Turnover of cell wall components during internode growth in <Emphasis Type="Italic">Merremia emarginata</Emphasis>

The internodes of Merremia emarginata plant showed exceptionally high stretchability throughout the development period. Therefore, it provides excellent material to study the changes undergoing during cell elongation. In this study, the influence of the hormone treatments (GA₃, PAA and NAA) on the wall component synthesis was analyzed in relation to elongation growth during internode development. A clear increasing trend of wall components was observed with increase in internode length. The non-esterified pectic substances were markedly correlated with internode length while esterified pectic substances showed correlation only in hormone treated internodes. Low molecular weight xyloglucans content showed correlation only in GA₃ and NAA treated internodes, while high molecular weight xyloglucans were significantly correlated with length of internodes treated with PAA and NAA.     

Isolation and characterisation of cell wall polysaccharides from cocoa (Theobroma cacao L.) beans

 Cell wall material (CWM) was prepared from sun-dried cocoa (Theobroma cacao L.) bean cotyledons before and after fermentation. The monosaccharide composition of the CWM was identical for unfermented and fermented beans. Polysaccharides of the CWM were solubilised by sequential extraction with 0.05 M trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (CDTA), 0.05 M Na₂CO₃, and 1 M, 4 M and 8 M KOH. The non-cellulosic sugar composition for each fraction was similar for unfermented and fermented samples, indicating that fermentation caused no significant modification of the structural features of individual cell wall polysaccharides. Pectic polysaccharides accounted for 60% of the cell wall polysaccharides but only small amounts could be solubilised in solutions of CDTA, Na₂CO₃, and 1 M and 4 M KOH. The bulk of the pectic polysaccharides were solubilised in 8 M KOH and were characterised by a rhamnogalacturonan backbone heavily substituted with side-chains of 5-linked arabinose and 4-linked galactose. Linkage analysis indicated the presence of additional acidic polysaccharides, including a xylogalacturonan and a glucuronoxylan. Cellulose, xyloglucan and a galactoglucomannan accounted for 28%, 8% and 3% of the cell wall polysaccharides, respectively. It is concluded that the types and structural features of cell wall polysaccharides in cocoa beans resemble those found in the parenchymatous tissue of many fruits and vegetables rather than those reported for many seed storage polysaccharides. Received: 29 May 1999 / Accepted: 19 October 1999     

Water stress and cell wall polysaccharides in the apical root zone of wheat cultivars varying in drought tolerance

Glycosyl composition and linkage analysis of cell wall polysaccharides were examined in apical root zones excised from water-stressed and unstressed wheat seedlings (Triticum durum Desf.) cv. Capeiti ("drought-tolerant") and cv. Creso ("drought sensitive"). Wall polysaccharides were sequentially solubilized to obtain three fractions: CDTA+Na(2)CO(3) extract, KOH extract and the insoluble residue (alpha-cellulose). A comparison between the two genotypes showed only small variations in the percentages of matrix polysaccharides (CDTA+Na(2)CO(3) plus KOH extract) and of the insoluble residues (alpha-cellulose) in water-stressed and unstressed conditions. Xylosyl, glucosyl and arabinosyl residues represented more than 90mol% of the matrix polysaccharides. The linkage analysis of matrix polysaccharides showed high levels of xyloglucans (23-39mol%), and arabinoxylans (38-48mol%) and a low amount of pectins and (1-->3), (1-->4)-beta-d-glucans. The high level of xyloglucans was supported by the release of the diagnostic disaccharide isoprimeverose after Driselase digestion of KOH-extracted polysaccharides. In the "drought-tolerant" cv. Capeiti the mol% of side chains of rhamnogalacturonan I and II significantly increased in response to water stress, whereas in cv. Creso, this increase did not occur. The results support a role of the pectic side chains during water stress response in a drought-tolerant wheat cultivar.     

Cell wall changes in immature Asparagus stem tissue after excision.

Cell wall material (CWM) was prepared from sections of fresh and aerobically-stored asparagus (Asparagus officinalis, L. cv. Connovor Collossus) stems. Polymers were solubilized from the CWM by successive extraction with cyclohexane-trans-1,2-diamine-N N N' N'-tetraacetate (CDTA), Na2CO3 and KOH to leave the alpha-cellulose residue which contained a significant amount of cross-linked pectic polysaccharides. The polymers were fractionated by anion-exchange chromatography and selected fractions were subjected to methylation analysis. The storage-related decrease in (1-4)-linked Galp was detected in all the fractions rich in pectic polysaccharides, particularly in the CDTA, Na2CO3, 0.5 M KOH fractions and alpha-cellulose residue. A smaller decrease in Araf was also observed. This was mainly due to a decrease in (1-5)-linked Araf in the Na2CO3-1-soluble polymers, and terminal Araf in the alpha-cellulose residue. There was evidence for the occurrence of significant amounts of complexes containing pectic polysaccharides and xylans having a relatively low degree of polymerization in the dilute alkali-soluble polymers, and some of these contained phenolic compounds; the storage-induced increase in (1-4)-linked Xylp was confined to these polymers. Interestingly, no free acidic xylans could be detected in the 1 M and 4 M KOH-soluble polymers; instead, the bulk of the hemicellulosic polysaccharides appeared to be mixtures of xyloglucans and xylans in which the ratio of xyloglucan to xylan increased with increasing strength of alkali used for extraction of the polymers. The non-degradative extraction and fractionation procedures revealed heterogeneity in pectic polysaccharides, pectic polysaccharide-xylan complexes and xyloglucans in close association with xylans. The possible relationship between pectic polysaccharide-xylan-phenolic complexes and the onset of lignification in maturing tissues is discussed.     

Composition of the cell wall formed by protoplasts isolated from cell suspension cultures of Vinca rosea

The biochemistry of cell-wall regeneration in protoplasts obtained from Vinca rosea L. (Catharanthus roseus (L.) G. Don) cells grown in suspension culture by isolating the regenerated wall and the extracellular polysaccharides of protoplasts cultured for various periods, and investigating their composition. Gas-liquid chromatography and tracer studies with D-[U-¹⁴C]glucose showed that the sugar composition of the extracellular polysaccharides was similar to that of the original cell culture, consisting mainly of polyuronide and 3,6-linked arabinogalactan. the regenerated cell wall was composed of non-cellulosic glucans having 1,3- and 1,4-linkages, while its content in pectic and hemicellulosic components was very low.     

Structural features of cell-wall polymers of the apple

Cell-wall material was isolated from ripe-apple cortical tissues by sequential extraction with aqueous 1.5% sodium dodecyl sulphate and aqueous 90% methyl sulphoxide. The wall material, which contained ～1% of protein, with proline and hydroxyproline as the preponderant amino acids, was sequentially extracted with water at 80°, oxalate at 80°, m KOH at 1°, and m and 4m KOH at 20°, to leave a residue of α-cellulose, which was associated with an appreciable amount of arabinose-rich pectic material. The depectinated material was also extracted with 6m guanidinium thiocyanate at 20° to solubilise preferentially polysaccharides rich in mannose. The hot-water-soluble pectic substances were richer in arabinose compared with the oxalate-soluble ones and were resolved into five fractions by anion-exchange chromatography. The bulk of the hemicelluloses, which were xyloglucans, were solubilised by 4m KOH. The alkali-soluble hemicellulose polymers were resolved by anion-exchange chromatography into polysaccharides, mainly xyloglucans, arabinoxylan-pectic-xyloglucan, and arabinoxylan-pectic complexes. Small amounts of polysaccharide-protein-polyphenol complexes (where the polysaccharide moieties were arabinoxylans), pectic substances, and xyloglucans were also present. The glycosidic linkages of the above polymers were determined by methylation analysis. The general structural features of the cell-wall polymers are discussed.     

Modification of cell wall polysaccharides during cell elongation in Phaseolus vulgaris hypocotyls

The effect of gibberellic acid (GA) and naphthylacetic acid (NAA) on hypocotyl elongation and cell wall polysaccharides was studied using Phaseolus vulgaris seedlings grown in light condition. The hypocotyl was demarcated into two segments — one near the root was called lower and the one near the cotyledon was called upper. The upper segment showed a typical sigmoidal growth curve while lower segment did not show any growth at all. GA promoted the growth of upper segment while NAA showed clear inhibition in both the segments. Xyloglucan content showed a clear inverse correlation with growth. Pectic polysaccharides did not show a clear trend, though showed an initial inverse correlation with growth. It is concluded that degradation of low and high molecular weight xyloglucans are involved in cell wall loosening which in turn may be responsible for the elongation growth of Phaseolus hypocotyls in light.     

Changes in Wall Polysaccharides of Squash (Cucurbita maxima Duch.) Hypocotyls under Water Stress Condition: II. Composition of Pectic and Hemicellulosic Polysaccharides

Hypocotyl growth of dark-grown squash (Cucurbita maxima Duch.)seedlings was greatly reduced by the addition of polyethyleneglycol (60 mM) to the hydroponic solution through inhibitionof cell elongation. Measurement of the mechanical propertiesof the cell walls revealed that the cell wall of stressed hypocotylswas loosened as much as that of the unstressed hypocotyls, suggestingthat the stressed hypocotyl could not elongate even though thecell wall loosened. Galactose and arabinose in the pectic fraction,which are probably attached to high mol wt rhamnogalacturonans,increased under stressed as well as under unstressed condition.Other polysaccharides including pectic low mol wt galacturonans,hemicellulosic xyloglucans, galactoglucomannans, arabinans,and glucuronoarabinoxylans increased more under unstressed condition.The mol wt of xyloglucans in the hemicellulosic fraction increasedunder unstressed but not under stressed condition. These results suggest that changes in wall structure, such asincreases in high mol wt rhamnogaracturonans rich in arabinoseand galactose residues, and the suppression of polymerizationof xyloglucans are involved in the process of cell wall loosening. (Received December 15, 1986; Accepted June 8, 1987)     

Auxin-induced changes in the cell wall structure: Changes in the sugar compositions, intrinsic viscosity and molecular weight distributions of matrix polysaccharides of the epicotyl cell wall of Vigna angularis

Rapid effects of indole-3-acetic acid (IAA) on the mechanical properties of cell wall, and sugar compositions, intrinsic viscosity and molecular weight distribution of cell wall polysaccharides were investigated with excised epicotyl segments of Vigna angularis Ohwi et Ohashi cv. Takara.

• 1 IAA caused cell wall loosening as studied by stress-relaxation analysis within 15 min after the IAA application.
• 2 IAA stimulated the decrease in the content of arabinose and galactose in the hemicellulose 1 h after its application. The amounts of other component sugars in the cell wall polysaccharides remained constant during the IAA-induced segment growth.
• 3 The intrinsic viscocity of the pectin increased as early as 30 min after the IAA application. This effect was not prevented when elongation growth of the segment was osmotically suppressed by 0.15 M mannitol.
• 4 Gel permeation chromatography of the pectin on a Sepharose 4 B column demonstrated that IAA caused increase in the mass-average molecular weight of the pectin. Analysis of the sugar compositions of the pectin eluted from the Sepharose 4 B column indicated that IAA increased the molecular weight of the polysaccharides composed of uronic acid, galactose, rhamnose and arabinose. This effect became apparent within 30 min after the IAA application. Furthermore, IAA increased the molecular weight of the pectin when elongation growth of the epicotyl segments was osmotically suppressed by 0.15 M mannitol.
• 5 Hemicellulose of the cell wall chromatographed on a Sepharose CL-4 B column. Analysis of the neutral sugar compositions and the iodine staining property (specific for xyloglucans) of the polysaccharide solution eluted from the column indicated that the hemicellulose consisted of xyloglucans, arabinogalactans and polysaccharides composed of xylose and/or mannose. IAA caused a decrease in the arabinogalactan content and depolymerization of xyloglucans. These IAA effects became apparent within 30 min after the IAA application. These changes occurred even when elongation growth of the epicotyl segments was osmotically suppressed by 0.15 M mannitol.

Polymerization of the pectin, degradation of arabinogalactans and depolymerization of xyloglucans appear to be involved in the mechanism by which IAA induces cell wall loosening and therefore extension growth of cells.     

Cell-wall polysaccharides and glycoproteins of parenchymatous tissues of runner bean (Phaseolus coccineus).

1. Polymers were solubilized from the cell walls of parenchyma from mature runner-bean pods with minimum degradation by successive extractions with cyclohexane-trans-1,2-diamine-NNN'N'-tetra-acetate (CDTA), Na2CO3 and KOH to leave the alpha-cellulose residue, which contained cross-linked pectic polysaccharides and Hyp-rich glycoproteins. These were solubilized with chlorite/acetic acid and cellulase. The polymers were fractionated by anion-exchange chromatography, and fractions were subjected to methylation analysis. 2. The pectic polysaccharides differed in their ease of extraction, and a small proportion were highly cross-linked. The bulk of the pectic polysaccharides solubilized by CDTA and Na2CO3 were less branched than those solubilized by KOH. There was good evidence that most of the pectic polysaccharides were not degraded during extraction. 3. The protein-containing fractions included Hyp-rich and Hyp-poor glycoproteins associated with easily extractable pectic polysaccharides, Hyp-rich glycoproteins solubilized with 4M-KOH+borate, the bulk of which were not associated with pectic polysaccharides, and highly cross-linked Hyp-rich glycoproteins. 4. Isodityrosine was not detected, suggesting that it does not have a (major) cross-linking role in these walls. Instead, it is suggested that phenolics, presumably linked to C-5 of 3,5-linked Araf residues of Hyp-rich glycoproteins, serve to cross-link some of the polymers. 5. There were two main types of xyloglucan, with different degrees of branching. The bulk of the less branched xyloglucans were solubilized by more-concentrated alkali. The anomeric configurations of the sugars in one of the highly branched xyloglucans were determined by 13C-n.m.r. spectroscopy. 6. The structural features of the cell-wall polymers and complexes are discussed in relation to the structure of the cell walls of parenchyma tissues.     

Inhibition of fucosylation of cell wall components by 2‐fluoro 2‐deoxy‐l‐fucose induces defects in root cell elongation

Screening of commercially available fluoro monosaccharides as putative growth inhibitors in Arabidopsis thaliana revealed that 2‐fluoro 2‐l ‐fucose (2F‐Fuc) reduces root growth at micromolar concentrations. The inability of 2F‐Fuc to affect an Atfkgp mutant that is defective in the fucose salvage pathway indicates that 2F‐Fuc must be converted to its cognate GDP nucleotide sugar in order to inhibit root growth. Chemical analysis of cell wall polysaccharides and glycoproteins demonstrated that fucosylation of xyloglucans and of N‐linked glycans is fully inhibited by 10 μm 2F‐Fuc in Arabidopsis seedling roots, but genetic evidence indicates that these alterations are not responsible for the inhibition of root development by 2F‐Fuc. Inhibition of fucosylation of cell wall polysaccharides also affected pectic rhamnogalacturonan‐II (RG‐II). At low concentrations, 2F‐Fuc induced a decrease in RG‐II dimerization. Both RG‐II dimerization and root growth were partially restored in 2F‐Fuc‐treated seedlings by addition of boric acid, suggesting that the growth phenotype caused by 2F‐Fuc was due to a deficiency of RG‐II dimerization. Closer investigation of the 2F‐Fuc‐induced growth phenotype demonstrated that cell division is not affected by 2F‐Fuc treatments. In contrast, the inhibitor suppressed elongation of root cells and promoted the emergence of adventitious roots. This study further emphasizes the importance of RG‐II in cell elongation and the utility of glycosyltransferase inhibitors as new tools for studying the functions of cell wall polysaccharides in plant development. Moreover, supplementation experiments with borate suggest that the function of boron in plants might not be restricted to RG‐II cross‐linking, but that it might also be a signal molecule in the cell wall integrity‐sensing mechanism.     

Distribution of cell wall components in<Emphasis Type="Italic"> Sphagnum</Emphasis> hyaline cells and in liverwort and hornwort elaters

Spiral secondary walls are found in hyaline cells of Sphagnum, in the elaters of most liverworts, and in elaters of the hornwort Megaceros. Recent studies on these cells suggest that cytoskeletal and ultrastructural processes involved in cell differentiation and secondary wall formation are similar in bryophytes and vascular plant tracheary elements. To examine differences in wall structure, primary and secondary wall constituents of the hyaline cells of Sphagnum novo-zelandicum and elaters of the liverwort Radula buccinifera and the hornwort Megaceros gracilis were analyzed by immunohistochemical and chemical methods. Anti-arabinogalactan–protein antibodies, JIM8 and JIM13, labeled the central fibrillar secondary wall layer of Megaceros elaters and the walls of Sphagnum leaf cells, but did not label the walls of Radula elaters. The CCRC-M7 antibody, which detects an arabinosylated (16)-linked -galactan epitope, exclusively labeled hyaline cells in Sphagnum leaves and the secondary walls of Radula elaters. Anti-pectin antibodies, LM5 and JIM5, labeled the primary wall in Megaceros elaters. LM5 also labeled the central layer of the secondary wall but only during formation. In Radula elaters, JIM5 and another anti-pectin antibody, JIM7, labeled the primary wall. The distribution of arabinogalactan–proteins and pectic polysaccharides restricted to specific wall types and stages of development provides evidence for the developmental and functional regulation of cell wall composition in bryophytes. Monosaccharide-linkage analysis of Sphagnum leaf cell walls suggests they contain polysaccharides similar to those of higher plants. The most abundant linkage was 4-Glc, typical of cellulose, but there was also evidence for xyloglucans, 4-linked mannans, 4-linked xylans and rhamnogalacturonan-type polysaccharides.Abbreviations AGP Arabinogalactan–protein - Araf Arabinofuranose - Fucp Fucopyranose - GalAp Galacturonopyranose - Galp Galactopyranose - GlcAp Glucuronopyranose - HGA Homogalacturonan - Manp Mannopyranose - RG Rhamnogalacturonan - Rhap Rhamnopyranose - XG Xyloglucan - Xylp Xylopyranose     

Effect of ripening on texture, microstructure and cell wall polysaccharide composition of olive fruit (Olea europaea)

Olive fruits at the green, cherry and black stages were used to investigate the structural and microstructural changes in tissues during ripening. Scanning electron microscopy (SEM) tissue fracture of green olives resulted in cell wall breakage of epicarp and mesocarp cells. Tissue fracture resulted in fewer broken cells in cherry than in green olives and even less in black olive tissues. Cell separation occurred in the middle lamella region in some of the cells of the cherry fruit and in most of the black olive cells. Solubilization and loss of pectic polysaccharides, mainly the arabinan moiety, and glucuronoxylans occurred in the green to cherry stages. The pulp cell wall constituent polysaccharides, pectic polysaccharides, cellulose, glucuronoxylans and xyloglucans, were degraded and/or solubilized at the cherry to black ripening stages. The resultant depolymerization of the pectic polymers, especially those of the middle lamella region, was consistent with the progressive cell separation at the different ripening stages by SEM. This showed that partial solubilization of pectic, hemicellulosic and cellulosic polysaccharides within the cell wall matrix weakened the cell wall structures, preventing the breaking of cells when the tissues were fractured.     

Galactose loss and fruit ripening: high-molecular-weight arabinogalactans in the pectic polysaccharides of fruit cell walls

Cell wall material (CWM) was prepared from nine fruit species at two ripening stages (unripe and ripe) and extracted sequentially with 0.05 M trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (CDTA), 0.05 M Na₂CO₃ and 4 M KOH. Each solubilised fraction and the CWM-residue remaining after 4 M KOH extraction was analysed for non-cellulosic sugar composition. A common pattern of distribution for polyuronide and pectin-associated neutral sugar was observed for all unripe fruit. Most polyuronide was extracted in the CDTA/Na₂CO₃ fractions while 70–93% of the neutral sugar was located on pectic polysaccharides in the 4 M KOH-soluble and CWM-residue fractions. During ripening, most of the galactose was lost from pectic polysaccharides in the CWM-residue. Partial solubilisation of these polysaccharides was achieved by treating the CWM-residue with endopolygalacturonase. The solubilised polysaccharides were separated into two fractions by ion-exchange chromatography. One of these contained polysaccharides with average molecular weights of 400 kDa or larger and consisted of between 70 and 90% arabinogalactan. The galactosyl residues were 80–90% β-1→4 linked, indicating largely unbranched side-chains. The arabinosyl residues were distributed among terminal, 3-, 5-, 2,5-, and 2,3,5-linked residues, indicating a highly ramified structure. The results are discussed with regard to the relationship between pectin solubilisation and galactose loss and their respective contribution to fruit softening. Received: 28 January 1997 / Accepted: 11 March 1997     

Structure of the Primary Cell Walls of Suspension-Cultured Rosa glauca Cells: I. Polysaccharides Associated with Cellulose

Cell walls of suspension-cultured cells of Rosa glauca were fractionated by two different extraction procedures. The first involved a stepwise fractionation scheme based on alkaline extraction. The second took advantage of the powerful cellulose solvent system N-methylmorpholine N-oxide/dimethyl sulfoxide which is capable of solubilizing whole cell walls. From the analytical composition of each solubilized fraction and of the corresponding residues, the fate of each type of cell wall polysaccharide constituent was followed at each step of the extraction scheme and the mode of action of the extractant was interpreted. Although the two fractionation procedures were very different, they yielded very similar cellulosic complex residues and extracts, thus delimiting two blocks of polysaccharides in the cell wall. The cellulose residues still comprised uronic acid-containing polysaccharides and hemicelluloses in association with cellulose. Graded acid hydrolysis provided evidence for the central role of a homogalacturonan core interconnecting xyloglucans and arabinogalactans. A tentative model showing the possible interaction existing between the constituent polysaccharides still associated to cellulose after alkaline extraction is presented. Hydrogen bonding between xyloglucan and cellulose is confirmed, and glycosidic linkages between xyloglucans and pectic polymers are suggested.     

Turnover of cell wall polysaccharides of a Vinca rosea suspension culture

Turnover of cell wall components was examined in two growth phases of a batch suspension culture of Vinca rosea L. Three-day-cultured cells (cell division phase) and 5-day-cultured cells (cell expansion phase) were incubated with d -[U-¹⁴C]glucose. After various periods of incubation, extra-cellular polysaccharides (ECP) and cell walls were isolated, and then the cell walls were fractionated to pectic substance, hemicellulose, and cellulose fractions. The results of the measurement of radioactivities and amounts of total carbohydrate in the ECP and cell wall fractions indicated that synthesis of pectic substance was more active in the cell division phase than in the cell expansion phase. From the results of the pulse-chase experiments, in which cells prelabelled by incubation with d -[U-¹⁴C]glucose for 3 h were incubated in a medium containing unlabelled glucose for various periods, the gross degradation, net synthesis, and gross synthesis of cell wall components were estimated. Active degradation and synthesis were observed in the hemicellulose fraction, indicating that active turnover occurred in the hemicellulose fraction, while little degradation was found in the pectic substance and cellulose fractions.     

Crystallinity of lyophilised carrot cell wall components

The aim of this work was to investigate the effect of removal of cell wall components on the crystallinity of cell walls using X-ray diffraction. Various insoluble cell wall residues were prepared following a sequential extraction of carrot cell wall material. X-ray diffraction patterns were typical of cellulose although there was a possible contribution of pectic polysaccharides to the crystallinity. As more amorphous material was removed to produce a cellulose rich residue, the crystallinity index increased from 12 to 16%, larger than that estimated from cellulose alone. For the last residue treated with 4M KOH, a lower value of crystallinity was found (14%) which resulted from the change of some crystalline domains of cellulose into amorphous regions. Pressing conditions (temperature, water content) have been investigated and did not alter the crystallinity index significantly.     

Composition of the walls of pollen grains of the seagrass Amphibolis antarctica

The composition of walls isolated from pollen grains of the seagrass Amphibolis antarctica was determined. Glucose, galactose, and rhamnose were the major neutral monosaccharides in the wall polysaccharides, and fucose, arabinose, xylose, and mannose were present in minor proportions. No apiose, a monosaccharide present in the wall polysaccharides of the vegetative parts of the seagrass Heterozostera tasmanica, was found. Large amounts of uronic acid (mainly as galacturonic acid) were found in the walls. The monosaccharides were probably present in cellulose and pectic polysaccharides, the latter comprising neutral pectic galactans, and rhamnogalacturonans containing high proportions of rhamnose. The walls contained a small amount of protein; glycine and lysine were the amino acids present in the highest proportions. Histochemical examination of isolated walls confirmed the presence of polyanionic components (pectic polysaccharides), -glucans (cellulose), and protein. The composition of the walls is discussed in relation to analyses of the walls of pollen grains and vegetative organs of other plants.     

Comparative characterization of degraded and non-degradative hemicelluloses from barley straw and maize stems: Composition, structure, and thermal properties

Three organic solvents and one aqueous alkaline solution for fully fractional dissolving hemicelluloses from mild ball-milled cell wall of lignified barley straw and maize stems are described: 90% neutral dioxane, 80% dioxane containing 0.05 M HCl, dimethyl sulfoxide (DMSO), and 8% aqueous KOH. The four successive extractions resulted in dissolution of 94.6% and 96.4% of the original hemicelluloses and 93.7% and 95.3% of the original lignin from barley straw and maize stems, respectively. The structures of the hemicellulosic fractions released during the treatment with the neutral solvents of 90% dioxane and DMSO was found to remain intact, while the extractions with 80% acidic dioxane and 8% KOH under the conditions used resulted in a partial depolymerization of dissolved polysaccharides by cleavage of the glycosidic bonds and saponification of the ester groups in the polymers. The 90% neutral dioxane-soluble hemicellulosic fractions consisted mainly of the more branched arabinoxylans and mixed-linkage glucans such as β-glucans, whereas the hemicellulosic fractions solubilized during the sequential treatments with 80% acidic dioxane, DMSO, and 8% KOH are composed of arabino-(4-O-methyl-d-glucurono) xylans as the major hemicellulosic materials. In addition, the hemicellulosic polymers contained small amounts of ferulic and p-coumaric acids and lignins, revealing that the hemicelluloses removed are mostly unbound to the lignins in the cell walls of cereal straws. This non-degradative cell wall dissolution offers the potential to analyze polysaccharide components for the first time, and improve current hemicellulosic isolation method by using high concentration of aqueous alkali from the delignified cell walls.     

Altered cell wall disassembly during ripening of Cnr tomato fruit: implications for cell adhesion and fruit softening

The Cnr ( C olourless n on- r ipening) tomato ( Lycopersicon esculentum Mill.) mutant has an aberrant fruit-ripening phenotype in which fruit do not soften and have reduced cell adhesion between pericarp cells. Cell walls from Cnr fruit were analysed in order to assess the possible contribution of pectic polysaccharides to the non-softening and altered cell adhesion phenotype. Cell wall material (CWM) and solubilised fractions of mature green and red ripe fruit were analysed by chemical, enzymatic and immunochemical techniques. No major differences in CWM sugar composition were detected although differences were found in the solubility and composition of the pectic polysaccharides extracted from the CWM at both stages of development. In comparison with the wild type, the ripening-associated solubilisation of homogalacturonan-rich pectic polysaccharides was reduced in Cnr. The proportion of carbohydrate that was chelator-soluble was 50% less in Cnr cell walls at both the mature green and red ripe stages. Chelator-soluble material from ripe-stage Cnr was more susceptible to endo-polygalacturonase degradation than the corresponding material from wild-type fruit. In addition, cell walls from Cnr fruit contained larger amounts of galactosyl- and arabinosyl-containing polysaccharides that were tightly bound in the cell wall and could only be extracted with 4 M KOH, or remained in the insoluble residue. The complexity of the cell wall alterations that occur during fruit ripening and the significance of different extractable polymer pools from cell walls are discussed in relation to the Cnr phenotype.