SEVERE INHIBITION OF MAIZE WALL DEGRADATION BY SYNTHETIC LIGNINS FORMED WITH CONIFERALDEHYDE

Although the enzymatic or ruminal degradability of plants deficient in cinnamyl alcohol dehydrogenase (CAD) is often greater than their norm al counterparts, factors responsible for these degradability differenc es have not been identified. Since lignins in CAD deficient plants oft en contain elevated concentrations of aldehydes, we used a cell-wall m odel system to evaluate what effect aldehyde-containing lignins have o n the hydrolysis of cell walls by fungal enzymes. Varying ratios of co niferaldehyde and coniferyl alcohol were polymerised into non-lignifie d primary walls of maize (Zea mays L) by wall-bound peroxidase and exo genously supplied H2O2. Coniferaldehyde lignins formed fewer cross-lin ked structures with other wall components, but they were much more inh ibitory to cell wall degradation than lignins formed with coniferyl al cohol. This suggests that the improved degradability of CAD deficient plants is not related to the incorporation of p-hydroxycinnamaldehyde units into lignin. Degradability differences were diminished if enzyme loadings were increased and if hydrophobic aldehyde groups in lignins were reduced to their corresponding alcohols by ethanolic sodium boro hydride. (C) 1998 Society of Chemical Industry.