bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pattern formation in the blue-green alga Anabaena ii. controlled proheterocyst regression
Authors: Wilcox Michael , Mitchison G. J. , Smith R. J. 
Published: April 2021

ABSTRACT
We present further evidence for an interactive mechanism in the formation of the spaced pattern of heterocysts in Anabaena. The evidence comes from experiments which are an extension of those described earlier, in which filaments of the alga are broken near to a proheterocyst. We argue that a proheterocyst depends upon neighbouring vegetative cells for the removal of an inhibitory substance: when the proheterocyst is deprived of these supporting vegetative cells it will be forced to regress. We showed earlier that such regressions do occur in early proheterocysts when a filament is broken on one side only. We now find that advanced proheterocysts can be made to regress when double breakages are performed to leave small fragments containing the proheterocysts.
The probability of a proheterocyst regressing is correlated with its stage of development and with the size of the fragment : the smaller the fragment, the more advanced is the stage at which regression will occur. To formulate this we have defined developmental stages in terms of ultrastructure and compiled the results of a diversity of breakage operations with the cells at these specified stages.
Certain compounds affect the spacing of the heterocyst pattern, causing it to become wider or narrower. These compounds have the predicted effect upon regression frequencies, upholding our assumption that regressions express an underlying competitive mechanism.
Vital marking of single cells in developing tissues: India ink injection to trace tissue movements in hydra
Authors: Campbell R. D. 
Published: April 2021

ABSTRACT
A new vital marking procedure was devised, studied, and applied to the phenomenon of hydra column tissue movements. The method involves injecting colloidal carbon (India ink) into the ectodermal epithelium of hydra. The carbon is taken up specifically by epithelial cells and packed into lysosome residual bodies. Each marked cell is then identifiable by its aggregated carbon particle, which appears as a black dot; this is passed to a daughter cell during cell division. Using this method to stain vitally the ectoderm of the green hydra, Chlorohydra viridissima, whose endodermal cells were marked by symbiotic algae, the relative movements of ectoderm and endoderm along the body column were analysed. Ectoderm and endoderm move in different directions or at different rates in the top quarter of the gastric column, but move together in the lower part of the column. This indicates that some epithelial cell movements involve cells migrating relative to the mesoglea; other movements involve translocation of the entire body wall, including ectoderm, mesoglea and endoderm.
Cyclic membrane flow in the ingestive-Digestive system of peritrich protozoans i. vesicular fusion at the cytopharynx
Authors: Mckanna J. A. 
Published: April 2021

ABSTRACT
Food vacuoles in peritrichs form by pinching off the distal half of the cytopharynx; and thus the pharyngeal membrane must be renewed during feeding. Correlation of light- and electron-microscopic observations indicates that the membranes of the ingestive—digestive system recycle. As the young food vacuoles enter the first stage of digestion (condensation of the vacuole), they pinch off cup-shaped coated vesicles which, in association with the microtubular post-oral fibres, return to the pharynx. In the peripharyngeal region, the 0·25-μm diameter cups flatten into 0·42-μm diameter disks, which then fuse with the pharyngeal membrane, thereby providing membrane for future food vacuoles. Ultrastructural evidence for similar patterns of cyclic membrane flow and the functional implications of the association of the pharyngeal membrane with the microtubules of the pharyngeal ribs are considered for other protozoa, including suctorians.
Membrane specializations in the form of regular membr ane-to-m emb r ane attachment sites in Paramecium. a correlated freeze-etching and ultrathin-sectioning analysis
Authors: Plattner H. , Miller F. , Bachmann L. 
Published: April 2021

ABSTRACT
The outer membrane complex of Paramecium was investigated by ultrathin-sectioning techniques and by freeze-etching of unfixed cells without cryoprotectants. Granules were found in the freeze-etched cortical membrane complex in a highly ordered arrangement; morphometric analyses and partial disruption of this membrane complex showed that some of these granular membrane specializations (which we call types a, b, e, f, g) represent membrane-to-membrane attachment sites. Type a: granules arranged in rings (single or double), 300 nm in diameter, connect plasmalemma and alveolar membranes around trichocysts. Type b: within these a-type rings, a concentric zone (180 nm diameter) of granules connects plasma membrane and trichocyst membrane. Type c: the trichocyst membrane further contains a central ring or patch, 80 nm in diameter, of rather large granules where it is in contact with the crystalline trichocyst matrix. Type d: ‘ciliary necklaces’ are formed by groups of triple rows of 3–6, most frequently 5 granules, with 21-nm periodicity. Rows of granules also connect the alveolar membranes to the apical portion of the trichocyst membrane (type e) and the alveolar membrane to the plasmalemma around cilia (type f). Type g: the inner alveolar membrane displays an intense granularity and contains double rows of granules along alveolar septa at attachment sites between 2 alveolar membranes. Upon experimental discharge of the majority of trichocysts only the innermost concentric circles of membrane-bound granules of this region (b- and c-type) disappeared from the plasmalemma, while the outermost a-type rings of granules persisted for a longer time. Among other possible functions, these regular membrane-to-membrane attachments are likely to maintain the specific cellular shape.
Ultrastructural changes in Euglena after ultraviolet irradiation
Authors: Michaels A. , Gibor A. 
Published: April 2021

ABSTRACT
The structural changes associated with the ultraviolet-induced bleaching of light-grown cells of Euglena gracilis were investigated. Our light- and electron-microscopic observations of the bleaching process indicate that there is a continuity of plastid structure in cells 5 generations after receiving a bleaching dose of ultraviolet light. There seems to be a continuous dilution of the plastid thylakoids and a decrease in plastid size in the bleaching cells. There also seems to be a change in the position of the plastids in relation to the mitochondria in the bleaching cells. The plastids and possibly the mitochondria are the only organelles which are affected by the ultraviolet irradiation. The continuity of plastids in bleaching cells of Euglena is discussed in relation to the proposed effect of the ultraviolet light.
Correction of genetic defects in mammalian cells by the input of small amounts of foreign genetic material
Authors: Boyd Yvonne L. , Harris H. 
Published: April 2021

ABSTRACT
Chinese hamster cells lacking inosinic acid pyrophosphorylase and mouse cells lacking thymidine kinase were fused with chick erythrocytes. The resultant heterokaryons were cultivated in a selective medium in which possession of these enzymes was essential for cell survival and growth. Clones of cells able to grow in this medium were isolated and studied. A detailed karyological analysis of these clones failed to reveal any chick chromosomes; nor could any chick-specific antigens be detected on the surface of the cells. Nonetheless, clones arising from the fusion of chick erythrocytes with Chinese hamster cells were shown to possess an inosinic acid pyrophosphorylase which had the electrophoretic characteristics of chick inosinic acid pyrophosphorylase. However, the clones arising from the fusion of the chick erythrocytes with the mouse cells had a thymidine kinase with the electrophoretic mobility and heat sensitivity of murine, not chick, thymidine kinase. Both types of hybrid ceil have now been cultivated in vitro for 18 months without the loss of thymidine kinase or inosinic acid pyrophosphorylase activity.
Clonal growth of mouse cells (strain l)
Authors: Miyamoto Hiroshi , Zeuthen E. , Rasmussen L. 
Published: April 2021

ABSTRACT
Clones of mouse fibroblast cells (strain L) have been cultivated in a nutrient-rich, complex medium in monolayer cultures. Cell multiplication was followed by time-lapse photography or video recording. In both cases exposures were made every hour, which is sufficiently frequent to keep track of the original cell and its progeny from the 1-cell stage to 128-cell stage, or for about a week. Cell lines were followed, ‘family trees’ were constructed and individual and average generation times were calculated in all cases.
The data showed that the average durations of at least 4 generations (from the fourth up to and including the seventh) were rather constant. Division synchrony deteriorated with time but could still be perceived at the end of 7 generations. As would be expected from these observations, the coefficient of variation of generation times within one single clone in our experimental system is low (about 9%), compared to previously reported values.
Ruthenium-red-induced cell agglutination and surface glycoprotein and mucopolysaccharide
Authors: Utsumi Kozo , Oda Takuzo 
Published: April 2021

ABSTRACT
Ruthenium red induces the agglutination of ascites hepatoma cells. The agglutination was inhibited by acidic polysaccharides but not by haptenic inhibitors of some plant agglutinins. The agglutination was also abolished by treatment of the cells with a low concentration of papain. Papain digestion causes a decrease in the number of microvilli on the cell surface and the release of carbohydrate-containing materials into the suspending medium. The ‘papainate’ has more than 2 kinds of ruthenium red-binding substance. One of them is a heparan sulphate-like mucopolysaccharide and the other is a glycoprotein which contains sialic acid. The ruthenium red-binding fractions inhibit the cell agglutination induced by ruthenium red.
Fine structure and staining behaviour of heterochromatic segments in two plants
Authors: LA Cour L. F. , Wells B. 
Published: April 2021

ABSTRACT
With the use of the light and electron microscopes, the chromosomes of Fritillaria lanceolata and Scilla sibirica are shown to differ in respect of the heterochromatin they contain. In root meristems of the former, the heterochromatic regions (H-segments) were recognizable at all phases of the mitotic cycle by their slighter opacity to electrons than that of euchromatic parts. This was due both to less tight packing of the chromatin fibrils and lower opacity of the fibrils themselves, even though both had the same diameter, about 3 nm.
In root tips of the Scilla, the heterochromatin was invariably of similar opacity to euchromatin and thus only recognizable at telophase and interphase as large chromocentres. The opacity to electrons in the heterochromatin of the 2 species, was at all times closely paralleled by the staining behaviour seen with the light microscope in sections (0·07–0·5 μm in thickness) stained with toluidine blue.
The disparity in the Fritillaria, as seen in sections with the light microscope, in respect of the stainability of the hetero- and euchromatin, was masked in Feulgen squash preparations of root tips from plants grown at 18–20 °C; at metaphase by the thickness of the chromosomes and at interphase by the density of the chromocentres. When, on the other hand, the plants were grown for 4 days at 2 °C, the masking effect of thickness was circumvented in metaphase chromosomes by differential super-contraction in euchromatin.
The implications of these findings in respect to previous interpretations of the differential reactivity of H-segments to low temperature, as well as the phenomenon of enhanced and reduced fluorescence in these segments with fluorochromes are discussed.
Observations on the growth of Eictyostelium discoideum in axenic medium: Evidence for an extracellular growth inhibitor synthesized by stationary phase cells
Authors: Yarger J. , Stults K. , Soll D. R. 
Published: April 2021

ABSTRACT
By analysing the growth kinetics of Dictyostelium. discoidettm amoebae in varying combinations of the components of the nutrient medium HL-5 (Cocucci & Sussman, 1970), we have demonstrated that Dictyostelium amoebae enter stationary phase when they deplete the medium of one or more nutrient components. However, if the medium of a stationary phase culture is supplemented with any of the initial components of HL-5 medium and even when supplemented with all components of HL-5 medium, it does not support the growth of freshly inoculated cells, indicating that stationary phase cultures produce a potent growth inhibitor. The possible function of this inhibitor is discussed.
Parental age and life span versus progeny life span in Paramecium
Authors: Smith-Sonneborn Joan , Klass M. , Cotton D. 
Published: April 2021

ABSTRACT
It has been possible to investigate for the first time at the cellular level, the influence of parental age on progeny life span, using Paramecium. As parental age increased, progeny life span decreased. The process of generating progeny clones from aging parents yielded paramecia with different life spans, allowing the study of the influence of parental life span on progeny life span. We found that parental life span was also a significant variable in the progeny life span. The theoretical basis for cellular aging and rejuvenation (the reinitiation of the life cycle) in paramecia is discussed in relation to the present data and previous studies.
Localization of calcium in the smooth endoplasmic reticulum of rat isolated fat cells
Authors: Hales C. N. , Luzio J. P. , Chandler J. A. , Herman L. 
Published: April 2021

ABSTRACT
The cytoplasm of the rat isolated fat cell contains a highly organized, interconnected system of smooth endoplasmic reticulum having close association with the central lipid mass, mito-chondria and cytoplasmic lipid droplets. Elements of smooth endoplasmic reticulum approach, but do not fuse with, the plasma membrane.
When fat cells were treated with potassium pyroantimonate during fixation for electron microscopy a precipitate was produced inside the smooth endoplasmic reticulum. Analysis with an AEI-EMMA 4 analytical electron microscope showed that the precipitate contained calcium but not sodium, magnesium or manganese.
It is possible that the smooth endoplasmic reticulum of fat cells may be structurally and functionally analogous to the sarcoplasmic reticulum in skeletal muscle, and that redistribution of calcium from a calcium store inside the smooth endoplasmic reticulum may be a consequence of the action of lipolytic hormones.
Dna repair synthesis in human heterokaryons: II. a test for heterozygosity in xeroderma pigmentosum and some insight into the structure of the defective enzyme
Authors: Giannelli F. , Pawsey Susan A. 
Published: April 2021

ABSTRACT
Heterokaryons between fibroblasts from patients with classical Xeroderma pigmentosum (X.P.) and fibroblasts from normal or heterozygous subjects have indicated that normal cells contain at least three- to fourfold the amount of ‘X.P.-enzyme’ necessary for maximal unscheduled DNA synthesis and that the reduced enzyme levels in heterozygotes can be detected using heterokaryons with a high ratio of X.P. to heterozygous nuclei. Furthermore, a kinetic study of complementation in heterokaryons suggests that the ‘X.P.-enzyme’ is, probably, not a monomer and that its function may be dependent upon binding to an acceptor and formation of a stable complex which turns over slowly. Patients with the same clinical form of X.P. (classical type) may carry defective enzymes which do or do not bind to the acceptor.
Our findings and the evidence in favour of a close correlation in the kinetics of the different aspects of the excision repair of DNA prompt us to suggest that the enzymes of this repair system may assemble to form a ‘repair organelle ‘.
A re-examination of succinic dehydrogenase activity and its association with cell death in the interdigit of the chick foot
Authors: Fallon J. F. , Brucker R. F. , Harris Cynthia M. 
Published: April 2021

ABSTRACT
Massive cell death, which accompanies the freeing of the digits, occurs in the inter digits of the developing chick foot during stages 30–35. The possibility was reexamined that mitochondrial succinic dehydrogenase activity disappears in the interdigital cells of the chick foot 24 h before cell mortality. Using standard histochemical means it was found that succinic dehydrogenase activity was demonstrable in the interdigital cell population up to and including the time when cell death begins. This was confirmed quantitatively employing biochemical methods which indicated that succinic-cytochrome c reductase specific activity was approximately the same in homogenates of digital and interdigital tissues harvested just prior to the death of interdigital cells. Further, NADH-cytochrome c reductase specific activity was comparable in digital and interdigital tissue homogenates. These data make it unlikely that ‘biochemical degeneration’ associated with alterations in aerobic energy metabolism occurs in the interdigital cells before death as has been suggested by other workers previously. The methods used by these authors to demonstrate succinic dehydrogenase were repeated on chick feet in our laboratories and an alternative interpretation of the results is offered.
Movement in a confluent 3t3 monolayer and the causes of contact inhibition of overlapping
Authors: Martz E. , Steinberg M. S. 
Published: April 2021

ABSTRACTThe existence of contact inhibition of nuclear overlapping (monolayering) has previously been interpreted to mean that intercellular contact locally inhibits the cell’s locomotory apparatus and hence that cells in a confluent monolayer should be immobilized. Garrod & Steinberg, however, observed gross movements and exchanging of nuclear nearest neighbour relationships in a confluent monolayer of chick epithelial-like cells. Data presented in the present report reveal that similar movements occur in confluent monolayers of mouse 3T3 fibroblasts, previously shown to display contact inhibition of speed, contact inhibition of overlapping, and postconfluence inhibition of cell division.Cytoplasmic boundaries frequently could not be resolved in the present study. However, during a 22-day period, more than one third of originally adjacent pairs of nuclei became separated by 1·5 intervening nuclei, and their average distance of separation increased more than 2-fold. Also, each nucleus was displaced, on average, more than one mean cell diameter in a random direction. These indications of gross cellular movements were seen during the stationary density phase of perfused culture, as well as during the doubling of cell density which occurs after confluence but before the stationary phase.If the intensity of cell-substratum adherence exceeds that of cell-cell adherence, this differential in adhesive strength could, by itself, produce the observed avoidance of overlapping, without invoking local inhibition of the cell’s internal ‘motor’ by contact. This differential adhesion hypothesis for contact inhibition of overlapping is consistent with the extensive movements very likely occurring in at least certain confluent monolayers. On the other hand, the probable existence of these movements seems less easily reconciled with the hypothesis that contact inhibition of overlapping results from contact-induced local paralysis of an intracellular locomotory apparatus, although this latter hypothesis is not excluded.
Macromolecular physiology of plastids ix. development of plastid membranes during greening of dark-grown barley seedlings
Authors: Henningsen K. W. , Boynton J. E. 
Published: April 2021

ABSTRACT
The development of plastid membranes was studied in relation to chlorophyll accumulation in dark-grown barley seedlings of various ages after transfer to light. Quantitative electron microscopy showed that the prolamellar body membranes are reorganized into primary lamellar layers which contain sufficient membranes to support grana formation during 24 h of greening. Structural reorganization of the plastid membranes is completed rapidly in young seedlings, but is slow in older seedlings. Chlorophyll accumulates rapidly in young leaves after a short lag. In older leaves there is a longer lag phase before the onset of chlorophyll synthesis, and the final rate of synthesis is lower.
Shortly after transferring to light, the crystalline prolamellar bodies in the etioplasts are transformed and then dispersed into lamellar layers with numerous perforations and protuberances. Before the phase of rapid chlorophyll synthesis, many small-diameter 2-disk grana are formed. When chlorophyll begins to accumulate, the perforations are rapidly eliminated from the lamellar layers and a maximum number of 2-disk grana are formed. As greening proceeds additional disks are added to these original 2-disk grana.
During the phase of rapid chlorophyll synthesis, pairing of the lamellae is positively correlated with the accumulation of chlorophyll. During greening less chlorophyll appears to be incorporated into the paired regions of the lamellae in young leaves as compared to old leaves. The results on the structural aspects of plastid development are discussed in relation to the formation of photosynthetic capacity.
Distribution of microtubules in the golgi apparatus of Euglena gracilis
Authors: Mollenhauer H. H. 
Published: April 2021

ABSTRACT
A system of microtubules has been demonstrated as a consistent feature within the Golgi apparatus of Euglena gracilis. The microtubules are between 12 and 17 nm in diameter and are usually positioned in the intercisternal space between adjacent cisternae. There are seldom more than 2–5 microtubules per dictyosome section, and these may be distributed variously throughout the stack. At least some of the microtubules are continuous with the surrounding cytoplasm, so they may act to transfer products into or out of the Golgi apparatus or as structural elements to orient or position the dictyosomes and secretion vesicles.
Microtubules in relation to flagellogenesis in Pteridium sperm atozoids
Authors: Bell P. R. 
Published: April 2021

ABSTRACT
Differentiating spermatocytes have been examined in a diploid culture of Pteridium gameto-phytes. Spermatogenesis is similar to that in haploid antheridia. Although the nucleus of the diploid gamete is larger, no differences have been detected in the dimensions of components such as microtubules and flagella.
Microtubules scattered in the cytoplasm of the young spermatocytes follow an irregular course and show no particular relationship to the blepharoplast, even during the differentiation of its periphery into basal bodies with characteristic triplets. Subsequently short lengths of notably straighter microtubules appear in quantity adjacent to the osmiophilic material lying along the microtubular ribbon of the developing gamete. These microtubules are particularly frequent around the distal ends of flagella beginning to develop from basal bodies, and often appear to converge upon them.
The view is put forward that the osmiophilic material adjacent to the microtubular ribbon, ontogenetically continuous with that originally at the centre of the differentiating blepharoplast, is responsible for the organization of the flagella. This material remains close to the ribbon throughout the differentiation of the gamete. If contact between the osmiophilic material and the flagella remains essential throughout their development, it would follow that they complete most or all of their growth parallel to the microtubular ribbon, possibly becoming emergent structures only as differentiation of the gamete is completed.