bluuebunny/crossref_metadata_2025_split huggingface dataset:
Autoradiographic evidence for the effects of light on rna and dna synthesis during chloroplast replication in spores of Polytrichum
Authors: Kass L. B. , Paolillo D. J. 
Published: April 2021

ABSTRACT
Light stimulates the incorporation of [3H]uridine and [3H]thymidine in addition to plastid replication in germinating Polytrichum spores. Significant amounts of [3H]uridine and [3H]-thymidine are incorporated in darkness but not to the same level as in light. Plastids continue to produce nucleic acids when their capacity to multiply is suspended due to the absence of light. However, a higher amount of DNA synthesis in the light is correlated with the result that chloroplast replication begins again in the light after prolonged dark incubation. An imperfect association of plastid replication and nucleic acid synthesis is suggested by the lack of stimulation of DNA synthesis by light during plastid replication in the first 8 h of incubation. A temporal separation can be demonstrated for chloroplast and nuclear DNA synthesis at the beginning of germination in Polytrichum spores, with DNA synthesis in the chloroplasts preceding that in the nucleus. The mitotic S phase is longer than 16 h for at least half of the nuclei.
Genetic analysis of developmental mechanisms in hydra. ii. isolation and characterization of an interstitial cell-deficient strain
Authors: Sugiyama Tsutomu , Fujisawa Toshitaka 
Published: April 2021

ABSTRACT
A mutant strain (nf-I) of Hydramagmpapillata isolated that contained no interstitial cells, nerve cells or nematocytes. This strain appeared spontaneously in a sexually inbred clone of hydra, and it was recognized by its inability to eat. When force-fed, however, it grew, multiplied by budding and regenerated. In this and in many other respects, nf-I was very similar to the interstitial cell-deficient strain produced by Campbell (1976) by means of colchicine.
A chimera strain was produced by the reintroduction of interstitial cells from another strain into nf-I. The properties of nf-I, the chimera and other related strains were examined, and the possible roles that the interstitial cells and the nerve cells play in growth and morphogenesis of hydra are discussed.
Radioautographic and chemical studies of incorporation into sycamore vascular tissue walls
Authors: Wooding F. B. P. 
Published: April 2021

ABSTRACT
Chemical and radioautographic studies on sycamore seedling stems have shown an involvement of the Golgi body in cell-wall polysaccharide synthesis from tritiated glucose. Tritiated phenylalanine is shown to be incorporated only into lignin after short incubation times. The patterns of labelling are compared and discussed for the two precursors.
The ultrastructure and ontogeny of pollen in Helleborus Foetidus l. II. pollen grain development through the callose special wall stage
Authors: Echlin P. , Godwin H. 
Published: April 2021

ABSTRACT
During the early stages of microsporocyte ontogeny in Helleborus foetidus L. there is protoplasmic continuity between the cells of the tapetum and between the individual sporogenous cells, but not between the two tissues. The plasma canals and plasmodesmata are progressively sealed off by the deposition of thick callose walls, so that by the first meiotic division, each pollen mother cell is isolated from its neighbours and from the surrounding tapetum. Callose is formed by dictyosomes in the individual pollen mother cells. The four meiocytes are separated by the deposition and coalescence of masses of çallose forming in the cell plate area. The exine pattern is initiated at the surface of the young microspores while they are still invested with a thick wall of callose. Periclinally arranged endoplasmic reticulum lying just below the microspore cell membrane corresponds with the position of the furrows. The cell membrane in the interfurrow region thickens and becomes highly convoluted. A fibrous layer appears between the outer part of the convolutions and the callose, and locally it becomes less electron-dense at places that become filled with material of moderate electron density corresponding to the probacula; these in turn will become the bacula of the mature exine. In spite of an extensive examination of material prepared by a variety of techniques, no organelle or cytoplasmic component may be consistently associated with the positioning of the first signs of exine patterning.
The topographical relationship between the plane of the central pair of flagellar fibrils and the transverse axis of the head in guinea-pig spermatozoa
Authors: Fawcett D. W. 
Published: April 2021

ABSTRACT
Earlier studies on the arrangement of sperm-tail components have suggested that a line through the central pair of fibrils is always perpendicular to the broad face of the flattened sperm head. The principal plane of bending of proximal regions of the tail was therefore assumed to coincide with the transverse axis of the head.
The heads of guinea-pig epididymal sperm are flexed 45-50° from the long axis of the tails and are stacked one upon the other in coherent packets. The parallel arrangement of the heads ensures that all of the associated tails will be similarly oriented, and certain planes of section transect heads and tails of the same sperm packet. Taking advantage of this circumstance, it was possible to demonstrate that in quiescent sperm of this species the plane of the central pair is not at 90o to the transverse axis of the head, but is inclined 20-30° off the perpendicular and always in the same direction.
Attention is drawn to examples from the literature on cilia and flagella, where there appears to be a similar inclination of the axis of the central pair with respect to external landmarks.
Freeze-etched surfaces of membranes and organelles in the cells of pea root tips
Authors: Northcote D. H. , Lewis D. R. 
Published: April 2021

ABSTRACT
The structure of the inner and outer surfaces of the plasmalemma, the tonoplast and the membranes of the nucleus and endoplasmic reticulum have been investigated. The structure of the plasmalemma probably varies with the metabolic state of the cell, in particular with the synthesis and transport of material for cell-wall formation. The organization of the plasmalemma during the deposition of material in the wall by reverse pinocytosis is shown, and evidence is presented for the possible synthesis of the microfibrillar structure of the wall by synthetic units arranged as particles on and near the plasmalemma surface. A clear indication of substructure along the length of microtubules has been shown, and since views of large surface areas are possible the distribution of the microtubules at the cytoplasmic surface inside the plasmalemma has been revealed; they bound the cell by running around the circumference in one direction only. A definite organization of nuclear pores has been observed and the structure and shape of the pores is described. By the freeze-etch technique it is possible to investigate crystal-containing bodies, amyloplasts with starch grains and bundles of fibres in addition to mitochondria and Golgi bodies. The method also distinguishes certain spherical organelles by their characteristic surface appearance.
Cytological and cytochemical studies on cell death and digestion in the foetal rat foot: The role of macrophages and hydrolytic enzymes
Authors: Ballard Kathleen J. , Holt S. J. 
Published: April 2021

ABSTRACTPhysiological cell death and degeneration in the interdigital mesenchyme of the hind foot of the rat foetus have been studied using classical staining methods and staining methods for enzyme localization. Individual mesenchymal cells die and shrink as the result of some unknown mechanism. Their acid phosphatase and esterase activities are not significantly different from those of viable loose mesenchymal cells. The dead cells are engulfed by viable neighbouring cells which resemble other loose mesenchymal cells in their morphology and in their acid phosphatase and esterase activities. These phagocytes then differentiate and become typical macrophages. Expressions of this process are the altered appearance of their nuclei and the increase in cytoplasm and in acid phosphatase and esterase activities. Many dead cells may be engulfed by a single macrophage and are then digested by its acid hydrolases. No evidence was found suggesting that cell death might be initiated by the intracellular release of lysosomal enzymes.
Mitosis and the cell cycle in the metamorphic moult of the milkweed bug, Oncopeltus Fasciatus. A radioautographic study
Authors: Lawrence P. A. 
Published: April 2021

ABSTRACT
A simple method of whole-mount radioautography is devised to investigate aspects of the cell cycle during metamorphosis in the epidermis of the milkweed bug, Oncopeltus. Tritiated thymidine is used to indicate DNA synthesis. As the label only lasts in the insect for about 2 h, a wave of labelled cells passes through the different phases of the cell cycle. The S period is found to overlap with an exceptionally long prophase and there is thus no G2 period. The length of prophase (408 ±10 min) is estimated from a plot of the fraction of labelled prophases against time after injection of label. By an equivalent method the length of the 5 period is found to be 289 ± 12 min. No labelled cells divide again until about 24 h after the previous mitosis, when some cells embark on a second mitosis. The minimum interphase (G1) period is approximately 16 h. In the area studied, the cell number more than doubles during the proliferative mitoses; and it is thus possible, but not certain, that every cell divides at least once.
Fifth-stage larvae injected during the differentiative divisions (which are involved in the development of dense hairs) show that each of the three kinds of differentiative divisions has its own peculiar timing. The timing of the very first division, that of the epidermal cell which will become the hair mother cell, suggests that the cell is already different from its progenitors prior to prophase.
Cytochemical adenosinetriphosphatase in plant root meristem
Authors: Shifrin Norma , Levine L. 
Published: April 2021

ABSTRACT
Root tip meristems were stained to demonstrate ATPase activity by two different methods, with general agreement in localization but not specificity, and with emphasis on mitotic cells.
In interphase, ATPase was localized in nucleoli and nuclear membranes, with lesser activity in the nuclear substance. In prophase, chromosomes were outlined by ATPase stain which gradually declined in intensity at prometaphase, becoming least evident in metaphase. Staining activity increased again in anaphase, and remained high in telophase. In prometaphase, anaphase and late anaphase-early telophase, the ATPase was concentrated in a fibril which appeared to coil around the chromosomes. The ATPase fibril was thinnest at metaphase and shorter and thicker at telophase. In addition, granules farmed in association with the coils of the fibril in late anaphase and early telophase. Later on, these granules may have fused and contributed to nucleolar reformation.
The ATPase never localized in the chromosomal fibre nor in any other region of the spindle. RNA generally localized like ATPase, but ATPase loci were unchanged after ribonuclease (RNase) treatment.
Because of certain similarities between ATPase and argentaffin localization, some relationship between the nucleolus and ATPase is suggested. A mechanochemical transducing role is postulated for the ATPase, because cytochemical properties were like those of ATPase in the A-band of myofibrillae, and because other changes in it could be correlated with chromosome movement.
Surface features of striated muscle: II. guinea-pig skeletal muscle
Authors: Rayns D. G. , Simpson F. O. , Bertaud W. S. 
Published: April 2021

ABSTRACT
A study of the structure of the terminal part of the T-tubule system and the distribution of subsarcolemmal caveolae was undertaken in guinea-pig psoas muscle. The results were correlated with the array of cell surface features as revealed by frozen-etched, shadowed replicas of the cell membrane.
Freeze-etching revealed numerous small rounded objects overlying the Z- and I-bands and the A-I junction regions of the sarcomeres. These objects appeared as pits or excrescences, depending on whether the cell membrane was viewed from outside or inside the cell, and were interpreted as apertures in the membrane.
Conventional thin sections demonstrated the presence of numerous subsarcolemmal caveolae with a similar distribution to the rounded features seen in the replicas. Such sections also showed that the T-tubules, lying at the A-I junctions, seem to change direction when approaching the cell surface and may occasionally appear to branch in the subsarcolemmal region. The T-tubules often terminated in caveolae. Caveolae were sometimes seen in direct communication with the extracellular space. No simple direct communications of T-tubules with the cell surface were observed.
After treatment of the muscle with lanthanum during fixation, thin sections revealed apparently continuous dense deposits from the cell surface, through the caveolae to the T-tubule proper. It thus appears that each T-tubule communicates indirectly with the extracellular space via one or more subsarcolemmal caveolae.
Displacement of valine from intact sea-urchin eggs by exogenous amino acids
Authors: Piatigorsky J. , Tyler A. 
Published: April 2021

ABSTRACT
Unfertilized and fertilized eggs of the sea urchin Lytechinus pictus were preloaded with [14C]valine and exposed to individual solutions of each of the twenty ‘coded’ [14C]amino acids in artificial sea water. After 1 h incubation the amount of radioactivity in the medium was determined. The radioactivity was effectively displaced by most of the other neutral [14C]amino acids that are known to compete with valine for uptake. A chromatographic test with fertilized eggs showed the displaced radioactivity to be [14C]valine and not some metabolic product. Addition of acidic, basic or some neutral amino acids that are known to be poor inhibitors of valine uptake did not cause significant quantities of label to appear in the medium. For the unfertilized eggs, the concentration of acid-soluble label remained many hundreds of times greater in the egg fluid than in the sea water.
Tests indicated that efflux of [14C]valine and subsequent competition for re-entry is a primary factor responsible for the displacement phenomenon. That this may not be the sole factor is suggested by the fact that some amino acids that are known to be powerful inhibitors of valine uptake were found to be only weak displacers of [14C]valine. Neither [14C]arginine nor [14C]glutamic acid were displaced in significant amounts from preloaded unfertilized or fertilized eggs by any of the tested [14C]amino acids.
Attempts were made to utilize the displacement of [14C]valine to elevate the incorporation of [14C]valine and of other labelled amino acids into protein by intact eggs. Unfertilized and fertilized eggs were pretreated with related [14C]amino acids and then exposed to [14C]valine or a mixture of [14C]amino acids. The results varied in the different tests, ranging from no significant increase to 2-fold.
Translational movements of macrophages through media of different viscosities
Authors: Folger R. , Weiss L. , Glaves D. , Subjeck J. R. , Harlos J. P. 
Published: April 2021

ABSTRACT
The extent of the migration of guinea-pig peritoneal macrophages from capillary tubes over the surfaces of plastic Petri dishes, was quantitated by planimetry. It was observed that the amount of migration decreased as the viscosity of the medium was increased by the addition of agarose.
An essential component of translational movement is the formation of adhesions between cells and their substrata. It is suggested on the basis of the present migration and adhesion experiments, that the increased viscosity reduces migration by retarding the formation of adhesions between the cells and their substrata. The experiments do not support the suggestion that agarose adsorbed to the dish surface affects the adhesion-dependent arm of migration or that viscous ‘drag’ on whole cells (over the viscosity range of 0·71 to 3·9 × 10−3; N s m-2) reduces their movements.
Cell interactions in the developing somite; in vivo comparisons between Amputated (am|am) and normal mouse embryos
Authors: Flint O. P. , Ede D. A. 
Published: April 2021

ABSTRACT
Light and electron microscopy coupled to a quantitative analysis form a powerful technique for the analysis of cell behaviour in mutant and normal tissues. Using this approach the morphology of the cells and their contacts are examined in the somites of a recessive mouse mutant, amputated, and of its normal littermates. The results of the analysis show that cell density is the same in both mutant and normal sclerotome but that mutant cells tend to form small clumps whereas normal cells disperse individually. There is a correspondingly greater area of cell contact per cell in the mutant. Filopodia are equally numerous in the mutant and normal but where in the normal they stretch across wide intercellular spaces to make contact at their tips with other cells, in the mutant they form a tangled web sticking back on to the surface of the cell of origin and adjacent cells. The appearance of mutant and normal sclerotome is compared with presomitic cells and with the cells of other mutants whose abnormal development has been shown to depend on cell contact morphology and behaviour.
Electrical control of flagellar activity in impaled bull spermatozoa
Authors: O’Day Peter M. , Rikmenspoel Robert 
Published: April 2021

ABSTRACT
The control of bull spermatozoon flagellar activity has been investigated using direct current injection into the cells through an impaling glass microelectrode. Negative current injection results in a decrease in the flagellar frequency. Flagellar frequencies can be decreased to zero with high negative currents. This current injection response is dependent on the magnesium concentration available to the spermatozoon interior. The current injection response is nearly independent of ATP concentrations. Resistance measurements indicate that the current injection pathway has a resistance of about 200 ± 300 kΩ, and that the current flowing through the cell membrane is not exceedingly large. Measurements of the induced potentials indicate transmembrane potentials during current injection of about —35 ± 30 mV per μA of injected current. The results are compatible with an active transport process in bull spermatozoa that controls the flagellar activity in response to current injection by decreasing the internal Mg2+ concentrations during the injection of current.
Plasma membrane vesiculation in 3T3 and SV3T3 cells: II. factors affecting the process of vesiculation
Authors: Scott Robert E. , Maercklein Peter B. 
Published: April 2021

ABSTRACT
Plasma membrane vesicles are shed from monolayer cell cultures during incubation in low concentrations of formaldehyde and other sulphydryl blocking reagents. In both 3T3 and SV3T3 cells disulphide reducing agents, including dithiothreitol and mercaptoethanol, potentiate formaldehyde-induced vesiculation. Plasma membrane vesiculation is shown to be a temperature-dependent phenomenon which occurs optimally between 22 and 37 °C and at pH 7·0 to 7·5. Membrane shedding is an energy-dependent phenomenon, requiring monovalent and divalent cations and slightly hypertonic medium. Plasma membrane vesiculation is not affected by pretreatment of cells with inhibitors of protein synthesis, i.e. cycloheximide, nor by agents which disrupt the cytoskeleton.
Altered patterns of ribonucleic acid synthesis during the cell cycle: a mechanism compensating for variation in gene concentration
Authors: Fraser R. S. S. , Nurse Paul 
Published: April 2021

ABSTRACT
In the fission yeast Schizosaccharomyces pombe, a series of diploid mutants divides at smaller cell sizes than wild type. In these smaller strains, the mean gene concentration (defined by previous authors as the DNA to protein ratio) is higher than in wild type. Such an increase in gene concentration should also increase the concentration of those components such as messenger and ribosomal RNA, whose rate of synthesis is determined by gene dosage. We show that the mean concentrations of these 2 RNA species in the small cells are not increased, but are the same as in wild type. The small mutant cells are thus able to compensate for changes in gene concentration. This compensation is shown to operate through differences in the patterns of synthesis of RNA during the cell cycle. In all the strains of the diploid series, the rates of synthesis of messenger and ribosomal RNA double as steps once in each cell cycle. The timings of the steps in the cell cycle appear to be cell-size related, since the smaller the cell at division, the later are the steps in the cell cycle. In contrast, there is comparatively little variation in the timing of DNA replication in the cycles of cells of different sizes. We propose that after DNA replication, there is a delay before doubling in the rate of transcription. Such a cell mass-related delay is all that is required to compensate for increased gene concentration, and results in the same mean functional DNA concentration in all strains. This mechanism will maintain the same mean messenger and ribosomal RNA concentrations in cells dividing at different sizes. Ways in which the cell size-related control over transcription may operate are discussed.
Pollen-pistil incompatibility in Petunia hybrida: changes in the pistil following compatible and incompatible intraspecific crosses
Authors: Herrero M. , Dickinson H. G. 
Published: April 2021

ABSTRACT
The structural events in the stigma and transmitting tissue of Petunia hybrida pistils that accompany compatible and incompatible intraspecific pollinations have been investigated in detail, together with the changes in reserve levels that also take place at this time. Many of these phenomena may be explained in terms of 3 phases of secretion by the cells in the upper regions of the transmitting tissue. The first, independent of pollination, results in the deposition of an intercellular matrix, rich in protein and carbohydrate. The second, triggered by pollination, although independent of the compatibility of the pollen grain, involves synthesis of molecules believed to be specific to the S(incompatibility)-gene system. The third phase of secretion occurs only following a compatible mating, and involves the transfer of stylar reserves to support the growth of the pollen tubes. These observations are discussed in terms of current models of the incompatibility mechanism operating in Petunia.