Ferulic acid cross-links between

Piber, M., Koehler, P. 2005. Identification of dehydro-ferulic acid-tyrosine in rye and wheat Evidence for a covalent cross-link between arabinoxylans and proteins. J Agric Food Chem 53 5276-5284. 

Cross-linking between polysaccharide-polysaccharide units can occur in different forms such as ester-linked hydroxycinnamate dimers (Ralph et al., 2004), ferulic acid and/orp-coumaric acid monomers as cyclic dimers (Grabber et al., 2004), and direct linkage between polysaccharides and xyloglucans (Harris and Stone, 2009). Some important interactions between lignin and polysaccharides in the cell walls are the following ... 

Figure 4. (A). A partial structure of homogalacturonan. In primary walls between 50 and 80% of the GalpA are esterified. (B). A partial structure of rhamnogalacturonan I (1) the backbone of RG-I is composed of the disaccharide repeating unit — 4)-a-D-GalpA-(l— 2)-a-L-Rhap-(l—The GalpA residues are often O-acetylated. Some of the rhamnosyl residues are substituted at C-4 with oligosaccharides composed predominantly of Ara/ and Galp residues (2 and 3). Some side chains contain (4-0-Me)GlcpA (4). In the Chenopodiaceae, the side chains are esterified with phenolic acids such as ferulic acid (5). Oxidative coupling of the phenolic acids may be a way in which pectins are cross-linked.

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