bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of contractile vacuole pore morphogenesis in Tetrahymena Pyriformis by 180° rotation of ciliary meridians
Authors: Ng Stephen F. 
Published: April 2021

ABSTRACT
The contractile vacuole pores (CVPs) in Tetrahymena pyriformis are usually found to the left of ciliary meridians (CVP meridians). When the CVP meridians are experimentally rotated 180° (‘inverted’), the CVPs are now found to the right of the rotated CVP meridians. In other words, the CVP is almost invariably found on the same side with respect to the CVP meridian. Thus, the 2 sides of the CVP meridian have different morphogenetic properties and such differences are determinative in the asymmetrical fine-positioning of the CVP.
The number of CVPs per animal and their general placement on the animal (i.e. with which ciliary meridians the CVPs are associated) are known to be a function of the total number of ciliary meridians possessed by the animal. Rotation of the CVP meridians affects both the number of CVPs per animal and their general placement. The specificity of such effects appears to depend on whether both, or one, or which one, of the CVP meridians is rotated. Rotation of ciliary meridians may be used as a tool in analysing the mechanism determining the number of CVPs per animal and their general placement.
Studies of anionic sites on the cell surface of the amoeba Naegleria gruberi using cationized ferritin
Authors: King C. A. , Preston T. M. 
Published: April 2021

ABSTRACT
Interaction of cationized ferritin with the anionic groups on the cell surface of Naegleria was studied using transmission electron microscopy in conjunction with fluorescence microscopy. Most of the experiments involved the use of fluorescein-labelled cationized ferritin (FITC-CF) incubated with living amoebae. Initially the FITC-CF was located over the posterior two-thirds of the amoebae but the label was rapidly redistributed to form a cap at the posterior end in the region of the uroid; frequently this cap was shed. Pinosomes containing FITC-CF were clearly visible within the amoebae. Amoebae prefixed in glutaraldehyde were uniformly stained and did not show redistribution of the label. Exposure of live amoebae, previously incubated with cationized ferritin and allowed to cap, to fresh FITC-CF failed to produce fluorescent staining of the general cell surface, i.e. depletion of binding sites had occurred. The binding of the FITC-CF was not affected by pretreatment of the amoebae with neuraminidase or pronase. The possible nature of the anionic sites on the membrane is discussed.
Membranes in lupin root nodules: I.the role of golgi bodies in the biogenesis of infection threads and peribacteroid membranes
Authors: Robertson J.G. , Lyttleton P. , Bullivant S. , Grayston G. F. 
Published: April 2021

ABSTRACT
The process of infection of lupin nodule cells by rhizobia was examined using thin-section and freeze-fracture electron-microscopic techniques to characterize the properties of different membranes and to establish relationships between them. The membranes of the Golgi bodies and the endoplasmic reticulum stained with zinc iodide-osmium tetroxide but not with phos-photungstic acid or silver. By contrast the infection thread membranes, peribacteroid membranes, plasma membranes and membranes of cytoplasmic vesicles did not stain with zinc iodide-osmium tetroxide but stained with phosphotungstic acid and silver. The peribacteroid membranes and plasma membranes are, however, different from each other since the particle density on the E face of freeze-fracture replicas of plasma membranes was twice that on the E face of the peribacteroid membranes.
An examination of the tips of the infection threads in the cytoplasm of the plant cells, showed that the rhizobia bud off from the infection threads enclosed in the infection thread membranes. The rhizobia continue to divide still surrounded by membranes of plant origin, namely the peri-bacteroid membranes. Cytoplasmic vesicles are observed in both thin-section and freeze-fracture preparations of nodule tissue closely associated with, and apparently produced by, Golgi bodies. Formation of the walls and membranes of the infection threads and of the peribacteroid membranes involves fusion of the cytoplasmic vesicles with these membranes. It is proposed that the process of infection of plant cells in lupin nodules involves a change in the function of the Golgi body system for the biogenesis of plant cell walls and plasma membranes to include the synthesis of the walls and membranes of the infection threads and also the peribacteroid membranes.
Ultrastructural localization of cationic proteins in human polymorphonuclear leukocytes
Authors: Brown William J. , Wood Eunice M. 
Published: April 2021

ABSTRACT
The present investigation is concerned with the use of the post-formalin ammoniacal silver reaction to detect the arginine-rich cationic proteins in human polymorphonuclear leukocytes at the ultrastructural level. These proteins appear to function as neutral proteases in antibacterial action and as mediators of inflammation. Originally, the ammoniacal silver reaction relied upon primary fixation in dilute formalin which prevented optimum fixation of tissues. This study shows that by using the proper sequence of glutaraldehyde fixation and the ammoniacal silver solution in conjunction with osmium tetroxide treatment, better fixation of the tissue and localization of the ammoniacal silver reaction can be achieved. Also, the ammoniacal silver reaction in human polymorphonuclear leukocytes is exclusively located in the large, crystalline cytoplasmic granules of eosinophils. All other cytoplasmic granules of neutrophils, eosinophils, and basophils were found to be devoid of the ammoniacal silver reaction product. These results are contrary to previously published experimental data. Possible explanations for this discrepancy are discussed.
Supercoiling of dna and nuclear conformation during the cell-cycle
Authors: Warren A. C. , Cook P. R. 
Published: April 2021

ABSTRACT
When cells are lysed in solutions containing high concentrations of salt and a non-ionic detergent, structures are released which retain many of the morphological features of nuclei. These nucleoids contain superhelical DNA but are depleted of nuclear protein. We have analysed DNA conformation in nucleoids derived from HeLa cells synchronized at different stages in the cell cycle. The gross differences in nuclear morphology seen during the cell cycle are reflected in the morphology of the nucleoids; for example, the individual chromosomes of mitotic cells remain identifiable and aggregated within the mitotic nucleoid. The sedimentation rate of nucleoids in sucrose gradients reflects the gross nuclear morphology; the small S-phase nucleoids sediment 9 times faster than the large mitotic nucleoids. Despite these large differences at the gross level of organization, both the degree of supercoiling and the size of the units in which supercoiling is maintained are roughly similar in the nucleoids derived from cells in the different phases. The protein content of the various nucleoids is also very similar. Like the nucleoids made from randomly growing cultures of cells, mitotic nucleoids are excellent templates for the RNA polymerase of Escherichia coli.
Cellular actin and junction formation during re aggregation of adult rat hepatocytes into epithelial cell sheets
Authors: Miettinen A. , Virtanen I. , Linder E. 
Published: April 2021

ABSTRACTAggregation of adult rat hepatocytes, isolated by the collagenase perfusion technique, was studied by ultrastructural methods and the indirect immunofluorescence technique using anti-actin antibodies. In a primary culture the cells rapidly made contact with each other by filopodia-like structures, as seen by scanning electron microscopy. In a few hours this led to stable adhesion of the cells. No identifiable junction formation occurred during the first 17 h in culture. Within 48 h the cells had formed epithelial cell sheets with junctional complexes consisting of tight junctions, bile canaliculus-like structures and zonula adhaerens-type junctions.The distribution of cytoplasmic actin fluorescence remained homogeneous in the contacting cells during the first 24 h in culture, as seen with anti-actin antibodies by the indirect immunofluorescence technique. The first short, fluorescent actin filaments appeared in the periphery of the developing lamellipodia of the spreading cell islands. In organized epithelial cell sheets these filaments were seen as long fibres ending at the perinuclear region of the marginal cells. In the submarginal cells fluorescent actin fibres were distinct at the junctional regions of the cells. This filamentous fluorescence seemed to extend throughout the entire cell sheet in an organized manner and correspond to the apical layer of parallel microfilaments seen in transmission electron microscopy. Our results suggest that filamentous actin plays a role in the contact-induced spreading of the cells and in the maintenance of the internal organization of the epithelial cell sheets.
Insect axopods
Authors: Bradley Timothy J. , Satir Peter 
Published: April 2021

ABSTRACT
Using the electron microscope we have found axopods, a cell organelle previously undescribed in multicellular animals, in the lower Malpighian tubule of the insect, Rhodnius prolixus. The axopods, which are 0 · 2 to 0 · 8 μm in diameter and 10 or more μm in length, derive from the luminal surface of the tubule and contain an array of 1 to about 46 microtubules each. These microtubules arise within the cell near the cell junctions or near clumps of mitochondria.
Uric acid crystals which occur naturally in the lower tubule have been observed to move down the tubule under experimental conditions where peristalsis and fluid secretion can be ruled out. We suggest that the axopods are motile and serve to transport the crystals along the narrow tubule lumen. Since cilia are not found on somatic cells of arthropods, we suggest that axopods have evolved in the lower tubule to perform a function analogous to a ciliated epithelium in other animals.
The role of algal antigenic determinants in the recognition of potential algal symbionts by cells of Chlorohydra
Authors: Pool R. R. 
Published: April 2021

ABSTRACT
Algal cells grown in the green hydra Chlorohydra viridissima were shown to possess characteristic antigenic determinants not found in algae cultured in vitro. These antigenic determinants, including those localized on the algal cell surface, were shown to be responsible for the phagocytic recognition of potential algal symbionts by digestive cells of Chlorohydra. The results of this study indicate the existence of two systems governing phagocytosis in Chlorohydra, one specific for algal cells grown in hydra, another governing the uptake of other particles by the hydra digestive cells.
The association of chloroplast dna with photosynthetic membrane vesicles from spinach chloroplasts
Authors: Rose R. J. 
Published: April 2021

ABSTRACT
To investigate the association between chloroplast DNA (cp DNA) and the photosynthetic membranes of spinach chloroplasts, previously suggested by electron-microscope autoradiography, use has been made of vesicles formed by isolating chloroplasts directly in 3·5 Mm Mg2+. These chloroplast vesicles consist of photosynthetic membranes, separate from chloroplast envelope membranes. Light and electron microscopy confirm that the vesicles consist of swollen stroma lamellar membranes with some peripheral grana lamellae that are much less swollen. Vesicles labelled with [3H]thymidine were obtained from [3H]thymidine-labelled chloroplasts from spinach disks in which chloroplast division and cp DNA synthesis and segregation were occurring. The chloroplast vesicle fraction retains about 45 % of the cp DNA as determined by liquid scintillation counting. The cp DNA-membrane associations do not appear to be dependent on the presence of Mg2+. The chloroplast vesicles can be autoradiographed for light microscopy if they are fixed in formaldehyde and no centrifugation steps are used. Lightmicroscope autoradiography is consistent with a preferential labelling of grana as opposed to stroma membranes, and long lengths of membrane are labelled. It appears that in spinach chloroplasts cp DNA is associated with granal thylakoids at intervals along the length of a continuous photosynthetic membrane system. Such an organization would facilitate cp DNA segregation during chloroplast division.
Marginal bands in camel erythrocytes
Authors: Cohen William D. , Terwilliger Nora Barclay 
Published: April 2021

ABSTRACT
The elliptical, anucleate erythrocytes of camels have been examined for the presence of marginal bands and their constituent microtubules. Lysis of erythrocytes under microtubulestabilizing conditions readily revealed marginal bands in at least 3 % of the cells, as observed by phase-contrast and darkfield light microscopy. Microtubules plus a marginal bandencompassing network of material are visible in lysed cell whole mounts with transmission electron microscopy. Marginal band microtubules are also evident in electron micrographs of thin-sectioned camel erythrocytes identifiable as reticulocytes on the basis of submaximal electron density (reduced haemoglobin iron content) and presence of polysomes. The results suggest that marginal bands may be involved in morphogenesis of camel erythrocytes but are not required for maintenance of their ellipticity after cells are fully differentiated.
Blue light-induced, intrinsic vacuolar fluorescence in onion guard cells
Authors: Zeiger Eduardo , Hepler Peter K. 
Published: April 2021

ABSTRACT
Guard cells of onion irradiated with broad-band blue light display a green intrinsic fluorescence. The fluorescence has been found in eleven species of Allium, but it has not been observed in any other monocot or dicot examined. The fluorescence occurs only in guard cells and is absent in neighbouring epidermal cells. During development it is first apparent in guard mother cells soon after the asymmetric division. Microscopic observation reveals that the fluorescence is associated with the vacuole and examination of vacuoles isolated from guard cell protoplasts suggests that it may be localized on the tonoplast. Microspectrophotometric analysis of single cells reveals an emission peak at around 520 nm. Our results are consistent with the view that this blue light receptor is a flavin or flavoprotein and that it might be related to the blue light-enhanced stomatal opening observed in onion.
Colchicine-induced paracrystals in the tapetum of wheat anthers
Authors: Bennett M. D. , Smith J.B. 
Published: April 2021

ABSTRACT
Prolonged colchicine treatment induced the formation of numerous cytoplasmic para crystals in tapetal cells of wheat anthers containing germ line cells at pre-meiotic mitosis or early pre-meiotic interphase. Such paracrystals were up to 8 μm long and 0·7 μm in diameter, and filled up to about 8% of the volume of the cytoplasm. Paracrystals were not bounded by a membrane. A paracrystal consisted of tubules running in parallel with its long axis. Paracrystals cut at right angles to their long axes revealed hexagonal arrays of circles with a maximum diameter of about 35 nm and electron-dense walls 6-7 nm in thickness. Similar paracrystals were not seen in any cell type of untreated anthers, or in germ line cells of treated anthers, containing stages between pre-meiotic mitosis and first metaphase of meiosis inclusive. The possible significance of the paracrystals in relation to the function of the tapetum is discussed.
Specific end-to-end attachment of chromosomes in Ornithogalum virens *
Authors: † Terry Ashley 
Published: April 2021

ABSTRACT
C-banding of nonhomologous chromosomes in haploid generative nuclei of Ornithogalum virens (n = 3) reveals a high degree of specificity with respect to end-to-end connexions. The centromeric end of chromosome 2 preferentially associates with the centromeric end of chromosome 3 and the telomeric end of chromosome 3 associates preferentially with the telomeric end of chromosome 1. This same association of nonhomologous chromosomes persists in prophase nuclei of diploid root tips. In addition, the telomeric ends of the 2 chromosome 2s are connected to one another as are the centromeric ends of the chromosome is. This results in a ring of chromosomes in which homologues lie opposite one another. Centromeric ends lie on one side of the nucleus and telomeric ends on the other. It is proposed that this specific association of chromosome ends reflects an order which was probably established at the preceding anaphase or telophase and which persists throughout interphase. The suggestion is made that the proximity of homologous ends and consequently homologous alignment may facilitate initiation of pairing at meiosis.
Isolation of a residual protein structure from nuclei of the myxomycete Physarum polycephalum
Authors: Mitchelson K. R. , Bekers A. G. M. , Wanka F. 
Published: April 2021

ABSTRACT
A nuclear framework structure has been obtained from isolated interphase nuclei of Physarum polycephalum by extraction with 2·5 M NaCl and subsequent digestion with DNase. Wholemount electron micrographs showed a nuclear lamina containing residual pore structures associated with the fibrous internal matrix. The matrix was continuous with fibrillar remnants of the nucleolus. The structure was shown to consist of 2 major polypeptides of 23000 and 36 500 Daltons as well as 30 to 40 minor polypeptides of various molecular weight classes. The 2 major polypeptides were also prominent in preparations of the residual nucleolar material, suggesting that matrix proteins are common to both structures. The predominance of low-molecular-weight polypeptides in Physarum nuclear matrix suggests that there may be significant differences in composition of nuclear structural proteins between lower and higher eukaryotes.
Immunoelectron-microscopic studies of endoplasmic reticulum-golgi relationships in the intracellular transport process of lipoprotein particles in rat hepatocytes
Authors: Matsuura Shiro , Tashiro Yutaka 
Published: April 2021

ABSTRACT
Endoplasmic reticulum (ER) –Golgi relationships in the intracellular transport process of secretory proteins in rat hepatocytes have been studied using lipoprotein particles as a marker for the secretory protein and cytochrome P-450 as a marker enzyme for the ER membranes. Ferritin immunoelectron-microscopic observation revealed that, while almost all the microsomal vesicles derived from ER membranes are heavily labelled with ferritin anti-cytochrome P-450 antibody conjugates, labelling of the small peripheral vesicles containing lipoprotein particles, the stacks of Golgi saccules, especially the outermost saccule which is sometimes fenestrated, condensing vacuoles in the trans-Golgi region and the secretion droplets of lipoprotein were scanty and at the control level. Such a characteristic pattern of labelling was especially evident when these structures were prepared from phenobarbital-treated rats.
These findings indicate that the membranes of the small peripheral vesicles do not contain cytochrome P-450 and that the cytochrome is probably not transferred to Golgi saccules in the transport process of lipoprotein from ER to Golgi. It is suggested, therefore, that the small peripheral vesicles are formed by budding of the special regions of ER membrane where microsomal marker proteins such as cytochrome P-450 are excluded and the membrane proteins destined to the Golgi complexes are clustered.
It is also shown that lysosomal membranes are not labelled with the anti P-450 antibody conjugates.
Rhizoplast and rootlet system of the flagellar apparatus of Chlamydomonas moewusii
Authors: Katz Kenneth R. , McLEAN Robert J. 
Published: April 2021

ABSTRACT
The ultrastructure of the flagellar apparatus of Chlamydomonas moewusii was examined in detail. Two rhizoplasts were found associated with the basal bodies of this biflagellate and were observed to extend to the central area of the cell. A segment of smooth endoplasmic reticulum ran parallel to each rhizoplast. These 2 segments anastomose beneath the basal bodies and the tubule proceeds over the top of the distal connecting fibre. A functional role for the smooth endoplasmic reticulum in these locations is discussed. Four sets of rootlet microtubules emanate from a region between the 2 basal bodies and the distal connecting fibre. Two sets have a three-over-one arrangement and the other 2 sets are doublets. Cytoplasmic microtubules were seen associated with possible nucleating sites on the rootlet microtubules. The associations of the observed structures are discussed and compared to the flagellar apparatus of C. reinhardtii.
The structure and some properties of the isolated mitotic apparatus
Authors: Goldman R. D. , Rebhun L. I. 
Published: April 2021

ABSTRACT
The morphology of the isolated sea-urchin mitotic apparatus (MA) was examined by light and electron microscopy. With the polarization microscope and the Nomarski differential interference microscope, the isolated MAs appeared to be similar to in vivo MAs. Electron microscopy of the isolated MAs revealed the presence of microtubules, ribosome-like particles and vesicles. A close association between the ribosome-like particles and the MA microtubules resulted in the appearance of chains of particles running along the length of the microtubules.
Isolated MAs washed two to three times in isolation medium showed fine-structural changes in the electron microscope, which were reflected by lower retardation values obtained with the polarization microscope. The addition of magnesium and calcium or sucrose to the washing medium prevented these structural changes. Varying the pH of the isolation medium also resulted in changes in birefringence and ultrastructure of unwashed MAs.
Isolated MAs stored in the original isolation medium gradually became less birefringent and lost their microtubules. At pH 6·1 and pH 6·2 a residual birefringence was retained, even after several weeks of storage. Electron microscopy of these MAs revealed the presence of linear aggregates of ribosome-like particles oriented parallel to the long axis of the spindle. On the other hand, at pH 6·3 and pH 6·4, MAs lost their birefringence completely, and the ribosome-like particles became more randomly dispersed. 2M sucrose or 0·003 M Mg2+ greatly retarded the loss of birefringence in stored MAs.
Glutaraldehyde-fixed MAs stained intensely with azure B bromide, demonstrating the presence of RNA. Treatment with RNase resulted in a loss of this staining. RNase-treated MAs examined with the electron microscope, revealed changes in the ribosome-like particles.
The results are discussed in the light of recent biochemical analyses of the isolated MA, structural similarities to in situ MAs and the interpretation of the birefringence of the MA.
The sperm centriole persists during early egg cleavage in the insect Chrysopa carnea (neuroptera, chrysopidae)
Authors: Friedlander Michael 
Published: April 2021

ABSTRACT
The giant centriole of the sperm of Chrsyopa carnea persists in the fertilized egg. The giant centriole appears together with a regular small centriole at one pole of the first cleavage spindle; two small centrioles are found at the other pole. During the subsequent divisions, the giant centriole appears either at one pole of one of the spindles, as in the first cleavage, or close to one inter-kinetic nucleus. All the other centrioles are regular in size. Therefore, the assumption that the mature spermatozoa of insects contain no true centrioles is not valid, at least for Chrysopa.