The fine structure and function of the tentacle in Tokophrya infusionum

The feeding apparatus of Suctoria consists of long, thin, stiff tubes called tentacles. When a swimming prey attaches to the tip of the tentacle a number of events follow in rapid succession. The tentacle broadens, a stream of tiny granules starts to move upward at its periphery to the tip, the prey becomes immobilized and shortly thereafter the cytoplasm of the still living prey begins to flow through the center of the tentacle to the body of the predator. An electron microscope study of the tentacle in Tokophrya infusionum, a protozoan of the subclass Suctoria, has disclosed a number of structural details which help to clarify some of the mechanisms involved in this unusual way of feeding. Each tentacle is composed of two concentric tubes. The lumen of the inner tube is surrounded by 49 tubular fibrils most probably of contractile nature. In the inner tube the cytoplasm of the prey is present during feeding, and in the outer tube are small dense bodies. It was found that the dense bodies originate in the cytoplasm of Tokophrya. They have an elongate, missile-like appearance, pointed at one end, rounded at the other, and are composed of several distinct segments. At the tip of the tentacle they penetrate the plasma membrane, with their pointed ends sticking out. It is assumed that the missile-like bodies play a major role in the feeding process. Their composite structure suggests that they might contain a number of enzymes which most probably are responsible for the various events preceding the actual food intake.     

THE SYNTHESIS OF MICROTUBULE AND OTHER PROTEINS OF THE ORAL APPARATUS IN TETRAHYMENA PYRIFORMIS

Several proteins, including microtubule proteins, have been isolated from the oral apparatus of the ciliate Tetrahymena. The synthesis of these proteins has been studied in relation to formation of this organelle system by the cell. Electron microscopy has shown that the isolated oral apparatus consists primarily of basal bodies, pellicular membranes, and a system of subpellicular microtubules and filaments. Cilia were removed during the isolation; therefore none of the proteins studied was from these structures. Evidence was obtained from the study of total oral apparatus protein which indicates that at least some of the proteins involved in formation of this organelle system may be synthesized and stored in the cytoplasm for use over long periods. This pattern of regulation was found for three individual proteins isolated from the oral apparatus fraction after extraction with a phenol-acetic acid solvent. A different pattern of regulation was found for microtubule proteins isolated from the oral apparatus of Tetrahymena. The data suggest that microtubule proteins, at least in logarithmically growing cells, are not stored in a cytoplasmic pool but are synthesized in the same cell cycle in which they are assembled into oral structures.     

Ultrastructural Localization of Acid Phosphatase in Feeding Tokophrya infusionum*

A combined cytochemical and electronmicroscopic study of feeding Tokophrya revealed that it has 2 sources of acid phosphatase. One is from the prey, Tetrahymena, supplying newly formed food vacuoles with large amounts of enzyme. The other source is in Tokophrya itself, the enzyme being found in small vesicles, small dense elongate bodies surrounded by a membrane, or in residue vacuoles. It seems that the 2 former small structures contain insignificantly small amounts of phosphatase; however, large deposits of lead phosphate are present in residue vacuoles, former food vacuoles. Since Tokophrya has no cytopyge these vacuoles are not excreted. On the contrary, when feeding is resumed, they merge with food vacuoles, presumably supplying them with acid phosphatase. Whether this enzyme ultimately is derived from the prey Tetrahymena and persists undegraded in the residue vacuoles, or whether it is synthesized by Tokophrya cannot be determined from present work.     

Configurational changes in helical microtubule frameworks in feeding tentacles of the suctorian ciliateTokophyra

Microtubules at the tip of a resting (non-feeding) tentacle are arranged helically in two concentric tube-shaped arrays. The pitches of the helical paths followed by tubules in the two arrays differ. At the start of feeding these microtubules bend along their longitudinal axes and splay outwards and downwards away from the tentacle tip as it ‘everts’. Tubules in the two arrays slideacross each other as this occurs. Comparison of the fine structure of the tips of feeding and resting tentacles with a dynamic model of the microtubular framework indicates that movement of the tubules is not brought about by active sliding of the tubules against each other or by the action of contractile elements attached along the lengths of tubules. The tips of microtubules forming the inner tube may be pulled downwards by contractile elements in the tentacular pellicle; these tubules apparently push those in. the outer tube to their new positions. The pattern of configurational changes in a tentacle tip at the start of feeding appears to be largely defined by the elastic resistance of the microtubules to bending, and the ways in which tubules are packed and linked together and attached to the pellicle.     

THE AXOSTYLE OF SACCINOBACULUS : I. Structure of the Organism and Its Microtubule Bundle

The axostyle of the flagellate Saccinobaculus is a motile ribbon composed of microtubules, cross-bridged to form interconnected rows. We find a centriole-related row of dark-staining tubules near the nucleus at the anterior end of the axostyle. Other tubule rows bind parallel to this primary row, acquire ordered relationships, and become the tubules of the axostyle proper. The number of tubule rows is constant in Saccinobaculus lata from the region near the nucleus to within a few micrometers of the posterior tip of the cell. In Saccinobaculus ambloaxostylus a few tubule rows are added to the axostyle posterior to the nucleus, giving this axostyle a leaf spring construction. The tubules of S. lata are held in rows by links with a 140 Å periodicity along the tubule axis; bridges between rows of tubules are also seen but are not apparently periodic. Each tubule in S. ambloaxostylus shows an axial periodicity of 150 Å due to pairs of arms, one of which is always part of the intrarow link. Interrow bridges in this species run either from tubule to tubule or from tubule to the free arm, but as in S. lata they do not display an obvious axial periodicity. An average unit cell is presented for the axostyle of each species, and the relation of the intertubule links to the microtubule substructure is discussed.     

THE ULTRASTRUCTURE OF PHALACROCLEPTES VERRUCIFORMIS, AN UNCILIATED CILIATE PARASITIZING THE POLYCHAETE SCHIZOBRANCHIA INSIGNIS

The organization of Phalacrocleptes verruciformis is, in general, less complex than that of other ciliates, and no kinetosomes have been observed. However, there are numerous suctorial tentacles at the surface of the body, and the pellicle is characterized by close-set villus-like projections. The tentacles are very small (about 430 mµ in length, and about the same in diameter), but show the essential features of tentacles of suctorians such as Tokophrya, Podophrya, and Ephelota. Each tentacle is reinforced by eight pairs of fibrils arranged concentrically just within its wall, and contains a single missile-like body (MLB). The tentacles become attached to the cilia of the host, and serve for feeding upon the plasmatic contents of the cilia as well as for maintaining contact with the host. The MLB's originate in the endoplasm, and then migrate toward the surface and become incorporated into the tentacles. When feeding is initiated, the membrane covering the outermost nozzle-like portion of the MLB becomes continuous with the membrane of the cilium, and there are other changes in the structure of the MLB which suggest enzymatic activity. Although it appears that Phalacrocleptes is a suctorian, the complete absence of kinetosomes sets this organism apart from other members of the group.     

OBSERVATIONS ON THE STRUCTURE OF RHODOSPIRILLUM RUBRUM

Sections of Rhodospirillum rubrum cells from cultures of different ages have been examined to obtain information on the development of chromatophores in this organism. Cells from the 12-hour cultures studied contain neither distinct invaginations of the cytoplasmic membrane nor distinct chromatophores. The first structures that can be related to chromatophore development occur peripherally in the cells, are relatively few in number, relatively high in density, and have an indistinct membrane. In cells from 26-hour cultures numerous distinct invaginations of the cytoplasmic membrane are present, and all layers of the cytoplasmic membrane are involved in the formation of each invagination. As the invaginations become more numerous, the ends of the invaginations become constricted to form one or more structures similar to the chromatophores previously described in this organism. Cells of R. rubrum, therefore, develop a structural continuum which initially consists of invaginations of the cytoplasmic membrane, and later of the chromatophores produced by and attached to these invaginations. The presence of this continuum, however, does not necessarily exclude the existence of discrete chromatophores within these cells. Several other structures previously reported in this organism are described in greater detail.     

Comparative ultrastructure of catch tentacles and feeding tentacles in the sea anemone Haliplanella

TEM observations of catch tentacles revealed that the tentacle tip epidermis is filled with two size classes of mature holotrich nematocysts and a gland cell filled with electron-dense vesicles. Vesicle production is restricted to upper-middle and tentacle tip regions, whereas holotrich development occurs in the lower-middle and tentacle base regions. Thus, catch tentacles have a maturity gradient along their length, with mature tissues concentrated at the tentacle tip. Occasional feeding tentacle cnidae (microbasic p-mastigophores and basitrichs) and mucus gland cells occur in proximal portions of catch tentacles, but are phagocytized by amoeboid granulocytes and transported to the gastrodermis for further degradation. No feeding tentacle cnidae or mucus cells occur distally in catch tentacles. Unlike catch tentacles, feeding tentacles are homogeneous in structure along their length with enidocytes containing mature spirocysts, microbasic p-mastigophore or basitrich nematocysts distributed along the epithelial surface. Cnidoblasts are recessed beneath cnidocytes, occurring along the nerve plexus. Mucus gland cells and gland cells filled with electron-dense vesicles are present in feeding tentacles, distributed at the epithelial surface. Granular phagocytes are rare in the feeding tentacle tip, but common in the tentacle base.     

CYCLIC ACTIVITY AND EPITHELIAL RENEWAL IN THE DIGESTIVE GLAND TUBULES OF THE MARINE PROSOBRANCH MAORICRYPTA MONOXYLA (LESSON)

Three cell types are present in tubules of the digestive glandof the marine prosobranch Maoricrypta monoxyla (Lesson). Histochemistry,and feeding and starvation experiments established that themain type, the digestive cell, is involved in endocytotic uptakeof food material from the lumen. Digestion of this materialoccurs within vacuoles, and indigestible material (indicatedby the dye trypan blue) accumulates in basal residual bodiescontaining lipofuscin pigment. Another cell type, the cryptcell, appears to secrete a glycoprotein, probably enzymaticin function. The third cell type contains large vacuoles butit has not been Established whether the contents are secretoryor excretory. The tubules undergo a cycle of digestive activity not relatedto the tidal cycle as in some marine molluscs, but probablyan indirect result of the feeding regime. The cycle begins withimmature tubules in which some endocytosis occurs. These developinto absorbing tubules involved mainly in food uptake. In maturetubules intracellular digestion occurs. At a later stage thetubules fragment to produce spherules which may conserve usefulmaterial, and finally they, disintegrate completely. Eighty per cent of the dividing cells in the epithelium occurin crypts, which are therefore considered to be the main sitesof epithelial renewal. The processes by which tubules may bereformed after breakdown are discussed (Received 28 September 1978;     

THE STRUCTURE AND FUNCTION OF CENTRIOLES AND THEIR SATELLITES IN THE JELLYFISH PHIALIDIUM GREGARIUM

Testes of jellyfish Phialidium gregarium were fixed in 2 per cent OsO₄ in Veronal-acetate buffer at pH 7.4. Thin sections showed that in young spermatids the spindle fibers of the last maturation division are attached to satellites of the filament-forming centriole. In more mature spermatids this attachment is not observed. During the developmental phase, nine satellites can be observed emanating from the interspaces between the nine tubular triplets of this centriole. A circular region on each of the enlarged distal ends of the satellites attaches them to the cell membrane. The satellites apparently provide a firm anchor for the axial filament. Each of the epithelial cells covering the testis produces a single long flagellum. On the filament-forming centriole often a satellite can be observed to which tubules are attached. These tubules are 180 A in diameter and probably represent remnants of spindle fibers. It is suggested that the distal centriole has the ability to form several satellites or appendages at appropriate times during the cell cycle. These satellites are distinct from the daughter centrioles in that they are supportive structures: in certain phases of cell life, spindle fibers may attach to them, while in other instances the distal centriole and the flagellum it is forming are anchored by them.     

Ultrastructural studies of the commensal suctorian,Choanophrya infundibulifera hartog

Summary The feeding tentacles of Choanophrya contain a central canal lined by microtubules. Only one tentacle develops during metamorphosis of the embryo into the adult, but others develop at intervals throughout adult life. Each tentacle forms adjacent to a solitary, subcortical kinetosome which lies parallel to the body surface, lacks accessory elements and never develops a cilium. Small condensations of electron-dense material and short bundles of microtubules form adjacent to the cartwheel region of the kinetosome. Initially these bundles are orientated randomly but later they become radially arranged and curved into prolamellae around a disc-shaped condensation centre, to form a paddlewheel-like tentacle primordium 0.8–1.1 m in diameter. The condensation centre consists of alternating concentric electron-dense and electron-transparent zones, and lies with its axis perpendicular to both the kinetosome and the cortex. The microtubules in each prolamella increase in number and pairs of short tip microtubules develop between adjacent prolamellae. Subsequently the developing lamellae become enclosed by a cylinder of ring microtubules. Once all the microtubule components of the tentacle primordium are established it increases in length by addition of material to the basal ends of the microtubules to form a short microtubule canal. As the canal elongates the epiplasm above it disappears and the pellicle membranes become uplifted around the protruding tentacle. An epiplasmic collar differentiates around the growing tentacle whilst spheroid vesicles and solenocysts begin to accumulate in the surrounding cytoplasm.This investigation was supported by the J.S. Dunkerley Fellowship in Protozoology, awarded by the University of Manchester.     

TIP CELL GROWTH AND THE FREQUENCY AND DISTRIBUTION OF CELLULOSE MICROFIBRIL-SYNTHESIZING COMPLEXES IN THE PLASMA MEMBRANE OF APICAL SHOOT CELLS OF THE RED ALGA PORPHYRA YEZOENSIS1

The supramolecular organization of the plasma membrane of apical cells in shoot filaments of the marine red alga Porphyra yezoensis Ueda (conchocelis stage) was studied in replicas of rapidly frozen and fractured cells. The protoplasmic fracture (PF) face of the plasma membrane exhibited both randomly distributed single particles (with a mean diameter of 9.2 ± 0.2 nm) and distinct linear cellulose microfibril-synthesizing terminal complexes (TCs) consisting of two or three rows of linearly arranged particles (average diameter of TC particles 9.4 plusmn; 0.3 nm). The density of the single particles of the PF face of the plasma membrane was 3000 μm^?2, whereas that of the exoplasmic fracture face was 325 μm^?2. TCs were observed only on the PF face. The highest density of TCs was at the apex of the cell (mean density 23.0 plusmn; 7.4 TCs μm^?2 within 5 μm from the tip) and decreased rapidly from the apex to the more basal regions of the cell, dropping to near zero at 20 μm. The number of particle subunits of TCs per μm² of the plasma membrane also decreased from the tip to the basal regions following the same gradient as that of the TC density. The length of TCs increased gradually from the tip (mean length 46.0 plusmn; 1.4 nm in the area at 0–5 μm from the tip) to the cell base (mean length 60.0 plusmn; 7.0 μm in the area at 15–20 μm). In the very tip region (0–4 μm from the apex), randomly distributed TCs but no microfibril imprints were observed, while in the region 4–9 μm from the tip microfibril imprints and TCs, both randomly distributed, occurred. Many TCs involved in the synthesis of cellulose microfibrils were associated with the ends of microfibril imprints. Our results indicate that TCs are involved in the biosynthesis, assembly, and orientation of cellulose microfibrils and that the frequency and distribution of TCs reflect tip growth (polar growth) in the apical shoot cell of Porphyra yezoensis. Polar distribution of linear TCs as “cellulose synthase” complexes within the plasma membrane of a tip cell was recorded for the first time in plants.     

Studies on calmodulin isolated from Tetrahymena cilia and its localization within the cilium

Tetrahymena calmodulins from cilia, cell bodies and whole cells were isolated separately and compared. These calmodulins showed just the same properties: they co-migrated in SDS-polyacrylamide gel electrophoresis, had a Ca²⁺-dependent electrophoretic mobility change in alkali gel, held the same antigenic determinants in common, and activated brain cyclic nucleotide phosphodiesterase Ca²⁺-dependently with identical activation curves. Distributions of calmodulin and calmodulin-counterpart in Tetrahymena cilium were investigated by using alkali gel electrophoresis in the presence of Ca²⁺ or EGTA, and by immunoelectron microscopy. Calmodulin was detected in the membrane plus matrix fraction and outer-doublet microtubule fraction, and its Ca²⁺-dependent counterpart existed exclusively in the latter fraction. However, neither calmodulin nor its counterpart was detected in the crude dynein fraction. Immunoelectron microscopy revealed that calmodulin was localized along the longitudinal axis of outer-doublet microtubules at regular intervals of about 90 nm. The calmodulin-binding site in the ciliary axoneme was suggested to be interdoublet links.     

STRUCTURE OF THE CEPHALIC TENTACLES OF SOME SPECIES OF PROSOBRANCH LIMPET (PATELLIDAE AND FISSURELLIDAE)

The morphology and ultrastructure of the cephalic tentaclesand eye (optic vesicle) of some patellid and a fissurellid limpetspecies are described. The epithelium of the tentacle bearsciliated cells which have neural connections suggesting a sensoryfunction. In patellid limpets the density of these cells variesbetween species, with the greatest density (18 ciliated tufts.100 µm^–2) being recorded in the territorial limpet,Patella cochlear. The surface of the tentacle of a fissurellidlimpet, Fissurella mutabilis, is papillate, which contrastswith the smooth surface of a patellid tentacle. Ciliated tuftsare borne at the tip of most papillae. Movement of the tentacleis controlled by longitudinal muscle and a radial muscle-collagentissue association, which function as a muscular hydrostat.The eye of a patellid consists of a simple open vesicle anda retina which is comprised of one type of cell. By contrastthe optic vesicle of a fissurellid contains a lens, enclosedby a cornea and a retina which is composed of two types of cell,pigmented and photoreceptive. The ultrastructural features ofthe cells resemble those described for other molluscan eyes. (Received 5 June 1989; accepted 16 August 1989)     

La Flora E La Vegetazione Pel Capo S. Elia (Sardegna Meridionale)

Abstract

Morphological organization of the lomasomes. — From a study on morphological organization of the lomasomes, in Avena coleoptile cells, it has been reported: 1) lomasomes form is quite variable, nevertheless, usually they resemble to a cone having a flattened tip and the base line against the cellular wall. 2) the external border of the lomasoma towards the cytoplasm is represented by the plasma membrane; such external profile results very sinuous and deep invaginations are present. 3) the internal structure is characterized by the presence of an unstructurated matrix containing spherical vescicles, flattened vescicles and tubules all showing an higher density to the electron radiations than the cytoplasmic matrix. Both vescicles and tubules are delimited by a single membrane.     

THE TETRAHYMENA HOMOLOG OF BACTERIAL AND MAMMALIAN 4-HYDROXYPHENYLPYRUVATE DIOXYGENASES LOCALIZES TO MEMBRANES OF THE ENDOPLASMIC RETICULUM

The expression and intracellular localization of the Tetrahymena homolog of 4-hydroxyphenylpyruvate dioxygenase (HPPD) were investigated in wild-type Tetrahymena thermophila strain B1868 VII and the mutant strains IIG8, defective in food vacuole formation, MS-1, blocked in secretion of lysosomal enzymes, and SB 281, defective in mucocyst maturation. Immunoelectron microscopy and confocal laser scanning microscopy demonstrated that Tetrahymena HPPD primarily localized to membranes of the endoplasmic reticulum. In addition, Tetrahymena HPPD was detected in association with membranes of the Golgi apparatus, and transport vesicles in exponentially growing wild-type and mutant strains. In starved cells, Tetrahymena HPPD localized exclusively to membranes of small vesicles. Since no de novo synthesis ofTetrahymena HPPD takes place in cells starved for more than 30min, these results suggest that there is a flow ofTetrahymena HPPD from the endoplasmic reticulum to small vesicles, possibly via the Golgi apparatus, and thatTetrahymena HPPD contains a signal for vesicle membrane retrieval or retention.     

ON THE STRUCTURAL CONTINUITIES OF THE TRANSVERSE TUBULAR SYSTEM OF RABBIT AND HUMAN MYOCARDIAL CELLS

An electron microscopic study of rabbit and human myocardium provides further evidence of the existence of two distinct components of the sarcoplasmic reticulum. A thin-walled tubular system (termed longitudinal system) is arranged in anastomosing channels sur-surrounding each sarcomere and has transverse and possibly also longitudinal connections with the tubules of adjacent sarcomeres. A thick-walled tubular system traverses the myofiber transversely at the level of the Z lines of the myofibrils. The structure of these tubules very closely resembles that of deep sarcolemmal invaginations. Indeed, the membranes of the tubules appear to be continuous with the sarcolemma in favorable sections so that there seems to be an extension of the cell membrane and extracellular fluid to all depths of the myocardial fiber. Certain physiologic data which support this concept are discussed. The calculations of A. V. Hill comparing the kinetics of diffusion and the time-distance relationships between excitation and activation in frog sartorius muscle are reconsidered for cardiac muscle.     

OBSERVATIONS ON THE STRUCTURE OF RHODOSPIRILLUM MOLISCHIANUM

The lamellae of the bacterium Rhodospirillum molischianum originate as extensions of the cytoplasmic membrane into the cytoplasm of the cell. Initially, these extensions are narrow folds and occur independently of one another. The first lamellae to appear average about 80 A in width, representing one side of the infolded cytoplasmic membrane, or 160 A when the two sides of the fold are closely appressed. The 160-A lamellae increase in number and may associate to form larger lamellae, which represent varying degrees of association between adjacent folds. Later, the space within each fold increases; the two appressed regions of the cytoplasmic membrane in each fold separate to form distinct invaginations, and the lamellae observed at this stage are formed by an association of the sides of adjacent invaginations.     

Fine structure of postgonopodial glands of a myriapod Glomeris marginata (Villers)

The postgonopodial gland of the myriapod Glomeris marginata (Villers), which produces a pheromone, is an integumentary gland comprising numerous functional secretory units. Each secretory unit consists of two proximal secretory cells, an intermediary cell lacking secretory characteristics and a canal cell surrounding the canal, which is secretory in nature. Secretory proximal cells exhibit a zone of small channels originating from invaginations of the plasma membrane and through which secreted material is released. Apposing each invagination of these cells is a corresponding invagination of the intermediary cell: the two units in the centre of the intermediary cell join another which communicates with the canal. Secretion produced by the latter passes through the canal wall and blends with secretion of the two proximal cells. The most striking feature of all these cells is the abundance of tubules and fibrils in the small canal zone in the proximal cells, which also exhibits a centriole; in the intermediary cell around cytoplasmic membrane invaginations where a diplosome is present, and in almost the entire canal cell.