Pea Xyloglucan and Cellulose

Abstract

Two auxin-induced endo-1,4-0-glucanases (EC 3.2.1.4) were purified from pea (Pisum sativum L. var. Alaska) epicotyls and used to degrade purified pea xyloglucan. Hydrolysis yielded nonasaccharide (glucose/ xylose/galactose/fucose, 4:3:1:1) and heptasaccharide (glucose/xylose, 4:3) as the products. The progress of hydrolysis, as monitored viscometrically (with amyloid xyloglucan) and by determination of residual xyloglucan-iodine complex (pea) confirmed that both pea gluses acted as endohydrolases versus xyloglucan. K. values for amyloid and pea xyloglucans were approximately the same as those for cellulose derivatives, but V.,, values were lower for the xyloglucans. Auxin treatment ofepicotyls in vivo resulted in increases in net deposits of xyloglucan and cellulose in spite of a great increase (induction) of endogenous 1,4-,5-glucanase activity. However, the average degree of polymerization of the resulting xyloglucan was much lower than in controls, and the amount of soluble xyloglucan increased. When macromolecular complexes of xyloglucan and cellulose (cell wall ghosts) were treated in vitro with pea 1,44-glucanase, the xyloglucan component was preferentially hydrolyzed and solubilized. It is concluded that xyloglucan is the main cell wall substrate for pea endo-1,4-,f-glucanase in growing tissue.

Suppression and acceleration of cell elongation by integration of xyloglucans in pea stem segments

“…To prepare pea xyloglucan, we used the expanded tissues from epicotyls previously sprayed with 2.5 mM 2,4-D, because this tissue yielded a homogenous xyloglucan fraction with a mean molecular mass of 50 kDa (14). The epicotyl tissue (5 kg) was sequentially extracted three times with 0.1 M EDTA (pH 7.0) at 85°C for 3 h, three times with 4% KOH͞0.1% NaBH 4 at 35°C for 3 h, and three times with 24% KOH͞0.1% NaBH 4 at 35°C for 3 h. Xyloglucan was purified from the 24% KOH extract.…”

Wall-Associated Kinases Are Expressed throughout Plant Development and Are Required for Cell Expansion

“…Cellulose is directly secreted by cellulose synthase into the ECM, where it assembles with hemicelluloses and pectins, which are produced in the endomembrane system and secreted by vesicles. The cell wall also includes endoglucanases (Hayashi et al, 1984;Zuo et al, 2000), xyloglucan endotransglycosylases (Fry et al, 1992;Vissenberg et al, 2000), expansins (McQueen-Mason et al, 1992;Cho and Cosgrove, 2000), and a number of other glycosyl transferases that alter carbohydrate linkages and modify secreted cell wall components. Other cell wall proteins, some of which are heavily glycosylated, have been proposed as structural cell wall components or have been implicated in mediating multiple aspects of plant development (reviewed in : Showalter, 1993;Cosgrove, 1997;Kohorn, 2000).…”

Action of a pure xyloglucan endo‐transglycosylase (formerly called xyloglucan‐specific endo‐(1‐4)‐β‐d‐glucanase) from the cotyledons of germinated nasturtium seeds

“…There is convincing evidence that the metabolism of xyloglucan is associated closely with cell-extension in dicotyledonous plants (Labavitch and Ray, 1974) and (1+4)-p-~-glucanases of the 'cellulase' type have been implicated (Fan and Maclachlan, 1966;Ridge and Osborne, 1967;Tracey, 1950). If, as has been suggested (Keegstra et a/., 1973;Fry, 1989;McCann et al, 1990), the relative movement of cellulose microfibrils is normally restricted by xyloglucan, the action of a 'cellulase' (which hydrolyses cell wall xyloglucan rapidly but scarcely attacks cellulose (Hayashi et a/., 1984)) would facilitate cell extension, but the scission of the xyloglucan chains would be irreversible. By contrast, an enzyme with an action similar to the one described here would be capable of catalysing the controlled rearrangement of xyloglucan.…”