bluuebunny/crossref_metadata_2025_split huggingface dataset:
The relationship between chromosome volume and dna content in unsquashed metaphase cells of barley, Hordeum vulgare cv. Tuleen 346
Authors: Bennett M. D. , Smith J. B. , Ward J. P. , Finch R. A. 
Published: April 2021

ABSTRACT
The present work used haploid and diploid cells of barley, Hordeum vulgare L. cv. Tuleen 346 (2n 2x =14), which has three reciprocal translocations. All seven chromosomes of the haploid set are distinguishable using morphological criteria in Feulgen-stained root-tip squashes seen in the light microscope, as are five of the bivalents at diakinesis. The relative DNA content per bivalent was estimated in pollen mother cells at diakinesis. The results showed that all seven chromosomes or bivalents of Tuleen 346 can be identified using relative DNA content as sole criterion. The absolute and relative volumes of the seven chromosomes were estimated from electron micrographs of serial sections of unsquashed root-tip cells of a haploid. The results show that, using relative chromosome volume as sole criterion, it is highly probable that all seven chromosomes in single unsquashed cells of Tuleen 346 can be correctly identified. Consequently, tests for various non-random spatial arrangements of chromosomes in unsquashed cells of Tuleen 346 using this character to identify the chromosomes should be feasible. There was a very highly significant positive relationship (r&gt;0·99) between relative chromosome volume and mean relative DNA content per chromosome for each cell examined at metaphase of mitosis or meiosis. Thus, some mechanism ensures that the degree of condensation of all seven chromosomes within a cell is usually very similar in Tuleen 346, lespite its grossly abnormal karyotype.
Cell wall texture along the growth gradient of the mung bean hypocotyl: Ordered assembly and dissipative processes
Authors: Roland Jean-Claude , Reis Daniele , Mosiniak Michele , Vian Brigitte 
Published: April 2021

ABSTRACT
A step-by-step analysis of wall characteristics was performed along a defined growth gradient in order to follow the dynamics of changes in wall organization according to the state of elongation of the cell. Specimens were taken from the elongating zone of 3-day-old mung bean (Vigna radiata L. Wilczek) hypocotyls grown in constant culture ∞nditions. A technical procedure was developed in order to perform a complete series of observations along the growth gradient of individual hypocotyls and at the same time to locate the levels in relation with the growth state. Weight and thickness measurements were performed in parallel with observations of changes in wall texture using ultrastructural cytochemistry (periodic acidμhiocarbohydrazide/silver proteinate test for polysaccharides associated with dimethylsulphoxide and methylamine extractions). Ultrastructural observations were made on cortical cells, mainly on epidermal cells.
For a cell that runs through the complete growth process the preliminary phase is a massive elaboration of wall subunits. The wall thus built is highly ordered (twisted plywood). Both thickness and order are maximal when the cell reaches the exponential phase of extension. An unstable balance exists between ordered assembly (with new layer deposition) at the inner wall, and dispersion of subunits (resulting from extension) at the outer wall. Growth takes place at the expense of thickness and the pre-established order. The balance is rapidly shifted and the dispersion of the subunits progressively predominates. Wall construction being no longer continued, elongation slows down and stops.
The wall acts as a dissipative structure changing from order to a subsequent irreversible disorder. In terms of growth capacity, the more ordered the wall is, the more extendible is the cell. The cessation of growth occurs when order has been completely lost. The results indicate that apparently conflicting concepts proposed in the literature, for the organization of the wall during cell elongation, are not mutually exclusive in the tissues studied.
Subpellicular microtubules of Euplotes eurystomus: their geometry relative to cell form, surface contours and ciliary organelles
Authors: Grim J. Norman 
Published: April 2021

ABSTRACT
There is a layer of microtubules (MT) beneath the innermost pellicular membrane of the ciliated protozoan Euplotes eurystomus. These MT have been revealed for scanning electron microscopic study by chemical dissection techniques. In much of the body of this ciliate, these MT are oriented parallel to its long axis. Those directed towards cirri, which are complex ciliary structures of the ventral surface, either abut or bend around the cirral base. MT adjacent to or closely associated with the ciliary feeding structures (membranelies of the adoral zone of membranelies or AZM) are oriented parallel to the long axis of the AZM. Some of the MT within the oral cavity have quite complex paths. The various orientations of these subpellicular MT are discussed and evaluated for hypothetical functions of cyto-skeletal support, cell shaping and organelle movement. Each of these roles is considered to be theoretically possible.
Ultrastructural analysis of the x, X2X3O sex chromosome system during the spermatogenesis of Tegenaria domestica (arachnida)
Authors: Benavente Ricardo , Wettstein Rodolfo , Papa Mercedes 
Published: April 2021

ABSTRACT
An ultrastructural study was performed on the sex chromosomes (&lt;J XjXtXaO) during the spermatogenesis of Tegenaria domestica (Arachnids, Agelenidae). This study was carried out using random and serially cut sections. During pachytene and diplotene the three × chromosomes are longitudinally paired. Each of these consists of a central core of condensed chromatin, surrounded by a field of dense chromatin projections through which the chromosomes are in contact with one another. These projections may be responsible for the recognition and pairing of the sex chromosomes and in some way participate in their non-disjunction during anaphase I. A study of the structure and behaviour of the sex chromosomes during spermatogenesis is also presented. The available information on non-synaptonemal complex-mediated chromosome pairing and a systematization of sex chromosome structure in spiders are discussed.
Membrane lipid metabolism in Chlamydomonas reinhardtii 137+ and Y-l:: I. Biochemical localization and characterization of acyltransferase activities
Authors: Jelsema Carole L. , Michaels Allan S. , Janerox David R. , Barrnet Russell J. 
Published: April 2021

ABSTRACT
The acyltransferases involved in the synthesis of the chloroplast membrane glycerolipids were analysed biochemically in dark-grown and greening Chlamydomonas reinhardtii y-1 as well as in the synchronous wild-type algae (strain 137+) and wild-type membranes. Using oleoyl-CoA as a substrate, three acyltransferase enzyme activities were detected. Glycerol-3-phosphate (glycerol-3-P) acyltransferase exhibited a pH optimum of 8·0 and was inhibited by addition of N-ethylmaleimide (MalNEt). Lysophosphatidate (PtdLys) acyltransferase exhibited a pH optimum of 7·0 and was not affected by the addition of MalNEt. From preliminary analyses, the activity at pH 5 ·5 appeared to be associated with dihydroxyacetone phosphate acyltransferase activity.
Both glycerol-3-P and PtdLys acyltransferases were analysed further and found to be present in dark-grown and light-induced y-1 cells as well as in synchronous 137+ cells and their photo-synthetic membranes. Both enzyme activities were enriched at least 10-fold in the photosynthetic membranes of 137+ chloroplasts relative to the activities present in the whole cells. This enrichment is indicative of their intrinsic localization in the thylakoids, suggesting that the photosynthetic membranes exhibit a greater degree of autonomy with respect to the synthesis of their membrane lipids than previously reported.
A role for glycerol-3-P and PtdLys acyltransferases in the synthesis of the chloroplast membrane lipids is suggested further by the increases in both enzyme activities coincident with and preceding thylakoid biogenesis following light induction of dark-grown y-1 cells. Increased acyltransferase activity preceded the increase in the chlorophyll content of greening y-t cells, which is a generally accepted marker for thylakoid synthesis. The increase in the PtdLys acyltransferase activity upon light-induclion of the y-1 cells was both more immediate and more dramatic than the increase in glycerol-3-P acyltransferase activity. PtdLys acyltransferase activity was negligible in dark-grown cells and the dramatic increase upon light induction may be important in the subsequent initiation of chloroplast membrane lipid synthesis. On the basis of the localization of acyltransferase enzyme activities to the photosynthetic membranes of 137 + cells and the increase in acyl transferase activity both preceding and occurring in concert with thylakoid synthesis, we propose a direct role for the photosynthetic membranes in the synthesis of their membrane lipid components.
Chinese hamster cells can be reversibly blocked before mitosis with the protein synthesis inhibitor, emetine
Authors: Westwood J. Timothy , Wagenaar Emile B. 
Published: April 2021

ABSTRACT
The inhibition of protein synthesis in eukaryotic cells will prevent them from entering mitosis. Emetine inhibits peptide elongation. When it was added to asynchronous populations of Chinese hamster ovary (CHO) cells, the mitotic index decreased sharply 30 to 40 min later. It was found that the inhibitory effect of emetine could be reversed when it was removed and the reversibility was dependent on both the initial concentration of emetine and the pH of the medium. Cell populations that were blocked by emetine for up to 2 h showed a four-to fivefold increase in mitotic index approximately 1 h after the emetine was removed. These results indicate that there is a point or period in G2 phase at which critical ‘mitotic proteins’ are being synthesized, and if their synthesis is interrupted cells will fail to enter mitosis.
Ultrastructural studies relating to the surface morphology of cultured cells
Authors: Pugh-Humphreys R. G. P. , Sinclair W. 
Published: April 2021

ABSTRACT
Scanning electron microscopy and a surface-replica technique for transmission electron microscopy have been used to study the ultrastructural features of cultured-cell surfaces The presence of microvilh measuring 0·1–0·2 μm in diameter by up to 5 μm in length has been noted as a regular feature of Landschutz ascites, ‘fibroblastic’ HeLa, and canine kidney, cells. The surfaces of chick mesenchyme cells were notably almost devoid of microvilh. The presence of microvilh at the cell surface is discussed briefly.
The proliferation of myofibrils during muscle fibre growth
Authors: Goldspink G. 
Published: April 2021

ABSTRACT
Myofibrils in muscle fibres of different sizes and different ages were examined and measured using phase-contrast and electron microscopy. During the post-natal growth of the mouse biceps brachii muscle the number of myofibnls in some fibres increases from about 75 to 1200 The range of myofibnl size was from 0·4–12 μm. The distribution of myofibnl sizes in muscles of all ages studied was bimodal
A high incidence of longitudinal splitting of myofibrils was observed with the electron micro scope in differentiating muscle fibres and in some medium and large muscle fibres. Size measurements with the electron microscope showed that the splitting myofibrils were about twice as large as non-splitting myofibrils and that the myofibrils split more or less down the middle. A possible explanation for the splitting is that the peripheral I filaments are pulled at an angle slightly oblique to the myofibnl axis, because of the discrepancy in the A and I-filament lattice spacings. When the myofibnl reaches a certain size the oblique pull of the peripheral I filaments is strong enough to cause the Z disks to rip.
From data on the size, shape and number of myofibnls at different stages of growth it was concluded that longitudinal splitting is the means by which the number of myofibrils increases during post-natal growth.
Enlarged synaptic vesicles as an early sign of secondary degeneration in the optic nerve terminals of the pigeon
Authors: Cuénod M. , Sandri Clara , Akert K. 
Published: April 2021

ABSTRACT
The terminal degeneration of retino-tectal fibres was studied electron microscopically in the pigeon Synaptic vesicles seem to undergo systematic changes which can best be observed in aldehyde-fixed material. Initially (i.e. within 12–24 h) the vesicles begin to swell. The enlargement is clearly visible after 4 days (40 % increase in diameter) and reaches a maximum at 14 days (100% increase). At the latter stage, the enlargement is almost invariably associated with the well known opacity of degenerating terminals. In contrast, normal control tissue contains nerve endings with only a few enlarged and no ballooning vesicles. The conclusion seems warranted that the ballooning of synaptic vesicles is an early sign of terminal degeneration, it appears to precede vesicular disintegration.
Control points in Neurospora crassa nuclear division cycle: Different effects of the inhibition of protein accumulation
Authors: Martegani Enzo , Tomé Franca , Trezzi Federica 
Published: April 2021

ABSTRACT
The correlation between protein synthesis and the nuclear division cycle in Neurospora crassa hyphae was studied by inhibiting protein accumulation by two different experimental procedures: (1) starvation for lysine in a lysine-requiring mutant (lys-); and (2) addition of cycloheximide.
Lysine starvation in a lys-1 strain of N. crassa quickly blocked the nuclear division cycle and nuclei accumulated in Gi phase, as judged by their DNA content. After re-addition of lysine to starved cultures, a discontinuous pattern of uridine incorporation into DNA can be seen, showing that the nuclei were well synchronized. On the other hand, treatment with cycloheximide caused the arrest of a large proportion of the nuclei, also, in the G2 phase of the cell cycle. These results indicate that inhibition of protein synthesis may have multiple effects on the cell cycle in N. crassa and that, while moderate inhibition specifically blocks nuclei at a regulatory point in late G1, strong or complete inhibition demonstrates requirement for protein synthesis at other points in the cycle that are not necessarily regulatory points.
Kinetic analysis of cell spreading: II. Substratum adhesion requirements of amniotic epithelial (FL) cells
Authors: Aplin John D. , Bardsley William G. , Niven Veronica M. 
Published: April 2021

ABSTRACT
The kinetics of spreading of trypsinized FL cells on plastic or glass substrata covalently or passively coated with various proteins to make simplified model extracellular matrices have been measured. Kinetics have also been obtained in the presence and absence of serum and amniotic fluid. Data from such experiments are shown to be sigmoid and have been computer-fitted with great accuracy to 12 mathematical models discussed in the accompanying paper. A log normal distribution function is shown to give the best fit over 18 different types of experiment. For the first time, therefore, such data can be characterized quantitatively and compared. We obtain the simple parameters μ(mean time to spread) and a (standard error of the mean) and show that the cells spread most rapidly in amniotic fluid or on fibronectin ‘carpets’. They also spread rapidly on a fibronectin-fibrinogen complex extracted from placenta. Spreading is slower in serum, in amniotic fluid lacking fibronectin and on type I collagen or cellular microexudate from FL cells or fibroblasts. On concanavalin A, spreading is rapid but the distribution of times to spread (as expressed by cr) is relatively wide.
Immunofluorescence microscopy of the flagella and multilayered structure in two mosses, Sphagnum palustre L. and Polytrichum juniperinum Hedw
Authors: Miller C. C. J. , Duckett J. G. , Sheterline P. , Carothers Z. B. 
Published: April 2021

ABSTRACT
Antibody against tubulin from porcine brain was used to examine the distribution of tubulin in developing spermatids of Poly trichum and mature spermatozoids of Sphagnum. Cells were prepared for indirect immunofluorescence microscopy after fixation in buffered paraformaldehyde and brief incubation in cellulase. Pretreatment with cold methanol resulted in considerably enhanced immunofluorescence but exposure to Triton X-100, with or without sonication, had no effect. The antibody showed similar immunological cross-reactivity with the flagella (both basal bodies and axonemes) and the spline microtubules of the multilayered structure. This is the first direct evidence that this rigid array of stable cytoskeletal microtubules consists of tubulin. Particularly intense fluorescence from the lamellar strata of the MLS in developing spermatids provides strong support for the notion that the lamellae comprise a highly structured microtubule organizing centre (MTOC), responsible for the ordered assembly of the overlying spline tubules. The demonstration of immunological cross-reactivity with antitubulin from porcine brain tubulin, within a plant structure other than fully formed microtubules, suggests that immunocytochemistry may have considerable potential for the detection of other MTOCs. By contrast, no detectable fluorescence emanated from the granular matrix cementing the flagellar basal bodies to the spline or the spindle-shaped sheath of fibres present in the spermatozoids of Sphagnum. Disruption of the mature gametes by sonication and treatment with Triton X-100 reveals the presence of particularly strong links between the spline and subjacent nuclear envelope.
Insect intercellular junctions: rapid freezing by jet propane
Authors: Swales Lesley S. , Lane Nancy J. 
Published: April 2021

ABSTRACT
The ventral nerve cord of the cockroach, Periplaneta americana, and that of the locust, Schis-tocerca gregaria, have been studied after rapid freezing by cryo-jet, using liquid propane. Such tissues, unfixed and uncryoprotected, have been compared with unfixed cryoprotected tissues, as well as with material fixed with glutaraldehyde and cryoprotected with glycerol or polyvinyl-pyrrolydone. The perineurial tight junctions in the cryo-jet-frozen tissues exhibit characteristic intramembranous P-face ridges, but frequently these are composed of smooth-surfaced strands, comparable to those seen with fast-freezing in mammalian tissues, rather than of bead-like fibres. The intramembranous PF ridges, characteristic of axonal and glial processes in the insect central nervous system, also display a smooth surface in rapidly frozen preparations. Prior fixation and/or cryoprotection produces a bead-like appearance in the ridges. The interglial gap junctions, after fast-freezing, exhibit both clustered connexon arrays in the E-face and loosely aggregated ones; hence the coupled state cannot be unequivocally associated with the latter configuration. The septate junctions between glial cells are unchanged after rapid freezing, exhibiting the typical rows of P-face intramembranous particles with complementary E-face pits that are found in replicas from fixed and cryoprotected tissues. The surfaces of the axons and glial processes exhibit pleiomorphic depressions and associated particles as well as PF pits with complementary EF mounds, both with associated I MPs. These structures are not usually seen after fixation or cryoprotection and may represent some kind of receptor structure, or axo-glial specialization.
Isolation and Characterization of invertebrate smooth septate junctions
Authors: Green C. R. , Noirot-Timothée C. , Noirot C. 
Published: April 2021

ABSTRACT
Using modifications of techniques used for the isolation of macula type intercellular junctions (gap junctions and desmosomes) the arthropod smooth septate junction has been isolated from insect midgut tissue. Midguts from cockroaches or mealworms were used and membrane fractions were obtained by sucrose gradient and ultracentrifugation techniques. Preparations with reasonable concentrations of septate junction were obtained and have been studied by thin-section, negativestain and freeze-fracture electron microscopy. The junctions appeared to be well preserved, although there was evidence that the junction strands were able to slide within the plane of the membrane. Septa were seen to have a cross-striated appearance when viewed after negative staining but their exact structure remained difficult to determine.
Polyacrylamide gel electrophoretic studies demonstrated the reproducibility of the isolation procedure and showed that septa may have a 47 000 molecular weight glycoprotein component. Gel electrophoresis also gave some indication of the intramembrane biochemistry of the smooth septate junction, with proteins of 31 000 and 32000 molecular weight always occurring in the junction fractions. The junctions were, however, very sensitive to both mechanical and chemical treatments, the septa were destroyed by tough homogenization or by treatment with urea at a concentration as low as 1 M. Freeze-fracture of untreated, isolated junctions demonstrated no differences from junctions in intact tissue, while replicas of urea-treated material were more difficult to interpret as the component parts of the junctions became separated once the septa had been destroyed.
Gap junctions were also obtained and resisted both mechanical and chemical treatments, which destroyed the septate junctions. Their major protein component appeared to have a molecular weight of 36 000. Attempts to isolate pleated septate junctions (from insects, molluscs and annelids) by the same techniques failed, implying a significant difference in the structures of the two types of septate junction.
Morphology of hyaluronidase-sensitive cell coats as seen in the SEM after freeze-drying
Authors: Bard J. B. L. , Mcbride W. H. , Ross A. R. 
Published: April 2021

ABSTRACT
Many adherent cells in vitro are surrounded by a transparent exclusion zone or halo, several pm thick, which red blood cells, bacteria and carbon particles cannot penetrate. This halo is rapidly and specifically removed by hyaluronidase and its high degree of hydration is demonstrated by the fact that, although fixation does not eliminate the halo, solvent dehydration does. This latter observation means that the halo cannot be visualized by conventional electron microscopic techniques. We report here that the exclusion-zone material can, however, be seen in the scanning electron microscope if cells are fixed and frozen rapidly and then freeze-dried. Many cells in cultures from a murine fibrosarcoma or from human embryonic lung treated in this way appear to be covered by a matrix that obscures the microvilli that are visible on critical-point-dried or hyaluronidase-treated, freeze-dried cells. Only where the coat is, for some reason, missing can microvilli be seen on freezedried cells. The coat structure varies from amorphous to an assembly of fine fibres ∼100 nm in diameter and its appearance is very similar to that of small drops of hyaluronic acid (10−5μgml-1) treated in the same way. Halo material is fragile and detaches itself from the cell surface within an hour of fixation. These observations suggest that the halo phenomenon reflects only the production of extracellular matrix and its turnover. The fragility of the haloes implies that, if they do exist in vivo, they are unlikely to play any structural role. The results suggest that the technique will yield information on other highly hydrated, unstable structures.