The Fine Structure of Colpoda maupasi with Special Emphasis on Food Vacuoles*

SYNOPSIS. An electron microscope study of Colpoda maupasi Enriques, isolated from the intestine of the blue-tongued skink Tiliqua nigrolutea, showed that the fine structure of this ciliate is similar in all respects to that of free-living ciliates. The correspondence applies particularly to the structure, distribution and number of mitochondria. This organelle has a rich intramitochondrial structure in the form of microvilli; it is found close to the periphery, near the nuclear apparatus and in other parts of the cytoplasm. It was concluded that the association between Colpoda maupasi and Tiliqua nigrolutea was probably accidental and limited to the cyst stage. Thus electron microscopy confirmed a conclusion arrived at by light microscopy. The presence of numerous food vacuoles made it possible to study stages of digestion within this organelle. Four major types of food vacuole were distinguished. Type 1 food vacuoles are characterized by their large size, the presence of intact bacteria and abundance of water. In type 2 the food vacuole is deprived of water, the bacteria are pressed together and the nuclei have lost their structure. Type 3 food vacuoles contain only bacterial ghosts, cytoplasmic and nuclear material having been digested. Food vacuoles of this type are found only occasionally, suggesting their short duration. It is of interest that during this transient stage the bulk of digestion takes place. In type 4 nothing reminiscent of bacteria is found; there are only myelin figures and vesicles of different sizes. Evaginations and invagnations of the vacuolar membrane and vesicles of different size and structure inside and outside the food vacuoles of types 1, 3 and 4 suggest that extensive communication exists between the cytoplasm and the food vacuole. It seems likely that enzymes are delivered to the food vacuole and digested materials are released from the food vacuole to the cytoplasm.     

An Ultrastructural Study of Ingestion and Digestion in Tetrahymena pyriformis*

SYNOPSIS. When the structures involved in digestive events in T. pyriformis are examined at the electron microscope level, some information is added to that long known from light microscopy. The food trapping mechanism consists of the three membranelles, undulating membrane, oral ribs, and a “valve” apparently closing the opening to the cytopharynx. Both of the latter structures are supported by microtubules. Fibers extend internally from the cytopharynx and are closely associated with the food vacuole as it forms. Clear vacuoles resembling pinocytic vacuoles appear to arise from differentiated areas of the pellicle and plasma membrane. These vacuoles may fuse with primary lysosomes. Hydrolases are thus contributed to the pinocytic vacuoles which may then fuse with food vacuoles. When first formed food vacuoles contain no hydrolases but may acquire them directly, from primary lysosomes or from pinocytic vacuoles. Digestion proceeds to completion in the food vacuole, at which time soluble food products are released to the cytoplasm. Undigested materials are lost through the cytopyge. In stationary growth phase cells autophagic vacuoles form containing mitochondria and other cellular particulates. Such vacuoles probably contain hydrolases when formed and they may receive others by fusion with primary lysosomes.     

Phagotrophy and Two New Structures in the Malaria Parasite Plasmodium berghei

Blood collected from rats infected with Plasmodium berghei was centrifuged and the pellet was fixed for 1 hour in 1 per cent buffered OsO₄ with 4.9 per cent sucrose. The material was embedded in n-butyl methacrylate and the resulting blocks sectioned for electron microscopy. The parasites were found to contain, in almost all sections, oval bodies of the same density and structure as the host cytoplasm. Continuity between these bodies and the host cytoplasm was found in a number of electron micrographs, showing that the bodies are formed by invagination of the double plasma membrane of the parasite. In this way the host cell is incorporated by phagotrophy into food vacuoles within the parasite. Hematin, the residue of hemoglobin digestion, was never observed inside the food vacuole but in small vesicles lying around it and sometimes connected with it. The vesicles are pinched off from the food vacuole proper and are the site of hemoglobin digestion. The active double limiting membrane is responsible not only for the formation of food vacuoles but also for the presence of two new structures. One is composed of two to six concentric double wavy membranes originating from the plasma membrane. Since no typical mitochondria were found in P. berghei, it is assumed that the concentric structure performs mitochondrial functions. The other structure appears as a sausage-shaped vacuole surrounded by two membranes of the same thickness, density, and spacing as the limiting membrane of the body. The cytoplasm of the parasite is rich in vesicles of endoplasmic reticulum and Palade's small particles. Its nucleus is of low density and encased in a double membrane. The host cells (reticulocytes) have mitochondria with numerous cristae mitochondriales. In many infected and intact reticulocytes ferritin was found in vacuoles, mitochondria, canaliculi, or scattered in the cytoplasm.     

Structural Aspects of Digestion of Escherichia coli in Tetrahymena1

Tetrahymena pyriformis ingested Escherichia coli for 15–20 min and the fine structure of food vacuoles was analyzed 5, 15, 30, 60, 90, 120, and 180 min after uptake began. From this analysis, eight vacuolar stages could be defined, and three to four stages were found in each sample. Stage 1 represents forming and newly detached vacuoles with a random distribution of bacteria. Stage 2 is the “dehydration” vacuole in which the bacteria are compacted and a few may lyse. Stage 3, corresponding to the acid phosphatase-positive stage, has an electron-dense vacuolar matrix revealing components of lysed bacteria and the translucent coat of intact bacteria. Stage 4 is the “halo” stage where centrally located, intact bacteria are surrounded by lysed material being removed by pinocytic activity of the vacuolar membrane. Stage 5 represents lysis of bacteria remaining intact until this stage; the stage is apparently followed by a second stage 4. Stage 6 contains few bacterial profiles in a smeared homogeneous mass. Stage 7 contains numerous vesicular membranous structures which apparently become transferred to the cytoplasm as such. Stage 8 represents defecation vacuoles derived from fusion of smaller vacuoles. The main findings are as follows: I) Bacterial lysis may occur during acidification of the vacuole prior to fusion with lysosomes. II) Digestion of bacteria apparently occurs in “bursts” as indicated by the extended time that vacuoles in stages 4 and 5 are present. III) Bacterial membranous structures seem to be transferred directly to the cytoplasm of Tetrahymena. IV) Mass defecation occurs 2 h after uptake begins.     

Evidence of phagotrophy in Dinophysis fortii (Dinophysiales, Dinophyceae), a dinoflagellate that causes diarrhetic shellfish poisoning (DSP)

Food vacuoles were found in one species of pho‐totrophic Dinophysis, Dinophysis fortii Pavillard, collected in Okkirai Bay. Under transmission electron microscopy, almost 70% of observed food vacuoles were characterized by membranous profiles and contained large numbers of mitochondria. The mitochondria in the food vacuole had different morphologies from those in the D. fortii cytoplasm. This indicates that these vacuoles are not autolytic accumulation bodies, but ‘true’ food vacuoles. Identification of the origin of the contents failed, but the existence of large amounts of foreign mitochondria implies that the contents in the vacuoles were derived from eukaryotic prey. Other than the observation of the food vacuoles, bacterial cells were observed in the flagellar canal. Because the flagellar canal and connecting pusule sacs had been reported to relate to macromolecule uptake, the prey organisms of D. fortii were assumed to be both eukaryotic and prokaryotic organisms.     

Digestion in the peritrich ciliateOphrydium versatile

Summary Digestion in the peritrich ciliateOphrydium versatile O.F.M. involves a complex sequence of intracytotic and exocytotic membrane fusion and recycling events. Food particulates are concentrated in the lower cytopharynx which forms a fusiform-shaped food vacuole. Upon release from the cytopharynx, this food vacuole begins to condense, concentrating the food particulates. Excess membrane is removed intracytotically. These released membranes pieces form discoidal vesicles which are recycled to the base of the cytopharynx, thus providing additional membrane for subsequent food vacuole formation. In the condensed food vacuole, digestion proceeds; hydrolytic enzymes are delivered to the food vacuole via rough endoplasmic reticulum and/or by the cup-shaped coated vesicles (CSCV). As these vesicles fuse with the food vacuole, the food vacuole enlarges, digestion proceeds and an electron-dense membrane coat appears along the luminal surface of the food vacuole. Prior to defecation, the food vacuole undergoes a final condensation; irregularly-shaped, electron dense, single-membrane bound vesicles are cut-off intracytotically from the old food vacuole. These vesicles undergo condensation and invagination to form the cup-shaped coated vesicles (CSCV) which fuse with younger food vacuoles.     

ULTRASTRUCTURE OF DEVELOPING AND MATURE NONARTICULATED LATICIFERS IN THE MILKWEED ASCLEPIAS SYRIACA L. (ASCLEPIADACEAE)

The ultrastructure of developing and mature nonarticulated laticifers in Asclepias syriaca L. (the common milkweed) was studied by conventional fixation and staining techniques and by osmium impregnation techniques. The mature laticifer protoplast in A. syriaca possesses a large central vacuole with an intact vacuolar membrane. Formation of this vacuole apparently results from dilation and subsequent enlargement of endoplasmic reticulum and possibly in part by fusion of smaller vacuoles and limited cellular-lytic autophagy. Widespread digestion or autophagy of cytoplasm within vacuoles is not evident. Nuclei, mitochondria, dictyosomes, and small vesicles are the most prominent components distributed in the peripheral cytoplasm. Plastids appear to degenerate as the laticifer matures. The specialized cellular component, latex, which is the vacuolar content of the laticifer, is interpreted to be produced in the cytoplasm and subsequently incorporated into the large central vacuole. Rubber globules, the most prominent latex component, are surrounded by a membrane that does not have a trilaminate structure. Globules are associated with an electron-dense fibrillar component in the vacuole.     

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.     

Fine Structure of a Marine Ameba Associated with a Blue-Green Alga in the Sargasso Sea*,†

SYNOPSIS An ameba, bearing a fringe of scales on the plasmalemma surface, dwells among the filaments of the colonial, blue-green alga Trichodesmium thiebautii (Sournia), and preys upon bacteria growing within the colony. The cytoplasm is clearly differentiated into a fine fibrillar ectoplasm at the periphery of the cell and a central endoplasm containing most of the membranous organelles. The nucleus contains a spheroidal nucleolus which is centrally located, and a double membrane containing pores. The tubular mitochondria, microbodies, lysosomes, and endoplasmic reticulum are typical for protozoa. The Golgi apparatus consists of an array of elongate flattened cisternae. One surface is associated with a fine fibrillar layer and the opposite surface contains electron-dense vesicles (perhaps primary lysosomes) and scale-containing vesicles that appear to be the origin of the scales deposited on the plasma membrane. Three kinds of bacteria-containing vacuoles are presnt: (a) vacuoles surrounded by 3 membranes and containing bacteria that are either healthy or in an early stage of digestion, (b) singlemembrane vacuoles which are food vacuoles that become converted to digestive vacuoles, and (c) larger vacuoles resembling those in (b) which contain prey in an advanced stage of digestion. The presence of amebae within pelagic algal communities provides further evidence for the diversity of their habitats in the ocean.     

Phagotrophy and two new structures in the malaria parasite Plasmodium berghei

Blood collected from rats infected with Plasmodium berghei was centrifuged and the pellet was fixed for 1 hour in 1 per cent buffered OsO(4) with 4.9 per cent sucrose. The material was embedded in n-butyl methacrylate and the resulting blocks sectioned for electron microscopy. The parasites were found to contain, in almost all sections, oval bodies of the same density and structure as the host cytoplasm. Continuity between these bodies and the host cytoplasm was found in a number of electron micrographs, showing that the bodies are formed by invagination of the double plasma membrane of the parasite. In this way the host cell is incorporated by phagotrophy into food vacuoles within the parasite. Hematin, the residue of hemoglobin digestion, was never observed inside the food vacuole but in small vesicles lying around it and sometimes connected with it. The vesicles are pinched off from the food vacuole proper and are the site of hemoglobin digestion. The active double limiting membrane is responsible not only for the formation of food vacuoles but also for the presence of two new structures. One is composed of two to six concentric double wavy membranes originating from the plasma membrane. Since no typical mitochondria were found in P. berghei, it is assumed that the concentric structure performs mitochondrial functions. The other structure appears as a sausage-shaped vacuole surrounded by two membranes of the same thickness, density, and spacing as the limiting membrane of the body. The cytoplasm of the parasite is rich in vesicles of endoplasmic reticulum and Palade's small particles. Its nucleus is of low density and encased in a double membrane. The host cells (reticulocytes) have mitochondria with numerous cristae mitochondriales. In many infected and intact reticulocytes ferritin was found in vacuoles, mitochondria, canaliculi, or scattered in the cytoplasm.     

An Ultrastructural and Cytochemical Study of the Cell Surface of a Suctorian Ciliate1

The surfaces of the main cell body, tentacle shaft, and knob of Discophrya collini, a freshwater suctorian ciliate, were characterized using various cytochemical techniques. Cells prepared for conventional transmission electron microscopy exhibited a 50–60 nm thick fuzzy layer over the cell body surface; this layer was absent from the tentacle knob. A thick (240 nm), two-layered surface coat surrounding the main cell body was stained with ruthenium red. This heavy coat was absent from the surface of the knob where a thin, dense, ruthenium red-positive layer and projecting filaments were present. Freeze-etched material revealed a “particle region” (150–250 nm in thickness) closely associated with the outer cell surface of the suctorian. Fixed specimens were treated with four different lectins and analyzed with electron microscopy in order to obtain information about the carbohydrate composition of the outer surface of D. collini. Concanavalin A bound to the surface of the cell body and tentacle shaft as a dense, particulate layer (80 nm thick) but thinned to 13–16 nm over the surface of the knob. Wheat germ agglutinin-treated cells also displayed a heavy, electron-dense layer (128 nm thick) that surrounded the main cell body and tentacle shaft, but only scattered patches of bound wheat germ agglutinin were observed on the surface of the knob. Discophrya treated with Helix agglutinin or peanut agglutinin appeared similar to control cells. Suctorians were treated with lectins in vivo in an attempt to inhibit capture and ingestion of their prey, Tetrahymena pyriformis, by masking prey receptor sites on the knob. Concanavalin A and, to a lesser degree, wheat germ agglutinin, successfully inhibited attachment of the prey organism. Helix agglutinin and peanut agglutinin had little effect on prey capture.     

The Correlation of Digestive Vacuole pH and Size with the Digestive Cycle in Paramecium caudatum1

ABSTRACT. The temporal changes in the size and pH of digestive vacuoles (DV) in Paramecium caudatum were reevaluated. Cells were pulsed briefly with polystyrene latex spheres or heat-killed yeast stained with three sulfonphthalein indicator dyes. Within 5 min of formation the intravacuolar pH declined from ～7 to 3. With the exception of a transient and early increase in vacuolar size, vacuole condensation occurred rapidly and paralleled the acidification so that vacuoles reached their lowest pH and minimal size simultaneously. Neutralization and expansion of vacuole size began when vacuoles were GT8 min old. No labeled vacuoles were defecated prior to 21 min after formation but almost all DV were defecated within 1 h so that the digestive cycle of individual vacuoles ranged from 21 to 60 min. Based on these size and pH changes, the presence of acid phosphatase activity, and membrane morphology, digestive vacuoles can be grouped into four stages of digestion. The DV-I are GT6 min old and undergo rapid condensation and acidification. The DV-II are between 4 to 10 min old and are the most condensed and acidic vacuoles. The DV-III range in age from 8 to ～20 min and include the expanding or expanded vacuoles that result from lysosomes fusing with DV-II. The DV-IV are GD21 min old, and since digestion is presumably completed, they can be defecated. The rise in intravacuolar pH that accompanies vacuole expansion suggests that lysosomes play a role in vacuole neutralization in addition to their degradative functions. The acidification and condensation processes in DV-I appear to be unrelated to lysosomal function, as no acid phosphaiase activity has been detected at this stage, but may be related to phagosomal functions important in killing food organisms, denaturing proteins prior to digestion, and preparing vacuole membrane for fusion with lysosomes.     

On Food Vacuoles in Tetrahymena pyriformis GL

SYNOPSIS. The following problems concerning food vacuoles were studied by in vivo observations of Tetrahymena: (A) Formation of food vacuoles . The process may be divided into 4 stages. Stage 1—gradual growth of the limiting membrane of the open food vacuole (of short duration). Stage 2—"filling up" of the fully expanded vacuole (of long duration). Stage 3—"closing off" of the vacuole (of brief duration). Stage 4—initial movement of the detached vacuole away from the cy-tostome. The possible role of the oral components (apart from membranellar beating) in the process is discussed. (B) Change of pH in the food vacuole . After ingestion of heat-killed yeast stained with indicator dyes (neutral red, bromcresol purple, bromcresol green, bromphenol blue), the observed color changes indicate that pH is neutral in the forming vacuole as well as in newly formed vacuoles; that a pH value of 6.0–5.5 is reached after ∼ 5 min; and that the lowest pH value between 4.0 and 3.5 is reached after 1 hr. Before egestion the pH again increases. (C) Length of the digestive cycle . A determination of the time required to deplete the cells of labeled vacuoles formed during a short exposure, was attempted. Defecation was observed after 1/2 hr and it was frequent after 2 hr. About 25% and 50% of the labeled vacuoles were removed after 1 hr and 2 hr, respectively; however, labeled vacuoles may still be seen in some cells 6 hr after ingestion. The conclusion is that the digestive cycle lasts ∼ 2 hr and that egestion of undigestible material is a random process.     

Feeding Characteristics of an Amoeba (Lobosea: Naegleria) Grazing Upon Cyanobacteria: Food Selection, Ingestion and Digestion Progress

Bacterivory by heterotrophic nanoflagellates and ciliates has been widely studied in aquatic environments, but data on the grazing of amoebae, are still scarce. From the water samples of Dianchi Lake (Kunming, Yunnan Province, China), we isolated an amoeba, designated as Naegleria sp. strain W2, which had potent grazing effects on some kind of cyanobacteria. The food selection mechanism and the digestion process of the amoeba were investigated in batch experiments. Predation experiments showed that filamentous cyanobacteria (e.g., Anabaena, Cylindrospermum, Gloeotrichia, and Phormidium) were readily consumed, with clearance rates ranging from 0.332 to 0.513 nL amoeba⁻¹ h⁻¹. The tight threads (Oscilltoria) and aggregates (Aphanizomenon) could not be ingested; however, their sonicated fragments were observed inside food vacuoles, suggesting that their morphologies prevent them from being ingested. Live video microscopy noted that unicellular Chroococcaceae (e.g., Synechococcus, Aphanocapsa, and Microcystis) were excreted after ingestion, indicating that food selection takes place inside food vacuoles. To determine whether the tastes or the toxins prevented them from being digested, heat-killed cells were retested for predation. Digestion rates and ingestion rates of the amoebae for filamentous cyanobacteria were estimated from food vacuole content volume. Through a “cold-chase” method, we found that the food vacuole contents declined exponentially in diluted amoebae cells, and digestion rates were relatively constant, averaging about 1.5% food vacuole content min⁻¹ at 28°C. Ingestion strongly depended on the satiation status of the amoebae, starved amoebae fed at higher rates compared with satiated amoebae. Our results suggest that the food selection and food processing mechanisms of the amoeba are similar to those of interception feeding flagellates; however, filamentous cyanobacteria cannot obtain a refuge under the grazing pressure of phagotrophic amoebae, which may widen our knowledge on the grazing of protists.     

Intrazelluläre Zellzotten in Nahrungsvakuolen von Ciliaten

Zusammenfassung 1. Die Nahrungsvakuolen vonMetafolliculina andrewsi entwickeln mit zunehmendem Alter einen Faltensaum, der seine höchste Differenzierung in dem Altersstadium erreicht, wo die stärkste Resorption der Nährstoffe zu vermuten ist.2. Dieser Faltensaum besteht aus lamellenartigen Cytoplasmaprotuberanzen und bewirkt — ähnlich wie der Bürstensaum an der freien Zelloberfläche — innerhalb der Zelle eine erhebliche Oberflächenvergrößerung der Nahrungsvakuole zugunsten der Permeation der Nährstoffe.3. Bei alten Nahrungsvakuolen werden die Falten wieder zurückgebildet, eine Tatsache, die die funktionelle Bedeutung dieser Struktur weiterhin unterstreicht.4. An Hand des Verdauungsgrades des Vakuoleninhalts und der morphologischen Veränderungen der Vakuolenwand lassen sich bei den Nahrungsvakuolen vonMetafolliculina deutlich vier Alters- beziehungsweise Funktionsstadien unterscheiden: 1. Ingestionsvakuolen, 2. Digestionsvakuolen, 3. Resorptionsvakuolen und 4. Egestionsvakuolen.5. Die morphologischen Befunde an der Resorptionsvakuole, die strukturelle und funktionelle Parallelen mit den resorbierenden Darmepithelien von Metazoen aufweist, werden im Rahmen der heutigen Vorstellungen über die zelluläre Stoffaufnahme diskutiert.

---

Lamellar microvilli in food vacuoles of ciliates

With progressing age, the food vacuoles ofMetafolliculina adrewsi develop a border of folds, which attains its most pronounced differentiation at a stage where maximum resorption of nutrient substances presumably takes place. This border of folds, similar to the well known brush border at the free cell surface, consists of lamellar cytoplasm protuberances and causes a considerable enlargement of the membrane area of the food vacuole within the cell, thus favoring the permeation of nutrient substances. In old food vacuoles the border of folds undergoes involution, an observation that also points to the functional significance of this structure. InMetafolliculina the degree of digestion of the vacuole contents and the morphological changes of the vacuole wall enable a distinction to be made between 4 different stages of age and function of the food vacuoles respectively: (1) ingestion vacuoles, (2) digestion vacuoles, (3) resorption vacuoles and (4) egestion vacuoles. The resorption vacuole evidently shows structural and functional analogies to the resorbing intestinal epithelia of Metazoa. The morphological findings are discussed in the light of current concepts on substance uptake by the cell.

---

---

Mit Unterstützung der Deutschen Forschungsgemeinschaft.     

Ultrastructural and Other Observations Which Suggest Suctorian Affinities for the Taxonomically Enigmatic Ciliate Cyathodinium*

SYNOPSIS. Two species of the taxonomically enigmatic genus Cyathodinium, C. piriforme and C. cunhai, were studied in some detail at both light and electron microscopic levels. Data obtained strongly suggest suctorian affinities for the genus, since a number of structures or features are strikingly reminiscent of similar (if not homologous) structures recently discovered in ciliates belonging to the order Suctorida. Endosprits (suctorial tentacles?) of Cyathodinium show an arrangement of microtubules not unlike that known for several suctorians, especially Acineta and Tokophrya. Haptocysts or missile-like bodies, ca. 600 mμ long, have been observed within endosprits and free in the cytoplasm; again this is reminiscent of the complex organelles recently described from several suctorian groups. Mouthlessness, coupled with the presence of a ventral depression (functioning in gathering prey at distal ends of endosprits?) and the presence of food vacuoles in the cytoplasm, further support a suctorian mode of feeding. Finally, stages in the curious life cycle of Cyathodinium suggest neoteny and a basic similarity to endogenous budding processes in certain suctorians.     

Fine Structural Observations of the Erythrocytic Stages of Plasmodium chabaudi Landau, 1965*

SYNOPSIS. Electron microscopic examination of Plasmodium chabaudi in mouse erythrocytes revealed many characteristics resembling those observed in other mammalian malarial parasites. A double unit membrane surrounds the trophozoite cytoplasm which contains many ribonucleoprotein particles, a limited amount of endoplasmic reticulum and membraned organelles including sausage-shaped vacuoles and multilaminated membraned bodies. More or less circular double membraned vacuoles, possibly cross sections of the sausage-shaped vacuoles, are common. Typical protozoan mitochondria are lacking. The limiting membrane of the merozoites is triple-layered. Paired organelles and small dense bodies are found in the merozoites along with dense granular masses in the nuclei. Trophozoites have cytostomal structures as well as invaginations of the plasma membrane at sites where no cytostomes are evident. Digestion appears to occur in single membrane-bound vesicles which contain one to several pigment grains. P. chabaudi frequently contains multiple food vacuoles and has polymorphism manifested in part by the presence of cytoplasmic extensions and of nuclei with a variety of shapes. Several apparently free forms are noted, often accompanied by a thin rim of host cytoplasm. “Appliqué” forms are common among the trophozoites as are forms in which 2 or more trophozoites are joined together. Finally, alterations in the host cytoplasm resembling the socalled Maurer's clefts are frequent. Ferritin-containing vacuoles also appear in the host cell.     

Acid hydrolases and their Release in Food Vacuole-Less Mutants of Tetrahymena thermophila*

SYNOPSIS. Mutants (NP1 and PSJ5) of Tetrahymena thermophila strains B and D 1968 exist that are unable to construct a functional oral apparatus and form food vacuoles at 37 C but which do so normally at 30 C. Food vacuole-less cells starved in dilute salt solution released similar amounts of acid phosphatase, β-N-acetyl-glucosaminidase and ±-glucosidase activity into the medium as wildtype cells during an 8-h period. Actively growing, food vacuole-less cells had ?50% less total protein, acid phosphatase, β-N-acetyl-glucosamin-idase, and ±-glucosidase per cell than wildtype cells after 72-h growth. During this time food vacuole-less cells released significant amounts of the 3 acid hydrolases into the growth medium. For each hydrolase, the total activity released from growing, food vacuole-less cells was less, on a per cell basis, than the amount released from food vacuole formers. The proportion of the total activity secreted by the mutant and the wildtype cells was the same for acid phosphatase and β-N-acetyl-glucosaminidase and somewhat lower for ±-glucosidase. It is concluded that the release of a significant amount of acid hydrolase activity from Tetrahymena is independent of food vacuole formation and may be analogous to the secretory activity of other nonphagocytic eukaryotic cells.     

THE FATE OF MITOCHONDRIA DURING AGING IN TETRAHYMENA PYRIFORMIS

During the growth cycle of Tetrahymena pyriformis the mitochondria undergo changes in position, number, and structure. Ciliates in the logarithmic growth phase possess elongated mitochondria which are aligned along the plasma membrane and are closely associated with the kinetosomes and kinetodesmata. Mitochondria appear to divide across the long axis at this time, resulting in two or more products. Throughout this phase of growth mitochondrial divisions keep pace with cytokinesis so that the population of mitochondria remains at essentially the minimal level. As the ciliates enter the stationary growth phase the mitochondria increase in number, become oval to spherical in shape, and some migrate into the cytoplasm. Intramitochondrial masses of various configurations appear at this time. Some of the mitochondria lying in the cytoplasm become incorporated into vacuoles. Within these vacuoles either a single mitochondrion appears or several mitochondria may be seen along with other cytoplasmic structures. Later in the stationary growth phase the contained mitochondria are dense and the tubules are more compact than normal. Various stages in disorganization of the mitochondria are observed in a single large vacuole. Cytochemical tests reveal the presence of acid phosphatase, suggesting that hydrolysis of the vacuolar contents occurs. Lipid droplets increase in number during the middle and late stationary phase of growth. These events are interpreted as being associated with the normal process of aging in T. pyriformis.     

Glucose repression and autolysis ofSaccharomyces cerevisiae cells: alterations in the cytochemical localization of acid phosphatase

Summary Allerations in the localization of acid phosphatase inSaccharomyces cerevisiae during glucose repression and during autolysis have been studied. Cell morphology becomes distinctly changed after only 2 h in the presence of high glucose concentration while after 3 h of glucose repression the majority of the mitochondirial structures resemble promitochondria. Yeast cells repressed for 6 h contain almost completely degraded mitochondrial structures and numerous lipid droplets in the central vacuole and cytoplasm. Destruction of mitochondria is accompanied by the accumulation of acid phosphatase in these organelles and in the cytoplasm whereas its activity in the central vacuole is lowered, most probably because of the leakage of the enzyme into the cytoplasm.No preferential breakdown of mitochondria is observed during autolysis. On the contrary, mitochondria are apparently the last to be degraded. Digestion of cytoplasmic regions and membranous elements occurs intravacuolarly after sequestration by protrusions of the central vacuole which are formed at the initial stages of autolysis. Acid phosphatase is not released from the central vacuole, suggesting indirectly that vacuole enzymes do not migrate into the cytoplasm during autolysis.