bluuebunny/crossref_metadata_2025_split huggingface dataset:
Feeding in ciliated protozoa: I. pharyngeal disks in Euplotes: A source of membrane for food vacuole formation?
Authors: Kloetzel John. A. 
Published: April 2021

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT35SO42− 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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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.
Ultrastructure of mitotic arrest induced by isoprenaline in rat parotid acinar cells
Authors: Radley J.M. 
Published: April 2021

ABSTRACT
The mitotic arrest of acinar cells in the rat parotid gland in response to isoprenaline has been investigated at the ultrastructural level. The arrested cells were characterized by the presence of both centriole pairs at the cell centre, around which chromosomes formed an approximately spherical array. Microtubules radiated out from both centriole pairs, indicating that they were part of a bipolar system. The microtubule population included both non-kinetochore and kinetochore microtubules. Metaphase arrest appeared to be due to failure of the poles to separate, or to remain separated in the case of cells already in metaphase at the time of drug administration. This could be explained by the drug interfering with the ability of interpolar microtubules from opposite poles to interact with one another.
The distribution of the chromosomes around the centrioles appears to depend on the presence of kinetochore microtubules, which are thought to act as tethers, either by themselves or in conjunction with non-kinetochore microtubules. It is suggested that tension is necessary between the kinetochores and poles to attain the arrest configuration. Chromosomes were observed in which both kinetochores had attached microtubules but whether or not they were linked to opposite poles remains to be investigated.
Two types of arrested cell were distinguished by their content of secretory granules. Cells already in mitosis at the time of isoprenaline administration were not depleted by drug action, and during the period of arrest numerous large secretory granules were intermingled with the chromosomes. Those cells which entered mitosis after the drug was given were initially blocked in the G2 phase, during which time they were depleted of secretory granules. On entering mitosis, these cells possessed only small secretory granules, which were newly synthesized. In the metaphase-arrested state the small secretory granules were clustered around the centriolar complexes, demonstrating the presence of a poleward force operating on them. It is possible that the same force acts on the secretory granules in the first type of arrested cell, but because of the relatively large size of the granules, the clustering around the poles is not pronounced. The nature of the forces acting on the chromosomes and on the secretory granules is discussed. The functioning of these forces during the arrest state has to be considered in any general model for mitosis.
Nucleolar development in the interphase of the cell cycle
Authors: Sacristán-Gárate A. , Navarrete M. H. , Torre C. De La 
Published: April 2021

ABSTRACT
Stereology of nucleoli at 3 different points of the cell cycle, in the middle of the G1 S and G2 of interphase, was accomplished in a naturally synchronous cell population rendered binucleate and thus ‘labelled’ and made identifiable by 1 h caffeine treatment in root meri-stems of Allium cepa L.
Consistent structural changes were found so that nucleolar parameters by themselves can locate a cell at any interphase period.
The growth of the nucleolus in the course of interphase takes place exclusively in its granular portion. The growth rate of this last component was found to be greater in the first half of interphase (5·4μm3h−1) than in the second (2·9 μm3 h”−1), as calculated for a nucleus with only one fused nucleolus. The changes in volume of the nucleolar components during interphase do not parallel the gene dosage.
Nucleolar surface at each point seems to be the factor which determines the growth rate in the preceding interval, since these rates are inverted for fused and unfused nucleoli.
The nucleolar volume occupied by lacunae is minimal in the S-period and shows an enormous increase by the middle of G2.
We think our data may be the structural basis on which a model for nucleolar functioning in proliferating cells could be built.
The antagonistic effects of antimitotic agents on contraction and re-extension in the ciliate Spirostomum ambiguum
Authors: Ettienne E. M. , Selitsky M. 
Published: April 2021

ABSTRACT
Contraction in Spirostomum is apparently directed by 2 antagonistic systems which respond to changes in free calcium concentration. The system responsible for imparting contractile tension consists of bundles of 4–5 nm microfilaments which can be calcium-activated. The second system consists of pellicular microtubules which may have the capacity to impart tensile force and react with each other through cross-bridging. Cells subjected to electrical stimulation to induce contraction in the presence of 0·1 mM 2,4-dinitrophenol and KCN failed to recover their original resting lengths. Similar treatment with colchicine produced the same effect, implying an interruption in the activity or structural integrity of the microtubular system. Treatment with 0·5 μg/ml cytochalasin B inhibited all contractile responses, presumably by blocking the activity of microfilaments.
Descriptive and quantitative study of ultrastructural changes in the apical meristem of mustard in transition to flowering: II. the cytoplasm, mitochondria and proplastids
Authors: Havelange A. , Bernier G. , Jacqmard A. 
Published: April 2021

ABSTRACT
Transition to flowering was induced in the shoot apical meristem of Sinapis alba (mustard), a long-day species, by subjecting vegetative plants to a single 22-h long day. The ultrastructural changes occurring in the meristematic cells during the complete morphogenetic switch were investigated by quantitative methods.
The earliest detectable changes are seen 18 h after the start of the inductive long day. One of these changes is the replacement of the large vacuoles of the cells of vegetative meristems by an increased number of smaller vacuoles in the cells of meristems of plants induced to flower (evoked meristems). The other earliest change is an increase in size of the chondriome. Remarkably enough both changes have in common that they lead to an increase in membrane area and are thus concerned with increased membrane synthesis. In this respect this very early effect of the leaf-generated floral stimulus is very similar to that produced by various animal and plant hormones in their respective target tissues.
The large rise in chondriome size is paralleled by an increase in succinic dehydrogenase activity. Both changes certainly reflect a rise in cellular respiratory activity which produces the necessary energy supply for the morphogenetic switch.
As the size of the plastidome does not change during the transition to flowering, the plasti dome: chondriome ratio decreases markedly.
The size of the cytoplasmic matrix is greater in cells of evoked meristems than in cells of vegetative meristems. A first size maximum is reached at 26 h after the start of the long day and a second at 54 h. These 2 maxima occur just prior to 2 mitotic waves culminating respectively at 26–30 and 62 h. The increases in amount of endoplasmic reticulum (ER) and dictyosome number that are found in evoked meristems collected just prior to or at the time of the second mitotic wave are also probably related to the mitotic activation of the tissue.
As the size of the vacuolar apparatus considered as a whole does not change at all and the size of the cytoplasmic matrix increases, the vacuoles:cytoplasm ratio decreases in evoked meristems collected following 26 h after the start of the long day. Also, there is an unexpected decrease in the nucleus:cytoplasm ratio in the cells of evoked meristems after 46 h.
Protoplast regeneration from normal and bromodeoxyuridine-resistant sycamore callus
Authors: Bright S. W. J. , Northcote D. H. 
Published: April 2021

ABSTRACT
Protoplasts have been prepared from normal and mutant lines of sycamore callus, maize root and tobacco leaf. Fusion was rare in sodium nitrate solutions. A mutant tissue culture was selected for by its resistance to 10 μg/ml bromodeoxyuridine. The mutant is sensitive to the Hypoxanthine-Aminopterin-Thymidine (HAT) selective medium but has normal thymidine transport and thymidine kinase activity.
Sodium exchange in the cytoplasm and nucleus of amphibian oocytes
Authors: Century T. J. , Horowitz S. B. 
Published: April 2021

ABSTRACT
Oocytes of Rana pipiens were incubated in 22Na-Ringer’s solution and 22Na - 23Na exchange in the nucleus and cytoplasm followed by low-temperature microdissection. Cytoplasmic sodium consists of 2 kinetic fractions: the larger (88 %) slowly exchanging (t1/ 2 ∼ 2 days), and the smaller (12%) rapidly exchanging (t1/2 ∼53 min). Nuclear sodium consists of a single fraction whose concentration is similar and whose rate constant is identical with that of the rapidly exchanging cytoplasmic fraction. Our findings are consistent with a model of compartmentalization in which rapidly exchanging sodium is nearly uniformly distributed in the water of the nucleus and cytoplasm and its exchange limited by movement through the cell surface. On the other hand, slowly exchanging sodium is restricted to the cytoplasm, sorbed to or sequestered in some as yet unidentified cytoplasmic constituent.
The reaction of mitochondria in the coleoptiles of rice (Oryza sativa L.) with diaminobenzidine
Authors: Öpik Helgi 
Published: April 2021

ABSTRACT
Diaminobenzidine, DAB, was applied to segments of aerobically and anaerobically grown coleoptiles of rice, Oryza sativa L., with the object of studying the location of cytochrome oxidase at the electron-microscope level. A specific staining of mitochondrial cristae and inner membrane was obtained, with no reaction in other organelles; with extended periods of incubation, the reaction product filled the mitochondria completely. In anaerobically grown coleoptiles, the reaction was much slower and the difference was particularly marked in vascular bundle companion cells and parenchyma, which gave the strongest reaction in aerobic tissue, but in the anaerobic stained even less than the cortical parenchyma. The reaction was inhibited by boiling and slowed very much by lowering of the incubation temperature from 27 to 4 °C. This indicated the involvement of an enzymic reaction and cyanide inhibition indicated that a haem enzyme was involved. The catalase inhibitor aminotriazole did not inhibit DAB oxidation. Nevertheless the specificity of the reaction for cytochrome oxidase must be questioned, because preheating of the tissue to 60 °C before incubation, which would be expected to destroy cytochrome oxidase activity, failed to decrease the oxidation, at least in aerobically grown coleoptiles. It is concluded that DAB is oxidized in the rice coleoptile tissue by a cytochrome system, and the development of this system is inhibited by anaerobiosis, but the oxidation cannot be claimed to represent cytochrome oxidase activity exclusively. Perhaps other autoxidizable, more heat-stable cytochromes participate in the reaction.
Role of zinc in cell division of Euglena gracilis
Authors: Falchuk K. H. , Fawcett D. W. , Vallee B. L. 
Published: April 2021

ABSTRACT
Euglena gracilis is a suitable model system to investigate the role of zinc in the process of cell division. In zinc-deficient organisms there is a characteristic arrest of cellular proliferation, the DNA content of the cells doubles, whereas RNA and protein contents decrease. The present investigations include the growth characteristics, changes in cellular morphology at various stages in the growth cycle, quantitation of zinc uptake and incorporation of tritium-labelled precursors into RNA by organisms grown in zinc sufficient (Zn+), (Zn,+ content 1 ×10−5 M) or zinc-deficient (Zn−), (Zn+ content 1 × 10−7 M) medium. Cell division ceases on depletion of zinc from the medium. There are 20-fold less cells in (Zn−) medium than in control cultures. The size of (Zn+) cells decreases during log phase due to a reduction in the paramylon content of the cytoplasm. The size of (Zn−) cells, however, increases, due to an accumulation of paramylon. This results in a 13-fold increment in dry weight compared to control. Other cytoplasmic organelles, including Golgi bodies, mitochondria, etc. are normal. Nuclear morphology also is unchanged. There is a reduction in the rate of incorporation of labelled precursors into RNA by (Zn−) cells.
The DNA content of (Zn−) E. gracilis, the absence of morphologic evidence to indicate that cell division has followed the doubling of the DNA, and the arrest in proliferation suggests that a critical zinc-dependent step in the cell cycle, localized to G2, is blocked in zinc deficiency.