EFFECT OF XYLOGLUCAN OLIGOSACCHARIDES ON GROWTH, VISCOELASTIC PROPERTIES, AND LONG-TERM EXTENSION OF PEA SHOOTS

The growth-promoting effect of xyloglucan-derived oligosaccharides was investigated using a bioassay with entire pea (Pisum sativum L., var Alaska) shoots. After a 24-h incubation period at 25 degrees C, xylogl ucan oligosaccharide (XGO) solutions with concentrations of 10(-6) M n otably increased the growth rate of pea shoots, whereas the same oligo saccharides at 10(-7) M were less effective. To investigate the possib le correlation between growth rate changes in the XGO-treated shoots a nd changes in the wall mechanical properties of their growing regions (third internodes), we used a shortterm creep assay. The promotion of elongation by XGOs was reflected in an enhancement of the viscoelastic ity of the growing regions of the shoots. To show whether this effect on wall viscoelastic properties was the cause or a consequence of thei r growth promotion, we tested the effect of XGOs on the long-term exte nsion of isolated cell walls. We characterized an acid-induced extensi on in isolated cell walls from pea shoots that was not inhibited by pr eincubation in neutral buffers. Exogenously added XGOs did not alter t he pattern of pea segment extension at any pH tested, indicating that XGOs have no direct effect on cell wall viscoelasticity. Finally, prei ncubation of pea segments in neutral buffers with XGOs enhanced their capacity to extend under acidic conditions. This finding suggests that XGOs at a neutral pH can act via transglycosylation, weakening the wa ll matrix and making the wall more responsive to other mechanisms of a cid-induced extension as an expansin-mediated extension.