidy is a common phenomenon in the conidial stage of the fungus H. turcicum, and possibly also in other imperfect fungi. 相似文献
14.
Summary The organization of the microtubule cytoskeleton in the generative cell of Convallaria majalis has been studied during migration of the cell through the pollen tube and its division into the two sperm cells. Analysis by conventional or confocal laser scanning microscopy after tubulin staining was used to investigate changes of the microtubule cytoskeleton during generative-cell migration and division in the pollen tube. Staining of DNA with 4,6-diamidino-2-phenylindole was used to correlate the rearrangement of microtubules with nuclear division during sperm cell formation. Before pollen germination the generative cell is spindle-shaped, with microtubules organized in bundles and distributed in the cell cortex to form a basketlike structure beneath the generative-cell plasma membrane. During generative-cell migration through the pollen tube, the organization of the microtubule bundles changes following nuclear division. A typical metaphase plate is not usually formed. The generative-cell division is characterized by the extension of microtubules concomitant with a significant cell elongation. After karyokinesis, microtubule bundles reorganize to form a phragmoplast between the two sperm nuclei. The microtubule organization during generative-cell division in Convallaria majalis shows some similarities but also differences to that in other members of the Liliaceae.Abbreviations CLSM
confocal laser scanning microscopy
- EM
electron microscopy
- GC
generative cell
- GN
generative nucleus
- MT
microtubule
- SC
sperm cell
- SN
sperm nucleus
- VN
vegetative nucleus 相似文献
15.
Summary In strain 137F of Chlamydomonas reinhardi, the zygospores undergo one round of nuclear DNA replication followed by three divisions to produce octospores. The third division without replication has been interpreted by Sueoka et al. (1967, 1969) to mean that the gametes and vegetative cells have at least binemic chromosomes. We have repeated their experiments using the same strain. However, the meiotic products were inviable — unable to undergo postmeiotic vegetative growth, DNA replication or division. On the other hand, using a variant of strain 137C which also has three divisions during germination we have shown that meiosis is normal. Zygospores from this strain undergo two rounds of nuclear DNA replication prior to the formation of octospores. These meiotic products are viable and capable of postmeiotic vegetative growth, replication and division. Since the third division without DNA replication subsequent to the two meiotic divisions leads to inviable products, and the strain which has viable products after three divisions does not lack the additional replication, meiosis in Chlamydomonas reinhardi provides no evidence of a bineme chromosome structure. 相似文献
16.
Each stage of nuclear division in Micrasterias americana was investigated by electron microscopy. Some chromosomes in metaphase had two or more centromeres on them, that is, they
were polycentric. The centromere was roundish, moderately dense, and partially embedded in the chromosomes. Many microtubules
of the spindle fibers were attached to the centromere. Abundant granules of high electron density, derived from dictyosomes
in the cytoplasm, were seen in the metaphase spindle. Only the chromosomes moved towards the poles in anaphase, while these
granules remained at the equatorial plate. Many nucleoli appeared in early telophase in one or more regions in almost all
chromosomes. These nucleoli fused and enlarged during telophase. 相似文献
17.
In order to identify argyrophilic proteins of nuclei and nucleoli, in particular those responsible for the ‘nucleolar Ag staining’ widely used in cytology, we have utilized oocytes of Xenopus laevis because of the abundance of ‘pure’ extrachromosomal nucleoli. Examination of oocytes by light and electron microscopy shows that the large extrachromosomal nucleoli are heavily stained with the Ag technique and that the Ag deposits are largely enriched in, if not exclusive to, the internal, fibrillar region. The same pattern of Ag staining in internal regions of nucleoli is observed in isolated nucleoli from which soluble nuclear proteins were removed by extensive washing. Argyrophilic proteins of isolated oocyte nuclei and purified nucleoli have been identified by reaction with AgNO 3 and formaldehyde on gel-electrophoretically separated polypeptides. Among nuclear proteins, the most prominent argyrophilia is associated with nucleoplasmin, a soluble MW 30000 phosphoprotein of the nuclear sap. In addition, four minor Ag-staining nuclear proteins have been observed. By contrast, the only strongly argyrophilic protein observed on gel electrophoresis of proteins of purified nucleoli is a high molecular weight component (apparent MW 195000) which is often resolved in a characteristic ‘pair’ of closely spaced polypeptide bands. The enrichment of this high molecular weight argyrophilic protein in isolated nucleoli and the corresponding absence of argyrophilic proteins of the nuclear sap, including nucleoplasmin, indicates that this protein contributes to the nucleolus-specific Ag staining observed in histological sections. The possible nature of this polypeptide of MW 195000 is discussed. 相似文献
18.
Labelled chromosomal RNA of the dipteran Chironomus tentans was studied with respect to its migration properties during electrophoresis in agarose. The RNA was isolated from polytene chromosomes which had been microdissected from fixed salivary glands and obtained free from nucleoli and nuclear sap. Labelled material migrates as 4–5 S RNA and as polydisperse material in a range where the lower limit corresponds to 10–15 S, the upper limit to 80–90 S RNA and the maximum in the distribution to 30–40 S RNA. The data indicate that the latter fractions are formed by unbroken, single-stranded RNA molecules, partly of very high molecular weights. It is shown in a number of tests that the distribution is not a consequence of formation of complexes or aggregates between RNA molecules on one hand and DNA, proteins or other RNA molecules on the other. 相似文献
19.
The relationships of the first nuclear division during pseudo-mycelial outgrowth in the infectious yeast Candida albicans to pseudo-mycelial length and DNA replication have been investigated. Evidence is presented that the first nuclear division does not occur until the pseudo-mycelium grows to a minimum length equal to or greater than the diameter of the mother cell and until the cells pass through a minimum time period of approx. 150 min which probably reflects the time necessary to complete nuclear DNA replication. Evidence is also presented that pseudo-mycelial outgrowth and nuclear migration occur independently of DNA replication, and that nuclear migration is probably regulated by the length rather than by the volume of the growing pseudomycelium. Similarities to the requirements for nuclear division during budding in Saccharomyces are discussed, and a model for nuclear migration is proposed. 相似文献
20.
Ionizing irradiation induces positive or negative changes in plant growth (M1) depending on the amount of irradiation applied to seeds or plant parts. The effect of 50–350 Gy gamma irradiation of kernels on nucleolar activity, as an indicator of metabolic activity, in root tip cells of tetraploid wheat Triticum turgidum ssp. durum L. cv. Orania (AABB) was investigated. The number of nucleoli present in nuclei and micronuclei as well as the mitotic index in the different irradiation dosages was used as an indicator of the cells entering mitosis, the chromosomes with nucleolar organizer regions that are active as well as chromosome doubling in the event of unsuccessful mitotic division. Nucleolar activity was investigated from 17.5 to 47.5 h after the onset of imbibition to study the first mitotic division and its consequences on the cells that were in G2 and G1 phases at the time of gamma irradiation. Untreated material produced a maximum of four nucleoli formed by the nucleolar organizing regions (NORs) on chromosomes 1B and 6B. In irradiated material, additional nucleoli were noted that are due to the activation of the NORs on chromosome 1A in micronuclei. The onset of mitosis was highly significantly retarded in comparison to the control due to checkpoints in the G2 phase for the repairing of damaged DNA. This study is the first to report on the appearance of nucleoli in micronuclei as well as activation of NORs in the micronuclei that are inactive in the nucleus and the effect of chromosome doubling on nucleolar activity in the event of unsuccessful mitotic division. 相似文献
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