Cell Wall Matrix Polysaccharides Research Articles

Formation of plant cell wall supramolecular structure

Plant cell wall is an example of a widespread natural supramolecular structure: its components are considered to be the most abundant organic compounds renewable by living organisms. Plant cell wall includes numerous components, mainly polysaccharidic; its formation is largely based on carbohydrate-carbohydrate interactions. In contrast to the extracellular matrix of most other organisms, the plant cell compartment located outside the plasma membrane is so structured that has been named "wall". The present review summarizes data on the mechanisms of formation of this supramolecular structure and considers major difficulties and results of research. Existing approaches to the study of interactions between polysaccharides during plant cell wall formation have been analyzed, including: (i) characterization of the structure of natural polysaccharide complexes obtained during cell wall fractionation; (ii) analysis of the interactions between polysaccharides "at mixing in a tube"; (iii) study of the interactions between isolated individual plant cell wall matrix polysaccharides and microfibrils formed by cellulose-synthesizing microorganisms; and (iv) investigation of cell wall formation and modification directly in plant objects. The key stages in formation of plant cell wall supramolecular structure are defined and characterized as follows: (i) formation of cellulose microfibrils; (ii) interactions between matrix polysaccharides within Golgi apparatus substructures; (iii) interaction between matrix polysaccharides, newly secreted outside the plasma membrane, and cellulose microfibrils during formation of the latter; (iv) packaging of the formed complexes and individual polysaccharides in cell wall layers; and (v) modification of deposited cell wall layers.

Characterization of the cell wall matrix polysaccharides and glycoside-hydrolyzing enzymes of Distylium racemosum callus

The non-cellulosic (matrix) polysaccharides found in the cell walls of callus tissues derived from healthy Distylium racemosum leaves have been analyzed in this study. The amounts of rhamnose, arabinose, and glucose in the cell walls increased 2-fold over the culture period of 70 d, but galactose content remained more or less constant. Comparisons were also made among the polysaccharides found in callus tissues, those from healthy leaves, and those from aphid-induced galls in D. racemosum leaves. After successive extraction with 50 mM CDTA, 50 mM Na 2CO 3, 1 M KOH, and 4 M KOH, the amounts of pectic fractions (CDTA- and Na 2CO 3-soluble) from the cell walls of callus, gall, and leaf tissues accounted for 17%, 11%, and 4%, respectively, of cell wall dry weight. The callus cell walls had less xylose in 4 M KOH-soluble polymers (HII-2 and HII-3) fractionated by anion-exchange chromatography than did the cell walls from healthy leaves. Polysaccharides in fractions HII-2 and HII-3 from callus cell walls were subfractionated into the void fraction, a 250 kDa fraction, and a 40 kDa fraction by size-exclusion chromatography. These results appear to more closely resemble the situation in the aphid-induced gall tissues than that in the leaf tissues. In addition, the activities of β-xylosidase and α- l-arabinofuranosidase in the LiCl-soluble protein fraction increased notably during callus development.

Cell wall disassembly during papaya softening: Role of ethylene in changes in composition, pectin-derived oligomers (PDOs) production and wall hydrolases

Cell wall disassembly in ripening climacteric fruit is a highly complex process where ethylene plays a crucial role. Ethylene inhibitors can be used to explore the changes in the cell wall matrix and cross-linked polysaccharides in ethylene-regulated processes. The results of applying the ethylene receptor blocking inhibitor 1-methylcyclopropene (1-MCP) and the ethylene-releasing compound ethephon (2-chloroethylphosphonic acid) indicate that softening of ‘Maradol’ papaya fruit is dependent on ethylene. When fruit were induced to ripen extensively by exposure to a high dose of ethephon, 1-MCP inhibited the subsequent softening dramatically, but when inhibition of the ethylene response was caused by application of 1-MCP, subsequent fruit treatment with ethephon promoted extensive loss of galactose from the water-soluble polysaccharides, but this was not accompanied by fruit softening. The cell wall changes accompanying normal fruit softening were pectin solubilization and polyuronide depolymerization and these processes occurred simultaneously. Polygalacturonase likely is responsible for the ripening-associated changes in ‘Maradol’ papaya fruit texture and pectin polymer integrity. An increase in extractable fruit polygalacturonase follows the increased presence of pectin-derived oligosaccharides.

Genome-wide analysis of the UDP-glucose dehydrogenase gene family in Arabidopsis, a key enzyme for matrix polysaccharides in cell walls

Arabidopsis cell walls contain large amounts of pectins and hemicelluloses, which are predominantly synthesized via the common precursor UDP-glucuronic acid. The major enzyme for the formation of this nucleotide-sugar is UDP-glucose dehydrogenase, catalysing the irreversible oxidation of UDP-glucose into UDP-glucuronic acid. Four functional gene family members and one pseudogene are present in the Arabidopsis genome, and they show distinct tissue-specific expression patterns during plant development. The analyses of reporter gene lines indicate gene expression of UDP-glucose dehydrogenases in growing tissues. The biochemical characterization of the different isoforms shows equal affinities for the cofactor NAD(+) ( approximately 40 microM) but variable affinities for the substrate UDP-glucose (120-335 microM) and different catalytic constants, suggesting a regulatory role for the different isoforms in carbon partitioning between cell wall formation and sucrose synthesis as the second major UDP-glucose-consuming pathway. UDP-glucose dehydrogenase is feedback inhibited by UDP-xylose. The relatively (compared with a soybean UDP-glucose dehydrogenase) low affinity of the enzymes for the substrate UDP-glucose is paralleled by the weak inhibition of the enzymes by UDP-xylose. The four Arabidopsis UDP-glucose dehydrogenase isoforms oxidize only UDP-glucose as a substrate. Nucleotide-sugars, which are converted by similar enzymes in bacteria, are not accepted as substrates for the Arabidopsis enzymes.

Differential changes in cell wall matrix polysaccharides and glycoside-hydrolyzing enzymes in developing wheat seedlings differing in drought tolerance

The growth kinetics and variations in cell wall matrix polysaccharides and glycoside hydrolases during seedling development of the drought-tolerant wheat cultivar (cv. Hong Mang Mai) were compared with the drought-sensitive cultivar (cv. Shirasagikomugi). After 15 d of culture in water at 22 degrees C under constant irradiance of 98 micromol m(-2) s(-1), the length of the coleoptile and leaf sheath of Hong Mang Mai seedlings was 1.7 times longer than those of Shirasagikomugi seedlings. In the cell walls isolated from coleoptiles and leaf sheaths of the seedling of the two cultivars, the contents of arabinose, xylose, and glucose changed during development. The cell walls were fractionated progressively with 50 mM CDTA, 50 mM Na(2)CO(3), 1 M KOH and 4 M KOH, and sugar composition was determined. The amount of CDTA-soluble fraction from the Hong Mang Mai cell walls was 2.4-fold higher than that from the Shirasagikomugi cell walls at 6 d of culture, and a considerable decrease was observed during development. The ratio of arabinose to xylose in 1 M KOH-soluble fraction from the two cultivars decreased. The amount of 4 M KOH-soluble fraction from the Shirasagikomugi cell walls was affected much more than those of the Hong Mang Mai cell walls. Many glycoside hydrolase activities were detected in the protein fractions from coleoptiles and leaf sheaths of the two cultivars, and the activities of licheninase, 1,3-1,4-beta-glucanase, and 1,3-beta-glucanase in the LiCl-soluble protein fraction increased drastically during development of the Shirasagikomugi seedlings. These findings suggest that the metabolism of the cell wall matrix polysaccharides of the drought-tolerant wheat cultivar is far different from that of the drought-sensitive wheat cultivar during seedling development.

Papaya fruit softening, endoxylanase gene expression, protein and activity

Papaya (Carica papaya L.) cell wall matrix polysaccharides are modified as the fruit starts to soften during ripening and an endoxylanase is expressed that may play a role in the softening process. Endoxylanase gene expression, protein amount and activity were determined in papaya cultivars that differ in softening pattern and in one cultivar where softening was modified by the ethylene receptor inhibitor 1-methylcyclopropene (1-MCP). Antibodies to the endoxylanase catalytic domain were used to determine protein accumulation. The three papaya varieties used in the study, 'Line 8', 'Sunset', and 'Line 4-16', differed in softening pattern, respiration rate, ethylene production and showed similar parallel relationships during ripening and softening in endoxylanase expression, protein level and activity. When fruit of the three papaya varieties showed the respiratory climacteric and started to soften, the level of endoxylanase gene expression increased and this increase was related to the amount of endoxylanase protein at 32 kDa and its activity. Fruit when treated at less than 10% skin yellow stage with 1-MCP showed a significant delay in the respiratory climacteric and softening, and reduced ethylene production, and when ripe was firmer and had a 'rubbery' texture. The 1-MCP-treated fruit that had the 'rubbery' texture showed suppressed endoxylanase gene expression, protein and enzymatic activity. Little or no delay occurred between endoxylanase gene expression and the appearance of activity during posttranslational processing from 65 to 32 kDa. The close relationship between endoxylanase gene expression, protein accumulation and activity in different varieties and the failure of the 1-MCP-treated fruit to fully soften, supported de novo synthesis of endoxylanase, rapid posttranslation processing and a role in papaya fruit softening.

The inositol oxygenase gene family of Arabidopsis is involved in the biosynthesis of nucleotide sugar precursors for cell-wall matrix polysaccharides

The nucleotide sugar UDP-glucuronic acid (UDP-GlcA) is the principal precursor for galacturonic acid, xylose, apiose and arabinose residues of the plant cell-wall polymers. UDP-GlcA can be synthesized by two different functional pathways in Arabidopsis involving either UDP-glucose dehydrogenase or inositol oxygenase as the initial enzyme reaction to channel carbohydrates into a pool of UDP sugars used for cell-wall biosynthesis. The genes for the enzyme myo-inositol oxygenase (MIOX) were analyzed in Arabidopsis. They represent a small gene family containing four members. The transcription of all those members indicates a transient and organ-specific gene expression pattern in growing plant tissues as analyzed by RT-PCR and in promoter::GUS reporter gene lines. Two isoforms (MIOX1, MIOX2) are expressed in almost all tissues of the plant, whereas the expression of MIOX4 and MIOX5 is largely restricted to flowers, particularly maturing pollen. T-DNA insertion lines in MIOX genes were isolated; however, single knock-outs show growth phenotypes similar to the wild type. The monosaccharide composition of the cell wall in these mutants is not significantly changed compared to wild type plants. However, the incorporation of 3H-inositol into wall polymers of seedlings is greatly impaired in the mutant lines (Delta)MIOX1 and (Delta)MIOX2, which are the only isoforms that are expressed in seedlings.

Suppression of Avocado (Persea americana Mill.) Fruit Softening and Changes in Cell Wall Matrix Polysaccharides and Enzyme Activities: Differential Responses to 1-MCP and Delayed Ethylene Application

Pre-ripe `Booth 7' avocado (Persea americana Mill.) fruit, a cross of West Indian and Guatemalan strains, were treated with 0.9 μL·L-1 1-methylcyclopropene (1-MCP) for 12 hours at 20 °C. After storage for 18 days in air at 13 °C, at which time whole fruit firmness values averaged about 83 N, half of the 1-MCP-treated fruit were treated with 100 μL·L-1 ethylene for 12 hours and then transferred to 20 °C. 1-MCP delayed softening, and fruit treated with 1-MCP retained more green color than air-treated fruit when full ripe (firmness 10 to 15 N). 1-MCP affected the activities of pectinmethylesterase (EC 3.2.1.11), α-(EC 3.2.1.22) and β-galactosidases (EC 3.2.1.23), and endo-β-1,4-glucanase (EC 3.2.1.4). The appearance of polygalacturonase (EC 3.2.1.15) activity was completely suppressed in 1-MCP-treated fruit for up to 24 days, at which time the firmness of 1-MCP-treated fruit had declined nearly 80% compared with initial values. The effect of exogenous ethylene applied to partially ripened 1-MCP-treated fruit differed for different ripening parameters. Ethylene applied to mid-ripe avocado exerted no effect on the on-going rate or final extent of softening of 1-MCP-treated fruit, even though polygalacturonase and endo-1,4-β-glucanase activities increased in response to ethylene. β-galactosidase decreased in 1-MCP-treated fruit in response to ethylene treatment. 1-MCP delayed the increase in solubility and depolymerization of water- and CDTA (1,2-cyclohexylenedinitrilotetraacetic acid)-soluble polyuronides, likely due to reduced polygalacturonase activity. At the full-ripe stage, the levels of arabinose, galactose, glucose, mannose, rhamnose, and xylose associated with the CDTA-soluble polyuronide fraction were similar among all treatments. In contrast, the galactose levels of water-soluble polyuronides declined 40% and 17% in control and 1-MCP treated fruit, respectively. Hemicellulose neutral sugar composition was unaffected by 1-MCP or ethylene treatment. The data indicate that the capacity of avocado fruit to recover from 1-MCP-mediated suppression of ripening can be only partially amended through short-term ethylene application and differs significantly for different ripening parameters.

Altered matrix polysaccharides in cell walls of pocket galls formed by an aphid on Distylium racemosum leaves

ABSTRACTThe present work reports the results of a study on the isolation and characterization of matrix polysaccharides in the cell walls of galls formed by an aphid (Neothoracaphis yanonis) on Distylium racemosum leaves. Cell walls were isolated from both healthy Distylium leaf and gall tissues and then extracted sequentially with cyclohexane‐trans‐1,2‐diaminetetra‐acetate (CDTA), Na2CO3, 1 m KOH, and 4 m KOH. The amount of pectin solubilized from gall cell walls was approximately 2.6‐fold higher than the pectin solubilized from leaf cell walls, whereas the amount of hemicellulose solubilized from gall cell walls was 1.4‐fold higher than that from normal leaf cell walls. When the polysaccharides were fractionated by anion‐exchange chromatography, considerable increases in arabinose and galactose were observed in CDTA‐soluble pectic polymer (fraction PI‐1) from gall cell walls, whereas the gall cell walls had less xylose in 1 m KOH‐soluble hemicellulosic polymers (fractions HI‐2, HI‐3, and HI‐4) than did the cell walls from the healthy leaf. The hemicellulosic polymers of the gall cell walls exhibited distinctly different patterns of molecular mass, compared with the healthy leaf cell walls. These results suggest that an extensive change occurs in the matrix polysaccharide structure of the cell walls of Distylium galls formed by an aphid. In addition, many glycosylhydrolase activities were detected in the protein fraction solubilized with strong saline solution from the gall cell walls, and the activities of β‐galactosidase, β‐xylosidase and α‐l‐arabinofuranosidase were considerably increased under gall formation.

Comparative subcellular immunolocation of polypeptides associated with xylan and callose synthases in French bean (Phaseolus vulgaris) during secondary wall formation

The Golgi apparatus of plant cells is thought to be the main site of synthesis of cell wall matrix polysaccharides and the terminal glycosylation of glycoproteins. Much of this evidence still depends on earlier biochemical studies employing subcellular fractionation. However acquiring pure Golgi membranes is still difficult and the question of spatial organisation of glycosyl transferases can be addressed by immunolocation of the enzymes. An antibody to a xylan synthase-associated polypeptide from French bean, the enzyme which synthesises the core polysaccharide for secondary wall xylan, has been raised and shown to inhibit its activity. Xylan is deposited in secondary thickenings and the xylan synthase was only detected in appreciable amounts in developing xylem cells. The location within the Golgi stack was observed throughout the dictyosomes. Some enzyme subunits were also detected in post-Golgi vesicles. A second antibody to a non-catalytic Mr 65 000 subunit of β 1,3- glucan (callose) synthase was used for a comparative study. Although the bulk of this enzyme has been detected in previous studies at plasmamembrane-wall interfaces in sieve plates and stressed tissue, a Golgi-location can be observed in root tip meristematic cells during cell plate formation. The enzyme was present throughout the stacks. Callose was also immunolocated in a similar manner to xylan in secondary walls and thickenings and in pits in developing xylem. In these cells, the callose synthase was detected at the surface of the growing thickenings and the plasmamembrane within the pits.

Microscopic studies on mature flax fibers embedded in LR white: immunogold localization of cell wall matrix polysaccharides.

Flax fibers have been the subject of many biochemical studies, which revealed that cellulose and pectins are the major constituents of their walls. In contrast, little is known about the location of these polymers within the walls of mature fibers by microscopic methods. This has been technically hampered by the very thick secondary wall of fibers, resulting in inadequate tissue preservation unsuitable for immunogold microscopy. In this study, we adapted the basic chemical fixation, dehydration and infiltration methods to achieve a good preservation of the cell structures of mature fibers and reduced damage to antigens. We were able to apply postembedding immunocytochemical techniques to map the location of various pectic epitopes within the walls of mature fibers. Our immunolabeling data show that homogalacturonans were exclusively found in the middle lamellae and the cell junctions but were not detectable in the secondary wall. In contrast, rhamnogalacturonan I (RG I)-associated epitopes, as well as galactan and arabinan epitopes, were abundantly distributed over the secondary wall of mature fibers.

Influence of 1-methylcyclopropene (1-MCP) on ripening and cell-wall matrix polysaccharides of avocado (Persea americana) fruit

Abstract West Indian-type avocado (Persea americana Mill. cv. ‘Simmonds’) fruit were treated with two different concentrations (0.09 and 0.45 μl l−1) of 1-methylcyclopropene (1-MCP) for three exposure times (6, 12, and 24 h) at 20 °C. The fruit were then stored at 20 °C in ethylene-free air for ripening assessment. Firmness, weight loss, respiration and C2H4 production, peel color, cell-wall enzymes (polygalacturonase (PG), pectinmethylesterase, α-,β-galactosidase, and Cx-cellulase) and cell-wall matrix polysaccharides (polyuronides and hemicellulose) were monitored during storage. 1-MCP treatment at 0.45 μl l−1 for 24 h at 20 °C delayed the ripening of avocado fruit by 4 days at 20 °C. This delay was characterized by a significant reduction in the rate of fruit softening and in the timing and intensity of the ethylene and respiratory climacterics. Avocado treated with 1-MCP (0.45 μl l−1) for 24 h at 20 °C also showed significantly less weight loss and retained more green color than control fruit at the full-ripe stage (10–20 N). The delay in avocado ripening was influenced by 1-MCP concentration, exposure duration, and exposure temperature. 1-MCP treatment affected the activity trends of all cell-wall enzymes measured and completely suppressed increases in PG activity for up to 12 days. Consistent with the activity trends of PG, polyuronides from 1-MCP treated fruit when fully ripe exhibited less extensive molecular mass downshifts compared with the control fruit. The data indicate that the primary phase of avocado fruit softening occurs in the absence of appreciable PG activity. 1-MCP treatment also delayed and slightly reduced the depolymerization of 4 M alkali-soluble hemicelluloses, including xyloglucan.

Molecular characterisation of a membrane-bound galactosyltransferase of plant cell wall matrix polysaccharide biosynthesis.

Galactomannan biosynthesis in vitro is catalysed by membrane preparations from developing fenugreek seed endosperms. Two enzymes interact: a GDP-mannose dependent (1-->4)-beta-D-mannan synthase and a UDP-galactose dependent (1-->6)-alpha-D-galactosyltransferase. The statistical distribution of galactosyl substituents along the mannan backbone, and the degree of galactose substitution of the primary product of galactomannan biosynthesis appear to be regulated by the specificity of the galactosyltransferase. We now report the detergent solubilisation of the fenugreek galactosyltransferase with retention of activity, the identification on gels of a putative 51 kDa galactosyltransferase protein, and the isolation, cloning and sequencing of the corresponding cDNA. The solubilised galactosyltransferase has an absolute requirement for added acceptor substrates. Beta-(1-->4)-linked D-manno-oligosaccharides with chain lengths greater than or equal to 5 acted as acceptors, as did galactomannans of low to medium galactose-substitution. The putative galactosyltransferase cDNA encodes a 51282 Da protein, with a single transmembrane alpha helix near the N terminus. We have also confirmed the identity of the galactosyltransferase by inserting the cDNA in frame into the genome of the methylotrophic yeast Pichia pastoris under the control of an AOX promoter and the yeast alpha secretion factor and observing the secretion of galactomannan alpha-galactosyltransferase activity. Particularly high activities were observed when a truncated sequence, lacking the membrane-spanning helix, was expressed.

Effect of GA3 on the Molecular Mass of Polyuronides in the Cell Walls of Alaska Pea Roots

3The role of cell wall matrix polysaccharides in gibberellin-regulated root growth is unknown. We examined pectic polysaccharides from pea roots treated with or without gibberellin A3 (GA3) in the presence of ancymidol, an inhibitor of gibberellin biosynthesis. Pectic polymers solubilized by CDTA (trans-l,2-cyclohexanediamineA r ,iV,./V,W-tetraacetic acid) at 23°C and subjected to gel permeation analysis exhibited high polydispersity with a molecular mass in excess of 500 kDa. Subsequent extraction of cell walls with CDTA at 100°C solubilized polymers with an average mol mass of 10 to 40 kDa. Subjecting the high molecular mass pectic polymers extracted at 23 °C to 70-100°C for 2h generated 10 to 40 kDa fragments, similar in size distribution to those solubilized directly from cell walls by CDTA solutions at 100°C. Pectic polymers from (GA 3+Anc)-treated roots were of higher average mol mass than those from Anc-treated roots in both the elongation zone and in the basal maturation zone. Since (GA3 + Anc)-treated roots elongate more quickly than Anc-treated roots [Tanimoto (1994) Plant Cell Physiol. 35:1019], the slender, GA3-treated roots may produce and deposit highly integrated pectins more rapidly than the thicker, Anc-treated roots in the elongating or elongated cell walls.

Effect of Brefeldin A on the synthesis and transport of cell wall polysaccharides and proteins in pea root seedlings

The in vivo effect of Brefeldin A (BFA) on the synthesis and transport of cell wall polysaccharides and proteins in the roots of pea seedlings (Pisum sativum L. cv. Alaska) was investigated. BFA (10μgml—1 inhibited the synthesis of cell wall matrix polysaccharides by approximately 43%. Under the same conditions, cellulose synthesis was inhibited by approximately 77%. The percentage of incorporation of L—[U—14C]leucine and L-[U-14C]proline into cytosolic, membrane and cell wall proteins was only slightly changed in the presence of BFA. In addition, the drug did not change the pattern of newly synthesized proteins in the three fractions as judged by SDS—PAGE fluorography. Double labelling of proteins and cell wall polysaccharides confirmed the above reported data. All these results showed that the synthesis and transport of proteins to the cell wall was only slightly affected by BFA under similar conditions to those which brought about a strong inhibition of the synthesis of matrix and cellulosic polysaccharides. BFA had no effect on the activity of membrane-bound and digitonin-solubilized mannan and glucomannan synthase isolated from the third internode of pea seedlings. This would exclude an effect of BFA at the level of the catalytic site of the synthases. The inhibition of polysaccharide synthesis by the drug was rapidly eliminated after its removal. It is concluded that the effect of BFA on the biosynthesis of cell wall polysaccharides could be caused by an interaction of the drug with the topological organization of the synthase complexes in the membranes. This effect would precede the action of the drug at the level of vesicle transport to the walls.

Accumulation of diferulic acid during the hypersensitive response of oat leaves to Puccinia coronataf.sp. avenaeand its role in the resistance of oat tissues to cell wall degrading enzymes

The relationship between diferulic acid formation and locally induced resistance was investigated in the interactions of two physiological races of Puccinia coronataf.sp. avenaewith Shokan 1 oat. Diferulic acid was detected in the hemicellulosic fraction extracted with oxalic acid from the cell wall. The amount of ferulic acid bound in the cell wall matrix polysaccharides did not vary in uninoculated and inoculated primary leaves of oats during the time course of the experiment. In contrast, the formation of diferulic acid bound to wall polysaccharides became significantly higher in the incompatible than the compatible interaction at approx. 36h after inoculation. The timing of increased formation of diferulic acid was correlated with the accumulation of avenalumins and inhibition of protoplast liberation from infected primary leaves. Activities of soluble, and of ionically- and covalently-bound cell wall peroxidases from uninoculated and inoculated leaves were measured. Ionically-bound cell wall peroxidase activity increased in the incompatible interactions at about 36h after inoculation. This was the same time that increased levels of diferulic acids were observed. This may indicate that the cross-linking of matrix polysaccharides by ferulic acids bound in cell walls is caused by a coupling reaction initiated by ionically-bound cell wall peroxidases. It is postulated that the diferulic acid formation occurs in oat cell walls at the infection sites in incompatible interactions and may contribure to locally induced resistance in oats by providing a barrier to pathogen ingress.

The supramolecular organization of red algal cell membranes and their participation in the biosynthesis and secretion of extracellular polysaccharides: a review

The relationship between the supramolecular organization of red algal cell membranes and the biosynthesis and secretion of the cell wall skeletal and matrix polysaccharides is reviewed. Freeze-fracture studies have revealed that organized macromolecular structures — “linear terminal complexes” and “tetrads” — are present on the plasma membrane and on membranes of the endomembrane system. The “linear terminal complexes” seem to be involved in the biosynthesis, assembly, and orientation of the cellulose microfibrils and the “tetrads” in the synthesis of the matrix polysaccharides. It is shown how the research on the supramolecular organization of cell membranes has increased the knowledge on the biosynthesis and secretion of the extracellular crystalline and non-crystalline polysaccharides in red algae. In this review, the progress to date is discussed.

The Relationship between the Constituents of Cell Wall Polysaccharides and Hardness of Brined Ume Fruit.

The cell wall polysaccharides in fresh and brined ume fruits were fractionated, and the relation between their chemical composition and hardness was investigated. The main components of each cell wall polysaccharide were as follows: pectin fraction (PS) containing galacturonic acid (AGA), hemicellulose I fraction (HC-I) containing neutral sugars and proteins, hemicellulose II (HC-II) containing neutral sugars and ash, and cellulose fraction (CL) containing neutral sugars. In the Control (ume fruit brined with NaCl solution), there was a decrease in HC-I and CL in the cell Wall. and an increase in PS, as well as a softening of texture. On the other hand, a decrease of PS and an increase of CL Were observed in the Ca-added group (ume fruit brined with NaCl solution and Ca hydroxide), which maintained a hard texture. A decrease in the methoxyl group and an increase in ash and Ca content were observed in PS of the Ca-added group. A decrease of neultral sugar (especially, glucose composition) and an increase in ash, Ca and AGA content were observed in CL. CL contained AGA and neutral sugars such as arabinose and galactose, which were thought to be firmly bound to cellulose microfibrils. Therefore, it was assumed that the hardness in Umezuke may reflect a difference in the mechanism of bonding between CL existing in the Secondary cell Wall and other matrix polysaccharides.

Cellulose Hydrolysis by Bacteria and Fungi

The chapter focuses on the recent advances in understanding the structural and functional organization of individual cellulases, their regulation, and the ways in which the multiple enzyme components of cellulolytic systems cooperate. It overviews the cellulose structures because cellulose is more than a homopolymer of β-1 ,4 linked glucose units. An appreciation of its complex physical organization and its interactions with other plant cell wall components is central for understanding of the mechanisms of cellulase action. Cellulose nearly always occurs in close association with plant cell wall matrix polysaccharides so that enzymes such as xylanases are intimately involved in the attack of cellulose in vivo. Cellulases effect important changes to their substrate before releasing soluble products and the key to understanding cellulase action rest in the examination of these events. Progress in this area is limited by the availability of appropriate analytical tools although new techniques, such as atomic force microscopy are promising. The properties of cellulases are profoundly altered by the presence of trace enzyme contaminants. Future studies in vitro are proposed to be restricted to enzymes from recombinant sources. The reasons for the individual cellulolytic bacteria and fungi requiring many related cellulases with specificities that overlap is still not clear, but perhaps this is because the complexity of the substrates and of the task these microorganisms face is underestimated.

Influence of avocado (Persea americana) Cx-cellulase on the structural features of avocado cellulose

Avocado (Persea americana Mill.) fruit produce copious quantities of the enzyme Cx-cellulase (EC 3.2.1.4) during ripening. The possibility that Cx-cellulase is able to disrupt cellulose microfibril oranization was investigated using molecular weight (Mr), x-ray diffraction, and ultrastructural analyses of cell walls from unripe avocado fruit incubated with the purified enzyme. Results indicate that Cx-cellulase causes a downshift in the Mr of unbranched cell-wall polymers in the Mr range of 106–107 Da. There is an increase in the proportion of crystalline cellulose, and cellulose fibrils appear to lose cohesiveness in response to enzyme activity. We propose that Cx-cellulase attacks avocado cellulose at accessible sites in the peripheral and integral noncrystalline regions of the microfibril, resulting in a loss of cohesiveness within the fibril structure and an alteration in the binding of associated cell-wall matrix polysaccharides. The initial loss of avocado mesocarp firmness during fruit ripening may be linked to the onset of Cx-cellulase activity.