Fine structure of nitrogen-fixing leguminous root nodules from the Canadian Arctic

Effective (nitrogen-fixing) root nodules of Oxytropis maydelliana Trautv., O. arctobia Bunge and Astragulus alpinus L. were collected in the high Arctic tundra and subsequently processed for structural studies. The cylindrically-shaped perennial nodules consisted of the following tissues: nodule cortex, nodule meristem, nodular vascular bundles, an active central region with uninfected and infected cells at various stages of development, and a proximal region of senescent cells. The active central region was dark red-coloured due to the presence of the pigment leghemoglobin. The host cells became infected by the growth of infection threads into cells recently derived from the nodule meristem and the subsequent endocytotic release of rhizobia from unwalled membrane-bound regions of the infection thread. The host plasma membrane adjacent to the unwalled regions of infection thread gave rise to the peribacteroid membrane which surrounded the released bacteria. Thus, nodule development and the basic tissue arrangement of the arctic nodules was similar to that of cylindrically-shaped nodules formed on temperate species of legumes.
The arctic legume nodules are unique in having large numbers of lipid droplets present in the cytoplasm of the nodule cortex and uninfected cells of the central active region. Newly infected cells also have lipid droplets. More developed infected cells lack lipid droplets but often contain amyloplasts. Mature differentiated bacteria were spherically-shaped and contained electron-dense inclusions. Electron-dense material was also present in vesicles formed from dilated endoplasmic reticulum and in the peribacteroid space. The lipid droplets present in the host cytoplasm of the nodule cortex and uninfected cells of the central tissue may be storage products which are used to support nitrogen-fixation in nodules growing under cool temperatures of this harsh environment.     

Cellular bodies in developing chlemydospores of Thielaviopsis basicola1,2

The development of chlamydospores of Thielaviopsis basicola from hyphal cells involves the thickening and pigmentation of the cell wall. Electron microscope studies showed that membrane-bound cellular bodies appearing in the cytoplasm of differentiating cells developed from dilated cisternae in the endoplasmic reticulum. Within the membrane-bound bodies, vesicles of up to 0.2-micronm diameter were observed which contained electron-dense particles. Vesicles resembling those seen in the cellular body were also present in the cytoplasm close to the plasmalemma. In newly formed chlamydospore cells where wall thickening was complete, the cellular bodies showed loss of internal organization, and most of the vesicles disappeared, leaving a structure resembling a vacuole. The cellular bodies were not present in undifferentiated hyphae or in mature chlamydospores.     

Plasmalemmasomes in cotyledon leaves of germinating Vigna radiata L. (mung beans)

Abstract. Storage parenchyma, vascular parenchyma and phloem companion cells are found adjacent to sieve tubes in the vascular bundles of cotyledon leaves of mung bean ( Vigna radiata L.) seedlings. The paramural bodies of storage parenchyma cells are characterized by flask shaped invaginations of the plasmalemma whereas the plasmalemmasomes of the adjacent vascular parenchyma and companion cells consist of numerous finger-like evaginations which are not enclosed in plasmalemma pockets. Phloem associated transfer cells are not present and it is suggested that the fine tubular plasmalemmasomes may act as the interface between apoplast and symplast in the transport of rapidly mobilized reserves during germination. Tubular structures observed within the protoplasts of storage cells close to vascular tissue were also observed in vascular parenchyma and companion cells between the plasmalemmae and cell walls.     

Bacterium release into host cells of nitrogen-fixing soybean nodules: the symbiosome membrane comes from three sources

The release process of bacteria into the cytoplasm of soybean nodule cells has been studied, and three functional zones of the infection thread are delineated. Zone 1 is found over the greatest length of very long infection threads. Zone 2 is a short region where membrane mobilization by exocytosis of endoplasmic reticulum (ER) into the infection-thread membrane takes place; the result is that much new membrane and wall degradation enzymes can be provided. In addition, de novo membrane formation takes place inside the infection thread in apposition to the bacterial outer membrane. Zone 3 is the endocytic region where both bacteria and infection-thread wall degradation vesicles are released into the host cytoplasm and constitute a second product of endocytosis at the infection thread tip. Evidence is presented indicating that the symbiosome membrane, even at its time of origin, is composed of membrane from three sources: the host infection-thread membrane, ER, and de novo synthesis; the membrane formation that is so large for these purposes is probably carried out both from the ER directly and also through the Golgi-apparatus synthesis. Evidence is also given that the bacteria have lost their exopolysaccharide coatings before release into symbiosomes.     

Diversity and structure of bacterial communities in Arctic versus Antarctic pack ice

A comprehensive assessment of bacterial diversity and community composition in arctic and antarctic pack ice was conducted through cultivation and cultivation-independent molecular techniques. We sequenced 16S rRNA genes from 115 and 87 pure cultures of bacteria isolated from arctic and antarctic pack ice, respectively. Most of the 33 arctic phylotypes were >97% identical to previously described antarctic species or to our own antarctic isolates. At both poles, the alpha- and gamma-proteobacteria and the Cytophaga-Flavobacterium group were the dominant taxonomic bacterial groups identified by cultivation as well as by molecular methods. The analysis of 16S rRNA gene clone libraries from multiple arctic and antarctic pack ice samples revealed a high incidence of closely overlapping 16S rRNA gene clone and isolate sequences. Simultaneous analysis of environmental samples with fluorescence in situ hybridization (FISH) showed that approximately 95% of 4',6'-diamidino-2-phenylindole (DAPI)-stained cells hybridized with the general bacterial probe EUB338. More than 90% of those were further assignable. Approximately 50 and 36% were identified as gamma-proteobacteria in arctic and antarctic samples,respectively. Approximately 25% were identified as alpha-proteobacteria, and 25% were identified as belonging to the Cytophaga-Flavobacterium group. For the quantification of specific members of the sea ice community, new oligonucleotide probes were developed which target the genera Octadecabacter, Glaciecola, Psychrobacter, Marinobacter, Shewanella, and Polaribacter: High FISH detection rates of these groups as well as high viable counts corroborated the overlap of clone and isolate sequences. A terrestrial influence on the arctic pack ice community was suggested by the presence of limnic phylotypes.     

红豆草根瘤侵入线的超微结构研究

用透射电镜对红豆草根瘤侵入线的超微结构进行了观察研究.结果表明,(1)红豆草根瘤侵入线由胞间隙和胞间层细胞壁内陷形成,它们的体积较小,多为管状,基质丰富,含菌很少,常有分叉和1个以上的基质区,而且不同基质区的电子密度、细菌数量和侵入线壁厚度都不相同.(2)红豆草根瘤的侵入线十分丰富,它们不仅大量存在于根瘤分生细胞和幼龄侵染细胞中,也经常出现在发育成熟的侵染细胞内.(3)红豆草根瘤中有一种近似圆形的特殊结构,表面由一层膜包围,其内电子密度较低且无固定结构,且只位于侵染细胞的细胞质中,常在侵入线附近,从不出现在侵染细胞的液泡内和非侵染细胞里面.     

Structure of nitrogen-fixing nodules formed by Rhizobium on roots of Parasponia andersonii Planch.

The structure of nitrogen-fixing nodules produced by Rhizobium infection of the non-legume Parasponia andersonii was examined by light and electron (both SEM and TEM) microscopy. Comparisons were made with the nodules previously described on P. rugosa. Like the nodules on different non-legumes formed by other types of endophytes, the Rhizobium nodules on Parasponia resembled modified roots by having a central vascular bundle surrounded by an endophyte-infected zone. The intimate association between the Rhizobium and the host nodule cell was compared with the Rhizobium association found in legumes. The rhizobia were not released from the infection thread as happens in the legume. The infection thread, which propagates the Rhizobium infection to new cells, was transformed within a nodule cell from a darkly stained (light microscopy) or very electron-dense (TEM) structure to a number of thread types. The walls of the threads varied greatly in thickness and often the thread structures were without rigid walls and were only enclosed by a plasma membrane. If the rhizobia are transformed into bacteroids, as in the legumes, it would have to occur when the threads had reached their mature size, when bacterial division had ceased. Nitrogen fixation was considered to occur in all thread types.     

Further characterization of the chondroprogenitor zone in mandibular condyles of suckling mice. An ultrastructural and cytochemical study

In the neonatal mouse the mandibular condyle serves as an important growth center for the developing mandible. The youngest cells in this organ are the chondroprogenitor cells that are the source for new differentiating chondroblasts. The present study provides new data concerning the fine structure and cytochemical characteristics of the cartilage precursor cells as seen in suckling mice. The condylar chondroprogenitor cells normally reveal a mesenchyme-like appearance with multiple, elongated cell processes that enable close contact between neighboring cells. These cells also exhibit a variety of pinocytotic vesicles, coated pits and appear to be actively involved in the internalization of a fluid-phase marker horseradish peroxidase. Further, the progenitor cells were found to contain trimetaphosphatase reaction products within lysosomal bodies and alkaline phosphatase reactivity along their plasma membrane. Precipitates of calcium complexes in the form of calcium pyroantimonate could be demonstrated in association with the plasmalemma of the cells as well as with the extracellular collagen fibrils. Matrix granules, representing cartilage proteoglycans, became a distinct feature following staining with ruthenium red and were found to be in close contact with the extracellular collagen fibrils and with the plasmalemma. Hence, in addition to their active role in cell proliferation, the progenitor cells are also involved in the synthesis and secretion of major extracellular macromolecules such as collagen and proteoglycans.     

Isolation and characterization of mutants of Rhizobium leguminosarum bv. viciae 248 with altered lipopolysaccharides: possible role of surface charge or hydrophobicity in bacterial release from the infection thread

Effects of alterations in lipopolysaccharide (LPS) structure of Rhizobium leguminosarum bv. viciae on effective symbiosis and on a number of cell surface characteristics were studied. Tn5 mutants with altered LPSs were screened for their inability to bind monoclonal antibody 3, one of three monoclonal antibodies to the tentative O-antigenic part of the wild-type LPS of strain 248. Ten class I LPS mutants completely lacked the O-antigen-containing LPS species. The class II LPS mutant had a severely diminished amount of an antigenically altered O-antigen-containing LPS. The class III LPS mutant had normal amounts of an altered, O-antigen-containing LPS. Class I and II mutants, but not the class III mutant, showed abnormal nodule development (i.e., blocked in the stage of bacterial release from the infection thread) resulting in nodules in which very few, at the most, plant cells contained bacteroids and which were unable to fix nitrogen. Class I and II mutants were nonmotile and were more sensitive to hydrophobic compounds than the parent strain. The most striking difference between the symbiotically defective class I and II LPS mutants on one hand and the wild-type strain and the class III mutant on the other hand was that the class I and II mutants have a more hydrophobic cell surface and a higher electrophoretic mobility. A role for an O-antigen-containing LPS in bacterial release from the infection thread, through its effects on general physicochemical cell surface characteristics, is proposed.     

Plant Cell Wall Remodelling in the Rhizobium–Legume Symbiosis

Colonization of host cells by rhizobium bacteria involves the progressive remodelling of the plant–microbial interface. Following induction of nodulation genes by legume-derived flavonoid signals, rhizobium secretes Nod-factors (lipochitin oligosaccharides) that cause root hair deformations by perturbing the growth of the plant cell wall. The infection thread arises as a tubular ingrowth bounded by plant cell wall. This serves as a conduit for colonizing bacterial cells that grow and divide in its lumen. The transcellular orientation of thread growth is controlled by the cytoskeleton and is coupled to cell cycle reactivation and cell division processes. In response to rhizobium infection, host cells synthesize several new components (early nodulins) that modify the properties of the cell wall and extracellular matrix. Root nodule extensins are a legume-specific family of hydroxyproline-rich glycoproteins targeted into the lumen of the infection thread. They have alternating extensin and arabinogalactan (AGP) glycosylation motifs. The structural characteristics of these glycoproteins suggest that they may serve to regulate fluid-to-solid transitions in the extracellular matrix. Extensibility of the infection thread is apparently controlled by peroxide-driven protein cross-linking and perhaps also by modification of the pectic matrix. Endocytosis of rhizobia from unwalled infection droplets into the host cell cytoplasm depends on physical contact between glycocalyx components of the plant and bacterial membrane surfaces. As endosymbionts, bacteroids remain enclosed within a plant-derived membrane that is topologically equivalent to the plasma membrane. This membrane acquires specialist functions that regulate metabolite exchanges between bacterial cells and the host cytoplasm. Ultimately, however, the fate of the symbiosome is to become a lysosome, causing the eventual senescence of the symbiotic interaction.     

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.     

Immunogold localisation of endogenous immunoglobulin-G in ultrathin frozen sections of the human placenta

Summary Endogenous immunoglobulin-G was localised in ultrathin frozen sections of human term placenta by use of an indirect immuno electron-histochemical methodology. Immunoreactivity of endogenous IgG to rabbit anti-human immunoglobulin-G antibody was visualised by use of protein-A — colloidal gold complex. Gold marked the syncytiotrophoblast in both coated and uncoated regions of the apical plasmalemma, in vesicles and multivesicular bodies, and in vesicles near the basal plasmalemma. Immunoreactivity was also seen in the interstitial space between the trophoblast and the fetal endothelial layer as well as in various types of vesicles within the endothelial cells. No immunoreactivity was seen in the intercellular clefts of the endothelium. The pattern of localisation observed is consistent with receptor-mediated uptake of immunoglobulin-G into the syncytiotrophoblast of the human placenta followed by release into the interstitial space and then vesciular transport through the endothelium.     

Comparative cytopathology of Crinivirus infections in different plant hosts

We used transmission electron microscopy to compare the cytopathology induced in plants by five criniviruses (genus Crinivirus; Lettuce infectious yellows virus (LIYV), Cucurbit yellow stunting disorder virus (CYSDV), Tomato infectious chlorosis virus (TICV), Tomato chlorosis virus (ToCV) and Beet pseudo‐yellows virus (BPYV) (Hartono et al., 2003)). We also compared the patterns of infection for plants and mesophyll protoplasts infected by LIYV and Beet yellows virus (BYV), type members of genera Crinivirus and Closterovirus, respectively. The main cytopathological effects induced in plants by criniviruses were common in young leaves and included alterations of the chloroplasts and the presence of BYV‐type inclusion bodies in companion cells. Virus‐like particles were present in sieve tubes and vascular parenchyma cells as scattered particles, or in companion cells as large masses forming cross‐banded inclusions. Depending on the virus and the plant, it was possible to find virions or virus‐like particles out of the phloem cells, but only in cells of the bundle sheath. Virion‐like particles were never found outside of the vascular tissue. Accumulation of electron‐dense material at the plasmalemma was common for criniviruses, but only LIYV infections produced characteristic conical electron‐dense plasmalemma deposits (PDs). The LIYV‐induced PDs have a crystalline‐like structure and were found at the internal side of plasmalemma.     

Invaginations in plant cell protoplasts containing mycoplasma-like bodies (MLO)

MLO containing invaginations were found in protoplasts of phloem parenchyma cells in symptomless young leaves ofRibes houghtonianum Jancz. infected with a yellows disease. The invaginations originate between the cell wall and plasmalemma, usually at plasmodesmata, and change apparently into superficial vesicles in the protoplast; they are entirely or partially limited by host plasmalemma. The formations mentioned occur in parenchyma cells which contain normal organelles. Sometimes they are divided by a smooth membrane system enclosing MLO. Besides MLO the invaginations contain in some cases slimy fibrils resembling the P-protein in sieve tubes. The MLO bodies seen in invaginations have usually a diameter of 50–250 nm and their plasmalemma (unit membrane) is identical with the plasmalemma of MLO bodies occurring in sieve tubes. However, only few MLO bodies in invaginations are electron dense, so that they resemble naturally degenerated forms of MLO. Similar MLO containing invaginations were formerly described from some leafhoppers transmitting MLO.     

Zostera capensis setchell: III. Some aspects of wall ingrowth development in leaf blade epidermal cells

Summary The development of wall ingrowths in leaf blade epidermal cells of the marine angiospermZostera capensis was studied by electron microscopy. Prior to the appearance of ingrowths long profiles of endoplasmic reticulum cisternae become arranged peripherally closely following the contours of the walls. The plasmalemma assumes a wavy appearance and in regions where wall ingrowths first start forming (i.e., along the radial, inner tangential and transverse walls) the plasmalemma becomes separated from the walls by an undulating extracytoplasmic space. Small, irregular projections of secondary wall material make their appearance here. Paramural bodies, dictyosomes, endoplasmic reticulum (ER) and possibly also microtubules seem to be closely associated with the initiation and subsequent development of wall projections. As the cells mature, new ingrowths arise in a centrifugal direction along the radial and transverse walls. When wall ingrowths reach a certain stage of their development, mitochondria become strongly polarized towards them and become closely associated with the plasmalemma which ensheaths the ingrowths. There is often also a close association between ER cisternae and the involuted plasmalemma of the wall projections. Initially ingrowths are slender, curved structures, but become more complex as the cells mature. Ingrowths are most extensively developed along the inner tangential and transverse walls. As epidermal cells age there is a loss of wall material from the ingrowths. The probable significance of the formation of wall ingrowths in the epidermal cells is also discussed.     

Diversity and Structure of Bacterial Communities in Arctic versus Antarctic Pack Ice

A comprehensive assessment of bacterial diversity and community composition in arctic and antarctic pack ice was conducted through cultivation and cultivation-independent molecular techniques. We sequenced 16S rRNA genes from 115 and 87 pure cultures of bacteria isolated from arctic and antarctic pack ice, respectively. Most of the 33 arctic phylotypes were >97% identical to previously described antarctic species or to our own antarctic isolates. At both poles, the α- and γ-proteobacteria and the Cytophaga-Flavobacterium group were the dominant taxonomic bacterial groups identified by cultivation as well as by molecular methods. The analysis of 16S rRNA gene clone libraries from multiple arctic and antarctic pack ice samples revealed a high incidence of closely overlapping 16S rRNA gene clone and isolate sequences. Simultaneous analysis of environmental samples with fluorescence in situ hybridization (FISH) showed that ~95% of 4′,6′-diamidino-2-phenylindole (DAPI)-stained cells hybridized with the general bacterial probe EUB338. More than 90% of those were further assignable. Approximately 50 and 36% were identified as γ-proteobacteria in arctic and antarctic samples,respectively. Approximately 25% were identified as α-proteobacteria, and 25% were identified as belonging to the Cytophaga-Flavobacterium group. For the quantification of specific members of the sea ice community, new oligonucleotide probes were developed which target the genera Octadecabacter, Glaciecola, Psychrobacter, Marinobacter, Shewanella, and Polaribacter. High FISH detection rates of these groups as well as high viable counts corroborated the overlap of clone and isolate sequences. A terrestrial influence on the arctic pack ice community was suggested by the presence of limnic phylotypes.     

Mechanische Verletzung des Plasmalemmas als mögliche Voraussetzunlg Für die Virsinfektion von Pflanzen

Mechanical injury of the plasmalemma As a possible pre requisite for virus infection of plants
A basic requirement of the infection in case of mechanical inoculation f viruses could be that the plasmalemma of cells is to be injured, for a clearance between cell wall and plasmalemma at the time of inoculation in cells, which are suitable for primary infection prevented the infection.
By means of the hypertonic concentration of 0.7 mol/l of the plasmolytica ethylenglycol, sucrose, glucose, sorbitol and mannitol, which permeate with different speeds, and by modifications of the mannitol treatment, a withdrawal of the plasmalemma to varied distances from the cell wall was induced in cell of the upper side of leaf disk from Nicotiana glutinosa and N tabacum "samsun" This could be observed microscopically in the leaf disks after embedding in liquid paraffin
Treated leaf disk were inoculated with tobacco mosaic virus and incubated floating on tap water
The infection rate, determined by the number of local lesions in case of leaf disks from Nicotiana glutinosa and by the extractable infectivity in case of "Samsun"proved to be dependent on the degree of withdrawal of the plasmalemma from the wall of cell of the upper disk side A strong withdrawal by rounding of the protoplasts in all or almost all cells, caused by the non permeating mannitol or sorbitol, did hardly permit infection     

Exocytosis of cytolytic T-lymphocytes studied by cryofracture and stereophotogrammetry

Cryofracture, stereophotogrammetry and three-dimensional reconstruction were used to study the membranes of cytolytic T lymphocytes (CTL) and target cells (TC) conjugates. Circular bulges free of intramembrane granules and ring-shaped structures, analogous to the sites of vacuole release in secretory cells, appear on the surface of the lymphocyte plasmalemma after 30 to 60 minutes of interaction with TC. Polymorphic vacuoles 70 to 140 nm in diameter are observable in the contact space between lymphocytes and TC. Part of the vacuoles are found on the surface or near the CTL plasmalemma. The data confirm an assumption about the secretory mechanism of the cytolytic effect of T killers.     

Occurrence of Coated Vesicles and Alterations in Plasmalemma in Tomato Leaf Cells Infected by Phytophthora infestans Mont. (de Bary) After Treatment with Fosetyl-Al

Treatment of tomato ( Lycopersicum esculentum Mill. cv. Bonny Best) leaves with the systemic fungicide Fosetyl-Al (Tris-o-ethyl phosphonate aluminium) induced the formation of haustorial encasements or cell wall deposits in the leaf cells infected by Phytophthora infestans Mont (de Bary). Numerous coated vesicles and extremely invaginated, saclike plasmalemma were found in close spatial association with wall deposits in haustorium infected cells. Wall deposits in non-infected cells bordering degenerated, infected, cells were also accompanied by the presence of coated vesicles. In leaf tissues without treatment with Fosetyl-Al, no substantial change in the plasmalemma of infected cells was observed and coated vesicles were found only in close contact with large, smooth-surfaced vesicles. No coated vesicles were found associated with wall deposits in non-infected, neighbouring cells. The results are discussed in connection with possible functions of both coated vesicles and plasmalemma.     

A comparative light microscopic study of two types of root nodule bacteria dispersal into the bacteroid zone cells

Root nodule bacterial dispersal into the cells and formation of bacteroid zone cells of root nodules have been observed in several species of Leguminosae. Two different types of bacterial dispersal were recognized comparable to those briefly mentioned by a few authors. Cell division type: From the very beginning of nodule development there exist two different kinds of cell in the meristematic region. In bacteria-containing cells the bacteria are distributed into two new cells with host cell division, the bacteria being located outside the spindle region during mitosis. In those cells not containing bacteria, amyloplasts develop in the cytoplasm. These cells also divide mitotically, increasing the numbers of amyloplast-containing cells. These two different cell populations compose the bacteroid zone. This type was seen inSophora flavescens andCytisus scoparius. Infection thread type: In the transitional zone from the nodule meristem to the bacteroid zone, some cells are penetrated by infection threads and others are not. Infected cells become bacteroid-filled cells, no mitosis taking place after penetration of the infection thread. Uninfected cells become amyloplast-containing cells, increasing their numbers by mitosis. These two cell populations compose the bacteroid zone. This type was seen inVicia sativa, V. faba, Trifolium repens andAstragalus sinicus.