Localization of arabinogalactan-proteins in roots of Echinacea purpurea by immunofluorescent labelling

From the high molecular weight fraction of an aqueous extract from roots of Echinacea purpurea (L.) MOENCH, arabinogalactan-proteins (AGPs) were purified and characterized with special regard to the structure of the polysaccharide moiety. It is highly branched and shows a linkage composition comparable to AGPs from the aerial parts of E. purpurea [1] with 1,3-, 1,6- and 1,3,6-linked galactopyranosyl residues as basic structural elements and arabinofuranosyl residues predominantly as terminal and 1,5-linked residues. Some terminal units of glucuronic acids could also be detected.

A new method of localization of AGPs in plant tissue has been developed. The synthetic (β-D-Glc)₃ Yariv phenylgycoside (βGlcY) is known to bind specifically to AGPs and was used for their isolation. For immunolocalization, polyclonal βGlcY-antibodies have been generated and were used to label Yariv-treated thin sections of roots from E. pupurea. After addition of a FITC-conjugated secondary antibody, the sections were analyzed by confocal laser scanning microscopy. AGPs were mainly detected in the central cylinder in xylematic elements. Cell walls of vessels and tracheids are strongly labeled, especially at the inner area of the wall. Furthermore, there was an intense labelling of pit canals. The proposed involvement of AGPs in xylem differentiation [2] thus could be confirmed, and in addition it is suggested that AGPs are involved in the formation of pit canals during xylem development.

References: [1] Classen, B. et al. (2000) Carbohydr. Res. 327:497–504.

[2] Motose, H. et al. (2004) Nature 429:873–878.