Conversion of guaiacyl to syringyl moieties on the cinnamyl alcohol pathway during the biosynthesis of lignin in angiosperms

Aglycons derived from 4-O-beta-D-glucosides of both caffeyl and 5-hydroxyco niferyl alcohols were incorporated into guaiacyl (G) and syringyl (S) units in the lignin of newly formed xylem of several angiosperms. It is likely t hat these aglycons enter the cinnamyl alcohol pathway as intermediates in t he introduction of methoxyl groups onto aromatic rings, and serve as precur sors for the biosynthesis of lignin. The S/G ratio in this pathway was coin cident with the ratio in the cell wall lignin of each tree. Our results ind icate that the cinnamyl alcohol pathway involves the same mechanisms as the cinnamic acid and cinnamyl CoA pathways and they suggest that this novel p athway might be part of a metabolic grid in the biosynthesis of lignin.