Specific localization of arabinogalactan-protein epitopes at the surface of maize root hairs

Arabinogalactan-proteins (AGPs) are often localized at plant surfaces. Howe ver, their function there is unknown. We have used immunogold/silver and im munofluorescence techniques to study the developmental occurrence of an glu curonic acid (GlcA)-containing AGP epitope and beta- (1-->6)-galactan AGP e pitope at the surfaces of maize roots, especially during root hair formatio n and growth. Both techniques revealed that the GlcA AGP epitope was locali zed specifically at the surface of maize root hairs of all developmental st ages, This epitope was most strongly expressed within the early bulge durin g initiation of root hairs and within the tip of elongating roof hairs, whi le it was depleted from the tips of growth-terminating root hairs. The patt ern of distribution of GlcA epitope was modified by ethrel treatment and wa ter incubation, The beta(1-->6)-galactan epitope was not specific to the ro ot hairs as it occurred also on the root surface within the root-hair formi ng zone, Nevertheless, this AGP epitope was similarly regulated during root hair morphogenesis as the GlcA epitope. These results indicate that surfac es of initiating and growing maize root hairs are equipped with AGP epitope s containing GlcA and of beta-(1-->6)-galactan. Possible roles of AGPs on t he root and root hair surface are discussed.