The ultrastructure of the salt gland of Spartina foliosa

Summary The salt gland in Spartina foliosa is composed of two cells, a large basal cell and a smaller, dome-shaped cap cell which is located on a neck-like protrusion of the basal cell. There is no cuticular layer separating the salt gland from the mesophyll tissue. The basal cell has dense cytoplasm which contains numerous mitochondria, rod-like wall protuberances, and infoldings of the plasmalemma which extend into the basal cell and partition the basal cell cytoplasm. The protuberances originate on the wall between the basal and the cap cells and are isolated from the basal-cell cytoplasm by the infoldings of the plasmalemma. While the cap cell has no partitioning membrane system or wall protuberances, it resembles the basal cell by having dense cytoplasm and numerous mitochondria.The basal cell seems to be designed for efficient movement of ions toward the cap cell. The long, dead-end extracellular channels in the basal cell of Spartina appear comparable to surface specializations seen in the secreting epithelium of animal cells which carry out solute-linked water transport. The number of mitochondria and their close association with the plasmalemma extensions suggest that they have an important role in the transfer of ions through the basal cell.The accumulated ions would move into the extracellular spaces along an osomotic gradient where the accompanying passive flow of water would move the ions into the cap-cell wall and from there the solution would pass out through the pores in the cuticle.     

THE ULTRASTRUCTURE OF THE SALT GLANDS OF CYNODON AND DISTICHLIS (POACEAE)

The epidermal salt glands of the grasses Cynodon and Distichlis consist of a small outer cap cell and a large, flask-shaped basal cell. The wall of the basal cell is contiguous with those of the adjacent epidermal cells and underlying mesophyll cells. The basal cell is connected symplastically with all adjoining cells via plasmodesmata. The outer, protruding portion of the glands is covered by a cuticle continuous with that of the adjoining epidermal cells. However, the lateral cell walls of the glands are not incrusted by this cuticle. The cap cell wall has a loose, mottled appearance quite different from the compact striated appearance of the basal cell wall. The cap cell is characterized by dense cytoplasm containing many organelles and a varying number of small vacuoles. The basal cell cytoplasm is distinguished by the presence of an intricate system of paired membranes that are closely associated with mitochondria and microtubules. These membranes are infoldings of the plasmalemma that originate adjacent to the wall separating the cap and basal cells. The space enclosed by the paired membranes, therefore, is an extracellular channel that is open only in the direction of secretory flow. The consistent orientation of this system of paired membranes suggests that it represents a structural specialization which is directly and functionally involved in the secretory process. The close association of mitochondria and microtubules with the paired membranes implies that these structures are also functionally related to the secretory process. Finally, the results of this study indicate that these glands are ultrastructurally similar to those of Spartina and that the glands of these three grasses are structurally distinct from those of dicotyledonous plants.     

The Ultrastructure of Ion-Secreting and Non-Secreting Salt Glands of Limonium platyphyllum

The ultrastructure of salt glands in developing leaves of Limoniumplatyphyllum is described prior to exposure to 3% NaCl solution(with non-secreting glands) and after 4.5 and 18 h exposureto the salt solution. It is shown that in most glands, the transitionto active chloride transport was accompanied by the displacementof vacuoles toward the cell periphery and by the establishmentof plasmalemma contact sites with the tonoplast which appearedsimilar to gap junctions in animal epithelial cells. No evidencefor the exocytosis of vacuoles was found. It is suggested thatgland vacuoles may have a primary role in chloride secretionand that the tonoplast may be functionally asymmetrical, sothat the free part facing the hyaloplasm bears ion pumps, whereashighly permeable ion channels are active along the zone of contactwith the plasmalemma. It follows that the active step in chloridetransport in Limonium glands is the influx of ions into thevacuoles. Within the inner cup cells of the gland, vacuolescome into contact with the plasmalemma only at sites where thecell wall is adjacent to secretory and accessory cells. Suchan asymmetry appears to ensure the directed flux of ions intothis cell wall. Wall protuberances in the gland cells are rudimentaryand presumably not involved directly in NaCl secretion. Thenucleolus is activated during secretion and the frequency offree ribosomes is significantly increased, which is suggestiveof their involvement in the synthesis of membrane transportproteins. The ultrastructure of about one-third of the glandsremained unchanged in salt-treated leaves. Key words: Salt glands, ultrastructure, ion fluxes     

OBSERVATIONS ON THE STRUCTURE OF SOME FORMS OF GOMPHONEMA PARVULUM KÜTZ. III. FRUSTULE FORMATION1

Gomphonema parvulum Kütz. was investigated by electron microscopy for details of frustule formation. An expansion of the cell along the pervalvar plane occurs prior to cell division. After nuclear division the organelles are, separated into 2 entities, either by division or by dispersion. The cell divides into 2 halves by the invagination of the plasmalemma which is derived from Golgi vesicular activity. When cytoplasmic cleavage, is complete, the Golgi actively produces electronlucent vesicles which collect and coalesce beneath the. plasmalemma to form the silicalemma around the silicon deposition vesicle. The endoplasmic reticulum is also closely associated with this vesicular activity. The vesicle gradually expands and becomes extremely electron dense as silica is deposited within it—first in the region, followed by the mantle edge. When the valve is mature, Golgi vesicles collect and fuse to form the silicalemma of the first girdle band. The first girdle band becomes aligned against the mantle edge on completion, by the “sloughing off” of the external silicalemma and plasmalemma. The second and third bands are formed, individually in a similar manner. Separation of the 2 daughter cells commences at the apical pole and progresses to the basal pole. The plasmalemma and external silicalemma are “sloughed off” so that the 2 cells can separate. The inner segment of the silicalemma becomes the new plasmalemma of the daughter cell.     

Comparative ultrastructure of coxal glands in unfed larvae of Leptotrombidium orientale (Schluger, 1948) (Trombiculidae) and Hydryphantes ruber (de Geer, 1778) (Hydryphantidae)

Coxal glands of unfed larvae Leptotrombidium orientale (Schluger, 1948) (Trombiculidae), a terrestrial mite parasitizing vertebrates, and Hydryphantes ruber (de Geer, 1778) (Hydryphantidae), a water mite parasitizing insects were studied using transmission electron microscopy. In both species, the coxal glands are represented by a paired tubular organ extending on the sides of the brain from the mouthparts to the frontal midgut wall and are formed of the cells arranged around the central lumen. As in other Parasitengona, the coxal glands are devoid of a proximal sacculus. The excretory duct, joining with ducts of the prosomal salivary glands constitutes the common podocephalic duct, opening into the subcheliceral space. The coxal glands of L. orientale are composed of a distal tubule with a basal labyrinth, an intermediate segment without labyrinth, and a proximal tubule bearing tight microvilli on the apical cell surface and coiled around the intermediate segment. The coxal glands of H. ruber mainly consist of the uniformly organized proximal tubule with apical microvilli of the cells lacking the basal labyrinth. This tubule shows several loops running backward and forward in a vertical plane on the side of the brain. In contrast to L. orientale , larvae of H. ruber reveal a terminal cuticular sac/bladder for accumulation of secreted fluids. Organization of the coxal glands depends on the ecological conditions of mites. Larvae of terrestrial L. orientale possess distal tubule functioning in re‐absorption of ions and water. Conversely, water mite larvae H. ruber need to evacuate of the water excess, so the filtrating proximal tubule is prominent.     

Progress in mechanism of salt excretion in recretohalopytes

The recretohalophyte with specialized salt-secreting structures including salt glands and salt bladders can secrete salt from their bodies and easily adapt themselves to many kinds of salt habitats. Salt glands and salt bladders, arose from dermatogen cells, are excretory organs specially adapted for dealing with ionic homeostasis in the cells of recretohalophytes. The main function of salt glands or salt bladders is to secrete excess ions that invade the plant. The structures of salt glands or salt bladders differ among plant species. In addition to structural differences, salt glands also differ in their secretion abilities. In this review, we mainly focus on recent progress in the mechanism of salt excretion of salt glands and salt bladders, and in particular, emphasize the vesicle-mediated secretion systems from the vacuole to the plasmalemma and the possibly involved membrane-bound translocating proteins for salt secretion of plant gland secretory cell.     

Unusual transfer cells in the epithelium of the nectaries ofAsclepias curassavica L.

Summary The secretory cells of the nectaries ofAsclepias curassavica form a glandular epithelium in the inner parts of the stigmatic chambers. They resemble transfer cells in having many infoldings of the plasmalemma. The wall protuberances, however, are poorly developed and often lacking. The plasmalemma is highly convoluted and forms, in places, external compound membranes where the extracytoplasmic space is collapsed completely. Active glands contain dilated cisternae of the ER and large vesicles which are mainly associated with the cis face of the dictyosomes. In addition, small vesicles are observed in high number. It is discussed whether the secretion is granulocrine or eccrine and whether the enlargement of the plasmalemma is the cause or the consequence of the high secretory activity. After the secretory phase the outer peripheral part of the cytoplasm disintegrates. The remaining part of the protoplast is covered by a new plasmalemma.     

Endoplasmic reticulum as the initiator of bud formation in yeast (S. cerevisiae)

Summary An electron microscopical investigation of synchronously dividing yeast cells (S. cerevisiae) prepared by freeze-etching revealed that ER is inducing bud formation. In the first step, ER elements join and form a nearly-closed bag-like envelope which surrounds the nucleus and vacuoles. From the small opening of the ER-envelope, vesicles are produced by a splitting or proliferation of the ER-membranes. The vesicles fuse with the plasmalemma and release their content into the cell wall. In this limited area, bud formation starts explosively by a local evagination of the cell wall. The ER-derived vesicles are concluded to contain proteindisulfide-reductase. The limited introduction of the enzyme into the cell wall explains bud formation to be initiated by a local increase of wall plasticity caused by the reduction of disulfide bonds between cell wall proteins. The wall is forced to extrude by the internal pressure (turgor) of the cell.     

Phenylalanine ammonia-lyase and chalcone synthase in glands ofPrimula kewensis (W. Wats): immunofluorescence and immunogold localization

Phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS) were localized by indirect immunofluorescence and immunogold labeling in glands ofPrimula kewensis. Both enzymes were exclusively present in the head cells of the glands. Phenylalanine ammonialyase was located in the regions of the dense tubular endoplasmic reticulum and occasionally found in more or less spherical organelles that have not yet been identified. Furthermore, an appreciable proportion of the enzyme protein was associated with the plasmalemma and the cell wall of the head cell. In contrast, the occurrence of CHS was restricted to the spherical, unidentified cell compartments. Our findings indicate that the gland cells have the potential for flavonoid biosynthesis. When a mutant ofP. kewensis forming structurally intact glands but incapable of farina excretion was studied, neither PAL nor CHS were found in the head cells.Abbreviations CHS chalcone synthase - IgG immunoglobulin G - PAL phenylalanine ammonia-lyase Financial support from the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie is gratefully acknowledged. We are grateful to Mrs. Karin Schlattmann and Mrs. Susanne Otter for preparing the ultrathin sections and to Mrs. Marianne Opalka for taking the photographs.     

Membrane deletion during plasmolysis in hardened and non-hardened plant cells

Abstract Video recordings of interference phase contrast microscopy were used to study plasmalemma deletion during plasmolysis in hardened and non-hardened suspension cultured cells of Brassica napus, alfalfa, and cells isolated from rye seedlings. Although different hardening regimes and different cells were used, the responses to plasmolysis were consistent. Hardened cells uncoupled the volume to surface area ratio during plasmolysis both by forming a large number of strands between the cell wall and protoplast and by leaving rivulet-like networks of membranes on the cell wall surface. Tonoplast membrane was deleted as sac-like intrusions into the vacuole. Non-hardened cells produced few strands during plasmolysis. They also deleted plasmalemma and tonoplast into the vacuole as endocytotic vesicles. During deplasmolysis of hardened cells both the individual membrane strands and the rivulets of membrane material vesiculated into strings of vesicles. The vesicles were osmotically active and were re-incorporated into the expanding protoplast. Conversely, deplasmolysis in non-hardened cells resulted in few osmotically active vesicles and many broken strands. The vacuolar sac-like intrusions in hardened cells were re-incorporated into the vacuole whereas the endocytotic vesicles in non-hardened cells were not re-incorporated. Therefore, the non-hardened cells underwent expansion-induced lysis.     

The Digestive Glands of Pinguicula: Structure and Cytochemistry

The digestive glands of the carnivorous genus Pinguicula havethree functional compartments, (a) a basal reservoir cell, (b)an intervening cell of endodermal character and (c) a groupof secretory head cells. The gland complex is derived from asingle epidermal initial. The reservoir cell, which is richin Cl^– ions, is highly turgid before discharge; it islinked by plasmodesmata to the surrounding epidermal cells,and is ensheathed by a pectin-rich inner wall layer. The endodermalcell is bounded by a Casparian strip to which the plasmalemmais tightly attached; it contains abundant storage lipid andnumerous mitochondria. The head cells of the developing glandhave labyrinthine radial walls of the transfer-cell type, theingrowths being composed of pectic polysaccharides. The boundingcuticle is discontinuous, although lacking well-formed pores.Mitochondria are numerous, with well-developed cristae; theplastids are large and ramifying, and invested by ribosomalendoplasmic reticulum. Dictyosomes are sparse, and where theyoccur, are associated with coated vesicles. Ribosomal endoplasmicreticulum is moderately abundant in the head cells, and so alsoare free ribosomes. Optical and electron microscopic localizationmethods indicate that the digestive enzymes are synthesizedin the head cells and transferred both into the vacuoles andinto the walls. There is no evidence of a granulocrine modeof secretion, and the transfer seems to be initially by directperfusion through the plasmalemma. During the final phase ofmaturation of the head cells they suffer a form of autolysis,vacuoles, cytoplasm and wall becoming confluent as all of themembranes of the cell undergo dissolution. The gland head isthus, in effect, simply a sac of enzymes at the time of theultimate discharge. Pinguicula, carnivorous plant, insectivorous plant, enzyme secretion, digestive gland     

Ultrastructural study of the mental body of Hydromantes genei (Amphibia: Plethodontidae)

The mental glands of Hydromantes genei are considered a specialized form of the urodele serous cutaneous glands. Use of a variety of techniques of maceration and digestion as well as transmission electron microscopy (TEM) and scanning electron microscopy (SEM) has shown the three-dimensional morphology of secretory and myoepithelial cells. Secretory cells are pyramidal and rest on an almost continuous layer of myoepithelial cells. The latter have a long ribbon-like body from which branch off transversal and longitudinal processes with swallow-tailed ends. Cytoplasmic processes of secretory cells, containing irregular dense vesicles, squeeze through clefts between myoepithelial cells and may reach, at some points, the basal lamina. The interstices between myoepithelium and secretory cells are extraordinarily rich in nerve endings with clear vesicles. The glandular outlets appear as elliptical stomata in the superficial layer of the epidermis and are lined by horny cells, which invaginate to circumscribe the excretory duct. The morphological results indicate that the myoepithelium of Plethodontidae mental glands differ in some respects from that of amphibian serous cutaneous glands. A double polarity for the secretory cells is also suggested. © 1993 Wiley-Liss, Inc.     

Simultaneous Measurement of the Bioelectric Potential of the Cell Wall and the Vacuoles during the Oscillatory Response to the Nitella Cell

Simultaneous measurements of bioelectric potentials of the vacuole and cell wall in cells of Nitella mucronata were made by inserting glass microelectrodes into the vacuole and cell wall respeclively. During the oscillation of the bioelectric potential of the vacuole. induced by sudden changes of the external bathing solution or by the impalement of the cell with a microelectrode. the cell wall potential also exhibited fluctuations of variable intensities in phase and concomitant with spikes of the vacuolar potential oscillation. However, the polarity of the pulses of the cell wall potential was reverse to that of the spikes of the vacuolar potential. These results suggest that the same event is registered at both sides of the plasmalemma membrane across which these phenomena are occurring. The results also support the voltage clamp and tracer flux measurements on these cells which indicate that during the generation of single action potentials, induced by current, the plasma lemma transiently increases its permeability to Cl^? and K⁺ ions expelling them from the cell. The variable intensity of the transient hyperpolarizations of the cell wall potential is explained by the distance of the microelectrode in the cell wall from the plasmalemma.     

Fine structure of the silk gland in the mite Ornithocheyletia sp. (Prostigmata,Cheyletidae)

Silk spinning is widely-spread in trombidiform mites, yet scarse information is available on the morphology of their silk glands. Thus this study describes the fine structure of the prosomal silk glands in a small parasitic mite, Ornithocheyletia sp. (Cheyletidae). These are paired acinous glands incorporated into the podocephalic system, as typical of the order. Combined secretion of the coxal and silk glands is released at the tip of the gnathosoma. Data obtained show Ornithocheyletia silk gland belonging to the class 3 arthropod exocrine gland. Each gland is composed of seven pyramidal secretory cells and one ring-folded intercalary cell, rich in microtubules. The fine structure of the secretory cells points to intensive protein synthesis resulted in the presence of abundant uniform secretory granules. Fibrous content of the granules is always subdivided into several zones of two electron densities. The granules periodically discharge into the acinar cavity by means of exocytosis. The intercalary cell extends from the base of the excretory duct and contributes the wall of the acinar cavity encircling the apical margins of the secretory cells. The distal apical surface of the intercalary cell is covered with a thin cuticle resembling that of the corresponding cells in some acarine and myriapod glands. Axon endings form regular synaptic structures on the body of the intercalary cell implying nerve regulation of the gland activity.     

The development and ultrastructure of gum ducts inCitrus plants formed as a result of brown-rot gummosis

Summary Young stems ofCitrus plants were infected with the fungusPhytophthora citrophthora. The effect of the infection on gum duct development was studied. The following sequence of structural changes was observed in the cambial zone: 1. The middle lamellae between layers of xylem mother cells dissolve forming duct cavities. 2. The cells around the duct cavities differentiate into epithelial cells rich in cytoplasm. 3. The amount of Golgi bodies and associated vesicles increases. The vesicles and small vacuoles, some of which seem to originate from the fusion of Golgi vesicles, contain fibrillar material that stains for polysaccharides. Vesicles and vacuoles appear to fuse with the plasmalemma. Material staining positively for polysaccharides accumulates between the plasmalemma and cell wall, and penetrates the latter. 4. The protoplast shrinks and the space below the cell wall, which contains polysaccharides, increases in volume. 5. After a period of 10 days or more the gum ducts become embedded in the xylem, and the activity of the epithelial cells ceases. The cell walls of many of them break, and the gum still present in the cells is released.     

Paramural bodies of Albugo candida

The paramural bodies of Albugo candida were formed solely by elaboration of the plasmalemma. Two major forms were recognized: one consisting of plasmalemmal invaginations projecting into the cytoplasm; the other appearing like a pocket containing a number of vesicles and tubules. It is suggested that the first is the basic form of paramural body. In sporangia the paramural bodies break away from the plasmalemma and undergo autodigestion while in vegetative hyphae their tubules and lamellae break up into vesicles that are finally sequestered into the wall.     

天麻大型细胞消化蜜环菌过程中溶酶体小泡的作用

蜜环菌(Armillaria mellea Fr.)菌丝由天麻(Gastrodia elata Bl.)皮层细胞经纹孔侵入大型细胞。初期大型细胞的原生质膜凹陷,同时细胞壁产生乳突状加厚阻止菌丝侵入。当菌丝侵入大型细胞以后,凹陷的质膜将菌丝紧密包围,大量由单位膜围成的小泡聚集在其周围。随后这些小泡的膜与质膜融合并将其内含物释放到菌丝周围的空间中,凹陷质膜逐渐膨大成为一个包围菌丝的消化泡。小泡和消化泡中均具酸性磷酸酶活性反应产物,证实其分别相当于植物溶酶体系统中的初级和次级溶酶体。菌丝在消化泡中被彻底消化。     

Zur Cytologie der Rectaldrüsen von Knorpelfischen

The stratified epithelium of the central collecting duct of the elasmobranch(Scylliorhinus canicula, Galeorhinus galeus andRaja batis) rectal gland consists of 3 to 6 layers of cells: one superficial, and several basal cell layers. In the superficial layer normally three different types of cells can be distinguished (a) goblet cells, (b) cells with apical secretory granules and (c) flask-shaped cells. The superficial layer ofScylliorhinus canicula reveals a further cell type, so-called mitochondria-rich cells. The epithelial areas built by these cells are always single-layered. The goblet-cells are very similar to goblet cells found in the intestine of vertebrates. Their dominant structures are a well developed ergastoplasm, a large Golgi-apparatus and mucous granules compactly filling the apical cell region. The cells with apical secretory granules are columnar or dumbbell shaped. They contain a rough-surfaced endoplasmic reticulum and a well developed Golgi-apparatus. The secretory granules are loosely distributed within the Golgi-field and are arranged in one or more rows just below the cell apex. The flask shaped cells are characterized by a cytoplasm rich in small vesicles. They posses few dictyosomes and several small mitochondria. There is some evidence for endocytotic activity. The mitochondria-rich cells are characterized by lateral cell interdigitations, by a basal labyrinth and by numerous mitochondria. They are similar to the excretory cells of rectal gland parenchyma. The cells of the basal epithelium layers are differenciated only to a small extent. They are joined in a loose formation with white blood cells often found in the intercellular spaces. The function of the elasmobranch rectal gland is not restricted to the excretion of concentrated salt solutions. There is also a significant secretion of mucous substances. The tubule glands are primarily excretory, the epithelium cells of the central collecting duct mainly secretory in function.     

Ultrastructure du canal des glandes agrégées et flagelliformes d'Araneus diadematus Clerck (Araneae,Araneidae)

Summary The excretory ducts of the silk glands which produce the viscid spiral of the webs ofAraneus diadematus show a complex structure. The duct of aggregate glands consists of three superposed types of cells. Several connective layers cover large and irregular nodule-forming cells which are rich in glycogen and mitochondria surrounded by invaginations of the plasma membranes. The internal cells, whose apical poles are lined by a cuticular intima, would be quite ordinary if not for the fact that they often carry large vacuoles which seem to empty themselves by exocytosis. Activity in the nodule cells is perceived from variations in the glycogen level and from the appearance of the mitochondria. Internal cells of the duct, when within the posterior spinneret, gradually acquire the characteristics of absorbing cells.The duct of flagelliform glands consists of two types of cells. The external cells, bounded by a simple basal lamina, are rich in mitochondria, glycogen, and invaginations of the plasma membranes; their activity is shown by variations in glycogen level and the extent of the extracellular spaces. The internal cells show numerous mitochondria either at the apical or basal poles, variable glycogen levels, long microvilli, and signs of apical absorption by pinocytosis; the sub-cuticular layer of the intima is particularly thick.We propose a functional interpretation of the aspects described above, and discuss it in terms of recent data on the chemical composition of silks. The excretory ducts are held to modify, by their activity, the secretory products of both types of glands. Solutes, especially phosphate ions, cross both cells and intima and would enter the glue of the aggregate glands which then undergoes partial dehydration in the posterior spinnerets. The product of the flagelliform glands seems to all appearance dehydrated during its passage in the duct and up to about the half-way through the posterior spinnerets. The liquid would flow through an extracellular path below the apical septate junctions of the internal cells. This study therefore favours attributing important role to the excretory ducts of silk glands in the final phase of the formation of silk fibres by spiders.