Duckweed pectic-arabinogalactan-proteins can crosslink through borate diester bonds

Material containing pectin and arabinogalactan-protein (AGP) was released and purified from Spirodela alcohol insoluble residues. Results of carbohydrate analyses and two-dimensional NMR spectroscopy suggest that this material is composed of apiogalacturonan and rhamnogalacturonan-I covalently attached to AGPs. 11B NMR spectroscopy indicated that some of the glycoses in this complex exist as their boric acid monoesters. Borate diesters were formed when the pectic-AGPs were allowed to react at pH above 6.2 with the boron-depleted pectic-AGPs, suggesting that in vitro two pectic-AGP molecules can crosslink to one another through borate. Borate diesters also formed when the pectic-AGPs were incubated with monomeric rhamnogalacturonan-II in the presence of Pb2+ ion at pH 9.2. This data presents evidence of the first wall polymer after rhamnogalacturonan-II to crosslink through borate diesters. We suggest that the formation of these borate-crosslinks may help Spirodela respond to high-pH condition.

Automated summary

A material rich in pectin and arabinogalactan-protein (AGP) was extracted and purified from Spirodela alcohol insoluble residues. Analysis and spectroscopy studies revealed that the material consists of apiogalacturonan and rhamnogalacturonan-I covalently attached to AGPs. The formation of borate crosslinks was observed when reacting pectic-AGPs at high pH or with monomeric rhamnogalacturonan-II in the presence of Pb2+ ion, indicating a potential role of borate-crosslinks in Spirodela's response to high-pH condition.