Lignin degradation and detoxification of lignin-derived products (By similarity). Involved in lignin synthesis in seed coats, in seed coat permeability, in seed germination, and in root elongation. Required for the seed coat (testa) brown pigmentation by mediating the polymerization of proanthocyanidin (tannin) from its monomer precursor epicatechin. Slightly promotes seed dormancy. 4 hydroquinone + O2 = 4 benzosemiquinone + 2 H2O Binds 4 Cu cations per monomer. Mostly expressed in siliques, particularly in developing seeds. Also detected at low levels in stems, seedlings, and flowers. Transcript levels increase during rosette leaves development. In the inflorescence stem, highest levels in the young, developing tip and lowest levels in the basal stem tissues. Strong increase 4 days after fertilization. Specifically localized in developing seed coat (testa). Detected in the endothelium and in the pigment strand at the chalaza zone during early stages of embryo morphogenesis. Later, the activity increased and spread to the outer integument, mostly in the oil penultimate cell layer. Strongly expressed in early aborted seeds and in the transmitting tissue of the silique. Belongs to the multicopper oxidase family.