Outer Cap Research Articles

Septal Plugs in a Green Alga

Septal plugs, resembling those found in red algae, occur in the transverse wall between all cells in a newly discovered marine green alga, Pilinia earleae Gallagher & Humm.3 No plasmodesmata traverse the cross-wall, and the septal plug blocks cytoplasmic continuity between cells. The septal plug consists of an electron-translucent core bordered at each end by two electron-opaque caps. Cytochemical procedures demonstrate that the plug consists of protein and polysaccharide, but lacks peroxidase. The outer cap is highly proteinaceous while the inner cap is composed primarily of polysaccharide. The plug core is not routinely stained by Coomassie Blue but it is pronase sensitive and probably proteinaceous. Historically, septal plugs have been considered unique to the red algae and the fungi, but ultrastructural and biochemical data provide no support for derivation of the septal plug in this green alga from a symbiotic relationship. The discovery of septal plugs in a green alga makes the hypothesis of an independent origin of this structure in a number of plant groups more likely.

SEPTAL PLUGS IN A GREEN ALGA

Septal plugs, resembling those found in red algae, occur in the transverse wall between all cells in a newly discovered marine green alga, Pilinia earleae Gallagher & Humm.3 No plasmodesmata traverse the cross‐wall, and the septal plug blocks cytoplasmic continuity between cells. The septal plug consists of an electron‐translucent core bordered at each end by two electron‐opaque caps. Cytochemical procedures demonstrate that the plug consists of protein and polysaccharide, but lacks peroxidase. The outer cap is highly proteinaceous while the inner cap is composed primarily of polysaccharide. The plug core is not routinely stained by Coomassie Blue but it is pronase sensitive and probably proteinaceous. Historically, septal plugs have been considered unique to the red algae and the fungi, but ultrastructural and biochemical data provide no support for derivation of the septal plug in this green alga from a symbiotic relationship. The discovery of septal plugs in a green alga makes the hypothesis of an independent origin of this structure in a number of plant groups more likely.

局部義歯の維持装置に関する一考察

Based on clinical experience over ten years, provision of ridge support for fabrication of removable partial denture was considered to be important for support and stability of the dentures.About 1960, Dr. K.H. Körber improved some disadvantages of the old telescope system and developed so-called Konuskronen telescope. Many clinical results have been reported, since the theoretical background and prognosis of the new device were introduced to Japan.It is without doubt a superb device, however, avthor has experienced some difficulty in it, as follows:1) In the case where anterior teeth are the abutments, those are replaced by full-veneered gold crowns. when the partial denture is removed, anterior gold crowns show. This may cause an esthetic problem, which delicately affects to the patient's psychology.2) Retention of Konuskrone is derived from the forces of friction between inner and outer caps. In this mechanism, very slight space is required between the occlusal surface of an inner cap and the inside of an outer cap. The existence of this space, however, causen such problems as follows:(a) Substance of an outer cap of an abutment tooth at the time when it functions, may loose centric stops.(b) When veneered with resin on the outer cap and if shoulder is made at the cervical part of an inner cap, the retention may be lost due to contact of this part.It is considered, as a counterplan, that the shoulder part of an outer cap should be cut away slightly or an inner cap to be tapered. The former has a demerit in plaue intrusion, while the latter in contour of an outer cap.(c) The support depending merely upon the effect of friction, author feels, show some difficulties in revelation of such grasping force as per an operator intends, and in adjusting at the time supporting force decreases after years later.In order to overcome these disadvantages, author has conceived a new supporting device combining those advantages of the abovementioned device with I.C. attachment. Author has obtained, thereupon, good results in clinical application. Since the device has been newly conceived, author will need time to observe and pursue the prognosis after years.

Ultrastructure of septal pore apparatus in the lamellae of Nematoloma puiggarii

The lamellae of Nematoloma puiggarii have dolipore–parenthesome septa like the majority of the basidiomycetes. The septal pore canal is almost always transected by a central electron-dense zone. Often two more electron-dense zones, one on each side of the central one, are present in the canal. Pore canal openings are normally occluded by granular electron-dense plugs which are ring like in subbasidial and subhymenial septa and appear solid in some tramal septa. A hemispherical fibrous outer cap is always present outside the parenthesomes of subhymenial septa. Tramal septa do not have outer caps, and the subbasidial septa have them only on the subhymenial sides. The outer caps are usually delimited externally by either the cisternae of endoplasmic reticulum or by the tonoplast of adjacent vacuoles.

The fine structure of septal pore apparatus in the lamellae of Pholiota terrestris

The lamellae of Pholiota terrestris, when viewed in thin sections cut perpendicular to the hymenial surface, consist of a hymenial layer of basidia and scattered cystidia, an interwoven subhymenium, and a trama. The inner trama is composed of a zone of relatively large, vacuolated hyphal elements, whereas the outer trama consists of smaller hyphal elements with relatively dense cytoplasmic contents. The septal pore apparatus throughout the lamellae are similar to those described in most other Homobasidiomycetes and saprobic Heterobasidiomycetes. In the center of the septal pore there is a narrow electron-dense zone that intersects the pore canal. In some septal pores similar electron-dense zones occur near one or both orifices. The septal cap consists of three membranes, of which the two defining membranes appear clearly tripartite in cross section. The pores in the septal cap are arranged hexagonally and are 70–105 nm in diameter. The proximal septal caps of the subbasidial septa and those in the subhymenium develop an electron-dense, granular outer cap that is usually delimited externally by endoplasmic reticulum or, less often, by the tonoplast of an adjacent vacuole. The septal pores of the subbasidial septa become plugged by the expanded septal swelling following basidiospore discharge. The septal pore apparatus in the trama are not associated with outer caps; however, many septal pores in the trama become occluded with electron-dense plugs near both orifices. The observations of the septal pore apparatus in the lamellae of P. terrestris are compared with studies of other Homobasidiomycetes and saprobic Heterobasidiomycetes.

Hyphal ultrastructure in fruit-body primordia of the basidiomycetesSchizophyllum commune andCoprinus cinereus

Light and electron microscopic investigations of fruit-body primordia of the basidiomycetesSchizophyllum commune andCoprinus cinereus showed that hyphal fusions are common in specific areas of the fruit-body primordia of both species. In these areas conspicuous amounts of a mucilaginous substance occur between the closely packed hyphae. A possible function of this mucilage is to aid the adhesion of hyphae prior to fusion. In the fruit-body primordium ofCoprinus cinereus the dolipore/parenthesome septum is surrounded by an additional hemispherical membranous cap (outer cap). Such a cap was never found inSchizophyllum commune fruit-body primordia.

A HISTOCHEMICAL STUDY OF PHENOLIC MATERIALS IN MYCORRHIZAL AND UNINFECTED ROOTS OF EUCALYPTUS FASTIGATA DEANE AND MAIDEN

SUMMARYThe distribution of phenols in uninfected and mycorrhizal Eucalyptus fastigata roots has been examined by application of a range of histochemical tests to thin sections.The vacuoles of most cap cells and many epidermal cells of E. fastigata mycorrhizas contain considerable quantities of phenolic materials. Cap cells of uninfected fine roots similarly contain materials with the staining properties of phenols, but uninfected root epidermal cells rarely do. It is suggested that accumulation of phenols in the epidermal cells of mycorrhizas is a response to the presence of the fungal symbiont. Further evidence is provided that the hyphae of the fungal symbiont penetrate and grow through the phenolic materials of the outer root cap cells. No evidence was found to suggest that these areas contain appreciable quantities of polysaccharide.Phenols were also detected in the endodermis and outermost layer of cortical cells. Judged on their staining reactions, these seem to be chemically different from those of the cap and epidermis. They are present in both mycorrhizal and uninfected roots, but appear much closer to the tip in the former. The outer layer of cortical cells has other specialized features, including the presence of a suberin layer in the walls, which are characteristic of mature differentiated endodermal cells in E. fastigata. These features are discussed from the viewpoint that the outer cortical layer acts as a barrier to further hyphal penetration in eucalypt mycorrhizas.

A HISTOCHEMICAL STUDY OF POLYSACCHARIDE DISTRIBUTION IN EUCALYPT MYCORRHIZAS

SUMMARYThis paper describes a histochemical study of the distribution of polysaccharides in un‐infected and mycorrhizal Eucalyptus fastigata roots. The most striking influence of mycorrhizal infection is the suppression of starch accumulation in the root cap cells and meristematic region of the root. In addition, there is a very substantial reduction in the amount of acidic polysaccharide (root cap slime) accumulated around the outer root cap cells in mycorrhizal roots, compared with uninfected roots. These observations generally hold for roots collected from a wide variety of conditions and at different times of the year. The reduction in amounts of these two important polysaccharides is presumed to result from lack of availability of precursors for polysaccharide synthesis, due to diversion of carbohydrate into the fungus partner. The histochemical observations in E. fastigata mycorrhizas are thus in accord with experimental data from other mycorrhizas which indicate transfer of large quantities of carbohydrate from root to fungus, and suggest that carbohydrate transfer is likely also to occur in mycorrhizas of E. fastigata.

The Integrity and Organization of Nuclear DNA in Cells of the Root Cap of Zea mays probed by Terminal Deoxynucleotidyl Transferase and Microdensitometry

Summary A search was made for strand-breaks in the DNA of nuclei in different regions of the root cap of Zea mays using terminal deoxynucleotidyl transferase and 3 H-dCTP. Quantitative autoradiography of the resulting reaction product showed that DNA strand-breaks do not accumulate as the cells pass from a proliferative state in the cap meristem to a degenerative state on the outer surface of the cap. A microdensitometric investigation of root cap nuclei with a 4 C DNA content showed that the proportion of dense chromatin is higher in the outer cap cells than it is in either the central or meristematic cells.

Adventitious Root Development from the Coleoptilar Node in Zea mays L.

Department of Botany and Bacteriology, University of Arkansas, Fayetteville, Arkansas 72701 Zea mays L. root development from the coleoptilar node was observed by light and electron microscopy. Roots developed opposite collateral vascular bundles in the coleoptilar nodal region. Three distinct histogens (stelar, cortical-protoderm, and root cap) became evident in early development. In median sections of the young roots, root cap and cortical regions formed a “hat” configuration over the stelar region. As the root matured, this “hat” developed centripetally to encapsulate the stelar region. Central core cells of the root cap were characterized by having numerous dictyosomes, amyloplasts, vacuoles, and thin cell walls. As these cells matured into outer or peripheral cap cells, the Golgi vesicles became hypertrophied. These hypertrophied vesicles contained a granular PAS-positive material which accumulated between the plasma membrane and the cell wall and formed a thick layer. As the PAS-positive material passed through the cell wall, it changed to a fibrillar texture. A PAS-positive material similar to that in the outer root cap cells was found adjacent to the outer walls of the protodermal cells. In median sections, PAS-positive material was not present in the promeristem region. Root cap cells as well as parent cortical cells were crushed as the young root forced its way through the parent tissue.

ADVENTITIOUS ROOT DEVELOPMENT FROM THE COLEOPTILAR NODE IN ZEA MAYS L.

Department of Botany and Bacteriology, University of Arkansas, Fayetteville, Arkansas 72701Zea mays L. root development from the coleoptilar node was observed by light and electron microscopy. Roots developed opposite collateral vascular bundles in the coleoptilar nodal region. Three distinct histogens (stelar, cortical‐protoderm, and root cap) became evident in early development. In median sections of the young roots, root cap and cortical regions formed a “hat” configuration over the stelar region. As the root matured, this “hat” developed centripetally to encapsulate the stelar region. Central core cells of the root cap were characterized by having numerous dictyosomes, amyloplasts, vacuoles, and thin cell walls. As these cells matured into outer or peripheral cap cells, the Golgi vesicles became hypertrophied. These hypertrophied vesicles contained a granular PAS‐positive material which accumulated between the plasma membrane and the cell wall and formed a thick layer. As the PAS‐positive material passed through the cell wall, it changed to a fibrillar texture. A PAS‐positive material similar to that in the outer root cap cells was found adjacent to the outer walls of the protodermal cells. In median sections, PAS‐positive material was not present in the promeristem region. Root cap cells as well as parent cortical cells were crushed as the young root forced its way through the parent tissue.

Cytochalasin B, but not colchicine, inhibits migration of secretory vesicles in root tips of maize.

The effects of colchicine and cytochalasin B on the structure of dictyosomes of maize root tips were studied. Colchicine did not significantly affect dictyosome structure or change the distribution of dictyosome-derived secretory vesicles. Cytochalasin B did not significantly change dictyosome structure or intercisternal fibers, but did alter markedly the distribution of the secretory vesicles in both the epidermal and outer cap cells. With cytochalasin B, the vesicles accumulated in a region close to their site of formation and did not migrate to the cell surface. The results show that a cytochalasin B-sensitive subcellular component is involved in the vectorial movement of secretory vesicles from sites of formation at dictyosomes to sites of fusion at the cell surface.

Differentiation of septal ultrastructure according to cell type in the basidiomycete, Agrocybe praecox

The gill of the Agrocybe fruit body is composed of three regions: the outer hymenium, the subhymenium, and the central trama. Hyphae within each of these regions contain dolipore/parenthosome septa; however, the septa present in subhymenial hyphae are further characterized by a novel outer hemispherical cap of fibrillar material that covers the parenthosome. This outer cap is absent from hymenial and tramal septa. Hyphae from subhymenial/hymenial transition zones possess the outer cap only on the subhymenial side of the septum.

A possible role for intercisternal elements in the formation of secretory vesicles in plant Golgi apparatus.

ABSTRACT Oriented fibres in the intercisternal regions of plant dictyosomes are usually associated with flattened portions of cisternae. In outer cap cells of maize roots, however, the intercisternal fibres are associated mainly with unique secretory vesicles which are elongate or kidney-shaped during their formative stages. Fibres are oriented parallel with the long axes of the vesicles even at early stages of vesicle formation. Because of their early presence and orientation, the fibres may aid in organizing and/or shaping the secretory vesicles in this tissue.

Effects of Cytochalasin B on the Golgi Apparatus of Maize Root Cells

Seedlings of maize (Zea mays L.) var. WF-9 X M-14 were exposed to cytochalasin B for 1/2, 1, and 2 hr at concentrations of 0, 10, and 100 ppm. The root tips were then fixed for electron microscopy and the epidermal and outer cap cells examined for changes in dictyosome form, intercisternal fibers or secretory vesicles.Cytochalasin B did not cause significant changes in dictyosome form (Fig. 1) or intercisternal fibers. However, it did induce alterations in the distribution patterns of Golgi apparatus-derived secretory vesicles.In epidermal and outer cap cells of the maize root, following cytochalasin B treatment, secretory vesicles accumulated within the central portions of the cytoplasm in those regions occupied by Golgi apparatus (Fig. 2, 3). Cytoplasmic regions along the cell surface were devoid of secretory vesicles, and very few vesicles were found at the cell surface (Fig. 2, 3). We interpret these findings to mean that secretory vesicles formed by the Golgi apparatus did not move to the cell surface, but accumulated at or near their sites of origin following treatment with cytochalasin B.

Cell wall and plasmalemma modifications in diseased and injured plant tissues

Pathological modifications in structure at the cell wall – plasmalemma interface are common in diseased plant tissues. These modifications vary from small, localized structures which invaginate the protoplast to large, irregularly contoured elaborations which envelop haustoria. Some published electron micrographs suggest that the plasmalemma may be discontinuous in areas adjacent to modified cell walls. Structural changes in cell walls, similar to those in diseased plants, are common in plant roots exposed to uranyl acetate. In such roots, the plasmalemma appeared distinctly discontinuous in cells with highly modified walls, whereas it was continuous in adjacent cells with little or no wall modification. In both types of cells, internal membranes and organelles appeared normal. This suggests that the breaks seen in the plasmalemma were not fixation artifacts. In untreated roots, apparent discontinuities in the plasmalemma were observed only in secretory outer root cap cells which contained masses of mucilaginous material between the wall and protoplast. Since uranyl treatment does not increase the rate of electrolyte loss from tissue, these observations suggest that modified cell walls may assume some of the permeability functions usually attributed to the plasmalemma.

Tooth development in sharks

The histogenesis of tooth development in five species of sharks was investigated by the use of light microscopy, microradiography and electron microscopy. The highly mineralized outer cap of tissue on shark teeth is not enamel but a form of modified dentine. The organic matrix of the entire crown is formed by odontoblasts and laid down on the pulpal side of the basement membrane. The sequence in which the organic matrix of the crown is formed and the sequence of mineralization in these tissues demonstrate that the highly mineralized outer layer of shark teeth is not homologous to ectodermal enamel. The function of the inner dental epithelium of shark tooth germs is apparently limited to induction, morphodifferentiation and protection of tooth germs during development.

The use of radioautography for investigating wall secretion in plant cells

The paper summarises results of simple radioautographic experiments using tritiated glucoses to investigate wall secretion in plant cells. In outer root cap cells, labelled material was first concentrated in the Golgi bodies; it later appeared in vesicles, and was incorporated into the wall immediately under the plasmalemma. It finally collected mainly in the slime layer surrounding the root tip. Biochemical analyses have indicated that this material was pectic in nature. In inner root cap and epidermal cells, labelled material incorporated into the walls and also the cell plates of dividing cells was also apparently mainly derived from Golgi bodies. In meristematic (less differentiated) cells, however, the endoplasmic reticulum was more frequently labelled than the Golgi bodies near walls that had incorporated derivatives of labelled glucose. Considerable incorporation of labelled derivatives into the wall thickenings in coleoptile xylem cells was often detected; nearby elements of the endoplasmic reticulum were again frequently labelled in these cells and less often, Golgi bodies and the cytoplasm in the region occupied by microtubules contained radioactivity. Labelling of starch grains in the plastids was generally observed, but not in cells secreting large amounts of wall materials (outer root cap and older xylem cells); however, addition of larger amounts of exogenous glucose to outer root cap cells, following their incubation in tritiated glucose, promoted such incorporation. The paper finally sets forth some considerations on experimental techniques for radioautography that might be of more general application.

Golgi apparatus mediated polysaccharide secretion by outer root cap cells of Zea mays

In the outer cap cells of roots of Zea mays, secretion is accompanied by hypertrophy of dictyosome cisternae with formation of large secretory vesicles. Vesicle contents are subsequently released from the protoplast by fusion of the vesicle membrane with the plasma membrane. The secreted material, a highly hydrated polysaccharide, was localized intracellularly by the periodic acid-Schiff reaction. Under appropriate conditions, the product moves outward through the cell wall after discharge from the protoplast, and appears as a droplet adhering to the root tip. Under conditions where the secretory product accumulates at the inner wall surfaces, no external droplet is formed.The secretory activity has an active phase that is sensitive to metabolic inhibitors and influenced by temperature (Q10>2), and a passive phase that is independent of temperature, insensitive to metabolic inhibitors but sensitive to osmotic agents. The active phase is characterized by a temperature-independent periodicity (3 hours). Sucrose supplied to the growth medium increases the amount of polysaccharide secreted. Polysaccharide synthesis, segregation into vesicles, and discharge from the protoplast are assumed to require active metabolism; the step involving extrusion of polysaccharide through the cell wall region appears to be a passive process influenced by the degree of hydration of the polysaccharide and by cell turgor.

The fine structure of the centriolar apparatus and associated structures in the complex flagellates Trichonympha and Pseudotrichonympha

The centriolar apparatus in the flagellate genera Trichonympha and Pseudotrichonympha is located at the anterior end of the cell, in the rostrum. It forms part of a complex system of structures which includes the rostral tube, inner and outer caps, and the rostral flagella. The fine structure of these organelles is described in detail on the basis of an electron-microscope study of sectioned and negatively stained material. In Trichonympha the rostral tube is a hollow cylinder, made of a cross-striated protein with a periodicity of about 450 Å. This is organized into radially arranged lamellae, which continue posteriorly as the parabasal filaments. The tube is continuous anteriorly with two finely striated crescentic bodies, which correspond to the so-called short centrioles of some previous workers. There is no evidence that they are centriolar in function. In the interphase cell the centriolar apparatus consists principally of a long centriolar rod, of complex fine structure, lying in the anterior end of the rostral tube. There is no evidence of typical centriolar structure in this, but at division an aster forms around one end of it. Surmounting the apex of the rostral tube is a dense, finely fibrous body, the inner cap. Lying within this there is a typical centriole (similar in structure to a basal body), and also the basal body of one flagellum, which appears to be distinct from all the rest. The functions of these two structures are not known. The margin of the inner cap connects with the complex system of delicate fibres which links the basal bodies of the rostral flagella. The function of the fibres, and possibly also of the inner cap, may be to coordinate the activities of the rostral flagella. The outer cap is composed mainly of tubules, 250 Å in diameter, but shows variations in structure in different species. The structures in Pseudotrichonympha which presumably serve similar functions are in many respects very differently organized. The rostral tube is more complex, with distinct inner and outer walls of different fine structure. There are also complex inner and outer surface layers. A striking feature is that although the various components of the tube are quite different in structure, they display a common periodicity in their organization. The centriolar apparatus appears to consist principally of two dense bands running along the inner wall of the tube, connecting anteriorly to an extended layer of centriolar material to which spindle fibres are attached in radially polarized fashion throughout interphase. There is no centriolar rod or typical centriole, such as is found in Trichonympha . Very elaborate systems of fibres are associated with the inner cap and the anterior end of the rostral tube. The two genera are compared, and the findings related to knowledge of centriolar structures in other types of cell. Possible evolutionary explanations for the complexity and variation in fine structure in these flagellates are considered.