Cell Wall Matrix Polysaccharides Research Articles

Cell wall anisotropy plays a key role in Zea mays stomatal complex movement: the possible role of the cell wall matrix

The opening of the stomatal pore in Zea mays is accomplished by the lateral displacement of the central canals of the dumbbell-shaped guard cells (GCs) towards their adjacent deflating subsidiary cells that retreat locally. During this process, the central canals swell, and their cell wall thickenings become thinner. The mechanical forces driving the outward displacement of the central canal are applied by the asymmetrically swollen bulbous ends of the GCs via the rigid terminal cell wall thickenings of the central canal and the polar ventral cell wall (VW) ends. During stomatal pore closure, the shrinking bulbous GC ends no longer exert the mechanical forces on the central canals, allowing them to be pushed back inwards, towards their initial position, by the now swelling subsidiary cells. During this process, the cell walls of the central canal thicken. Examination of immunolabeled specimens revealed that important cell wall matrix materials are differentially distributed across the walls of Z. mays stomatal complexes. The cell walls of the bulbous ends and of the central canal of the GCs, as well as the cell walls of the subsidiary cells were shown to be rich in methylesterified homogalacturonans (HGs) and hemicelluloses. Demethylesterified HGs were, in turn, mainly located at the terminal cell wall thickenings of the central canal, at the polar ends of the VW, at the lateral walls of the GCs and at the periclinal cell walls of the central canal. During stomatal function, a spatiotemporal change on the distribution of some of the cell wall matrix materials is observed. The participation of the above cell wall matrix polysaccharides in the well-orchestrated response of the cell wall during the reversible movements of the stomatal complexes is discussed.

Cell Wall Matrix Polysaccharides Contribute to Salt–Alkali Tolerance in Rice

Salt-alkali stress threatens the resilience to variable environments and thus the grain yield of rice. However, how rice responds to salt-alkali stress at the molecular level is poorly understood. Here, we report isolation of a novel salt-alkali-tolerant rice (SATR) by screening more than 700 germplasm accessions. Using 93-11, a widely grown cultivar, as a control, we characterized SATR in response to strong salt-alkali stress (SSAS). SATR exhibited SSAS tolerance higher than 93-11, as indicated by a higher survival rate, associated with higher peroxidase activity and total soluble sugar content but lower malonaldehyde accumulation. A transcriptome study showed that cell wall biogenesis-related pathways were most significantly enriched in SATR relative to 93-11 upon SSAS. Furthermore, higher induction of gene expression in the cell wall matrix polysaccharide biosynthesis pathway, coupled with higher accumulations of hemicellulose and pectin as well as measurable physio-biochemical adaptive responses, may explain the strong SSAS tolerance in SATR. We mapped SSAS tolerance to five genomic regions in which 35 genes were candidates potentially governing SSAS tolerance. The 1,4-β-D-xylan synthase gene OsCSLD4 in hemicellulose biosynthesis pathway was investigated in details. The OsCSLD4 function-disrupted mutant displayed reduced SSAS tolerance, biomass and grain yield, whereas the OsCSLD4 overexpression lines exhibited increased SSAS tolerance. Collectively, this study not only reveals the potential role of cell wall matrix polysaccharides in mediating SSAS tolerance, but also highlights applicable value of OsCSLD4 and the large-scale screening system in developing SSAS-tolerant rice.

The trans-Golgi-localized protein BICAT3 regulates manganese allocation and matrix polysaccharide biosynthesis.

Manganese (Mn2+) is essential for a diversity of processes, including photosynthetic water splitting and the transfer of glycosyl moieties. Various Golgi-localized glycosyltransferases that mediate cell wall matrix polysaccharide biosynthesis are Mn2+ dependent, but the supply of these enzymes with Mn2+ is not well understood. Here, we show that the BIVALENT CATION TRANSPORTER 3 (BICAT3) localizes specifically to trans-cisternae of the Golgi. In agreement with a role in Mn2+ and Ca2+ homeostasis, BICAT3 rescued yeast (Saccharomyces cerevisiae) mutants defective in their translocation. Arabidopsis (Arabidopsis thaliana) knockout mutants of BICAT3 were sensitive to low Mn2+ and high Ca2+ availability and showed altered accumulation of these cations. Despite reduced cell expansion and leaf size in Mn2+-deficient bicat3 mutants, their photosynthesis was improved, accompanied by an increased Mn content of chloroplasts. Growth defects of bicat3 corresponded with an impaired glycosidic composition of matrix polysaccharides synthesized in the trans-Golgi. In addition to the vegetative growth defects, pollen tube growth of bicat3 was heterogeneously aberrant. This was associated with a severely reduced and similarly heterogeneous pectin deposition and caused diminished seed set and silique length. Double mutant analyses demonstrated that the physiological relevance of BICAT3 is distinct from that of ER-TYPE CA2+-ATPASE 3, a Golgi-localized Mn2+/Ca2+-ATPase. Collectively, BICAT3 is a principal Mn2+ transporter in the trans-Golgi whose activity is critical for specific glycosylation reactions in this organelle and for the allocation of Mn2+ between Golgi apparatus and chloroplasts.

An Update on the Key Factors Required for Plant Golgi Structure Maintenance.

Plant Golgi apparatus serves as the central station of the secretory pathway and is the site where protein modification and cell wall matrix polysaccharides synthesis occur. The polarized and stacked cisternal structure is a prerequisite for Golgi function. Our understanding of Golgi structure maintenance and trafficking are largely obtained from mammals and yeast, yet, plant Golgi has many different aspects. In this review, we summarize the key players in Golgi maintenance demonstrated by genetic studies in plants, which function in ER-Golgi, intra-Golgi and post-Golgi transport pathways. Among these, we emphasize on players in intra-Golgi trafficking.

The graft framework: Quantitative changes in cell wall matrix polysaccharides throughout the tomato graft union formation

Plant cell walls provide essential functions in cell recognition, differentiation, adhesion and wound responses. Therefore, it is tempting to hypothesize that cell walls play a key role in grafting, but to date there are no quantitative studies targeting on cell wall changes during grafting. The aim of this work was to investigate the dynamics of pectic and hemicellulosic polysaccharides at the graft junctions in tomato homografts throughout the first 12 days after grafting. Cell wall fractionation, combined with ATR-FTIR spectroscopy and gas-chromatography, evidenced a marked increase in pectin content and a decrease in the degree of methyl-esterification of homogalacturonan in scion and rootstock throughout grafting. Also, recovery of tightly-bound hemicelluloses decreased at late times after grafting suggesting an increase of cross-linked hemicelluloses along grafting. In addition, immuno-dot assays revealed an increase in xyloglucan and arabinogalactan proteins in the first days after grafting, pointing to a presumed role in tissue adhesion-cohesion.

Gel-permeation chromatography-enzyme-linked immunosorbent assay method for systematic mass distribution profiling of plant cell wall matrix polysaccharides.

Cell walls are dynamic and multi-component materials that play important roles in many areas of plant biology. The composition and interactions of the structural elements give rise to material properties, which are modulated by the activity of wall-related enzymes. Studies of the genes and enzymes that determine wall composition and function have made great progress, but rarely take account of potential compensatory changes in wall polymers that may accompany and accommodate changes in other components, particularly for specific polysaccharides. Here, we present a method that allows the simultaneous examination of the mass distributions and quantities of specific cell wall matrix components, allowing insight into direct and indirect consequences of cell wall manipulations. The method employs gel-permeation chromatography fractionation of cell wall polymers followed by enzyme-linked immunosorbent assay to identify polymer types. We demonstrate the potential of this method using glycan-directed monoclonal antibodies to detect epitopes representing xyloglucans, heteromannans, glucuronoxylans, homogalacturonans (HGs) and methyl-esterified HGs. The method was used to explore compositional diversity in different Arabidopsis organs and to examine the impacts of changing wall composition in a number of previously characterized cell wall mutants. As demonstrated in this article, this methodology allows a much deeper understanding of wall composition, its dynamism and plasticity to be obtained, furthering our knowledge of cell wall biology.

Subcellular coordination of plant cell wall synthesis.

Organelles of the plant cell cooperate to synthesize and secrete a strong yet flexible polysaccharide-based extracellular matrix: the cell wall. Cell wall composition varies among plant species, across cell types within a plant, within different regions of a single cell wall, and in response to intrinsic or extrinsic signals. This diversity in cell wall makeup is underpinned by common cellular mechanisms for cell wall production. Cellulose synthase complexes function at the plasma membrane and deposit their product into the cell wall. Matrix polysaccharides are synthesized by a multitude of glycosyltransferases in hundreds of mobile Golgi stacks, and an extensive set of vesicle trafficking proteins govern secretion to the cell wall. In this review, we discuss the different subcellular locations at which cell wall synthesis occurs, review the molecular mechanisms that control cell wall biosynthesis, and examine how these are regulated in response to different perturbations to maintain cell wall homeostasis.

BRITTLE PLANT1 is required for normal cell wall composition and mechanical strength in rice.

A series of nucleotide sugar interconversion enzymes (NSEs) generate the activated sugar donors required for biosynthesis of cell wall matrix polysaccharides and glycoproteins. UDP-glucose 4-epimerases (UGEs) are NSEs that function in the interconversion of UDP-glucose (UDP-Glc) and UDP-galactose (UDP-Gal). The roles of UDP-glucose 4-epimerases in monocots remain unclear due to redundancy in the pathways. Here, we report a brittle plant (bp1) rice mutant that exhibits brittle leaves and culms at all growth stages. The mutant culms had reduced levels of rhamnogalacturonan I, homogalacturonan, and arabinogalactan proteins. Moreover, the mutant had altered contents of uronic acids, neutral noncellulosic monosaccharides, and cellulose. Map-based cloning demonstrated that OsBP1 encodes a UDP-glucose 4-epimerase (OsUGE2), a cytosolic protein. We also show that BP1 can form homo- and hetero-protein complexes with other UGE family members and with UDP-galactose transporters 2 (OsUGT2) and 3 (OsUGT3), which may facilitate the channeling of Gal to polysaccharides and proteoglycans. Our results demonstrate that BP1 participates in regulating the sugar composition and structure of rice cell walls.

Interaction between Autonomous and Microtubule Guidance Systems Controls Cellulose Synthase Trajectories.

The organization of cellulose microfibrils is critical for the strength and growth of plant cell walls. Microtubules have been shown to play a key role in controlling microfibril organization by guiding cellulose synthase complexes [1-4]. However, cellulose synthase trajectories can be maintained when microtubules are removed by drugs, suggesting a separate guidance mechanism is also at play [1, 5, 6]. By slowing down microtubule dynamics, we reveal such a mechanism by showing that cellulose synthase complexes can interact with the trails left by other complexes, causing them to follow the trails or disappear. The stability of the trails, together with the sensitivity of their directions to cellulase treatment, indicates they most likely reflect nascent cellulose microfibrils. Over many hours, this autonomous mechanism alone can lead to a change in the dominant orientation of cellulose synthase trajectories. However, the mechanism can be overridden by the microtubule guidance system. Our findings suggest a dual guidance model, in which an autonomous system, involving interaction between cellulose synthases and microfibrils, can maintain aligned cellulose synthase trajectories, while a microtubule guidance system allows alignments to be steered by environmental and developmental cues.

Fast MAS 1H-13C correlation NMR for structural investigations of plant cell walls.

Plant cell walls consist of a mixture of polysaccharides that render the cell wall a strong and dynamic material. Understanding the molecular structure and dynamics of wall polysaccharides is important for understanding and improving the properties of this energy-rich biomaterial. So far, solid-state NMR studies of cell wall structure and dynamics have solely relied on 13C chemical shifts measured from 2D and 3D correlation experiments. To increase the spectral resolution, sensitivity and upper limit of measurable distances, it is of interest to explore 1H chemical shifts and 1H-detected NMR experiments for analyzing cell walls. Here we demonstrate 2D and 3D 1H-13C correlation experiments at both moderate and fast MAS frequencies of 10-50kHz to resolve and assign 1H chemical shifts of matrix polysaccharides in Arabidopsis primary cell walls. Both 13C-detected and 1H-detected experiments are implemented and are shown to provide useful and complementary information. Using the assigned 1H chemical shifts, we measured long-range correlations between matrix polysaccharides and cellulose using 1H-1H instead of 13C-13C spin diffusion, and the 2D experiments can be conducted with either 13C or 1H detection.

Critical Review of Plant Cell Wall Matrix Polysaccharide Glycosyltransferase Activities Verified by Heterologous Protein Expression.

The life cycle and development of plants requires the biosynthesis, deposition, and degradation of cell wall matrix polysaccharides. The structures of the diverse cell wall matrix polysaccharides influence commercially important properties of plant cells, including growth, biomass recalcitrance, organ abscission, and the shelf life of fruits. This review is a comprehensive summary of the matrix polysaccharide glycosyltransferase (GT) activities that have been verified using in vitro assays following heterologous GT protein expression. Plant cell wall (PCW) biosynthetic GTs are primarily integral transmembrane proteins localized to the endoplasmic reticulum and Golgi of the plant secretory system. The low abundance of these enzymes in plant tissues makes them particularly difficult to purify from native plant membranes in quantities sufficient for enzymatic characterization, which is essential to study the functions of the different GTs. Numerous activities in the synthesis of the major cell wall matrix glycans, including pectins, xylans, xyloglucan, mannans, mixed-linkage glucans (MLGs), and arabinogalactan components of AGP proteoglycans have been mapped to specific genes and multi-gene families. Cell wall GTs include those that synthesize the polymer backbones, those that elongate side branches with extended glycosyl chains, and those that add single monosaccharide linkages onto polysaccharide backbones and/or side branches. Three main strategies have been used to identify genes encoding GTs that synthesize cell wall linkages: analysis of membrane fractions enriched for cell wall biosynthetic activities, mutational genetics approaches investigating cell wall compositional phenotypes, and omics-directed identification of putative GTs from sequenced plant genomes. Here we compare the heterologous expression systems used to produce, purify, and study the enzyme activities of PCW GTs, with an emphasis on the eukaryotic systems Nicotiana benthamiana, Pichia pastoris, and human embryonic kidney (HEK293) cells. We discuss the enzymatic properties of GTs including kinetic rates, the chain lengths of polysaccharide products, acceptor oligosaccharide preferences, elongation mechanisms for the synthesis of long-chain polymers, and the formation of GT complexes. Future directions in the study of matrix polysaccharide biosynthesis are proposed.

DRMY1, a Myb-Like Protein, Regulates Cell Expansion and Seed Production in Arabidopsis thaliana.

Plant organ development to a specific size and shape is controlled by cell proliferation and cell expansion. Here, we identify a novel Myb-like Arabidopsis gene, Development Related Myb-like1 (DRMY1), which controls cell expansion in both vegetative and reproductive organs. DRMY1 is strongly expressed in developing organs and its expression is reduced by ethylene while it is induced by ABA. DRMY1 has a Myb-like DNA-binding domain, which is predominantly localized in the nucleus and does not exhibit transcriptional activation activity. The loss-of-function T-DNA insertion mutant drmy1 shows reduced organ growth and cell expansion, which is associated with changes in the cell wall matrix polysaccharides. Interestingly, overexpression of DRMY1 in Arabidopsis does not lead to enhanced organ growth. Expression of genes involved in cell wall biosynthesis/remodeling, ribosome biogenesis and in ethylene and ABA signaling pathways is changed with the deficiency of DRMY1. Our results suggest that DRMY1 plays an essential role in organ development by regulating cell expansion either directly by affecting cell wall architecture and/or cytoplasmic growth or indirectly through the ethylene and/or ABA signaling pathways.

A half-type ABC transporter FeSTAR1 regulates Al resistance possibly via UDP-glucose-based hemicellulose metabolism and Al binding

Buckwheat (Fagopyrum esculentum) is highly tolerant to Al stress, but the molecular mechanisms remain largely unknown. This study aims to investigate a half-type ABC transporter gene (FeSTAR1) with respect to Al tolerance. The expression of FeSTAR1 was examined and complementation test in atstar1 mutant was conducted. Furthermore, Al distribution and cell wall polysaccharides content were analyzed. FeSTAR1 is an ABC transporter protein with nucleotide binding domain, but lack of transmembrane domain. Consistently, FeSTAR1 is a soluble protein, localizing to both cytoplasm and nucleus. Al rapidly and specifically induced FeSTAR1 expression. Heterologous expression of FeSTAR1 in atstar1 rescued its Al tolerance, and exogenous applied UDP-glucose could alleviate Al sensitivity of atstar1 mutant, suggesting the connection between FeSTAR1 and UDP-glucose in terms of Al tolerance. Furthermore, FeSTAR1 complemented lines accumulated less Al in root cell wall than atstar1 mutant. Further cell wall fraction analysis showed that Al was largely confined to cell wall hemicellulose1, at which Al content was significantly lower in complemented lines. Consistent with Al distribution in different cell wall polysaccharides, complemented lines had lower hemicellulose1 content. Our results indicate that FeSTAR1 is involved in Al resistance via possibly cell wall matrix polysaccharides metabolism in buckwheat.

Elicitors and defense gene induction in plants with altered lignin compositions.

A reduction in the lignin content in transgenic plants induces the ectopic expression of defense genes, but the importance of altered lignin composition in such phenomena remains unclear. Two Arabidopsis lines with similar lignin contents, but strikingly different lignin compositions, exhibited different quantitative and qualitative transcriptional responses. Plants with lignin composed primarily of guaiacyl units overexpressed genes responsive to oomycete and bacterial pathogen attack, whereas plants with lignin composed primarily of syringyl units expressed a far greater number of defense genes, including some associated with cis-jasmone-mediated responses to aphids; these plants exhibited altered responsiveness to bacterial and aphid inoculation. Several of the defense genes were differentially induced by water-soluble extracts from cell walls of plants of the two lines. Glycome profiling, fractionation and enzymatic digestion studies indicated that the different lignin compositions led to differential extractability of a range of heterogeneous oligosaccharide epitopes, with elicitor activity originating from different cell wall polymers. Alteration of lignin composition affects interactions with plant cell wall matrix polysaccharides to alter the sequestration of multiple latent defense signal molecules with an impact on biotic stress responses.

Expression of the human UDP-galactose transporter gene hUGT1 in tobacco plants' enhanced plant hardness

We reported previously that tobacco plants transformed with the human UDP-galactose transporter 1 gene (hUGT1) had enhanced growth, displayed characteristic traits, and had an increased proportion of galactose (hyper-galactosylation) in the cell wall matrix polysaccharides. Here, we report that hUGT1-transgenic plants have an enhanced hardness. As determined by breaking and bending tests, the leaves and stems of hUGT1-transgenic plants were harder than those of control plants. Transmission electron microscopy revealed that the cell walls of palisade cells in leaves, and those of cortex cells and xylem fibers in stems of hUGT1-transgenic plants, were thicker than those of control plants. The increased amounts of total cell wall materials extracted from the leaves and stems of hUGT1-transgenic plants supported the increased cell wall thickness. In addition, the cell walls of the hUGT1-transgenic plants showed an increased lignin contents, which was supported by the up-regulation of lignin biosynthetic genes. Thus, the heterologous expression of hUGT1 enhanced the accumulation of cell wall materials, which was accompanied by the increased lignin content, resulting in the increased hardness of the leaves and stems of hUGT1-trangenic plants. The enhanced accumulation of cell wall materials might be related to the hyper-galactosylation of cell wall matrix polysaccharides, most notably arabinogalactan, because of the enhanced UDP-galactose transport from the cytosol to the Golgi apparatus by hUGT1, as suggested in our previous report.

A glycosyl transferase family 43 protein involved in xylan biosynthesis is associated with straw digestibility in Brachypodium distachyon.

Summary The recalcitrance of secondary plant cell walls to digestion constrains biomass use for the production of sustainable bioproducts and for animal feed.We screened a population of Brachypodium recombinant inbred lines (RILs) for cell wall digestibility using commercial cellulases and detected a quantitative trait locus (QTL) associated with this trait.Examination of the chromosomal region associated with this QTL revealed a candidate gene that encodes a putative glycosyl transferase family (GT) 43 protein, orthologue of IRX14 in Arabidopsis, and hence predicted to be involved in the biosynthesis of xylan. Arabinoxylans form the major matrix polysaccharides in cell walls of grasses, such as Brachypodium. The parental lines of the RIL population carry alternative nonsynonymous polymorphisms in the Bd GT43A gene, which were inherited in the RIL progeny in a manner compatible with a causative role in the variation in straw digestibility. In order to validate the implied role of our candidate gene in affecting straw digestibility, we used RNA interference to lower the expression levels of the Bd GT43A gene in Brachypodium.The biomass of the silenced lines showed higher digestibility supporting a causative role of the Bd GT43A gene, suggesting that it might form a good target for improving straw digestibility in crops.

In the grass species Brachypodium distachyon, the production of mixed-linkage (1,3;1,4)-β-glucan (MLG) occurs in the Golgi apparatus.

Mixed-linkage (1,3;1,4)-β-glucan (MLG) is a glucose polymer with beneficial effects on human health and high potential for the agricultural industry. MLG is present predominantly in the cell wall of grasses and is synthesized by cellulose synthase-like F or H families of proteins, with CSLF6 being the best-characterized MLG synthase. Although the function of this enzyme in MLG production has been established, the site of MLG synthesis in the cell is debated. It has been proposed that MLG is synthesized at the plasma membrane, as occurs for cellulose and callose; in contrast, it has also been proposed that MLG is synthesized in the Golgi apparatus, as occurs for other matrix polysaccharides of the cell wall. Testing these conflicting possibilities is fundamentally important in the general understanding of the biosynthesis of the plant cell wall. Using immuno-localization analyses with MLG-specific antibody in Brachypodium and in barley, we found MLG present in the Golgi, in post-Golgi structures and in the cell wall. Accordingly, analyses of a functional fluorescent protein fusion of CSLF6 stably expressed in Brachypodium demonstrated that the enzyme is localized in the Golgi. We also established that overproduction of MLG causes developmental and growth defects in Brachypodium as also occur in barley. Our results indicated that MLG production occurs in the Golgi similarly to other cell wall matrix polysaccharides, and supports the broadly applicable model in grasses that tight mechanisms control optimal MLG accumulation in the cell wall during development and growth. This work addresses the fundamental question of where mixed linkage (1,3;1,4)-β-glucan (MLG) is synthesized in plant cells. By analyzing the subcellular localization of MLG and MLG synthase in an endogenous system, we demonstrated that MLG synthesis occurs at the Golgi in Brachypodium and barley. A growth inhibition due to overproduced MLG in Brachypodium supports the general applicability of the model that a tight control of the cell wall polysaccharides accumulation is needed to maintain growth homeostasis during development.

Local differentiation of cell wall matrix polysaccharides in sinuous pavement cells: its possible involvement in the flexibility of cell shape.

The distribution of homogalacturonans (HGAs) displaying different degrees of esterification as well as of callose was examined in cell walls of mature pavement cells in two angiosperm and two fern species. We investigated whether local cell wall matrix differentiation may enable pavement cells to respond to mechanical tension forces by transiently altering their shape. HGA epitopes, identified with 2F4, JIM5 and JIM7 antibodies, and callose were immunolocalised in hand-made or semithin leaf sections. Callose was also stained with aniline blue. The structure of pavement cells was studied with light and transmission electron microscopy (TEM). In all species examined, pavement cells displayed wavy anticlinal cell walls, but the waviness pattern differed between angiosperms and ferns. The angiosperm pavement cells were tightly interconnected throughout their whole depth, while in ferns they were interconnected only close to the external periclinal cell wall and intercellular spaces were developed between them close to the mesophyll. Although the HGA epitopes examined were located along the whole cell wall surface, the 2F4- and JIM5- epitopes were especially localised at cell lobe tips. In fern pavement cells, the contact sites were impregnated with callose and JIM5-HGA epitopes. When tension forces were applied on leaf regions, the pavement cells elongated along the stretching axis, due to a decrease in waviness of anticlinal cell walls. After removal of tension forces, the original cell shape was resumed. The presented data support that HGA epitopes make the anticlinal pavement cell walls flexible, in order to reversibly alter their shape. Furthermore, callose seems to offer stability to cell contacts between pavement cells, as already suggested in photosynthetic mesophyll cells.

Disentangling pectic homogalacturonan and rhamnogalacturonan-I polysaccharides: Evidence for sub-populations in fruit parenchyma systems

The matrix polysaccharides of plant cell walls are diverse and variable sets of polymers influencing cell wall, tissue and organ properties. Focusing on the relatively simple parenchyma tissues of four fruits – tomato, aubergine, strawberry and apple – we have dissected cell wall matrix polysaccharide contents using sequential solubilisation and antibody-based approaches with a focus on pectic homogalacturonan (HG) and rhamnogalacturonan-I (RG-I). Epitope detection in association with anion-exchange chromatography analysis indicates that in all cases solubilized polymers include spectra of HG molecules with unesterified regions that are separable from methylesterified HG domains. In highly soluble fractions, RG-I domains exist in both HG-associated and non-HG-associated forms. Soluble xyloglucan and pectin-associated xyloglucan components were detected in all fruits. Aubergine glycans contain abundant heteroxylan epitopes, some of which are associated with both pectin and xyloglucan. These profiles of polysaccharide heterogeneity provide a basis for future studies of more complex cell and tissue systems.

Dietary phytochemicals as inhibitors of primary amine oxidase

We reported previously that tobacco plants transformed with the human UDP-galactose transporter 1 gene (hUGT1) had enhanced growth, displayed characteristic traits, and had an increased proportion of galactose (hyper-galactosylation) in the cell wall matrix polysaccharides. Here, we report that hUGT1-transgenic plants have an enhanced hardness. As determined by breaking and bending tests, the leaves and stems of hUGT1-transgenic plants were harder than those of control plants. Transmission electron microscopy revealed that the cell walls of palisade cells in leaves, and those of cortex cells and xylem fibers in stems of hUGT1-transgenic plants, were thicker than those of control plants. The increased amounts of total cell wall materials extracted from the leaves and stems of hUGT1-transgenic plants supported the increased cell wall thickness. In addition, the cell walls of the hUGT1-transgenic plants showed an increased lignin contents, which was supported by the up-regulation of lignin biosynthetic genes. Thus, the heterologous expression of hUGT1 enhanced the accumulation of cell wall materials, which was accompanied by the increased lignin content, resulting in the increased hardness of the leaves and stems of hUGT1-trangenic plants. The enhanced accumulation of cell wall materials might be related to the hyper-galactosylation of cell wall matrix polysaccharides, most notably arabinogalactan, because of the enhanced UDP-galactose transport from the cytosol to the Golgi apparatus by hUGT1, as suggested in our previous report.