CHANGES IN DEHYDRODIFERULIC ACIDS AND PEROXIDASE-ACTIVITY AGAINST FERULIC ACID ASSOCIATED WITH CELL-WALLS DURING GROWTH OF PINUS-PINASTER HYPOCOTYL

Hydroxycinnamic acids associated with hypocotyl cell walls of dark-gro wn seedlings of Pinus pinaster Aiton were extracted with 1 N NaOH and identified by gas chromatography-mass spectrometry. The main hydroxyci nnamic acid found was ferulic acid. Diferulic acid dehydrodimers were also found, with the 8,8-coupled isomer (compound 11) being the dehydr odiferulate present in the highest amount. However, the 5,5-coupled is omer, commonly referred to as diferulic acid, was not detected. Two tr uxillic acids, 4-4'-dihydroxy-3-3'-dimethoxy-alpha-truxillic acids I a nd II, were tentatively identified. The 8,8-coupled dehydrodiferulic a cid (compound 11) was the phenolic acid that showed the most conspicuo us changes with hypocotyl age as well as along the hypocotyl axis. Per oxidase activity against ferulic acid was found in the apoplastic flui d as well as being ionically and covalently bound to the cell walls. T he peroxidase activity increased with hypocotyl age as well as from th e subapical toward the basal region of the hypocotyls. A key role in t he cell-wall stiffening of 8,8 but not 5,5 dimerization of ferulic aci d catalyzed by cell-wall peroxidases is proposed.