Variability in Lignin Composition and Structure in Cell Walls of Different Parts of Macauba (Acrocomia aculeata) Palm Fruit

The lignins from different anatomical parts of macauba (Acrocomia aculeata) palm fruit, namely stalks, epicarp, and endocarp, were studied. The lignin from stalks was enriched in S-lignin units (S/G 1.2) and beta-ether linkages (84% of the total) and was partially acylated at the gamma-OH of the lignin side-chains (26% lignin acylation), predominantly with p-hydroxybenzoates and acetates. The epicarp lignin was highly enriched in G-lignin units (S/G 0.2) and consequently depleted in beta-ethers (65%) and enriched in condensed structures such as phenylcoumarans (24%) and dibenzodioxocins (3%). The endocarp lignin was strikingly different from the rest and presented large amounts of piceatannol units incorporated into the polymer. This resulted in a lignin polymer depleted in beta-ethers but enriched in condensed structures and linked piceatannol moieties. The incorporation of piceatannol into the lignin polymer seems to have a role in seed protection.