Covalently linked pectin-arabinoglucuronoxylan complex from Siberian fir Abies sibirica Ledeb.

In this study, by NMR spectroscopy, first was proved that the pectic polysaccharides of Abies sibirica are covalently bound to arabinoglucuronoxylan (AGX). Namely, AGX is attached at the 4th position to the 1,2,4-α-L-Rha residues of the RG-I main chain, indicating the following fragment: …→2)-[(2,4-β-D-Xylp)-(1→4)]-[(α-D-GalpA-(1→2)]-α-L-Rhap-(1→4)-α-D-GalpA-(1→…. We present direct evidence of covalent attachment between C1 of 1,2,4-β-D-Xylp from arabinoglucuronoxylan and С4 of 1,2,4-α-L-Rhap from RG-I of pectin by detailed 2D NMR analyses. It can be concluded that the 1,2,4-α-L-Rhap residues, were substituted at the 4th position by 1,5-α-L-arabinan or 1,4-β-D-galactan or AGX. The discovery of this interglycosidic linkage between xylan and pectin contradicts the classical model of the cell wall, which describes networks of binding glycans and pectic polysaccharides as separate and independent of one another. We can conclude that pectin undoubtedly plays a more important supporting and cross-linking role in the cell wall than is commonly thought.