CHARACTERIZATION OF LIGNIN FROM CAD AND OMT DEFICIENT BM MUTANTS OF MAIZE

Internodes of the maize cell line W401 and bm(1) and bm(3) mutants exp ressed in W401 were harvested 5 days after anthesis (A5) and at silage (S) stage. The normal maize had a higher total phenolic (TP) content (80.5-90.5 g kg(-1) cell wall DM) than both bm(1) and bm(3) mutants (7 4.4-86.4 and 66.0-84.2 g kg(-1) cell wall DM, respectively). TP were i nversely related to cellulase digestibility with values of 85.4-91.5, 89.3-92.1 and 91.3-94.1% for normal, bm(1) and bm(3). Marked differenc es in p-coumaric acid concentrations were found ranging from 20.9 to 2 6.3 g kg(-1) cell wall DM for normal 14.9 to 15.3 g kg(-1) for bm(1) t o 10.1 to 14.4 g kg(-1) for bm(3). The ferulate pattern was entirely d ifferent with the bm(1) genotype providing the lowest total (9.1-10.7 g kg(-1)) and etherified (1.9-2.3 g kg(-1)) values. Although the bm(3) contained more total ferulate (11.5-13.1 vs 10.9-11.7 g kg(-1)), the normal variety had a significantly greater amount of etherified ferula te (2.8-3.4 vs 3.2-4.1 g kg(-1)) implying a greater extent of cross-li nking between wall polymers. Recovery of guaiacyl and syringyl residue s was greatest in the normal maize with the bm(1) occupying the middle position between the two extremes. Calculated S : G ratios from 4 M N aOH digestion and NMR were in good agreement with the normal line givi ng the highest ratio, bm(3) intermediate and bm(1) the lowest. Colorim etric analysis revealed a large increase in the aldehyde content of th e in situ bm(1) lignin compared to normal and bm(3) genotypes although NMR failed to reveal significant numbers of aldehydic resonances.