Vadim V. Salnikov

Cell-Wall Polysaccharides of Developing Flax Plants

Flax (Linum usitatissimum L.) fibers originate from procambial cells of the protophloem and develop in cortical bundles that encircle the vascular cylinder. We determined the polysaccharide composition of the cell walls from various organs of the developing flax plant, from fiber-rich strips peeled from the stem, and from the xylem. Ammonium oxalate-soluble polysaccharides from all tissues contained 5-linked arabinans with low degrees of branching, rhamnogalacturonans, and polygalacturonic acid. The fiber-rich peels contained, in addition, substantial amounts of a buffer-soluble, 4-linked galactan branched at the 0–2 and 0–3 positions with nonreducing terminal-galactosyl units. The cross-linking glycans from all tissues were (fucogalacto)xyloglucan, typical of type-I cell walls, xylans containing (1->)-[beta]-D-xylosyl units branched exclusively at the xylosyl O-2 with t-(4-O-methyl)-glucosyluronic acid units, and (galacto)glucomannans. Tissues containing predominantly primary cell wall contained a larger proportion of xyloglucan. The xylem cells were composed of about 60% 4-xylans, 32% cellulose, and small amounts of pectin and the other cross-linking polysaccharides. The noncellulosic polysaccharides of flax exhibit an uncommonly low degree of branching compared to similar polysaccharides from other flowering plants. Although the relative abundance of the various noncellulosic polysaccharides varies widely among the different cell types, the linkage structure and degree of branching of several of the noncellulosic polysaccharides are invariant.

The snap point : a transition point in Linum usitatissimum bast fiber development

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.

Specific type of secondary cell wall formed by plant fibers

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.

Intrusive growth of flax phloem fibers is of intercalary type.

Flax (Linum usitatissimum L.) phloem fibers elongate considerably during their development and intrude between existing cells. We questioned whether fiber elongation is caused by cell tip growth or intercalary growth. Cells with tip growth are characterized by having two specific zones of cytoplasm in the cell tip, one with vesicles and no large organelles at the very tip and one with various organelles amongst others longitudinally arranged cortical microtubules in the subapex. Such zones were not observed in elongating flax fibers. Instead, organelles moved into the very tip region, and cortical microtubules showed transversal and helical configurations as known for cells growing in intercalary way. In addition, pulse-chase experiments with Calcofluor White resulted in a spotted fluorescence in the cell wall all over the length of the fiber. Therefore, it is concluded that fiber elongation is not achieved by tip growth but by intercalary growth. The intrusively growing fiber is a coenocytic cell that has no plasmodesmata, making the fibers a symplastically isolated domain within the stem.

Aspen Tension Wood Fibers Contain β-(1---> 4)-Galactans and Acidic Arabinogalactans Retained by Cellulose Microfibrils in Gelatinous Walls.

Entrapment of pectic galactan and acidic arabinogalactan II within cellulose fibrils is a distinctive feature of aspen tension wood gelatinous fibers with contractile properties. Contractile cell walls are found in various plant organs and tissues such as tendrils, contractile roots, and tension wood. The tension-generating mechanism is not known but is thought to involve special cell wall architecture. We previously postulated that tension could result from the entrapment of certain matrix polymers within cellulose microfibrils. As reported here, this hypothesis was corroborated by sequential extraction and analysis of cell wall polymers that are retained by cellulose microfibrils in tension wood and normal wood of hybrid aspen (Populus tremula × Populus tremuloides). β-(1→4)-Galactan and type II arabinogalactan were the main large matrix polymers retained by cellulose microfibrils that were specifically found in tension wood. Xyloglucan was detected mostly in oligomeric form in the alkali-labile fraction and was enriched in tension wood. β-(1→4)-Galactan and rhamnogalacturonan I backbone epitopes were localized in the gelatinous cell wall layer. Type II arabinogalactans retained by cellulose microfibrils had a higher content of (methyl)glucuronic acid and galactose in tension wood than in normal wood. Thus, β-(1→4)-galactan and a specialized form of type II arabinogalactan are trapped by cellulose microfibrils specifically in tension wood and, thus, are the main candidate polymers for the generation of tensional stresses by the entrapment mechanism. We also found high β-galactosidase activity accompanying tension wood differentiation and propose a testable hypothesis that such activity might regulate galactan entrapment and, thus, mechanical properties of cell walls in tension wood.

Distribution of ryanodine receptors in rat ventricular myocytes.

Ryanodine receptors (RyRs) are the major ion channels in the sarcoplasmic reticulum responsible for Ca2+ release in muscle cells. Localization of RyRs is therefore critical to our understanding of Ca2+ cycling and Ca2+-dependent processes within ventricular cells. Recently, RyRs were reportedly found in non-classical locations in the middle of the sarcomere, between perinuclear mitochondria and in the inner mitochondrial membrane of cardiac mitochondria. However, for multiple reasons these reports could not be considered conclusive. Therefore, we modified immunogold labeling to visualize the distribution of RyRs in ventricular myocytes. Using antibodies to the voltage-dependent anion channel (i.e. VDAC) or cytochrome c along with our labeling method, we showed that these mitochondrial proteins were appropriately localized to the mitochondrial outer and inner membrane respectively. Immunogold labeling of ultrathin sections of intact and permeabilized ventricular myocytes with antibodies to three types of RyRs confirmed the existence of RyRs between the Z-lines and around the perinuclear mitochondria. However, we did not find any evidence to support localization of RyRs to the mitochondrial inner membrane.

Tissue-specific processes during cell wall formation in flax fiber

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.

Galactosidase of plant fibers with gelatinous cell wall: Identification and localization

Using a comprehensive approach, we have identified a tissue-specific β-galactosidase from flax (Linum usitatissimum L.) phloem fibers forming a gelatinous cell wall. It was found that when fibers started to develop gelatinous cell wall, β-galactosidase gene expression was enhanced.. Using the antibodies against β-galactosidase, we showed that the enzyme was located in flax phloem fibers where it was detected together with tissue-specific galactan in secreted Golgi vesicles and in gelatinous secondary cell wall. Similar β-galactosidase present in gelatinous cell wall of fibers was found in plants belonging to various taxa and produced by different meristems; these data presume the identical mechanisms of gelatinous cell wall formation and an important role of β-galactosidase. The role of this enzyme in developing the supramolecular structure of gelatinous cell wall is discussed.

X-ray Photoelectron Spectra of La0.7Ca0.3MnO3 and La0.7Ca0.3Mn0.97Cu0.03O3 Perovskite Oxides

X-ray photoelectron spectroscopy was used to identify the oxidation states of cations in La0.7Ca0.3MnO3 and La0.7Ca0.3Mn0.97Cu0.03O3 perovskite oxides, to determine the surface composition of the samples, and to assess the effect of the Cu dopant on the electronic spectrum of the material. The binding energies of the La 4d, Ca 2p, Mn 2p, and O 1s core levels were determined, and the effect of the Cu dopant on the shape of the La 4d and O 1s peaks was analyzed.

X-ray Photoelectron Spectra of La1 – xCaxCr1 – yMyO3 (M = Mn, Fe, Ni, Cu) Perovskite Oxides

X-ray photoelectron spectroscopy was used to identify the oxidation states of ions in La1 – xCaxCr1 – yMyO3 (M = Mn, Fe, Ni, Cu) perovskite oxides, to determine the surface composition of the samples, and to assess the effect of B-site substitutions on the electronic spectrum of the chromites. The binding energies of the La 4d, Ca 2p, Mn 2p, Ni 2p, Cr 2p, and O 1s core levels were determined, and the effect of the dopant on the shape of the La 4d and O 1s peaks was analyzed.