bluuebunny/crossref_metadata_2025_split huggingface dataset:
Inorganic phosphate accumulation and phosphatase activity in the nucleus of maize embryo root cells
Authors: Deltour R. , Fransolet S. , Loppes R. 
Published: April 2021

ABSTRACT
The nucleus of growing root cells of Zea mays contains a high concentration of inorganic phosphate. In order to verify whether this high nuclear Pt concentration is correlated with the metabolic activity of the nucleus, the P1 has been visualized in root cells of maize embryos at the electron-microscope level during 2 different periods which are both characterized by a spectacular reactivation of the nuclear metabolism, i.e. the early germination and the period of recovery following a thermal treatment given to the seeds after 48 h of germination. In both situations the P1 concentration increased in the nucleus during its reactivation.
To verify whether the high nuclear P1 concentration could be of endogenous origin, the phosphatase activities were measured in crude extracts of root tissues during nuclear reactivation. The specific activity was optimal at pH 4·5 and was shown to increase with cellular reactivation.
The ultrastructural localization of acid phosphatase activity showed that P1 may be produced at 3 distinct sites: plasmalemma, vacuoles and most probably nucleus itsef. High acid phosphatase activities were found in nuclei displaying a high metabolism.
Taking these results and previous data into account, we suggest that a correlation may exist between the rate of nuclear transcription, the level of nuclear acid phosphatase activity and the nuclear P1 accumulation.
Biophysical and morphological correlates of kinetic change and death in a starved human melanoma cell line
Authors: Sheridan J. W. , Bishop C. J. , Simmons R. J. 
Published: April 2021

ABSTRACT
An investigation was made of the sequential biophysical and morphological changes that occur as cultured human melanoma cells (MM96) outgrow their supply of nutrient. Simultaneous buoyant-density and velocity-sedimentation fractionation experiments were used to characterize cells from 3 kinetically differing types of culture. Cells from exponential cultures were large, moderately dense and rapidly sedimenting; cells from post-exponential cultures were of intermediate size, less dense and much more slowly sedimenting; and dye-excluding cells from reproductively non-viable late post-exponential cultures were small, of widely variable though generally high density and sedimented moderately rapidly. Although reproductive viability was high in cells from both exponential and post-exponential cultures, depletion of clonogenic cells was seen at the extremes of the distribution profiles of cells fractionated by either method. This was particularly evident at the low-density extreme of the buoyant-density profiles where cells retained viability despite their loss of proliferative potential.
As cells became post-exponential, nuclear size diminished in parallel with cell size, the number of microvilli declined, mitochondria condensed, cytoplasm vacuolated, the frequency of osmiophilic vacuolar inclusions rose, chromatin clumped and nucleoli became prominent. Progression to a reproductively non-viable late post-exponential state resulted in a continued parallel fall in nuclear size, increased cytoplasmic blebbing, further mitochondrial condensation, an increased proportion of cytoplasmic vacuoles containing osmiophilic material, the major part of which was melanin, and further clumping and margination of chromatin. Cells progressed rapidly from this newly described pre-apoptotic state to death by apoptosis, a process characterized by the budding and division of cells into a number of ultrastructurally well-preserved membrane-bound fragments.
The movement of cell clusters in vitro. morphology and directionality
Authors: Kolega John 
Published: April 2021

ABSTRACT
The movement of cells in small groups, or clusters, was studied in vitro using epithelioid cells from Gordon-Kosswig melanomas (from poecelid fish) and time-lapse cinemicrography. Tumour expiants cultured on glass yield cell sheets from which groups of cells separate and become independently motile clusters. These clusters typically contain 3–30 cells, but may have as many as 50. They propel themselves at speeds of 0·2–4·0 μm/min by means of broad hyaline lamellae. The distribution of lamellae around the perimeter of each cluster correlates with both direction and speed of cluster movement, i.e. a cluster moves with its most lamellar region at its leading edge, and the greater the extent of the leading lamellar region the greater the speed. Also, a cluster tends to keep moving in the same direction. This persistence is due to a relatively constant distribution of lamellae. Cells on the trailing edge usually lack lamellae and most are very elongate and oriented perpendicular to the direction of cluster movement. In general, whenever a cell elongates, there is a loss of lamellar activity along its taut edges, parallel to the axis of elongation. Thus, any region with less lamellar activity would tend to be elongated by the outward pull of the more active regions to either side and would, in consequence, suffer a further reduction in lamellar activity. In this way, the distribution of regions of lamellar activity is self-reinforcing and the result is persistence of movement in a particular direction. This phenomenon could play an important role in giving directionality to certain morphogenetic movements, such as neural crest cell migration.
Non-selective junctional communication between some different mammalian cell types in primary culture
Authors: Hunter Graeme K. , Pitts John D. 
Published: April 2021

ABSTRACT
Intercellular transfer of tritium-labelled uridine nucleotides has been used to detect junctional communication between various cell types in primary culture. Epidermal kératinocytes, melanocytes and dermal fibroblasts from new-born-mouse skin, and epithelial cells from baby mouse kidney form communicating junctions in all possible homologous and heterologous combinations. This lack of detectable communication specificity between cells in primary culture contrasts with the specificity shown by some established cell lines.
Desmosome frequency: Experimental alteration may correlate with differential cell adhesion
Authors: Wiseman Lawrence L. , Strickler John 
Published: April 2021

ABSTRACT
Differential cell adhesion, a suggested guiding force for tissue rearrangements during embryogenesis, could be affected by desmosome frequency. A model system for studying embryonic tissue-positioning behaviour involves combining different tissues and following their rearrangements. We have previously shown that for one tissue, embryonic chick heart ventricle, direction of tissue positioning can be altered experimentally. Heart tissue precultured for 2 5 days tends to segregate internally, while tissue pre-cultured for just half a day tends to segregate externally. Also, intact fragments of tissue tend to segregate internally, while reaggregates of trypsin-disaggregated tissues tend to segregate externally. We show here that treatments that increase the tendency to internalize also increase the frequency of adherens junctions and treatments that increase the tendency to externalize decrease the frequency of junctions. An identical hierarchical ordering of the 4 experimental tissues occurs with respect to positioning behaviour and desmosome frequency. In the hierarchy, 2 ·5-day-cultured fragments &gt; 2·5-day-cultured reaggregates &gt; 0·5-day-cultured fragments &gt; 0·5-day-cultured reaggregates, tissues to the left tend to segregate internally and to have more desmosomes. Tissues to the right segregate externally and have fewer desmosomes. This is what is expected if desmosomes are organelles for adhesion and if differential adhesion is a factor in tissue-positioning behaviour.
Partial reversion of the transformed phenotype of murine sarcoma virus-transformed cells in the presence of interferon: A possible mechanism for the anti-tumour effect of interferon
Authors: Hicks N. J. , Morris A. G. , Burke D. C. 
Published: April 2021

ABSTRACT
The effect of interferon (IFN) on a series of cellular properties which characterize the transformed state was studied, using normal mouse fibroblasts (both established lines and embryo cells) and cloned derivatives transformed by murine sarcoma virus. It was found that the transformed cells behaved in a more normal fashion in the presence of IFN. This was indicated by reduction in saturation density, decreased DNA synthesis in crowded cultures, decreased formation of foci on monolayers of normal cells, and decreased growth in soft agar. These effects were not due to generalized inhibition of cell growth, since IFN had little effect on the growth and cloning efficiency of the cells used. In the presence of IFN, cellular morphology also appeared more normal. These results suggest that growth control of transformed cells may be at least partly restored by IFN, an effect which could in part account for the antitumour effect of IFN.
The interpretation of interferencereflection images of spread cells: Significant contributions from thin peripheral cytoplasm
Authors: Gingell David 
Published: April 2021

ABSTRACT
In interference-reflection microscopy, used for investigating cell-substratum separation, it is commonly believed that cytoplasmic thickness can be ignored, provided a high illuminating numerical aperture (INA) is used. It is shown here that even when a maximal INA is used, cytoplasmic lamellae of 1 μm or less can be major determinants of the image. The leading lamella of spreading tissue cells and large peripheral areas of Dictyostelium discoideum amoebae on adhesive substrata are less than 1 μm thick and it is argued that hitherto unexplained features of the interference images of these cells may be interpreted in terms of the theory used here.
Determination of secretory vesicle production rates by dictyosomes in pollen tubes of Tradescantia using cytochalasin d
Authors: Picton Jill M. , Steer Martin W. 
Published: April 2021

ABSTRACT
Pollen tubes of Tradescantia were grown in vitro and exposed to 0·3 μg/ml cytochalasin D for 5 or 10 min. Fine-structural observations revealed no visible effect of the drug on the organelles. Stereological analysis, using a method recently developed by Rose (1980) to obtain sphere size-distributions corrected for section thickness, revealed a substantial increase in the number of secretory vesicles present in the cytoplasm around the dictyosomes. Equating the rate of vesicle accumulation with the rate of vesicle production, a total of 5388 vesicles per minute are formed by a growing tube. This corresponds to 2·4 vesicles per minute per dictyosome, and a turnover rate of 3·7 min for a single dictyosome cisterna, or about 15–18·5 min for a complete dictyosome. The calculated vesicle production rate agrees well with that required to sustain the observed growth rate of such tubes, based on the addition of membrane or wall material to the tube tip.
The effects of fibronectin on the adhesion and migration of chinese hamster ovary cells on collagen substrata
Authors: Schor Seth L. , Schor Ana M. , Bazill George W. 
Published: April 2021

ABSTRACT
Data are presented indicating that the adhesion of Chinese hamster ovary cells (CHO) to films of denatured type I collagen occurs by a fibronectin-dependent mechanism, whereas the adhesion of these cells to 3-dimensional gels of native type I collagen fibres may occur by either a rapid, fibronectin-dependent mechanism or by a slower, fibronectin-independent mechanism. Data are also presented indicating that fibronectin promotes the migration of CHO cells on native type I collagen fibres.
The effect of various cooling rates on the membrane ultrastructure of frozen human erythrocytes and its relation to the extent of haemolysis after thawing
Authors: Fujikawa Seizo 
Published: April 2021

ABSTRACT
Human erythrocytes suspended in buffered isotonic saline were frozen to the temperature of liquid nitrogen at various cooling rates of 3, 140,700, 1800,3500, 8000 and 11 500 deg. C/min. The membrane ultrastructure in the frozen state and the extent of haemolysis after thawing were examined at each cooling rate. As the cooling rates increased from 3 to 3500 deg. C/min, the extent of lysis gradually decreased, but further increase in cooling rates in excess of 8000 deg. C/min resulted in an abrupt increase of lysis. Membrane-associated vesicles devoid of intramembrane particles (IMPs) were formed in the erythrocyte membranes frozen at cooling rates slower than 1800 deg. C/min. The frequency and size of these vesicles were highly cooling-rate-dependent and they were no longer formed in the erythrocyte membranes frozen at cooling rates faster than 3500 deg. C/min. Another membrane ultrastructural change associated closely with the formation of intracellular ice crystals appeared at cooling rates faster than 8000 deg. C/min. The membrane regions in direct contact with intracellular ice crystals were physically damaged and had an appearance resembling worm-eaten spots. The erythrocytes frozen at a cooling rate of 3500 deg. C/min exhibited ultrastructural integrity of the membrane by avoiding the membrane changes caused by either slow or fast freezing. It is suggested, from the close relation between membrane ultrastructure and the extent of haemolysis, that the ultrastructural integrity of membrane in the frozen state is important for avoiding haemolysis after thawing, and that the membrane ultrastructural changes caused by both slow and fast freezing were responsible for the lysis after thawing.
Ultrastructure of sheep erythrocyte plasma membranes and cytoskeletons bound to solid supports
Authors: Lang Robert D. A. , Nermut Milan V. , Williams Lynn D. 
Published: April 2021

ABSTRACT
Sheep erythrocyte plasma membrane monolayers were formed on positively charged supports by means of controlled lysis and squirting of cells so that the original protoplasmic or inner surfaces (PS) were exposed. The appearance of the surface was studied by transmission electron microscopy of platinum/carbon replicas following freeze-drying of the membranes. After gentle washing with water or dilute buffer, a network of filaments and particles was found to cover the surface.
Whole cells bound to positively charged supports were treated with Triton X-100 and hypertonic KC1, which left the protein components of the cytoskeleton on the support. Stereo electron microscopy of Pt/C replicas of these residues showed complex networks of filaments, similar to those seen on the cytoplasmic surfaces of the intact membranes. In both cases the lengths of the filaments correspond to that of the spectrin dimer.
Removal of spectrin, actin and other proteins by alkaline treatment led to loss of this network and revealed 15·4-nm particles on the membrane PS. These particles, which were also visible after negative staining, could be removed by treatment with trypsin and were found to correspond to band 4 protein (the equivalent of human erythrocyte band 3 protein). Membranes freeze-fractured following treatment with alkali showed normal intramembranous particles with frequencies similar to those of native membranes. This indicates that band 4 protein spans the sheep erythrocyte membrane and forms a very high proportion of the intramembranous particles. The protoplasmic portions of these particles may be membrane binding sites for the cytoskeleton in sheep erythrocytes.
Structure of the chloroplast and its dna in chloromonadophycean algae
Authors: Coleman Annette W. , Heywood Peter 
Published: April 2021

ABSTRACT
The arrangement and ultrastructure of chloroplasts is described for the Chloromonadophycean algae Gonyostomum semen Diesing and Vacuolaria virescens Cienkowsky. The chloroplasts are present in large numbers and are discoid structures approximately 3–4 μm in length by 2–3 μm in width. In Gonyostomum semen the chloroplasts form a single layer immediately interior to the cell membrane; frequently their longitudinal axis parallels the longitudinal axis of the cell. The chloroplasts in Vacuolaria virescens are more than 1 layer deep and do not appear to be preferentially oriented. In both organisms, chloroplast bands usually consist of 3 apposed thylakoids, although fusion and interconnections between adjacent bands frequently occur. External to the girdle band (the outermost thylakoids) is the chloroplast envelope. This is bounded by endoplasmic reticulum but there is no immediately apparent continuity between this endoplasmic reticulum and the nuclear envelope. Electron-dense spheres in the chloroplast stroma are thought to be lipid food reserve. Ring-shaped electron-translucent regions in the chloroplast contain chloroplast DNA. The DNA is distributed along this ring in an uneven fashion and, when stained, resembles a string of beads. Each plastid has 1 ring, and the ring is unbroken in the intact plastid.
Quantitative cell fusion: The fusion sensitivity (fs) potential
Authors: Röhme Dan 
Published: April 2021

ABSTRACT
The dose response of Sendai virus-induced cell fusion was studied in 10 mammalian cell lines, comprising 5 continuous and 5 diploid cell lines originating from 5 species. The extent of fusion was calculated using a parameter directly proportional to the number of fusion events (t-parameter). At lower levels of fusion the dose response was found to be based on the same simple kinetic rules in all cell lines and was defined by the formula: t = FS FAU/(1 + FS. FAU), where FS (fusion sensitivity) is a cell-specific constant of the fusion rate and FAU (fusion activity units) is the virus dose. The FS potential of a cell line was determined as the linear regression coefficient of the fusion index (t/(1 — t)) on the virus dose. At higher levels of fusion, when the fusion extent reached cell-line-specific maximal levels, the dose response was not as uniform. In general, and particularly in the cases of the diploid cell lines, these maximal levels were directly proportional to the FS potentials. Thus, it was concluded that the FS potential is the basic quantitative feature, which expresses the cellular fusion efficiency. The fact that FS varied extensively between cell lines, but at the same time apparently followed certain patterns (being higher in continuous compared to diploid cell lines and being related to the species of origin of the cells), emphasizes its biological significance as well as its possible usefulness in studies of the efficiency of various molecular interactions in the cell membrane/cytoskeleton system.
Coiling of the flagellar shaft in the head region of the mature sperm of Nucella (Purpura) Lapillus (L.)
Authors: Walker Muriel 
Published: April 2021

ABSTRACT
The sperm of Nucella are long and threadlike. The fiagellar shaft runs from the acrosome at the front of the head to the tip of the tail. Its anterior portion, the head shaft, is ensheathed by the nucleus. If a suspension of sperm in normal-concentration sea water is observed under phase contrast, and allowed to dry out slowly, the nuclear material of sperm near the edge of the coverglass swells and the head shafts of these sperm are thrown into gentle spirals within the nuclei. In some sperm the nuclear material disperses completely, and the front three-quarters of the head shaft springs into a tight right-handed coil of 5–7 turns. Instantaneous coiling of the head shaft may also be induced by treatment of the sperm with x 2 concentrated sea water or 0·01 % (w/v) solution of sodium lauryl sulphate in sea water. The enzymes pronase and trypsin at a concentration of 50 μg/ml in sea water at pH 8·0 cause dispersion of the head nucleoprotein and subsequently the head shaft forms a loose coil. The appearance and activity of the sperm do not change perceptibly over a pH range of 5·5—8·5.
Sperm spread on a Langmuir trough containing normal concentration sea water were negatively stained with phosphotungstic acid and examined with an electron microscope. After such treatment the nuclei are partially spread and the fibrils of the head shafts appear twisted as the wires of an electrical flex. The twisted flagellar fibrils are seen more clearly in negatively stained head shafts of sperm whose nuclei have been completely dispersed by spreading on a Langmuir trough containing × 2 concentrated sea water. Negatively stained preparations of sperm treated with enzymes show sperm with twisted and coiled head shafts. The nucleoprotein of these sperm is disaggregated into strips or sheets, or may appear as a mass of branching fibres. The flagellar fibres of the enzyme-treated sperm are often bent or broken.
Longitudinal sections of mature sperm heads show that in the intact sperm the fibres of the head shaft are not twisted but run straight throughout the length of the head. Sections from the testis and testicular duct show that microtubules are present in sperm in the testis but absent from mature sperm in the testicular duct.
It is suggested that the head shaft, as a consequence of some event in spermiogenesis, has an inherent tendency to twist and coil but in the mature sperm it is ‘strait-jacketed’ by the sperm nucleus.
The crystal lattice of the pyrenoid matrix of Prorocentrum Micans
Authors: Kowallik K. 
Published: April 2021

ABSTRACT
The pyrenoid matrix of the marine dinoflagellate Prorocentrum micans is shown to consist of regular close-packed units, which form a cubic face-centred lattice. Numerous lamellae usually consisting of two apposed thylakoids traverse the pyrenoid matrix. They normally run strikingly parallel to each other, with an average distance of 139 nm between each stack. The three-layered unit membrane of the thylakoids penetrating the pyrenoid is 70Å thick, the same as the unit membrane of the chloroplast thylakoids. The total thickness of one thylakoid measures 190–220 Å.
The globular units of the pyrenoid matrix have a calculated mean diameter of 232 Å, forming different line and dot patterns (hexagonal and cubic arrays) due to different section angles. Hexagonal patterns on prints result from projections of superimposed close-packed layers; they do not belong to one close-packing. Line patterns parallel to the thylakoid direction are composed without exception of 11 contrasted lines (6 and 5 alternating). This fact suggests that a definite number of units is arranged between the thylakoid stacks, thus producing the constant matrix thickness. Comparable regions in the chloroplast matrix cannot be confused with the pyrenoid matrix, as they never display an ordered structure. A three-dimensional model of the matrix is presented.
Starch is stored only in the cytoplasm; there is no visible connexion with the pyrenoid. On the evidence of protein storage in similar crystal lattices both in plants and animals it is suggested that the pyrenoid may also be an organelle for protein storage in some groups of algae.