STRUCTURE AND REPRODUCTION OF THE ALGAL SYMBIONTS OF HYDRA VIRIDIS1

The algal symbionts of Hydra viridis are found within vacuoles of the gastrodermal digestive cells of the host. Electron microscopy reveals that the symbionts possess cell walls, and that their reproductive cycle follows the general pattern of free-living Chlorella. Nuclear and chloroplast divisions arc followed by formation of new cell walls, the Golgi apparatus being quite active during cell wall synthesis. Autospores are released when the parent wall ruptures. The autospores are then usually segregated into separate animal vacuoles. Remnants of the ruptured parent wall persist in the vacuoles for an indefinite period. The ruptured parent walls curl at the breakage clefts, forming double-layered scroll-like structures. The fate of these wall remnants has not been firmly established. Long-term starvation of the animals does not result in a detectable change in the structure of the symbionts, and they continue to divide and to store carbohydrate as starch grains.     

DEVELOPMENT OF PERIPHERAL VACUOLES IN PLANT CELLS

The vacuolar apparatus of various plant cells consists of two distinct features: the large central vacuole and peripheral vacuoles which are derived from invaginations of the plasma membrane. Peripheral vacuoles are conspicuous structures in both living and fixed hair or filament cells of Tradescantia virginiana. They occur as spherical structures along the inner boundary of the peripheral cytoplasm and can be recognized as projections into the central vacuole. These structures are variable in size and number within a cell and can represent a significant proportion of the volume of the vacuole. Peripheral vacuoles most frequently are observed in motion with the streaming cytoplasm although their velocity is usually somewhat slower that that of the cytoplasmic organelles. Ultrastructural studies show two closely approximated membranes, one for each vacuole, in areas where a peripheral vacuole projects into the central vacuole. These are separated by an intermembrane zone continuous with the peripheral cytoplasm. The movement of organelles over the perimeter of the peripheral vacuole is presumed to occur along this intermembrane zone. The internal area of the peripheral vacuoles may appear empty although some contain a vesicular content of unknown origin and function.     

Developmental sequence of the attack apparatus ofHaptoglossa mirabilis

Summary The most prominent ultrastructural characteristics of the cyst ofHaptoglossa mirabilis are a large centrally-placed nucleus which is partially ringed by three or four parallel cisternae of rough endoplasmic reticulum (r-ER), a centriole pair and single large Golgi complex which occupy the anterior end of the cell, and a population of provacuoles which occupies the posterior. During germination these organelles migrate into a narrow germ tube which subsequently expands to form the gun cell initial. The extracellular components of the attack apparatus (i.e. missile and injection tube) are formed entirely in the developing gun cell; indirect evidence suggests that both the Golgi complex and r-ER are involved in their synthesis. The intra-cellular component of the attack apparatus comprises the posterior, anterior and apical vacuoles. The posterior vacuole forms by fusion and expansion of the original cyst provacuoles; the formation of the anterior and apical vacuoles occurs late in gun cell differentiation and involves fusion of Golgi-derived vesicles.     

Dynamic organization of vacuolar and microtubule structures during cell cycle progression in synchronized tobacco BY-2 cells

In higher plant cells, vacuoles show considerable diversity in their shapes and functions. The roles of vacuoles in the storage, osmoregulation, digestion and secretory pathway are well established; however, their functions in cell morphogenesis and cell division are still unclear. To observe the dynamic changes of vacuoles in living plant cells, we attempted to visualize the vacuolar membrane (VM) by pulse-labeling tobacco BY-2 cells with a styryl fluorescent dye, FM4-64. By time-sequence observations using confocal laser scanning microscopy (CLSM), we could follow the dynamics of vacuolar structures throughout the cell cycle in living higher plant cells. We also confirmed the dynamic changes of VM structures by the observation using transgenic BY-2 cells expressing GFP-AtVam3p fusion protein (BY-GV). Furthermore, by using transgenic BY-2 cells that stably express a GFP-tubulin fusion protein [BY-GT16, Kumagai et al. (2001) Plant Cell Physiol. 42: 723], we could study the relationship between the dynamics of vacuoles and microtubules. From these observations, we identified, for the first time, some remarkable events: (1) at the late G(2) phase, tubular structures of the vacuolar membrane developed in the central region of the cell, probably in the premitotic cytoplasmic band (phragmosome), surrounding the mitotic apparatus; (2) from anaphase to telophase, these tubular structures invaded the region of the phragmoplast within which the cell plate was being formed; (3) at the early G(1) phase, some of the tubular structures expanded rapidly between the cell plate and daughter nuclei, and subsequently developed into large vacuoles at interphase.     

The electron microscopic and classic Golgi apparatus

The relationship of the membrane structure, designated in electron microscopy as the Golgi apparatus, to the classic Golgi apparatus in the light microscope were studied withFagopyrum. Comparison of these structures in plant cells with the same or similar structures in animal cells led to the following conclusions: there exist two groups of formations, impregnable with osmium or silver, considered as the classic Golgi apparatus. The first group contains the active membrane structures. These are the dictyosomes and the anastomosing form of the electron microscopic Golgi apparatus. To this group belongs also the endoplasmatic reticulum, which in plant cells forms dense vacuoles, having the appearance of the classic Golgi apparatus, and in animal cells occasionally has a similar arrangement as the anastomosing form of the Golgi apparatus. The second group comprises formation containing reserve and secretion material, i.e. predominantly products of the activity of the electron microscopic Golgi apparatus and of the endoplasmic reticulum (matter of the dense vacuoles, lipochondria, secretory granula etc.). In the plant cells, especially ofFygopyrum, the dictyosomes contained in the structures of the first group are separated from the formations of a reserve character in the second group, formed in the lumen of the endoplasmic reticulum (dense vacuoles). The identity of the dictyosomes with the osmiophilic platelets, considered by some authors in the light microscope as the classic Golgi apparatus, has not been proved up to present, because of the one-sidedness of the methods used nowadays. WithFagopyrum no foundation has been observed for the assumed formation of net-form structures by grouping of the dictyosomes. Structures similar to the net-form of the classic Golgi apparatus in the animal cell form only dense vacuoles. On the basis of the differentiation of both types of formations in the plant cell, the foundations were laid for the characterization of the classic Golgi apparatus in the animal cell. The net-form of the classic Golgi apparatus in the animal cell is obviously not artificial, but reflects the ultrastructural arrangement of the electron microscopic Golgi apparatus or of the endoplasmic reticulum. The problem of the suitability and specification of the name Golgi apparatus in the animal and plant cell was also discussed. In contrast to the opinion of some authors, it does not appear useful to remove the name golgi apparatus, designating the dictyosomes and the anastomosing forms of the smooth membranes.     

ABSOLUTE CONFIGURATION ANALYSIS OF THE FLAGELLAR APPARATUS OF PTEROSPERMA CRISTATUM (PRASINOPHYCEAE) AND CONSIDERATION OF ITS PHYLOGENETIC POSITION1

Pterosperma cristatum Schiller, a member of the Pra-sinophyceae, was examined with light and electron microscopy with special attention on the absolute configuration of flagellar apparatus components and associated structures. This alga is characterized by asymmetrically arranged basal bodies, connecting fibers and microtubular roots. The microtubular root system is homologous with the cruciate root system, the so-called X-2-X-2 root system typical of non-charophycean green algae. Two ducts are associated with microtubular roots. A similar flagellar apparatus and duct system was found in two other prasinophyte genera, Pyramimonas and Halosphaera. The close phylogenetic affinity of these three genera is discussed.     

The neural gland in tunicates: fine structure and intracellular distribution of phosphatases

Summary The cells comprising the neural gland in the ascidians Ciona, Styela, and Botryllus have been examined for their fine structural features and enzyme cytochemistry. The gland cells are either cuboidal or irregular in outline. They are full of small vesicles, of which some are pinocytotic, as well as larger vacuoles; they become increasingly vacuolated as their shape decreases in regularity. At the same time, glycogen deposits accumulate and the cisternae of the endoplasmic reticulum become distended. Some of the vacuoles contain an electron dense material or a fibrillar substance, but the cells contain no obvious electron opaque secretory granules associated with an extensive Golgi complex such as occur in the vertebrate adenohypophysis.Acid phosphatase is localized in some of the vesicles and vacuoles, indicating that they are a kind of lysosome, the latter possibly representing autophagic vacuoles. Thiamine pyrophosphatase is also found in many vacuoles as well as in the saccules of the Golgi apparatus which in these cells is in the form of dictyosomes.The results suggest a developmental cycle of increasing cytoplasmic vacuolation, ultimately leading to a breakdown and release of the vacuolar products. The significance of these observations is considered, particularly with respect to the hypothesis that the gland represents the ascidian equivalent of the vertebrate pituitary.I am grateful to Miss Yvonne R. Carter for technical assistance with the photography and to Mr. John Rodford for producing the diagram.     

Ultrastructure and anatomy of nematode-induced syncytia in roots of susceptible and resistant sugar beet

Summary Using susceptible and resistant sugar beet lines, comparative analyses of root histology and ultrastructure were made during invasion by nematodes and the induction and formation of specific feeding structures (syncytia).The resistant line carried the resistance geneHs1^pro–1.Nematodes were able to invade and induce functional syncytia in roots of resistant and susceptible lines. However, syncytia in resistant roots were smaller and less hypertrophied. The vacuolar system of syncytia in susceptible plants contained many small vacuoles. In resistant plants vacuoles were larger but less numerous. Smooth endoplasmic reticulum prevailed in syncytial protoplasts of susceptible plants, whereas almost only rough endoplasmic reticulum occurred in syncytia in resistant plants. The most conspicuous and hitherto undescribed trait of syncytia in resistant roots was the initial appearance of loose, and later compact, aggregations of the endomembrane system which composed most of the endoplasmicreticulum system of syncytia at later stages. Syncytia in resistant plants usually degraded before the nematodes reached their adult stage. The appearance of membrane aggregations and the other resistance-specific features are discussed in relation to their possible effects on syncytium function and role in nematode resistance.Abreviations DAI days after inoculation - ER endoplasmic reticulum - ISC initial syncytial cell - J2 second-stage juvenile - MA membrane aggregations - RER rough endoplasmic reticulum - SER smooth endoplasmic reticulum     

Histological study of organogenesis and embryogenesis inCyclamen persicum Mill. tissue cultures: Evidence for a single organogenetic pattern

Summary Evidence is given thatCyclamen persicum callus culture give rise to structures such as shoot-buds, roots, unipolar tubers, bipolar tubers and embryos. Observations made on their structure by means of morphological and histological analyses are reported and discussed in relation to the anatomy of someCyclamen structures such as zygotic embryos and seedling tubers. Such analyses demonstrate that the bipolar structures including somatic embryos and bipolar tubers lack vascular connection with the callus whereas unipolar structures establish vascular strands with the callus. Here, the relationship between these regenerated structures is depicted. The organogenetic pattern inCyclamen persicum callus culture could well be a derived pathway for somatic embryogenesis. A theoretical diagram concerning the morphogenetic program is presented.     

ELECTRON MICROSCOPE STUDIES ON THE DICTYOSOMES AND ACROBLASTS IN THE MALE GERM CELLS OF THE CRICKET

The dictyosome (Golgi body) in the secondary spermatocyte of the cricket appears in electron micrographs as a duplex structure composed of (a) a group of parallel double-membraned lamellae and (b) a group of associated vacuoles arranged along the compact lamellae in a chain-like fashion. This arrangement of ultramicroscopic structure for the dictyosomes is strikingly comparable to that described for the Golgi apparatus of vertebrates. Accordingly, the two are considered homologous structures. Associated with the duplex structure of the dictyosomes is a differentiated region composed of small vacuoles. This is thought to represent the pro-acrosome region described in light microscope preparations. In the spermatid the dictyosomes fuse, giving rise to the acroblast. Like the dictyosomes, the acroblasts are made up of double-membraned lamellae and associated vacuoles. In addition, a differentiated acrosome region is present which, in some preparations, may display the acrosome vacuole and granule. Both the dictyosomes and acroblasts are distinct from mitochondria.     

Uptake of Lucifer Yellow CH into intact barley roots: Evidence for fluid-phase endocytosis

Intact barley (Hordeum vulgare L.) roots have been shown to take up the highly fluorescent dye Lucifer Yellow CH (LYCH) into their cell vacuoles. In the apical 1 cm of root tip, differentiating and dividing cells showed a prolific uptake of LYCH into their provacuoles. The LYCH was retained during fixation, apparently becoming bound to electron-dense material in the vacuoles. The dye freely entered the apoplast of roots in which the Casparian band was not developed, being taken up into the vacuoles of cells in both the cortex and stele. However, when LYCH was applied to a 1-cm zone approx. 6 cm behind the root tip the Casparian band on the radial walls of the endodermis completely prevented the dye from entering the cells of the stele, only the cell walls and vacuoles of the cortical cells taking up the dye. The inability of LYCH to cross the plasmalemma of the endodermal cells and enter the stele via the symplast substantiates previous claims that the dye is unable to cross the plasmalemma of plant cells. The results are discussed in the light of recent demonstrations that LYCH is a particularly effective marker for fluid-phase endocytosis in animal and yeast cells. A calculation of the energetic requirements for LYCH uptake into barley roots supports the contention that LYCH is taken up into the vacuoles of plant cells by fluid-phase endocytosis.Abbreviation LYCH Lucifer Yellow CH     

Studies on microplasmodia ofPhysarum polycephalum: Endocytotic activity,morphology of the vacuolar apparatus and defecation mechanism

Summary The investigation of endocytotic processes in axenically cultured microplasmodia ofPhysarum polycephalum is considerably complicated by the development of an extensive cell membrane invagination system. Cross-sections through single channels of this system are difficult to distinguish from vacuoles formed endocytotically. Therefore the whole system was labelled by staining the extracellular slime with ruthenium red or lanthanum hydroxide. In this way endosomes produced during the incubation period could be clearly identified. Aerosil andThorotrast are suitable markers for food vacuoles because they can easily be detected with the electron microscope. The application of these substances revealed that submerged cultured microplasmodia are able to form endosomes which contain material of extracellular origin. However, the endocytotic uptake of food material is of much less intensity than in normal macroplasmodia. Microplasmodia seem to cover most of their requirements for metabolic substances by active trans-membrane transport.The intracellular digestive system of microplasmodia corresponds to the vacuolar apparatus of other cells. Preexisting lysosomes originating by autophagic processes play a central role in this system: They coalesce with endosomes or secondary lysosomes thus forming digestion vacuoles. Indigestible food components are extruded together withCa-containing granules into the cell surface invagination system by defecation. The physiological significance of theCa-granules is unknown.     

ULTRASTRUCTURAL ASPECTS OF CELL ELONGATION,CELLULOSE SYNTHESIS,AND SPORE DIFFERENTIATION IN ACYTOSTELIUM LEPTOSOMUM,A CELLULAR SLIME MOLD

Vegetative myxamoebae of Acytostelium leptosomum, a cellular slime mold, have the appearance of typical eucaryotic cells. The presence of dictyosomes has been established. Elongation of the cells during aggregation and culmination appears to be mediated by dense bundles of microfibrils traversing the cells longitudinally. Microtubules are present; however, they are randomly oriented and no correlation can be made with cell elongation or with the direction of the cellulose microfibrils within the stalk. A variety of vesicles, multivesicular bodies, and lysosome-like vacuoles seems to be involved in producing and transporting stalk material to the vicinity of the stalk. However, only rarely do the vesicles empty their contents directly to the outside of the cells. It seems rather that the fibrillar material of the stalk is assembled near or directly at the plasmalemma, and can then be seen to stream away and become an integral part of the stalk. An unusual structure, the H-body, is formed in great abundance during culmination indicating its possible involvement in stalk synthesis. The H-bodies are removed from the cells prior to spore formation together with other portions of the cytoplasm at least partly by a process involving autophagic vacuoles. These vacuoles, which are also present in the spores, appear to be part of a rather complex and extensive vacuolar apparatus including the food vacuoles, contractile vacuoles, lysosome-like structures, and possibly the H-bodies. The spore coat consists of a heavy outer wall with a fibrillar substructure and two thin, dense bands lining the inside of the plasmalemma. The fibrillar nature of both the outer spore wall and the stalk was accentuated by using barium permanganate to stain sectioned material.     

Auffällige ER-Konfigurationen in Protein-Polysaccharidschleim-sezernierenden pflanzlichen Drüsen

In the ovary of Aptenia cordifolia and Platythyra haeckeliana placentary papillae produce a slime containing polysaccharides and proteins. These papillae show two types of conspicuous vacuoles enclosed by rough ER cisternae and complexes of concentrically arranged rough ER. The enclosed vacuoles probably play an important role in the accumulation of the polysaccharide-protein slime. In the case of storage vesicles (first vacuole type) derivates of the Golgi apparatus are enclosed by ER. In other instances (second vacuole type) ER cisternae which have lost their membrane-bound ribosomes seem to delimit protoplasmic regions free of organelles.

     

STRUCTURE AND ABSOLUTE CONFIGURATION OF THE FLAGELLAR APPARATUS IN THE ISOGAMETES OF BATOPHORA (DASYCLADALES,CHLOROPHYTA)1

The overall appearance of the flagellar apparatus in the isogametes of Batophora oerstedii. J. Ag. is most like that which occurs in motile cells of the Ulvophyceae. Like other Ulvophyceae, the basal bodies overlap and are arranged in the 11/5 configuration, microtubular roots are arranged in a cruciate pattern and system II striated fibers are present. The basal body connective which generally lacks striation in the Ulvophyceae is clearly different in Batophora, being composed of two large non-striated halves which connect to the anterior surface of each basal body and are then connected to one another by a distinctly fibrous centrally striated region. This variation in the basal body connective and the presence of two posteriorly directed system II striated fibers is clearly different from homologous structures reported in siphonous green algae of the Caulerpales. Based upon these variations and similarities among flagellar apparatus components in siphonous green algae, it is suggested that the Dasycladales and Siphonodadales are more closely related to one another than to the Caulerpales.     

Ultrastructural features of the salt gland of Tamarix aphylla L.

Summary The salt gland in Tamarix is a complex of eight cells composed of two inner, vacuolate, collecting cells and six outer, densely cytoplasmic, secretory cells. The secretory cells are completely enclosed by a cuticular layer except along part of the walls between the collecting cells and the inner secretory cell. This non-cuticularized wall region is termed the transfusion are (Ruhland, 1915) and numerous plasmodesmata connect the inner secretory cells with the collecting cells in this area. Plasmodesmata also connect the collecting cells with the adjacent mesophyll cells.There are numerous mitochondria in the secretory cells and in different glands they show wide variation in form. In some glands wall protuberances extend into the secretory cells forming a labyrinth-like structure; however, in other glands the protuberances are not extensively developed. Numerous small vacuoles are found in some glands and these generally are distributed around the periphery of the secretory cells in association with the wall protuberances. Further, an unusual structure or interfacial apparatus is located along the anticlinal walls of the inner secretory cells. The general structure of the gland including the cuticular encasement, connecting plasmodesmata, interfacial apparatus, and variations in mitochondria, vacuoles, and wall structures are discussed in relation to general glandular function.     

Ultrastructural Characteristics of Three Chenopod Halophytes Lacking Salt Excretion Structures

Plants maintained in high soil salinity generally develop particular structures to either tolerate or survive such adverse environments. Excretion of excess ions by special salt glands or other similar structures is a well-known phenomenon for regulating the mineral content of many halophytes. However, the three chenopod halophytes of Suaeda inhabit high saline soils, yet they exhibit no signs of salt excretion structures. The current study has been undertaken to assess the structural attributes of these halophytes to reveal their cellular characteristics during growth in salt tolerance. Transmission and scanning electron microscopy, as well as ion chromatography, have been employed for the study. One of the most noticeable features uncovered was the epidermal cutinization shown to be heavy on the outer epidermis and characterized externally by thick wax plates. Numerous vesicles and membranous invagination in the vacuoles were common features within the mesophyll cytoplasm. Invaginations of the vacuolar and/or plasma membrane frequently formed secondary vacuoles which later became distinct, membrane-bound compartments. Significant accumulation of solid sodium chloride salts was well demonstrated in the vacuoles of air-dried epidermis. Finally, salt tolerance mechanisms in these Suaeda have been discussed with respect to other halophyte modifications that improve salt tolerance in various ways.     

Some observations on the morphological evidence for mechanism of the bile secretion

The morphological evidence of the intracellular route of bile secretion was investigated in the liver of goldfish (Carassius auratus) as revealed by electron microscopy. Smooth surfaced tubules or cisterns within or adjacent to the Golgi apparatus showed linear saccular forms and contained sparse particulate or cloudy materials of low electron density. The isolated vacuoles were restrictedly found between the Golgi apparatus and the intracellular bile canaliculus or hepatocytic side at the zone of transition. These vacuoles showed no reaction for acid phosphatase activity, and contained only a few cloudy materials similar to those found in the saccular tubules and within the bile canaliculus. Some of these vacuoles fused with the luminal cytolemmas of the bile canaliculus. Bases on these findings, it was assumed that these vacuoles are structures participating in transport and secretion of bile constituents and derive from the linearly sacculated tubules or cisterns in the Golgi zone. Duct cells showed no morphological evidence to suggest bile secretion.     

Movement of Amyloplasts in the Statocytes of Geotropically Stimulated Roots. The Pre-Inversion Effect

Previously inverted Lepidium roots were placed in a horizontal position and the amyloplasts in the statocytes of the root cap allowed to fall through their entire range of movement across the cell. Under these conditions the amyloplasts first follow a mainly downward course for 6 to 8 min at a speed between 0.5 and 0.8 μm per min. For the next 10 min they move slightly more slowly in a direction away from the apical end of the cell, still sinking somewhat, but without reaching the plasmalemma along the lower wall. Previous experiments have shown that conditions assumed to allow the amyloplasts to slide parallel to the longitudinal cell walls are those that give rise to the largest geotropic curvatures. Such conditions are for instance (1) stimulation at 135° (root tips pointing obliquely upward) and (2) inversion of roots for 16 min followed by stimulation at 45°. Treatments assumed not to permit extensive sliding of the amyloplasts produce smaller geotropic curvatures, namely (3) stimulation at 45° without pre-inversion and (4) inversion followed by stimulation at 135°. The location of the amyloplasts after these four kinds of treatment has now been determined on photomicrographs and the assumptions concerning the paths and extent of sliding of the amyloplasts confirmed. Observations on electron micrographs showed that under all conditions the amyloplasts are separated from the plasmalemma by other organelles, such as ER, nucleus or vacuoles. In roots rotated for 15 min parallel to the horizontal axis of the klinostat at 2 rpm, the amyloplasts are not clumped together as densely as in normal, inverted or stimulated roots, but they are not scattered over the entire cell volume. The statolith function of the amyloplasts is discussed in view of these and other observations.     

The classic Golgi apparatus and vacuoles

The dense vacuoles, considered to be the classic Golgi apparatus in the root meristem ofFagopyrum, were studied by the following methods: 1. Impregnation methods for the demonstration of the Golgi apparatus, 2. cytochemical methods, 3. electron microscopic methods in the light microscope and 4. the electron microscope. A comparison was made with the classic Golgi apparatus in animal cells in the light and electron microscope. Dense vacuoles inFagopyrum and also evidently in other plants, were taken for the classic Golgi apparatus on account of their morphological similarity to the Golgi apparatus in animal cells on impregnation with silver and osmium and their staining preperties with lipoid methods. Dense vacuoles differ from the classic Golgi apparatus in other chemical properties, such as content of phenol substances, etc. No formations were found in animal cells which were similar to dense vacuoles on investigating by electron microscopy. In the electron microscope dense vacuoles have the appearance of derivatives of the normal light vacuoles known in plant cells. They therefore belong to vacuome of plant cell and cannot be analogous to the classic Golgi apparatus in animal cells. Thus the use of the term Golgi apparatus for dense vacuoles is not well founded. A comparison was made of fixation and impregnation used in the light microscope with fixation in the electron microscope. After fixation with permanganate, dense vacuoles have the same shape as after impregnation. After fixation with permanganate, they stain an intense black in the same way as after impregnation with silver and osmium. The form of the vacuoles is dependent on the fixation used. The comparison was made in the light microscope.