Ferulate cross-linking in cell walls isolated from maize cell suspensions

Abstract

Cross-linking of arabinoxylans by ferulate dehydrodimers and incorporation of feruloylated arabinoxylans into lignin were modelled with maize walls ( Zea mays cv Black Mexican) containing 5.3–18.0 mg g −1 of total ferulates. The proportion of dehydrodimers to total ferulates increased from ca 20 to 45% when dilute hydrogen peroxide was added to walls containing bound peroxidase. About 45% of the dehydrodimers were coupled by 8-5 linkages, with 8-8, 8- O-4 and 5-5 coupled dehydrodimers each comprising 10–25% of the total. The quantity of ferulates released by saponification were reduced by 83–95% when exogenously supplied hydroxycinnamyl alcohols were polymerized into walls by wall-bound peroxidase and in situ generated hydrogen peroxide. Only 40% of the ferulates incorporated into lignin were recovered following hydrolysis of ether linkages. These results indicate that primary walls in grasses become extensively cross-linked by ferulic and dehydrodiferulic acids during lignification, and that only a portion of ferulates in lignified tissues are measurable by current solvolytic methods.