Nucleolar Volume Research Articles

Developmental studies on leafy spurge (Euphorbia esula). Histology of the adventitious shoot apex

Histological analyses of adventitious shoot apices of leafy spurge (Euphorbia esula L.) showed variation in the number of mantle layers at various stages of development. The older shoots (stages III and IV) tended to have a larger number of mantle layers than the younger ones (stages I and II) some of which contained two or three layers. The procambial differentiation was acropetal extending from the axis into the leaf primordium and the same pattern was noticed in all stages of development of adventitious buds and shoots. The shoot apex contained larger nuclei and nucleoli in the midsector than in the peripheral sectors and the nuclei in the former had fewer nucleoli. The total volume of nucleoli per nucleus was more in the midsector than in the peripheral sector. However, the ratio of total nucleolar volume to nuclear volume was very similar in all the sectors, suggesting uniform metabolic activity in the adventitious shoot apex.

The effect of inhibitors of protein and nucleic acid synthesis on nucleolar size and enzyme induction in Jerusalem artichoke tuber slices

The effects of various inhibitors of protein and nucleic acid synthesis on the development of invertase activity and increased nucleolar volume in discs excised from tubers of artichoke tissue are compared. The results are discussed with reference to the current theories relevant to the action of the inhibitors and to the nature of the increase in nucleolar volume.

A light- and electron-microscope study of the nucleolus during growth of the oocyte in the prepubertal mouse.

ABSTRACT The ordered changes which occur in the structural organization of the nucleolus during growth of the mouse oocyte have been studied by both light and electron microscopy. All observations have been made on those oocytes whose growth is initiated on the day of birth and completed by postnatal day 14 in prepubertal animals of the ICR albino mouse strain. During that period the oocyte nucleolus undergoes an approximate 90-fold increase in volume. During the unilaminar follicle stage (from birth to postnatal day 4), the growing nucleolus exhibits an overall reticulated-type of structure consisting of: (1) a moderately electron-dense fibrillogranular component occupying most parts of the nucleolar framework; (2) an electron-transparent nucleoplasm-like component filling the numerous interstices of the nucleolar framework; (3) an electron-dense fibrillar component located in the peripheral portion of a number of small islands widely and uniformly scattered within the nucleolar framework, and (4) a slightly less-dense fibrillar component situated in the central portion of these same islands and referred to as fibrillar centres. Increase in nucleolar volume during that stage is brought about mainly through an increase in the overall dimensions of the fibrillogranular framework, accompanied by a parallel increase in the number and, to a certain extent, the size of its electron-transparent interstices. During the bilaminar follicle stage (postnatal day 5 through 8), the following structural and organizational changes take place more or less concomitantly within the still enlarging nucleolar mass: (1) the fibrillogranular framework becomes predominantly fibrillar in texture as a result of what appears to be an unravelling or unfolding of its constituent granules of ribosomal dimensions; (2) the nucleolar interstices decrease rapidly both in number and size because of the accumulation within their interior of a material the texture and density of which match that present in the nucleolar framework itself; and (3) a number of rounded electron-transparent spaces, the nucleolar vacuoles, make their appearance in the regions formerly occupied by some of the fibrillar islands and adjacent interstices. Increase in nucleolar volume during that stage is largely due to the appearance and subsequent enlargement of the nucleolar vacuoles in question. During the plurilaminar follicle stage (postnatal day 9 through 14), the following sequential events take place within the nucleolar mass: (1) a moderately electron-dense fibrillogranular material accumulates within the nucleolar vacuoles; (2) this fibrillogranular material, which eventually fills all vacuolar spaces, undergoes degranulation and a concomitant increase in density, eventually matching that of the rest of the nucleolar mass; (3) ail remnants of the lightly stained nucleolar interstices disappear from view; and (4) the fully grown rounded nucleolus finally appears as a dense, compact mass, exclusively fibrillar in texture, and exhibiting no internal structural organization. An attempt is made to interpret these changes in the light of current knowledge concerning the architectural and functional organization of the mammalian nucleolus in general. The observations are consistent with the view that the nucleolus, during growth of the primary oocyte, is the site of massive synthesis and storage of nucleolar material.

Ultrastructure of the nucleolus during the Chinese hamster cell cycle.

Changes in the structure of the nucleolus during the cell cycle of the Chinese hamster cell in vitro were studied. Quantitative electron microscopic techniques were used to establish the size and volume changes in nucleolar structures. In mitosis, nucleolar remnants, "persistent nucleoli," consisting predominantly of ribosome-like granular material, and a granular coating on the chromosomes were observed. Persistent nucleoli were also observed in some daughter nuclei as they were leaving telophase and entering G(1). During very early G(1), a dense, fibrous material characteristic of interphase nucleoli was noted in the nucleoplasm of the cells. As the cells progressed through G(1), a granular component appeared which was intimately associated with the fibrous material. By the middle of G(1), complete, mature nucleoli were present. The nucleolar volume enlarged by a factor of two from the beginning of G(1) to the middle of S primarily due to the accumulation of the granular component. During the G(2) period, there was a dissolution or breakdown of the nucleolus prior to the entry of the cells into mitosis. Correlations between the quantitative aspects of this study and biochemical and cytochemical data available in the literature suggest the following: nucleolar reformation following division results from the activation of the nucleolar organizer regions which transcribe for RNA first appearing in association with protein as a fibrous component (45S RNA) and then later as a granular component (28S and 32S RNA).

Distinctive characteristics of nucleoli of two established cell lines.

Nucleoli of cultured cells of the established lines KB and L were found to possess a distinctive fine structural organization. The major portion of the nucleolar volume was composed of compact, particulate material. Spheroidal fibrillar zones about 0.4 micro in diameter occurred within the particulate mass. These fibrillar zones had a central light area and a denser rim. Toyocamycin treatment, which sharply inhibited the appearance of newly synthesized RNA in the cytoplasm, caused the gradual disappearance of the fibrillar material from nucleoli. Actinomycin D treatment, which inhibited virtually all RNA synthesis, caused varying types of segregation of nucleolar components. The morphology of nucleoli of KB and L cells and the reorganization of these nucleoli in response to drugs appear to be different from those of nucleoli of freshly initiated Chinese hamster and mouse cell lines.

Histological Study of Adventttious bud Formation onLactuca SativaCotyledons CulturedIn Vitro

Abstract Cyto-histological changes accompanying the formation of adventitious buds in excised cotyledons of Lactuca sativa were studied during the first 12 days after planting in vitro. Prospective proliferating cells can first be recognized, already on the first day after planting, by a marked increase in nuclear and nucleolar volumes, followed on the second day by a burst of cell divisions involving particularly mesophyll cells. Then lignified elements develop together with meristematic center, forming a callus-like tissue in the inner part of the cotyledons. At the third day of culture, the epidermal cells start to divide with a periclinal wall followed by an anticlinal division. In the following days of culture the epidermal cells, which divide mainly with periclinal walls, form layers of cells below the surface, gradually filling up the intercellular spaces. From the 8th day on, the buds protude above the surface and develops into shoots. These results are discussed in relation to DNA content of nucl...

Vacuoles in the Nucleoli ofZea MaysRoot Apices and their Possible Significance in Nucleolar Physiology

SUMMARYNucleolar vacuoles in eight regions of the root apex of Zea mays have been studied. The volume of the vacuoles ranges from about 1 μm3 to 0.001 μm3 with a mode value between 0.075 and 0.01 μm3. The number of vacuoles within a nucleolus ranges from 0–20 and is correlated with nucleolar volume. In all regions studied the average volume of the nucleolus occupied by vacuoles is about 3 percent. It is suggested that the metabolic capacity of the nucleolus may be reflected in the rate of formation of the vacuoles and the discharge of their contents to the cell.

Circadiane Rhythmik von Drosophila-Speicheldrüsen in vivo, in vitro und nach Ecdysonzugabe

Nuclear and nucleolar volumes of Bouin-fixed salivary glands of Drosophila larvae show a bimodal circadian rhythm (12 : 12 hr light-dark régime, 20°C). The phasing of this rhythm relative to the light-dark ‘Zeitgeber’ changes in the course of ontogeny, i.e. from day 4 to day 7 during larval development. The rhythms of nuclear and nucleolar volumes seem to follow the same pattern. Living nuclei from salivary glands freshly prepared at different times of day show a bimodal rhythm very similar to the rhythm of fixed salivary glands of the same developmental age. The transverse profiles of all data under normal and inverse light-dark conditions reveal significant differences between maxima and minima. Volumes of single nuclei from salivary glands cultured up to 10 days in a chemically defined medium also oscillate in a bimodal circadian rhythm (12 : 12 hr light-dark régime, 25°C); differences between maxima and minima extend to about 10 per cent of the mean volume. The rhythm of these nuclei measured longitudinally over 36 to 48 hr coincides with the rhythm of the fixed and living nuclei in the transverse profiles. Varying relative K + and Na + concentrations of the medium have no remarkable influence on the rhythm. The rhythm persists in constant light of about 200 lx for at least 4 days; it is phase-shifted by a 6 hr ‘Zeitgeber’ shift during larval development. Pulse- or stepwise addition of ecdysone-containing medium between 13 and 18 hr caused a phase shift of the nuclear rhythm in vitro: after a small maximum at 24 hr (coinciding with the controls) phase differences of 3 to 9 hr relative to the normal and control groups can be observed later. The addition of ecdysone between 9 to 12 hr failed to shift the rhythm.

Chromosomal control of foot pad development in Sarcophaga bullata. I. The puffing pattern.

The puffing schedule of 71 puffs of chromosome B in Sarcophaga bullata polytene foot pad cells were analyzed during an 8 day period of pupal development. The number of puffs fluctuates, with maxima at about day 7 and day 10. The nucleolar volume reaches two maxima which precede the maxima in the number of puffs by approximately one day. With respect to qualitative changes in the puffing pattern, the present study shows that all puffs appear and disappear in a sequential fashion which is related to development. The pattern of potentially active loci and the sequence in which they form puffs are identical in all foot pad cells. Nevertheless, two neighboring cells may differ characteristically in the timing of the activity of a few individual loci relative to the rest of the puffing sequence. Furthermore, pulvilli cells from different pairs of legs may differ in the timing of the entire puffing sequence. It is concluded that puffing, at least in part, is under the control of intracellular processes rather than of external factors such as hormones.

Interrelationships between developing oocytes and ovarian tissues in the chiton Sypharochiton septentriones (Ashby) (Mollusca, Polyplacophora).

AbstractOogenesis and the relationships between oocytes and other ovarian tissues have been studied in Sypharochiton septentriones. The ovarian tissues were examined by electron microscopy and by histochemical methods.The sac‐like ovary is dorsal, below the aorta, and opens to the exterior by two posterior oviducts. Ventrally, the ovarian epithelium is folded inwards to form a series of plates of tissue, which support the developing ova. Each ovum is attached to a tissue plate by a stalk, the plasma membrane of which is bathed by the blood in the tissue plate sinus. Dorsally, ciliated vessels from the aorta enter the ovary and open into blood sinuses in the top of the plates.After each germinal epithelial cell rounds up to become a primary oogonium, it undergoes four mitotic divisions to give rise to a cluster of 16 secondary oogonia. Of these, the outer ones become follicle cells and the inner ones become oocytes. As in other molluses, the increases in nuclear and nucleolar volume are relatively greatest towards the end of previtellogenesis, when chromosomal and nucleolar activity are most intense. This phase of activity is accompanied by a great increase in cytoplasmic basophilia. Subsequently this basophilia is decreased during vitellogenesis, when chromosomal and nucleolar activity diminish. Fluid filled interstices appear in the cytoplasm during early vitellogenesis. Protein yolk deposition is associated with these interstices, but the lipid yolk appears to arise de novo. The follicle cells do not appear to be directly involved in oocyte nutrition.At times during oogenesis, certain manifestations of polarity can be found in the oocyte. This polarity is based on an apical‐basal axis and can be related to the nutritive source of the oocyte, namely the blood which bathes the plasma membrane of the oocyte in the stalk.Numerous granulated cells are present in the ovarian tissue plates and ventral epithelium as storage cells containing lysosomes, and they are capable of phagocytosis and micropinocytosis of extracellular material. A scheme is outlined whereby reserves in these cells may be incorporated into the oocyte cytoplasm. Lysosomal activity is responsible for autolysis of the cells as well as resorption of unspawned ova.

Cytological study on the loss of dividing ability in renewal cell populations

The development of myeloid cells in the rat bone marrow into non-dividing, postmitotic forms was examined by preparing myelo- and haemograms and making light- and electromicroscopic, enzyme histochemical, cytophotometric, autoradiographic and tissue culture investigations we found, that the formation of non-dividing granulocytes is preceeded by the following alterations: 1. (a) Diminution of the nucleo-cytoplasmic ratio, which in rodents takes partly by the perforation of a compact nucleus place. In this perforation the centriole, granules and some enzymes, chiefly alkaline phosphatase, all participate. 2. (b) The chromatin becomes of coarser distribution, the nucleus more electrondense. 3. (c) Myeloblasts, promyelocytes and myelocytes synthesize DNA intensively and proliferate; in metamyelocytes only 10–15 per cent of the cells are in hyperdi-, and tetraploid state; the granulocytes are, without exception, diploid, unable to synthesize DNA or divide. 4. (d) The volume and density of nucleoli, and probably also the synthesis of messenger RNA decreases. 5. (e) A loss of cytoplasmic RNA was also shown, judged from the weakening of baso- and pyroninophylia, and the diminution of free ribosomes and ergastoplasm. 6. (f) The oxidative processes alter; too: the activity of peroxidase and the number of mitochondria decrease and in the cytoplasm glycogen—granules appear.

Polyploïdie hépatique du rat: IV. Variations expérimentales du volume nucléolaire des hépatocytes et leurs mécanismes de régulation

Hepatic cell suspensions were used for volume measurements of nucleoli. Nucleolar volumes, within the hepatic cell population, show a characteristic frequency distribution with increasing ploïdy. Hypophysectomy reduces nucleolar volume and the frequency of large nucleoli is significantly reduced in favor of small nucleoli without change in total number of nucleoli per cell. Protein deficiency, known to increase nucleolar volume in intact animals, does not reverse this situation. However cell proliferation induced by hepatectomy is accompanied by an increase in nucleolar volumes despite hypophysectomy. It is concluded that nucleolar function, reflected in the frequency distribution of nucleolar volumes, in hepatic cells is subject to at least two different controls, one of which operates during cell proliferation with priority over the second governed directly or indirectly by the hypophysis.

Polyploïdie hépatique du rat: III. Étude des nucléoles des cellules hépatiques du rat normal

The use of liver cell suspensions allows the examination of whole hepatic cells and their nucleoli. Under physiological conditions of adult and young rats, the volumes of the single nucleoli grouped from the total cell population fall into several distinct classes, the mean volumes of which are separated by a factor of 2. The frequency of maximum volume of single nucleoli and the number of nucleoli per nucleus, increases with rising ploïdy yet the number of nucleoli does not double. It is concluded that the increased nucleolar volume with rising ploïdy expresses nucleolar fusions.

Ultrastructural Differences Between Thymic and Lymph Node Small Lymphocytes of Mice : Nucleolar Size and Cytoplasmic Volume

Abstract Ultrastructural differences between small lymphocytes of the thymic cortex and those located in the cortical zone of lymph nodes of mice were examined by electron microscopy and cytometric methods. The particle size analyzer TGZ 3 (Zeiss) was used to measure the size-frequency distribution of nucleolar cross-section diameters, and the resulting data were computed mathematically and statistically to determine the corresponding mean volumina. It could be shown that thymic, as compared to lymph node cortical small lymphocytes, (1) have a smaller mean nucleolar volume (0.11µ3 versus 0.46µ3); (2) represent a more uniform population with regard to the frequency distribution of the nucleolar cross section diameters; and (3) are of smaller size due to less cytoplasm, while the mean nuclear volume does not differ significantly from that of small lymphocytes located in the cortex of lymph nodes. These findings are discussed in relation to qualitative ultrastructural peculiarities and probable differences in the magnitude of RNA turnover as estimated by the use of tritiated cytidine. The possible significance of cytometrically defined populations of small lymphocytes with regard to sensitized and nonsensitized cells is considered.

HISTOCHEMICAL CHANGES IN THE SHOOT TIP OF CAULIFLOWER DURING FLORAL INDUCTION

Cauliflower plants were induced to flower after being grown at 42 °F for varying periods of time, depending on the cultivar. Some of the histochemical changes in the shoot apex at the beginning of, during, and after floral induction were studied. During floral induction there is about a 20-fold increase in the volume of nucleoli and about a 3-fold increase in volume of nuclei. Apices of vegetative plants stained with bromophenol blue at pH 2.3, show small and dense nucleoli, dense and granular nuclei, and a small amount of weakly staining cytoplasm. In contrast, cells of apices of induced plants stained with bromophenol blue at pH 2.3, show large and dense nucleoli, large and weakly staining nuclei; however, these cells contain more and denser cytoplasm. Sections of vegetative and induced apices stained with alkaline fast green stained differently from those stained with bromophenol blue. Nucleoli did not stain and cytoplasm stained faintly with fast green while chromosomes stained strongly. Deoxyribonucleic acid (DNA) content of vegetative and induced apices are similar. Shoot apices of vegetative plants contained little or no starch. However, shoot apices of plants grown at 42 °F accumulate large amounts of starch. Floral primordia which develop into functional flowers are glutted with starch, while floral primordia which abort are void of starch.

Changes in nucleolar ultrastructure associated with differentiation in the root tip

The development of the nucleolus in the root apex of Plantago ovata has been studied primarily at the ultrastructural level. Nucleolar volumes in the quiescent center and selected regions of the root cap, cortex, and epidermis correlate qualitatively with cytoplasmic basophilia and mitotic frequency. The small nucleoli of the quiescent center have been shown by means of serial sections to contain intrusions of heterochromatin into the internal fibrillar zone. The number of intrusions corresponds to what would be expected if each represents the attachment of a nucleolar organizing chromosome. Differences in the chromosomal-nucleolar junction following different fixation procedures are described. One per cent collidine-buffered OsO 4 routinely produces a sharp nucleolar image with the fibrillar and ribosomal regions clearly distinguished. Other fixatives such as acrolein-glutaraldehyde followed by OsO 4 produce a more diffuse nucleolar image but make much clearer the differences between chromatin and nucleolar heterochromatin. Where cortical and epidermal nucleoli are largest (10–12 times the volume of those in the quiescent zone) the ribosomal regions are intermingled with the fibrillar regions and the general structure is less compact. Often present is a large central lacuna containing fibrils of a chromatin-like character as well as what appear to be free ribosome-like particles. As division ceases and cells increase in size, the vacuoles occupy an increasing proportion of the cell volume, the nucleoli return to a size and arrangement like that in the quiescent center.

Synthesis of nucleic acids in hair.

A STUDY of the cells of the hair cortex of rats1 showed that size changes of the nucleolus are not a reliable indication of changes in the rate at which cells are synthesizing proteins. The highest rate of protein synthesis was associated with the smallest nucleolar volume. It was not possible to demonstrate nucleoli in the cortical cells of the mid-keratogenous zone with specific stains for RNA.

Variation in the amounts of nucleic acids in the cells of different species of higher plants

Root tips of 12 species of higher plants have been analysed to measure DNA per cell, which showed a tenfold variation, and RNA per cell, which showed a fivefold variation. Average nucleolar volume and fresh weight per cell were measured on the same samples. Multiple regressions of DNA per cell and RNA per cell on nucleolar volume and fresh weight per cell were calculated, with all variates measured on logarithmic scales. Within a single species there was a direct proportionality between DNA per cell and RNA per cell. However, although the RNA DNA ratio was constant for any species, the ratio varied between species and was possibly related to taxonomic group. About 69 per cent of the variability between species in log RNA per cell could be accounted for by variability in log nucleolar volume. Evidence is presented that this correlation is due to some activity of the nucleolus rather than to the RNA which the nucleolus actually contains. About 76 per cent of the variability between species in log DNA per cell could be accounted for by variability in log fresh weight per cell. It is suggested that the principle, established for polyploid series of recent origin and for some closely related species, that increased chromosome material results in increased cell size, can be extended to include widely diverse species. The hypothesis is proposed that variations in DNA per cell may have evolved by selection for variations in cell size.

Cytological, radioautographic and ultrastructural studies on the effect of 5-fluorouracil on rat liver

Young rats were given two doses of 50 mg 5-fluorouracil with a 22-hour interval. One hour after the second dose they were given either cytidine-3H or leucine-3H and killed three hours later. Radioautographs of the livers revealed a decrease in RNA labelling, whereas the protein labelling was essentially uninfluenced. The liver cells exhibited an increase in nucleolar volume. Electron microscopy revealed changes in the ultrastructure of the liver cell nucleoli, while other parts of the cells were essentially unaltered.

Neurosecretory activity in supraoptic nucleus of normal rats.

The secretory rhythm of neurosecretory cells was studied in supraoptic nuclei of normally drinking rats. Both nuclei were divided in five zones, and in each one, the nuclear and nucleolar volumes of 50 neurons were measured. Parallel observations were made on the Nissl material and neurosecretory granules. Comparative effects of different fixatives showed Carnoy and Zenker to be the best fluids for this type of investigation.