Abstract
Peroxidase/H2O2-mediated radical coupling of hydroxycinnamaldehydes produced 81O14-, 8-5-, 818-, and 5-5dimers as had been documented earlier (although we found that the 815-dimer is produced in its cyclic phenylcoumaran form at neutral pH). Spectral data from dimers and oligomers has allowed a more substantive assignment of aldehyde components in lignins isolated from a CAD-deficient pine mutant and an antisense-CAD-downregulated transgenic tobacco. The CAD-deficient pine lignin shows the typical benzaldehyde and cinnamaldehyde peaks at levels significantly enhanced over the corresponding lignin from normal pine, along with evidence for two types of 81O14-coupled coniferaldehyde units. The CAD-downregulated tobacco has even higher levels of hydroxycinnamaldehyde (mainly sinapaldehyde) incorporation producing significant levels of the analogous two types of 81O14-coupled products. 818- Coupled units are also clearly evident. The isolated lignins do not appear to be artifacts: they are high molecular weight (~17 kDa), and there is clear evidence for coupling of hydroxycinnamaldehydes with each other and then incorporating into the lignin, as well as for the incorporation of coniferaldehyde monomers onto pre-formed lignin oligomers. The implication is that coniferaldehyde and sinapaldehyde (as well as vanillin and syringaldehyde) co-polymerize with the traditional monolignols, the hydroxycinnamyl alcohols (sinapyl, coniferyl, and 4-hydroxycinnamyl alcohol), into lignins and do so at markedly enhanced levels when the normal monolignol production is downregulated by CAD-deficiency.
Keywords
Lignin,
Aldehydes,
Spectral analysis,
Hydroxycinnamaldehydes,
Dimers,
Oligomers,
Coniferaldehyde,
Copolymers,
Coniferyl alcohol,
Synthetic lignins
Citation
Ralph, John.; Kim, Hoon.; Lu, Fachuang.; Ralph, Sally A.; Landucci, Larry L.; Ito, Takashi.; Kawai, Shingo. 1999. Incorporation of hydroxy-cinnamaldehydes into lignins. 10th International Symposium on Wood and Pulping Chemistry, Main Symposium, 1999 June 07-10, Yokohama, Japan . Atlanta, GA : TAPPI Press, 1999.:p. 58-63 : ill.
