Cortical ultrastructure of freeze-substituted protonemata of the mossFunaria hygrometrica

Summary The ultrastructural organization of the cortical cytoplasm has been examined in caulonemata, branches and buds of the mossFunaria hygrometrica, which were prepared by rapid freeze-fixation and freeze-substitution (FS). The same structural components occur in the cortex of all three cell types: microtubules (MTs), endoplasmic reticulum (ER), coated and uncoated vesicles, coated pits, and dictyosomes. However, the configuration and density of the cortical ER varies between the three. Caulonemata have an open, polygonal network of ER associated with long MTs oriented mostly parallel to the length of the cell. Lamellar ER, covered with polysomes, is interspersed in the network. Branches have a more tightly arranged ER network, at places occurring in a thick layer, and occasional polysome-decorated lamellae. MTs, which extend to the tip of the branch, are oriented mainly parallel to the cell's long axis and are associated with the cortical ER. Buds have the tightest ER network, which is frequently arranged in a thick layer. Tubules in the polygonal ER of buds are densely covered with ribosomes, whereas tubules in the ER network of caulonemata and branches range from nearly smooth to moderately rough. Closely-spaced ER lamellae, with many polysomes, occur in some buds. The MTs of buds extend into the apical dome and are associated with the cortical ER, but are more randomly oriented than in caulonemata or branches. Close appositions between the ER and PM are observed in all three cells, but are more frequent in buds.Abbreviations DiOC₆(3) 3,3-dihexyloxacarbocyanine iodide - ER endoplasmic reticulum - FS freeze-substitution - MT microtubule - MF microfilament - PM plasma membrane     

THE FINE STRUCTURE OF MITOSIS AND CELL DIVISION IN THE CHRYSOPHYCEAN ALGA OCHROMONAS DANICA1

At the ultrastructural level, cell division in Ochromonas danica exhibits several unusual features. During interphase, the basal bodies of the 2 flagella replicate and the chloroplast divides by constriction between its 2 lobes. The rhizoplast, which is a fibrous striated root attached to the basal body of the long flagellum, extends under the Golgi body to the surface of the nucleus in interphase cells. During proprophase, the Golgi body replicates, apparently by division, and a daughter rhizoplast, appears. During prophase, the 2 pairs of flagellar basal bodies, each with their accompanying rhizoplast and Golgi body, begin to separate. Three or 4 flagella are already present at this stage. At the same time, there is a proliferation of microtubules outside the nuclear envelope. Gaps then appear in the nuclear envelope, admitting the microtubules into the nucleus, where they form a spindle. A unique feature of mitosis in O. danica is that the 2 rhizoplasts form the poles of the spindle, spindle microtubules inserting directly onto the rhizoplasts. Some of the spindle microtubules extend from pole to pole; others appear to attach to the chromosomes. Kinetochores, however, are not present. The nuclear envelope breaks down, except, in the regions adjacent, to the chloroplasts; chloroplast ER remains intact throughout mitosis. At late anaphase the chromosomes come to lie against part of the chloroplast ER. This segment of the chloroplast ER appears to be incorporated as part of the reforming nuclear envelope, thus reestablishing the characteristic nuclear envelope—chloroplast ER association of the interphase cell.     

Ultrastructure of the salt glands of the mangrove,Avicennia marina (Forssk.) Vierh., as indicated by the use of selective membrane staining

Each salt-excreting gland of the mangrove Avicennia marina (Forsskål) Vierh. consists of two to four collecting cells, one stalk cell, and eight to twelve excretory cells. Differential membrane staining by zinc iodide-osmium tetroxide (as a post-fixative) or phosphotungstic acid (as a section-stain) was used to characterise the ultrastructure of the glands. A large amount of tubular endoplasmic reticulum was found in the stalk and excretory cells of the gland, but not in the collecting cells. The ultrastructural arrangement of the endoplasmic reticulum indicates that salt is loaded from the apoplasm into the endoplasmic reticulum of the symplasm at the base of the stalk cell, traverses both cell types in the endoplasmic reticulum, and is excreted at the outer edge of the gland by an eccrine-type mechanism. Increasing development of the tubular endoplasmic reticulum accompanied differentiation of the gland cells.Abbreviations ER endoplasmic reticulum - PTA phosphotungstic acid - ZIO zinc iodide-osmium tetroxide     

ONTOGENETIC STUDY OF FLORAL ORGANS OF PEACH (PRUNUS PERSICA) UTILIZING CYTOCHIMERAL PLANTS

Cell lineages were followed throughout floral ontogeny in cytochimeral peaches [Prunus persica (L.) Batsch] by observations of chromosome number and nuclear size. The contribution of the three apical cell layers to the organs of the flowers was determined. In addition to the epidermal tissue, L-I produced several layers of cells at the suture of the ovary wall, seven or eight cell layers of the nucellus at the micropylar end of the ovule, and almost all of the integuments. L-II gave rise to extensive internal tissue in the calyx and corolla tubes and to all internal tissue of the petal, anther, and ovule except for a small region at the base of the latter two organs. L-III contributed significantly only to the central region of the calyx and corolla tubes and the ovary wall. A single apical layer gave rise to several different tissues, and at times a single tissue was made up of cells from 1–3 different apical layers. Within the limits imposed by their genotype the final form of differentiated cells was determined by their position in the mature organ and not by the apical layer from which they were derived. The corolla tube was shown to be a single structure, congenitally fused, and the ovary to be ontogenetically fused at the suture.     

Cytodifferentiation of polar plant cells Use of anti-microtubular agents during the differentiation of statocytes from cress roots (Lepidium sativum L.)

The development of the structural polarity of statocytes from cress roots (Lepidium sativum L.) was studied in a time- and stage-dependent manner. Outgrowing radicles had statocytes with abundant lipid droplets, sparsely developed endoplasmic reticulum (ER) and nuclei located at the proximal cell poles. During differentiation, coincidentally the lipid droplets disappeared, while rough ER increased in length. The ER was translocated into the distal cell pole to establish a complex of stacked ER. Microtubules occurred first at the distal cell edges. As a second step, ER was produced in the vicinity of the nucleus and was also translocated distally. By application of the antimicrotubular agents heavy water (90%), colchicine (10^-4 mol·l^-1) and triethyl lead chloride (20 mol·l^-1), the involvement of microtubules in these events was studied. Triethyl lead chloride led to a complete cessation of differentiation; root-cap cells remained at a stage without polar arrangement of the ER. Colchicine affected the development of structural polarity slightly, as shown by a higher density of cortical ER cisternae. Heavy water inhibited the translocation of ER almost completely and yielded ER located also in the cell center. All anti-microtubular agents inhibited cell division and the differentiation of the distal cell layer of the dermatocalyptrogen into statocytes. It is hypothesized that microtubules serve as anchoring sites for microfilaments, which actually mediate the translocation of the ER. Hence, an intact system of microtubules and microfilaments is necessary for the expression of structural polarity.Abbreviations DC dermatocalyptrogen - ER endoplasmic reticulum - M meristem cell layer - MT microtubule - pI prospective story I - TrEl triethyl lead chloride     

Immunogold localization of prolamines in developingHaynaldia villosa endosperm

Summary Haynaldia villosa is a wild grass belonging to the tribe Triticeae, which includes important crops such as wheat, barley, and rye. The alcohol-soluble proteins ofH. villosa have extensive immunological relatedness with wheat prolamines as visualized by Western blot analysis. Amorphous protein inclusions surrounded by a limiting membrane are commonly found in the vacuoles of endosperm and subaleurone layers ofH. villosa seeds. A layer of cells just beneath the aleurone layer is rich in ER. Unlike that in other cell types, the ER in these cells is highly dilated and contains materials at its swollen distal ends. These materials are structurally similar to substances found in the protein bodies. Protein A-gold immunocytochemical localization studies employing antibodies against wheat prolamine confirmed that the inclusions found in the lumen of the ER do not contain prolamines. This observation indicates that the ER does not act as the site of prolamine accumulation inH. villosa. Protein bodies found in the vacuoles and the vesicles associated with the Golgi complexes were specifically labeled. This suggests that Golgi complexes mediate the transport of prolamines into vacuoles ofH. villosa endosperm cells, in a fashion analogous to that of other vacuolar proteins of dicotyledonous plants.     

Ultrastructure of vegetative organization and cell division in the freshwater red algaCompsopogon

Summary Uniseriate filaments of the freshwater red algaCompsopogon coeruleus were examined by transmission electron microscopy for details of vegetative organization and cell division with the goal of providing useful taxonomic characters. Each cell's single, complex chloroplast contains a peripheral encircling thylakoid, and unlike the vast majority of red algae, the cis-regions of dictyosomes are not consistently juxtaposed with mitochondria. These subcellular features, which are present in all examined genera in theCompsopogonales, Erythropeltidales, andRhodochaetales, along with certain unique reproductive characteristics, unify these three orders. During mitosis in uncorticated axial cells, a small, ring-shaped nucleus associated organelle (NAO) is located at each division pole, an intranuclear spindle comes to a moderately acute focus at the flattened, fenestrated metaphase-anaphase division poles and perinuclear ER partially encloses dividing nuclei, including a well-developed interzonal midpiece. The cleavage furrow penetrates the large, central vacuolar region to separate daughter nuclei. These cell division features most closely resemble the pattern described for the orderCeramiales. Our observations of vegetative and dividing cells ofC. coeruleus supplement the growing volume of evidence in favour of uniting all red algae into a single class without subclass designations.Abbreviations ER endoplasmic reticulum - IZM interzonal midpiece - MT microtubule - MTOC microtubule organizing center - NAO nucleus associated organelle - NE nuclear envelope - PER perinuclear endoplasmic reticulum     

The function of the aleurone layer during galactomannan mobilisation in germinating seeds of fenugreek (Trigonella foenum-graecum L.), crimson clover (Trifolium incarnatum L.) and lucerne (Medicago sativa L.): A correlative biochemical and ultrastructural study

Summary The reserve endosperm galactomannans of fenugreek (Trigonella foenum-graecum L.), crimson clover (Trifolium incarnatum L.) and lucerne (Medicago sativa L.) are broken down to free galactose and mannose in dry-isolated endosperms (devoid of embryo) incubated under germination conditions. Breakdown is prevented by inhibition of protein synthesis or of oxidative phosphorylation in the aleurone layer. Resting aleurone cells contain inter alia a large number of ribosomes more or less regularly distributed in the ground plasma. At the onset of germination, before galactomannan breakdown begins, polysomes are formed and seem, at least partly, to become associated with vesicles and flat cisternae both probably newly formed and derived from ER. Concurrently with galactomannan breakdown in the reserve cells, wall corrosion occurs in the aleurone layer, the contents of the aleurone grains disappear and the rough vesicles and cisternae proliferate. Later a large central vacuole is formed which incorporates smaller vacuoles emerging from the cytoplasm, and at the same time the rough ER vesicles and cisternae become highly distended.It is concluded that the cells of the aleurone layer are responsible for the synthesis and secretion into the storage cells of the enzymes necessary for galactomannan degradation. The physiology of galactomannan breakdown is compared and contrasted with that of starch mobilisation in the endosperm of germinating cereal grains.This is part three in a series of papers dealing with galactomannan metabolism. Part two: Planta (Berl.) 100, 131–142 (1971).     

BiP Inducer X: An ER Stress Inhibitor for Enhancing Recombinant Antibody Production in CHO Cell Culture

Prolonged endoplasmic reticulum (ER) stress reduces protein synthesis and induces apoptosis in mammalian cells. When dimethyl sulfoxide (DMSO), a specific monoclonal antibody productivity (q_mAb)‐enhancing reagent, is added to recombinant Chinese hamster ovary (rCHO) cell cultures (GSR cell line), it induces ER stress and apoptosis in a dose‐dependent manner. To determine an effective ER stress inhibitor, three ER stress inhibitors (BiP inducer X [BIX], tauroursodeoxycholic acid, and carbazole) are examined and BIX shows the best production performance. Coaddition of BIX (50 μm ) with DMSO extends the culture longevity and enhances q_mAb. As a result, the maximum mAb concentration is significantly increased with improved galactosylation. Coaddition of BIX significantly increases the expression level of binding immunoglobulin protein (BiP) followed by increased expression of chaperones (calnexin and GRP94) and galactosyltransferase. Furthermore, the expression levels of CHOP, a well‐known ER stress marker, and cleaved caspase‐3 are significantly reduced, suggesting that BIX addition reduces ER stress‐induced cell death by relieving ER stress. The beneficial effect of BIX on mAb production is also demonstrated with another q_mAb‐enhancing reagent (sodium butyrate) and a different rCHO cell line (CS13‐1.00). Taken together, BIX is an effective ER stress inhibitor that can be used to increase mAb production in rCHO cells.     

Effects of brefeldin A on the Golgi apparatus, the nuclear envelope, and the endoplasmic reticulum in a green alga,Scenedesmus acutus

Summary The effects of brefeldin A (BFA) on the structure of the Golgi apparatus, the nuclear envelope, and the endoplasmic reticulum (ER), and on the thiamine pyrophosphatase (TPPase) activity in these organelles were examined in a green alga,Scenedesmus acutus, to obtain evidence for the existence of a retrograde transport from the Golgi apparatus to the ER via the nuclear envelope. InScenedesmus, Golgi bodies are situated close to the nuclear envelope throughout the cell cycle and receive the transition vesicles not directly from the ER, but from the nuclear envelope. BFA induced the disassembly of Golgi bodies and an increase in the ER cisternae at the trans-side of decomposed Golgi bodies in interphase cells and multinuclear cells before septum formation. The accumulated ER cisternae connected to the nuclear envelope at one part. TPPase activity was detected in all cisternae of Golgi bodies, but not in the nuclear envelope or the ER in nontreated cells. On the contrary, in BFA-treated cells, TPPase activity was detected in the nuclear envelope and the ER in addition to the decomposed Golgi bodies. When septum-forming cells were treated with BFA, the disassembly of Golgi bodies was less than that in interphase cells, and TPPase activity was detected in the Golgi cisternae but not in the nuclear envelope or the ER. These results suggest mat BFA blocks the anterograde transport from the nuclear envelope to the Golgi bodies but does not block the retrograde transport from the Golgi bodies to the nuclear envelope in interphase and multinuclear cells.Abbreviations BFA brefeldin A - ER endoplasmic reticulum - TPPase thiamine pyrophosphatase     

Solitary bodies (S-bodies) in the parasitic red algaHarveyella mirabilis (Choreocolaceae,Cryptonemiales)

Summary Unusual spherical cytoplasmic inclusions identical to S-bodies described previously in three angiosperms were found in all cells of the parasitic red algaHarveyella mirabilis collected from several locations in the northeast Pacific. The inclusions are ca. 60–80 nm and consist of an outer double membrane bounding a granular mantle and a DNase sensitive central core. S-bodies are dispersed throughout the cytoplasm and are associated occasionally with nuclei, plastids, mitochondria, ER, and vacuoles. They have not been observed in any other alga except in host algal cells, connected to parasite cells by cellular pit connections. The possible function of these inclusions is considered with respect to the parasitic nature ofHarveyella mirabilis.     

The ultrastructure of zygotic embryo development in pearl millet (Pennisetum glaucum; Poaceae)

The ultrastructure, morphology, and histology of zygotic embryogenesis in pearl millet (Pennisetum glaucum) were examined using light and electron microscopic techniques. Embryogenesis was initially characterized by the presence of a vacuolated egg cell and zygote. The increased presence of Golgi bodies in the zygote suggested it was metabolically more active than the egg cell. The first zygotic division resulted in a densely cytoplasmic apical cell and a highly vacuolated basal cell. The club-shaped proembryo displayed a large amount of endoplasmic reticulum (ER) and ribosomes, very few lipids, and a continuous gradient of vacuoles from the highly vacuolated basal suspensor cells to the densely cytoplasmic apical cells. The embryo had well-defined parts by 8 days after pollination, including shoot and root meristems, coleoptile, scutellum, provascular system, and the first leaf primordium. Large increases in ER, lipids, starch, and vacuoles occurred in the scutellum during the maturation of the embryo, except in the provascular cells. Throughout zygotic embryogenesis, embryo cells were connected by plasmodesmata except where intercellular spaces occurred. Ultrastructural, morphological, and histological observations of zygotic embryogenesis in pearl millet are in agreement with previous reports for other grass species.     

Proteomics analysis of rough endoplasmic reticulum in pancreatic beta cells

Pancreatic beta cells have well‐developed ER to accommodate for the massive production and secretion of insulin. ER homeostasis is vital for normal beta cell function. Perturbation of ER homeostasis contributes to beta cell dysfunction in both type 1 and type 2 diabetes. To systematically identify the molecular machinery responsible for proinsulin biogenesis and maintenance of beta cell ER homeostasis, a widely used mouse pancreatic beta cell line, MIN6 cell was used to purify rough ER. Two different purification schemes were utilized. In each experiment, the ER pellets were solubilized and analyzed by 1D SDS‐PAGE coupled with HPLC‐MS/MS. A total of 1467 proteins were identified in three experiments with ≥95% confidence, among which 1117 proteins were found in at least two separate experiments and 737 proteins found in all three experiments. GO analysis revealed a comprehensive profile of known and novel players responsible for proinsulin biogenesis and ER homeostasis. Further bioinformatics analysis also identified potential beta cell specific ER proteins as well as ER proteins present in the risk genetic loci of type 2 diabetes. This dataset defines a molecular environment in the ER for proinsulin synthesis, folding and export and laid a solid foundation for further characterizations of altered ER homeostasis under diabetes‐causing conditions. All MS data have been deposited in the ProteomeXchange with identifier PXD001081 ( http://proteomecentral.proteomexchange.org/dataset/PXD001081 ).     

The organization of the lamina ganglionaris of the hemipteran insects,Notonecta glauca,Corixa punctata and Gerris lacustris

Summary Neuronal elements, i.e. first and second order neurons, of the first optic ganglion of three waterbugs, N. glauca, C. punctata and G. lacustris, are analyzed on the basis of light and electron microscopy.Eight retinula cell axons, leaving each ommatidium, disperse to different cartridges as they enter the laminar outer plexiform layer. Such a pattern of divergence is one of the conditions for neuronal superposition; it is observed for all three species of waterbugs. The manner in which the receptors of a single bundle of ommatidia split of within the lamina, whereby information from receptors up to three or five horizontal rows away can converge upon the same cartridge, differs among the species. Six of the eight axons of retinula cells R1-6, the short visual fibers end at different levels within the bilayered lamina, whereas the central pair of retinula cells R7/8, the long visual fibers, run directly through the lamina to a corresponding unit of the medulla. Four types of monopolar cells L1–L4 are classified; their branching patterns seem to be correlated to the splitting and termination of retinula cell axons. The topographical relationship and synaptic organization between retinula cell terminals and monopolar cells in the two laminar layers are identified by examination of serial ultrathin sections of single Golgi-stained neurons.An attempt is made to correlate some anatomical findings, especially the neuronal superposition, to results from physiological investigations on the hemipteran retina.     

FINE STRUCTURE STUDIES OF PHLEUM ROOT MERISTEM CELLS. II. MITOTIC ASYMMETRY AND CELLULAR DIFFERENTIATION

Avers , Charlotte J. (Douglass Coll., Rutgers—The State U., New Brunswick, N.J.) Fine structure studies of Phleum root meristem cells. II. Mitotic asymmetry and cellular differentiation. Amer. Jour. Bot. 50(2): 140–148. Illus. 1963.—An electron microscopical study showed that ultrastructural differences distinguished the cell dividing symmetrically from that undergoing asymmetrical division in timothy grass epidermis. The spindle orientation led to cytokinesis which produced either equal- or unequal-sized sister cells, but the mitotic apparatus itself varied in the mitoses. In asymmetrical cells, the basal pole showed more extensive endoplasmic reticulum (ER) polarizations, which intruded into the spindle area during metaphase and anaphase. Such ER polarity was not obvious in symmetrical mitosis or in the apical end of asymmetrically dividing cells. The mitotic sequence is described photographically. Foci of ER were observed as early as prophase in the polar region, and it is suggested that there is a resemblance to astral ray foci seen in prophase of animal cell mitosis. Cell plate formation could be detected in anaphase by accumulations of vesicles and ER fragments along the spindle equator. Phragmosomes apparently were not involved in cell plate formation in Phleum, unlike Allium, cytokinesis. The mitotic asymmetry is discussed as a consequence of an intracellular gradient separate from the intercellular gradient of differentiation along the entire length of growing root tip epidermis.     

Enhanced reactivation and enhanced mutagenesis of herpes simplex virus in normal human and xeroderma pigmentosum cells.

Enhanced reactivation (ER) and enhanced mutagenesis (EM) of herpes simplex virus type 1 were studied simultaneously in UV-irradiated stationary cultures of diploid normal human and xeroderma pigmentosum (XP) fibroblasts. Mutagenesis was assayed with unirradiated herpes simplex virus type 1 as a probe in a forward mutation assay (resistance to iododeoxycytidine). Dose-response studies showed that ER increased with the UV dose given to the virus. Optimal reactivation levels were obtained when normal cells and XP variant cells were exposed to a UV dose of 8 J . m-2 and the virus was irradiated with 150 J . m-2. Repair-deficient XP cells of complementation groups A, C, and D showed optimal reactivation levels with a UV dose to the cells of 1.0 J . m-2 and a UV dose to the virus of 40 J . m-2. The time course of appearance of ER and EM was also studied, both in the normal and XP cells. In all cell types except the XP variant cells, EM followed similar kinetics of appearance as did ER. Maximal activities occurred when infection was delayed 1 or 2 days after cell treatment. In XP variant cells, however, maximal expression of the EM function was significantly delayed with respect to ER. The results indicate that ER and EM are transiently expressed in normal and repair-deficient XP cells. Although both phenomena may be triggered by the same cellular event, ER and EM appear to be separate processes that occur independently of each other.     

Cellular succession in the epithelium lining the pharyngeal cavity of planarians

Regardin cell renewal of planarian epithelial tissue, little is known at present except for the epidermis (Tyler, 1984). According to Skaer (1965), the definitive epidermal cells in planarian embryos originate in the parenchyma where they develop as precursor cells which then migrate into the epidermis. This process of development is also reported in regenerating planarians (Spiegelman & Dudley, 1973; Morita & Best, 1974; Hori, 1978). Recently the validity of Skaer's conclusion has clearly been confirmed by Ishii & Sakurai (1998) using SEM and TEM.The present study deals with the origin and renewal of cells of another epithelium — that lining the pharyngeal cavity of a freshwater planarian Dugesia japonica. This epithelium is known to consist of cells with secretory granduls of fingerprint-like structure (Ishii, 1966; Bowen & Ryder, 1973; Gamo & Garcia-Corrales, 1988; Asai, 1991). The characteristic feature of these specific granules, as well as epitheliosomes (Tyler, 1984) of the epidermis, is very useful as a cell marker for distinguishing cell types and following cell differentiation. Gamo & Garcia-Corrales (1988) claimed the cell populations of the pharyngeal epithelium of Dugesia gonocephala is morphologically and functionally heterogeneous. The sequence of morphological alteration offers the oppurtunity to distinguish at least three functional stages. These represent different adaptive forms of a single cell type, and indicate transformation from one to the next induced by cell renewal. It suggests a beta cell (noeblast) origin of the epithelial cells.In the present study SEM observations revealed theat there are morphologically three distinct cell types which are considered to be juvenile, mature, and senile cells respectively, judging from the differences in cells and the many transitional forms among them (Fig. 1). When observed by TEM, the cytoplasmic patterns of these cell types are correspondingly different from one another, similarly the surface specializations of the plasma membranes of each cell type which facilitate their identification by TEM also vary. Apparently alterations of cell morphology are involved in ageing in a single cell type. Morphological features of each cell type are summarized. Juveniles (R) rarely occur, are small cells provided with prominent apical ruffles and considered to be phagocytic because the cells often contain newly formed phagosomes. Mature cells (F) predominate, are large, polygonal, flat cells, presumably with an intense secretory activity. The cells contain many profiles of granular ER and a small number of specific (secretory) granules. Senile cells (M) are intermittently distributed, irregularly contoured cells with heavy surface microvilli. The specific granules are dense in the apical cytoplasm, and profiles of granular ER decease in number.The precursor epithial cells that are seen in the parenchyma exhibit a considerable degree of differentiation before their translocation into the lining. The primordial cells observed are neoblast-like, with several cohromatoid bodies and many free ribosomes (Morita et al., 1969). These results obtain thus support the evidence and prediction of Gamo & Garcia-Corrales (1988). The observed mode of cell replacement appears to be the same as found in the epidermis (Lentz, 1967).     

Localization of ATPase in the endoplasmic reticulum and golgi apparatus of barley aleurone

Summary The cytochemical localization of adenosine triphosphatase (ATPase) was studied in the aleurone layer of barley (Hordeum vulgare L. cv. Himalaya). Isolated barley aleurone layers secrete numerous enzymes having acid phosphatase activity, including ATPase. The secretion of these enzymes was stimulated by incubation of the aleurone layer in gibberellic acid (GA₃). ATPase was localized using the metal-salt method in tissue incubated in CaCl₂ with and without GA₃. In sections of tissue incubated without GA₃, cytochemical staining was confined to a narrow band of cytoplasm adjacent to the starchy endosperm and to the cell wall of the innermost tier of aleurone cells. Cytochemical staining was absent from the organelles of tissues not treated with GA₃. In tissue incubated in the presence of GA₃, cytochemical staining was evident throughout the cytoplasm and cell walls of the tissue. In the cell wall, electron-dense deposits were found only in digested channels. The cell-wall matrix of GA₃-treated aleurone did not stain, indicating that it does not permit diffusion of enzyme. In the cytoplasm of GA₃-treated aleurone, all organelles except microbodies, plastids, and spherosomes stained for ATPase activity; endoplasmic reticulum (ER), Golgi apparatus, and mitochondria showed intense deposits of stain. The ER of the aleurone is a complex system made up of flattened sheets of membrane, which may be associated with both the Golgi apparatus and the plasma membrane. The dictyosome did not stain uniformly for ATPase activity; rather there was a gradation in staining of the cisternae from thecis (lightly stained) to thetrans (heavily stained) face. Vesicles associated with dictyosome cisternae also stained intensely as did the protein bodies of GA₃-treated aleurone cells.     

The endomembrane system and mechanism of membrane flow in the green alga,Gloeomonas kupfferi (Volvocales,Chlorophyta) I. An ultrastructural analysis

Summary The endomembrane system of the chlamydomonad flagellate,Gloeomonas kupfferi (Chlorophyta), is complex. It consists of a proliferating ER network, a perinuclear complex of 14–18 dictyosomes and 8–12 vacuoles and an anterior contractile vacuole complex. The ER network extends from the nuclear envelope outwards, ensheafhs a dictyosome, extends out through a lobe of the chloroplast and terminates in the thin zone of peripheral cytoplasm between the chloroplast and plasmamembrane. The individual dictyosome is polar with distinct cis- and trans-faces. The cis-face is closely associated with transition vesicles emerging from the adjacent ER. Large vesicles emerge from peripheral swellings of terminal cisternae. The dictyosome-associated ER is connected to the peripheral vacuolar system. During cell division and cytokinesis, changes in the endomembrane system occur. Dictyosomes divide and quickly separate to form perinuclear complexes around the daughter nuclei. Each dictyosome undergoes morphological changes during this wall precursor-producing stage. ER lines the furrow zone and is closely associated with phycoplast microtubules. A discussion of the endomembrane system in membrane flow mechanics is provided.Abbreviations ER endoplasmic reticulum - OsFeCN Osmium ferricyanide