An Ultrastructural and Radioautographic Investigation of the Nucleolonemal Component of Plant Interphase Nucleoli

1973 ◽  
Vol 12 (2) ◽  
pp. 369-383
Author(s):  
J.-G. LAFONTAINE ◽  
A. LORD
Keyword(s):  
High Resolution ◽  
Nucleolar Organizer ◽  
Ultrastructural Level ◽  
Central Core ◽  
Allium Porrum ◽  
Filamentous Structure ◽  
Meristematic Cells ◽  
Fibrillar Material ◽  
Chromosomal Origin ◽  
Complex Organization

The interphase nucleolus in Allium porrum meristematic cells is characterized by the presence of 1-4 dense fibrillar zones of rather complex organization. Each such zone appears to consist essentially of a convoluted, evacuolated, filamentous structure approximately 1.5 µm in diameter. At the ultrastructural level, these structures exhibit an intricate array of lacunar spaces each of which is surrounded by a dense coating. These lacunae are filled with a loose fibrillar material and the largest ones sometimes also show a dense central core. In appropriate preparations, certain of the peripherally located lacunae are found to be continuous with segments of chromosomes. High-resolution radioautography reveals, moreover, that DNA is present within both the dense and lighter portions of the nucleolar loops. These observations add further support to the hypothesis that the convoluted filamentous structures in question correspond to loops of chromosomal origin and are thus related to the nucleolar organizer.

An Ultrastructural and Radio-Autographic Study of the Evolution of the Interphase Nucleus in Plant Meristematic Cells (Allium Porrum)

1974 ◽  
Vol 14 (2) ◽  
pp. 263-287
Author(s):  
J. G. LAFONTAINE ◽  
A. LORD
Keyword(s):  
Interphase Nucleus ◽  
Structural Changes ◽  
Tritiated Thymidine ◽  
Light And Electron Microscopy ◽  
Allium Porrum ◽  
Meristematic Cells ◽  
Fibrillar Material ◽  
Nuclear Structures ◽  
S Period ◽  
Dense Chromatin

Radioautography under both light and electron microscopy was exploited to investigate the structural changes of the chromatin reticulum which characterizes the interphase nucleus of a number of plants. Allium porrum meristematic plant cells were used for this purpose. In this species, the telophase chromosomes uncoil into dense strands which, during the G1 period, gradually give rise to a coarse reticulum. There then follows an extensive unravelling of portions of these strands, and high-resolution radioautography reveals that labelling with tritiated thymidine predominantly occurs over zones of the nucleus consisting of diffuse fine fibrillar material. As the S-period progresses, a chromatin reticulum reappears throughout the nuclear cavity, the tortuous strands being approximately 0.25 µm in diameter. Most of the radioautographic grains still remain over the light nucleoplasmic areas but a number of these are now located on the outermost portion of the dense chromatin profiles. By the end of the S-period, the chromatin strands are slightly thicker (ca. 0.3 µm) and form a looser reticulum. Labelling has decreased noticeably in nuclei of that period, the radioautographic grains being grouped into clusters resting over more or less spherical regions of the chromatin reticulum. Judging from their localization at the surface of the nucleolus or close to the nuclear envelope, these structures correspond to chromocentres. The additional interesting finding that such nuclear structures appear much less compactly organized strongly suggests that chromocentres undergo important conformational modifications during duplication of their DNA.

Cytochemical study of the plant interphase nucleolus

1978 ◽  
Vol 36 (2) ◽  
pp. 206-207
Author(s):  
B. Luck ◽  
J.G. Lafontaine
Keyword(s):  
High Resolution ◽  
Light Microscopy ◽  
Secondary Constriction ◽  
Nucleolar Organizer ◽  
Central Portion ◽  
Chromosomal Segment ◽  
High Magnification ◽  
Filamentous Structure ◽  
Dense Structure ◽  
Cytochemical Study

Under light microscopy, plant interphase nucleoli show a heterogeneous organization due to the presence of a coarse, contorted filamentous structure which, at high magnification, may be demonstrated to give rise to the fibrillar zones. This thread-like structure, or nucleolonema, is continuous with extranucleolar segments of chromosomes and corresponds, therefore, to the nucleolar organizer. It is observed that this filamentous structure gradually contracts during prophase and eventually forms a nucleolar secondary constriction. The latter chromosomal segment differentiates during telophase and is intimately involved in the process of nucleolar reformation.A still unresolved feature of the nucleolonema is the presence of a series of complexly organized lighter areas referred to as lacunae. A dense structure, or core, sometimes observed in the central portion of these lacunae is believed to consist of compact chromatin whereas the surrounding lighter material presumably represents diffuse chromatin. Digestion with deoxyribonuclease as well as high resolution radioautography indicate that DNA is indeed present within the nucleolonema.

Ultrastructural association of the chromatin-containing lacunar spaces with the vacuolar component of the interphase nucleolus in Allium cepa

1982 ◽  
Vol 60 (12) ◽  
pp. 2624-2628 ◽  
Author(s):  
L. A. Chouinard
Keyword(s):  
Granular Material ◽  
Allium Cepa ◽  
Ultrastructural Level ◽  
Observational Evidence ◽  
The Other ◽  
Active Chromatin ◽  
Meristematic Cells ◽  
Fibrillar Material ◽  
Nucleolar Organizing Region ◽  
Root Meristematic Cells

At the ultrastructural level, some of the chromatin-containing lacunar spaces of the interphase nucleolus in root meristematic cells of Allium cepa are seen to be walled off, on one side, by dense-fibrillar material and to be contiguous, on the other side, to electron-transparent areas, of variable sizes and shapes, bordered by dense-granular material continuous with and indistinguishable from the dense-granular component of the nucleolar mass. These electron-transparent areas associated with the lacunar spaces are equated with nucleolar vacuoles since they contain scattered preribosomal-like granules and fibrils and are rimmed by dense-granular material. The relevant observational evidence would be consistent with the view that loops of transcriptionnally active chromatin emanating from the nucleolar organizing region project radially into either only the dense-fibrillar or both the dense-fibrillar and the interior of the electron-transparent vacuolar areas seen to be contiguous to the lacunar spaces in question. In relation to this problem, it is of interest to note that the vacuolar spaces of the interphase nucleolus in Allium cepa occasionally display within their confines discrete masses of fibrillar material, possibly chromatinic in character, and in various states of condensation and configuration.

Nucleolus-associated bodies in meristematic cells of two plant species (Cicer arietinum and Leucaena glauca) with different ploidy levels

1991 ◽  
Vol 69 (6) ◽  
pp. 1329-1336 ◽  
Author(s):  
J. G. Lafontaine ◽  
B. T. Luck ◽  
S. Gugg
Keyword(s):  
Cicer Arietinum ◽  
Plant Species ◽  
Diploid Species ◽  
Nucleolar Organizer ◽  
Ultrastructural Level ◽  
Serial Sections ◽  
Metaphase Chromosomes ◽  
Interphase Nuclei ◽  
Ploidy Levels ◽  
Meristematic Cells

Light microscopy has shown that plant interphase nuclei contain small, roundish bodies, some of which may be closely associated with the nucleolar surface. Serial sections were used to determine the location, size, and number of these nucleolus-associated bodies in two plant species having different ploidy levels. In Cicer arietinum, a diploid species, one or two such bodies were observed, whereas in Leucaena glauca, an octoploid species, four to six nucleolus-associated bodies were present. At the ultrastructural level, these bodies consistently exhibited a distinct fibrillogranular texture and were located close to segments of the interphase nucleolar organizer track, a meandering, coarse, filamentous structure particularly well developed within many plant species and known to consist partly of chromatin. The fact that the number of these bodies closely matches that of the satellite-bearing metaphase chromosomes suggests that they may represent terminal segments of the nucleolar chromosomes. Other equally plausible interpretations of the nature of the NABs are also considered. Key words: plant interphase nucleus, nucleolus-associated bodies, satellites.

Des variations d'activités de la 5′-nucléotidase et de l’adénylate-cyclase sont-elles des composantes de la levée d'inhibition du bourgeon cotylédonaire du pois?

1985 ◽  
Vol 63 (2) ◽  
pp. 309-323 ◽  
Author(s):  
Arlette Nougarède ◽  
Pierre Landré ◽  
Jacques Rembur ◽  
Mercedes Niebla Hernandez
Keyword(s):  
Cell Cycle ◽  
Alkaline Phosphatase ◽  
Plasma Membrane ◽  
Adenylate Cyclase ◽  
Sodium Fluoride ◽  
Shoot Apex ◽  
Cotyledonary Node ◽  
Ultrastructural Level ◽  
Meristematic Cells ◽  
Plant Enzyme

Adenylate cyclase and 5′-nucleotidase activities were localized at the ultrastructural level. Variations of these activities were checked in the transfer cells of the cotyledonary node in the intact or decapitated plant. They were also studied in the shoot apex of both inhibited (G0 state) and released cotyledonary buds, during the transitions G1–S orG2–M. The adenylate cyclase activity is mainly associated with the exterior side of the plasma membrane and it is identical in both specialized and meristematic cells, no matter what the phase of the cell cycle is. Sodium fluoride did not appear as an activator of the plant enzyme adenylate cyclase. The 5′-nuelcotidase activity was predominant on the outside of the plasma membrane and in the plasmodesmata with no variation of intensity in the meristematic cells of the bud in relation to the cell cycle phases. Use of inhibitors of alkaline phosphatase (L-p-bromotetramisole and L-phenylalanine) and 5′-nucleotidase activities (α-β-methylene adenosine 5′-diphosphate) demonstrated the specificity of the reaction along the plasma membrane. The constancy of adenylate cyclase and 5′-nucleotidase activities in both inhibited and released buds suggests that if the optimization of the pool of polynucleotides is a component of the release from inhibition in the cotyledonary bud of pea, it is not due to the variation of activities of enzymes which release adenosine from ATP.

scholarly journals Polytene chromosomes of an Indian Himalayan black fly Simulium (Nevermannia) praelargum (Diptera: Simuliidae)

2010 ◽  
Vol 56 (4) ◽  
pp. 437-444 ◽  
Author(s):  
Willie Henry ◽  
Subrata Kumar Dey ◽  
Rakesh Varma ◽  
Sachin Thapa ◽  
William S Procunier
Keyword(s):  
High Resolution ◽  
Polytene Chromosome ◽  
Polytene Chromosomes ◽  
Nucleolar Organizer ◽  
Metacentric Chromosome ◽  
Double Bubble ◽  
High Quality ◽  
Chromosomal Markers ◽  
Total Complement ◽  
Chromosome Maps

Abstract High quality polytene chromosome maps (n=3) of a Himalayan Simuliid Simulium praelargum Datta, 1973 are presented and represent the first cytological description of a taxon found in the feuerborni group, subgenus Nevermannia. Polytene chromosomes one (I) and two (II) are metacentric, chromosome three (III) is submetacentric with the length of each chromosome occupying 37.25 %, 31.36 % and 31.34 % of the total complement length, respectively. Typical simuliid diagnostic intergeneric chromosomal markers are found within the polytene complement of this species. The nucleolar organizer (N.O.) is found at the base of the short arm of chromosome one (IS), the Ring of Balbiani (R.B.), double bubble (D.B.) and triad occur in the short arm of chromosome two (IIS), the Parabalbiani Ring (P.B.) and grey band (gb) occur in the long arm of chromosome two (IIL) and the Blister (BL) and Capsule (Ca) occur in the short arm of chromosome three (IIIS).Terminal bands at the end of IIIS are heterochromatinized and present atypically with respect to other simuliid fauna. Populations studied so far are unique among the Simuliidae in that they exhibit chromosome structural monomorphism. These high resolution polytene chromosome maps will form the basis for future cytological characterization and phylogenetic comparisons amongst members of the feuerborni group.

The nucleolus in telophase, interphase and prophase

1980 ◽  
Vol 41 (1) ◽  
pp. 321-329
Author(s):  
M. Ashraf ◽  
M.B. Godward
Keyword(s):  
Electron Microscope ◽  
Green Alga ◽  
Relevant Literature ◽  
Nucleolar Organizer ◽  
Early Prophase ◽  
Condensed Chromosome ◽  
Fibrillar Material ◽  
Nucleolar Organizing Region ◽  
Early Stages ◽  
Late Anaphase

The ultrastructure of telophase to interphase has been followed in a green alga, Spirogyra submargaritata. A series of changes transitional between the late anaphase chromatid, the decondensing chromatid of telophase, and the ‘pale fibrillar material’ occupying channels in the nucleolus at interphase have been demonstrated. Early stages in the regeneration of the nucleolus are described. It has been shown that the pale fibrillar material in the nucleolus is attached to, and continuous with, the fully condensed (chromocentric) part of the nucleolar-organizing chromosome at interphase. It is also shown that in early prophase, the channels in the nucleolonema of the nucleolus are no longer occupied by pale fibrillar material, but instead a long section of condensed chromosome is present, traversing the nucleolonema. It is contended that these observations taken together constitute evidence that the pale fibrillar material of the nucleolus is the chromatin of the nucleolar-organizing region of the chromosome, expanded for transcription. A model of the nucleolus as it is seen in most electron-microscope sections, and as it can be interpreted in the light of present-day knowledge about it, is presented. A brief review of the relevant literature considers the views supporting the mode, and the contrary views, implicating the use of the term ‘nucleolar organizer’, that are still current at the present time.

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