bluuebunny/crossref_metadata_2025_split huggingface dataset:
The chloroplast nucleoid inOchromonas danica: II. evidence for an increase in plastid dna during greening
Authors: Gibbs Sarah P. , Mak R. , Ng R. , Slankis T. 
Published: April 2021

ABSTRACTDuring the first 24 h of light-induced chloroplast development in Ochromonas danica, the single plastid nucleoid increases 4-fold in volume. During this interval, the concentration of DNA within the nucleoid, as determined by eye and by counts of fibrils per /tm2 of nucleoid sectioned, remains constant. Thus, on morphological grounds, it appears that the amount of plastid DNA increases 4-fold during greening.To determine whether the chloroplasts of light-grown cells contain more DNA than the proplastids of dark-grown cells, exponentially growing cultures of dark- and light-grown cells were each labelled for exactly one generation with [3H]thymidine. After fixation, the cells were embedded in Araldite, and serial 1μm sections through entire plastids and nuclei were prepared for autoradiography. In this study, the chloroplasts of light-grown cells incorporated almost 4 times as much label into DNA as the proplastids did, whereas the nuclei of the dark- and light-grown cells were equally labelled. Another study showed that light-grown cells have slightly more total cell DNA than dark-grown cells. These 2 studies provide prima facie evidence that chloroplasts contain more DNA than proplastids and support the hypothesis that an increase in plastid DNA accompanies chloroplast development in Ochromonas.
Light- and electron-microscope observations on certain leukocytes in a teleost fish and a comparison of the envelope-limited monolayers of chromatin structural units in different species
Authors: Davies H. G. , Haynes Μ. E. 
Published: April 2021

ABSTRACT
Previously it was shown that the nuclear envelope-limited sheets of chromatin, monolayers of nucleoprotein structural units, are present in blood cells from 4 classes of vertebrates. Now we show that sheets of similar width are present in certain leukocytes of a fifth class, a teleost fish. We describe the fine structure of leukocytes in peripheral blood and in the main haematopoietic organ, kidney. We also examined the granulocytes of connective tissue in intestine. By May-Grunwald-Giemsa staining and electron microscopy heterophilic granulocytes, cosinophils but no basophils could be recognized in peripheral blood and kidney. Problems in classification of the cells are discussed. In one group (A) of 5 fish, sheets occurred at a frequency of roughly 1% in heterophilic (type 1) granulocytes and lymphocytes from peripheral blood. No sheets were found in a second group (B) of 5 fish. Kidney and intestine were examined in some fish from both groups and no sheets were present. In an atypical group (C) sheets were found in the eosinophilic (type 2) granulocytes from peripheral blood of one fish and in lymphocytes from connective tissue of intestine in another. Sheets were usually associated with nuclei of irregular shape and their width averaged 36 nm.
We tabulate data from other workers on occurence and width of sheets. They are found in all the main classes of tissue in mammals, namely blood and other connective tissues, in epithelial, nervous, germinal tissue and muscle, as well as in invertebrate and certain plants. Their nearly constant width, average value 35 nm, provides very convincing evidence for the hypothesis that the molecules of DNA and protein are organized into the same fundamental structural units, irrespective of species. We discuss the variable incidence of sheets among different cell types and the factors which might determine this.
Synthesis of ribosomal RNA in synkaryons and heterokaryons formed between human and rodent cells
Authors: Marshall C. J. , Handmaker S. D. , Bramwell Μ. E. 
Published: April 2021

ABSTRACT
A study has been made of the ribosomal RNA and chromosome constitution of man-mouse hybrid cells. Previous work has shown that no human 28 s rRNA is detectable in man-mouse synkaryons. In general human chromosomes are lost from such hybrids.
With a recently developed method for distinguishing mouse from human chromosomes, an analysis of various man-mouse hybrid cell lines has been made. This indicates that not all the human chromosomes bearing nucleolar organizers are lost in the hybrid cells and such loss cannot alone explain the absence of human 28 s rRNA.
An examination of the 28 s rRNA synthesized by heterokaryons formed from several different parent cells has revealed that both parental types of 28 s rRNA are present in heterokaryons. The control of rRNA synthesis in hybrid cells is discussed.
Ultrastructural localization of phosphohydrolases in gametes, zygotes and zoospores of Ulva mutabilis føyn
Authors: Bråten T. 
Published: April 2021

ABSTRACT
Gametes, zoospores, and zygotes of the multicellular, green alga Ulva mutabilis showed acid phosphatase reaction product in Golgi vesicles and on the membrane lining the vacuole. In addition gametes and zoospores showed enzyme reaction product on the entire surface membrane including the flagellar membrane. The surface membrane enzyme activity disappears from the zygote shortly after copulation and at the same time lysosome-like bodies start to appear in the cytoplasm. No alkaline phosphatase activity could be detected. The distribution of acid phosphatase is discussed in relation to the events taking place during and shortly after fertilization.
Intercellular adhesion and formation of aggregates in normal and Talpid3 Mutant chick limb mesenchyme
Authors: Ede D. A. , Flint O. P. 
Published: April 2021

ABSTRACT
It is demonstrated, using the Couette viscometer method, that talpid3 mutant chick wing mesenchyme cells are more adhesive to one another than are normal cells. The relation of this to differences in the size and shape, and the internal architecture, of aggregates produced in rotation cultures of these cells was investigated. Sequences of sections through aggregates in all stages of formation, from 2-cell aggregates up to those with large cell numbers, were prepared. These confirm the theoretically predicted relationships among adhering cells which would produce the observed small, spherical talpid3 aggregates and the larger, unevenly shaped normal aggregates. The cell contacts are further analysed with electron micrographs.
Histone proteases of avian erythroid cells
Authors: Harlow R. , Wells J. R. E. 
Published: April 2021

ABSTRACT
Protease activity associated with avian erythroid chromatin has been studied by gel electrophoresis of histones. Histone degradation is minimal at neutral pH, but is readily detected when chromatin is incubated at pH 3, and is evident to a lesser extent at pH 9.
As a result of the pH 3 activity, the f1 and f2 chistones are preferentially degraded when the histone complement is DNA-bound, but these histones are relatively resistant to attack when present as free histone.
The pH 3 activity reported here has properties similar to those of neutral histone proteases from other tissues, except that it is not inhibited by bisulphite. Added exogenous proteins are not degraded.
The activity of avian erythroid histone protease decreases as maturation of the cells proceeds. Since we have previously shown that turnover of DNA-bound f2c histone occurs in reticulocytes and histone synthesis is absent in erythrocytes, it is possible that the histone protease described here may be involved in f2c histone turnover.
A possible role for intercisternalelements in the formation of secretory vesicles in plant golgi apparatus
Authors: Mollenhauer H. H. , Morré D. J. 
Published: April 2021

ABSTRACT
Oriented fibres in the intercisternal regions of plant dictyosomes are usually associated with flattened portions of cisternae. In outer cap cells of maize roots, however, the intercisternal fibres are associated mainly with unique secretory vesicles which are elongate or kidney-shaped during their formative stages. Fibres are oriented parallel with the long axes of the vesicles even at early stages of vesicle formation. Because of their early presence and orientation, the fibres may aid in organizing and/or shaping the secretory vesicles in this tissue.
Lipid staining for the electron microscope: a new method
Authors: Wigglesworth V. B. 
Published: April 2021

ABSTRACT
Tissues fixed in osmium tetroxide or in combined osmium and glutaraldehyde (Hinde), embedded in Spurr’s medium, cut at 0 5–1 μm and mounted in Farrants’ gum medium containing ethyl gallate, show good staining of lipid-containing structures (droplets of triglyceride, membranes, mitochondria, etc.) in the light microscope.
Such preparations show moderate contrast in the electron microscope without further staining. But a specific increase in contrast in lipid-rich structures is obtained by partition of the tissues, before embedding, in 70 % ethanol saturated with the monoterpene hydrocarbon myrcene, with or without the addition of 0·1 % ethyl gallate, followed by osmium tetroxide.
This method will visualize both saturated and unsaturated lipids, including waxes.
Evidence for the presence of dna in the pellicle of Paramecium
Authors: Smith-Sonneborn Joan , Plaut W. 
Published: April 2021

ABSTRACT
Two lines of evidence for the existence of DNA in the pellicle of Paramecium are presented : fluorescence staining and autoradiography. The latter shows deoxyribonuclease-sensitive incorporation of tritiated thymidine in or near the kineties. Fluorescence microscopy permits the localization of DNA at the site of kinetosomes. The possibility that the DNA is not native to the pellicle but introduced during preparative procedures is tested experimentally and shown to be unlikely.
Interaction between normal and transformed bovine fibroblasts in culture: I. cells transformed by rous sarcoma virus
Authors: Macintyre Elizabeth , Pontén J. 
Published: April 2021

Abstract
Base layers of untransformed normal embryonic lung fibroblasts in different stages of growth were challenged with RSV (Rous sarcoma virus)-transformed bovine fibroblasts. The effect of this admixture on the growth of the RSV-transformed cells was studied. In all cases, the transformed cells proliferated freely, and it is concluded that the normal cells exerted no inhibition on the transformed cells.
The fine structure of cytoplasmic inclusions in a mycoplasma-like infection in mice
Authors: Gay F. W. , Attridge J. T. 
Published: April 2021

Abstract
A mycoplasma-like agent, which resembled grey lung ‘virus ‘of Andrewes and Glover in its sensitivity to chemotherapeutic substances in vivo, in its failure to grow in culture media, and in its failure to elicit immunity in infected animals, was derived from rats with naturally acquired chronic pneumonia. In mice it produced a chronic pneumonia from which mycoplasmas could not be cultured. When sections of diseased mouse lung were examined by electron microscopy, completely novel intracytoplasmic inclusions were observed in mononuclear cells lying free in the alveoli and bronchioles. The inclusions, which were less numerous in mice being treated with chemotherapeutic substances which inhibit the growth of mycoplasmas, appeared to represent successive stages in a developmental process. The fine structure of the inclusions is described and their possible nature is discussed.
Control of cell size and cycle time in Schizosaccharomyces pombe
Authors: Fantes P. A. 
Published: April 2021

ABSTRACT
Steady-state and perturbed cells of Schizosaccharomyces pombe have been observed through several division cycles by time-lapse photomicrography. Perturbed cells were produced by the use of a conditional cell division cycle mutant in which nuclear division is reversibly blocked at high temperature. These experiments show that in both populations cell length at division and cell cycle duration are homeostatically controlled, probably by a primary size-control mechanism. Cycle time is indirectly controlled, as cells which have an extended cycle are on average larger at division, so that daughters of such cells need to grow by a smaller amount and for a shorter period, before dividing again. In general, deviations from the mean are corrected within a single cycle, but in the case of very long cells the control breaks down because the cycle cannot be shortened by more than a quarter under the conditions used. These cells take more than one cycle to return to normal.
Differentiation of the tapetum in A Vena: I. the cell surface
Authors: Steer M. W. 
Published: April 2021

ABSTRACT
The development of the tapetal cell surface and associated structures in Avena has been followed from cell formation to senescence. Plasmodesmata initially connect the tapetal cells to each other, the pollen mother cells, and the inner loculus wall cells. These connexions are subsequently severed, those to the sporogenous cells being broken first at the pollen mother cell surface during callose wall formation. Loss of cellulose from the tapetal walls was followed using the decline in the ability of the wall to bind the fluorescent brightener, Calcofluor White M2R New. Subplasma-membrane microtubules persist after loss of the cellulose wall. The tapetal plasma membrane facing the meiocytes then develops a series of depressions, or cups, over its surface, which are later the site of pro-orbicule formation. Sporopollenin is laid down over the pro-orbicules, to form orbicules, and over other tapetal cell surfaces. No morphological evidence was found for the intracytoplasmic formation of pro-orbicules or polymerized sporopollenin precursors.
These observations on Avena are compared with those on other plants. The changes in the cell wall and associated structures, plasmodesmata and microtubules, are considered in detail, while the general significance of cell wall loss to the water relations of the tissue are assessed. Proposals that pro-orbicule formation results from non-specific accumulation of lipid at a free cell surface are rejected, instead this formation is considered to be related to the presence of a specially modified plasmamembrane surface.
Growth In Vitro of tumour cell × fibroblast hybrids in which malignancy is suppressed
Authors: Straus D. S. , Jonasson J. , Harris H. 
Published: April 2021

ABSTRACT
We have studied the growth in vitro of a lymphoma × fibroblast hybrid and several melanoma × fibroblast hybrids in which malignancy is suppressed. The parental cells, the hybrids, and malignant segregants derived from the hybrids were analysed for serum requirement, cloning efficiency in soft agarose, density-dependent inhibition of growth, and secretion of plasminogen-activating enzyme. One malignant segregant from the lymphoma × fibroblast cross was found by a number of criteria to have a more highly ‘transformed’ phenotype than the hybrid from which it was derived. However, in the case of the melanoma × fibroblast crosses, none of the parameters examined, could be correlated in a direct way with malignancy.
Synchrony in the rhythm of the contraction-relaxation cycle in two plasmodial strands of Physarum Polycephalum
Authors: Takeuchi Yuko , Yoneda Mitsuki 
Published: April 2021

ABSTRACT
Rhythmicity of contraction of plasmodial strands of Physarum polycephalum was studied, by measuring the isometric tension exerted by isolated segments of the strands. When 2 strands were connected by way of a plasmodial mass, the contraction–relaxation cycle of the 2 strands synchronized. Such cyclic activity of the strand was found to be well coordinated with shuttle streaming in the plasmodial mass which had been in connexion with the strand. The presence of a control system which induces synchrony of periodic activity over the entire body of a plasmodium is discussed.
An analysis of transport, exchange, and binding of sodium and potassium in isolated amphibian follicles and denuded oocytes
Authors: Morrill Gene A. , Ziegler David , Zabrenetzky Vivian S. 
Published: April 2021

ABSTRACT
The uptake and efflux of 22Na and 42,K were studied in fully grown, prophase-arrested Rana pipiens follicles and denuded oocytes. Follicles and denuded oocytes contained large stores of both cations, although only 15–30% of the total Na+ and 1–2% of the total K+ pools exchanged within the 12-h period studied. “Na uptake and efflux in follicles exhibited two-step kinetics with a smaller rapidly exchanging fraction (12–15%, t0·5 ∼ 15 min), and a larger slow fraction (t0·5. ∼ 0·5 day). Denuded oocytes displayed a single kinetic fraction with a rate constant similar to the slow fraction of follicles, suggesting that the fast fraction was associated with the follicular epithelium. Both follicles and denuded oocytes exhibited fast and slow 42K uptake kinetic fractions, although the follicular fast fraction was considerably larger. Conversely, whereas follicular 42K efflux also proceeded with two-step kinetics, 42K efflux from denuded oocytes appeared as a single slow fraction. Thus, a large portion of the fast K+ fraction taken up by the follicles is attributable to the somatic cells of the follicular envelopes. Na+ and K+ activities were measured in the cytoplasm of the in situ (follicular) oocyte using cation-selective microelectrodes. After correcting for Na+ and K+ associated with the follicular envelopes, only about 6% of the total ooplasmic Na+ and less than 1% of the K+ could be accounted for as bound or sequestered.
Ultrastructure of late oocyte nuclei in Rana temporaria
Authors: Gruzova M. N. , Parfenov V. N. 
Published: April 2021

ABSTRACT
The ultrastructural organization of the nucleus during late oogenesis in Rana temporaria was examined in normal and in hormone-stimulated maturing oocytes in vitro. At this stage numerous nucleoli are assembled around a knot of highly contracted chromosomes (the karyosphere) making up a karyosphere capsule. The nucleoli are fibrillar. They bear no pro-ribosomal granules and do not synthesize RNA. This period is characterized by segregation of nucleolar material into core and cortex. The nucleoli are of irregular shape. The presence of micronucleoli and nuclear bodies indicates an intensive fragmentation of nucleolar material.
In the central fibrous zone of the capsule separating the chromosomes from the nucleoli, abundant accumulations of annuli lacking any membranous component occur. The annuli are connected by fibrous material and are regularly packed, forming peculiar pseudomembranes which are connected directly to the chromatin. Pseudomembranes, though less abundant and less regularly packed, are also found in the middle zone of the capsule. Along with annuli, membranous areas of various sizes and shapes are found in the pseudomembranes. Pseudomembranes are linked to micronuclei by granular filaments 20–30 nm thick.
A variety of membranous structures in the form of intranuclear annulate lamellae or membranous tubular formations was detected in the peripheral zone of the capsule and outside it. The conclusion is drawn that the fibrous component of the karyosphere capsule consists of different membranous and pseudomembranous structures. It is suggested that chromatin participates directly in the formation of pseudomembranes and intranuclear membranous structures.
Electron-microscope observations on the organization of hetero-chromatin in certain cells
Authors: Davies H. G. 
Published: April 2021

ABSTRACT
Electron micrographs of sections through the heterochromatin (condensed chromosomes) of erythrocytes from chicken and lamprey reveal alternate equispaced electron-dense and relatively less dense bands lying adjacent and parallel to, and extending considerable distances along, the nuclear envelope. Frequently a triple-structured band (average half-width 183 Å), consisting of a less dense band, a dense band (width 130–170 Å), and a second less dense band is encountered; sometimes there are many (10–12) bands. The dense bands have a variable structure; they may appear continuous or consist of equispaced granules about 220 Å apart, which sometimes have a less dense centre. Similar but shorter dark bands and granules appear throughout the chromatin. Tilting the section in the microscope causes the micrographs to change, bands and granules disappearing and reappearing elsewhere, demonstrating that the images are produced by super position of structures small in dimensions compared with the thickness of the section. Tilting about an axis normal to the band may resolve it into granules. These data indicate that the heterochromatin contains a well-defined structural unit which can form ordered regions, namely layers in contact with the nuclear envelope. The possibility of errors in interpreting the substructure of the bands due to complexity of superposition effects is stressed. The simplest hypothesis to account for the images is that the units are microtubes of outside diameter 130–170 Å, perhaps microhelices formed by coiling DNA with protein, spaced apart equally, perhaps by spacing elements. Microtubes parallel to the optic axis would appear as hollow granules, several one above another in a plane parallel to the axis appearing as a dark band. A similar triple-structured band of average half-width 224 Å is found in cells from newt spleen, lymphocytes, polychromatophil erythroblasts, mature erythrocytes, basophilic granulocytes, reticular cells and macrophages. A survey of published micrographs shows a similar triple structured band of average half-width 212 Å to be a common feature of many cell types. A triple-structured band probably gives rise to the sheets of chromatin, now shown to have a similar triple-layered structure, limited on both sides by nuclear envelope, previously found attached to interphase nuclei and mitotic chromosomes in certain polychromatic erythroblasts from the newt. The effects of tilting the section were studied on objects of known geometry, membranes and cytoplasmic microtubules.
The fine structure of chloroplasts and pyrenoids in some marine dinoflagellates
Authors: Dodge J. D. 
Published: April 2021

ABSTRACT
The chloroplasts of some members of the Dinophyceae are bounded by an envelope consisting of three membranes and having a mean thickness of 230 Å. Within the chloroplast are arranged, in a more or less parallel manner, many lamellae normally composed of three apposed thylakoids, although the number of thylakoids often varies and may reach 30 in a single stack. By study of disintegrated chloroplasts it was found that the thylakoids are circular in shape with a diameter of 0·15 –3·6μ and a mean thickness of 240 Å. Ribosomes, lipid droplets and DNA areas are present in the chloroplast stroma. No connexions were seen between the chloroplasts and any other organelles, nor did the chloroplasts contain girdle lamellae. Stalked pyrenoids, which are found in some dinoflagellates, are shown to arise from the inner face of the chloroplasts, to contain a finely granular material and to be frequently surrounded by an electron-transparent area. These findings are discussed in relation to the fine structure of the chloroplasts and pyrenoids of other algal classes.