p-hydroxyphenyl, guaiacyl, and syringyl lignins have similar inhibitory effects on wall degradability

Studies with normal, mutant, and transgenic plants have not clearly established whether the proportion of p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) units in lignin directly affects the degradability of cell walls by hydrolytic enzymes. Dehydrogenation polymer-cell wall complexes containing varying ratios of H, G, and S lignins were formed by peroxidase/H2O2-mediated polymerization of p-coumaryl, coniferyl, and sinapyl alcohols into unindemnified avails isolated from cell suspensions of maize (Zea mays L). Lignification substantially reduced the degradability of cell walls by fungal hydrolases, but degradability was not affected by lignin composition. On the basis of these results, we propose that improvements in wall degradability, previously attributed to changes in lignin composition, were in fact due to other associated changes in wall chemistry or ultrastructure.