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.     

Structure of Plant Cell Walls : XIX. Isolation and Characterization of Wall Polysaccharides from Suspension-Cultured Douglas Fir Cells

The partial purification and characterization of cell wall polysaccharides isolated from suspension-cultured Douglas fir (Pseudotsuga menziesii) cells are described. Extraction of isolated cell walls with 1.0 m LiCl solubilized pectic polysaccharides with glycosyl-linkage compositions similar to those of rhamnogalacturonans I and II, pectic polysaccharides isolated from walls of suspension-cultured sycamore cells. Treatment of LiCl-extracted Douglas fir walls with an endo-α-1,4-polygalacturonase released only small, additional amounts of pectic polysaccharide, which had a glycosyl-linkage composition similar to that of rhamnogalacturonan I. Xyloglucan oligosaccharides were released from the endo-α-1,4-polygalacturonase-treated walls by treatment with an endo-β-1,4-glucanase. These oligosaccharides included hepta- and nonasaccharides similar or identical to those released from sycamore cell walls by the same enzyme, and structurally related octa- and decasaccharides similar to those isolated from various angiosperms. Finally, additional xyloglucan and small amounts of xylan were extracted from the endo-β-1,4-glucanase-treated walls by 0.5 n NaOH. The xylan resembled that extracted by NaOH from dicot cell walls in that it contained 2,4- but not 3,4-linked xylosyl residues. In this study, a total of 15% of the cell wall was isolated as pectic material, 10% as xyloglucan, and less than 1% as xylan. The noncellulosic polysaccharides accounted for 26% of the cell walls, cellulose for 23%, protein for 34%, and ash for 5%, for a total of 88% of the cell wall. The cell walls of Douglas fir were more similar to dicot (sycamore) cell walls than to those of graminaceous monocots, because they had a predominance of xyloglucan over xylan as the principle hemicellulose and because they possessed relatively large amounts of rhamnogalacturonan-like pectic polysaccharides.     

Structure of hemicellulosic polysaccharides of Avena sativa coleoptile cell walls

The glycosidic linkage compositions of intact and, in some cases, enzyme-degraded polysaccharides extracted from the cell walls of oat coleoptiles and subsequently purified have been examined. A major component is shown to be a glucuronoarabinoxylan similar in structure to those described for a variety of other monocots. The noncellulosic glucan component is a β-linked polymer containing both 1,4- and 1,3-linked glucosyl residues in a ratio of 2 to 1. Analysis of the oligosaccharide produced by ‘lichenase’ digestion of this β-glucan suggests that the the 1,3- and 1,4-glucosyl linkages repeat in regular fashion. A small amount of xyloglucan polysaccharides like those described for cell walls of dicots was also detected.     

Localization of cell wall polysaccharides in normal and compression wood of radiata pine: relationships with lignification and microfibril orientation

The distribution of noncellulosic polysaccharides in cell walls of tracheids and xylem parenchyma cells in normal and compression wood of Pinus radiata, was examined to determine the relationships with lignification and cellulose microfibril orientation. Using fluorescence microscopy combined with immunocytochemistry, monoclonal antibodies were used to detect xyloglucan (LM15), β(1,4)-galactan (LM5), heteroxylan (LM10 and LM11), and galactoglucomannan (LM21 and LM22). Lignin and crystalline cellulose were localized on the same sections used for immunocytochemistry by autofluorescence and polarized light microscopy, respectively. Changes in the distribution of noncellulosic polysaccharides between normal and compression wood were associated with changes in lignin distribution. Increased lignification of compression wood secondary walls was associated with novel deposition of β(1,4)-galactan and with reduced amounts of xylan and mannan in the outer S2 (S2L) region of tracheids. Xylan and mannan were detected in all lignified xylem cell types (tracheids, ray tracheids, and thick-walled ray parenchyma) but were not detected in unlignified cell types (thin-walled ray parenchyma and resin canal parenchyma). Mannan was absent from the highly lignified compound middle lamella, but xylan occurred throughout the cell walls of tracheids. Using colocalization measurements, we confirmed that polysaccharides containing galactose, mannose, and xylose have consistent correlations with lignification. Low or unsubstituted xylans were localized in cell wall layers characterized by transverse cellulose microfibril orientation in both normal and compression wood tracheids. Our results support the theory that the assembly of wood cell walls, including lignification and microfibril orientation, may be mediated by changes in the amount and distribution of noncellulosic polysaccharides.     

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.     

Cell wall polysaccharides from fern leaves: evidence for a mannan-rich Type III cell wall in Adiantum raddianum

Primary cell walls from plants are composites of cellulose tethered by cross-linking glycans and embedded in a matrix of pectins. Cell wall composition varies between plant species, reflecting in some instances the evolutionary distance between them. In this work the monosaccharide compositions of isolated primary cell walls of nine fern species and one lycophyte were characterized and compared with those from Equisetum and an angiosperm dicot. The relatively high abundance of mannose in these plants suggests that mannans may constitute the major cross-linking glycan in the primary walls of pteridophytes and lycophytes. Pectin-related polysaccharides contained mostly rhamnose and uronic acids, indicating the presence of rhamnogalacturonan I highly substituted with galactose and arabinose. Structural and fine-structural analyses of the hemicellulose fraction of leaves of Adiantum raddianum confirmed this hypothesis. Linkage analysis showed that the mannan contains mostly 4-Man with very little 4,6-Man, indicating a low percentage of branching with galactose. Treatment of the mannan-rich fractions with endo-β-mannanase produced characteristic mannan oligosaccharides. Minor amounts of xyloglucan and xylans were also detected. These data and those of others suggest that all vascular plants contain xyloglucans, arabinoxylans, and (gluco)mannans, but in different proportions that define cell wall types. Whereas xyloglucan and pectin-rich walls define Type I walls of dicots and many monocots, arabinoxylans and lower proportion of pectin define the Type II walls of commelinoid monocots. The mannan-rich primary walls with low pectins of many ferns and a lycopod indicate a fundamentally different wall type among land plants, the Type III wall.     

Structure of Hemicellulose Isolated from Rice Endosperm Cell Wall : Mode of Linkages and Sequences in Xyloglucan, β-Glucan and Arabinoxylan

A hemicellulosic polysaccharide, which was homogeneous on sedimentation analysis and also on electrophoresis, was isolated from the rice endosperm cell walls by the combination of alkaline extraction, ion exchange chromatography and iodine complex formation. It is composed of arabinose, xylose and glucose (molar ratio, 1.0: 2.0: 5.7) together with a small amount of galactose and rhamnose. Methylation analysis, Smith degradation and fragmentation with cellulase showed that this polysaccharide is composed of three distinct polysaccharide moieties i.e., xyloglucan, β-glucan and arabinoxylan. The xyloglucan consists of β-(1→4)-linked glucan back bone and short side chains of single xylose units or galactosylxylose both attached to C-6 of the glucose residues. The β-glucan contains both (1 →3)-and (1→4)-linkages similarly to the other cereal β-glucans, but differ from them in containing the blocks of (1→3)-linked glucose residues in the chain. The arabinoxylan has a highly branched structure, in which 78% of (1→4)-linked xylose residues have short side chains of arabinose at C-3 position.

On the basis of these findings, the interconnection of these polysaccharide moieties is discussed.     

Presence of xyloglucan-like polysaccharide in Spirogyra and possible involvement in cell–cell attachment

By methylation analysis, it was found that the cell walls of Spirogyra contained 4,6-linked glucose, 4-linked glucose and terminal xylose, which could be components of xyloglucan. Immunocytochemical analysis was carried out using an anti-serum against xyloglucan. After removal of pectic substances, the cell walls of both rhizoid cells and inner cells were stained. Crude protein extract from Spirogyra had a hydrolase activity for xyloglucans. In addition, the exogenously applied xyloglucan prevented the detachment of the cell wall of the severed cell. Involvement of xyloglucan-like polysaccharide in cell–cell attachment was discussed.     

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 walls of different asparagus (Asparagus officinalis) tissues

Portions of stems from the base of asparagus spears (Asparagus officinalis L. cv. Connovor Collossus) were dissected to give the following tissues: (1) pith, which was free of vascular bundles, (2) two surrounding layers, parenchyma and fibre I and II (PFI and PFII), containing parenchyma and vascular bundles, (3) sclerenchyma sheath, (4) epidermis and sub-epidermal layers and (5) asparagus vascular fibre (AVF). The alcohol-insoluble residues (AIRs) from these tissues were shown to be free of starch. They were analysed for moisture and protein, and the component sugars were released by two hydrolytic procedures, which helped to distinguish the sugars from non-cellulosic polysaccharides and cellulose. The AIRs from pith and epidermal tissues were relatively low in xylose, but were rich in cellulosic glucose, and sugars associated with pectic polysaccharides such as galacturonic acid, galactose and arabinose. Their major component polysaccharides (in decreasing amounts) were inferred to be pectic polysaccharides, cellulose, and hemicelluloses. AIR from sclerenchyma was rich in glucose and xylose, suggesting the presence of much cellulose and (acidic) xylans. The AIRs of PFI, PFII and AVF contained significant amounts of xylose in addition tn other sugars, and the major polysaccharides inferred to be present were pectic polysaccharides, cellulose and hemicelluloses, a significant proportion of which may be acidic xylans. Methylation analysis of the AIRs confirmed the above inferences. The bulk of the glucosyl residues were (1–4)-linked, and there were small but significant amounts of (1–4, 6)-linked glucosyl residues (the linkage characteristic of xyloglucans) in all the preparations. The presence of (1–4)-linked galactosyl, (1–5)-linked arabinosyl, terminal galactosyl, terminal arabinosyl, (1–2)- and (1–2, 4)-linked rhamnosyl residues in all the AIRs except that from sclerenchyma, confirmed the presence of significant levels of pectic polysaccharides in all the parenchyma tissues. All the preparations containing vascular tissues contained significant amounts of (1–4)-linked xylosyl residues, probably derived from acidic xylans. Even in the AIR of pith, a significant amount of (1–4)-linked xylosyl residues were detected. This may be due to the ability of these cells and the parenchyma cells associated with the vascular bundles, to undergo lignification in mature asparagus plants.     

Structure of Plant Cell Walls : XVIII. An Analysis of the Extracellular Polysaccharides of Suspension-Cultured Sycamore Cells

The water-soluble polysaccharides (SEPS) secreted into the medium by suspension-cultured sycamore cells were examined to determine whether the polysaccharides were the same as those present in the walls of sycamore cells. The SEPS were made more amenable to fractionation by treatment with a highly purified α-1,4-endopolygalacturonase (EPG). The EPG-treated SEPS were fractionated by anion-exchange and gelpermeation chromatography. The following polysaccharides were found: xyloglucan, arabinoxylan, at least two arabinogalactans, a rhamnogalacturonan-II-like polysaccharide, and a polygalacturonic acid-rich polysaccharide. The oligogalacturonide fragments expected from EPG-digested homogalacturonan were also identified. Evidence was obtained for the presence of a rhamnogalacturonan-I-like polysaccharide. All of the above polysaccharides have been isolated from or are believed to be present in sycamore cell walls. Furthermore, all of the noncellulosic polysaccharides known to be present in sycamore cell-walls appear to be present in the SEPS.     

Structure of Plant Cell Walls : XXVI. The Walls of Suspension-Cultured Sycamore Cells Contain a Family of Rhamnogalacturonan-I-Like Pectic Polysaccharides

Considerable information has been obtained about the primary structures of suspension-cultured sycamore (Acer pseudoplatanus) cell-wall pectic polysaccharides, i.e. rhamnogalacturonan I, rhamnogalacturonan II, and homogalacturonan. However, these polysaccharides, which are solubilized from the walls by endo-α-1,4-polygalacturonase, account for only about half of the pectic polysaccharides known to be present in sycamore cell walls. We now report that, after exhaustive treatment with endo-α-1,4-polygalacturonase, additional pectic polysaccharides were extracted from sycamore cell walls by treatment with Na₂CO₃ at 1 and 22°C. These previously uncharacterized polysaccharides accounted for ~4% of the cell wall. Based on the glycosyl and glycosyl-linkage compositions and the nature of the products obtained by treating the quantitatively predominant NaCO₃-extracted polysaccharides with lithium metal dissolved in ethylenediamine, the polysaccharides were found to strongly resemble rhamnogalacturonan I. However, unlike rhamnogalacturonan I that characteristically had equal amounts of 2- and 2,4-linked rhamnosyl residues in its backbone, the polysaccharides extracted in Na₂CO₃ at 1°C had markedly disparate ratios of 2- to 2,4-linked rhamnosyl residues. We concluded that polysaccharides similar to rhamnogalacturonan I but with different degrees of branching are present in the walls of suspension-cultured sycamore cells.     

Cell wall polysaccharides from cell suspension cultures of the Atlantic Forest tree Rudgea jasminoides (Rubiaceae)

Rudgea jasminoides (Rubiaceae) is a tropical tree species native of the Atlantic Forest in the south of Brazil. Previous studies with leaf cell walls of R. jasminoides showed a different proportion of cross-linked glycans compared to what is usually reported for eudicots. However, due to the difficulties of working with whole plant organs, cell suspensions of R. jasminoides, consisting of predominantly undifferentiated cells with mainly primary cell walls, were used to examine cell walls and extracellular soluble polysaccharides (EP) released into the culture medium. Sugar composition and linkage analysis showed homogalacturonans, xylogalacturonans and arabinogalactans to be the predominant EP. In the cell wall, homogalacturonans and arabinogalactans are the major pectins, and xyloglucans and xylans are the major cross-linking glycans. The presence of xylogalacturonans in the R. jasminoides cell cultures seems to be related to the occurrence of a homogeneous cell suspension with loosely attached cells. Although all alkali extractions from the cell walls yielded amounts of xyloglucan that exceed those of the xylans, the latter was found in a proportion that is higher than what has been usually reported for primary cell walls of most eudicots. The xyloglucan from cell walls of cell suspension cultures of R. jasminoides has low fucosylation levels and high proportion of galactosyl residues, a branching pattern commonly found in storage cell-wall xyloglucans.     

THE COMPOSITION OF THE DEVELOPING PRIMARY WALL IN ONION ROOT TIP CELLS. II. CYTOCHEMICAL LOCALIZATION

Jensen , William A. (U. California, Berkeley.) The composition of the developing primary wall in onion root tip cells. II. Cytochemical localization. Amer. Jour. Bot. 47(4) : 287—295. Illus. 1960.–The composition of the developing cell wall in the first 2 mm. of the onion root tip was studied using a cytochemical technique that permitted the detection of hemicellulose and the noncellulosic polysaccharides as well as the pectic substances and cellulose. The technique is based on the combination of a differential extraction procedure with the periodic acid-Schiff reaction for carbohydrates. The data obtained indicate that the cells of the apical initials are low in all wall substances but that all of the wall materials are present to some extent. Early in cell development, differences appear in the composition of the walls of the various tissues. The cortical cells are relatively high in the noncellulosic polysaccharides and cellulose while relatively low in the pectic substances and hemicellulose. Very early in development the protoderm is similar to the cortex, but differences develop during the radial enlargement of the cells. During this stage the walls of the protodermal cells are low in the noncellulosic polysaccharides and cellulose and high in pectic substances and hemicellulose. As elongation progresses, these differences are lost and the 2 tissues become very similar. The vascular cell walls are low in the noncellulosic polysaccharides and cellulose and are high in pectic substances and hemicellulose early in development. Later, hemicellulose becomes relatively more important. When the cell wall materials are sequentially extracted, no change in the general morphology of the cell occurs until only the noncellulosic polysaccharides and the cellulose remained. When the noncellulosic polysaccharides are then removed, the cells remain intact but are 30% less in diameter. This suggests that while cellulose is of critical importance, the noncellulosic polysaccharides may play a major role in determining the physical characteristics of the wall.     

Changes in cell wall polysaccharides in the internodes of submerged floating rice

In excised stem segments of floating rice (Oryza sativa L.), as well as in intact plants, submergence greatly stimulates the elongation of internodes. The differences in the composition of cell wall polysaccharides along the highest internodes of submerged and air-grown stem segments were examined. The newly elongated parts of internodes that had been submerged for two days contained considerably less cellulosic and noncellulosic polysaccharides than air-grown internodes, an indication that the cell walls of the newly elongated parts of submerged internodes are extremely thin. In the young parts of both air-grown and submerged internodes, the relative amounts of noncellulosic polysaccharides were equal to those of -cellulose, whereas the relative amounts of -cellulose were higher than those of noncellulosic polysaccharides in the upper, old parts. In the cell-elongation zones of both air-grown and submerged internodes, glucose was predominant among the noncellulosic neutral sugars of cell wall. The relative amount of glucose in noncellulosic neutral sugars decreased toward the upper, old parts of internodes, whereas that of xylose increased.     

Differences in the Composition of the Cell Walls of Two Morphologically Different Lines of Suspension-Cultured Catharanthus roseus Cells

Differences in the composition of cell walls of two morphologicallydifferent lines (A and B) of suspension-cultured Catharanthusroseus cells, which have the same origin, were investigated.The cells of strain A are nearly spherical, while those of strainB are cylindrical. In strain A, the amount of cell wall pergram fresh weight of cells increased during the logarithmicphase. In strain B, the amount of cell wall per cell decreasedduring the logarithmic phase. The level of matrix polysaccharides increased markedly duringthe logarithmic phase in strain A. The amount of cellulose incell wall was relatively larger in strain B than in strain A.The following differences in sugar composition between the twostrains were observed: (a) there was an increase in the relativelevels of 4-linked galactose in the EDTA-soluble fraction andof 3-linked glucose in the 5% KOH-soluble fraction during thelogarithmic phase in strain A; (b) there were significantlyhigher levels of arabinose, probably derived from 2,5- and/or3,5-linked arabinan, in the EDTA-soluble fraction and in theextracellular polysaccharides in strain B; (c) there were decreasesin the relative amounts of some kinds of sugar, probably thosederived from xyloglucan, during the stationary phase in strainB. (Received March 31, 1989; Accepted October 12, 1989)     

Ultrastructure and Chemical Analysis of the Cell Wall of Pythium debaryanum1

The ultrastructure and component polysaccharides of the cell wall of Pythium debaryanum IFO-5919 were investigated. From results obtained by means of acid, alkali, Schweitzer reagent and β-1, 3-glucanase treatments and electron microscopy, it was concluded that 1) the acid-extracted fraction was a 1,3-linked branched glucan, 2) the alkali-extracted fraction was a mixture of 1,3-, 1,6-, and 1,3,6-linked highly branched two glucans, 3) the Schweitzer reagent-extracted fraction was a β-1, 4-linked glucan, 4) the cell wall was constructed from two types of cullulosic microfibrils, as a frame and as a finer network, and amorphous β-1, 3-glucan including β-1, 6-linkage, 5) cellulosic microfibrils were covered by matrix material consisting of a mixture of amorphous β-1, 3-linked and β-1, 6-linked branching glucans.     

Patterns of incorporation of d-galactose into cell wall polysaccharide of growing maize roots

Summary ¹⁴C-1-d-galactose was rapidly taken up by excised corn root-tips and efficiently converted to hexose units in cell wall polysaccharides. The label recovered in both hydrolysed pectin and hemicellulose was predominantly in galactose and only the -cellulose contained appreciable amounts of labelled glucose. There was no evidence for breakdown of labelled units after incorporation into the cell wall. It is suggested that the utilisation of this free galactose has not appreciably affected the normal metabolic pathway by which galactose is incorporated into plant cell walls.Advantage was taken of the specificity of this labelling to follow patterns of galactosyl incorporation in roots. Autoradiographs were prepared from adjacent longitudinal sections that had been extracted with ammonium oxalate solution and 24% (w/v) KOH respectively. The distribution of silver grains over these sections was compared with that over an unextracted section. Galactosyl units of pectin were incorporated in young cell walls in all tissues investigated. The pattern closely resembled that noted in earlier work for uronosyl and pentosyl incorporation. In pith and cortical cells, galactosyl units of hemicellulose were deposited at a maximum rate in walls approaching the end of their growth when pentose incorporation was low. Because branched alkali-soluble polysaccharides containing galactose and pentose have been isolated from several tissues of corn, similar compounds are likely to exist in the root. It is proposed that the continued elaboration of such a polysaccharide might continue after deposition, and the addition of galactosyl units may be a factor which limits further plastic extension of the wall.     

A Barley xyloglucan xyloglucosyl transferase covalently links xyloglucan, cellulosic substrates, and (1,3;1,4)-beta-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.     

Spectroscopic and biochemical analysis of regions of the cell wall of the unicellular 'mannan weed', Acetabularia acetabulum

Although the Dasycladalean alga Acetabularia acetabulum has long been known to contain mannan-rich walls, it is not known to what extent wall composition varies as a function of the elaborate cellular differentiation of this cell, nor has it been determined what other polysaccharides accompany the mannans. Cell walls were prepared from rhizoids, stalks, hairs, hair scars, apical septa, gametophores and gametangia, subjected to nuclear magnetic resonance and Fourier transform infrared spectroscopy, and analyzed for monosaccharide composition and linkage, although material limitations prevented some cell regions from being analyzed by some of the methods. In diplophase, walls contain a para-crystalline mannan, with other polysaccharides accounting for 10-20% of the wall mass; in haplophase, gametangia have a cellulosic wall, with mannans and other polymers representing about a quarter of the mass. In the walls of the diplophase, the mannan appears less crystalline than typical of cellulose. The walls of both diploid and haploid phases contain little if any xyloglucan or pectic polysaccharides, but appear to contain small amounts of a homorhamnan, galactomannans and glucogalactomannans, and branched xylans. These ancillary polysaccharides are approximately as abundant in the cellulose-rich gametangia as in the mannan-rich diplophase. In the diplophase, different regions of the cell differ modestly but reproducibly in the composition of the cell wall. These results suggest unique cell wall architecture for the mannan-rich cell walls of the Dasycladales.