Figure 1.

Alternative pathways for the methylation of monolignols. The enzymes are: PAL, l-phenylalanine ammonia-lyase; C4H, cinnamate 4-hydroxylase; C3H, coumarate 3-hydroxylase; COMT, bispecific caffeic acid/5-hydroxyferulic acid O-methyltransferase; F5H, ferulate 5-hydroxylase; CC3H, coumaroyl CoA 3-hydroxylase; CCOMT, bispecific caffeoyl/5-hydroxyferuolyl CoA O-methyltransferase; 4CL, coumarate (hydroxycinnamate) CoA ligase; CCR, cinnamoyl CoA reductase; and CAD, coniferyl alcohol dehydrogenase. Dashed arrows represent reactions that have yet to be clearly demonstrated in vitro. cDNA clones encoding enzymes marked in bold were obtained from alfalfa. In some species, 4CL has very little activity with sinapate as substrate.