Fibrillar Elements Research Articles

Origin and significance of the discharge vesicle in Phytophthora

During zoospore release from sporangia, all Phytophthora species studied developed a discharge (germination) vesicle into which 30 to 70% of the total number of zoospores were released before the vesicle burst. Vesicles of P. cactorum, P. Palmivora, and P. cinnamomi reached maximal diameters of 26, 40, and 46 μm, respectively, when sporangia were placed in double-distilled water for zoospore release. The mean velocities of surface area enlargement of the vesicles represent ratios of 1:1.7:4.6, comparing P. cactorum with P. palmivora and with P. cinnamomi. For sporangia of P. cactorum, the surface area of the vesicle enlarged at a constant rate, whereas the increase in vesicle volume proceeded with an acceleration of about 79 μm3/second2. When sporangia produced by P. cactorum grown in either bean meal broth or a chloride mineral solution were transferred to double-distilled water they developed discharge vesicles that enlarged in surface area at velocities of 224 and 145 μm2/second, respectively, and had turgor pressures of about −8.0 and −4.8 bar, respectively. During zoospore release in P. palmivora, the outer sporangial wall and an amorphous cover layer were ruptured, and the papillar material (vesiculogen) was forced through the exit pore to form a continuous and plastic vesicle wall consisting of thin fibrillar elements of undetermined lengths (EM). The opening of the sporangium of P. palmivora, the enlargement of the vesicle, and subsequent zoospore release could be retarded or stopped in any stage by transferring germinating sporangia to CaCl2 or PEG solutions with osmotic potentials between −2.5 and −3.5 bar. During plasmolytic treatments, the papillae of sporangia of P. cactorum and P. palmivora kept their original shape, whereas the apices of P. cinnamoni sporangia collapsed.

Light and Electron Microstructure of a Sarcocystis Sp. from the Malaysian Long-Tailed Monkey, Macaca Fascicularis

The ultrastructure of the cyst wall and zoites of a species of Sarcocystis from the skeletal muscles of a naturally-infected Malaysian long-tailed monkey, Macaca fascicularis, is described in detail. The wavy, electron-dense primary cyst wall is thin (55 nm) and invaginated. Cytophaneres are absent. The ground substance contains electron-dense granules and bundles of parallel, fibrillar elements in some areas. Thin trabeculae are present. The zoites measure 1.2 X 4.7 microns and have an interior conoid, 22 subpellicular microtubules, 50-60 micronemes, 4-6 rhoptries, and a posteriorly situated nucleus. Some ultrastructural aspects of the cyst wall and the zoites of this parasite resemble those of Sarcocystis species of the moonrat, rhesus monkey, tamarin, and baboon. The light microscopic appearance of this species from M. fascicularis also bears some resemblance to that of parasites from the four cases of human Sarcocystis reported in Malaysia. The cyst in all these human cases were thin-walled, with no cytophaners. Although the final hosts of these species of Sarcocystis are not known, it is quite possible that man, monkeys, and perhaps the moonrat (an insectivore) may serve as common intermediate hosts for one or several species of Sarcocystis.

Elastic modulus and strength of fibrous material

AbstractAs a rule, the large increase of elastic modulus with increasing draw ratio obtainable in highly‐drawn or extruded semicrystalline polymers is not reflected in a similarly large increase of strength. This is closely connected with the wellknown fact that with increasing plastic deformation one obtains fibrous material with decreasing strain to break. The axial elastic modulus is mainly caused by the taut tie molecules which bridge the amorphous layers between consecutive crystal blocks and thus provide an efficient axial force transmission through the sample. The defects at the ends of microfibrils interrupt this transmission because they contain few if any taut tie molecules connecting the end of microfibril with adjacent fibrillar elements. As a consequence of the small number of such ends, they only marginally reduce the elastic modulus. But as the mechanically weakest areas of the fibrous material, they drastically depress the strength. They fail as soon as the strain concentration upon them reaches their strain to break. The growth and coalescence of resulting microcracks finally lead to bulk fracture as the growing crack reaches critical dimensions.

Ultrastructure and cytochemistry study of the yolk syncytial layer in the alevin of trout (Salmo fario trutta L.) after hatching. I. The vitellolysis zone.

After hatching, the yolk syncytial layer of Salmo fario trutta may be subdivided into two zones, namely, the vitellolysis zone (containing numerous yolk platelets), and the cytoplasmic zone (where yolk platelets are rare). In the vitellolysis zone, two stages in the utilization of the yolk are observed: 1) The first stage, comprises the formation of yolk platelets from coalescent yolk by spherical cutting out and basal scission. This process seems to be achieved by the invagination of fibrillar elements into the coalescent yolk to form individual yolk platelets surrounded by a limiting membrane. 2) The second stage essentially consists of the extrusion or budding of yolk matter from a yolk platelet. Again, where the yolk matter leaves a platelet, fibrillar elements are evident and show an alkaline phosphatase activity. The platelets of the vitellolysis zone have a homogeneous content and variable diameter; they never acquire a heterogeneous and polymorphic aspect which could be interpreted as an intermediate stage in their degradation.

Immuno electron microscopic localization of subcellular fibrillar elements using the unlabeled antibody enzyme method

Immuno electron microscopic localization of subcellular fibrillar elements using the unlabeled antibody enzyme method

Cell wall architecture of sporangia, chlamydospores, oogonia, and oospores in Phytophthora

The ultrastructure of the walls of sporangia, chlamydospores, oogonia, and oospores of Phytophthora was analyzed with thin sectioning, replica, and freeze-fracturing techniques. All walls produced by this fungus are built from two basic types of layers: A layers, which are amorphous throughout, and FA layers, in which a fibrillar network is embedded in an amorphous matrix. With the exception of the cyst wall, which consists entirely of an FA layer, all walls are composed of at least one A and one FA layer. The combination of thickness, type, and number of layers is different for each wall type, but there is a remarkable similarity between walls of chlamydospores and oogonia. The fibrillar elements in the sporangial wall are composed of cellulose, and indirect evidence suggests that this might be true for all wall types of Phytophthora. The primary sporangial wall is stretched during the expansion phase, leading to rupture of its external A layer and reorientation of the fibrils in the inner FA layer. As a result the surface of the mature sporangium bears characteristic patches of amorphous A-layer material from which the underlying microfibrils emanate in a stellate pattern.

Chemical relationship of the paired helical filaments of Alzheimer's dementia to normal human neurofilaments and neurotubules

Intraneuronal fibrillary tangles are prominent features of several neurological diseases, including especially Alzheimer presenile and senile dementia, and to a much lesser degree in the normal aged human brain. These tangles are made up of abnormal fibrillar elements each about 22 nm at its widest, periodically reduced to 10 nm at about every 80 nm. Each abnormal fiber seems to be a pair of 10 nm filaments helically wound around each other. In this study the protein subunit of these paired helical filaments isolated from cases of Alzheimer's dementia was compared with the major protein subunits of normal neurofilaments and neurotubules by two-dimensional peptide maps of the tryptic or chymotryptic digests of the proteins labelled with 125I. The paired helical filament protein is very similar in its peptide maps to identically treated major neurofilament protein and to the β monomer of neurotubule, while it is not so similar to the α tubulin. These data suggest that the paired helical filament protein subunit is closely related chemically to the normal neurofilament protein subunit, and the β tubulin.

Morphology and ultrastructure of Crenothrix polyspora Cohn

Naturally grown cell material of Crenothrix polyspora from the well of a waterworks was studied by means of phase-contrast and Nomarski interference microscopy as well as by transmission electron microscopy. The material consisted of clusters of sheathed filaments up to 2 cm long. Propagation forms observed were nonmotile, spherical cells that arose by simple ("macrogonidia") or multiple ("microgonidia") septation of the filamental tips. Ultrastructural analysis revealed Crenothrix to be procaryotic and gram negative, with several layers of sheath material surrounding the filaments. On thin sections, individual cells had elaborate membrane systems in the form of lamellar stacks. They resembled thylakoids of photosynthetic bacteria. Spectrophotometric analysis gave no indication of photosynthetic pigments. The cells also contained large hexagonal bodies, rod-shaped fibrillar elements, and polyphosphate granules.

The fatigue process in highly oriented nylon 6 fibers

AbstractThe micromechanism of the fatigue process in highly oriented nylon 6 fibers is discussed on the basis of changes in mechanical and structural properties during fatiguing. Experimental results show that the fatigue process can be divided into two stages. The characteristic features in the initial period are increases in breaking strength, long period, and molecular orientation, and a reduction in dye penetration. In the second period, after about 500 cycles, breaking strength and orientation decrease slightly, and the long period, permanent strain, and dye penetration increase with duration of fatiguing. It is demonstrated that the structural changes mainly occur in the amorphous regions of the fiber structure. The structural and mechanical changes in the initial period lead to the conclusion that the initial cyclic strain causes strain hardening caused by extended tie chains which do not rupture. A combination of load bearing by tie chains and sliding motion of the fibrillar elements can explain the progressive degradation of the fiber during the second stage of fatiguing.

Progression of <sup>226</sup>Ra-Induced Ocular Alterations in Beagles (with 1 color plate)

The temporal progression of ocular injury involving the iris and tapetum lucidum in beagles injected with 226Ra was quantitated by assigning subjective numerical indices. Concentration of radium in melanotic ocular tissue was measured by an auto-radiographic technique. The observed changes consisted of iris hyperpigmentation, de-pigmentation and progressive tapetal loss. Each change was dependent on the injected radium activity and on the time after injection. At higher radium levels iris depigmentation progressed centrally and peripherally, exposing fibrillar structural elements. Tapetal alteration progressed initially from a granular or finely stippled pattern to pigmented foci interspersed between hyporeflective tapetum and finally to a complete loss of tapetum and exposure of the choroidal vasculature. The average radiation dose from injections of 28.1 and 83.6 μCi 226Ra to ocular pigmented tissues integrated for 5 years was estimated at 150 and 460 rad, respectively. An injection of 0.18 μCi 226Ra did not induce an ocular alteration within 10 years of follow-up.

Scanning electron microscopy of isolated Chironomus polytene chromosomes.

Individual polytene chromosomes have been isolated from Chironomus stigmaterus for scanning electron microscope observations. The three dimensional ultrastructure of these chromosomes consists of a series of chromatin strands extended in the interbands and more tightly coiled or folded in the banded regions. The nucleolus is observed to be a dense disc or doughnut shaped structure surrounding the chromosome while the Balbiani Rings appear as diffuse regions consisting of both fibrillar and granular elements.

Surface coat transformation and capsule formation by Leuconostoc mesenteroides NCDO 523 in the presence of sucrose.

When Leuconostoc mesenteroides NCDO 523 was grown in MRS browth, electron microscopy of cells fixed in the presence of ruthenium red showed that the cell wall was covered with a thin layer of filamentous material. When MRS-grown cells were resuspended in the same medium supplemented with 3.6% sucrose, this surface coat doubled in thickness and a number of radial thickenings appeared within it. After 3 h, the filamentous component of the surface coat had disappeared leaving only the radial projections. The progressive accumulation of polymer to produce a capsule visible by light microscopy was observed in only about 20% of the population. In this minority of cells, a dense globular dextran composed of fibrillar and particulate elements was always produced in the initial stages of synthesis. After 18 h, the dextran capsule was generally composed of an inner globular and outer fibrillar layer. It appeared that the outer layer was derived from the globular dextran of the capsule by a process of dispersion.

44—THE SURFACE TOPOLOGY OF RAMIE FIBRE: OBSERVATIONS BY SCANNING ELECTRON MICROSCOPY

An investigation is described in which the surface structure of ramie fibre at various stages of degumming was examined by scanning electron microscopy. It was observed that, as the fibre was degummed, the overlying patches on the surface became smaller in area, and fine, distinct detail, consisting of longitudinal fibrillar elements, was progressively revealed on the fibre surfaces. From the polarizing microscopy of transverse sections, it was observed that the peripheral S1 layer of the secondary wall remained intact in the degummed sample. In the peeled fibre, the fibrils became well separated when the gum content was down to 1–2%. In the transverse sections of some of the fibres, containing 12–22% gum, the lumen was found to be closed, and only when the gum content was reduced to 6% could the lumen be seen clearly in the cross-sections. A brittle type of fracture generally existed in all the fibres, irrespective of the gum content.

Observations with cytochemistry and ultracryotomy on the fine structure of the expanding walls in actively elongating plant cells.

Ultracryotomy with negative staining and cytochemistry (periodic acid - thiocarbohydrazide - silver proteinate test for polysaccharides, in conjunction with mild extractions) were used to study the architecture of the cell wall and its modifications during expansion. Those techniques were applied to the study in situ of the walls of actively elongating parenchyma of mung bean (Phaseolus aureus), and pea (Pisum sativum) root and of collenchyma of celery (Apium graveolens) petioles. These complementary techniques provide information on the 3-dimensional disposition and fine structure of the subunits of the wall. In all the examples examined, the bulk of growing primary wall appears well-ordered and no progressive evolution from a transverse texture near the plasmalemma to a scattered texture near the middle lamella was observed. It seems unlikely that the development of the wall structure in relation to growth could be explained mechanically by a passive shift of the fibrillar elements in response to cellular stress. There is no evidence for an inert change in fibrillar orientation in the major part of the wall. If such occurs the process is limited to the outermost and senescent part of the wall. Thus, the texture observed does not agree with the classical multinet growth hypothesis but rather with the idea of an ordered structure of the primary wall. With the latter, the components should be able to respond in different ways to specific growth regulators and other environmental signals and thus exert a more positive control over the processes of oriented cell growth.

Structural model of mechanical properties and failure of crystalline polymer solids with fibrous structure

The failure of an axially strained polymer solid having a fibrous structure is caused by formation, coalescence, and growth of microcracks up to critical size crack, which then propagates catastrophically through the cross-section of the sample. The primary candidates for microcrack formation are the ends of microfibrils where the material connection by tie molecules to the rest of the sample is almost completely interrupted. The opening of microcracks and sliding motion of fibrillar elements ruptures locally the most strained taut tie molecules and, thus, produces radicals detectable by ESR. But, chain rupture is the consequence and not the cause of displacement of the strong fibrillar elements. It also does not substantially affect the load carrying properties of the sample which mainly depend on the lateral autoadhesion of microfibrils and fibrils and on their quasi-viscous resistance to axial displacement. Hence, one has to reject the completely inadequate models trying to base the observed load-elongation curve of such samples on the load carrying properties of those tie molecules which are eventually ruptured upon straining. Some examples of these models are treated explicitly.

Biosynthesis of Cellulose by Acetobacter Xylinum. II. Morphological Observations on the Formation of Cellulose Microfibrils by Acetobacter Xylinum

Electron-microscopic observations of an early stage of a logarithmic phase of bacterial cellulose formation show ill-defined and branched fibrillar elements extending from an amorphous substance of cell envelope. This may be interpreted as the initial crystallization of a cellulosic high polymer. In the photographs of cell cross sections, it has been observed that rather slightly staining rod-like materials about 30—40Å in breadth and ca. 1000Å in length are in the cytoplasm of some cells. Composite fibrils become predominant at a middle stage of a logarithmic growth phase. They were in the form of threads having a constant breadth of ca. 500Å with sharply defined boundaries, and consisting of a few microfibrils. The separate fibrils have intertwined to form tangled masses, and built tough membranes which could not be torn easily. Lysozyme treatment of the microfibril has demonstrated that the shape is a flat ribbon with a constant breadth and a thickness of ca. 50—100Å. This treatment has the effect of hydrolytic degradation across the axial direction of the microfibril. In addition, a pronounced swelling of the microfibril occurs anisotropically perpendicular to the axis of the microfibril. A bacterial cellulose membrane negatively stained with sodium phosphotungstate, showed a longitudinal periodicity with a ca. 200Å interval.

Prognostic elements of the "bone factor" analysis.

Prognostic elements of the "bone factor" analysis.

Ultrastructural and biochemical studies of the isolated fibrillar component of nucleoli from Novikoff hepatoma ascites cells

Nucleoli of Novikoff hepatoma ascites cells were fractionated into granular and fibrillar components with solutions containing polyvinsulphate and Mg 2+ (PVS/Mg 2+) or solutions containing EDTA. After treatment with the PVS/Mg 2+ solutions, the morphology of the fibrillar component was similar to that in situ inasmuch as they contain fibrillar clusters as well as other fibrillar elements ranging in diameter from 150–700 Å. The nucleotide composition of the RNA of the fibrillar and granular fractions was similar to that of ribosomal RNA. In agreement with earlier autoradiographic studies, the kinetics of incorporation of 32P-orthophosphate into RNA in both fractions showed that the specific activity of the RNA of the fibrillar fraction was fourfold greater than that of RNA in the granular region at 15 min. After 2 h the specific activity of the RNA in the granular region was 1.5 times greater than that in the fibrillar region. Two-dimensional polyacrylamide gel electrophoresis showed that the fibrillar fraction contained fewer proteins than the granular fraction. Some of the proteins were common to both the nucleolar granular particles and cytoplasmic ribosomes while others appeared to be unique to this fraction.

The fine structure of the coffee leaf rust, Hemileia vastatrix

The fine structure of two races of Hemileia vastatrix that cause leaf rust in Coffea arabica is similar in many respects to earlier descriptions of other rust fungi. Certain features, however, are distinctive. Both hyphae and haustoria contain occasional tubular complexes composed of tubules about 300 Å in diameter. These might function as a Golgi apparatus. The haustorium neck ring incorporates the entire wall thickness at its proximal end, but distally only the outer and innermost layers of the wall are involved. The invaginated host plasmalemma, which surrounds the body of the haustorium, has a furrowed surface and in the adjacent haustorial sheath fibrillar elements are prominent. The plasmalemma furrows and the sheath fibrillar elements are discussed in relation to the organization of the structure of the sheath and absorption of materials through it.

Fibrillar Structure of Starch. Evidence for Crossed Fibrils from Incipient Gelatinization

AbstractBy being brought to the threshold of gelatinization through careful heating in water, grains of native potato starch often were induced to swell differentially. At 55°C, radial elements (sectors) of the interior of these grains contracted centrifugally and expanded tangentially while the rigid exterior remained mostly unswollen and therefore was burst open due to the swelling of the interior. Evidence from the light microscope, the polarizing microscope, and the scanning electron microscope showed clearly the presence of radially oriented and near radial, crossed fibrillar elements, each of which traversed many lamellae, in the ungelatinized region. No ‘core’ was evident in the burst starch grain, nor was there any separation of lamellae.