The product of the alfalfa Caffeic acid/5-hydroxyferulic acid 3/5-O-methyltransferase (COMT) catalyzed methylation of 5-Hydroxyferulic acid is sinapic acid. 5-Hydroxyferulic acid O-methyltransferase activities (pkat mg-1 protein) in stem material from COMT downregulates transgenic alfalfa.