bluuebunny/crossref_metadata_2025 huggingface dataset:
Platelet Dense Bodies: A Quantitative Microprobe Analysis
Authors: Skaer R. J. , Peters Patricia D. , Emmines J. P.
Published: April 2021

The electron microprobe shows that the dense bodies of human platelets have a mean P:Ca peak ratio of 1·2. After treatment with dry chloroform/methanol this falls to 0·89. These ratios vary slightly from patient to patient. The use of calcium and phosphorus standards enables these peak ratios to be converted to atomic ratios. The size of the phosphorus peak remaining after lipid extraction was given absolute terms with reference to the known quantities of adenine nucleotides and inorganic pyrophosphate in dense bodies. From the mean P:Ca atomic ratio of 1·76 the quantity of calcium in dense bodies was 0·6 mg/1011 platelets or 2·97 mg Ca/g dry weight of platelets. This is within the published range for total platelet calcium. If all the phosphorus extracted by lipid solvents were phospholipid there would be 5·65 mg/1011 platelets, and it would occupy most of the space inside dense bodies. The dense bodies of pig platelets contain both magnesium and calcium in a varying ratio to each other. These results are discussed in relation to control mechanisms that may influence aggregation.
Surface morphology and agglutination of lectin-treated human lymphocytes and lymphoblasts
Authors: Temmink J. H. M. , Collard J. G. , Roosien J. , Bosch J. F. Van Den
Published: April 2021

Two human lymphoblasts (Raji and EB3) and normal human peripheral lymphocytes were exposed to different concentrations of Concanavalin A and wheat germ agglutinin. The lectininduced agglutination was determined and correlated with lectin-induced changes in the surface morphology of these cells as studied in a scanning electron microscope. Whenever the lectin induced high agglutinability in a cell type, it also invariably had a smoothing effect on the cell surface. In contrast, when cells did not agglutinate well with a certain lectin, their cell surface remained essentially rough (villous) after addition of the lectin. The correlation found between increased agglutinability and altered cell surface morphology upon treatment with certain lectins suggests that both phenomena result from one and the same process. Additional evidence for this postulate is presented.
Pollen ultrastructure in anther cultures of Datura innoxia: II. The generative-cell wall
Authors: Dunwell J. M. , Sunderland N.
Published: April 2021

In young pollen grains of Datura innoxia, a wall of the usual hemispherical type separates the 2 gametophytic cells initially and, in the electron, microscope, appears as an electron-translucent matrix which is contiguous with the intine. Before detachment of the generative cell from the intine, the matrix decreases in thickness and in places is dispersed altogether leaving the plasmalemmae on either side of it in close apposition. A particularly prominent zone, triangular in profile, is left where the wall joins with the intine. After detachment of the cell, remnants of the matrix can be seen distributed irregularly around the cell and it is supposed that these are partly derived from material in the triangular zone as the cell is drawn away from the intine. The wall residues persist throughout the maturation phase of the pollen and are considered to be either callose resulting from incomplete digestion of the initial wall, or some other polysaccharide material which is unevenly laid down along the wall and concentrated at the junction with the intine.

In pollen induced into embryogenesis by anther culture, wall material is also distributed irregularly around the detached cell in a series of discrete zones, but these are more extensive than in vivo, closer together and in many instances highly dilated. The wall profiles thus have a beaded appearance, the ‘beads’ being connected together by short links of the 2 apposed plasmalemmae. The contents of the swollen zones have a similar electron density to that of the matrix in vivo but also show traces of a fibrillar component. It is postulated that this unusual swelling is a prelude to dispersal of the wall by disruption of the plasmalemmal links and to the establishment of cytoplasmic continuity between the 2 cells. The significance of such binucleate pollen grains in the formation of non-haploid embryos is discussed.
Scanning electron-microscopical and other observations of sperm fertilization reactions in Limulus polyphemus L. (Merostomata: xiphosura)
Authors: Brown George Gordon
Published: April 2021

Sperm fertilization reactions of Limulus polyphemus were examined by scanning electron and/or light microscopy. The following were considered: sperm motility, attachment of sperm to egg, acrosome reaction, and penetration of the acrosomal filament. The spermatozoa after semination are non-motile and become active only in close proximity to a defined region surrounding the egg. Egg materials diffusing into this region induce sperm motility and stimulate large numbers of spermatozoa to move towards the egg surface. Each sperm initially attaches by the apical tip and undergoes the acrosome reaction which causes a more permanent secondary attachment by the adhesion of acrosomal contents to the egg surface. The acrosome reaction also initiates the penetration of the acrosomal filament through the egg envelope, an event occurring in 70–80% of the attached spermatozoa (about 106). Shortly after this penetration, a secondary reaction occurs which involves a spiralling of the flagellum and an incorporation into the sperm body of the flagellar fibrous components, which then become closely apposed to the sperm nucleus.

These sperm fertilization reactions were performed or initiated with 0·34 M CaCl2 in whole eggs, egg sections, excised egg envelopes and/or the outer basement lamina of the egg envelope. The Limulus fertilization system is very valuable since sperm reactions can be examined biochemically, which may lead to a better understanding of the chemical mechanisms involved in sperm-egg interactions in all animal species.
Mechanism of myofibril growth and proliferation in fish muscle
Authors: Patterson S. , Goldspink G.
Published: April 2021

The mechanisms of myofibril growth proliferation were investigated in the red and white muscles of fish. In both types of muscle the ratio of lattice filament spacings between the Z disk and M line was found to be greater than that required for perfect transformation of a square into a hexagonal lattice. This mismatch was considered to result in the thin filaments being pulled obliquely instead of at right angles to the Z disk. The angle of pull of the thin filaments was measured in longitudinal sections. The splitting process was found to decrease the degree of pull. Splitting was also observed in transverse sections of the peripheral myofibrils. In both red and white fibres these myofibrils were found to commence splitting when they reached a size of approximately 1·2 μm diameter. Evidence from ultrastructural and autoradiographical studies suggested that growth of the myofibrils within the fibres is centrifugal. The outermost myofibrils appear to be the ones which are being built up and which split. The data indicated that in fish muscle a considerable number of filaments may be added to the daughter regions whilst splitting of the myofibril is still continuing.
Occurrence of intercellular bridges between follicle epithelial cells in the ovary of Apis mellifica queens
Authors: Ramamurty P. S. , Engels W.
Published: April 2021

Hitherto unknown intercellular bridges or fusomes between the follicle epithelial cells investing the oocytes of Apis mellifica queens have been observed both with light and electron microscopy. Usually each follicle cell has 2–3 intercellular bridges. In surfacial paraffin sections, the intercellular bridges can be seen to connect a series of follicle cells which may be branching. The intercellular bridges lie close to the egg cortex and this position is relatively constant. The width of the fusomal ring canal varies in different develoμmental stages. In stages 3 and 4 of oogenesis, which are the main vitellogenic stages, the intercellular bridges measure 0·5 μm, while in stages 1 and 2 they have a diameter ranging from 1·5 to 3·5 μm. In these stages the intercellular bridges are provided with numerous transverse microfilaments which disappear later. The fusomal lips are thickened and consist of electron-dense material and an additional layer of less electron-dense material both inside and outside. Ribosomes flow across the bridge.

The intercellular bridges may serve to synchronize the differentiation and functional activity of the follicle epithelium during the course of oogenesis.
Studies on the de novo formation of centrioles: aster formation in the activated eggs of sea urchin
Authors: Miki-Noumura Taiko
Published: April 2021

Aster formation was studied in sea-urchin eggs artificially activated by Loeb’s double method. The number of asters found in an activated egg ranged from 15–40. Observation by electron microscopy revealed the presence of a centriole in a high percentage of isolated asters, strongly suggesting that these centrioles are formed de novo in the activated eggs. Using negatively stained specimens, which were isolated with 5 % hexylene glycol solution containing buffer and EGTA, the whole aster could be examined by electron microscopy. A microtubular framework in the aster, extending radially from the astral centre was observed. The effect of mitotic inhibitors on aster formation was found to be similar to that on cell division.
Substrate retention of fractured retraction fibres during detachment of trypsin1zed BHK21 fibroblasts
Authors: Whur P. , Koppel H. , Urquhart C. M. , Williams D. C.
Published: April 2021

When BHK21 fibroblasts adhering to glass were incubated in trypsin they became spherical within a few minutes. They did not, however, respond simultaneously; the most trypsin-resistant cells in an unsynchronized population were of greater length, had more processes projecting from the cell body, and were more spread out than the most trypsin sensitive cells. In no instance did trypsin detach cells from their substrate, even when the incubation period was prolonged to 5 h in trypsin concentrations almost sufficient to cause cell lysis. Scanning electron-microscope observations showed that initially flat cells rounded up in trypsin to reveal persistent adhesion sites joined to the cell body by retraction fibres. Such cells could be dislodged only by agitation; when this occurred parts of the cell remained attached to the substrate in the form of small spheres and fibres; these were remnants of the retraction fibres and adhesion sites. We propose that the adhesion sites are not susceptible to proteolytic degradation, presumably because of steric hindrance, and that this causes detachment to be dependent upon mechanical dislocation. We suggest that some of the descriptions of substrate-associated ‘cell exudates’ in the literature may refer to these cell remnants on the substrate which consist of membrane-bound fragments of cytoplasm rather than secreted products.
Constraints on the relative sizes of the cell populations in Hydra attenuata
Authors: Bode Hans R. , Flick Kristine M. , Bode Patricia M.
Published: April 2021

The steady-state relative population sizes of the several cell populations in Hydra attenuata were examined. In contrast to the constant average population size ratios between groups of animals, these ratios vary within limits between individual animals within a group. By maintaining animals on different feeding regimes (number of shrimp larvae ingested per day), the steady-state population size ratios were altered. The kinds of changes that occurred in these ratios suggest where controls may be operating to maintain the steady-state population sizes.
Studies on isolated smooth muscle cells: the contractile apparatus
Authors: Small J. V.
Published: April 2021

Smooth muscle cells may be isolated from the taenia coli muscle of the guinea pig which, when made permeable by treatment with Triton X-100 (0·05 %) show a sensitivity to Ca for contraction with MgATP. The rate of contraction, about 10 μm s− 1, corresponds closely to the maximum velocity of shortening of the intact muscle. Electron microscopy of such partially demembranated muscle cells shows that myosin filaments of about 16-nm diameter are present in both the rigor and the relaxed states. In addition, the actin and myosin filaments are commonly seen to be associated in groups corresponding approximately in size to the fibrils recognizable in cells in rigor in the light microscope. The dense bodies and the 10-nm filaments are found located between the actin-myosin filament groups. The thick myosin filaments may be isolated by fragmentation of the cells under relaxing conditions. These native filaments range up to about 8 μm in length and show the same structural organization as filaments assembled from purified smooth muscle myosin: there is no central bare zone and bare edges, about 0·2 μm long, occur at the filament ends. The lack of bipolarity on the native smooth muscle myosin filaments and the absence, in the contractile apparatus, of actin-associated structures equivalent to Z-lines suggests that the amount of shearing that can occur between the actin and myosin filaments is considerably greater than in skeletal muscle.
Binding of the herbicide trifluralin to Chlamydomonas flagellar tubulin
Authors: Hess F. D. , Bayer D. E.
Published: April 2021

Colchicine-binding tubulin was isolated from the centre 2 axoneme microtubules from the flagella of the alga Chlamydomonas eugametos. Incubating this tubulin with 5·8 μM [14C]tri-fluralin resulted in significant and reproducible binding of trifluralin to tubulin. The specificity of binding was determined by demonstrating that limited or no binding occurred to flagellar membrane and matrix protein, higher plant proteins, or bovine serum albumin. It was concluded that trifluralin, at obtainable soluble concentrations, specifically inhibits microtubule-mediated processes in plants. To date no effect of trifluralin on animal microtubule systems has been reported; therefore, it is suggested that trifluralin has revealed a pharmacological difference between plant and animal tubulin.
The nucleolar cycle in man
Authors: Anastassova-Kristeva Marlen
Published: April 2021

Tissue cultures of human embryonal kidney and ovary were examined. In the nuclei of both tissues, one to ten nucleoli have been found. The maximum number of nucleoli is connected with the gene expression of rDNA of the 10 nucleolus organizers of chromosome pairs Nos. 13, 14, 15, 21 and 22, which have secondary constrictions and are the satellite chromosomes in man. The small percentage of cells with 10, 9 and 8 nucleoli is attributed to the rapid association of 3 of the homologous acrocentrics (perhaps of group D). Two of the satellite (SAT) pairs probably associate later after mitosis. The process of fusion is dynamic, resulting in one interphase nucleolus - a manifestation of the association of all SAT chromosomes. Dissociation of the nucleolus occurs upon entering prophase, due to the condensation of the chromosomes and retreat of rDNA to the respective secondary constrictions. As a result, the nucleolar number increases again. The pattern of the nucleolar kinetics within the course of one mitotic division is described.
Comparative study of axopodial microtubule patterns and possible mechanisms of pattern control in the centrohelidian heliozoa Acanthocystis, Raphidiophrys and Heterophrys
Authors: Bardele Christian F.
Published: April 2021

The axopodial microtubule pattern of 9 centrohelidians belonging to the genera Acanthocystis, Raphidiophrys and Heterophrys, as well as the fine structure of their microtubule organizing centre, the ccntroplast, was studied to determine the rules which govern their patterns. Microtubules capable of binding a maximum of 4 linkers are arranged in regularly distorted hexagons and equilateral triangles. The number of microtubules present in each axoneme ranges from some 140 in Acanthocystis turfacea to as few as 6 in Heterophrys marina (Stock I). In the later species each axoneme contains a single hexagon of microtubules only. In other Heterophrys species, the central hexagon is surrounded by closely packed microtubules or by microtubules arranged in pentagons; only the central hexagon is anchored in the centroplast shell, whereas additional microtubules seem to originate from secondary nucleation sites somewhat distal to the centroplast. It is argued that the distortion of the basic unit hexagon (with alternate angles close to 134°and 106°) indicates that the microtubules are composed of 13 protofilaments.

While in the larger Acanthocystis and Raphidiophrys species, the pattern may result from self-linkage, the arrays found in the Heterophrys species seem to favour a template-determined linkage. To explain the formation of the central hexagon in Heterophrys and balanced lateral growth in the larger microtubule arrays, a ‘linker-nucleation hypothesis’ is proposed. The assumption is made that graded conformational changes in the microtubule subunits not only specify the position where the next linker will bind, but that this linker, through linkage, becomes able to induce secondary microtubule nucleation, which will result in balanced lateral growth of the array. The application of this hypothesis to other microtubule systems, e.g. basal body formation, is discussed.
Differentiated regions of human placental cell surface associated with exchange of materials between maternal and foetal blood: a new organelle and the binding of iron
Authors: Ockleford C. D. , Menon G.
Published: April 2021

To elucidate the method of uptake of a neutral iron compound into the placenta, isolated human chorionic villi were incubated in a medium containing the substance and were fixed at intervals and subsequently examined using transmission electron microscopy.

None of the specimens examined showed evidence of vesicular transport in either micro- or macro-pinocytic vesicles which were either coated or smooth-surfaced. Iron uptake may involve attachment of particles to differentiated regions of the cell surface of the syncytiotrophoblast. These differentiated zones in the syncytial cell surface are composed of morphologically distinct parts and therefore probably merit classification as an organelle. Our interpretation of the organelle’s structure is that it is flattened, with a maximum distance across of about 30 nm in the plane of the membrane. It is of otherwise uncertain shape but possesses a multilaminar structure. The external layer is apparently composed of the iron compound to be taken up. Beneath this is an electron-lucent layer possibly composed of glycocalyx. The next innermost layer is continuous with the trilaminar unit membrane of the cell surface, however no trilaminar appearance is observed within the organelle. Beneath the membrane layer is an electron-dense plaque of amorphous material. Occasionally in favourable sections there is the suggestion of a thin electron-lucent strip interposed between the dense plaque and the membrane layer. The whole structure is composed therefore of 4 or 5 different regions. One possible function is that of initial binding in a process of active as opposed to passive transport of iron into the cell.
Extracellular matrix synthesis in blastula and gastrula stages of normal and hybrid frog embryos :I. toluidine blue and lanthanum staining
Authors: Johnson Kurt E.
Published: April 2021

Four developmental stages of Rana pipiens, R. pipiens ♀ × R. catesbeiana ♂, and R. pipiens♀x R. escalenta ♂ embryos were fixed in standard electron microscopic fixatives with or without 1% lanthanum nitrate (LN) added. Embryos fixed without LN were embedded and sectioned at 0·5 μm and stained with toluidine blue. Embryos fixed with LN were embedded and sectioned at 70– 80 nm and examined in the electron microscope. Both techniques show a dramatic increase in the amount of stainable material in the extracellular matrix during development. Blastula stage embryos have a small amount of material in the extracellular matrix. Early gastrulae have more stainable material than blastulae and this increased amount appears to be due to an accumulation of material in the marginal zone of the embryo, especially near the dorsal lip of the blastopore. Late gastrulae have large amounts of stainable material in the extracellular spaces in almost all parts of the embryo. Interspecific arrested hybrid embryos do not show the same dramatic accumulation of stainable material in their extracellular matrices.
Gene transfer by means of cell fusion: II the mapping of 8 loci on human chromosome 1.by statistical analysis of gene assortment in somatic cell hybrids
Authors: Goss S. J. , Harris H.
Published: April 2021

A method is described which should permit determination of the order and spacing of genes on all human chromosomes by the analysis of just one set of man-mouse hybrid cells. This method is used to determine the map of 8 loci on human chromosome 1. A comparison of the statistical maps of chromosome 1 and of the X-chromosome with the cytogenetic maps of these chromosomes at metaphase indicates that the statistically derived distances between genes are related to the amount of Giemsa light-band material between the genes.
Preferential inhibition of rdna transcription by 5-bromodeoxyuridine
Authors: Lykkesfeldt Anne E. , Andersen H. A.
Published: April 2021

On a chemically defined growth medium the degree of substitution of thymidine with 5-bromodeoxyuridine (BUdR) in DNA of Tetrahymena pyriformis was controlled by the concentration of tetrahydrofolic acid, BUdR and thymidine in the medium. A correlation between the degree of BUdR substitution in DNA and the reduction in rate of total RNA synthesis has been established. It was found that the reduction of total RNA synthesis results from inhibition of transcription of all RNA species which have been measured. However, independent of the degree of BUdR substitution in DNA, a preferential inhibition of the synthesis of 25s and 17s ribosomal RNA was found. It is concluded that the various genes may respond differently to BUdR substitution with respect to transcription.
The surface of lipid droplets constitutes a barrier for endoplasmic reticulum-resident integral membrane proteins
Authors: Khaddaj Rasha , Mari Muriel , Cottier Stéphanie , Reggiori Fulvio , Schneiter Roger
Published: April 2021

Lipid droplets (LDs) are globular subcellular structures that store neutral lipids. LDs are closely associated with the endoplasmic reticulum (ER) and are limited by a phospholipid monolayer harboring a specific set of proteins. Most of these proteins associate with LDs through either an amphipathic helix or a membrane-embedded hairpin motif. Here, we address the question of whether integral membrane proteins can localize to the surface of LDs. To test this, we fused perilipin 3 (PLIN3), a mammalian LD-targeted protein, to ER-resident proteins. The resulting fusion proteins localized to the periphery of LDs in both yeast and mammalian cells. This peripheral LD localization of the fusion proteins, however, was due to a redistribution of the ER around LDs, as revealed by bimolecular fluorescence complementation between ER- and LD-localized partners. A LD-tethering function of PLIN3-containing membrane proteins was confirmed by fusing PLIN3 to the cytoplasmic domain of an outer mitochondrial membrane protein, OM14. Expression of OM14–PLIN3 induced a close apposition between LDs and mitochondria. These data indicate that the ER–LD junction constitutes a barrier for ER-resident integral membrane proteins.

This article has an associated First Person interview with the first author of the paper.
TORC2 inhibition of α-arrestin Aly3 mediates cell surface persistence of S. pombe Ght5 glucose transporter in low glucose
Authors: Toyoda Yusuke , Soejima Saeko , Masuda Fumie , Saitoh Shigeaki
Published: April 2021

In the fission yeast, Schizosaccharomyces pombe, the high-affinity hexose transporter, Ght5, must be transcriptionally upregulated and localized to the cell surface for cell division under limited glucose. Although cell-surface localization of Ght5 depends on Target of rapamycin complex 2 (TORC2), the molecular mechanisms by which TORC2 ensures proper localization of Ght5 remain unknown. We performed genetic screening for gene mutations that restore Ght5 localization on the cell surface in TORC2-deficient mutant cells, and identified a gene encoding an uncharacterized α-arrestin-like protein, Aly3/SPCC584.15c. α-arrestins are thought to recruit a ubiquitin ligase to membrane-associated proteins. Consistently, Ght5 is ubiquitylated in TORC2-deficient cells, and this ubiquitylation is dependent on Aly3. TORC2 supposedly enables cell-surface localization of Ght5 by preventing Aly3-dependent ubiquitylation and subsequent ubiquitylation-dependent translocation of Ght5 to vacuoles. Surprisingly, nitrogen starvation, but not glucose depletion, triggers Aly3-dependent transport of Ght5 to vacuoles in S. pombe, unlike budding yeast hexose transporters, vacuolar transport of which is initiated upon changes in hexose concentration. This study provides new insights into the molecular mechanisms controlling the subcellular localization of hexose transporters in response to extracellular stimuli.
Ultrastructural localization of acid phosphatase activity in root tips by the P-(Acetoxymercuric) aniline diazotate reagent and a comparison with a gomoriprocedure
Authors: Stewart P. , Pitt D.
Published: April 2021

The localization of acid phosphatase was studied in root tip cells of pea and mung bean by use of a heavy metal azo-dye technique. Diazotized p-(acetoxymercuric) aniline in a postcoupling procedure, using naphthol AS-BI phosphate as substrate, yielded a fine particulate reaction product within vacuoles, intercellular spaces, multivesicular bodies and at various sites throughout the cytoplasm of pea root cells and differentiating mung bean protoxylem cells. An ultrastructural comparison with a modified Gomori lead-salt precipitation method revealed differences in the subcellular location of β-glycerophosphatase and naphthol AS-BI phosphatase. The distribution of acid phosphatases within plant meristematic cells is discussed.
Synaptonemal complex karyotyping in Melanoplus Differentialis
Authors: Solari Alberto J. , Counce S. J.
Published: April 2021

The chromosomal axes of the spermatocytes of the grasshopper Melanoplus differentiate have been studied with a modification of the microspreading procedure used previously. The whole complement of synaptonemal complexes (SCs) and the axis of the X chromosome have been described and measured. The relative length of each SC is characteristic and constant and permits the construction of an idiogram. Relative lengths of SCs are almost equal to the relative lengths of mitotic chromosomes of spermatogonia (with the exception of the X chromosome), thus extending to an invertebrate the relationship between SCs and mitotic chromosomes that has been demonstrated in mammals. All the SCs except the 3 smallest (which are apparently telocentric) show a small short arm beyond the kinetochore. The progression of changes in the chromosomal axes during meiotic prophase has been staged by centriolar behaviour. During leptotene, axes are first formed near the nuclear envelope at a special (polar) region. SCs also begin to appear in the polar region and extend towards the nuclear interior. The beginning and completion of synapsis is not synchronous among bivalents. The X-axis is formed in midzygotene and shows a characteristic sequence of changes in shape during pachytene. Cells in post-synaptic stages show whole chromosome complements with characteristic chiasmatic configurations. Kinetochores are prominent and bipartite during diplotene-diakinesis.
Chromatin-like artifacts from nuclear sap
Authors: Skaer R. J. , Whytock Susan
Published: April 2021

Nuclear sap, on fixation in glutaraldehyde, forms a fibrous network that resembles chromatin in its dimensions and staining properties. This artifactual network is easily confused with true chromatin fibres in sections of nuclei. With formaldehyde a homogeneous array of beads is produced. These are approximately 10 nm in diameter – the size of nucleosomes – and are interconnected by exceedingly fine fibrils. Each fixative and buffer imposes its own distinctive, reproducible pattern on nuclear sap. The structure of nuclear sap in life cannot be deduced from this range of patterns.
The induction of cytoplasmic petite mutants of Saccharomyces Cerevisiae by hydrostatic pressure
Authors: Rosin Miriam P. , Zimmerman A. M.
Published: April 2021

This study demonstrates that hydrostatic pressure is a potent inductive agent of the petite mutation in cultures of Saccharomyces cerevisiae. The inductive capacity of this mutagen is dependent on the magnitude and the duration of the pressure treatment. Furthermore, the extent of petite induction varies with the growth stage of the culture. Induction occurs in pressure-treated (1·4×104 Ibf in.−2 or 9·66×104 kN m−2 for 4 h) log growth cultures but not in stationary or lag phase cultures. Petite induction and cell survival are also dependent on the particular strain of yeast which is pressure-treated. Tetrad analysis and complementation assays demonstrate that pressure-induced petite cells are cytoplasmic in nature. Moreover, induced petite cells show a wide range of suppressivity (2–99%) with a large proportion of the petite cells being highly suppressive.
Immunofluorescent localization of urease in the cotyledons of jack bean, Canavalia Ensiformis
Authors: Murray D. R. , Knox R. B.
Published: April 2021

Urease has been localized in sections of cotyledons from germinating seeds of jack bean, using FITC-labelled immunoglobulin prepared from urease antiserum raised in rabbits. The complication of lectin binding to the immunoglobulins was resolved by treatment of the sections with specific glycosides. Urease is localized in 2 sites : within the cytoplasm of storage parenchyma cells in spherical granules up to 3 μm in diameter, and within the intercellular spaces in spherical granules. Although similar in size, the latter are distinguished from the cytoplasmic granules by the presence of β-lectin and appear to function as an extracellular lytic compartment or lysosome.
Oscillations and cell development in Dictyostelium discoideum stimulated by folic acid pulses
Authors: Wurster Bernd , Schubiger Katrin
Published: April 2021

Folic acid is known to be a chemoattractant of pre-aggregation cells of Dictyostelium discoideum. When supplied in pulses, folic acid induces biochemical oscillations and stimulates the development of pre-aggregation to aggregation-competent amoebae. The continuous supply of folic acid has no stimulatory effect. Folic-acid-induced oscillations are accompanied by periodic changes in the cyclic AMP concentration. Pulses of folic acid applied with rhythms between 7 and 11 min efficiently induce oscillations. In contrast, a rhythm of 2 min neither induces oscillations nor suppresses them. Cells start to oscillate with a rhythm of about 8 min. This inherent rhythm is independent of the inducing rhythm. Oscillating cells are less sensitive to folic acid than pre-oscillating ones. They respond only to high concentrations of folic acid which also interact with the oscillating system.
Interactions between epithelial and fibroblast-like cells in cultures derived from monkey periodontal ligament
Authors: Brunette D. M. , Kanoza R. J. , Marmary Y. , Chan J. , Melcher A. H.
Published: April 2021

Explants of adult monkey periodontal ligament produced outgrowths containing both fibro-blast-like (F) and epithelial-like (E) cells. A number of multilayers of either E or F cells, or both E and F cells were seen. Electron-microscopic examination of mixed multilayers showed that E cells could form either the superficial or deep sheet of cells. Attachments by means of desmosomes between dorsal and ventral surfaces of multilayered E cells were demonstrated. Although the membranes of E and F cells were sometimes closely apposed, no special junctional structures could be detected between them. The E cell and F cell layers were also observed in a relationship, unusual for cell culture, in which the E cell layer was sandwiched between two F cell layers. This unusual relationship may be the result of cells mimicking in vitro their relationship in vivo, since the E cells are derived from the epithelial rests of Malassez which, in vivo, are surrounded by periodontal ligament F cells. When F cells were seeded on to the surface of E cells a significant fraction of them were found to attach, but the spreading of F cells on E cells was a rare event. These observations could be interpreted as being the result of heterogeneity in the F cell populations. A further indication of the heterogeneity of F cell populations was provided by time-lapse studies of colonies of F cells obtained by culturing cell suspensions of porcine periodontal ligament. In this system, it was found that statistically significant differences existed between the different F colonies with respect to their average cellular mobility. These findings suggest that light-microscopical morphological criteria do not adequately define cell types in terms of behavioural or functional characteristics.
Thermal transitions in the adhesiveness of hela cells: effects of cell growth, trypsin treatment and calcium
Authors: Deman J. J. , Bruyneel E. A.
Published: April 2021

The intercellular adhesiveness of density-inhibited (D.I.) and fast-growing (F.G.) HeLa cells and of trypsin-treated preparations of these, has been measured at temperatures between 37 and 6 °C.

In EDTA-containing buffer medium, F.G. cells differ from D.I. cells in that only the former display an increase in adhesiveness below 30 °C. This increase is prevented by previous treatment with trypsin.

The presence of Ca2+ in the buffer medium causes a narrowing of the thermal transition region of intact F.G. cells. On intact D.I. cells Ca+2 causes an increase in adhesiveness at temperatures below 20 °C. Previous trypsinization of F.G. cells diminishes the effect of subsequent Ca+2 addition. The adhesiveness of trypsinized D.I. cells is indifferent to changes in temperature in Ca*+-containing buffer medium.

The results are considered evidence for the occurrence of a phase transition in the glycoprotein domains of the plasma membrane of fast-growing cells. The transition is influenced by growth rate, trypsinization and Ca2+. The fluidity of the membrane glycoproteins is considered to be higher on density-inhibited cells than on fast-growing cells.

No phase transition could be detected after incorporation of the fluorescent compound 1,6-diphenyl 1,3,5-hexatriene into the lipid domain of the plasma membrane. The fluidity of the membrane lipids is lower on density-inhibited cells than on fast-growing cells.
Ultrastructure of the adrenal cortex in frozen thin sections
Authors: Magalhães M. M.
Published: April 2021

Pieces of both unfixed and fixed rat adrenal cortex were frozen and cut with a cryoultramicrotome. In unstained frozen sections of unfixed adrenals patches of heterochromatin were seen in the nucleus, while numerous round uniformly dense structures, the mitochondria, could be identified in the cytoplasm. Lipid droplets appear as small light round areas. Staining the sections with potassium permanganate, phosphotungstic acid, or uranyl acetate, or immersing them in glutaraldehyde, increased the contrast of cell organelles. In frozen sections of fixed material, membranes became visible in negative contrast. Mitochondria display vesicular cristae, whereas the Golgi complex, lysosomes and peroxisomes are easily recognizable. The possibility of cutting frozen sections of unfixed material with reasonable morphological preservation allows the fine-structural localization of steroids in adrenal cells after applying autoradiographic emulsion to the sections.
Effects of ultraviolet light on synchronized chinese hamster ovary cells; potentiation by hydroxyurea
Authors: Burg Kornel , Collins Andrew R. S. , Johnson Robert T.
Published: April 2021

We have examined the effects of hydroxyurea on u.v.-irradiated Chinese hamster CHO-Ki cells. Ultraviolet irradiation followed by incubation with hydroxyurea causes only slight disruption of DNA and chromosome structure in CHO-Ki cells compared with HeLa cells. There is, however, a clear potentiation by hydroxyurea of the u.v. killing of CHO-Ki cells, which is most pronounced at those points in the cycle which are reported to have small DNA precursor pools. This potentiation is reduced when DNA precursors are provided together with hydroxyurea. These data are discussed in terms of an uncoupling of excision and repair DNA synthesis.
Differentiation of the tapetum in A vena II. the endoplasmic reticulum and golgi apparatus
Authors: Steer M. W.
Published: April 2021

During the differentiation of the tapetai cell the endoplasmic reticulum develops into an extensive, regionally differentiated system, consisting of 2 types of smooth cisternae interconnected by rough cisternae. Smooth cisternae with narrow lumens encircle the plastids and mitochondria and lead into rough cisternae with a wider lumen containing a moderately densely staining material. This material is stored in an unusual system of distended smooth cisternae, rather than being transferred to the Golgi apparatus. This system is believed to represent a holocrine secretion system, since it disappears at cell senescence at the same time as the pollen grains accumulate metabolite reserves. No morphological evidence could be found for the contribution of products of the reticulum to orbicule or sporopollenin synthesis.

The dictyosomes and vesicles undergo a continuous series of changes as the tapetai cells differentiate. Development of flat dictyosome cisternae with dark amorphous contents is followed by a further change to more undulating, or curved cisternae. These different dictyosomes produce vesicles with morphologically distinct contents, some of which are observed fused with the plasma membrane. At maturity the vesicles form unique cylindrical channels, sometimes branched, which occur throughout the cytoplasm. Examination of thick sections by HVEM and STEM suggests that they are developed to facilitate movement of the dictyosome product through the masses of endoplasmic reticulum cisternae to the cell surface.
Control of flagellar motion in Chlamydomonas and Euglena by mechanical microinjection of Mg2+ and Ca2+ and by electric current injection
Authors: Nichols M.Kathleen , Rikmenspoel Robert
Published: April 2021

Upon impalement with a microelectrode in a Caa+-free medium containing 5 mM ATP, a Chlamydomonas cell lost its flagellar activity within 45 s, and the injection of either positive or negative direct current did not stimulate the flagella to beat after that time. When 3 mM Mg2+was added to the external medium, the impaled cell exhibited a flagellar frequency of 22 ± 7 Hz. With 5 mM ATP and 3 mM Mg2+ in a Ca2+-free medium, negative direct electric current inhibited flagellar frequency and positive direct electric current enhanced flagellar activity. The flagella recovered to approximately their characteristic frequency (20 ± 6 Hz) upon the cessation of current. Euglena and Chlamydomonas cells were mechanically microinjected with Ca2+ or Mg2+ ions contained in 1·0 M KCl-filled microelectrodes. In both cells, the injection of 0·02 M Ca2+ resulted in a decrease in flagellar frequency dependent on the amount of Ca2+ injected. The frequency decreased to zero Hz upon the injection of 16 × 10−14 1. in Euglena and 3·5× 10−141. in Chlamydomonas. The microinjection of 10 × 10−14 1. of o·2 M Mg2+ into Euglena cells resulted in an approximately 2-fold increase in flagellar frequency. Chlamydomonas flagella, which stop beating upon impalement in a Mg2+-free medium, began to beat when the cell was injected with Mg2+ ions. The flagella exhibited an average frequency of 16 ± 3 Hz when injected with 1·5 × 10−141. of 0·2 M Mg2+. The data indicate that an increase in internal Mg2+stimulates flagellar frequency. The microinjection of Ca2+ inhibits flagellar motility.
Cross-sectional myofibre and myofibril growth in immobilized developing skeletal muscle
Authors: Shear Charles R.
Published: April 2021

The effect of immobilization on skeletal muscle fibre and myofibril growth in the developing chick latissimus dorsi posterior muscle was investigated. Immobilization, immediately upon hatching, results in a 25% decrease in mean myofibre cross-sectional area within 24 h. Longer periods of immobilization further retard normal myofibre growth until by day 27 after hatching the mean myofibre cross-sectional area was 70% less than normal. The variation in individual myofibre cross-sectional areas (measured as the coefficient of variation, CV = standard deviation/mean × 100) was greater in immobilized muscles. The larger immobilized myofibres showed atypical myofibril and sarcotubular complex organization at the ultra- structural level of observation whereas the smaller immobilized myofibres appeared normal, except for their size. In 1- to 27-day-old chicks, freeing the immobilized muscles for 24 h resulted in myofibril reorganization and sarcotubular proliferation but little myofibre growth. Freeing the immobilized muscles for 72 h resulted in a nearly complete recovery, in chicks up to 18 days post-hatching, of both cross-sectional myofibre area and ultrastructural morphology. Myofibres immobilized for longer than 18 days and subsequently freed for 72 h develop a normal myofibrillar and sarcotubular morphology but remain 23 to 29% smaller in crosssectional area than myofibres from control muscles.

Normal myofibril growth and organization are severely retarded in the immobilized myofibres. The evidence presented here suggests that sarcomere shortening causes growing myofibrils to rupture. The ruptured myofibrils are filled with proliferating elements of the sarcotubular complex which, in turn, completely subdivide (split) the myofibril.
Dna replication studies in genus Vicia through fibre radioautography
Authors: Gaddipati J. P. , Sen S. K.
Published: April 2021

An experiment has been conducted to study the mode of replication in 3 species of Vicia having different C-values by means of fibre radioautography. Characteristics of the units involved in DNA replication of these species have been compared. It has been observed that replication occurs predominantly through bidirectional chain growth, replicating units are arranged in tandem, and replication proceeds from the point of origin in both directions. It has also been shown that there is a positive, though not proportionate, correlation between replication rates, the sizes of replication units and C-values.
Fine-structural localization of adenosine triphosphatase in the rectum ofCalliphora
Authors: Berridge M. J. , Gupta B. L.
Published: April 2021

Adenosine triphosphatase (ATPase) activity in the rectal papillae of Calliphora has been studied by biochemical and histochemical techniques. The microsomal fraction contained a Mg2+-activated ATPase with a pH optimum of 8·0. The enzyme was not stimulated by the addition of Na+ plus K+ and was insensitive to ouabain. Histochemical studies using modifications of the Wachstein–Meisel method showed that at pH 7·2 this Mg2+-activated ATPase was specifically localized on the intracellular surface of the lateral plasma membranes. A similar though less intense reaction was obtained with adenosine diphosphate and inosine triphosphate, but not with guanosine triphosphate, uridine triphosphate or β-glycerophosphate as substrates. At an acid pH (6·6–6·8), very little reaction occurred on the lateral plasma membrane but some reaction product was present in mitochondria and nuclei. Very little enzyme activity was found in the flattened rectal epithelium. These results are discussed in relation to the available data on transport ATPases and on the structural basis of fluid transport by rectal papillae. It is proposed that the ATPase localized on the stacks of lateral plasma membrane may be involved with ion secretion into the intercellular spaces to create the osmotic gradient necessary to extract water from the lumen.
The ultrastructure and ontogeny ofpollen in Helleborus Foetidus l. I. the development of the tapetum and ubisch bodies
Authors: Echlin P. , Godwin H.
Published: April 2021

The ontogeny of the tapetum and Ubisch bodies in Helleborus foetidus L. has been examined at the ultrastructural level, and their development has been closely linked with that of the sporo-genous cell and pollen grains. During development the tapetum passes through successive phases of synthesis, maturity and senescence, ending in complete dissolution. During the anabolic phase of growth, precursors of the Ubisch bodies are formed as spheroidal vesicles of medium electron density within the tapetal cytoplasm; they are associated with a zone of radiating ribosomes, which, as development proceeds, can clearly be seen to be situated on strands of endoplasmic reticulum. The callose special wall round the microspores and the tapetal cell wall now disintegrate and the pro-Ubisch bodies are extruded through the cell membrance of the tapetal cells, where they remain on the surface of the anther cavity and soon become irregularly coated with sporopollenin. Deposition of sporopollenin continues on the Ubisch bodies at the same time as upon the exines of the developing pollen grains. In both cases, the later stages of sporopollenin deposition are associated with electron-transparent layers of unit-membrane dimensions appearing in section as white lines of uniform thickness. Continuing deposition of sporopollenin leads to the formation of compound or aggregate Ubisch bodies. It is conjectured that the sporopollenin is synthesized from the compounds of low molecular weight released into the anther loculus by the breakdown of the callose special wall and the tapetal cell wall. The final stages of tapetal autolysis involve the disappearance of all the cell organelles. An attempt is made to relate the findings to those described in other recent studies on Ubisch body formation and to combine them in a common ontogenetic pattern.
An association between viral transformation and forssman antigen detected by immune adherence in cultured BHK21 cells
Authors: O’neill C. H.
Published: April 2021

A method of immune adherence applicable to tissue culture cells in monolayers is described. It is some twenty times more sensitive than cytotoxicity (dye-exclusion) as a quantitative immunoassay, applicable to the antigens of the cell surface. It has been found that adherence does not occur to confluent cell sheets, and this can be explained if immune adherence to tissue culture cells occurs only at the tips of pseudopods. This source of variation can be reduced to a minimum by the use of sparse cell layers, and under suitable conditions the antiserum titres obtained do not vary by more than one doubling dilution. With the aid of this method, the antigens of BHK21 hamster kidney cell surfaces have been studied after transformation by polyoma and other viruses. Using rabbit antisera, it was found that Forssman antigen, which is absent from BHK21 cells, appeared on the surfaces of all the transformed lines studied. Rous virus-transformed BHK21 cells also showed this antigen, and reversion to the normal cell morphology, which occurs in these lines, was accompanied by a loss of this antigen.