bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ultrastructural observations on deep-etched thylakoids
Authors: Park R. B. , Pfeifhofer A. O. 
Published: April 2021

ABSTRACT
Deep etching of spinach thylakoids frozen in water exposes the inner and outer surfaces of the thylakoid. Both these surfaces differ greatly in appearance from their respective adjacent fracture planes. This finding constitutes further evidence for membrane splitting during the fracture process. Modification of the fracture face by loss of shattered material or by plastic deformation may explain the partial mismatch between the two fracture faces observed in washed thylakoids.
The effect of ethylenediaminetetra-acetate washing on the structure of spinach thylakoids
Authors: Park R. B. , Pfeifhofer A. O. 
Published: April 2021

ABSTRACT
The particles removed from spinach thylakoids by washing with ethylenediaminetetraacetate were found to correspond to particles on the outside surface of the thylakoid, and not to the quantasome cores which remain within the membrane.
Cytoplasmic dna-containing bodies and the response of amoebae to dimidium bromide
Authors: Hawkins Shirley E. , Willis Lesley R. 
Published: April 2021

ABSTRACT
The growth of Amoeba proteus (T1P) and Amoeba discoides (T1D) in the trypanocidal phenanthridinium, dimidium bromide was examined. At concentrations of drug between 2 and 4 μg/ ml, A. proteus divided twice before inhibition and death. A. discoides was able to undergo an additional cycle of division before death. At other concentrations there were no differences in their response. Heterotransfers between these strains resembled A. discoides, both dividing three times before death. Examination of clones derived from the micro-injection of small quantities of A. discoides cytoplasm into A. proteus showed that the ability to divide additionally in dimidium bromide could be transferred. Some other strains of A. proteus (DP, T4P) also resembled A. discoides in their response.
Cells of all the strains used were treated with acridine orange and observed under the fluorescence microscope for the presence of DNA- and RNA-containing cytoplasmic ‘bodies’. All strains able to undergo an additional division cycle also possessed cytoplasmic DNA-containing bodies. The converse was not 100%, but this may be due to a quantitative difference in the number of DNA-containing bodies in the cytoplasm. It is proposed that the difference in response to dimidium bromide observed in A. proteus and A. discoides may be associated with the presence of DNA- and RNA-containing bodies in the cytoplasm of A. discoides.
Studies on the autonomy of pellicular DNA in Paramecium
Authors: Smith-Sonneborn Joan , Plaut W. 
Published: April 2021

ABSTRACT
This autoradiographic study was designed to elucidate the relationship between the macro-nucleus and pellicular DNA in Paramecium. The capacity of the cell to synthesize pellicular DNA in the absence of the macronucleus was established by demonstrating the incorporation of tritiated thymidine into DNase-sensitive material in the pellicles of amacronucleate cells. Moreover, using a technique which leads to selective labelling of the macronucleus in normal paramecia, we have looked for evidence of transfer of labelled DNA from the macronucleus to the pellicle with time. Finding none, we conclude that labelled pellicular DNA is not of macro-nuclear origin, and that labelled pellicular DNA synthesis is not directly dependent on the presence of the macronucleus.
Cell proliferation in the epithelium of the oesophagus, trachea and ureter in mice
Authors: Blenkinsopp W. K. 
Published: April 2021

ABSTRACT
Over a 24-h period, groups of mice were given a single injection of colchicine (to collect blocked metaphases) and tritiated thymidine (to label nuclei synthesizing deoxyribonucleic acid). Epithelial nuclei in the oesophagus, trachea and ureter were examined and counted in paraffin sections: the duration of deoxyribonucleic acid synthesis (Ts) was calculated from the numbers of blocked metaphases and labelled nuclei, the duration of the post-synthetic gap (Tc2) was estimated from the proportion of blocked metaphases labelled, and the cell cycle time (Tc) was calculated from Ts and the proportion of nuclei labelled. In each epithelium the different layers seen by light microscopy were analysed separately.
Ts was probably the same for the basal and superficial cells in the trachea (about 8 h), and was probably the same for the basal, intermediate and superficial cells in the ureter (about 5 h). In the oesophagus Ts was 8·5 h.
T G2 was probably the same for the basal and superficial cells in the trachea (3·6 h), and probably the same for the basal, intermediate and superficial cells in the ureter (about 4·6 h). In the oesophagus Tc. was 2’8 h.
Tc was about 380 h (basal cells) and 1400 h (superficial cells) in the trachea, and about 8000 h (basal and intermediate cells) and 2700 h (superficial cells) in the ureter. In the oesophagus Tc was 41 h.
The ultrastructure and ontogeny of pollen inHelleborus FoetidusL.: III. the formation of the pollen grain wall
Authors: Echlin P. , Godwin H. 
Published: April 2021

ABSTRACTThe first recognizable elements of the pollen grain wall of Helleborus foetidus are initiated in the cellulosic primexine which is formed immediately outside the microspore cytoplasm while the pollen grains are still in the tetrad configuration and enveloped in a thick layer of callose. Elements of the primexine give rise to the precursors of the rod-like bacula of the mature exine. The bacula increase in electron density due to the rapid deposition of sporopollenin, and begin to expand laterally at the outer side to form the tectum. There follows a lateral expansion on the inner side to form the foot-layer. Further deposition of sporopollenin is continued and all elements of the pollen grain wall expand outwards and laterally as the pollen grain enlarges. The enveloping callose disappears and the pollen grains are free in the thecal cavity. A secondary exine is deposited below the primary exine, particularly around the furrows. Initially this process involves a number of thin electron-transparent lines or lamellae about 4 nm thick that appear to arise from the cytoplasm and provide a locus around which sporopollenin is deposited. As the deposition proceeds, the lamellae thicken and finally merge with each other to form the secondary exine. No sign of the lamellae can be seen in the mature pollen grain wall. Towards the end of secondary exine formation the deposition of sporopollenin does not appear to be centred on thin lamellae, but appears as small granules which gradually coalesce. The secondary exine remains discontinuous in the region of the furrow, but becomes consolidated in the inter-furrow regions.As the pollen grain matures the sporopollenin, which is electron-dense when initially deposited, becomes progressively less so.The final stage in development is the deposition of the cellulosic intine, which forms inside the secondary exine and is associated with increased dictyosome activity and randomly oriented microtubules.
Observations on the fine structure of the eyespot and associated organelles in the dinoflagellate Glenodinium Foliaceum
Authors: Dodge J. D. , Crawford R. M. 
Published: April 2021

ABSTRACT
The eyespot of the marine dinoflagellate Glenodiniumfoliaceum is a flattened orange structure, more or less trapezoid in shape with an anterior hook-like projection. It is situated on the ventral side of the organism in the vicinity of the flagellar bases at the anterior end of the sulcus. In the electron microscope the eyespot is seen to contain two layers of osmiophilic granules 80-200 nm in diameter which usually show hexagonal close-packing. The eyespot is surrounded by a triple-membraned envelope and is not connected to any other organelle. Adjacent to the eyespot is a distinctive organelle termed the ‘lamellar body’. This consists of a stack of up to 50 flattened vesicles or disks, each 16 nm thick and about 750 nm wide, the whole being orientated in an antero-posterior direction. The lamellae are continuous, at the ends of the stack, with rough endoplasmic reticulum and are joined together by occasional bridges at their edges. The bases of the two flagella lie just ventral to the lamellar body and from them roots arise which pass by the eyespot and join the subthecal microtubular system.
The eyespot of Glenodinium is unique both in structure and the presence of the associated lamellar body. It differs from eyespots which have been described from other algal groups and also from the more complex ocellus found in certain dinoflagellates belonging to the order Warnowiaceae. The method by which the eyespot functions is discussed and it is suggested that unidirectional stimuli could be perceived by shading of the lamellar body.
Synapses on the axon hillocks and initial segments of pyramidal cell axons in the cerebral cortex
Authors: Jones E. G. , Powell T. P. S. 
Published: April 2021

ABSTRACT
The axon hillocks and initial segments of pyramidal cell axons can be clearly recognized in electron micrographs of the somatic sensory cortex. The initial segment is characterized by three features: bundles of neurotubules linked together by electron-dense bands, a layer of dense material attached to the inner surface of the plasmamembrane, and small membrane-bound dense bodies. All of these elements and the few ribosomes usually present disappear at the commencement of the myelin sheath. The initial segment of the axon often contains a cluster of cisternae similar to the spine apparatus, and this part of the axon sometimes gives off small branches. Axon terminals end on both the axon hillock and the initial segment, and there is an increase in number on the latter as the distance from the hillock increases. All of these terminals are relatively large, contain a high proportion of small flattened or pleomorphic synaptic vesicles and terminate in symmetrical synaptic contacts. These morphological features suggest that the synapses may be inhibitory in function.
Morphological variations in the dendritic spines of the neocortex
Authors: Jones E. G. , Powell T. P. S. 
Published: April 2021

ABSTRACT
The structural variations which occur in the dendritic spines of pyramidal neurons of the somatic sensory cortex of the cat are described, particular attention being paid to spines attached to different parts of the dendritic tree. Spines may be recognized particularly by the absence of neurotubules and the common presence of a spine apparatus, and they can be considered as pednnculated or sessile, depending upon the presence or absence of a narrow pedicle. Within these 2 categories spines may be rounded, cup-like or prismatic, can be large or small, and may show various degrees of inversion of the surface receiving a synaptic contact. While spines of every size and shape may be attached to dendrites of all diameters, there is a definite tendency for the largest spines to occur on the smallest dendrites and vice versa. Furthermore, the smallest dendrites possess the spines with the longest pedicles. Every dendritic spine receives 1 axon terminal containing spherical synaptic vesicles and ending in an asymmetrical synaptic contact. In addition, 10–20 % of the spines receive a second terminal, which in some cases may contain spherical vesicles and terminate asymmetrically but in others contains small, flattened or pleomorphic vesicles and ends in a symmetrical contact. The additional terminal may end on the pedicle of the spine or on the parent dendrite near the attachment of the pedicle. In the latter site, asymmetrical synapses are commonly associated with an additional spine apparatus.
A cytochemical study of lectin receptors on isolated chick neural retina neurons in vitro
Authors: Bee James A. 
Published: April 2021

ABSTRACT
The cell body, neurite and growth cone of isolated retinal neurons have been compared on the basis of their ability to bind a number of fluorescently labelled lectins, each possessing a unique carbohydrate specificity. The susceptibility of the respective binding patterns following pretreatment of these fixed cells with either neuraminidase or trypsin was also investigated. Neuronal cell bodies displayed the most intense binding of each lectin, with localization of limulin binding (specific for sialic acid) predominantly to the neurite hillock, the point on the cell body from which the neurite projects. Limulin binding was almost totally abolished by pretreatment with either neuraminidase or trypsin. In contrast to the cell body, limulin binding to the neurite or growth cone was not detected. These regions of the cell apparently possessed sialic acid, however, since pretreatment with neuraminidase reduced wheat germ agglutinin binding (to N-acetylglucosamine) and markedly enhanced Dolichos biflorus agglutinin binding (to JV-acetylgalactosamine) to both the neurite and growth cone. The initially low binding of Dolichos biflorus agglutinin to the neurite and growth cone was slightly enhanced by pretreatment with trypsin. Uniformly low levels of binding of either Ricinus communis agglutinin 60 (galactose, jV-acetylgalactosamine) or R. communis agglutinin 120 (galactose) was observed over the entire neuron. R. communis agglutinin 120 binding was not enhanced by pretreatment with neuraminidase. Receptors for either concanavalin A (mannose, glucose) or Ulex europaeus agglutinin I (fucose) were abundant over the entire nerve cell with the former exhibiting more marked trypsin sensitivity. From these data, it is apparent that the repertoire of lectin binding sites of the neurite and growth cone of these differentiating nerve cells differs markedly from that of the cell body, which itself demonstrates some degree of regionalization.
Pollination sub-systems distinguished by pollen tube arrest after incompatible interspecific crosses in Rhododendron (Ericaceae)
Authors: Williams Elizabeth G. , Knox R. Bruce , Rouse John L. 
Published: April 2021

ABSTRACT
The cytology of compatible and interspecific incompatible pollinations has been followed in selected species of the genus Rhododendron (Ericaceae). Pollinated pistils were fixed, cleared, stained in decolourized aniline blue, and observed by epifluorescence microscopy. Ten different abnormalities of arrested pollen tube tips have been detected, including burst, tapered, swollen, coiled, spiralling, spiky and variable diameter syndromes. A series of five errors of callose deposition in incompatible tubes has also been defined. Six different regions in the pistil for expression of pollen tube arrest have been found, including the stigmatic exudate, the mucilage of the upper and lower style canal, the ovary loculus, the micropyle. There may also be abnormal behaviour after entry into the embryo sac. Both the site of pollen tube arrest within the pistil, and the error syndrome of tip growth and callose deposition anomalies, are characteristic of each interspecific cross. These results are discussed in relation to the genetic control of reproduction.
Changes in wool follicles of sheep following administration of dexamethasone trimethylacetate
Authors: Chapman R. E. , Panaretto B. A. , Frith P. A. 
Published: April 2021

ABSTRACT
Intramuscular injection of 50 mg dexamethasone trimethylacetate produced variable effects on the fleeces of Merino sheep, ranging from an obvious discontinuity in the fleece, due to inhibition of growth of the majority of fibres, to no macroscopically observable effect. In the most affected animals, the mitotic activity and size of the follicle bulbs decreased during the first five days. Subsequently, fibre and inner root sheath cells withdrew from around the dermal papillae and were replaced by cells from the outer root sheaths. Autophagic vacuoles developed in these replacement cells. Regression of follicles proceeded until brush-ends formed on the fibres after 9–15 days. The amount of glycogen decreased inthe outer root sheath cells, which exhibited various responses at different levels in the follicles. The proportion of regressed follicles and to some extent the rate of regression were highest in the sheep with the most obvious discontinuity in the fleece. Regeneration of follicles was well advanced in all sheep 29 days after the injection.
Effect of the ionic environment on the incorporation of the intermediate-sized filament protein vimentin into residual cell structures upon treatment of ehrlich ascites tumour cells with triton x-100: II. Ultrastructural analysis
Authors: Nelson W. James , Traub Peter 
Published: April 2021

ABSTRACT
Ehrlich ascites tumour cells were extracted in buffers containing Triton X-100 and mono-, di- and polyvalent cations and then analysed by phase-contrast and electron microscopy. The results of this ultrastructural analysis confirm those of the biochemical analysis in the accompanying paper that the stability of intermediate-sized filaments is dependent on the ionic environment. Furthermore, the organization of filaments in long parallel arrays is dependent on the presence of divalent cations and can be inhibited, to some extent, by the presence of monovalent cations. The stability of other detergent-resistant structures, the boundary lamina, microfilaments, microtubules, centrioles, polyribosomes and the nuclear cortex, is also affected by the ionic environment but to a lesser extent.
Dissociation of cytological and functional differential in virgin mouse mammary gland during inhibition of DNA synthesis
Authors: Vonderhaar Barbara K. , Smith Gilbert H. 
Published: April 2021

ABSTRACT
Epithelial cells in mammary gland explants from mice assume a secretory appearance and synthesize the milk proteins, casein and α-lactalbumin, when cultured in the presence of insulin, hydrocortisone and prolactin. In cells from the glands of mature virgin animals such syntheses are known to require DNA synthesis. Addition of cytosine-β-D-arabinofuranoside to the explant cultures suppresses both hormonally induced DNA synthesis and enhanced production of milk protein. To determine the level at which this block in terminal differentiation occurs, epithelial cell pellets were prepared from virgin mouse mammary gland explants cultured with various combinations of insulin, hydrocortisone and prolactin, and subsequently examined by light and electron microscopy. We observed that the epithelial cells cultured in the presence of all three hormones developed fully, cytologically and ultrastructurally, even in the absence of DNA synthesis in vitro. Likewise, these cells were able to incorporate [3H]uridine into RNA efficiently and to incorporate amino acids into acid-precipitable polypeptides at levels equivalent to the untreated controls. However, immunoprecipitation of newly synthesized casein peptides showed that no new synthesis of casein occurred in cells prevented from synthesizing DNA. These data show uncoupling of cytological development and synthesis of milk protein in mammary explants from mature virgin mice inhibited from synthesizing DNA.
Temperature dependence of certain integrated membrane functions in macrophages
Authors: Shirazi Mahshid Faghihi , Aronson Nathan N. , Dean Roger T. 
Published: April 2021

ABSTRACT
We have studied the effect of temperature on uptake and degradation of molecules entering mouse peritoneal macrophages by fluid-phase, adsorptive and receptor-mediated p1nocytos1s, and on degradation of their intracellular proteins. Uptake of [3H]sucrose and uptake and degradation of formaldehyde-treated 125I-labelled human serum albumin and 125I -labelled mannose-bovine serum albumin continued, but were progressively slowed as the temperature decreased from 37 °C to 20 °C. The uptake and degradation were completely abolished at approximately 15 °C. Arrhenius plots for adsorptive and fluid uptake were unilinear, whereas that for receptor-mediated endocytosis showed an inflection point at approximately 20 °C. The results did not indicate any distinction between adsorptive and fluid p1nocytos1s. An ‘intracellular turnover time’ calculated for mannose-bovine serum albumin taken up by the specific route is 19 – 24 min and this time calculated for human serum albumin is, in contrast, 99 min. Studies of the kinetics of degradation of both endocytosed and endogenous proteins showed similarity in the temperature cut-off of degradation of endocytosed and endogenous long-half-life proteins (≃ 15 °C) and continuance of endogenous short-half-life degradation at much lower temperatures.
Effect of low molecular weight human serum factors and human somatomedin peptides on human lymphocyte cultures
Authors: Heulin M. H. , Artur M. , Straczek J. , Belleville F. , Nabet P. , Hermann A. , Lebeurre M. D. , Schimpff R. M. 
Published: April 2021

ABSTRACT
Using [3H]thymidine incorporation into DNA of human lymphocytes in culture, we have shown that human serum contains an ultrafiltrable factor(s) that sensitizes the activation of lymphocytes by phyto haemagglutinin. This (these) factor(s) can replace either human serum or foetal calf serum in the culture. In addition, it permits the expression, and therefore the assay, of human somatomedin A peptides. In somatomedin assays we have shown that the assay using lymphocytes is a much more sensitive test than the assay using sulphation of chick embryo cartilage.
Carbon dioxide induced disassembly of gap-junctional plaques
Authors: Lee William M. , Cran David G. , Lane Nancy J. 
Published: April 2021

ABSTRACT
When sheep ovarian follicle cells are maintained in an O2-rich environment their cells are metabolically coupled, as monitored by observing the exchange of [3H]choline ; choline metabolites were detected up to 4 mm from the explant under these control conditions. When the tissues were placed in a CO2,-rich environment the cells became uncoupled physiologically and choline metabolites were no longer exchanged. The cells in these two states, coupled and uncoupled, were examined by freeze-fracture. The initial controls were characteristic of ovarian follicular tissue exhibiting large macular plaques with regular outlines composed of PF intra-membranous particles (IMPs), which were arrayed in rows with IMP-free aisles. With uncoupling, the junctional plaques became irregular at the periphery, they became loosely packed and IMPs began to ‘stream’ out laterally across the membrane. Ultimately they were reduced to negligible IMP clusters or free IMPs. Analyses of the IMPs with an image analyser confirmed that in the uncoupled state the gap-junctional IMPs were dispersed over the membranes. On return to an O2-rich environment, the cells became recoupled as monitored by physiological criteria and in freeze-fracture replicas IMPs reclustered into macular, albeit smaller, plaques. These results support the contention that with uncoupling, gap-junctional particles are free to move and hence may become dispersed over the membrane face, with the possibility of being re-utilized to form junctions anew when conditions for coupling are re-established.
Migration of lymphocytes across specialized vascular endothelium : V. Production of a sulphated macromolecule by high endothelial cells in lymph nodes*
Authors: Andrews P. , Milsom D. W. , Ford W. L. 
Published: April 2021

ABSTRACT
High endothelial cells lining the post capillary venules in the paracortical areas of rat lymph nodes were found by autoradiography to incorporate [35S]sulphate, whether it was injected into the footpad to reach the draining popliteal lymph node or added to short-term cultures of cervical lymph node slices. The early localization of [35S]sulphate was confined to the Golgi apparatus, but before it disappeared from the cell radioactivity was associated with cytoplasmic vesicles. Sulphated material in macromolecular form was extracted from lymph nodes that had been labelled in vivo and was also found in the supernatant of lymph node cultures. The labelled material was not proteoglycan in nature. High endothelial cells apparently secrete a sulphated macromolecule but its relationship to the only known function of high-walled endothelium -the selective extraction of lymphocytes from the blood -remains to be clarified.