A role for arabinogalactan‐proteins in plant cell expansion: evidence from studies on the interaction of β‐glucosyl Yariv reagent with seedlings of Arabidopsis thaliana

Summary Seedlings of Arabidopsis thaliana were germinated and grown in medium containing β‐glucosyl Yariv reagent (βGlcY), a synthetic phenyl glycoside that interacts specifically with arabinogalactan‐proteins (AGPs), a class of plant cell surface proteoglycans. The effect of βGlcY on the seedlings was to reduce the overall growth of both the root and the shoot. βGlcY only accumulated in the root tissues and the reduced growth of the shoot appeared to be an indirect effect of impaired root growth. Reduced root growth was a consequence of a reduction in cell elongation during the postproliferation phase of elongation at the root apex and this was associated with extensive radial expansion of root epidermal cells. βGlcY penetrated roots as far as the endodermis and it is suggested that the interaction of βGlcY with AGPs in the load‐bearing cell layers inhibited root elongation. When βGlcY was added to carrot suspension‐cultured cells that had been induced to elongate rather than proliferate, cell elongation was inhibited. The AGP‐unreactive α‐galactosyl Yariv reagent (αGalY) had no biological activity in either of these systems.