Characterisation of Lignin from CAD and OMT DeficientBm Mutants of Maize

Internodes of the maize cell line W401 and bm1 and bm3 mutants expressed 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 bm1 and bm3 mutants (74·4–86·4 and 66·0– 84·2 g kg-1 cell wall DM, respectively). TP were inversely related to cellulase digestibility with values of 85·4–91·5, 89·3–92·1 and 91·3–94·1% for normal, bm1 and bm3. Marked differences in p-coumaric acid concentrations were found ranging from 20·9 to 26·3 g kg-1 cell wall DM for normal, 14·9 to 15·3 g kg-1 for bm1 to 10·1 to 14·4 g kg-1 for bm3. The ferulate pattern was entirely different with the bm1 genotype providing the lowest total (9·1–10·7 g kg-1) and etherified (1·9–2·3 g kg-1) values. Although the bm3 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 ferulate (2·8–3·4 vs 3·2–4.1 g kg-1) implying a greater extent of cross-linking between wall polymers. Recovery of guaiacyl and syringyl residues was greatest in the normal maize with the bm1 occupying the middle position between the two extremes. Calculated S: G ratios from 4 M NaOH digestion and NMR were in good agreement with the normal line giving the highest ratio, bm1 intermediate and bm3 the lowest. Colorimetric analysis revealed a large increase in the aldehyde content of the in situ bm1 lignin compared to normal and bm3 genotypes although NMR failed to reveal significant numbers of aldehydic resonances.