In vivo Degradation and Extracellular Polymer-Binding of Xyloglucan Nonasaccharide, a Naturally-Occurring Anti-Auxin

Abstract

Summary 1-10 nM Xyloglucan nonasaccharide (XG9) and its naturally-occurring acylated derivatives (XG9·Ac) antagonise the growth-promoting action of 1μM 2,4-dichlorophenoxyacetic acid in pea stem segments. To investigate the mechanisms involved in controlling the in vivo concentrations of these biologically-active oligosaccharides, we 3 H-labelled XG9 and XG9·Ac in their xylose or fucose residues, fed them at 10 nM to rapidly-growing Spinacia cell cultures, and monitored their fate by gel-permeation chromatography. Very little breakdown to low-M r products took place, and little 3 H entered or bound to the cells. However, a proportion of the 3 H appeared to become linked to a soluble, extracellular polymer. The linkage was stable to 31% acetic acid and to 0.5M NaOH at 25°C, but Trichoderma cellulase was able to disrupt it, liberating a [ 3 H]oligosaccharide similar to XG9. We speculate that XG9 and XG9·Ac became attached to soluble extracellular xyloglucans by transglycosylation.