CAFFEIC ACID - O-METHYLTRANSFERASES AND THE BIOSYNTHESIS OF FERULIC ACID IN PRIMARY-CELL WALLS OF WHEAT SEEDLINGS

The activity of O-methyltransferases (OMT) in tissues of wheat and the changes in their specificity for hydroxycinnamic acid substrates was followed during seedling development. In the early stages of developme nt, prior to lignin deposition, the OMT showed a preference for caffei c acid as a substrate. This acitivity peaked at day 3. Later, after li gnin deposition had begun, the activities of OMT and cinnamyl aldehyde dehydrogenase increased continuously and the OMT had a preference for 5-hydroxyferulic acid. It is suggested that the ''early'' OMT may be involved in the synthesis of ferulic acid destined for esterification of cell wall arabinoxylans whereas, the ''late'' OMT may be involved w ith the synthesis of ferulic and sinapic acids which are converted to the monolignol building blocks of lignin.