Enzymic Analysis of Feruloylated Arabinoxylans (Feraxan) Derived from Zea mays Cell Walls

Abstract

Changes in structural features of feraxan (feruloylated arabinoxylans) in cell walls during development of maize (Zea mays L.) coleoptiles were investigated by analysis of fragments released by feraxanase, a specific enzyme purified from Bacillus subtilis. The following patterns were identified: (a) The total quantity of carbohydrate dissociated from a given dry weight of cell wall by feraxanase remained rather constant throughout the initial 10 days of coleoptile development. However, during the same period the proportion of ferulic acid in the fraction increased 12-fold. The absolute amount of ferulic acid per coleoptile also increased rapidly during this developmental phase. (b) Fragments dissociated by the enzyme were resolved into feruloylated and nonferuloylated components by reversed phase chromatography. While the quantity of feruloylated fractions represented a small portion of the total arabinoxylan during the phase of maximum coleoptile elongation (days 2-4) this component increased in abundance to reach a plateau (after 8-10 days). In contrast, nonferuloylated fractions were most abundant during the stage of maximum elongation but declined to a constant level by day 6. (c) Glycosidic linkage analysis of carbohydrate reveals that substitution of the xylan backbone of feraxan by arabinosyl residues decreased during coleoptile growth. We conclude that significant incorporation of ferulic acid occurs and/or more feruloyated domains are added to the arabinoxylan during development. This augmentation in phenolic acids is accompanied by a concerted displacement of arabinosyl residues and/or a reduction in the incorporation of regions enriched in arabinosyl sidechains.