Pea Xyloglucan and Cellulose

Abstract

Lateral expansion of the third internodes of pea epicotyls was evoked by treatment with either 2,4dichlorophenoxyacetic acid (2,4-D) or ethylene gas. During growth, 2,4-D enhanced and ethylene inhibited the deposition of xyloglucan and cellulose in the cell wall, with the result that the wall framework (ghost) from ethylene-treated swollen tissue was much thinner than that from 2,4-D-treated. The level of activity of xyloglucan synthase, alkali-insoluble -glucan synthases, and endo-1,4-j8 glucanases were all enhanced by 2,4-D treatment but not by ethylene.Both 2,4-D and ethylene treatments led to increased osmotic potential in the swelling tissues. Accordingly, swelling after 2,4-D treatment was accompanied by xyloglucan degrdation, concomitant with substantial net synthesis, but swollen tissue as a result of ethylene treatment was characterized by walls whose integrity was weakened by relatively low levels of newly deposited polysaccharides rather than by the deradation.Treatment of intact pea epicotyls with supraoptimal auxin (sprayed) or ethylene gas inhibits elongation and induces immediately lateral expansion of apical growing regions (6, 13). This physiological phenomenon is accompanied and possibly caused by changes in orientation of microtubules and cellulose microfibrils (1,(12)(13)(14)19). Burg and Burg (2) proposed that the auxin effect is due to auxin-induced ethylene production. However, there is evidence (16,17,20) that auxin and ethylene often have very different and opposite effects on the metabolism of plant cells, particularly as this may affect cell wall metabolism. The main question addressed here is whether the metabolism of the major pea primary wall constituents, namely xyloglucan and cellulose, is influenced in the same way by auxin and ethylene treatments under conditions when both regulators promote an expansion.In previous papers (8, 11) of this series, we presented evidence for the structure and macromolecular organization of pea xyloglucan and cellulose in the primary cell wall and showed that auxin-induced pea endo-1,4-fl-glucanases were responsible for the hydrolysis and solubilization of pea xyloglucan during growth. In the present paper, results are reported on the changes which occur following 2,4-D (auxin) or ethylene treatment in levels of xyloglucan, cellulose, their synthases and hydrolases, in apical regions of the pea epicotyl. Comparisons were also made between effects on the osmotic potentials of pea tissues.

Xyloglucan Antibodies Inhibit Auxin-Induced Elongation and Cell Wall Loosening of Azuki Bean Epicotyls but Not of Oat Coleoptiles

“…Auxin causes degradation (18) or solubilization (32) of xyloglucans, as well as decrease in molecular mass (25,26) and stimulation of autolysis (9) of the polysaccharides. Auxin also stimulates the accumulation of endo-/3-(1-+4)-glucanase (2,8). However, it has not been clarified whether this enzyme is responsible for these changes in xyloglucans.…”

“…In dicotyledons, auxin causes degradation (18), solubilization (32), de-crease in molecular mass (25,26), and stimulation of autolysis (9) of the polysaccharides. Auxin also induces the accumulation of endo-f-( 1-+4)-glucanase, which is capable of hydrolyzing xyloglucans in dicotyledons (2,8). Auxin causes a decrease in molecular mass of xyloglucans also in oat coleoptile segments (16).…”

Differential Expression of Two Endo-1,4-β-Glucanase Genes in Pericarp and Locules of Wild-Type and Mutant Tomato Fruit

“…One class of cell-wall hydrolases, cellulases or EGases (EC 3.2.1.4), has been specifically implicated in a number of developmental processes, including cell expansion (Hayashi and Maclachlan, 1984) and organ abscission (Sexton and Roberts, 1982), as well as ripening-associated fruit softening (Hall, 1964;Hobson, 1968;Christoffersen et al, 1984).…”

Effect of Xyloglucan Oligosaccharides on Growth, Viscoelastic Properties, and Long-Term Extension of Pea Shoots

“…This network is considered by many to be the major component that endows the wall with its mechanical properties (Fry, 1989;Carpita and Gibeaut, 1993). Auxin-induced growth in pea (Pisum sativum L., var Alaska) shoots is accompanied by a partia1 solubilization of xyloglucan (Terry et al, 1981) and a decrease in its average molecular mass (Labavitch and Ray, 1974;Hayashi and Maclachlan, 1984;Talbott and Ray, 1992), suggesting that xyloglucan metabolism is closely associated with cell extension. It has been proposed that wall loosening can be achieved through hydrolases such as cellulase that act against the xyloglucan network (Fry, 1989) and/or through the action of an XET (Albersheim, 1976;Fry et al, 1992a).…”