bluuebunny/crossref_metadata_2025_split huggingface dataset:
Descriptive and quantitative study of ultrastructural changes in the apical meristem of mustard in transition to flowering: I. the cell and nucleus
Authors: Havelange A. , Bernier G. 
Published: April 2021

ABSTRACT
Transition to flowering was induced in the shoot apical meristem of Sinapis alba (mustard), a long-day species, by subjecting vegetative plants to a single 22-h long day. The ultrastructural changes occurring in the meristematic cells during the complete morphogenetic switch were quantitatively investigated using both the planimetric and the point-counting stereological methods. The 2 methods yield very similar results and are thus equally appropriate for the study.
The cell, nucleus, and dispersed chromatin sizes are greater in meristems of plants induced to flower (evoked meristems) than in meristems of control vegetative plants. A first size maximum is reached at 26 h after the start of the inductive long day and a second at 54 h. These 2 maxima occur just prior to 2 mitotic waves culminating respectively at 26–30 and 62 h.
Neither the condensed chromatin size nor the number of chromocentre profiles per nucleus section change. Consequently the dispersed chromatin: condensed chromatin ratio increases in evoked meristems. This change is discussed in relation to current views on the differential genetic activity of the 2 kinds of chromatin.
There is a late but large increase in size of the nucleolus. Dramatic changes in texture are associated with the enlargement of this organelle. These changes are the disappearance of the segregation of fibrillar and granular components and a loss of compactness due to marked vacuolation. All these changes in size and structure are interpreted as indicating a late increase in nucleolar synthesis of ribosomes in the evoked meristems.
Avian sarcoma virus transformed hamster cells made resistant to ethidium bromide
Authors: Altaner C. , Matoska F. 
Published: April 2021

ABSTRACT
Hamster cells transformed with the Schmidt-Ruppin strain of avian sarcoma virus were selected for resistance to ethidium bromide (EB). The resistant cell lines proliferated in the presence of up to 30 μg/ml EB.
From avian sarcoma virus-transformed hamster cells already resistant to bromodeoxyuridinu (BrdU), ethidium bromide-resistant cells which were able to grow in 10μg/ml EB were also prepared. These cells remain deficient in thymidine kinase activity and are suitable for selective preparation of hybrid cells.
The EB resistance was genetically stable. The EB-resistant cell lines, and doubly resistant cells (BrdU, EB) showed no differences in mitochondrial ultrastructure compared with the original cell lines. Thymidine incorporation into mitochondrial DNA was not influenced by EB resistance.
All resistant cell lines, including the doubly resistant cell line, contained the avian sarcoma virus genome. The number of cells needed for positive rescue experiments for avian sarcoma virus genome by cell fusion with permissive chicken embryo cells was the same as with the original cell lines. The single EB-resistant cell lines contained R-type virus-like particles, while in BrdU-rcsistant and doubly resistant cells the R-type particles were absent.
The possible nature of EB resistance is discussed.
Cytofluorimetric analysis of nuclear dna during meiosis, fertilization and macronuclear development in the ciliate Tetrahymena pyriformis, syngen 1
Authors: Doerder F. P. , Bault L. E. De 
Published: April 2021

ABSTRACT
Fluorescence cytophotometry was used to study nuclear DNA content and synthesis patterns during meiosis, fertilization and macronuclear development in the ciliated protozoon, Tetra-hymena pyriformis, syngen i. It was found that cells entered conjugation with a G1 (45C) macronucleus and a G2 (4C) micronucleus. During meiosis the micronucleus was reduced to 4 haploid nuclei, each with a 1C amount of DNA; each meiotic product then replicated to 2C, but only the nucleus next to the attachment membrane in each conjugant divided to form the two 1C gametic nuclei. The gametic nuclei replicated to 2C prior to fertilization; hence there was no S-period in the 4C fertilization nucleus (synkaryon). The first postzygotic division products immediately entered an S-period to become 4C, and at the second postzygotic division, each of the two 4C nuclei in each conjugant divided to form one 2C micronucleus and one 2C macro-nuclear Anlage. The macronuclear Anlagen began DNA synthesis immediately and were about 8C at the completion of conjugation; the micronuclei did not undergo rapid DNA doubling and measured between 2C and 3C when the conjugants separated. The old macronucleus did not participate in any S-period during conjugation and began to decompose after the second postzygotic division; it contained an average of 24C at the end of conjugation. From this sequence of nuclear divisions a pattern emerges that, unless a general cytoplasmic signal for DNA synthesis is suppressed, DNA synthesis always occurs in micronuclear division products immediately following separation of sister chromatids.
Nuclear development continued in the first two cell cycles after conjugation. In exconjugants (the first cycle), macronuclear Anlagen underwent two rounds of DNA synthesis to become 32C and both micronuclei also underwent DNA synthesis. However, prior to the first cell division, one micronucleus and the old macronucleus completely disintegrated, and at the first cell division the remaining 4C micronucleus divided and one macronuclear Anlage was distributed to each resulting caryonide. At the end of the second cell cycle, the dividing macronucleus of each caryonide contained about 128C.
These results relate to the question of ploidy of macronuclear subunits. It is argued that the G1 macronucleus contains 22 or 23 diploid subunits, each subunit being a copy of the diploid micronuclear genome. It is suggested that unequal macronuclear division relates to the question of subunit ploidy by playing a role in the phenomenon of macronuclear assortment.
Observations on the sorting-out of embryonic cells in monolayer culture
Authors: Steinberg M. S. , Garrod D. R. 
Published: April 2021

ABSTRACT
Two problems are raised concerning the movement of cells during tissue-specific sorting-out of chick embryo cells in mixed aggregates, (i) A possible expectation from the hypothesis of ‘contact inhibition’ is that cells which are entirely surrounded by other cells in monolayer should be held stationary. Cells within solid aggregates, being totally surrounded by others, might also not be expected to move. How is it then that cell movement takes place within solid aggregates during sorting-out ? (ii) Are the movements of cells within sorting aggregates ‘passive’, being driven by adhesive differentials, or ‘active’, being merely guided by such differentials ?
In order to study these questions, sorting-out experiments with chick embryonic limb bud mesenchyme and liver cells were carried out in monolayer culture, permitting direct observation of cell movements. Cell behaviour was observed by time-lapse cinematography. Sorting-out of these cells in monolayer began before and continued after the cells had spread to confluency. During sorting, liver cells showed ruffling activity even when they appeared to be totally surrounded by other cells.
Both cell types showed contact inhibition as judged by the criterion of monolayering, for they did not move over each other but remained attached to the substratum. Yet the cells in the confluent monolayer were not immobilized. Because of this, we suggest that the observed restraint against overlapping did not result from an inhibition of movement.
Several considerations, detailed in the text, suggest that cell movement during sorting-out involves active locomotion.
Previous work suggests that sorting-out configurations are determined by the relative intensities of intercellular adhesive strengths, the more cohesive of 2 cell populations tending to adopt the internal position. While limb bud cells form internal islands surrounded by liver cells in solid aggregates, the reverse was found to be the case in these monolayers. This suggests that, in the monolayer, limb bud cohesiveness is depressed relative to liver cell cohesiveness. This is consistent with the observation that the limb bud cells flattened themselves markedly against the substratum, significantly decreasing their area of mutual apposition.
Transformation of plastids in the leaves of Acer negundo L. var. odessanum (H. rothe)
Authors: Wrischer M. , Ljubešlć N. , Devidé Z. 
Published: April 2021

ABSTRACT
The leaves of Acer negundo L. var. odessanum (H. Rothe), if permanently exposed to strong sunlight, do not green, but remain yellow and finally become bleached. In yellow leaves the plastids contain single thylakoids and no grana. In plastids of bleached leaves, however, only vesicles are present. The concentration of chlorophylls and photosynthetic activity are much lower in those leaves than in the green ones.
If the illumination is reduced (e.g. by shading) both the yellow and the bleached leaves become greenish, and even fully green after a few days at a sufficiently low light intensity. The plastids of yellow-green leaves contain small grana. In dark green leaves the thylakoid system of the chloroplasts is normally developed forming true grana, regardless of whether the leaves were originally green, or became green by shading the yellow or bleached ones. Their pigment concentration and photosynthetic activity are also normal.
If green leaves are exposed to sunlight they do not yellow or bleach. During a 3-week period the structure of the thylakoid system did not perceivably change, with the exception that large plastoglobules formed in the stroma.
The localization of retinol-binding protein in rat liver by immunofluorescence microscopy
Authors: Poole A. R. , Dingle J. T. , Mallia A. K. , Goodman DeW. S. 
Published: April 2021

ABSTRACT
The localization of immunoreactive retinol-binding protein (RBP) in rat liver was studied by immunofluorescence microscopy. The study employed specific antisera to rat RBP prepared in a rabbit and in a sheep. The indirect, two-stage method of localizing tissue antigens was employed, and livers of both normal and vitamin A-deficient rats were examined. Fab′ fragments of immunoglobulins were used, to minimize non-specific labelling of the frozen sections of liver. With these techniques, the specific immune staining of RBP was observed within liver parenchymal cells. This staining appeared as both particulate and diffuse within the cytoplasm of the parenchymal cells, and was not concentrated within one region of the liver cell or lobule. Staining for RBP was not observed in nuclei or in cells other than parenchymal cells. Similar particulate and diffuse immune staining for RBP was observed in liver sections from both vitamin A-deficient and normal rats. More intense immune staining appeared to be present in the sections of vitamin A-deficient animals, in good correlation with the expected higher levels of RBP in deficient as compared to normal liver.
When liver sections were exposed to an antiserum to rat albumin, instead of one to rat RBP, immune cytoplasmic staining was observed which was entirely of a diffuse nature, and did not appear particulate or granular. The findings suggest that RBP, unlike albumin, is localized in part within cytoplasmic vesicles or granules which are large enough to be detected with immunofluorescence, and which are present in livers of both normal and vitamin A-deficient animals. The nature of these putative RBP-containing particles remains to be explored.
Colony-stimulating factor (csf) in the uterus of the pregnant mouse
Authors: Rosendaal M. 
Published: April 2021

ABSTRACT
During the growth of the pregnant uterus of inbred Balb/c mice uterine colony-stimulating factor (CSF) content increased 800-fold. This corresponded to a 75-fold increase in CSF concentration. The size of the increase was the same in the uteri of inbred Balb/c mice and the uteri of F1 hybrid C57Bl/Balb/c mice mated with F1 males. It was about four times greater in these uteri than it was in the uteri of randomly mated TO mice. After unilateral Fallopian tubal ligation of TO mice the concentration of CSF was as great in the non-gravid uterine horns as it was in the gravid uterine horns.
Physicochemical characterization of CSF from extracts of pregnant uterus showed that it differed from that found in foetal extracts and that found in the circulation. Its function in the pregnant uterus is discussed.
The arrangement of germ cells in the rat seminiferous tubule: an electron-microscope study
Authors: Moens P. B. , Hugenholtz A. D. 
Published: April 2021

ABSTRACT
The spermatogonia and early spermatocytes of 13 samples of rat seminiferous epithelium (about 0·05 mm2 each) were mapped from electron micrographs of serial sections. Clones of cells, connected by cytoplasmic bridges (syncytia of 2–100 cells), in various stages of spermatogenic development were identified. Maps of 7 separate areas are illustrated. It is concluded that, contrary to the models of spermatogonial proliferation based on light-microscope observations, regions of seminiferous epithelium which are identical in terms of spermatid and spermatocyte criteria have, in fact, quantitative and qualitative differences in their spermatogonial population. The data are interpreted that for a given epithelial area there is a periodic build-up of spermatogonia which then produce several successive quanta of spermatocytes and when the spermatogonia are depleted the process repeats.
That cell numbers less than double following a mitotic cycle has generally been attributed to systematic degeneration. Evidence from electron microscopy indicates, however, that at the mitotic peaks not all the syncytia undergo division but that some remain arrested. Similarly, within a dividing syncytium a few cells do not divide while they advance developmentally with the syncytium as a whole. The observed large size of spermatocyte syncytia further argues against systematic degeneration with its attendant fragmentation of syncytia.
Macronuclear differentiation during oral regeneration in Stentor coeruleus
Authors: Paulin J. J. , Brooks A. Susan 
Published: April 2021

ABSTRACT
The moniliform macronucleus of Stentor coeruleus coalesces and renodulates during division, reorganization and regeneration. These nuclear events are spatially and temporally synchronized with oral primordium development occurring at stages six and seven of membranellar morphogenesis. Coalesced, elongating and early renodulating macronuclei at stages six and seven contained microtubules within double membrane-bound channels, passing through the nucleus parallel to the long axis. The number of microtubules per channel varied between 4 and 23. Microtubules were also found in the perinuclear cytoplasm at these stages, forming a loose network around the nucleus. The microtubules and channels are absent in control cells and macronuclei of regenerating cells prior to stage six. These transient microtubules and channels appearing in late stage six and stage seven may provide the axial plane on which elongation of the macronucleus proceeds.
Ultrastructural changes and a second mode of flagellar degeneration during ageing of Phytophthora palmivora sporangia
Authors: Hemmes D. E. , Hohl H. R. 
Published: April 2021

ABSTRACT
Ageing of sporangia in Phytophthora palmivora is accompanied by a gradual breakdown of flagella, a transformation of the ‘fingerprint’ vacuoles, extensive vacuolization of the cytoplasm, accumulation of bundles of microtubules (mastigonemes) contained within cisternae of the rough endoplasmic reticulum, formation of a germination wall lining the inside of the sporangial wall and production of secondary sporangia. The mechanism of fiagellar degeneration differs from that observed in directly germinating sporangia. In ageing sporangia and in sporangia induced to germinate directly with germ tubes, there is a close correlation between loss of competence for zoosporogenesis and breakdown of the flagella.
Pattern of incorporation of [3H]uridine into rna of amphibian oocyte nucleoli
Authors: Macgregor H. C. 
Published: April 2021

ABSTRACT
Amphibian oocytes were incubated in vitro in the presence of [3H]uridine, and autoradiographs were made of nucleoli isolated from these oocytes and of sections of oocytes.
After incubations of 2 h or less the nucleoli of oocytes larger than 0·6 mm diameter are asymmetrically labelled. With longer incubations nucleoli from oocytes of 0·6 tori mm diameter become more uniformly labelled. Those of oocytes larger than 1·2 mm diameter remain asymmetrically labelled whatever the incubation time. Autoradiographs of 1-μ sections through oocytes larger than 0·6 mm diameter show, after short incubations, asymmetrically labelled nucleoli. In these autoradiographs silver grains are concentrated over a distinct component of each nucleolus which is eccentrically placed towards the nuclear envelope. Thin sections of oocytes show nucleoli consisting of core and cortex. The core material is always concentrated into the half of the nucleolus which, lies nearer the nuclear envelope. Autoradiographs of separated nucleolar cores and cortices from oocytes larger than 0·6 mm diameter show, after short incubations, silver grains over cores but not over cortices. Similar autoradiographs prepared from oocytes of 0·6 to 1·1 mm diameter, after longer incubations, show grains over cores and cortices.
These results appear to indicate that nucleolar RNA is synthesized in the nucleolar core, in association with the nucleolar DNA, and is thence transferred to the cortex where it is built into ribonucleoprotein particles. Initial asymmetrical labelling is a consequence of the eccentric location of the nucleolar core. The nucleoli of oocytes smaller than 0·6 mm diameter always label symmetrically; such nucleoli consist entirely of core material. It is suggested that the nucleoli of oocytes larger than 1·2 mm diameter always label asymmetrically because transfer of RNA from core to cortex proceeds more slowly than in smaller oocytes.
Fine structure of the eye of a nudibranch mollusc, hermissenda crassicornis
Authors: Eakin R. M. , Westfall Jane A. , Dennis M. J. 
Published: April 2021

Abstract
The eye of a nudibranch, Hermissenda crassicornis, was studied by light and electron microscopy. Three kinds of cells were observed : large sensory cells, each bearing at one end an array of microvilli (rhabdomere) and at the other end an axon which leaves the eye by the optic nerve ; large pigmented supporting cells ; and small epithelial cells, mostly corneal. There are five sensory cells, and the same number of nerve fibres in the optic nerve. The receptor cells contain an abundance of small vesicles, 600–800 A in diameter. The lens is a spheroidal mass of osmiophilic, finely granular material. A basal lamina and a capsule of connective tissue enclose the eye. In some animals the eye is ‘infected’ with very small bodies, 4–5 μin diameter, thought to be symbionts.
Spindle Birefringence of Isolated Mitotic Apparatus Analysed by Pressure Treatment
Authors: Forer A. , Zimmerman A. M. 
Published: April 2021

ABSTRACT
Sea-urchin zygote mitotic apparatus (MA) isolated in a glycerol/dimethylsulphoxide medium were treated with pressure. Pressure treatment had no effect on spindle birefringence when MA were in full-strength isolation medium. After placing MA in quarter-strength isolation medium, pressures of 4·0 × 103– 1·8 × 104 Ibf in.−2 (2·76 × 104–1·24 × 105 kN m−2) for 15 min caused reduction of birefringence which occurred in 2 steps: firstly 20–30% of the birefringence was lost, and then, at higher pressures, the rest of the birefringence was lost. Electron microscopy suggested that pressure-induced changes were in non-microtubule material. Pressure treatment had no effect on MA isolated with hexylene glycol when the MA were pressurized in hexylene glycol; but pressure treatment did cause loss of birefringence when MA isolated in hexylene glycol were transferred immediately into glycerol/dimethylsulphoxide medium and were subsequently treated with pressure (after dilution into quarter-strength glycerol/dimethylsulphoxide). We discuss the differences in response between isolated MA and in vivo MA, and we discuss the possibility that 2 components contribute to MA birefringence.
Spindle Birefringence of Isolated Mitotic Apparatus Analysed by Treatments With Cold, Pressure, and Diluted Isolation Medium
Authors: Forer A. , Zimmerman A. M. 
Published: April 2021

ABSTRACT
Mitotic apparatus (MA) were isolated from sea-urchin zygotes using glycerol-dimethyl-sulphoxide. Cold treatment had no effect on MA birefringence when MA were in isolation medium, but caused a 10–15% reduction of MA birefringence when MA were in quarter-strength isolation medium. Pressure treatment also caused a reduction in MA birefringence, but the cold and pressure treatments were not additive, suggesting that both treatments affected the same MA component. MA were not stable in quarter-strength isolation medium, and birefringence gradually decayed, with a half-life of about 40 h. Electron microscopy after cold treatment, or after decay of 55 % of the MA birefringence showed abundant, normal-looking microtubules, suggesting that alterations in non-microtubule components cause the reductions in birefringence. Addition of EGTA eliminates the effect of cold treatment, suggesting that Ca*+ has a role in maintenance of spindle structure. We discuss possible reasons why isolated MA do not respond to cold treatment like MA in vivo.
A comparison of membrane fracture faces of fixed and unfixed glycerinated tissue
Authors: Breathnach A. S. , Gross M. , Martin B. , Stolinski C. 
Published: April 2021

ABSTRACT
Fixed (glutaraldehyde, 3%) and unfixed specimens of rat buccal epithelium, striated muscle, and liver, were cryoprotected with glycerol, freeze-fractured, and replicated without sublimation. A comparison of fracture faces of general plasma membranes, nuclear membranes, mitochondrial membranes, and membranes of rough endoplasmic reticulum revealed no significant differences as between fixed and unfixed material. Apart from some membranes of liver endoplasmic reticulum, there was no evidence of aggregation or redistribution of intramembranous particles in the unfixed material. The results demonstrate that chemical prefixation of tissues for freeze-fracture is not always necessary, or even desirable, and that glycerol may not be as deeply or directly implicated in particle aggregation as previously thought. Fixation with glutaraldehyde alters the cleaving behaviour of plasma membrane at desmosomes and tight junctions, but not at gap junctions.
A morphometric and biochemical investigation of the vesiculation of kidney microvilli
Authors: Booth A. G. , Kenny A. J. 
Published: April 2021

ABSTRACT
The vesiculation of kidney proximal tubule microvilli has been examined in tissue slices, isolated brush borders and isolated microvilli. Vesiculation could be induced in tissue slices by 2,4-dinitrophenol and anoxia. Cycloheximide and fluoride had no effect. In brush borders and microvilli, the vesiculation was found to be essentially temperature-dependent. Whilst an osmotic swelling could be produced by hypo-osmolar media, the temperature-dependent vesiculation could not be prevented in hyper-osmolar media. Of a wide variety of reagents tested, only glutaraldehyde, mercuric chloride and mersalyl were effective in arresting the vesiculation. Electron micrographs show that vesiculation involves a collapse of the internal structure of the microvillus. However, the collapse was not associated with depolymerization of the microvillus actin filaments. Rather it appeared to be due to the parting of cross-bridges between the membrane and the actin filaments. The nature of these cross-bridges is discussed: it is suggested that α-actinin possesses the characteristics for the cross-bridging protein and that vesiculation might be explained by the displacement of α-actinin by tropomyosin.