Seed mucilages as examples of polysaccharide denaturation

633

155

Degradative enzymes have been used to obtain defined fragments of the isolated cell walls of suspension-cultured sycamore cells. These fragments have been purified and structurally characterized. Fragments released from endopolygalacturonasepretreated cell walls by a purified endoglucanase and the fragments extracted from these walls by urea and alkali provide evidence for a covalent connection between the xyloglucan and pectic polysaccharides. Fragments released by a protease from endopolygalacturonase-endoglucanase-pretreated cell walls provide evidence for a covalent connection between the pectic polysaccharides and the structural protein of the cell wall.Based on these interconnections and the strong binding which occurs between the xyloglucan and cellulose, a tentative structure of the cell wall is proposed.The polymer composition and partial structures of the pectic and hemicellulosic components of isolated sycamore cell walls are described in the preceding papers (6, 26). There remains the problem of how these components are connected to make a functional wall matrix. It has been suggested that the wall is held together by noncovalent interactions between the various macromolecular components (20). However, the evidence presented in this and in the preceding papers suggests that, with the exception of cellulose, the macromolecules of the wall are covalently cross-linked, and that even the linkage between cellulose and the other cell wall polymers has the strength of a covalent bond.

Section: Resultsmentioning

confidence: 85%

The Structure of Plant Cell Walls

Keegstra¹,

Talmadge²,

Bauer³

et al. 1973

633

155

“…Polysaccharides appearing in the classical hemicellulose fraction of plant cell walls (xylans, arabinoxylans, mannans, glucomannans, and galactoglucomannans) also have structures which are well suited for hydrogen bonding to cellulose chains. Several such polysaccharides have, in fact, been reported to bind to cellulose in vitro (5,10). These polysaccharides and the xyloglucans may belong to a single class of functionally related polymers which have in common the ability to bind noncovalently to cellulose.…”

Section: Isolationmentioning

confidence: 99%

The Structure of Plant Cell Walls

Bauer¹,

Talmadge²,

Keegstra³

et al. 1973

360

131

The molecular structure, chemical properties, and biological function of the xyloglucan polysaccharide isolated from cell walls of suspension-cultured sycamore (Acer pseudoplatanus) cells are described. The sycamore wall xyloglucan is compared to the extracellular xyloglucan secreted by suspension-cultured sycamore cells into their culture medium and is also compared to the seed "amyloid" xyloglucans.Xyloglucan-or fragments of xyloglucan-and acidic fragments of the pectic polysaccharides are released from endopolygalacturonase-pretreated sycamore walls by treatment of these walls with 8 M urea, endoglucanase, or 0.5 N NaOH. Some of the xyloglucan thus released is found to cochromatograph with the acidic pectic fragments on diethylaminoethyl Sephadex. The chemical or enzymic treatments required for the release of xyloglucan from the walls and the cochromatography of xyloglucan with the acidic pectic fragments indicate that xyloglucan is covalently linked to the pectic polysaccharides and is noncovalently bound to the cellulose fibrils of the svcamore cell wall.The molecular structure of sycamore xyloglucan was characterized by methylation analysis of the oligosaccharides obtained by endoglucanase treatment of the polymer. The struc. ture of the polymer is based on a repeating heptasaccharide unit which consists of 4 residues of 8-1-4-linked glucose and 3 residues of terminal xylose. A single xylose residue is glycosidically linked to carbon 6 of 3 of the glucosyl residues.In the first paper of this series (24), recently developed techniques for the methylation analysis of polysaccharides were used in order to study the structure of the primary cell wall of suspension-cultured sycamore cells and in order to characterize structurally the defined fragments released from these walls by a highly purified endopolygalacturonase. This study indicated

“…Wright and Northcote (34) proposed that the organization of maize root slime is similar to that of mustard seed slime (16), that is, a central cellulosic polymer encased in a hydrophilic uronic acid-containing pectic-like material. Other earlier reports of high levels of uronic acids in "crude slime" preparations could be attributed to material arising from cell wall polymers included in the preparation rather than from secreted slime.…”

mentioning

confidence: 99%

Structural Analysis of Secreted Root Slime from Maize (Zea mays L.)

Bacic¹,

Moody²,

Clarke³

1986

129

Secreted slime isolated from the incubation medium of Zea mays roots maintained axenically contains fucose, arabinose, xylose, plactose, and glucose as the major monosaccharides. The slime preparation contains low levels (3% weight/weight 1w/wi) of uronic acids. Methylation analysis reveals an extraordinarily diverse range of glycosyl residues. The fucosyl residues are primarily terminal (60%) and 3-linked (33%) with a relatively small proportion being 2-linked (6%). The methylation data are consistent with, but not proof of, the presence of a range of polymers including arabinogalactan-proteins (AGPs), xyloglucans, arabinoxylans, and glucans in the slime. The specific binding of the -fglucosyl Yariv reagent, a dye which binds and precipitates AGPs, to the slime preparation and to the outer periclinal epidermal cell wall surface in root sections, is further evidence for the presence of AGPs. Low levels of phenolic acids (approximately 0.17% w/w), in particular trans-ferulic acid, and protein (approximately 6% w/w) were also detected.The root surface forms the interface between the plant, the soil and the soil microorganisms. A slime, secreted primarily from the root cap and possibly the epidermal cells, coats the root surface and forms a primary site for colonization of the root by microbial symbionts and pathogens. Colonization requires adhesion of microorganisms to the host root surface and, in some cases, specific interactions involving slime saccharides are apparently involved in the interaction between the root and soil microorganisms (20). In addition, the slime acts as a lubricant aiding the passage of the root through the soil.In spite of the importance of root slime in rhizosphere colonization and plant root function, our knowledge of the structure of high mol wt components of root slime collected under sterile conditions is poor (26). Monosaccharide analyses of slime collected under axenic conditions (26) are limited to Zea mays (7,19) Caryopses were surface sterilized by sequential soaking in 70% (v/v) ethanol (1 min), 0.1% (w/v) mercuric chloride (10 min) and 6% NaOCl (10 min). Each treatment was followed by several washes with sterile distilled H20 (5-10 min). The caryopses were then imbibed in distilled H20 containing chloramphenicol (60 sg/ml), streptomycin (100 tg/ml) and penicillin (100 units/ml) with continuous shaking (120 rpm) for 24 h at 24°C prior to a second soaking in 0.1% (w/v) mercuric chloride (10 min). The antimicrobial agents were subsequently removed from the caryopses by washing with sterile distilled H20 over a period of 15 to 20 min. Surface sterilized caryopses were germinated on moist glass fiber filter discs in culture dishes which were covered with aluminum foil. The caryopses were incubated at 25°C in the dark, until the roots were approximately 1 to 2 cm long (96 h).