I Lomasomi: Loro Probabili Rapporti con la Crescita per Distensione della Parete Cellulare

Abstract

« Lomasomes »: their probable role in the expansion growth of the cell wall. — It was previously reported that lomasomes are present in higher plant cells. In a preliminary comunication Authors described the morfological characteristics of the lomasomes and their position in the cell. It was shown that lomasomes vary in organization which appears to be granular or vescicular and in distribution along the cell wall. Both these characters seemed directly related with the level of cellular differentiation.

In this paper it has been reported that the number of lomasomes per cell was sharply decreased when Avena Coleoptiles were illuminated per 3 hours. During this period of time also the growth of the Coleoptiles was inhibited about 8%. These data seem favorable to the hypothesis that lomasomes are tigtly involved in the mechanisms controlling the expansion growth of the cell wall.     

Una Struttura Comparabile Con I Lomasomi Nelle Cellule Austoriali di Cuscuta Pentagona Engelm

Abstract

A structure comparable with the lomasomes in baustorial cells of « Cuscuta pentagona » Engelm. — Electron microscopic observations of haustorial cells in « Cuscuta pentagona » revealed to the A. the presence of some vesicular structures, outside the plasma membrane, comparable to the lomasomes of Moore and McAlear. The vesicles usually group in a bag of the plasma membrane and show an envelope consisting of unit membrane; their shape and size are variable and some of them are not well distinct while some others show ribosome-like bodies inside .In the examined cells the plasma membrane shows prominences which are in connection with the vesicle membrane, so that the A. thinks it possible the derivation of the vesicles from the peripherical cytoplasm. The function of these structures is not yet explained; they are only found in non photosyntetic cells, such as some Mycophyta, dark grown « Avena » coleoptiles and dodder's haustorial cells. The previously ultrastructural researchs on dodder have not pointed out lomasomes, which seem to be exclusive of the haustoria, so that it is possible to suppose a connection between the lomasome function and that of the haustoria.     

The tubular network of the Golgi apparatus

 Golgi apparatus of both plant and animal cells are characterized by an extensive system of approximately 30 nm diameter peripheral tubules. The total surface area of the tubules and associated fenestrae is thought to be approximately equivalent to that of the flattened portions of cisternae. The tubules may extend for considerable distances from the stacks. The tubules are continuous with the peripheral edges of the stacked cisternae, but the way they interconnect differs across the stack. In plant cells, for example, tubules associated with the near-cis and mid cisternae often begin to anastomose close to the peripheral edges of the stacked cisternae, whereas the tubules of the trans cisternae are less likely to anastomose and are more likely to be directly continuous with the peripheral edges of the stacked cisternae. Additionally, the tubules may blend gradually into fenestrae that surround some of the stack cisternae. Because of the large surface area occupied by tubules and fenestrae, it is reasonable to suppose that these components of the Golgi apparatus play a significant role in Golgi apparatus function. Tubules clearly interconnect closely adjacent stacks of the Golgi apparatus and may represent a communication channel to synchronize stack function within the cell. A feasible hypothesis is that tubules may be a potentially static component of the Golgi apparatus in contrast to the stacked cisternal plates which may turn over continuously. The coated buds associated with tubules may represent the means whereby adjacent Golgi apparatus stacks exchange carbohydrate-processing enzymes or where resident Golgi apparatus proteins are introduced into and out of the stack during membrane flow differentiation. The limited gradation of tubules from cis to medial to trans offers additional possibilities for functional specialization of Golgi apparatus in keeping with the hypothesis that tubules are repositories of resident Golgi apparatus proteins protected from turnover during the flow differentiation of the flattened saccules of the Golgi apparatus stack. Accepted: 3 November 1997     

Ultrastructure of Acrasis rosea,a Cellular Slime Mold,During Development*

SYNOPSIS. An ultrastructural study of the myxamoebae of Acrasis rosea in the vegetative, aggregative and culminative stages was made. An intracytoplasmic system of microfibrillar bundles develops as the cells enter the aggregative stage and commence the morphogenetic sequence leading to the construction of a fruiting body. The fibrillar bundles disappear in the cells of the mature fruiting body. No relevant ultrastructural differences were observed between spores, stalk cells and microcysts. Each of these cells is surrounded by a single-layered coat of fibrillar material that is oriented parallel to the cell surface. Tubular structures were observed between the plasma membrane and the cell coat. The tubules may be layered along the cell periphery or they may be recessed in pockets formed by the plasma membrane. They resemble lomasomes typical of fungal cells. The myxamoebae of A. rosea clearly differ from the Dictyostelium-type myxamoebae in mitochondrial structure, the presence of lamellate structures in the nucleolus and the absence of prespore vacuoles.     

The membrane systems of the cardiac muscle cell of Meganychtiphanes norvegica (M. Sars), euphauciacea,crustacea

Summary The membrane systems of cardiac muscle cells of the euphausiacean Meganychtiphanes norvegica are described. Transverse tubules are found both at the Z-band level (T_z-tubules) and at the H-band level (T_h-tubules). Within the sarcomere narrow longitudinal tubules branch off from the T_z-tubules. At the H-band level these tubules expand forming flattened cisternae in dyadic and triadic couplings with the sarcoplasmic reticulum (SR). Adjacent myofibrils are separated by a well developed SR. Modifications of the SR are seen at the H-band level where junctional cisternae are formed.     

THE HOST-PARASITE INTERFACE OF ALBUGO CANDIDA ON RAPHANUS SATIVUS

The fine structure of the intercellular hyphae of the obligate parasite Albugo candida infecting radish does not differ markedly from that described previously for cells of Peronospora manshurica. The stalked, capitate haustoria do not contain nuclei and are packed with mitochondria and lomasomes. The fungal plasma membrane and cell wall are continuous from the intercellular hypha throughout the haustorium except that there is no evidence of fungal cell wall around a portion of the haustorial stalk proximal to the haustorial head. Within the vacuolate host mesophyll cell, the haustorium is always surrounded by host plasma membrane and with at least a thin layer of host cytoplasm. The host cell wall invaginates at the point of haustorial penetration to form a short sheath around the region of penetration, but normally there is no host cell wall around the balance of the haustorium. About 1% of the haustoria observed were necrotic, and these were invariably walled-off completely from host cytoplasm by host cell wall. An amorphous, moderately electron-dense encapsulation lies between the haustorium proper and the host plasma membrane and extends into the penetration region between the sheath and the fungal cell wall. Invaded host cells contain more ribosomal-rich ground cytoplasm than uninfected cells. Glandular-like systems of tubules and connecting vesicles are often numerous in host cytoplasm in the vicinity of haustorial heads. These tubules open into the encapsulation, their limiting unit membranes being continuous with the host plasma membrane. We suggest that these represent a secretory mechanism of the host specifically induced by the parasite.     

Membrane Dynamics of the Contractile Vacuole Complex of Paramecium1

ABSTRACT. Membrane dynamics of the contractile vacuole complex of Paramecium were investigated using conventional electron microscopy of cells so that the vacuoles were serial-sectioned longitudinally and transversely. During systole, vacuolar membrane collapses first into flattened cisternae which undergo further modification into a mass of interconnected small membrane tubules. These tubules retain their connections with the radiating microtubular ribbons; consequently they are found only in the poleward hemisphere. Permanent connections between ampullae and the collapsed vacuole membrane could not be verified nor was a sphincter-like mechanism for closing such a junction observed. Membranes of the ampullae and the collecting canals also collapse to varying extents into arrays of tubules that remain bound to microtubular ribbons during diastole. Thus vacuole, ampullae, and collecting canal membranes all assume tubular forms when internal volume is at a minimum. Having failed to observe a microfilamentous encasement of the vacuole, we suggest that an alternative mechanism for the “contractile” function should be sought. One such is based on fluid volume increase and fluid flow within transiently interconnected tubular membrane systems that cycle between a tubular and a planar membrane form as internal volume is periodically increased and reduced. The driving force for this mechanism might best be sought in the molecular structure of the membranes of the contractile vacuole complex.     

Ultrastructural studies on the secretory cavities ofCitrus deliciosa ten. I. Early stages of the gland cells differentiation

Summary Secretory cavities ofCitrus deliciosa seem to originate from a pair of meristematic cells (an epidermal cell and a second one placed under it). These cells undergo successive divisions resulting in the formation of a globular/oval gland situated in the parenchyma, and a conical stalk, which joins the gland with the epidermis. The young gland consists of a central group of polyhedral cells ensheathed by layers of radially flattened cells.During the early differentiation stages of the gland cells a close association of cytoplasmic microtubules with various organelles is observed. Plastids increase progressively in number and size and their matrix locally contains tubular networks accompanied by small oil droplets. In peripheral cytoplasm numerous myelin-like lomasomes have been observed. Peripheral cells of the gland are gradually modified from the inner cells following a different developmental pattern. Their walls become thicker and plastids do not contain tubular complexes, but only a few thylakoids partly surrounding the newly formed starch grains.     

Ultrastructure of the myocardial cell and its membrane systems in the adult fly Calliphora erythrocephala (Insecta: Diptera)

Summary Calliphora erythrocephala has cross-striated cardiac muscle cells with A, I and Z-bands. The diameters of the myosin and actin filaments are 200–250 Å and 85 Å respectively and the length of the myosin filaments (A-band) is approximately 1.5 . Usually 8–10 actin filaments surround each myosin filament.The myocardial cells show a well-developed membrane system and interior couplings. A perforated sheet of SR envelopes the myofibrils at the A-band, dilates into flattened cisternae at both A-I band levels before it merges into a three-dimensional net-work between the actin filaments of the I-bands and between the dense bodies of the discontinuous Z-discs. The T-system consists of broad flattened tubules running between the myofibrils at the A-I band levels forming dyads with the SR-cisternae. Longitudinal connections between the transverse (T-) tubules often occur.It is suggested that this well-developed SR may be an adaptation to facilitate a rapid contraction/relaxation frequency by an effective Ca²⁺ uptake.     

Elektronenmikroskopische Untersuchung alternder Zellen von Pseudomonas rhodos

During a 10 day-incubation on agar surfaces at 30°C, cells of the gram-negative soil bacterium Pseudomonas rhodos pass through three phases distinguishable by physiological and morphological criteria. When viewed by electron microscopy, typically “rolled” mesosomes could frequently be observed in young cells. In aged cells instead, loosely rolled or stretched-out, flattened tubules could be discerned, presumed to be degenerate mesosomes. Tubular flattened structures have been isolated from these cells by lysozyme treatment or sonication and were concentrated by differential centrifugation. Electron micrographs of these preparations showed long, straight tubules which sometimes appeared sealed at one end. Their width was 34±5 nm. They contained a lining of material, which could be digested by trypsin leaving behind an electron-transparent matrix. In rare cases, isolated tubules showed a periodic fine structure composed of ellipsoidal subunits. Optical diffraction analysis yielded a lattice consisting of subunits arranged in helices of pitch-angle 27°; the unit cell dimensions were shown to be 112×56 Å. Owing to their sensitivity to trypsin, components of the regular lattice are supposed to consist of protein. It is postulated that these protein components are layered onto a tubular membrane. These tubules are clearly distinguishable by their shape and fine structure from the periodic structure of a P. rhodos cell wall layer, which exhibits a tetragonal pattern, and also from polyheads and polysheaths of defective bacteriophages. Their possible origin from intact mesosomes is discussed.     

ULTRASTRUCTURE OF THE CONCHOCELIS STAGE OF THE MARINE RED ALGA PORPHYRA LEUCOSTICTA1

The ultrastructure of the Conchocelis or filamentous stage of Porphyra leucosticta was investigated. Each cell contains 1 or 2 parietal, stellate chloroplasts with a single pyrenoid in each chloroplast. The centrally located nucleus is irregularly shaped and contains 1–2 nucleoli. The cytoplasm has typical floridean starch grains and nonmernbrane-bound lipid bodies. The cell wall is divided into an outer and an inner wall. Many lomasomes are associated with the cell membrane. Pit connections are found between cells, and their taxonomic significance is discussed.     

The zoospore and meiospore of the aquatic phycomyceteCatenaria anguillulae

Summary The zoospore and meiospore of the aquatic phycomyceteCatenaria anguillulae (Phycomycetes, Blastocladiales, Catenariaceae) have a nuclear cap enclosing the cellular ribosomes within a double membrane, and a side body complex which is very similar to that observed in zoospores ofBlastocladiella andCoelomomyces and is structurally related to the side body complex observed in spores ofAllomyces. The structural organization of the side body complex and striated rootlet is analyzed from serial sections.The meiospore also contains an array of flattened cisternae which are in direct contact with, and appear to be derived from, the outer nuclear membrane and the backing membrane of the side body complex.The structural organization of the zoospore and meiospore ofC. anguillulae is compared to and contrasted with the structural organization observed in spores of members of theChytridiales, Blastocladiales, Monoblepharidales, andHarpochytriales. It is concluded that the structural organization of the spores of theBlastocladiales, Monoblepharidales, andHarpochytriales is similar, and affinities in spore organization can be found in some members of theChytridiales.     

MICROTUBULE ARMS AND CYTOPLASMIC STREAMING AND MICROTUBULE BENDING AND STRETCHING OF INTERTUBULE LINKS IN THE FEEDING TENTACLE OF THE SUCTORIAN CILIATE TOKOPHRYA

Microtubules attached to the pellicle at the tips of tentacles pivot through about 140° on these attachments, splay apart, and bend along their longitudinal axes when feeding occurs. The tubules could be bending in response to pellicular contractions; active bending, sliding, or contraction of the tubules may not be involved. Intertubule links apparently prevent tubules from splaying apart at certain levels. These links are probably under tension during feeding. They stretch; they sometimes become half as thick and eight times as long as they are before feeding. Often, tubules joined together by these links also change in shape; they become slightly flattened and elliptical in cross section. Cytoplasm from the ciliate Tetrahymena is drawn down a feeding tentacle inside an invagination of the Tokophrya cell membrane from the tentacle tip. The positions of arm-bearing microtubules around such invaginations indicate that arms are involved in moving invaginations along. The edges of the perforated Tetrahymena cell membrane are "sealed" to the cell membrane of Tokophrya around each feeding tentacle tip.     

Transformational process of the endosomal compartment in nephrocytes of Drosophila melanogaster

Summary This study investigates by electron microscopy the transformational process of the endosomal compartment of the Drosophila nephrocyte, the garland cell, which occurs during endocytotic processing of internalized material. The endosomal compartment of the garland cell consists of a prominent tubular/vacuolar complex in the cortical cytoplasm. When internalization of coated pits is blocked at 29°C using the endocytosis mutant, shibire ^ts, the tubules gradually disappear after 7 min at 29°C. By 12 min at 29°C, the vauoles also disappear. Thus, the endosomal compartment appears to constantly undergo a transformational process that necessitates continuous replenishment by coated vesicles. The data suggest that the tubular component of the endosomal compartment gradually transforms into vacuoles by the expansion of the tubular membrane. The vacuoles then transform by invaginating into themselves, creating flattened cisternae. The electron-lucent substance in the lumina of the vacuoles appears to be extruded into the cytoplasm through the invaginating membrane. No shuttle vehicles such as vesicles or tubules could be identified that might have been involved in the transporting of endocytosed materials and membrane from the endosomal compartment to lysosomes or back to the plasma membrane.     

Ricerche istochimiche e al micro scopio elettronico sui tubi malpighiani di Dacus oleae Gmel.

Summary The Dacus oleae larva possesses four Malpighian tubules, two anterior and two posterior ones, which in pairs enter into a ureter. Before opening into the gut, at the level of the transition zone between the mid- and hindgut, each ureter is dilated into an ampulla.The anterior tubules are divided into four regions: distal, transition, middle and proximal ones: while in the posterior tubules only middle and proximal segments are detectable. The distribution of the enzyme systems is indicated in Fig. 3, while the ultrastructural organization which is typical of the cells composing the different regions is schematically represented in Fig. 1. According to the ultrastructural and enzymatic findings, and the discussion on this subject in the literature, the authors are led to assume that in the distal segment occurs the segregation of uric acid, urates and calcium salts. In the transition segment, and still more in the intermediate one, an indiscriminate transport of water and solutes occurs from the haemocoel into the lumen of the tubule by pinocytosis. A fraction of the catabolites is precipitated as chromolipoidal pigments. The transition stages between cytosomes and pigment are described. Along with secretory phenomena the resorption of useful substances occurs in the proximal region. A similar function is performed by the ureter. In the ampulla, which is characterized by a conspicuous system of deep tubular infoldings both at the apical and basal surfaces of its cells, a massive water resorption is presumed to occur.     

Identification and characterization of Toxoplasma SIP,a conserved apicomplexan cytoskeleton protein involved in maintaining the shape,motility and virulence of the parasite

Apicomplexa possess a complex pellicle that is composed of a plasma membrane and a closely apposed inner membrane complex (IMC) that serves as a support for the actin‐myosin motor required for motility and host cell invasion. The IMC consists of longitudinal plates of flattened vesicles, fused together and lined on the cytoplasmic side by a subpellicular network of intermediate filament‐like proteins. The spatial organization of the IMC has been well described by electron microscopy, but its composition and molecular organization is largely unknown. Here, we identify a novel protein of the IMC cytoskeletal network in Toxoplasma gondii, called TgSIP, and conserved among apicomplexan parasites. To finely pinpoint the localization of TgSIP, we used structured illumination super‐resolution microscopy and revealed that it likely decorates the transverse sutures of the plates and the basal end of the IMC. This suggests that TgSIP might contribute to the organization or physical connection among the different components of the IMC. We generated a T.gondii SIP deletion mutant and showed that parasites lacking TgSIP are significantly shorter than wild‐type parasites and show defects in gliding motility, invasion and reduced infectivity in mice.     

ULTRASTRUCTURAL STUDIES OF PINUS PINASTER NEEDLES: THE ENDODERMIS

The endodermis in the needles of Pinus pinaster was examined with light and electron microscopy. The endodermis is composed of very long, radially flattened cells, filled with a large central vacuole, which contains spherical dense bodies whose concentration decreases from the ends of the cell to the middle part. They are individually surrounded by a fine granular matrix. The central vacuole is bounded by a thick tonoplast. Other small, clear vacuoles are limited by a thin tonoplast. The parietal cytoplasm contains relatively few ribosomes, long slender chloroplasts, and lipid bodies. The smooth endoplasmic reticulum is highly developed along the tangential walls and frequently connected, or apposed, to the plasma membrane. Numerous primary pit fields are seen in the radial walls which are lignified and in the tangential walls; the latter exhibit a characteristic loosening of the outer layer of the wall. The lipid bodies are connected to endoplasmic reticulum tubules. The role of the endodermis in the active transport of water inside the needle is discussed in reference to previous physiological studies. The chemical composition of the vacuolar dense bodies is as yet unknown.     

Morphology of the intermediate stages in the lamellar to hexagonal lipid phase transition

Summary The addition of calcium to suspensions of egg phosphatidylcholine and cardiolipin converts multiwalled liposomes to the hexagonal (H_II) phase (Rand, R.P., Sengupta, S. (1972)Biochim. Biophys. Acta 255:484–492). We have studied this lamellar to hexagonal phase transition by freeze-fracture, thin-section electron microscopy, and X-ray diffraction and have morphologically characterized the intermediate stages. The first step in the transition involves the invagination and fusion of bilayers, marked by the appearance of lipidic intramembrane particles and crater-like indentations, as the large liposomes are converted to smaller flattened and elongated vesicles. The next step is the formation of tightly packed hexagonal arrays of tubules, each tubule being about 11 to 15 nm in diameter. These tubules are filled with fluid and a lipid bilayer forms the wall of each cylinder. Finally this tubular bilayer phase is converted to the hexagonal (H_II) phase, where the distance between tubes is 5.5 to 7.5 nm.     

Modifications ultrastructurales provoquees par Puccinia graminis f. sp. tritici chez le ble

Susceptible varieties of wheat infected withPuccinia graminis (Pers.) f. sp.tritici Eriks. &E. Henn. were studied using chlorotic samples fixed with glutaraldehyde and postfixed in potassium permanganate or osmium tetroxide. Intercellular mycelium and haustoria are surrounded with a thick wall covered with dense material. Many kinds of organelles or structures were found in the electron-dense cytoplasm of fungi: nucleus, mitochondria, endoplasmic reticulum and lomasomes. Golgi apparatus was not recognized. Haustorium is characterized by pinocytosis figures lined with fungal plasmalemma and by numerous mitochondria. The haustorium is enclosed in an encapsulation of electron-dense, fibrillar or granular material. The thickness of the encapsulation increases with age. A membrane, which seems to be continuous with the host plasmalemma, forms the interface between the encapsulation and the host cytoplasm. This membrane is invaginated by lomasomes and small vesicles occur in his vicinity. The origin of the encapsulation and of the encapsulation membrane remains unknown.Many host organelles (mitochondria, endoplasmic reticulum, nucleus, chloroplasts) are closely appressed to the encapsulation membrane. The host nucleus appears to encase the haustorium; the chloroplasts develop excrescences and are devoid of starch, while photosynthesis is reduced. A large number of mitochondria encircles the haustorium and may be related with respiratory increase in the host. Rough-surfaced endoplasmic reticulum develops into long threads. Lipid droplets were observed in the host infected cytoplasm.

---

Résumé L'étude de l'ultrastructure de variétés de Blé sensibles parasitées parPuccinia graminis (Pers.) f. sp.tritici Eriks. &E. Henn a été conduite sur des échantillons chlorotiques fixés à la glutaraldéhyde et postfixés par le permanganate de potassium ou l'acide osmique. Une paroi peu dense et recouverte d'exsudat entoure le mycélium intercellulaire et les haustorias. Le cytoplasme, dense aux électrons, renferme diverses structures ou organites: lomasomes, mitochondries, noyau, réticulum endoplasmique. Aucun dictyosome n'a été relevé. L'haustoria se caractérise par des figures de pinocytose qui tapissent la membrane plasmique et par la présence de nombreuses mitochondries. Une encapsulation de densité variable selon la fixation, encapsulation qui s'épaissit en vieillissant, sépare l'haustoria du protoplaste de l'hôte. Elle contient des produits fibrillaires ou granuleux, plus opaques aux électrons. La membrane qui recouvre l'encapsulation au contact du cytoplasme de l'hôte semble en continuité avec le plasmalemme de ce dernier. Elle est interrompue par des lomasomes et de nombreuses vésicules la cotoient. L'origine de l'encapsulation et de cette membrane demeure hypothétique.De nombreux organites de la plante (mitochondries, réticulum endoplasmique, noyau, chloroplastes) établissent des liens étroits avec le parasite. Le noyau devient lobé et les chloroplastes présentent parfois des excroissances. L'absence d'amidon indique un ralentissement de la photosynthèse. L'élévation du rythme respiratoire se traduit par la présence de nombreuses mitochondries qui encerclent l'haustoria. Le réticulum endoplasmique, souvent long et flexueux est riche en ribosomes. Le cytoplasme des cellules infectées contient des globules lipidiques.

---

---

Contribution No. 105 de la Faculté d'Agriculture, Université Laval, Québec 10e.     

Ultrastructure of the Flagellar Apparatus and Attachment of Herpetomonas ampelophilae in the Gut and Malpighian Tubules of Drosophila melanogaster1

Electron microscopy was used to examine the flagellar apparatus of Herpetomonas ampelophilae from the gut and malpighian tubules of Drosophila melanogaster. The flagellates attach to the microvilli either by weaving their flagella between the microvilli or by engulfing several microvilli with an external flagellar membrane. The first type predominated in the gut while the second type was limited to the malpighian tubules. Desmosomes were not involved in either type of attachment. A subpellicular collar with emerging microtubules was found to be adjacent to the desmosome of the flagellar pocket of herpetomonads in the gut.