Hydroxycinnamates in suberin formation

Hydroxycinnamates are found associated with suberin in several forms: covalently linked to the aliphatic suberin; in the residue after suberin-removal; and in the non-polar extractives of suberized tissues in the form of alkyl ferulates. Suberin-associated hydroxycinnamates have been found mainly as ferulic acid-derivatives, sometimes as feruloylamides and in a lesser extent as caffeates. Ferulic acid esters of long-chain omega-hydroxyacids are prevalent in the partial depolymerisation products of suberin. Also, enzymes able to catalyze the feruloylation of omega-hydroxyacids were found timely-associated with the suberization process. It is proposed that ferulic acid, and its dimers, through esterification to omega-hydroxyacids, covalently link the suberin aliphatic polyester to suberin-associated polyaromatics. In this case, the known role of ferulates, and related hydroxycinnamates, as cross-linkers of structurally different polymers would be enlarged to suberized cell-walls.