bluuebunny/crossref_metadata_2025_split huggingface dataset:
An ultracytochemical study of nucleolar organization in meristematic plant cells (Allium porrum)
Authors: Luck B. T. , Lafontaine J. G. 
Published: April 2021

ABSTRACT
The interphase nucleolus in Allium porrum, as in many of the plant species studied so far, is highly heterogeneous in ultrastructure owing to the presence of coarse, contorted, thread-like structures, or nucleolonemata. Each nucleolonema appears to be sharply twisted and to give rise to a skein within the nucleolar mass. In order to characterize further these nucleolar components, a variety of cytochemical techniques were exploited. For that purpose, specimens were mostly fixed in 4% formaldehyde and stained in the block according to procedures known to reveal the presence of nucleic acids or proteins. Certain specimens were also digested with deoxyribonuclease, ribonuclease or proteinase K before staining. By staining with phosphotungstic acid or bismuth oxynitrate, the presence of a high concentration of proteins can be demonstrated within thin (0.15 µm), filamentous structures which are believed to correspond to the outer region of the nucleolonema. Such convoluted formations disappear upon sufficiently long extraction with proteinase K. Using Bernhard’s regressive staining technique for chromatin, the distribution of this substance throughout the nucleolar mass was found to match closely that of the nucleolonemata as revealed by several other procedures. As a last test for investigating the cytochemical make-up of the nucleolus, blocks of tissues were stained with 3,3’-diaminobenzidine, a substance known to react specifically with nucleic acids. When such specimens are digested with ribonuclease for 1 h, there persist within the nucleolus, fibrillo-granular zones the localization of which is highly reminiscent of that of the nucleolonemata. Combination of ribonuclease hydrolysis with subsequent treatment with proteinase K (30 min) induces the extraction of a large proportion of the nucleolar material, the persisting loose and rather evenly distributed fibrils exhibiting a diameter of 3-5 nm. The possibility is considered that these units may correspond to chromatin fibrils although they have most likely been displaced from their original localization during the extraction procedures.
Our cytochemical data suggest that, in Allium porrum, the nucleolonema is approximately 0.3 µm in diameter and may consist of a central axis from which chromatin loops project radially. A possible interpretation for the presence of protein-rich, 0.1 µm-thick, annular structures throughout the nucleolonemal skein is that the newly synthesized RNP products are accumulated transiently at the extremities of these loops before migrating to the immediately adjacent granular nucleolar zones.
Aggregation properties of chondrocytes infected with a temperature-sensitive mutant of rous sarcoma virus
Authors: Tanaka Akio , Kaji Akira 
Published: April 2021

ABSTRACT
Aggregation capacity of chicken embryo chondrocytes decreases when transformed by Rous sarcoma viruses. Cell-to-cell aggregation capacity of chondrocytes infected with a T class temperature-sensitive mutant (tsNY68) (with the temperature-sensitive lesion at the src gene) of Rous sarcoma virus is dependent upon the temperature at which these cells are grown. When grown at the permissive temperature (36 °C), where the transforming gene is expressed, aggregation capacity was lower than normal while infected cells grown at the non-permissive temperature (41-5 °C) had similar capacity to aggregate to that of normal chondrocytes. However, after a prolonged period of culture (10 days), chondrocytes transformed by wild type SR-RSV regained the normal level of aggregation capacity. Cells transformed by tsNY68 and incubated at the permissive temperature for 10 days also regained the normal level of aggregation capacity. It appears therefore that RSV-transformed chondrocytes first become less adhesive but during long-term cultivation they regain their property to aggregate. The decrease of aggregation capacity due to T class mutants of RSV at 36 °C is dependent on constant maintenance of protein synthesis because addition of cycloheximide restored the aggregation capacity even at the permissive temperature.
The occurrence of period IV elementsin dinoflagellate chromatin: an X-ray microanalytical study
Authors: Kearns L. P. , Sigee D. C. 
Published: April 2021

ABSTRACT
X-ray microanalysis of unfixed frozen-dried cryosections, and of unfixed cryosections collected by a sucrose drop technique, revealed the presence of Ca, Mn, Fe, Ni, Cu and Zn (Period IV, Periodic Table) in association with the permanently condensed chromosomes of Prorocentrum micans.
All of these metals, with the exception of Mn, routinely occurred in the chromatin of cells that had been fixed in glutaraldehyde, ethanol-dehydrated, and resin-embedded. Their detection at high levels in chemically dehydrated chromatin of Prorocentrum micans, and 3 other dinoflagellate species cultured in the laboratory, suggests they are important as bound (insoluble) components of the chromatin.
Detailed analysis of the fixed, ethanol-dehydrated material showed that for these particular cultures, each species had its own characteristic mass fraction pattern of chromatin-bound elements which differed markedly from that of the other species. Calculation of relative numbers of atoms from the mass fraction data showed that for each species about 40–50 atoms of bound Period IV elements were present per too atoms of phosphorus. This is approximately equivalent to one Period IV atom per 2 DNA nucleotides or per base pair.
Although considerable variation exists between species in terms of individual element levels, the total number of atoms of Period IV elements relative to phosphorus is remarkably constant.
Studies on the surface properties of hybrid cells: I. Sialyl-transferase activity in homogenates of malignant and non-malignant cells
Authors: Atkinson M. A. L. , Bramwell M.E. 
Published: April 2021

ABSTRACT
We report here a method for the assay of the sialyl-transferase activity in crude homogenates of a wide range of cell lines growing in tissue culture. Our results indicate that particulate preparations from both malignant and non-malignant cells show a Km of 0·25 mM towards CMP-sialic acid in the presence of an excess of glycoprotein acceptor. There appear to be increased amounts of the enzyme associated with the preparations from malignant sources which are reflected in an increase in the apparent Vmax of these.
The elevated level of sialyl-transferase activity seen in the malignant cell populations is, paradoxically, associated with a decrease in the amount of bound sialic acid associated with both the whole cell homogenate preparations and the surface of these cells.
Studies on the surface properties of hybrid cells: II Sialyl-transferase activity on the surface of malignant and non-malignant cells
Authors: Atkinson M. A. L. , Bramwell M. E. 
Published: April 2021

ABSTRACT
A measurable surface activity of sialyl-transferase is demonstrated by a number of different methods to exist on the plasma membranes of both malignant and non-malignant cells. The amount of enzyme present on the surface of malignant cells is found to be higher than that on the non-malignant ones in a wide range of malignant and non-malignant cell lines. It is proposed that the difference in apparent activity results in part from the presence of incomplete glycoproteins in the surface membranes of the malignant cells and in part from an increased rate of membrane synthesis in these cells.
Surface binding and uptake of polycationic ferritin by neonatal piglet intestinal epithelium
Authors: Chase Carol C. , Munn Edward A. 
Published: April 2021

ABSTRACT
Pieces of small intestine from newborn, 1- and 6-day-old piglets were incubated in vitro and ligated segments were incubated in vivo with polycationic ferritin (PCF) to determine the distribution and possible role in protein uptake of anionic sites on membranes at the luminal surfaces of the epithelial cells. Most PCF binding to the absorptive cells occurred on the upper third or half of the villi and to some non-absorptive cells (tuft cells) throughout the length of the villi.
Pieces of intestine which were fixed before incubation had PCF on microvilli and apical invaginations of absorptive cells, but none in the sub-apical tubules. When samples were incubated with PCF in vitro before fixation PCF was bound to the surfaces of microvilli of absorptive cells and to the membranes lining the apical invaginations, some sub-apical vesicles and some sub-apical tubules in all age-groups. In vivo experiments with longer incubation times resulted in a similar distribution, with increased amounts of PCF in the sub-apical tubules in samples from newborn and 1-day-old piglets only. In the newborn there were small vesicles containing PCF which had apparently moved further into the cells. At the same concentration (2 mg/ml) ferritin did not enter the sub-apical tubules; but it did enter and was taken up by the cells in the presence of 4 % (w/v) serum albumin.
It is concluded that the mechanism of protein uptake does not involve the microvillar membrane and that non-specific interaction with the invaginated plasma membrane, as a function of charge-density, leads to opening of the sub-apical tubular system to protein. Movement further into the cell depends on other factors.
Numerical, morphological and topographical heterogeneity of the chondriome during the vegetative life cycle of Polytoma papillatum
Authors: Gaffal K. P. , Schneider G. J. 
Published: April 2021

ABSTRACT
Numerical, morphological, and topographical changes in the mitochondrial inventory (= chondriome) during the vegetative (= asexual) life cycle of Polytoma papillatum were examined by means of the serial-sectioning technique. At the onset of interphase the chondriome consists primarily of one highly reticulated basket-shaped complex, which lines the periphery of the cell. Up to 3 additional fragments could be analysed, which, however, were much smaller and either spherical to ovoid, or elongated and poorly branched. During interphase growth both the size of the mitochondrial basket and the number of additional fragments (ca. 40) increases. During mitosis 1 (1. division cycle) the multiplication of the number of mitochondria gradually continues; the maximum (ca. 250) was counted at late telephase 1 and early cytokinesis 1, but it cannot be excluded that the sparser short-lived meta- and anaphase cells, which were unfortunately missed, contain an even higher number of mitochondrial units. Concomitant with mitosis 1, the mitochondrial basket is subdivided into several fragments; at the same time the mitochondria tend to form clusters and to occupy no longer merely peripheral but also more central regions. An irregular distribution of the chondriome results, with either local accumulations or local absence of mitochondria within definite regions of the cell. After completion of cytokinesis 1 the total number of mitochondria (ca. 80) is drastically reduced but it seems to increase again during the 2. division cycle. Irrespective of the number of preceding division cycles, the chondriome of young daughter cells enclosed in the sporangium usually resembles that of young interphase cells. Our results are discussed in relation to some of the current problems on mitochondriogenesis.
Arginase and sucrase potential in the fission yeast Schizosaccharomyces pombe
Authors: Benitez Tahia , Nurse P. , Mitchison J. M. 
Published: April 2021

ABSTRACT
The induction potentials of 2 enzymes, sucrase and arginase, have been measured in asynchronous and synchronous cultures of the fission yeast Schizosaccharomyces pombe.
The effect on potential of inhibiting DNA synthesis in asynchronous cultures has been studied using 2 temperature-sensitive cdc mutants, one blocked in DNA replication and the other blocked in mitosis. The results show that despite inhibition of DNA synthesis, sucrase and arginase potential both continue to increase exponentially for at least a generation of growth after shifting the cdc mutants from the permissive to the restrictive temperature. A second method of inhibiting DNA synthesis, using deoxyadenosine, has also been tested. Cells treated with deoxyadenosine stop the increase in potential for a short period. However, experiments carried out using a cdc mutant together with deoxyadenosine show that the block to the increase in potential is due to a side effect of the inhibitor.
It appears that increase in potential is not dependent upon continued DNA replication, and that gene dosage does not control potential in the normal cell cycle. This conclusion is supported by measurements on mutants of different cell sizes. Potential is proportional to size (protein content per cell in asynchronous culture) and not to DNA content.
Although potential is not gene limited in normal cells, it does appear to be so in the abnormally large cells produced by a cdc block. If cdc mutants of different sizes are grown asynchronously, and DNA synthesis is inhibited by a shift to the restrictive temperature, potential continues to increase until the cells reach a critical DNA/protein ratio beyond which there is no increase in potential. This critical ratio is different for the 2 enzymes, but for each enzyme it is similar in all the mutants tested. When large cells (produced by a mutant block for 4 5 h) are shifted down in temperature, there are synchronous rounds of DNA synthesis and division and also step doublings in potential.
In synchronous cultures of wild type cells, both enzymes show a stepwise doubling of potential at 0 2 of a cycle after DNA replication. In synchronous cultures of cdc mutants blocked either in replication or in mitosis, the potential steps continue with the normal timing observed in wild type cells. This shows that the steps are not dependent on the events of the DNA-division cycle but are controlled by another mechanism. Attainment of a critical size might be part of this mechanism, but tests with size mutants argue against this.
On the involvement of the Golgi apparatus and GERL in processing of secretion products and some enzyme activities in the rat pituitary mammotroph
Authors: Nevorotin A. J. 
Published: April 2021

ABSTRACT
Whole pituitary glands of Wistar albino rats were either (a) immediately fixed in an aldehyde fixative (Kamovsky), or incubated prior to the fixation in (b) unaltered medium 199, (c) medium 199 supplemented with 1·65 M sucrose, or (d) medium 199 diluted with distilled water (1 : 2). Incubation time was for 0·5 h, at a temperature of 4° or 37 °C. All specimens were routinely processed for acid phosphatase (AcPase) or thiamine pyrophosphatase (TPPase) demonstration and examined ultrastructurally. In the control series a and b AcPase activity in the mammotroph was associated with the cistemae of GERL, dense bodies, coated vesicles, immature secretion granules often continuous with the cistemae of GERL, and occasionally with the innermost lamellae of the Golgi apparatus (GA). TPPase activity was found within the innermost lamellae and the fenestrated element of GA. Occasional granular cores were seen within TPPase-positive lamellae. In all mammotrophs of series c (4° and 37 °C) severe shrinkage of the lamellae of GA and other membrane-bound structures in the Golgi area was apparent. In some mammotrophs of the series c (37 °C) AcPase activity, in addition to its usual sites, was revealed within all lamellae of GA, as well as in some tubular and fenestrated elements continuous with GA. The innermost AcPase-positive lamellae of GA were sometimes partially separated from the others and continuous with immature secretion granules or dense bodies, thus qualifying as cistemae of GERL in the course of their gradual formation from the Golgi lamellae. A gradual increase in AcPase activity from the cis to trans poles of GA could sometimes by noted. TPPase activity in this series spread over all lamellae of GA and its fenestrated elements. The occasional profiles of rough endoplasmic reticulum and some smooth-surfaced vesicles near GA also gave positive reactions for the enzyme. At 4 °C the distributions of both enzyme activities were as in the controls. In all series d (4 or 37 °C) the membrane-bounded organelles of the mammotroph were greatly swollen except for occasional cells (at 37 °C) in which all lamellae of GA were paradoxically shrunk as in series c. The distributions of AcPase and TPPase activities in series d were as in the controls, except for some cells with shrunken lamellae (at 37 °C) in which TPPase activity was spread throughout GA. The results suggest that experimental dehydration of GA in the mammotroph acts by overcoming latency of AcPase and TPPase or by accelerating maturation of AcPase and TPPase activities from their hypothetical precursors thereby tracing the intracellular pathways of these enzymes. It also follows that GA may participate in the initial stage of secretion-granule formation and enzyme-activity maturation whereas GERL finalizes the process.
The secretion of the eggshell of Schistocerca gregaria: ultrastructure of the follicle cells during the termination of vitellogenesis and eggshell secretion
Authors: Kimber Susan J. 
Published: April 2021

ABSTRACT
The secretion of the eggshell by the follicle cells in the desert locust, Schistocerca gregaria, was studied using the electron microscope. The 3 layers of the eggshell, the vitelline membrane, the endochorion, and the exochorion, are produced in sequence over a short period of about 30—36 h. The follicle cells contain little rough endoplasmic reticulum (RER) and small inconspicuous Golgi bodies during vitellogenesis. As eggshell secretion approaches there is an increase in the amount of RER and number of Golgi bodies. During vitelline membrane and endochorion secretion the RER and Golgi cistemae contain electron-dense product. At each stage of the 3-phase secretion cycle the follicle cells contain Golgi bodies and secretion vesicles with distinct morphology. The follicle cells increase in breadth and decrease in height between the beginning and end of eggshell secretion. The endochorion ridges arise at the junction between follicle cells and appear to be moulded by the microvilli formed at this position. In the ovary prior to ovulation, the eggshell consists of a thin (0·5 μm) electron-dense vitelline membrane, a 5–10-μm-thick endochorion consisting of crystalline tubules in a granular matrix, and an outer fibrillar exochorion layer, 20–30 μm thick. Further changes take place in the vitelline membrane and the endochorion after oviposition, and a layer of curly fibres, the extrachorion, is secreted in the oviduct.
Chloroplast division in spinach leaves examined by scanning electron microscopy and freeze-etching
Authors: Chaly N. , Possingham J. V. , Thomson W. W. 
Published: April 2021

ABSTRACT
Spinach leaf disks were cultured for 5 days in low-intensity green light and then were transferred to high-intensity white light. Harvests over the next 16 h established that cell area increased by about 80% and chloroplast number per cell increased by about 65 %, while the percentage of dumbbell-shaped chloroplasts per cell decreased by 65 %. Freeze-etch replicas of fixed and unfixed leaf disks, as well as scanning electron-microscope preparations of fixed material, contained dumbbell-shaped chloroplasts constricted to various degrees. Freeze-etch replicas of unfixed cells from young leaf bases, in which the number of chloroplasts per cell is known to be rapidly increasing, also contained many constricted chloroplasts. It is concluded that dumbbell-shaped chloroplasts occur in vivo and represent a stage in the division of chloroplasts.
Isolation of the cytoskeleton from Giardia. tubulin and a low-molecular-weight protein associated with microribbon structures
Authors: Holberton D. V. , Ward A. P. 
Published: April 2021

ABSTRACT
The sucking disk of Giardia is supported by a large, plate-like organelle: the ventral disk cytoskeleton. Extraction by Triton-X 100 of Giardia trophozoites from the mouse gut, or of G. duodenalis or G. lamblia grown from cultures, yields cell-free disk cytoskeletons. Up to 8 flagellar axonemes may be attached to an isolated disk.
Disks are seen in the electron microscope to be composed of concentrically coiled microtubules bonded to microribbons. Microribbons are large, laminated structures, linked by dense networks of crossbridges. They are made up of regularly arranged subunits. Microtubules and microribbons are preserved in Triton for long periods, but crossbridges are slowly dissolved.
Whereas the addition of ATP causes axonemes to resume bending, active movements were not detected in disks. It seems more likely that a disk is a passive effector, which may be acted upon by other contractile structures of the cytoplasm. It is a highly specialized and quintessential cytoskeleton.
Disks and axonemes will dissolve in sodium dodecyl sulphate (SDS), and after SDS-gel electrophoresis 2 prominent bands are apparent. One, corresponding to tubulin, migrates in low ionic strength, high pH buffers as 2 closely spaced bands of equal staining density. The other, a smaller protein, is a complex polypeptide band of molecular weight 30000 Daltons. Allowing for staining differences, the 2 proteins are probably present in cytoskeletons in roughly equal amounts. Because of their size, microribbons account for at least 75 % of the structured material stained by electron stains in pellets of cytoskeletons. Disk and axoneme microtubules comprise the minority fraction. This result suggests that, like microtubules, microribbons are a source of structural tubulin and probably also contain the 30000 mol. wt protein.
The appearance of carbohydrate-rich material in the developing golgi apparatus of amoebae
Authors: Flickinger Charles J. 
Published: April 2021

ABSTRACTThe silver proteinate reaction was used to stain carbohydrate-rich substances in normal Amoeba proteus and in the developing Golgi apparatus of renucleated amoebae. Normal cells contained stained material, which probably is glycoprotein, in the cell surface, cisternae at the concave pole of the Golgi apparatus, and cytoplasmic vesicles and vacuoles. Previous radioautographic studies had shown that glycosylation occurs in the Golgi apparatus, and that material in the Golgi apparatus is precursor to the cell surface. Amoebae were enucleated for 5 d, which results in a decline of the Golgi apparatus, the disappearance of the glycoproteincontaining cisternae preceding that of the rest of the organelle. A new nucleus was then transplanted into the enucleate amoebae, bringing about the regeneration of the Golgi apparatus. Small curved cisternae that appeared 30 min after renucleation lacked staining with silver proteinate. By i h after renucleation, however, the content of cisternae toward the concave poles of Golgi bodies stained with silver proteinate. The Golgi apparatus in cells fixed 6 h and 1 d after operation resembled that of normal amoebae in both morphology and staining pattern. The results suggest that the developing Golgi apparatus acquired the capacity to participate in assembly of cell-surface material within 1 h after renucleation. This occurred before development of the normal enzymic activity of the Golgi apparatus was completed.