ER Cisternae Research Articles

Fallopia japonica and Fallopia × bohemica extracts cause ultrastructural and biochemical changes in root tips of radish seedlings.

Japanese knotweed (Fallopia japonica) and Bohemian knotweed (Fallopia × bohemica) are invasive plants that use allelopathy as an additional mechanism for colonization of the new habitat. Allelochemicals affect the growth of roots of neighboring plants. In the present study, we analyze the early changes associated with the inhibited root growth of radish seedlings exposed to aqueous extracts of knotweed rhizomes for 3 days. Here, we show that cells in the root cap treated with the knotweed extracts exhibited reduced cell length and displayed several ultrastructural changes, including the increased abundance of dilated ER cisternae filled with electron-dense material (ER bodies) and the accumulation of dense inclusions. Moreover, mitochondrial damage was exhibited in the root cap and the meristem zone compared to the non-treated radish seedlings. Furthermore, malfunction of the intracellular redox balance system was detected as the increased total antioxidative capacity. We also detected increased metacaspase-like proteolytic activities and, in the case of 10% extract of F. japonica, increased caspase-like proteolytic activities. These ultrastructural and biochemical effects could be the reason for the more than 60% shorter root length of treated radish seedlings compared to controls.

Benzo[ghi]perylene induces cellular dormancy signaling and endoplasmic reticulum stress in NL-20 human bronchial epithelial cells

Benzo[ghi]perylene (BghiP) is produced by the incomplete combustion of gasoline and it is a marker of high vehicular flow in big cities. Nowadays, it is known that BghiP functions as ligand for the aryl hydrocarbon receptor (AhR), which can cause several molecular responses. For this reason, the aim of the present study was to assess the in vitro effects of the exposure to BghiP, specifically, the induction of cellular dormancy and endoplasmic reticulum stress (ER stress) in NL-20 human cells. Our results proved that a 24 h exposure of BghiP, increased the expression of NR2F1 (p < 0.05). NR2F1 is the main activator of cell dormancy, therefore, we analyzed the expression of its target genes SOX9 and p27 showing an increase of the transcripts (p < 0.05), suggesting a pathway that could produce a cell cycle arrest. Interestingly, this effect was only observed with BghiP exposure, and not with a classic AhR ligand: benzo[a]pyrene. Moreover, in the presence of the AhR antagonist, CH223191, or when the expression of AhR was knock-down using dsiRNAs, the cellular dormancy signaling pathway was blocked. Morphological and ultrastructure analysis demonstrated that BghiP also induces ER stress, characterized by the dilated ER cisternae and the overexpression of PERK and CHOP genes (p < 0.05). Moreover, the halt of cell proliferation and the ER stress are both associated to the increase of pro-inflammatory cytokines (IL-6 and IL-8) and the cell survival in response to microenvironmental cues. These responses induced by BghiP on bronchial cells open new horizons on the research of other biological effects induced by environmental pollutants.

The E-Syt3 cleavage and traffic uncovers the primordial cisterna, a new organelle that mothers the lipid droplets in the adipocyte.

Extended synaptotagmins are endoplasmic reticulum proteins consisting of an SMP domain and multiple C2 domains that bind phospholipids and Ca2+ . E-Syts create contact junctions between the ER and plasma membrane (PM) to facilitate the exchange of glycerophospholipids between the apposed membranes. We find in the differentiating adipocyte that the E-Syt3 carboxyl domain is cleaved by a multi-step mechanism that includes removing the C2C domain. Confocal and live-cell time-lapse studies show that truncated E-Syt3ΔC2C, as well as endogenous E-Syt3 and the coat protein PLIN1, target the LDs from an annular, single giant ER cisterna. Inhibition of the proteasome blocks the proteolytic cleavage of Esyt3 and E-Syt3ΔC2C and causes the E-Syt3ΔC2C retention in the giant cisterna. The Esyt3 and PLIN1 distributions and LDs biogenesis show that the primordial cisterna, as we call it, is the birth and nurturing site of LDs in the adipocyte. Isoproterenol-induced lipolysis results in loss of cytoplasmic LDs and reappearance of the primordial cisterna. Electron microscopy and 3D-electron tomography studies show that the primordial cisterna consists of a tightly packed network of varicose tubules with extensively blistered membranes. Rounds of homotypic fusions from nascent to mature LDs play a central role in LD growth. The knockdown of E-Syt3 inhibits LD biogenesis. The identification of the primordial cisterna, an organelle that substitutes the randomly scattered ER foci that mother the LDs in non-adipose cells, sets the stage for a better understanding of LD biogenesis in the adipocyte.

Age-related alterations in fertilization-induced Ca2+ oscillations depend on the genetic background of mouse oocytes†.

Maternal aging affects various aspects of oocytes’ physiology, including the functionality of their nuclear apparatus and mitochondria. In the present paper, we wished to investigate whether advanced reproductive age impacts oocytes’ ability to generate proper Ca2+ oscillations in response to monospermic fertilization. We examined three different mouse strains/crosses: inbred C57BL/6Tar, outbred Tar:SWISS, and hybrid F1 (C57BL/6Tar × CBA/Tar). The females were either 2–4 months old (young) or 13–16 months old (aged). We observed that the Ca2+ oscillatory pattern is altered in a strain-dependent manner and changes were more profound in aged C57BL/6Tar and F1 than in aged Tar:SWISS oocytes. We also showed that maternal aging differently affects the size of Ca2+ store and expression of Itpr1, Atp2a2, Erp44, and Pdia3 genes involved in Ca2+ homeostasis in oocytes of C57BL/6Tar, Tar:SWISS, and F1 genetic background, which may explain partially the differences in the extent of age-dependent changes in the Ca2+ oscillations in those oocytes. Maternal aging did not have any visible impact on the distribution of the ER cisterns in oocytes of all three genetic types. Finally, we showed that maternal aging alters the timing of the first embryonic interphase onset and that this timing correlates in C57BL/6Tar and Tar:SWISS oocytes with the frequency of fertilization-induced Ca2+ oscillations. Our results indicate that extreme caution is required when conclusions about oocyte/embryo physiological response to aging are made and complement an increasing amount of evidence that mammalian (including human) susceptibility to aging differs greatly depending on the genetic background of the individual.

Vitamin B12b Enhances the Cytotoxicity of Diethyldithiocarbamate in a Synergistic Manner, Inducing the Paraptosis-Like Death of Human Larynx Carcinoma Cells.

We have shown that hydroxycobalamin (vitamin B12b) increases the toxicity of diethyldithiocarbamate (DDC) to tumor cells by catalyzing the formation of disulfiram (DSF) oxi-derivatives. The purpose of this study was to elucidate the mechanism of tumor cell death induced by the combination DDC + B12b. It was found that cell death induced by DDC + B12b differed from apoptosis, autophagy, and necrosis. During the initiation of cell death, numerous vacuoles formed from ER cisterns in the cytoplasm, and cell death was partially suppressed by the inhibitors of protein synthesis and folding, the IP3 receptor inhibitor as well as by thiols. At this time, a short-term rise in the expression of ER-stress markers BiP and PERK with a steady increase in the expression of CHOP were detected. After the vacuolization of the cytoplasm, functional disorders of mitochondria and an increase in the generation of superoxide anion in them occurred. Taken together, the results obtained indicate that DDC and B12b used in combination exert a synergistic toxic effect on tumor cells by causing severe ER stress, extensive ER vacuolization, and inhibition of apoptosis, which ultimately leads to the induction of paraptosis-like cell death.

Calcium activated nucleotidase 1 (CANT1) is critical for glycosaminoglycan biosynthesis in cartilage and endochondral ossification

Desbuquois dysplasia type 1 (DBQD1) is a chondrodysplasia caused by mutations in CANT1 gene encoding an ER/Golgi calcium activated nucleotidase 1 that hydrolyses UDP. Here, using Cant1 knock-in and knock-out mice recapitulating DBQD1 phenotype, we report that CANT1 plays a crucial role in cartilage proteoglycan synthesis and in endochondral ossification. Specifically, the glycosaminoglycan synthesis was decreased in chondrocytes from Cant1 knock-out mice and their hydrodynamic size was reduced, whilst the sulfation was increased and the overall proteoglycan secretion was delayed. Interestingly, knock-out chondrocytes had dilated ER cisternae suggesting delayed protein secretion and cellular stress; however, no canonical ER stress response was detected using microarray analysis, Xbp1 splicing and protein levels of BiP and ATF4. The observed proteoglycan defects caused deregulated chondrocyte proliferation and maturation in the growth plate resulting in the reduced skeletal growth. In conclusion, the pathogenic mechanism of DBQD1 comprises deregulated chondrocyte performance due to defective intracellular proteoglycan synthesis and altered proteoglycan properties in the extracellular matrix.

Gonads and gametogenesis in Chaetodactylus osmiae (Acariformes: Astigmata: Chaetodactylidae) a parasite of solitary bees

Chaetodactylus osmiae (Dufour, 1839) is a mite parasitizing the solitary bee - Osmia rufa L.- used as a commercial pollinator. In this study we present the anatomy of female and male reproductive systems of this species as well as its gonadal structure and gametogenesis at the ultrastructural level. The reproductive systems are similar to those of other Astigmata. The ovaries are paired and each contains germ-line cells – a giant nutritive ovarian cell connected via funnel-type intercellular bridges to oogonia and previtellogenic oocytes. Germinal cells are embedded in several large somatic stroma cells. Remarkable numerous protrusions of the nutritive ovarian cell penetrate into the stroma cell cytoplasm. Conspicuous ER cisterns run close and parallel to the surface of the germinal cells. Oocytes entering vitellogenesis disassociate with the nutritive cell and a vitelline envelope composed of heterogeneous material appears on their surface. When vitellogenesis is completed, the oocytes are full of lipid droplets and two types of yolk spheres; the vitelline envelope transforms into a thin and homogeneous chorion.Paired testes are located on one side of the body, whereas the opposite side is filled by a male accessory gland. In testis, germinal cells are embedded in a few somatic stroma cells. The earliest spermatogonia form a compact germarium, whereas later stages are dispersed randomly within the testis. Spermatocytes are characterized by a superficial spongy layer, formation of mitochondrial derivatives, loss of nuclear envelope and condensation of chromatin in threads. A single electron-dense lamella appears during the spermatid stage, separating chromatin threads from a large spongy body surrounded by arcuate, double-membrane bounded cisterns. In spermatids, the superficial spongy layer is absent. The testicular central cell in the germarium and structures related to meiotic division were not observed in the testes. Spermatozoa are multiform cells (approx. 4x11µm) containing electron-dense lamella (ca. 45 nm thick) surrounded by mitochondrial derivatives which separate chromatin threads 45-50 nm thick from remnants of the spongy body i.e. arcuate cistern profiles. Spermatozoa deposited in female spermatheca are more electron dense; the electron-dense lamella is deeply folded several times, whereas chromatin threads are present in the center of the spermatozoon and are either flanked by lamella folds or located more peripherally under the plasmalemma. Remnants of the spongy body are not discernible.

Arabidopsis tonoplast intrinsic protein and vacuolar H+-adenosinetriphosphatase reflect vacuole dynamics during development of syncytia induced by the beet cyst nematode Heterodera schachtii

Plant parasitic cyst nematodes induce specific hypermetabolic syncytial nurse cell structures in host roots. A characteristic feature of syncytia is the lack of the central vacuole and the formation of numerous small and larger vesicles. We show that these structures are formed de novo via widening of ER cisternae during the entire development of syncytium, whereas in advanced stages of syncytium development, larger vacuoles are also formed via fusion of vesicles/tubules surrounding organelle-free pre-vacuole regions. Immunogold transmission electron microscopy of syncytia localised the vacuolar markers E subunit of vacuolar H+-adenosinetriphosphatase (V-ATPase) complex and tonoplast intrinsic protein (γ-TIP1;1) mostly in membranes surrounding syncytial vesicles, thus indicating that these structures are vacuoles and that some of them have a lytic character. To study the function of syncytial vacuoles, changes in expression of AtVHA-B1, AtVHA-B2 and AtVHA-B3 (coding for isoforms of subunit B of V-ATPase), and TIP1;1 and TIP1;2 (coding for γ-TIP proteins) genes were analysed. RT-qPCR revealed significant downregulation of AtVHA-B2, TIP1;1 and TIP1;2 at the examined stages of syncytium development compared to uninfected roots. Expression of VHA-B1 and VHA-B3 decreased at 3 dpi but reached the level of control at 7 dpi. These results were confirmed for TIP1;1 by monitoring At-γ-TIP-YFP reporter construct expression. Infection test conducted on tip1;1 mutant plants showed formation of larger syncytia and higher numbers of females in comparison to wild-type plants indicating that reduced levels or lack of TIP1;1 protein promote nematode development.

Insight into the Pathology of a COL1A1 Signal Peptide Heterozygous Mutation Leading to Severe Osteogenesis Imperfecta

Osteogenesis imperfecta or “brittle bone disease” is a congenital disorder of connective tissue causing the bone to break easily. Around 85–90% of cases are due to autosomal dominant mutations in the genes encoding type I collagen, the major organic component of bone. Genotype–phenotype correlations have shown that quantitative defects of collagen type I lead to mild OI, whereas structural defects show a wide clinical range from mild to perinatal lethal. This may partially be explained by the type of amino acid substitution and the relative location in the domain structure. To fully understand the variability of the clinical manifestation and the underlying pathomechanisms, further investigations are required. Here we provide the first biochemical characterization of a mutation at the signal peptide cleavage site of COL1A1, a domain not yet characterized. By steady-state analysis, we observed reduced production of collagen type I. Furthermore, by pulse-chase analysis we detected delayed secretion and partial intracellular retention of collagen I. In the cellular fraction, the electrophoretic migration was abnormal; however, secreted type I collagen showed a normal migration pattern. The intracellular retention of collagen I was confirmed by immunofluorescent staining. Moreover, transmission electron microscopy of cultured fibroblasts revealed enlargement of ER cisternae. These results further support the hypothesis that mechanisms interfering with ER integrity play an important role in the pathology of severe OI.

IP3R, TRPM6 and Homer1 are Localized to ER‐PM Contact Sites at Tubulobulbar Complexes in Rat Testis

The seminiferous epithelium is the site of spermatogenesis; the cellular basis for male fertility. Large junction complexes between Sertoli cells act to control the movement of differentiating spermatogenic cells while those between Sertoli cells and late spermatids connect these late spermatids to the apex of the epithelium. During spermatogenesis, turnover of these junction complexes must occur so that the next generation of spermatogenic cells can move into the epithelium, and mature spermatozoa can be released into the seminiferous tubules. Structures called Tubulobulbar Complexes (TBCs) have been implicated in junction turnover due to their appearance during turnover and their necessity in allowing sperm release. TBCs likely drive the internalization of junction complexes but how Sertoli cells control the development and degradation of TBCs is unknown. TBC regulation may be a product of a well‐known yet functionally unestablished contact site between TBC bulbs and cisternae of ER. Because calcium exchange occurs at other ER‐plasma membrane contact sites such as those between ER and endosomes, we chose to probe for the IP3R calcium channel. Using bioinformatics, we found potential protein binding partners for IP3R in the form of the TRPM6 plasma membrane calcium channel and the homer1 scaffolding protein. Using a high‐resolution pre‐embedding immunoelectron microscopy technique we localized all three proteins to the TBC‐ER contact site. This data suggests the potential for scaffolding of IP3R to TRPM6 via homer1 at TBC‐ER contacts and opens up the possibility for calcium exchange as an important function of the ER at these sites.Support or Funding InformationSupported by a NSERC Discovery Grant (#155397‐2013) to AWV

Three-dimensional and immune electron microscopic analysis of the secretory pathway in Saccharomyces cerevisiae.

Until now, the mechanisms of ER-to-Golgi and intra-Golgi transport remain obscure. This is especially evident for the Golgi of S. cerevisiae where different Golgi compartments are not organized in stacks. Here, using improved sample preparation protocols, we examined the 3D organization of pre-Golgi and Golgi compartments and found several new features of the structures functioning along the secretory pathway. In the cytoplasmic sheet ER, we found narrow pores that aggregated near the rims, and tubular networks tightly interconnected with sheets of several cytoplasmic ER cisternae. Within the Golgi compartments, we found disks with wide pores, disks with narrow pores, and disk-like networks with varicosities or nodules at the point of branching and thick membranes. Sometimes, these compartments contained 30nm buds coated with a clathrin-like coat. The lumen of these Golgi compartments was more osmiophilic than the lumen of the ER. In contrast to ER elements, Golgi compartments were isolated and in the majority of cases not connected, although we observed some connections between Golgi compartments and also between Golgi disks with wide pores and the ER. Two types of free vesicles of 35-40 and 45-50nm were found, the former being sometimes partially coated with a clathrin-like coat. Sec31, a COPII component, was found near narrow pores in the cytoplasmic sheets of the ER, over edge aggregates of narrow pores, and within the ER network. The cis-Golgi marker Rer1p was detected on disks or semi-spheres with wide pores, while the medial Golgi marker Gos1p was found on disks or semi-spheres with narrow pores. Gos1p was found to be enriched on 45-50nm vesicles, while Rer1p was depleted. The 35-40nm vesicles did not show either label. These findings are discussed from the point of view of mechanisms of transport.

Understanding the role of synaptopodin and the spine apparatus in Hebbian synaptic plasticity – New perspectives and the need for computational modeling

Synaptopodin (SP) is a proline-rich actin-associated protein essential for the formation of a spine apparatus (SA) in dendritic spines. The SA consists of stacks of smooth endoplasmic reticulum (sER) contiguous with the meshwork of somatodendritic ER. Spines of SP-deficient mice contain sER but no SA, demonstrating that SP is necessary for the assembly of ER cisterns into the more complex SA organelle. Although the SA was described decades ago, its function was difficult to investigate and remained elusive, in part because reliable markers for the SA were missing. After SP was identified as an essential component and a reliable marker of the SA, a role of SP/SA in hippocampal synaptic plasticity could be firmly established using loss-of-function approaches. Further studies revealed that SP/SA participate in the regulation of Ca2+-dependent spine-specific Hebbian plasticity and in activity-dependent changes in the spine actin cytoskeleton. In this review we are summarizing recent progress made on SP/SA in Hebbian plasticity and discuss open questions such as causality, spatiotemporal dynamics and complementarity of SP/SA-dependent mechanisms. We are proposing that computational modeling of spine Ca2+-signaling and actin remodeling pathways could address some of these issues and could indicate future research directions. Moreover, reaction-diffusion simulations could help to identify key feedforward and feedback regulatory motifs regulating the switch between an LTP and an LTD signaling module in SP/SA-containing spines, thus helping to find a unified view of SP/SA action in Hebbian plasticity.

Flowering biology and structure of floral nectaries in Galanthus nivalis L.

In Poland &lt;em&gt;Galanthus nivalis&lt;/em&gt; L. is partially protected. The flowers of this species are one of the first sources of nectar and pollen for insects from February to April. The aim of this study was to present the flowering biology as well as the topography, anatomical, and ultrastructural features of the floral nectary. The flower lifespan, the breeding system, and the mass of pollen and nectar produced by the flowers were determined. Examination of the nectary structure was performed using light, fluorescence, scanning and transmission electron microscopy. The flower of &lt;em&gt;G. nivalis&lt;/em&gt; lives for about 30 days. The stamens and pistils mature simultaneously and during this time nectar is secreted. The anthers of one flower produced the large amount of pollen (4 mg). The breeding system of &lt;em&gt;G. nivalis&lt;/em&gt; was found to be characterized by partial self-compatibility, outcrossing, and xenogamy. The nectary is located at the top of the inferior ovary. The nectary epidermal cells are characterized by striated cuticular ornamentation. Initially, the secreted nectar formed vesicle-like protuberances under the cuticle. The epidermal and parenchymal cells contain numerous plastids, mitochondria, dictyosomes, ER cisterns, and vesicles fused with the plasmalemma, which indicates granulocrine nectar secretion.

Molecular Consequences of the SERPINH1/HSP47 Mutation in the Dachshund Natural Model of Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is a heritable connective tissue disease characterized by bone fragility and increased risk of fractures. Up to now, mutations in at least 18 genes have been associated with dominant and recessive forms of OI that affect the production or post-translational processing of procollagen or alter bone homeostasis. Among those, SERPINH1 encoding heat shock protein 47 (HSP47), a chaperone exclusive for collagen folding in the ER, was identified to cause a severe form of OI in dachshunds (L326P) as well as in humans (one single case with a L78P mutation). To elucidate the disease mechanism underlying OI in the dog model, we applied a range of biochemical assays to mutant and control skin fibroblasts as well as on bone samples. These experiments revealed that type I collagen synthesized by mutant cells had decreased electrophoretic mobility. Procollagen was retained intracellularly with concomitant dilation of ER cisternae and activation of the ER stress response markers GRP78 and phospho-eIF2α, thus suggesting a defect in procollagen processing. In line with the migration shift detected on SDS-PAGE of cell culture collagen, extracts of bone collagen from the OI dog showed a similar mobility shift, and on tandem mass spectrometry, the chains were post-translationally overmodified. The bone collagen had a higher content of pyridinoline than control dog bone. We conclude that the SERPINH1 mutation in this naturally occurring model of OI impairs how HSP47 acts as a chaperone in the ER. This results in abnormal post-translational modification and cross-linking of the bone collagen.

Female gametophyte and pollen tube of Epilobium palustre L.

The monosporic, tetranucleate embryo sac of &lt;i&gt;Epilobium palustre (Onagraceae)&lt;/i&gt; develops from the micropylar megaspore in a linear tetrad. In mononucleate embryo sacs a peculiar chromatic structure associated with a nucleolus appears in the nucleus. This structure seems to be formed by fibrillar material and is not visible in the subsequant stages of development. A large amount of rough ER cisternae occurs in the late mononucleate stage, during the binucleate stage their contents become optically dense. It the early tetranucleate stage the amount of ER is small, it increases again in the developing synergids and central cell. Numerous amyloplasts present in the mononucleate embryo sac loose their starch grains and some are transformed into cup-shaped plastids or proplastids. They are passed on to each of the embryo sac cells. The growth of the pollen tube ceases immediately after the penetration through the filiform apparatus of a synergid. At the apex of the tube a pore is formed. At the last stages of the penetration the apical part of the pollen tube becomes separated by a transverse partition from the distal part of the tube. The contents of the both parts differ in their internal structure. The distal part contains cytoplasm with numerous organoids, while the apical part is mainly filled with spherical bodies.

STIM1L traps and gates Orai1 channels without remodeling the cortical ER.

STIM proteins populate and expand cortical endoplasmic reticulum (ER) sheets to mediate store-operated Ca2+ entry (SOCE) by trapping and gating Orai channels in ER-plasma membrane clusters. A longer splice variant, STIM1L, forms permanent ER-plasma membrane clusters and mediates rapid Ca2+ influx in muscle. Here, we used electron microscopy, total internal reflection fluorescence (TIRF) microscopy and Ca2+ imaging to establish the trafficking and signaling properties of the two STIM1 isoforms in Stim1−/−/Stim2−/− fibroblasts. Unlike STIM1, STIM1L was poorly recruited into ER-plasma membrane clusters and did not mediate store-dependent expansion of cortical ER cisternae. Removal of the STIM1 lysine-rich tail prevented store-dependent cluster enlargement, whereas inhibition of cytosolic Ca2+ elevations or removal of the STIM1L actin-binding domain had no impact on cluster expansion. Finally, STIM1L restored robust but not accelerated SOCE and clustered with Orai1 channels more slowly than STIM1 following store depletion. These results indicate that STIM1L does not mediate rapid SOCE but can trap and gate Orai1 channels efficiently without remodeling cortical ER cisternae. The ability of STIM proteins to induce cortical ER formation is dispensable for SOCE and requires the lysine-rich tail of STIM1 involved in binding to phosphoinositides.

The structure of the endodermis during the development of wheat (Triticum aestivum L.) roots

Four stages of development in the process of differentiation of the root endodermis of wheat (&lt;em&gt;Triticum aestivum&lt;/em&gt; L. var. Grana) are described. The proendodermis cells have a meristematic nature. Their vacuoles accumulated an osmophilic material. In the next stage, Casparian strips arose in the walls of the endodermis. Dictyosomes and ER cisterns were numerous in the protoplasts of these cells. In the following stage, a suberin lamella was deposited over the entire internal surface of the primary cell wall. In the final stage, a secondary cell wall, thickened in the form of a letter U, was formed. In secondary wall simple pits arose. The endodermis of the wheat root developed asynchronously, more quickly over the phloem bundles.

Changes in the ultrastructure of meristematic root cells of Allium sativum L. treated with selenium

Ultrastructure of meristematic cells of garlic (&lt;em&gt;Allium sativum&lt;/em&gt; L.) roots treated with sodium selenate and sodium selenite was assessed using transmission electron microscopy. Both selenium compounds applied at the concentrations: 80, 160 and 320 µM caused many malformations in the ultrastructure of mitochondria, plastids, endoplasmic reticulum and Golgi apparatus such as deformation in shape and size, disturbances in inner membranes organization, appearance of concentric or parallel arrangement of ER cisternae. Moreover, in the presence of selenium, beside uneven thickening of cell wall, many vacuoles of different dimensions filled with wall-like material even in the vicinity of nucleus were visible. The latter results suggest that selenium not only intensified the synthesis of cell wall material but also inhibited the process of cell wall material deposition. The similarity of all observed ultrastructural changes in garlic root cells after selenium treatment with those appearing after action of other stress factors are discussed.

Embryo sac development in Stellaria media

Osmiophilic granules were observed during certain stages of intermitotic periods in one, two and four nucleate embryo sacs in &lt;em&gt;Stellaria media&lt;/em&gt;. The granules, some inside the short ER cisternae, were mainly distributed along the walls of nucleate embryo sacs. It is assumed that the osmiophilic granules may he involved in the deposition of substances within the wall of the megagametophyte.

Callose and osmiophilic material deposition into walls of developing megagametophyte in Stellaria

Extensive rough ER cisternae are developing and disappearing during each of intermitotic periods in two and four nucleate embryo sac and synergids. The synergid cisternae are transformed into vesicles. Some long cisternae come in close contact with the embryo sac and the synergid walls. Numerous osmiophilic droplets from the cytoplasm seem to be incorporated into the walls during the period of wall-cisternae relation.