Page Banner

United States Department of Agriculture

Agricultural Research Service


item Ralph, John
item Kim, Hoon
item Lu, Fachuang
item Ralph, Sally
item Landucci, Larry
item Ito, Takashi
item Kawai, Shingo
item Ohashi, Hideo
item Higuchi, Takayoshi

Submitted to: International Symposium on Wood and Pulping Chemistry
Publication Type: Proceedings
Publication Acceptance Date: 12/9/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Peroxidase/H2O2-mediated radical coupling of hydroxycinnamaldehydes produced 8-O-4-, 8-5-, 8-8-, and 5-5-dimers as had been documented earlier (although we found that the 8-5-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 sisolated 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 8-O-4-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 8-O-4-coupled products. 8-8-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.

Last Modified: 05/28/2017
Footer Content Back to Top of Page