Ultrastructure of meristematic epidermal cells of maize root under water deficit conditions

Summary Structural components of meristematicZea mays primary root epidermal cells were observed after osmotic stress of the nutrient medium (12.5 atm.) and after rehydration. After non-lethal osmotic stress (24 hours), aggregation of nuclear chromatin, parallel ER arrangement, and reduction of mitochondrial cristae were found. Increased number of Golgi cisternae indicated vesicle production inhibition, and microtubules were absent in treated cells, although plastid structure remained unchanged. After lethal osmotic stress (48 hours), fragmentation of cytoplasmic membranes and a more severe structure damage of all cellular components occurred. Structure of the nucleus, mitochondria, Golgi apparatus and microtubules reappeared in the cells after rehydration. The only new feature of these cells was occurrence of smooth ER, which may indicate that the ER system has acquired a different function in regenerated cells.     

Effect of osmotic stress on the ultrastructure and viability of the yeast Saccharomyces cerevisiae

Exposure of the yeast Saccharomyces cerevisiae to hypertonic solutions of non-permeating compounds resulted in cell shrinkage, without plasmolysis. The relationship between cell volume and osmolality was non-linear; between 1 and 4 osM there was a plateau in cell volume, with apparently a resistance to further shrinkage; beyond 4 osM cell volume was reduced further. The loss of viability of S. cerevisiae after hypertonic stress was directly related to the reduction in cell volume in the shrunken state. The plasma membrane is often considered to be the primary site of osmotic injury, but on resuspension from a hypertonic stress, which would have resulted in a major loss of viability, all cells were osmotically responsive. The effects of osmotic stress on mitochondrial activity and structure were investigated using the fluorescent probe rhodamine 123. The patterns of rhodamine staining were altered only after extreme stress and are assumed to be a pathological feature rather than a primary cause of injury. Changes in the ultrastructure of the cell envelope were examined by freeze-fracture and scanning electron microscopy. In shrunken cells the wall increased in thickness, the outer surface remained unaltered, whilst the cytoplasmic side buckled with irregular projections into the cytoplasm. On return to isotonic solutions these structural alterations were reversible, suggesting a considerable degree of plasticity of the wall. However, the rate of enzyme digestion of the wall may have been modified, indicating that changes in wall structure persist.     

Fine Structure of Blue-Green Algae and the Cells Lined along the Endophyte Cavity in the Coralloid Root of Cycas

The ultrastructure of vegetative cells of blue-green alga, Anabaena cycadae, in the coralloid root of Cycas revoluta has the general characteristics of the cyanophycean cells. Their heterocysts are characterized by heavy envelope deposition, well developed pore channel with its plug, absence of large granules as inclusions and reduced and flattened photosynthetic thylakoids. By these characteristical features, the frequency of heterocysts occurring in this algal population of the coralloid root may be estimated to ca. 40%. This high heterocyst frequency is a sign of relatively high activity of nitrogen fixation in this symbiont. The ultrastructure of the cells lined along the endophyte cavity in the coralloid root shows that they have the function to maintain vigorous nutritional transport in short distance. These cells are especially characterized by the presence of numerious outgrowths on the cell wall into the endophyte cavity. Correspondingly, there are abundant mitochondria, dictyosomes and numerious vesicles in the cytoplasm. The plasma membrane becomes tortuous along the cell wall and many secretory granules are present between the plasma membrane and cell wall in the cytoplasm amyloplasts and starch granules also occur constantly. The ultrastructure observed above indicates the fact that there is sound structural basis for the metabolic relationship between the host cells and the symbiont.     

Ultrastructure of cortical cells of maize root under water stress conditions

Following moderate water stress in the cortical cells of theZea mays primary roots, the condensation of the nuclear chromatin, a higher density of free ribosomes and a reduction of polyribosomes, the reduction of mitochondrial cristae, elongation of ER elements, less compact dictyosomes and inhibited production of the Golgi vesicles were observed. Severe water stress would cause more severe structural damage in the cortical cells. The more differentiated cortical cells showed more expressive ultrastructural damage when compared with the meristematic nonvacuolated cells. Similarly, the cells of the peripheral layers of the cortex suffered more from water deficit than the cells of the layers situated closer to the central cylinder.     

Short-term Salinity and High Temperature Stress-associated Ultrastructural Alterations in Young Leaf Cells ofOryza sativaL.

Salinity and high temperature stresses adversely affect growthand development of rice plants. To investigate the responseof rice cells to these stresses, we have analysed short-termstress-induced subcellular alterations in undifferentiated leafcells of rice seedlings by transmission electron microscopy.Perturbations noted particularly with respect to plasma membrane,mitochondrial membranes, endoplasmic reticulum, polyribosomesand dictyosomes are highlighted. The subcellular changes evokedby both stresses after 4 h were lysis of the cytoplasm, accumulationof electron-dense granules in the cytoplasm, distension in theER membranes, enhanced association of ribosomes with the endoplasmicreticulum, reduction in the number of mitochondrial cristae,as well as disorganization of cell wall fibrillar material.Certain changes were found to be unique to either the salinityor high temperature stress. Plasmolysis and increased cytoplasmicvesiculation were seen only in response to salinity stress,while discontinuity in the plasma membrane with close associationof the osmiophilic granules were observed only in response tohigh temperature.Copyright 1997 Annals of Botany Company Electron dense granules; high temperature stress; leaf cells; Oryza sativaL.; rice; salinity; ultrastructure     

Comparative characteristics of the ultrastructure of the causative agents of glanders and melioidosis]

The authors examined the ultrastructure of the causative agents of glanders and melio idosis. It was revealed that the structure of their cell wall and of the cytoplasmic membrane was characteristic of Gram negative bacteria. The cytoplasm of both types of the causative agents showed the presence of ribosomes, membrane structure, nucleoid, and also osmiophilic and osmiophobic inclusions.     

The ultrastructure of Blastocystis galli from chickens

The ultrastructure stages of Blastocystis galli were studied in chicken's intestine and in laboratory cultures. There were found morphological structures: surface coat (cell from chickens' intestine showed a very thick surface coat); cell membrane--there were some small electron-opaque deepening "pockets" on the membrane; inner membrane; endoplasmic reticulum with attached ribosomes, which present in the cytoplasm; all cells contained numerous of small vacuoles and large glycogen inclusions in cytoplasm; mitochondria with tubular cristae; nucleus with granules condensed chromatin; central vacuole; Golgi complex was represented by number of plates grouped in a pite; the cyst-like forms were surrounded by multilayered wall.     

Ultrastructure of the tegument of Metamicrocotyla macracantha (Alexander, 1954) Koratha, 1955 (Monogenea, Microcotylidae).

The ultrastructure of the body tegument of Metamicrocotyla macracantha (Alexander, 1954) Koratha, 1955, parasite of Mugil liza from Brazil, was studied by transmission electron microscopy. The body tegument is composed of an external syncytial layer, musculature, and an inner layer containing tegumental cells. The syncytium consists of a matrix containing three types of body inclusions and mitochondria. The musculature is constituted of several layers of longitudinal and circular muscle fibers. The tegumental cells present a well-developed nucleus, cytoplasm filled with ribosomes, rough endoplasmatic reticulum and mitochondria, and characteristic organelles of tegumental cells.     

胡杨细胞和组织结构与其耐盐性关系的研究

The characteristics of the cell and organ structures of Populus euphratica Oliv. in relation to salt and osmotic tolerance were compared with those of P. tomentosa Cart. in vitro under the electron and light microscopic observation. P. euphratica exhibited characteristic structure which was associated with salt stress. It had well-developed epidermis and exodermis in the root tip and poorly developed conducting tissue in leaf. Root hairs were formed closer to the root tips. AsP. euphratica were stressed with salt and PEG, more abundance of chondriosomes and plastids in the cytoplasm and more containing substance in the plastid were observed and the osmophilic substance was obviously displayed in the cytoplasm and in the posterior margin of the vacuole. The filamentous structure, bigger nucleus and nucleolus were visualized in the stressed suspension-cultured cells of P. euphratica. The meristemic cells in the root tip of P. euphratica could maintain their structure when the plant was subjected to 8 g/L NaCl stress. It was also demonstrated that the cell wall and plasmalemma of P. euphratica were tightly combined as a dentate form, explaining why the cell could endure severe salt or osmotic stress and resist to plasmolysis indicating that P. euphratica possesses a solid structure base as a defense to salt stress.     

Immunoelectron microscopical studies on synthesis and localization of uncoupling protein in brown adipocytes: Evidence for cotranslational transport of uncoupling protein into mitochondria

Through the use of the immunoelectron microscopical technique, uncoupling protein (UCP) was analyzed in the brown adipocytes of room temperature- and cold-acclimated rats, in rat brown adipocytes developed in vitro, and in the brown adipocytes of mice, hamsters, and hedgehogs. Using rat anti-UCP-antibody, it is shown that UCP is located in the cristae of brown adipocytes mitochondria (UC-mitochondria) of all analyzed species, whereas mitochondria of nonadipose cells, i.e., C-mitochondria of endothelium, fibrocytes, smooth muscle cells, Schwann cells, axons of neural cells, and white blood cells, do not contain UCP. Cold stress in rats exposed to temperatures of +4 and -20 degrees C caused the amount of UCP per 1 micron 2 of mitochondria to more than double compared with room temperature-acclimated rats. This increase was especially dramatic on the outer mitochondrial membrane: fourfold more UCP molecules compared to the control rats. The ground cytoplasm of adipocytes showed very intensive labeling with RNase-gold complex, indicating that cytoplasm was an active site for protein synthesis, while the absence of UCP-labeling in ground cytoplasm was interpreted to mean that ground cytoplasm did not serve as a site for UCP synthesis. On the other hand, the protrusions of the outer mitochondrial membrane covered with ribosomes, clusters of UCP molecules, and clusters of RNase-gold particles supported the idea that UCP was one of the mitochondrial proteins synthesized on the ribosomes which were in contact with the outer mitochondrial membrane. After being synthesized there, UCP, which could be either extruded into intermembranous space or directed by lateral movement to intermembranous contact sites, was incorporated into inner mitochondrial membrane. Thus, UCP is imported using the so-called "cotranslational transport system."     

Effect of Osmotic Stress on Ion Transport Processes and Phospholipid Composition of Wheat (Triticum aestivum L.) Mitochondria

The effect of osmotic stress on wheat (Triticum aestivum L.) mitochondrial activity and phospholipid composition was investigated. Preliminary growth measurements showed that osmotic stress (−0.25 or −0.5 megapascal external water potential) inhibited the rate of shoot dry matter accumulation while root dry matter accumulation was less sensitive. We have determined that differences in sensitivity to osmotic stress existed between tissues at the mitochondrial level. Mitochondria isolated from roots or shoots of stressed seedlings showed respiratory control and ADP/O ratios similar to control seedlings which indicates that stressed mitochondria were well coupled. However, under passive swelling conditions in a KCl reaction mixture, the rate and extent of valinomycin-induced swelling of shoot mitochondria were increased by osmotic stress while root mitochondria were largely unaffected. Active ion transport studies showed efflux transport by stressed-shoot mitochondria to be partially inhibited since mitochondrial contraction required the addition of N-ethylmaleimide or nigericin. Efflux ion transport by root mitochondria was not inhibited by osmotic stress which indicates that stress-induced changes in ion transport were largely limited to shoot mitochondria. Characterization of mitochondrial fatty acid and phospholipid composition showed an increase in the percentage of phosphatidylcholine in stressed shoot mitochondria compared to the control. Mitochondrial fatty acid composition was not markedly altered by stress. No significant changes in either the phospholipid or fatty acid composition of stressed root mitochondria were observed. Hence, these results suggest that a tissue-specific response to osmotic stress exists at the mitochondrial level.     

Ultrastructural and physiological changes in root cells of Sorghum plants (Sorghum bicolor S. sudanensis cv. Sweet Sioux) induced by NaCl

The xerophytic, but salt-sensitive Sorghum cultivar ‘SweetSioux’ is known as an ion excluder with a high K/Na selectivityat the plasmalemma and tonoplast of epidermal root cells. Theaim of this study is the correlation of salt-effected changesin physiological parameters with structural and ultrastructuralchanges in root cells. The investigation was carried out withroot cells because these cells are most directly exposed tothe growth medium. Sorghum bicolor S. sudanensis cv. Sweet Sioux plants weregrown under steady-state conditions on nutrient solutions withor without 40 mol m^–3 NaCl. Sorghum sustained this treatmentbut showed several salt-induced structural and physiologicalchanges which were studied in various cell types of the roottip. (1) NaCl salinity led to a shorter growth region and to salt-inducedalterations in the chemical and physical properties of the cellwalls in the root tips. (2) Salt treatment also increased the membrane surface in rootcells: root cells showed an increase in the quantity of vesiclesin the epidermis and in the middle cortex cells. Additionally,some of the epidermis cells of salt-treated plants revealeda characteristic build-up of transfer cells, suggesting an increasein membrane surfaces to increase the uptake and storage of substances. (3) The number of mitochondria increased in the epidermal andin the cortex cells after salt stress thus indicating an additionalsupply of energy for osmotic adaptation and for selective uptakeand transport processes. (4) In the epidermal cytoplasm NaCl stress led to a significantdecrease of the P, K, Ca, and S concentrations accompanied byan increase of Na concentration. Electron micrographs show anincrease in electron optical contrast within the cytosol andin the matrix of the mitochondria. These results are discussedwith regard to the possibility of influence on the part of metabolicfunctions. (5) The NaCl concentrations were seen to increase and the Kconcentrations to decrease during salt stress in the vacuolesof the epidermis and cortex cells. The salt-induced increasein vacuolar NaCl concentrations of epidermis and cortex cellsare in the region 2 cm behind the root tip, which is sufficientfor an osmotic balance towards the growth medium. Additionalsolutes are necessary 0.5 mm behind the root tip to facilitateosmotic adaptation. The results show ultrastructural changes caused by an Na-avoidingmechanism characterized by a high level of energy consumption.The exclusion of Na from the symplast seems to lead additionallyto a decrease in cytoplasmic concentrations of such essentialelements as Mg, P, S, and Ca and is thus responsible directly(via energy supply in mitochondria, homeostasis, selectivityof K over Na) or indirectly (via enzyme conformation, cytoplasmichydration) for the ultra-structural degradation indicated. Thesalinity-induced multiplicity of structural and functional changeswithin cell compartments constitutes a group of indicators forthe limited NaCl tolerance of Sorghum. Key words: Sorghum bicolor S. sudanensis, ultrastructure, salt tolerance, NaCl, Ca-deficiency     

胡杨细胞和组织结构与其耐盐性关系的研究

利用电子显微镜和光学显微镜中相差和微分干涉等技术对胡杨（ＰｏｐｕｌｕｓｅｕｐｈｒａｔｉｃａＯｌｉｖ．）悬浮培养的细胞和试管苗的组织和细胞结构以及盐胁迫对其结构影响进行了研究。与毛白杨（Ｐ．ｔｏｍｅｎｔｏｓａＣａｒ．）相比,胡杨存在与耐盐相关的结构,如根尖具有较发达的表皮和外皮层,根毛着生靠近根端;叶片输导组织不发达;细胞中线粒体和质体较丰富。盐胁迫和渗透胁迫可使胡杨细胞质中的线粒体和质体变得更为丰富,质体中内含体增多,在细胞质中和液泡内缘出现明显的嗜锇物质,在悬浮培养的细胞内表现出明显的丝状结构,细胞核变大,核仁明显。受到８ｇ／ＬＮａＣｌ胁迫的胡杨根尖分生细胞仍可维持正常的结构。在超微结构研究中还发现,胡杨细胞膜与细胞壁之间呈齿状结合,说明了膜与壁之间结合的牢固性和稳定性,解释了胡杨细胞在胁迫中不易发生质壁分离的原因。     

Some observations on coleoptile cell ultrastructure in ungerminated grains of rice (Oryza sativa L)

Summary The ultrastructure of coleoptile cells of ungerminated rice grains has been examined following fixation in glutaraldehyde and osmium tetroxide. In many respects the cell structure resembles that reported for other dormant seed tissues: the cells contain protein bodies and lipid droplets, mitochondria and plastids show little internal structure but cytoplasm invaginates into many plastids; golgi cisternae cannot be discerned. Rough ER is present as cisternae surrounding protein bodies, as occasional regions of parallel layers, and in concentric whorls where it alternates with smooth paired membranes of an unknown nature. The ribosomes on the ER are at least partly arranged into regular rows. Various crystalline, presumably proteinaceous, inclusions lie in the groundplasm, plastids and nuclei.     

Mast cells of lymph hearts during ontogenesis of frogs Rana temporaria

Electron microscopic observations of the lymph hearts of tadpoles and yearling frogs of Rana temporaria showed that mast cells (MCs) were present not only between muscle fibers (population of resident MCs), but in the cavities of lymph heart (population of circulating MCs), too. There were some differences in the ultrastructure of the resident MCs at each studied stage of larval development. The first recognizable MCs were revealed in the lymph hearts at premetamorphosis (stages 39-41). MCs presented as mononuclear relatively small and slightly elongated cells with a few immature secretory granules and numerous free ribosomes, polysomes and short cisternae of rough endoplasmic reticulum (RER) in the cytoplasm. Chromatin of their nuclei was poorly condensed; the Golgi apparatus was moderately developed. At pro-metamorphosis (stages 44-45), we revealed MCs at different levels of their differentiation. Some MCs demonstrated an active process of granulogenesis in their cytoplasm. Among densely packed cytoplasmic organelles, immature secretory granules were closely associated with cisternae of RER and free ribosomes. Other MCs appeared as more differentiated cells. They were characterized by a predominantly heterochromatic nuclei and cytoplasm filled with polymorphic and heterogeneous granules. MCs also showed a reduction in the number of free ribosomes and cisternae of RER in the cytoplasm. On the contrary, the Golgi apparatus was well developed. Stacks of Golgi cisternae, detaching vacuoles, and progranules occupied the perinuclear region. The majority of the outlines above ultrastructural features of differentiated MCs were typical for MCs of yearling frogs. At metamorphic climax (stages 52-53), MCs often tightly contacted with macrophages. We did not reveal apoptotic MCs. However, some MCs exhibited morphological features typical for programmed necrosis-like death, which was characterized by mitochondria swelling, dilatation of cisternae of RER and nuclear envelope, plasma membrane rupture and subsequent loss of intracellular contents. Electron microscopical immunocytochemistry revealed the localization of atrial natriuretic peptide (ANP), substance S (SP) and heat shock protein (Hsp70) in the secretory granules of the resident and circulating MCs at different stages of tadpole development and in yearling frogs.     

Fine structural study of keratinization of the filiform papillae in the tongue in humans]

The fine structure of the keratinization of the papilla filiformis of the human tongue was described for the first time; Two biopsies of normal tongue tissue were fixed in 2,5% phosphate-buffered glutaraldehyde, postfixed in 1% osmiumtetroxyde, embedded in Durcopan und contrasted ultrathin sections were examined by electron microscopes JEM 7A and 100B. The findings show a highly configurated epithel-connective tissue border with basal lamina and irregular hemidesmosomes. The epithelial structure of the interpapillary area is identical with the fine structure of the human buccal mucosa, which was classified as non-keratinized or incompletely keratinized. Accordingly, a stratum granulosum is missing. After loss of nucleus and organelles, surface cells become flattened, parallel to the surface of the tongue and have a fine fibrillar cytoplasm. The papilla filiformis is formed by cell growth along the secondary connective tissue papillae and consequently tube-like epithelial structures appear. In the papillary area basal and stratum spinosum cells show epidermal structural features. A difference from epidermal and other oral epithelial cells becomes apparent for the first time in the stratum granulosum by the appearance of a great number of round, small, electron-dense KHG, surrounded by ribosomes. The KHG are not associated with tonofilaments. In the area of the walls of the tubes 1...3 mum large, electron-dense structures are formed by fusion of several KHG. With further differentiation these large KHG disintegrate into bulky or granular masses, filling the cell cytoplasm and thus mask the tonofilaments. The cells at the borders of the tubes show a great structural variability. After the disintegration of nucleus and organelles, the cytoplasm is formed by randomly oriented filaments of different packing or by fiber-bundles. Yet the interfibrilla embedding substance, typical of orthokeratinization is mostly lackingmin some cells of the tubeborders, masses of disintegrated KHG substance are masking the fibrillar cell cytoplasm. In other areas, where the KHG do not increase by fusion, intense fibrillar packing and abrupt keratinization becomes apparent. At the rim of the tube fully keratinized epithelial threads are regularly found. These are lacking at the bottom of the tubes. All surface areas show a strong tendency towards desquamation. Thus a more or less wide surface plaque is formed on the tongue, consisting of desquamated and disintegrated surface cells and of bacterial. Groups of little differentiated basal cells, which can be considered as the initial material for an accelerated regeneration, can be evaluated as a truly remarkable finding. This accelerated regeneration might be due to an increased wear of the inclompletely keratinized cells of the bulk of the papilla filiformis of the human tongue. Based on the findings of this study, an attempt was made, to explain the pathological reactions of human tongue epithelium in various systemic diseases.     

The morphological site of synthesis of cytochrome c in mammalian cells (Krebs cells)

In Krebs ascites-tumour cells, cytochrome c is segregated in the mitochondria and the level in microsomes could not be measured. At 22° in glucose–buffer Krebs cells synthesized a spectrum of proteins including cytochrome c. Mild osmotic shock in the presence of ribonuclease had little effect on incorporation of [¹⁴C]-leucine or [¹⁴C]valine into mixed mitochondrial protein but strongly inhibited synthesis of non-mitochondrial cytoplasmic proteins. Under these conditions, labelling of cytochrome c was also strongly inhibited. After pulse labelling of Krebs cells at 22° for 10min. the cytcchrome radioactivity found in mitochondria was higher than in microsomes. After addition of unlabelled amino acid as `chase' there was 137% increase in radioactivity of cytochrome c but only a 3% increase in radioactivity of whole-cell protein. It is concluded that the peptide chain of cytochome c is synthesized on cytoplasmic ribosomes. Mitochondria therefore do not have the character of self-replicating entities, but are formed by the cooperative function of messenger RNA of cytoplasmic ribosomes and, possibly, of intramitochondrial messenger derived from the mitochondrial DNA.     

Mitochondrial ultrastructure in roots of mesophyte and hydrophyte at anoxia and after glucose feeding

Summary In order to investigate the nature of the tolerance of mesophytes and hydrophytes to root anaerobiosis, changes in the mitochondrial ultrastructure of excised roots (with and without added glucose under anoxia) were studied in plants from two ecologically opposite types-pumpkin and rice.A 12-hour exposure to anoxia led to mitochondrial degradation in roots of adult rice and pumpkin plants. The addition of glucose preserved cell ultrastructure for up to 72–96 hours. During this period mitochondrial ultrastructure changed. In rice roots this primarily involved an increased number of cristae and a change in their arrangement into parallel rows. Cells of pumpkin roots displayed long mitochondria (up to 55 m) of different profiles which fused to form a complex mitochondrial network that was in close association with parts of the endoplasmic reticulum carrying a large number of ribosomes. This may be regarded as an adaptive development that facilitates the transport of glycolytic energy along mitochondrial membranes to the sites of protein synthesis.It is concluded that root cells of a hydrophyte are not more tolerant to anoxia than mesophyte. Thus, the ability of hydrophytes to grow on anaerobic soils should be attributed not so much to peculiar features of the roots' metabolism but to the ability of these plants to perform an easy transport of O₂ from leaves to roots. With respect to mesophytes it is stressed that the supply of assimilates is important for the resistance of roots to soil anaerobiosis.     

Wheat Streak Mosaic Virus-induced Cytoplasmic Expansion and Membrane Proliferation

The cytoplasmic volume of wheat streak mosaic virus-infected cells was significantly greater than that of cells in healthy control tissue. Ultrastructural examination revealed that mainly cellular membranes and ribosomes filled the expanded cytoplasm. Imperfectly spherical inclusions, containing continuous endoplasmic reticulum membranes at the periphery and a mixture of membranes and ribosomes in the centre, were observed near nuclei at early infection stages. The inclusions became larger as infection progressed. Membranes and ribosomes proliferated also throughout the cell, forming a matrix in which organelles and various cytopathic structures were enclosed. Numerous vesicles were observed in the cytoplasm of other WSMV-infected cells. Multi-layered membrane bodies were found at later infection stages. Virus particles were present in the central space of these myelin-like structures. The presence of apparently intermediate stages in myelin-like structure development in chloroplasts suggest that at least some of the myelin-like structures originated from the chloroplasts.