Configural changes in the plastidome ofPolytoma papillatum after completion of cytokinesis and during fusion of the gametes

Summary Changes in plastidome morphology in several definite stages of both the vegetative (asexual) and generative (sexual) life cycle ofPolytoma papillatum were examined by means of serial sectioning technique. Just after completion of cytokinesis daughter cells contain a simple through-shaped, bulky and scarcely perforated leucoplast whose opening faces the original plane of cell cleavage (=lateral part of the new daughter cell). In the course of progressive reorganization the trough-shaped leucoplast is first transformed into a hollow oviform meshwork whose reticulated frame is irregular in shape, size and distribution and whose interior is traversed at the base by two sheets, thus forming separate chambers. This then becomes the typical cup-shaped leucoplast of interphase cells, whose elongated cylindrical lateral part is thin and highly perforated and whose cup-opening faces the apical part of the cell. The changes in leucoplast morphology, probably due to reshuffling and reorganization processes, are correlated to leucoplast areas characterized both by starch and membrane breakdown and by frequent appearance at times of upheaval during leucoplast differentiation. Fusion of two leucoplasts to again form a large, highly perforated cup was also investigated; union of both gametic leucoplasts in such a spherical quadriflagellate zygote is demonstrated by a reconstructed model. Finally the relevancy of these morphological data to extranuclear inheritance is discussed.     

The ultrathin structure of amoeboid flagellate <Emphasis Type="Italic">Thaumatomastix</Emphasis> sp. (Thaumatomonadida (Shirkina) Karpov, 1990)

The ultrathin structure of amoeboid flagellate Thaumatomastix sp. is considered. The cell is surrounded by two-layered triangular scales. They are formed on the surface of mitochondria. Pseudopodia grabbing bacteria run from ventricular furrow, which is armored with two longitudinal bands of microtubules. Heterodynamic flagella run from small flagellar pocket. Long back flagellum has thin mastigonemes. Proximal area of short flagellum is covered with flat oval scales. Transitional flagellant zone has no spiral or other additional elements. Transverse plate is localized above cell surface. Kinetosomes are parallel to each other. Vesicular nucleus and Golgi apparatus have typical structure. Oval mitochondria contain tubular cristae. Within cytoplasm, extrusive organelles (kinetocysts) containing amorphous material and capsule were found. The latter consists of muff and cylinder. Plasmodial and cystic phases of development have not been discovered. Contractile vacuole is absent. The resemblance between Thaumatomastix sp. and other thaumatomonads has been discussed.     

Behavior of leucoplast nucleoids in the epidermal cell of onion (Allium cepa) bulb

Summary The behavior of nucleoids during the leucoplast division cycle in the epidermis of onion (Allium cepa) bulbs was investigated using DNA-specific fluorochrome 4'6-diamidino-2-phenylindole (DAPI) staining. The leucoplast was morphologically amoeboid and continuously changed its shape. A dumbbell-shaped leucoplast divided into two spherical daughter ones by constriction in the middle region of the body. Leucoplasts contained 4–10 mostly spherical, oval, partly rodand dumbbell-shaped nucleoids which were dispersed within the bodies. The proportion of one DNA molecule of a T4 phage particle to the small leucoplast nucleoid in the grain density of negative film was 1 to 0.91. Comparison of the present result and another groups' biochemical results suggested that a small leucoplast nucleoid contains one DNA molecule. The dumbbell-shaped leucoplast probably before division contained about twice as many nucleoids as the spherical leucoplast after division, and each half of the dumbbell contained about half the number of nucleoids. Nucleoids increased in number with growth of the leucoplast. The behavior of nucleoids during the leucoplast division cycle in onion bulbs was basically similar to that during the chloroplast division cycle in higher plants and green algae, which was previously reported (Kuroiwa et al. 1981 b).     

Electron Microscopic Observations on the Symbiosis of Paramecium bursaria and its Intracellular Algae*

SYNOPSIS. Observations were made on the fine structure of Paramecium bursaria and its intracellular Chlorella symbionts. Emphasis was placed on the structure of the algae and structural aspects of the relationship between the organisms. The algae are surrounded by a prominent cell wall and contain a cup-shaped chloroplast which lies just beneath the plasma membrane. Within the cavity formed by the chloroplast are a large nucleus, a mitochondrion, one or more dictyosomes, and numerous ribosomes. The chloroplast itself is made up of a series of lamellar stacks each containing 2–6 or more thylakoids with a granular stroma and starch grains intercalated between the stacks. The thylakoid stacks of mature algae are frequently more compact than those of recently divided algae. A large pyrenoid is located within the base of the chloroplast. It is made up of a granular or fibrillar matrix surrounded by a shell of starch. The matrix is bisected by a stack of 2 thylakoids. Prior to the division of the chloroplast the pyrenoid regresses; pyrenoids subsequently form in the daughter chloroplasts thru condensation of the matrix material and the reappearance of a starch shell. This shell appears to be formed by the hollowing-out of starch grains already present in the chloroplast stroma. Accordingly, in this case, starch moves from the stroma to the pyrenoid. The algae are located thruout the peripheral cytoplasm of the Paramecium. Each alga is located in an individual vacuole except immediately following division of the algae when the daughter cells are temporarily located in the vacuole which harbored the parental cell. Shortly thereafter the vacuole membrane invaginates, thereby isolating the daughter algae into individual vacuoles. Degenerating symbiotic algae are seen; because these are frequently found in vacuoles with bacteria, they are presumed to be undergoing digestion. Due to the conditions of culture these algae could have been either of intracellular or extracellular origin.     

THE DEVELOPMENT OF MUCILAGINOUS RAPHIDE CRYSTAL IDIOBLASTS IN YOUNG LEAVES OF TYPHA ANGUSTIFOLIA L. (TYPHACEAE)

Raphide crystal idioblast initiation occurs in the uppermost region of intercalary meristems in young leaves of Typha angustifolia L., and development proceeds acropetally. Idioblast differentiation commences with a loss of stored lipids, depletion of starch from amyloplasts, enlargement of the nucleus and nucleolus, cell elongation, and the formation of a central vacuole. Crystalloplastids are formed via dedifferentiation of amyloplasts, followed by an increase in plastid number as cell volume increases with cell elongation. Crystalloplastid membranes stain intensely with periodic acid-thiocarbohydrazide-silver proteinate (PA-TCH-SP). Following crystal production within the central vacuole, crystalloplastids differentiate lobed regions, dense with plastid ribosomes, thylakoids, lamellae, and plastoglobuli. Mucilage, which stains with PA-TCH-SP, appears to be formed at the tonoplast in the central vacuole and follows differentiation of crystalloplastid lobes. Crystal chambers are surrounded by lamellae during mucilage accumulation and the crystals undergo a change in shape. Lobed crystalloplastids may be involved in vacuolar mucilage formation in these types of raphide crystal idioblasts.     

An electron microscopic study of Babesia microti invading erythrocytes

Summary Intracellular sporozoan parasites invade the host cell through the invagination of the plasma membrane of the host and a vacuole is formed which accommodates the entering parasite. The vacuole may disappear and the invaginated membrane of the host then becomes closely apposed to that of the parasite's own membrane. As a result the parasite is covered by two membranes. Members of the class Piroplasmea differ from other Sporozoa in that their trophozoites are covered by a single membrane. By screening numerous sections of intraerythrocytic Babesia microti belonging to the class Piroplasmea, it was found that merozoites of Babesia enter the erythrocytes of hamsters in the same way as those of other Sporozoa. When a merozoite touches the red blood cell with its anterior end it becomes attached to the membrane of the host, which starts to invaginate and a parasitophorous vacuole is formed. The vacuolar space disappears rapidly and the membrane of the vacuole and that of the parasite become closely adjacent. At this stage the parasite is surrounded by two plasma membranes. The outer membrane derived from the invaginated host membrane disintegrates quickly and the parasite is left with a single membrane throughout its life span.Supported by Grant AI 08989 from the U.S. Public Health Service. The excellent technical assistance of Ms. Renata Klatt is gratefully acknowledged     

Acidity of the Thylakoid Lumen in Plastids Makes Sense from an Evolutionary Perspective

An acid pH in the lumen of chloroplast thylakoids is necessary in order to derive the required amount of CO₂ to account for the observed rates of carbon fixation. We point out that the endosymbiotic derivation of the chloroplast from a cyanobacterium would have resulted in the lumen of the thylakoid having an acid pH. The thylakoids of cyanobacteria are continuous with the plasma membrane, resulting in the lumen of the thylakoid being open to the outside of the cell. Endosymbiosis resulted in the cyanobacterium being taken up into a food vacuole of a protozoan. The vacuole would have had an acid pH, probably around pH 5, so the endosymbiotic bacterium would have been surrounded by an environment with an acidic pH. The lumen of the thylakoids would have been at an acid pH since they were open to the exterior of the cell, and to the contents of the vacuole.     

Leucoplast of the cryptomonad Chilomonas paramecium: Evidence for presence of a true plastid in a colorless flagellate

Chilomonas paramecium is a colorless cryptomonad flagellate which contains a leucoplast. The structural features of the leucoplast parallel those shown in the cryptomonad chloroplast, exemplified by Cryptomonas ovata. An electron microscopic study of this colorless organelle shows it to be divided into two compartments: the outer compartment contains starch granules and 220 Å ribosomes similar to cytoplasmic RNP particles. The inner compartment often contains carotenoid-like masses, 160 Å ribosomes significantly smaller than those in the outer compartment, and DNA-like filaments. Cesium-chloride density gradients of the whole-cell DNAs show three DNase-sensitive satellites in addition to the major fraction. One of them is presumed to be associated with the leucoplast. Evidence for the existence of true plastids in bleached and colorless flagellates is reviewed.     

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.     

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.     

LIGHT AND ELECTRON MICROSCOPY OF GRAZING BY POTERIOOCHROMONAS MALHAMENSIS (CHRYSOPHYCEAE) ON A RANGE OF PHYTOPLANKTON TAXA1

Grazing of fluorescent latex beads, bacteria, and various species of phytoplankton by Poterioochromonas malhamensis (Pringsheim) Peterfi (about 8.0 μm in diameter) was surveyed. The alga ingested fluorescent beads and various live or killed and nomnotile or motile organisms including bacteria, blue-green algae, green algae, diatoms, and chrysomonads. The size range of grazed prey was from 0.1 to 6.0 μm for latex beads and from 1.0 μm (bacteria) to about 21 μm (Carteria inverse) for organisms. As many as 17 latex beads (2.0 μm) or more than 10 Microcystis cells (5–6 μm) were ingested by a single P. malhamensis cell. Following such grazing, the cell increased in volume by up to about 30-fold. The range of cell volume of ingested prey was from 0.52 μm³ (bacteria) to about 3178 μm³(Carteria inversa). This study demonstrates for the first time that P. malhamensis is capable of grazing algae 2–3 times larger in diameter than its own cell and of grazing intact motile algae. Poterioochromonas malhamensis is an omnivorous grazer. Food vacuole formation and digestion processes were examined. The membrane that was derived from the plasma membrane and surrounded the prey disappeared sometime after ingestion. The food vacuole was then formed by successive fusion of numerous homogeneous vesicles accumulated around the prey. The prey was enclosed in a single membrane-bound food vacuole and then digested.     

Spatial organization and volume density of leucoplasts in pine secretory cells

Summary Spatial reconstructions of pine leucoplasts were obtained from thin serial sections of resin duct cells. Plastid volume and envelope surface were estimated using morphometric methods and compared to chloroplasts of adjacent parenchyma cells.The high number of plastid sections in secretory cells is not related to leucoplast division occurring during the secretory stage, but to the differentiation of complex, amoeboid plastids, closely imbricated with each other. Furthermore, there is no leucoplast network resulting from the fusion of preexisting plastids.In contrast to chloroplasts, leucoplast shape is not ruled by a single morphogenetic program but results from rapid growth in all directions, filling most of the free cytoplasmic space. The plastid surface is enclosed by a continuous sheath of endoplasmic reticulum.The leucoplast volume per cytoplasm volume unit in a secretory cell is 2.5 times that of chloroplasts in a parenchyma cell. Owing to the overlapping of plastid structures, the leucoplast surface is more than 3 times larger than that of chloroplasts with the same space factor. The active production of terpenes during the short period of secretion is supported by a very specialized structure, the leucoplastidome, where the biosynthetic process is optimized by an increase in plastid volume and enlargement of the plastid surface allowing rapid processing of precursors and free outflow of the end products.     

杉木小孢子核内双膜包绕的内含体(简报)

杉木小孢子的发育已进行了系统的电子显微镜研究。在研究中我们发现小孢子发育到一定阶段,细胞核内出现一种双膜包绕的内含体。这种有膜内含体无论在结构上,发生的普遍性和阶段性上都与已有的报道不同,是首次发现。研究材料为杉木(Cunninghamia lanceola-     

Light and electron microscope observations on Unikaryon legeri (Microsporida,Nosematidae), a parasite of the metacercaria of Meigymnophallus minutus in Cardium edule

Nosema legeri from the metacercariae of Meigymnophallus minutus in Cardium edule has been shown by light and electron microscopy to be disporous and to lack nuclei in diplokaryon form throughout its development. Although its ultrastructure resembles that of Encephalitozoon cuniculi and mature spores often lay in vacuoles surrounded by host membranes, dividing stages were never present in a common vacuole. Sporoblasts showed a cytoplasmic protuberance suggestive of a locomotory organelle. It is possible that movement of these stages disrupts the host cell cytoplasm and creates the vacuole in which the spores mature. The species has been transferred to the genus Unikaryon Canning, Lai and Lie and named Unikaryon legeri(Dollfus, 1912).     

Fine Structure of Yellow-Brown Symbionts (Prymnesiida) in Solitary Radiolaria and Their Comparison with Similar Acantharian Symbionts1

Yellow-brown, algal symbionts varying in diameter from approximately 5 μ m to 20 μ m, associated with solitary Radiolaria with spongiose skeletons (i.e. Spongodrymus sp.), exhibit fine structural features resembling the Prymnesiida (botanical class, Prymnesiophyceae). A large central vacuole is surrounded by a thin layer of cytoplasm containing plastids with lamellae composed of three thylakoids and granular pyrenoids with internal tubules immersed between the thylakoids. The pyrenoids lack internal thylakoid membranes. The nucleus is surrounded by a dilated cisterna of the nuclear envelope that also encloses the plastids and gives rise to saccules of the endoplasmic reticulum. The algal symbionts appear coccoid; hence no flagella nor surface scales were observed. The symbiont fine structure is compared to similar yellow-brown symbionts associated with Acantharia. Thus far, three kinds of algal symbionts have been observed to be associated with solitary Radiolaria: dinoflagellate, prasinomonad, and this apparent prymnesiomonad.     

Amyloplast Sedimentation in Shoot Statocytes having a Large, Central Vacuole: Further Interpretation from Electron Microscopy

The claim (Lawton, Juniper, and Hawes, 1986) that amyloplastssediment through the central vacuole of geostimulated shootstatocytes has been critically examined. As the result of ourTEM study of Taraxacum statocytes and from theoretical considerationsof amyloplast sedimentation, we conclude that it is possiblefor individual amyloplasts surrounded by a layer of tonoplast-boundedcytoplasm to travel occasionally through the vacuole, but unlikelythat the majority of the amyloplasts in a statocyte sedimentin this manner. We put forward a scheme for amyloplast movementin shoot statocytes which emphasizes the fluidity of the tonoplastmembrane. In this scheme, it is expected that most amyloplastssediment in peripheral cytoplasm down the statocyte cell wall,but amyloplasts may also, as they sediment, create or breaktransvacuolar strands, or move through already existing transvacuolarstrands, or fall through the vacuole while enclosed by somecytoplasm and tonoplast membrane. Finally, it is suggested thatthe tonoplast membrane may have been neglected as a membranesite for detection of the gravity stimulus through interactionwith sedimenting amyloplasts. Key words: Amyloplast sedimentation, statocytes, geotropism, Taraxacum officinale     

Structure and behavior of contractile vacuoles inChlamydomonas reinhardtii

Summary The contractile vacuole (CV) cycle ofChlamydomonas reinhardtii has been investigated by videomicroscopy and electron microscopy. Correlation of the two kinds of observation indicates that the total cycle (15 s under the hypo-osmotic conditions used for videomicroscopy) can be divided into early, middle, and late stages. In the early stage (early diastole, about 3 s long) numerous small vesicles about 70–120 nm in diameter are present. In the middle stage (mid-diastole, about 6 s long), the vesicles appear to fuse with one another to form the contractile vacuole proper. In the late stage (late diastole, also about 6 s long), the CV increases in diameter by the continued fusion of small vesicles with the vacuole, and makes contact with the plasma membrane. The CV then rapidly decreases in size (systole, about 0.2 s). In isosmotic media, CVs do not appear to be functioning; under these conditions, the CV regions contain numerous small vesicles typical of the earliest stage of diastole. Fine structure observations have provided no evidence for a two-component CV system such as has been observed in some other cell types. Electron microscopy of cryofixed and freeze-substituted cells suggests that the irregularity of the profiles of larger vesicles and vacuoles and some other morphological details seen in conventionally fixed cells may be shrinkage artefacts. This study thus defines some of the membrane events in the normal contractile vacuole cycle ofChlamydomonas, and provides a morphological and temporal basis for the study of membrane fusion and fluid transport across membranes in a cell favorable for genetic analysis.Abbrevations CV contractile vacuole - PM plasma membrane     

Ultrastructural Evidence for Bacterial Incorporation and Myxotrophy in the Photosynthetic Cryptomonad Chroomonas Pochmanni Huber-Pestalozzi (Chyptomonadida)

Ultrastructural evidence indicates that bacteria are routinely incorporated into the Cells Chroomonas Pochmanni. This strain has a specialized vacuole for capturing bacteria and retaining them in this vacuole. Bacteria appear to be drawn into the vacuole through a small opening which becomes occluded by membranes, completely enclosing the Bacteria. On rare occasions, ohter membrane components and intact ejectisomes also become incorporated into this vacuole. Bacteria-like remnants in small vesicles, in other locations in the cell, suggest that bacteria are digested in these vesicles.     

Chloroplast development in isolated roots of Convolvulus arvensis (L.)

Summary The fine structure of chloroplast development is described for isolated roots of Convolvulus arvensis. Stages in the transition from the leucoplast, characteristic of dark-grown roots, to the chloroplast, found in light-grown roots, are defined and related to chlorophyll content of the root tissue. The interdependence of tissue type and organellogenesis has been investigated for three tissues in the primary root: cortical parenchyma, pericycle and stelar parenchyma tissue. Plastids in cells of all three tissues follow the same sequence of chloroplast development, although the rate of development is dependent on the tissue type.This work was supported by National Science Foundation grant GB-5040 and U.S. Public Health Service grant No. GM-16353.