Major Non-cellulosic Polysaccharides Research Articles

Engineering Non-cellulosic Polysaccharides of Wood for the Biorefinery.

Non-cellulosic polysaccharides constitute approximately one third of usable woody biomass for human exploitation. In contrast to cellulose, these substances are composed of several different types of unit monosaccharides and their backbones are substituted by various groups. Their structural diversity and recent examples of their modification in transgenic plants and mutants suggest they can be targeted for improving wood-processing properties, thereby facilitating conversion of wood in a biorefinery setting. Critical knowledge on their structure-function relationship is slowly emerging, although our understanding of molecular interactions responsible for observed phenomena is still incomplete. This review: (1) provides an overview of structural features of major non-cellulosic polysaccharides of wood, (2) describes the fate of non-cellulosic polysaccharides during biorefinery processing, (3) shows how the non-cellulosic polysaccharides impact lignocellulose processing focused on yields of either sugars or polymers, and (4) discusses outlooks for the improvement of tree species for biorefinery by modifying the structure of non-cellulosic polysaccharides.

Glucuronoarabinoxylan structure in the walls of Aechmea leaf chlorenchyma cells is related to wall strength

In CAM-plants rising levels of malic acid in the early morning cause elevated turgor pressures in leaf chlorenchyma cells. Under specific conditions this process is lethal for sensitive plants resulting in chlorenchyma cell burst while other species can cope with these high pressures and do not show cell burst under comparable conditions. The non-cellulosic polysaccharide composition of chlorenchyma cell walls was investigated and compared in three cultivars of Aechmea with high sensitivity for chlorenchyma cell burst and three cultivars with low sensitivity. Chlorenchyma layers were cut from the leaf and the non-cellulosic carbohydrate fraction of the cell wall fraction was analyzed by gas–liquid chromatography. Glucuronoarabinoxylans (GAXs) were the major non-cellulosic polysaccharides in Aechmea. The fine structure of these GAXs was strongly related to chlorenchyma wall strength. Chlorenchyma cell walls from cultivars with low sensitivity to cell burst were characterized by an A/X ratio of ca. 0.13 while those from cultivars with high sensitivity showed an A/X ratio of ca. 0.23. Xylose chains from cultivars with high cell burst sensitivity were ca. 40% more substituted with arabinose compared to cultivars with low sensitivity for cell burst. The results indicate a relationship in vivo between glucuronoarabinoxylan fine structure and chlorenchyma cell wall strength in Aechmea. The evidence obtained supports the hypothesis that GAXs with low degrees of substitution cross-link cellulose microfibrils, while GAXs with high degrees of substitution do not. A lower degree of arabinose substitution on the xylose backbone implies stronger cell walls and the possibility of withstanding higher internal turgor pressures without cell bursting.

A Barley Xyloglucan Xyloglucosyl Transferase Covalently Links Xyloglucan, Cellulosic Substrates, and (1,3;1,4)-β-D-Glucans

Molecular interactions between wall polysaccharides, which include cellulose and a range of noncellulosic polysaccharides such as xyloglucans and (1,3;1,4)-beta-D-glucans, are fundamental to cell wall properties. These interactions have been assumed to be noncovalent in nature in most cases. Here we show that a highly purified barley xyloglucan xyloglucosyl transferase HvXET5 (EC 2.4.1.207), a member of the GH16 group of glycoside hydrolases, catalyzes the in vitro formation of covalent linkages between xyloglucans and cellulosic substrates and between xyloglucans and (1,3;1,4)-beta-D-glucans. The rate of covalent bond formation catalyzed by HvXET5 with hydroxyethylcellulose (HEC) is comparable with that on tamarind xyloglucan, whereas that with (1,3; 1,4)-beta-D-glucan is significant but slower. Matrix-assisted laser desorption ionization time-of-flight mass spectrometric analyses showed that oligosaccharides released from the fluorescent HEC:xyloglucan conjugate by a specific (1,4)-beta-D-glucan endohydrolase consisted of xyloglucan substrate with one, two, or three glucosyl residues attached. Ancillary peaks contained hydroxyethyl substituents (m/z 45) and confirmed that the parent material consisted of HEC covalently linked with xyloglucan. Similarly, partial hydrolysis of the (1,3;1,4)-beta-D-glucan:xyloglucan conjugate by a specific (1,3;1,4)-beta-D-glucan endohydrolase revealed the presence of a series of fluorescent oligosaccharides that consisted of the fluorescent xyloglucan acceptor substrate linked covalently with 2-6 glucosyl residues. These findings raise the possibility that xyloglucan endo-transglucosylases could link different polysaccharides in vivo and hence influence cell wall strength, flexibility, and porosity.

Plant cell wall polysaccharide biosynthesis: real progress in the identification of participating genes

Plant cell walls are comprised of cellulosic microfibrils embedded in a matrix of complex non-cellulosic polysaccharides, which generally include pectic polysaccharides, xyloglucans and heteroxylans as major constituents and heteromannans as minor constituents (Bacic et al. 1988). However, primary walls in grasses and commercially important cereals of the graminaceous monocotyledons are characterized by relatively low levels of pectic polysaccharides and xyloglucans; the major non-cellulosic polysaccharides in these species are glucuronoarabinoxylans and (1 fi 3,1 fi 4)-b-D-glucans (Smith and Harris 1999). Smaller amounts of protein, phenolic acids and glycoproteins are present in the walls of most plants, callose is detectable in some walls, and lignin is often found after secondary thickening. Here, we review recent progress towards the characterization of genes that encode enzymes responsible for the biosynthesis of major wall polysaccharides, and consider emerging technologies that can be used to define the functions of other genes involved in the synthesis, assembly and re-modelling of wall polysaccharides.

Cytochemistry and immunolocalisation of polysaccharides and proteoglycans in the endosperm of green Arabica coffee beans

The major noncellulosic polysaccharides and proteoglycans in the coffee bean (Coffea arabica) cell wall are (galacto)mannans and arabinogalactan proteins. Immunological and chemical probes demonstrated that the mannans and arabinogalactan proteins were located continuously across the width of the cell wall, but that the concentration of different structural epitopes within these polysaccharide types showed considerable spatial variation. For the mannans this was implied by the striated pattern demonstrated by fluctuation of the affinity between the mannan monoclonal antibody BGM C6 and (galacto)mannan. The arabinogalactan proteins labelled by the Yariv reagent and the arabinogalactan protein-specific antibody LM2 appeared to be located in all regions of the wall except the middle lamella, but showed some differences in intensity of labelling. However, the LM6 antibody, specific for (1-->5)-alpha-arabinan epitopes, was located only as a compact region adjacent to the cell lumen in the body of the endosperm; though, it did label throughout the wall of epidermal cells. This implied that either some of the more highly arabinosylated arabinogalactan proteins contained contiguous 5-arabinosyl residues or that a rhamnogalacturonan which contained 5-arabinosyl residues as side chains existed in the cell wall. In either case the polymers were very restricted in their distribution. A second category of pectin, a homogalacturonan detected by JIM7, was located only in the middle lamella region. The architecture of the wall, as revealed by resin etching, appeared to reflect the chemical heterogeneity, with three distinct physical zones identifiable in a cross section across a single wall.

Ferulic acid is esterified to glucuronoarabinoxylans in pineapple cell walls

The ester-linkage of ferulic acid (mainly E) to polysaccharides in primary cell walls of pineapple fruit ( Ananas comosus) (Bromeliaceae) was investigated by treating a cell-wall preparation with ‘Driselase’ which contains a mixture of endo- and exo-glycanases, but no hydroxycinnamoyl esterase activity. The most abundant feruloyl oligosaccharide released was O-[5- O-( E-feruloyl)- α- l-arabinofuranosyl](1→3)- O- β- d-xylopyranosyl-(1→4)- d-xylopyranose (FAXX). This indicated that the ferulic acid is ester-linked to glucuronoarabinoxylans in the same way as in the primary walls of grasses and cereals (Poaceae). Glucuronoarabinoxylans are the major non-cellulosic polysaccharides in the pineapple cell walls.

Polysaccharide compositions of primary cell walls of the palms Phoenix canariensis and Rhopalostylis sapida

The polysaccharide compositions of unlignified primary cell walls from two species of palms were examined. Cell-wall preparations were isolated from the stem apex, including the pre-emergent leaflets and rachides, of Phoenix canariensis (Canary Island date palm), and from leaflets and rachides dissected from pre-emergent leaves in the stem apex of Rhopalostylis sapida (Nikau palm). The non-cellulosic polysaccharides in the cell-wall preparations from both species had similar monosaccharide compositions, with arabinose and galactose being the predominant neutral monosaccharides, together with large amounts of galacturonic acid. These monosaccharide compositions indicated the presence of large proportions of pectic polysaccharides, including homogalacturonans. This was confirmed by linkage analyses of the cell-wall preparations which showed the presence of large proportions of pectic arabinans, together with pectic galactans and/or Type I arabinogalactans. Evidence for rhamnogalacturonan I and small amounts of rhamnogalacturonan II was also obtained. In addition to pectic polysaccharides, the cell-wall preparations contained smaller amounts of xyloglucans and even smaller amounts of heteroxylans, probably glucuronoarabinoxylans, and glucomannans and/or galactoglucomannans; (1→3,1→4)-β-D-glucans were not present. Although palms (Arecaceae) are commelinoid monocotyledons, the polysaccharide compositions of their primary cell walls resemble those of non-commelinoid monocotyledons and dicotyledons. These compositions contrast with those of primary cell walls of other commelinoid families which have glucuronoarabinoxylans rather than pectic polysaccharides as the major non-cellulosic polysaccharides. The results are discussed in relation to the possible evolution of the composition of primary cell walls of monocotyledons.

Characterisation of Rosa Mosqueta seeds: cell wall polysaccharide composition and light microscopy observations

The utilisation of enzymes for the extraction of vegetable oils from seeds has been a topic of growing interest in recent years. Knowledge of the cell wall polysaccharide composition is important to select the enzyme(s) necessary for the most effective degradation of the cell walls. The purpose of the present work is to characterise the seeds of Rosa Mosqueta (Rosa aff rubiginosa) by light microscopy (where several differential staining methods were applied to analyse the seed structure) and by the isolation of cell wall polysaccharide extracts. The mature seed of Rosa Mosqueta has a very thick and structurally complex seed coat comprising heavily lignified tissue. The embryo has two cell layers of remaining endosperm tissue (indicating that this is an exalbuminous seed), two voluminous cotyledons that contain the oil, and bundles of provascular tissues distributed perpendicularly to the transverse axis of the embryo. The major non-cellulosic polysaccharides from the non-lignified tissues are glucuronoxylans and pectic polysaccharides; glucans are also present in small amounts. The major non-cellulosic polysaccharides from the lignified tissues are glucuronoxylans. Concerning the use of enzymes for oil extraction, microscopy and cell wall polysaccharide analysis showed that the use of pectic enzymes followed by a xylanase or a cellulase should be explored. # 2000 Society of Chemical Industry

Monosaccharide compositions of unlignified cell walls of monocotyledons in relation to the occurrence of wall-bound ferulic acid

The families of monocotyledons can be divided into two groups on the basis of the presence (Group A) or absence (Group B) of ester-linked ferulic acid in their unlignified cell walls (UCW). In the Poaceae this ferulic acid is linked to glucuronoarabinoxylans, which are major components of these cell walls (CW). The hypothesis was examined that the UCW of the other Group A families also contain glucuronoarabinoxylans as their major noncellulosic polysaccharides, whereas pectic polysaccharides are the major noncellulosic polysaccharides in the UCW of the Group B families. Monosaccharide compositions were determined of UCW from one species in each of nine Group A families, eight Group B families, and, for comparison, two families of dicotyledons. The results mostly supported the hypothesis. The UCW of Group A monocotyledons contained large proportions of arabinose and xylose and greater proportions of glucuronic acid than the CW of Group B. This is consistent with the presence of large proportions of glucuronoarabinoxylans in these CW. In contrast, the UCW of Group B monocotyledons had monosaccharide compositions similar to those of the dicotyledons. They contained large proportions of galactose and galacturonic acid, consistent with the presence of large proportions of pectic polysaccharides. Two Group B species [ Egeria densa (Hydrocharitaceae) and Potamogeton crispus (Potamogetonaceae)] were unusual in having CW containing large proportions of xylose. One Group A species, Phoenix reclinata (Arecaceae) was exceptional in having CW with a monosaccharide composition similar to dicotyledons. The results are discussed in relation to cladograms constructed from DNA nucleotide sequences from the chloroplast gene rbcL and a possible sequence is proposed for the evolution of the composition of UCW of monocotyledons.

Polysaccharides in primary cell walls of Japanese cypress cells in suspension culture

Extracellular polysaccharides in the medium of Hinoki cells in suspension culture were mainly composed of xyloglucan and 3,6-linked arabinogalactan. The non-cellulosic polysaccharides in the primary cell walls of the suspension-cultured cells were mainly composed of rhamnogalacturonan, xyloglucan, 4-linked galactan and 5-linked arabinan, which have been widely reported to be major non-cellulosic polysaccharides in dicotyledons.

Polysaccharide Composition of Unlignified Cell Walls of Pineapple [Ananas comosus (L.) Merr.] Fruit

The polysaccharides of cell walls isolated from the fleshy, edible part of the fruit of the monocotyledon pineapple [Ananas comosus (L.) Merr.] (family Bromeliaceae) were analyzed chemically. These cell walls were derived mostly from parenchyma cells and were shown histochemically to be unlignified, but they contained ester-linked ferulic acid. The analyses indicated that the noncellulosic polysaccharide composition of the cell walls was intermediate between that of unlignified cell walls of species of the monocotyledon family Poaceae (grasses and cereals) and that of unlignified cell walls of dicotyledons. Glucuronoarabinoxylans were the major non-cellulosic polysaccharides in the pineapple cell walls. Xyloglucans were also present, together with small amounts of pectic polysaccharides and glucomannans (or galactoglucomannans). The large amounts of glucuronoarabinoxylans and small amounts of pectic polysaccharides resemble the noncellulosic polysaccharide composition of the unlignified cell walls of the Poaceae. However, the absence of (1-->3,1-->4)-beta-glucans, the presence of relatively large amounts of xyloglucans, and the possible structure of the xyloglucans resemble the noncellulosic polysaccharide composition of the unlignified cell walls of dicotyledons.