FERULATE CROSS-LINKING IN CELL-WALLS ISOLATED FROM MAIZE CELL-SUSPENSIONS

Cross-linking of arabinoxylans by ferulate dehydrodimers and incorpora tion of feruloylated arabinoxylans into lignin were modelled with maiz e walls (Zea mays cv Black Mexican) containing 5.3-18.0 mg g(-1) of to tal ferulates. The proportion of dehydrodimers to total ferulates incr eased from ca 20 to 45% when dilute hydrogen peroxide was added to wal ls containing bound peroxidase. About 45% of the dehydrodimers were co upled by 8-5 linkages, with 8-8, 8-0-4 and 5-5 coupled dehydrodimers e ach comprising 10-25% of the total. The quantity of ferulates released by saponification were reduced by 83-95% when exogenously supplied hy droxycinnamyl alcohols were polymerized into walls by wall-bound perox idase and in situ generated hydrogen peroxide. Only 40% of the ferulat es incorporated into lignin were recovered following hydrolysis of eth er linkages. These results indicate that primary walls in grasses beco me extensively cross-linked by ferulic and dehydrodiferulic acids duri ng lignification, and that only a portion of ferulates in lignified ti ssues are measurable by current solvolytic methods.