bluuebunny/crossref_metadata_2025 huggingface dataset:
An electron-microscope study of the reaction of collagen with some monoaldehydes and bifunctional aldehydes
Authors: Cox R. W. , Grant R. A. , Kent C. M.
Published: April 2021

Rat tail tendon collagen has been treated with the monoaldehydes, formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde and benzaldehyde, and with the dialdehydes, glyoxal and glutaraldehyde. The treated collagen was then examined in the electron microscope using a negative stain. Alterations to the native collagen pattern were seen with formaldehyde, acetaldehyde, propionaldehyde, glyoxal and glutaraldehyde. A correlation was noted between the changes in the band pattern and the degree of cross-linking estimated from chemical and physical changes in the treated collagen and from measurements of cross-linking made by other workers. The results indicate that the use of electron microscopy and negative staining may be a valuable method of assessing the degree of cross-linking in collagen treated with aldehydes and other reagents.
Chemical and structural differences between cilia and flagella from the lamellibranch mollusc, Aequipecten irradians
Authors: Linck R. W.
Published: April 2021

Gill cilia and sperm flagella from the lamellibranch mollusc Aequipecten irradians were isolated by several methods and chemically fractionated by low-ionic-strength dialysis. These organelles differ in their forms of dynein and in the stabilities of their homologous microtubules and subsidiary structures (i.e. nexin fibres and spoke material). In flagella more than 80% of the axoneme ATPase is solubilized, appearing as a 14s peak in the ultracentrifuge, and the whole axoneme is broken down to unlinked, doublet outer fibres. In cilia only half of the ATPase is solubilized from axonemes as a 14S component. The ciliary B-tubules and one member of the central pair also dissolve, leaving the A-tubules and the other central tubule held together by nexin fibres and matrix material as a 9 + 1 singlet axoneme, to which is bound the remaining half of the ATPase. This tightly bound form of the ciliary ATPase can be removed in an enzymically active form by brief trypsin treatment which causes the breakdown of the singlet axoneme. The trypsin-solubilized ATPase behaves like native 14s dynein in the ultracentrifuge but breaks down to polypeptides when electrophoresed in the presence of sodium dodecyl sulphate (SDS).

The native 14 s material containing the dynein was partially purified by column chromatography and was shown on SDS-polyacrylamide gels to be composed of 2 components. The molecular weights of these as determined by 3% acrylamide SDS-gels are 450000 and 500000, and they are not reduced by prior treatment with 8 M urea. Parallel SDS-gels loaded with identical amounts of ciliary and flagellar axonemes show very nearly identical components; the ratio of the amounts of the 500000 and 450000 mol. wt. components is about 2:1 respectively. The fractionation of ciliary and flagellar axonemes was analysed quantitatively on SDS-gels. Essentially all of the 450000 and 500000 mol. wt. components are found in the soluble fraction from dialysed flagella. The soluble fraction from cilia contains the 2 components in a 1:1 ratio, along with half the axoneme ATPase, while the singlet axoneme fraction contains the remainder of the 500000 material and the remaining half of the ATPase. On this basis it is believed that the 500000 component is the dynein ATPase, while the 450000 material represents a non-ATPase protein.

The chemical and structural differences between cilia and flagella may offer an explanation for their different modes of beat.
A simple light-microscope technique for the examination of cell surfaces
Authors: Ross A. , Gormley I. P.
Published: April 2021

A simple technique for the examination of cell surfaces by shadowing them with a heavy metal and examining by light microscopy has been described. Stained preparations can be examined and photographed initially prior to investigation by this technique. It is suggested that this technique could be used instead of the scanning electron microscope or replica techniques where the limited resolution of the light microscope is sufficient.
Kinetics of the regeneration of sea-urchin cilia
Authors: Burns R.G.
Published: April 2021

The kinetics of the regeneration of cilia of the sea urchin Tripneutes gratilla have been examined. The maximum cilia length is attained asymptotically which may reflect the transport of precursors to the distal tip. However, a detailed analysis indicates that the maximum length is regulated by a mechanism other than the availability of precursors at the distal end. It is argued that this control is independent of the size of the precursor pool, the rate of protein synthesis or the rate of precursor transport to the distal tip.
The secretion and development of nematocysts in a siphonophore
Authors: Skaer R. J.
Published: April 2021

Nematocyst development was watched in living cells of a siphonophore, Rosacea cymbiformis. The secretion differentiates in the formative cell into an ovoid capsule, continuous with a long apical tube. The entry of this ‘external’ tube into the capsule creates the coiled internal’ thread’ of the mature nematocyst. Electron microscopy shows that the tip of the external tube inverts and moves down the tube towards the capsule. Complex pleats form during inversion. Thus formation of the internal thread is the geometrical converse of discharge. Extensive repacking of the triply pleated, internal thread occurs, and subsequently the barbs form.
Further experiments on the role of the nucleolus in the transfer of rna from nucleus to cytoplasm
Authors: Deák I. I.
Published: April 2021

The role of the nucleolus in the transfer of RNA from nucleus to cytoplasm was examined by means of experiments in which the nucleolus or other parts of the nucleus were inactivated by a microbeam of ultraviolet light. These experiments confirmed previous work in showing that such inactivation of the nucleolus inhibited the appearance in the cytoplasm, not only of ribosomal RNA, but also of other types of RNA made in the nucleus, in particular transfer RNA.
Clonal variability of adenovirus transformed cells
Authors: Weber Joseph
Published: April 2021

Cells transformed by DNA oncogenic viruses acquire characteristic properties which have been considered criteria for transformation. SV40- and polyoma virus-transformed cells are capable of selective reversion for several of these properties. Until now, reversion of trans-formed cell properties has not been reported in the adenovirus system. The stability of several transformed cell properties was examined in a line (HTC) of Ad. 12-transformed (in vivo) cells after several hundred generations of in vitro passage. From a large number of clones isolated by the soft-agar suspension technique, 7 were selected for detailed examination. The clones, as the parental cells, were free of infectious virus and type-specific antigen, but contained intranuclear Ad. 12 T antigen. Cell growth profiles with o, 1 and 10% serum in the culture medium revealed that while 4 clones retained the parental characteristic of growth in the absence of serum, 3 lost this ability and grew only in serum concentrations greater than 1 %. Agglutination profiles with 4-fold dilutions of concanavalin A (Con. A) and wheat germ agglutinin (WGA) directly or after trypsin treatment revealed 2 clones which failedto agglu-tinate with Con. A; trypsin treatment reversed this effect. Each clone agglutinated with WGA directly, though one clone showed reduced agglutination. On the basis of superinfection with Ad. 2 the clones could be grouped into low, intermediate and high yielders with 10-fold intervals. All clones were transplantable into random-bred adult Syrian hamsters. There was no marked correlation between the reversion or modification of individual transformed cell properties among the clones. The phenotypic stability of these transformed cell properties was confirmed by re-cloning the tumours induced by one of the revertant clones. It was concluded that some of these properties are not essential for the maintenance of oncogenic potential.
On the In Vitro behaviour of mouse submaxillary gland cells
Authors: Marcante Maria Luisa
Published: April 2021

Investigations on the morphological features and some biochemical properties of cells isolated from mouse C3H/He (IRE/Ar) submaxillary glands cultivated in vitro are reported. Two types of cells have been recognized: the dark cells differ from the light in the shape of their mitochondria, and number of vacuoles, while endoplasmic reticulum is absent. The enzymic activities, which have been tested, are phosphofructokinase, pyruvate kinase, amylase and lactate dehydrogenase. The values for enzyme activities in vitro are in good agreement with those obtained for submaxillary gland in vivo.

Therefore, it can be concluded that during their growth in vitro cells from submaxillary glands retain their enzymic properties.
A rapidly sedimenting fraction of rat liver endoplasmic reticulum
Authors: Lewis J. A. , Tata J. R.
Published: April 2021

Balance-sheet experiments carried out to account for the distribution of endoplasmic reticulum fragments during subcellular fractionation of rat liver showed that a large proportion of these fragments are present in the pellets of low-speed centrifugation. Using glucose-6-phosphatase and RNA as markers we found that approximately 50 % of the fragments of endo-plasmic reticulum sedimented in the pellet of a 640-g centrifugation, 10 % in that of a 6000-g centrifugation and 35 % in the pellet of a 105000-g centrifugation. Starvation of the animals before use did not alter this distribution, nor did the use of more vigorous homogenization conditions. We have developed a procedure for removing nuclei and erythrocytes from the material sedimenting at 640 g to give a fraction (rapidly sedimenting ER fraction or RS-ER) similar to the standard microsomal preparation. Centrifugation of this RS-ER fraction over 1·3 M sucrose yields sub fractions of high and low RNA content analogous to the rough and smooth microsomal fractions. Electron-microscopic studies showed that, whereas the rough microsomal fraction consisted of ribosome-studded vesicles of varying size and content density, the rough RS-ER fraction contained a mixture of mitochondria and double lamellar membranes with ribosomes attached. These double lamellar membranes closely resemble the endoplasmic reticulum of intact rat liver. The double lamellar membranes are frequently observed grouped in stacks and in close association with the mitochondria. The significance of the association between endoplasmic reticulum and mitochondria of the RS-ER fraction and the relation between it and the standard microsomal preparation are discuased.
Peroxidases in tobacco abscission zone tissue i. fine-structural localization in cell walls during ethylene-induced abscission
Authors: Henry E. W. , Jensen T. E.
Published: April 2021

The fine-structural localization of peroxidases during ethylene-induced abscission of flower pedicels of Nicotiana tabacum L. cv. ‘Little Turkish’ has been investigated. Peroxidase activity has been localized in both the cell walls and intercellular spaces of ethylene-treated flower pedicels which were fixed in glutaraldehyde, incubated in diaminobenzidine (DAB) medium with postfixation in 2 % osmium tetroxide. Peroxidase staining is present in the cell walls and intercellular spaces of control tissue but is not as intense as in ethylene-treated tissue. Increased peroxidase staining is evident in the intercellular spaces and cell walls after 2 h of exposure to ethylene and increases in intensity between 2 and 5 h. At 5 h, ethylene-induced abscission occurs. Fine-structural investigations revealed prominent staining in the middle-lamellar and peripheral areas of the cell walls in ethylene-treated tissue. The peroxidase staining appears to be due to peroxidase as prior incubation with potassium cyanide gives a marked reduction in the staining reaction. Incubation of the ethylene-exposed tissue in aminotriazole, a specific inhibitor of catalase, does not reduce peroxidase staining, except in the microbodies, which reportedly contain catalase.
Fracture planes of the plasmalemma of some higher plants revealed by freeze-etch
Authors: Hereward F. V. , Northcote D. H.
Published: April 2021

Freeze-substitution studies have been carried out on plant material which had been fractured while frozen in order to locate the planes of fracture. It was clearly shown that in some cases the plasmalemma was split along the hydrophobic interface while in others the fracture passed on either side of the membrane. The freeze-etch process exposed different surfaces at the cell periphery and these were related to both types of fracture seen in the freeze-substituted material.
Pattern formation in the blue-green alga Anabaena ii. controlled proheterocyst regression
Authors: Wilcox Michael , Mitchison G. J. , Smith R. J.
Published: April 2021

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The 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

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

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

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.
Feeding in ciliated protozoa: I. pharyngeal disks in Euplotes: A source of membrane for food vacuole formation?
Authors: Kloetzel John. A.
Published: April 2021

The ciliate Euplotes is able to expend a very large amount of membrane in the formation of food vacuoles. Calculations based on the rate of ingestion of the food organism Tetrahymena indicate that an amount of food vacuole membrane equivalent to approximately 50-150% of the total Euplotes cell surface area can be produced within 5-10 min. An aggregation of osmio-philic, membrane-limited ‘pharyngeal disks’ is found packed in the cytoplasm just beneath the cell surface membrane in the region of the cell mouth and cytopharynx. These disks, which can be seen also in living cells, have average dimensions of 2 μm diameter by too nm thickness, and contain tightly packed layers of a thin lamellar material. Electron micrographs have revealed the apparent fusion of the limiting membrane of disks with the cell’s plasma membrane at the base of the gullet. The lamellar disk contents are thereby released to the exterior medium in the buccal cavity, where they form a loosely packed layer over the surface membrane. It is postulated that the pharyngeal disks represent a repository of preformed membrane for use in food vacuole formation. The disk contents may also play a role in food ingestion, although this is not well defined at present. The myeloid content of old food vacuoles is very similar to that of nearby disks in the cytoplasm, suggesting that the disks may form by pinching from shrinking food vacuoles during the digestive cycle. Thus a cycle of membrane flow is envisaged, with the pharyngeal disks (1) coalescing with the surface membrane during food vacuole formation, (2) reforming by pinching from these food vacuoles during digestion, and (3) migrating back to the oral region to serve as a membrane store for subsequent food vacuole formation.
The histidine requirement of a normal and a leukaemia cell-line from man: comparative effects on cell growth, metabolism and composition
Authors: Griffiths J. B.
Published: April 2021

The object was to determine whether the depletion of histidine would have a more marked inhibitory effect on human leukaemia cells than on normal human cells, thus indicating a wider use for enzymes in cancer therapy. Studies of the effect of histidine concentration on cell growth, death, metabolism, protein composition, histidine uptake and utilization by cells were carried out. The medium and intracellular concentrations of histidine required for optimum cell growth and metabolism were much lower than for any other amino acid that has been studied. Also, there was very little evidence of cell death occurring in the absence of histidine. The results showed that cells in culture have a very low histidine requirement and that although the leukaemia cells were slightly more dependent upon histidine than normal cells the effect of histidine depletion is not critical enough to show much promise as a method of controlling leukaemia by therapeutic enzymes.
The effect of trifluralin on the ultrastructure of dividing cells of the root meristem of cotton (Gossypium hirsutum L. ‘acala 4-42’)
Authors: Hess D. , Bayer D.
Published: April 2021

Ultrastructural studies of trifluralin-treated cells in lateral root meristems of cotton (Gossy-pium hirsutum L.) revealed that mitotic disruptions were due to the absence of microtubules. The extent of disruption varied between individual roots and correlated with the presence or absence of microtubules. Where microtubules were absent, cells began division with a normal prophase chromosome cycle. The chromosomes did not line up along a metaphase plate, but coalesced in the cell. If cell division had begun prior to microtubule disappearance the mitotic process was arrested at the stage that had been reached when the disappearance occurred. In some cell divisions randomly oriented microtubules were noted, with mitosis apparently arrested at those stages. Nuclear envelope reformation yielded cells that were polyploid, polymorphonucleate, binucleate, or occasionally multinucleate. If microtubules were present and if their orientation were normal, all stages of mitosis occurred. The range of mitotic disruption observed can be explained by the threshold concentration for microtubule disappearance being very near aqueous saturation of trifluralin.
Light microscopy of meiotic zoosporogenesis and mitotic gametogenesis in Ulva mutabilis føyn
Authors: Nordby Ø
Published: April 2021

The light-microscopical cytology of synchronized meiotic zoosporogenesis and mitotic gametogenesis in the sea-lettuce Ulva mutabilis Føyn, is described. The similarity in time course and morphological events of the 2 processes is stressed and discussed with particular reference to the use of Ulva in the biochemical study of cellular preparation for meiosis and mitosis.
Studies on the synthesis and composition of extracellular mucilage in the unicellular red algaRhodella
Authors: Evans L. V. , Callow Maureen E. , Percival Elizabeth , Fareed V.
Published: April 2021

35SO42− has been used to investigate the production of extracellular mucilage by log-phase cells. Uptake of isotope occurs most rapidly in the light, when cells are actively dividing. The mucilage comprises about 50 % carbohydrate, 16 % protein and 10% sulphate. The major sugar is xylose; uronic acid, a small amount of galactose, glucose (trace) and 2 reducing substances are also present. Methylation studies have established the major linkages. Electron-microscope autoradiography shows that the mucilage is packaged in the Golgi bodies, passing to the plasmalemma in large vesicles. Sulphation of the mucilage occurs in the Golgi cisternae.
The transition from tadpole to frog haemoglobin during natural amphibian metamorphosis: ii immunofluorescence studies
Authors: Benbassat J.
Published: April 2021

Rabbits were immunized with frog or tadpole haemoglobin purified either by chromatography or by polyacrylamide gel electrophoresis. The obtained rabbit antisera were shown to be specific for frog or tadpole haemolysates by double diffusion, immunoprecipitation and immunofluorescence. Indirect immunofluorescent staining of peripheral blood smears of Rana catesbeiana tadpoles at the metamorphic climax revealed that 16 % of the red cells were stained with antibodies against frog haemolysates, while almost all of them (98 %) were stained with antibodies against tadpole haemolysates. These results are compatible with the possibility that some of the circulating red cells in metamorphosing tadpoles contain both tadpole and frog haemoglobins.
The analysis of malignancy by cell fusion: VI. hybrids between different tumour cells
Authors: Wiener F. , Klein G. , Harris H.
Published: April 2021

Previous studies with a variety of transplantable mouse tumours showed that in hybrids between malignant and non-malignant cells, malignancy behaved as a recessive character: the hybrid cells, so long as they retained something close to the complete parental chromosome sets, had little or no ability to grow progressively in vivo. In the experiments we now describe the heritable lesions determining the malignant phenotype were further explored by comple mentation analysis in which the various tumour cells were fused with each other. Forty-two clonal populations derived from twelve crosses between different kinds of tumour cells were examined. Only one cross generated hybrid cells with reduced tumorigenicity: in all other cases the hybrid cells formed were highly malignant. It thus appears that, in a wide range of different tumours, the lesions determining the malignant phenotype, although recessive, fail to complement each other.
Electron microscopy of frog photoreceptor outer segments after fixation with aldehydes
Authors: Jones G. J.
Published: April 2021

The appearance of the outer segments of isolated retinae fixed with glutaraldehyde or formaldehyde alone, or with these aldehydes and postfixed with osmium tetroxide, is described. Rod outer segments and, to a lesser extent, cone outer segments of retinae fixed only with glutaraldehyde show shrinkage or swelling artifacts which are dependent on the fixative buffer concentration. The rod outer segments are most normal with a fixative phosphate buffer about 50% isotonic with retinal Ringer solution. The disks fixed with glutaraldehyde alone have a granular pentalaminar structure. At the edge of the rod disks, the loops formed by folding over of the disk membranes are seen after glutaraldehyde fixation alone to be filled with stainable material and the edges of adjacent loops to be in contact. The edge of the disk stack thus appears to be a more solid structure than previously thought, and it only partly survives osmium tetroxide treatment, even after glutaraldehyde fixation. Similarly, the arrangement of the disk membranes after glutaraldehyde fixation also appears to be weakened by postfixation with osmium tetroxide. For rod outer segments showing severe shrinkage after glutaraldehyde fixation alone, the interdisk clear spaces are lost and stainable cytoplasmic material, probably protein, is trapped between the disks. The disk membranes then appear as light lines on a dark background, since the central, unstained hydrophobic regions of each disk membrane become prominent.
Plasmalemma invaginations as characteristic constituents of plasmodia of Physarum Polycephalum
Authors: Wohlfarth-Bottermann K. E.
Published: April 2021

Plasmodia of Physarum polycephalum giown on agar or filter paper and fed with rolled oats as food or with a partially defined medium were morphologically analysed in the living state and after fixation. Observation of the living plasmodium growing on agar reveals plasmalemma indentations in the outer regions of protoplasmic strands, which were studied in more detail by phase-contrast microscopy of unstained 1-μm sections. Plasmodia fixed and embedded in situ, i.e. in close contact to their substrate, exhibit an extensive system of plasmalemma invaginations as characteristic constituents throughout all regions.

In plasmodial strands measuring between 40 μm and 1·5 mm in diameter and involved in shuttle streaming, the plasmalemma invaginations are found within the outer ectoplasmic wall. Rounded-up parts of this branched extracellular labyrinth limit the endoplasmic core engaged in the mass transport of protoplasm by shuttle streaming. Despite this clearcut borderline, the central endoplasmic core and the ectoplasmic cortex are connected by occasional protoplasmic bridges.

The extracellular phase within the ectoplasmic regions of the strands can be interpreted either as a result of plasmalemma invaginations fiom the outer border of the strand, or as a consequence of pseudopodial-like processes originating from the central core and extending into the surrounding medium.

The invagination system provides an extensive enlargement of the surface area within the multinucleate protoplasmic mass, probably important for food absorption, excretion processes and motility phenomena.

In thick protoplasmic strands with diameters between 0·2 and 15 mm, there is an intimate connexion between the actomyosin fibrils and the invagination system. The fibrils are attached to the plasmalemma invaginations and/or run parallel to the invaginated plasmalemma sheets. The close relations between the invagination system and actomyosin fibrils will be described in detail in a subsequent paper.