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The article considers the possibility of using composite binders and magnetite as components of concrete with radiation-proof properties. The use of the developed concrete is possible not only when it is necessary to build nuclear power plants, but also to create bunkers or anti-radiation shelters. A special feature of concretes used for the protection and design of nuclear reactor cranes is their properties, which they must have. These properties include: low thermal conductivity, increased density, high temperature resistance, reduced values of the coefficient of thermal expansion, shrinkage and creep. Technogenic raw materials for the production of very heavy concrete are studied, the main physical and mechanical characteristics, the requirements that need to be considered in the selection of raw mix composition for protective concrete are analyzed. The paper presents a comparison of physical and mechanical characteristics, the advantages and disadvantages of introducing a binder of various types: cement, cement with a superlasticizer and a binder of low water consumption. It was found that the use of a low-water-consumption binder increases the physical and mechanical characteristics while reducing the consumption of cement in the raw material mix compared to traditional heavy concrete with cement.

The possibility of reuse of heavy residues (oily sludge) of low-sulfur, highly paraffinic Mangyshlak oils as a basis for fuel with improved environmental characteristics for engines to marine, river and railway transport, gas turbine and boiler plants, steam boilers and industrial furnaces was shown. A variant of the joint application of the methods of nuclear magnetic resonance, laser confocal microscopy and rheology for study of micro- and mesoscopic structure and some physicochemical properties of crude oil products has been developed. It has been shown that preliminary heating to 90 ° C leads to disruption of the structure and hydrogen bonds between oil associates and complexes, increasing sample homogeneity due to precipitation of solid impurities, partial removal of water content, air bubbles and dissolved gases. The addition of medium distillate diesel fractions to preliminary heated oil residues will make it possible to obtain a higher quality version of the fuel with a reduced resinous and asphaltene substances, lower pour point, good energy content and low sulfur content. Thus, valuable energy-containing raw materials can be reused. It should also be noted that the reuse of accumulated oil waste will reduce the harmful effects of landfills, will preserve the natural landscape, and will cut the cost of extracting natural resources.

One of the effective ways to reduce the material consumption of structures, to save all types of resources due to this, is the transition to porous constructional materials instead of traditional dense materials. In this regard, non-autoclaved gas concrete is of great interest. This material has a high manufacturability and has a good potential for improving the strength properties due to the replacement of traditional portland cement by special composite binders. Available publications confirm the effectiveness and prospects of this direction. An important disadvantage of such works is the fact that the binder indicators and the final cellular concrete characteristics are considered mainly independently. In our opinion, it is more correct to consider at least two structure-forming processes proceeding in parallel and sequentially at different scale levels. Micro level is a stone structure formation based on the composite binder; macro-level is a gas porization of cellular mass concrete. These processes have a great mutual influence on each other, and therefore this article attempts to observe the gassing products effect on the stone hardening based on composite binders, as well as the composite binder makeup on the viscosity change of the molding compound, as an important condition for the formation of high-quality less defective pore structure of cellular concrete.

Intrusive growth is a type of growth in which a cell exceeds the growth rate of its neighbours and intrudes between them, reaching a much greater length. This process provides plant fibres with their exceptional length. Fibres are the most abundant cell type in the mechanical tissues of plants. At the same time, the plant fibres are of fundamental importance for the production of textiles, paper, biocomposites, etc. Here we describe a mutant of flax (reduced fibre 1, rdf) in which intrusive growth of fibres is impaired in both phloem and xylem. In addition to the intrinsic differences in fibre length, the mutant is characterized by a constitutive gravitropic response, mechanical aberrations at the macro- and nanolevels, disruption of the cambium and uneven transition of xylem cells to secondary cell wall formation. Gelatinous cell walls in both phloem and xylem of mutant plants have disturbed structure and reduced elasticity. The existence of this mutant-control pair offers both prospects for finding the molecular players involved in triggering intrusive growth, cell wall thickening and for understanding the principles of plant mechanical tissue functioning.

In the fibers of many plant species after the formation of secondary cell walls, cellulose-enriched cell wall layers (often named G-layers or tertiary cell walls) are deposited which are important in many physiological situations. Flax (Linum usitatissimum L.) phloem fibers constitutively develop tertiary cell walls during normal plant growth. During the gravitropic response after plant inclination, the deposition of a cellulose-enriched cell wall layer is induced in xylem fibers on one side of the stem, providing a system similar to that of tension wood in angiosperm trees. Atomic force microscopy (AFM), immunochemistry, and transcriptomic analyses demonstrated that the G-layer induced in flax xylem fibers was similar to the constitutively formed tertiary cell wall of bast (phloem) fibers but different from the secondary cell wall. The tertiary cell walls, independent of tissue of origin and inducibility, were twice as stiff as the secondary cell walls. In the gravitropic response, the tertiary cell wall deposition rate in xylem was higher than that of the secondary cell wall. Rhamnogalacturonan I (RG-I) with galactan side chains was a prominent component in cellulose-rich layers of both phloem and xylem flax fibers. Transcriptomic events underlying G-layer deposition in phloem and xylem fibers had much in common. At the induction of tertiary cell wall deposition, several genes for rhamnosyltransferases of the GT106 family were activated in xylem samples. The same genes were expressed in the isolated phloem fibers depositing the tertiary cell wall. The comparison of transcriptomes in fibers with both inducible and constitutive tertiary cell wall deposition and xylem tissues that formed the secondary cell walls is an effective system that revealed important molecular players involved in the formation of cellulose-enriched cell walls.

There are “molecular switchers” that transform peaceful coexistence of plants with phytopathogenic pectobacteria to symptomatic infection. These switchers seem to be perspective “targets” for plant protection approaches.

The plant cell wall is a complex structure consisting of a polysaccharide network. The rearrangements of the cell wall during the various physiological reactions of plants, however, are still not fully characterized. Profound changes in cell wall organization are detected by microscopy in the phloem fibers of flax (Linum usitatissimum) during the restoration of the vertical position of the inclined stems. To characterize the underlying biochemical and structural changes in the major cell wall polysaccharides, we compared the fiber cell walls of non-inclined and gravistimulated plants by focusing mainly on differences in non-cellulosic polysaccharides and the fine cellulose structure. Biochemical analysis revealed a slight increase in the content of pectins in the fiber cell walls of gravistimulated plants as well as an increase in accessibility for labeling non-cellulosic polysaccharides. The presence of galactosylated xyloglucan in the gelatinous cell wall layer of flax fibers was demonstrated, and its labeling was more pronounced in the gravistimulated plants. Using solid state NMR, an increase in the crystallinity of the cellulose in gravistimulated plants, along with a decrease in cellulose mobility, was demonstrated. Thus, gravistimulation may affect the rearrangement of the cell wall, which can enable restoration in a vertical position of the plant stem.

In the present study, we have monitored the process of systemic plant colonization by the plant pathogenic bacterium Pectobacterium atrosepticum (Pba) using RNA-Seq analysis in order to compare bacterial traits under in planta and in vitro conditions and to reveal potential players that participate in switching from stealth to brute force strategy of the pathogen. Two stages of tobacco plant colonization have been assayed: i) the initial one associated with visually symptomless spread of bacteria throughout the host body via primary xylem vessels where bacterial emboli were formed (stealth strategy), and ii) the advanced stage coupled with an extensive colonization of core parenchyma and manifestation of soft rot symptoms (brute force strategy). Plant-inducible genes in Pba and potential players switching the pathogen’s behavior were revealed. Genes from the cfa locus responsible for the production of coronafacic acid displayed the strongest induction in the asymptomatic zone relative to the symptomatic one and were shown experimentally to act as the true strategy “switchers” of Pba behavior in planta. Surprisingly, cfa genes appeared to be unnecessary for establishment of the asymptomatic stage of plant colonization but were required for the transition to soft-rot-associated symptomatic stage coupled with over-induction of jasmonate-mediated pathway in the plant.

Plants, although sessile organisms, are nonetheless able to move their body parts; for example, during root contraction of geophytes or in the gravitropic reaction by woody stems. One of the major mechanisms enabling these movements is the development of specialized structures that possess contractile properties. Quite unlike animal muscles, for which the action is driven by protein-protein interactions in the protoplasma, the action of plant 'muscles' is polysaccharide-based and located in the uniquely designed, highly cellulosic cell wall that is deposited specifically in fibers. This review describes the development of such cell walls as a widespread phenomenon in the plant kingdom, gives reasons why it should be considered as a tertiary cell wall, and discusses the mechanism of action of the 'muscles'. The origin of the contractile properties lies in the tension of the axially oriented cellulose microfibrils due to entrapment of rhamnogalacturonan-I aggregates that limits the lateral interaction of microfibrils. Long side chains of the nascent rhamnogalacturonan-I are trimmed off during cell wall maturation leading to tension development. Similarities in the tertiary cell wall design in fibers of different plant origin indicate that the basic principles of tension creation may be universal in various ecophysiological situations.

Our study is the first to consider the changes in the entire set of matrix plant cell wall (PCW) polysaccharides in the course of a plant infectious disease. We compared the molecular weight distribution, monosaccharide content, and the epitope distribution of pectic compounds and cross-linking glycans in non-infected potato plants and plants infected with Pectobacterium atrosepticum at the initial and advanced stages of plant colonization by the pathogen. To predict the gene products involved in the modification of the PCW polysaccharide skeleton during the infection, the expression profiles of potato and P. atrosepticum PCW-related genes were analyzed by RNA-Seq along with phylogenetic analysis. The assemblage of P. atrosepticum biofilm-like structures—the bacterial emboli—and the accumulation of specific fragments of pectic compounds that prime the formation of these structures were demonstrated within potato plants (a natural host of P. atrosepticum). Collenchyma was shown to be the most “vulnerable” tissue to P. atrosepticum among the potato stem tissues. The infection caused by the representative of the Soft Rot Pectobacteriaceae was shown to affect not only pectic compounds but also cross-linking glycans, the content of the latter was increased in the infected plants compared to the non-infected ones.

Chromatography and histochemical analysis of soluble phenolic compounds demonstrated their higher content in the roots of cycloheximide-treated pea plants. These substances accumulated together with lignin in the endodermis and xylem cells of conducting bundles. This finding confirms the antipathogenic cycloheximide effect based on the previous results of proteome analysis.

The morphogenesis of macromycetes is a complex multilevel process resulting in a set of molecular-genetic, physiological-biochemical, and morphological-ultrastructural changes in the cells. When the xylotrophic basidiomycetes Lentinus edodes, Grifola frondosa, and Ganoderma lucidum were grown on wood waste as the substrate, the ultrastructural morphology of the mycelial hyphal cell walls differed considerably between mycelium and morphostructures. As the macromycetes passed from vegetative to generative development, the expression of the tyr1, tyr2, chi1, chi2, exg1, exg2, and exg3 genes was activated. These genes encode enzymes such as tyrosinase, chitinase, and glucanase, which play essential roles in cell wall growth and morphogenesis.

Cell wall thickening and development of secondary cell walls was a major step in plant terrestrialization that provided the mechanical support, effective functioning of water-conducting elements and fortification of the surface tissues. Despite its importance, the diversity, emergence and evolution of secondary cell walls in early land plants have been characterized quite poorly. Secondary cell walls can be present in different cell types with fibers being among the major ones. The necessity for mechanical support upon increasing plant height is widely recognized; however, identification of fibers in land plants of early taxa is quite limited. In an effort to partially fill this gap, we studied the fibers and the composition of cell walls in stems of the sporophyte of the living fossil Psilotum nudum. Various types of light microscopy, combined with partial tissue maceration demonstrated that this perennial, rootless, fern-like vascular plant, has abundant fibers located in the middle cortex. Extensive immunodetection of cell wall polymers together with various staining and monosaccharide analysis of cell wall constituents revealed that in P. nudum, the secondary cell wall of its cortical fibers is distinct from that of its tracheids. Primary cell walls of all tissues in P. nudum shoots are based on mannan, which is also common in other extant early land plants. Besides, the primary cell wall contains epitope for LM15 specific for xyloglucan and JIM7 that binds methylesterified homogalacturonans, two polymers common in the primary cell walls of higher plants. Xylan and lignin were detected as the major polymers in the secondary cell walls of P. nudum tracheids. However, the secondary cell wall in its cortical fibers is quite similar to their primary cell walls, i.e., enriched in mannan. The innermost secondary cell wall layer of its fibers but not its tracheids has epitope to bind the LM15, LM6, and LM5 antibodies recognizing, respectively, xyloglucan, arabinan and galactan. Together, our data provide the first description of a mannan-based cell wall in sclerenchyma fibers, and demonstrate in detail that the composition and structure of secondary cell wall in early land plants are not uniform in different tissues.

The results of the selection of compositions of stowing mixes on the basis of technogenic raw materials KMA region, set mikrostukturnye particularly developed composites, illustrates the activation process Rolv hydration of granulated blast slag and tailings.

We show here, to our knowledge for the first time, that the brown mycelial mat of the xylotrophic shiitake medicinal mushroom, Lentinus edodes, not only performs a protective function owing to significant changes in the ultrastructure (thickening of the cell wall, increased density, and pigmentation of the fungal hyphae) but also is a metabolically active stage in the development of the mushroom. The cells of this morphological structure exhibit repeated activation of expression of the genes lcc4, tir, exp1, chi, and exg1, coding for laccase, tyrosinase, a specific transcription factor, chitinase, and glucanase, which are required for fungal growth and morphogenesis. This study revealed the maximum activity of functionally important proteins with phenol oxidase and lectin activities, and the emergence of additional laccases, tyrosinases, and lectins, which are typical of only this stage of morphogenesis and have a regulatory function in the development and formation of fruiting bodies.

Activation of expression of the lcc4 and tir genes encoding laccase and tyrosinase was observed during transition of a xylotrophic basidiomycete Lentinus edodes from the vegetative to the generative growth stages. This was especially pronounced in the brown mycelial mat (the stage preceding formation of the fruiting bodies). Development of this structure was shown to be associated with a sharp increase of laccase and tyrosinase activities, as well as with rearrangements in the phenol oxidase complex. Formation of the tissues with thickened cell walls was associated with enhanced expression of the chi and exg1 genes encoding chitinase and glucanase, respectively. Exogenous treatment of the vegetative mycelium with laccase preparation from the brown mycelial mat promoted formation of this morphological structure. Activation of the lcc4, tir, chi, and exg1 genes may be used as a marker of readiness to fruition in xylotrophic fungi.

In the present study, we identified exopolysaccharides of the harmful phytopathogenic bacterium Pectobacterium atrosepticum SCRI1043 and characterized the molecular structure of these polymers. The synthesis of the target polysaccharides was shown to be induced under starvation conditions. Moreover, intensive accumulation of exopolysaccharides occurred during the colonization by bacteria of the xylem vessels of infected plants, where microorganisms formed specific 3D "multicellular" structures-bacterial emboli. Thus, the identified polymers are likely to be involved in the adaptation and virulence of bacteria of Pectobacterium genus.

Background and aims Plant cell enlargement is unambiguously coupled to changes in cell wall architecture, and as such various studies have examined the modification of the proportions and structures of glucuronoarabinoxylan and mixed-linkage glucan in the course of cell elongation in grasses. However, there is still no clear understanding of the mutual arrangement of these matrix polymers with cellulose microfibrils and of the modification of this architecture during cell growth. This study aimed to determine the correspondence between the fine structure of grass cell walls and the course of the elongation process in roots of maize (Zea mays). Methods Enzymatic hydrolysis followed by biochemical analysis of derivatives was coupled with immunohistochemical detection of cell wall epitopes at different stages of cell development in a series of maize root zones. Key results Two xylan-directed antibodies (LM11 and ABX) have distinct patterns of primary cell wall labelling in cross-sections of growing maize roots. The LM11 epitopes were masked by mixed-linkage glucan and were revealed only after lichenase treatment. They could be removed from the section by xylanase treatment. Accessibility of ABX epitopes was not affected by the lichenase treatment. Xylanase treatment released only part of the cell wall glucuronoarabinoxylan and produced two types of products: high-substituted (released in polymeric form) and low-substituted (released as low-molecular-mass fragments). The amount of the latter was highly correlated with the amount of mixed-linkage glucan. Conclusions Three domains of glucuronoarabinoxylan were determined: one separating cellulose microfibrils, one interacting with them and a middle domain between the two, which links them. The middle domain is masked by the mixed-linkage glucan. A model is proposed in which the mixed-linkage glucan serves as a gel-like filler of the space between the separating domain of the glucuronoarabinoxylan and the cellulose microfibrils. Space for glucan is provided along the middle domain, the proportion of which increases during cell elongation.

The adaptive reactions of plant pathogenic bacterium Pectobacterium atrosepticum SCRI1043 under starvation conditions were studied. The main emphasis was given to the peculiarities of stress responses depending on the bacterial population densities. When bacteria were subjected to starvation at high population densities (10(7)-10(9) CFU ml(-1)), their adaptive reactions conformed to the conventional conception of bacterial adaptation related to autolysis of part of the population, specific modification of cell ultrastructure, activation of expression of stress responsive genes and acquiring cross protection against other stress factors. In contrast, at low initial population densities (10(3)-10(5) CFU ml(-1)), as described in our recent work, the cell density increased due to multiple cell division despite the absence of exogenous growth substrate. Here we present data that demonstrate that such unconventional behavior is part of a stress response, which provides increased stress tolerance while retaining virulence. Cell morphology and gene expression in high- and low-cell-density starving Pba cultures were compared. Our investigation demonstrates the existence of alternative adaptive strategies enabling pathogenic bacteria to cope with a variety of stress factors, including starvation, especially necessary when residing outside of their host.

This is the first study to demonstrate that the medicinal basidiomycete Lentinula edodes can reduce gold (III) ions from hydrogen tetrachloaurate (chloroauric acid) H[AuCl4] to the elementary state with the formation of spherical nanoparticles (nanospheres). When a culture was grown under submerged conditions in the presence of chloroauric acid, the appearance of an intense purple-red color of L. edodes filamentous hyphae was recorded, which indicates that gold ions were reduced to gold nanoparticles. Using transmission electron microscopy and X-ray fluorescence, we observed accumulation of colloidal gold by the fungal mycelium in the form of electron-dense nanospheres of 5 to 50 nm in diameter on the surface and inside fungal cells.

Representatives of Pectobacterium genus are some of the most harmful phytopathogens in the world. In the present study, we have elucidated novel aspects of plant-Pectobacterium atrosepticum interactions. This bacterium was recently demonstrated to form specific 'multicellular' structures - bacterial emboli in the xylem vessels of infected plants. In our work, we showed that the process of formation of these structures includes the pathogen-induced reactions of the plant. The colonisation of the plant by P. atrosepticum is coupled with the release of a pectic polysaccharide, rhamnogalacturonan I, into the vessel lumen from the plant cell wall. This polysaccharide gives rise to a gel that serves as a matrix for bacterial emboli. P. atrosepticum-caused infection involves an increase of reactive oxygen species (ROS) levels in the vessels, creating the conditions for the scission of polysaccharides and modification of plant cell wall composition. Both the release of rhamnogalacturonan I and the increase in ROS precede colonisation of the vessels by bacteria and occur only in the primary xylem vessels, the same as the subsequent formation of bacterial emboli. Since the appearance of rhamnogalacturonan I and increase in ROS levels do not hamper the bacterial cells and form a basis for the assembly of bacterial emboli, these reactions may be regarded as part of the susceptible response of the plant. Bacterial emboli thus represent the products of host-pathogen integration, since the formation of these structures requires the action of both partners.

Plant fibers represent specialized cells that perform a mechanical function. Their development includes the following phases, typical for the most plant cells: determination, extension growth, specialization, senescence, and death. Ultrastructural analysis of these cells has been carried out at the late phases of their development (senescence and dying off) using flax phloem fibers, a classical object for the analysis of sclerenchyma fiber formation. The results of the performed analysis show that flax fiber protoplasts remain viable until the end of a vegetation season. The ultrastructural analysis of flax phloem fibers has not revealed any typical apoptosis features. Gradual degradation of the cytoplasm starts during the active thickening of a secondary cell wall and occurs via the intensification of autolytic processes, causing a partial loss of cell content. The rupture of tonoplast is the final stage. The obtained data allow us to suppose that the protoplast dying off occurs during process of the senescence, and its program is similar to the cell death program realized in the xylem fibers of woody plants.

A sensitive electrochemical sensor based on a composite containing silver nanoparticles and a redox active thiacalixarene with catechol fragments in the substituents at the lower rim has been developed and used for dopamine detection. The electrochemical investigation of thiacalixarene in homogeneous solution and on the electrode interface showed the reversible character of the redox conversion of catechol fragments and its involvement in the chemical reduction of silver which resulted in formation of uniform nanoparticles of 4–6 nm in diameter. The use of such a material for electrode modification made it possible to record a high amplitude cathodic signal at −700 mV that was proportional to the dopamine concentration within 1 nM–1 µM. (limit of detection 0.5 nM).

The review sums data indicating that, in many plant fibers, the secondary cell wall contains so-called gelatinous layers of peculiar structure along with those of common (xylan) structure. Sometimes these gelatinous layers comprise the main bulk of the cell wall. Key characteristics of gelatinous cell wall are presented and compared with those of classic xylan-type cell wall. The process of gelatinous cell wall formation is considered in detail for flax phloem fibers; several characteristic features of this process were revealed: intense rearrangement of already deposited cell-wall layers, unusual dynamics of Golgi vesicles, the occurrence of the stage-specific polysaccharide with specific properties, high activity of β-galactosidase, and the presence of substantial amount of free galactose. Similarity and differences in the gelatinous cell wall formation in the fibers of various plant species are discussed.

Restoration of stem vertical position after plant inclination is a widely spread version of plant orientation in accordance with gravity vector direction. Gravitropic behaviour of flax plants involves the formation of curvature in stem region that has ceased elongation long in advance of stem inclination. The important participants of such behaviour are phloem fibres with constitutively formed tertiary cell wall (G-layer). We performed the large-scale transcriptome profiling of phloem fibres isolated from pulling and opposite sides of gravitropic curvature and compared with control plant fibres. Significant changes in transcript abundance take place for genes encoding proteins of several ion channels, transcription factors and other regulating elements. The largest number of upregulated genes belonged to the cell wall category; many of those were specifically upregulated in fibres of pulling stem side. The obtained data permit to suggest the mechanism of fibre participation in gravitropic reaction that involves the increase of turgor pressure and the rearrangements of cell wall structure in order to improve contractile properties, and to identify the regulatory elements that operate specifically in the fibres of the pulling stem side making gelatinous phloem fibres an important element of gravitropic response in herbaceous plants.

Reversible transition of the phytopathogenic gram-negative bacterium Erwinia carotovora, subsp. atroseptica, strain SCRI1043, to a dormant state was demonstrated; it was associated with a complete loss of cell ability to form colonies on the standard medium, i.e., with acquiring “non-culturability”. Entering of Erwinia cells to a nonculturable state occurred after long-term incubation (100–150 days) of the stationary-phase cell suspensions in either a fresh complete medium or in the carbon-free mineral medium or treatment with a chemical analogue of microbial anabiosis autoinducers (4 × 10−4 M of C12-alkylhydroxybenzene, AHB). However, confocal laser microscopy of the cells stained with the Live/Dead BacLight kit revealed that the majority of E. carotovora cells (90%) from long-incubated suspensions retained membrane integrity. In these suspensions, round cells of smaller size prevailed, with the envelope, containing an electron-dense outer layer and an underlying layer of lower density; the cytoplasm was coarse-granulated. Detection of “nonculturable” E. carotovora cells by quantitative real-time PCR analysis (Q-PCR) with specific primers by using standard procedures of sample preparation was shown to be inefficient. A special procedure including cell washing from the incubation medium in the absence of growth stimulation was developed, which promoted recovery of the colony-forming ability of the cells (up to 10% of the initial CFU number) and improved cell detection by Q-PCR from the number of genomic copies. The results provided further insight into the ways of long-term survival of phytopathogenic bacteria under environmental changes and carbon starvation.

Bacteria have high adaptive potential that ensures their survival during various environmental challenges. To adapt, bacteria activate a physiological program of stress response that makes them able to persist under adverse conditions. The present study sought to examine the ability of a particular bacterial species to induce a stress response in alternative scenarios. Cells of the phytopathogenic microorganism Pectobacterium atrosepticum were taken as a model. The cells were exposed to starvation in different physiological states (actively growing exponential phase and stationary phase cells), and the resulting starving cultures were monitored using CFU counting, quantitative PCR and electron microscopy. When exponential phase cells were subjected to starvation, the nucleoids of the cells became condensed and their DNA was detected by qPCR less effectively than that of cells growing in nutrient-rich medium, or stationary phase cells after starvation. Exponential phase cells subjected to starvation showed increased expression of genes encoding DNA binding histone-like proteins, whereas, in cultures inoculated by stationary phase cells, cell-wall-deficient forms that were inefficient at colony forming and that had a non-culturable phenotype were formed. The cell-wall-deficient forms displayed reduced expression of genes encoding synthases of cell wall components.

The major mechanism of gravitropism that is discussed for herbal plants is based on the nonuniform elongation of cells located on the opposite stem sides, occurring in the growing zone of an organ. However, gravitropic response of flax (Linum usitatissimum L.) is well-pronounced in the lower half of developing stem, which has ceased elongation long in advance of plant inclination. We have analyzed the stem curvature region by various approaches of microscopy and found the undescribed earlier significant modifications in primary phloem fibers that have constitutively developed G-layer. In fibers on the pulling stem side, cell portions were widened with formation of “bottlenecks” between them, leading to the “sausage-like” shape of a cell. Lumen diameter in fiber widening increased, while cell wall thickness decreased. Callose was deposited in proximity to bottlenecks and sometimes totally occluded their lumen. Structure of fiber cell wall changed considerably, with formation of breaks between G- and S-layers. Thick fibrillar structures that were revealed in fiber cell wall by light microscopy got oblique orientation instead of parallel to the fiber axis one in control plants. The described changes occurred at various combinations of gravitational and mechanical stimuli. Thus, phloem fibers with constitutively formed gelatinous cell wall, located in nonelongating parts of herbal plant, are involved in gravitropism and may become an important element in general understanding of the gravity effects on plants. We suggest flax phloem fibers as the model system to study the mechanism of plant position correction, including signal perception and transduction.

Intrusively growing plant cells insert themselves between surrounding cells, thus increasing the number of membranes on the tissue cross-section. This parameter can be assessed by spin echo NMR method with a magnetic field pulse gradient. Diffusion echo decay was measured for stem regions of long-fiber flax (Linum usitatissimum L.) differing in the stages of primary fiber development, which elongate thousand-fold during intrusive growth. Additionally, the number of fibers on stem cross-sections was counted under microscope. An increase in the slow component of the echo diffusion decay was correlated with an increase in the number of fibers on the stem cross-section in the zone of intrusive growth, while other stem-structure characteristics remained unchanged. Thus, NMR method can be used for characterization of intrusive fiber growth in situ.

Plant fibres – cells with important mechanical functions and a widely used raw material – are usually identified in microscopic sections only after reaching a significant length or after developing a thickened cell wall. We characterized the early developmental stages of hemp stem phloem fibres, both primary and secondary, when they still had only a primary cell wall. We gave a major emphasis to the role of intrusive elongation, the specific type of plant cell growth, by which fibres commonly attain large cell length. Intrusive growth is the key determinant of final bundle structure, both for primary and secondary phloem fibres., Plant fibres—cells with important mechanical functions and a widely used raw material—are usually identified in microscopic sections only after reaching a significant length or after developing a thickened cell wall. We characterized the early developmental stages of hemp (Cannabis sativa) stem phloem fibres, both primary (originating from the procambium) and secondary (originating in the cambium), when they still had only a primary cell wall. We gave a major emphasis to the role of intrusive elongation, the specific type of plant cell growth by which fibres commonly attain large cell length. We could identify primary phloem fibres at a distance of only 1.2–1.5 mm from the shoot apical meristem when they grew symplastically with the surrounding tissues. Half a millimeter further downwards along the stem, fibres began their intrusive elongation, which led to a sharp increase in fibre numbers visible within the stem cross-sections. The intrusive elongation of primary phloem fibres was completed within the several distal centimetres of the growing stem, before the onset of their secondary cell wall formation. The formation of secondary phloem fibres started long after the beginning of secondary xylem formation. Our data indicate that only a small portion of the fusiform cambial initials (

Flax (Linum usitatissimum L.) phloem fiber elongation is separate from secondary cell wall formation. The indicator for the developmental transition is the manually determinable “snap point”. Sharp increase in the mechanical strength at certain level of flax stem. It helped to characterize fiber-specific and stage-specific processes: soluble galactan turnover (revealed in pulse-chase experiments), specialized Golgi vesicle accumulation, and cell wall postsynthetic modification.

The developing stem of fibre flax (Linum usitatissimum L.) contains a specific region called the ‘snap point’, where the fiber-enriched bast tissues considerably change their mechanical properties. The snap point was found to be present during a restricted period of plant development */the fast growth phase, and to disappear when stem growth was completed. To relate this snap point to bast fiber formation stages, the number of bast fiber cells and the thickness of their cell walls were followed on the stained cross-sections of the flax stem throughout plant development, using the progressing snap point as the reference. The snap point was shown to be the spot, above which the elongation of bast fiber cells is fully completed. This fast growth stage is the period when the maximum length of all bast fibers in the mature plant (a major characteristic of flax fiber quality) is fixed and would not be changed later. Autoradiography was used to visualize the mode of flax bast fiber elongation above the snap point. The even distribution of label was indicative for surface (diffusive) growth type. Elongation of individual fiber cells was estimated to take only 2 � /4 days with a rate of 1 � /2 cm per day, while cell wall thickening occurs mainly below snap point and lasts around 2 months. The special cell wall structural order, characteristic for mature bast fibers, first appeared at the snap point in the outer layer of the secondary cell wall. Schemes are included, illustrating the course of cell wall thickening and the localization of various stages of fiber formation on the stem of growing flax plant. The established exact localization and duration of flax bast fiber formation stages, and the existence of snap point as the manually identified morphological reference for the transition, permit to separate the bast fibers at different stages of development and make flax an attractive model system to study the functional genomics of fiber formation in technical crops. # 2003 Elsevier B.V. All rights reserved.

The population dynamics of Pectobacterium atrosepticum SCRI1043 (Pba) within tobacco plants was monitored from the time of inoculation until after long-term preservation of microorganisms in the remnants of dead plants. We found and characterised peculiar structures that totally occlude xylem vessels, which we have named bacterial emboli. Viable but non-culturable (VBN) Pba cells were identified in the remnants of dead plants, and the conditions for resuscitation of these VBN cells were established. Our investigation shows that dissociation of the integrated bacterial population during plant colonisation forms distinct subpopulations and cell morphotypes, which are likely to perform specific functions that ensure successful completion of the life cycle within the plant.