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ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Research » Publications at this Location » Publication #102658
Title: INCORPORATION OF HYDROXYCINNAMALDEHYDES INTO LIGNINS

Author
item Ralph, John
item KIM, HOON - UNIV OF WISCONSIN MADISON
item LU, FACHUANG - UNIV OF WISCONSIN MADISON
item RALPH, SALLY - US FOREST PRODUCTS LAB
item LANDUCCI, LARRY - US FOREST PRODUCTS LAB
item ITO, TAKASHI - GIFU UNIV JAPAN
item KAWAI, SHINGO - GIFU UNIV JAPAN
item OHASHI, HIDEO - GIFU UNIV JAPAN
item HIGUCHI, TAKAYOSHI - GIFU UNIV JAPAN

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.