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ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Research » Publications at this Location » Publication #113262
Title: CROSS-COUPLING OF HYDROXYCINNAMYL ALDEHYDES INTO LIGNINS

Author
item KIM, HOON - UNIVERSITY OF WISCONSIN
item Ralph, John
item YAHIAOUI, NABILA - UNITE MIXTE DE RECHERCHE
item PEAN, MICHAEL - COMM A L ENERGIE ATOMIQUE
item BOUDET, ALAIN - UNITE MIXTE DE RECHERCHE

Submitted to: Organic Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/22/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Mutant and transgenic plants provide useful insights into biochemical processes occurring in normal plants. It has recently been found that plants will change the makeup and structure of their lignin (the polymer that holds fibers together in woody and forage plants) if they are not able to produce lignins normally. In this case, the final step in the biosynthetic pathway was blocked and the lignins incorporated significant quantities of aldehydes. The structures that are produced in the lignins were studied so that the mechanism of their incorporation can be elucidated and their utilization can be addressed. One of the aldehydes, coniferyl aldehyde, was found (using NMR spectroscopy) to react only with one of the two major types of units in lignin, whereas the other, sinapyl aldehyde, reacted with both. In a basic sense, the findings provide new evidence for the so-called "endwise" mechanism of polymerization, and revealed that the lignins are apparently made under simple chemical control. It is increasingly evident that plants are able to incorporate substantial amounts of components that are not normally considered to be precursors of lignins. This means that breeding or genetic engineering can be used to enhance these components if they are found to be of value. Such studies are at the heart of efforts to improve the utilization of valuable plant resources in a variety of processes.

Technical Abstract: Pathways for hydroxycinnamyl aldehyde incorporation into lignins are revealed by examining transgenic plants deficient in cinnamyl alcohol dehydrogenase, the enzyme that converts hydroxycinnamyl aldehydes to the hydroxycinnamyl alcohol lignin monomers. In such plants the aldehydes incorporate into lignins via radical coupling reactions. As diagnostically revealed by long-range 13C-1H correlative NMR, sinapyl aldehyde (3,5-dimethoxy-4-hydroxy-cinnamaldehyde) 8-O-4-cross-couples with both guaiacyl (3-methoxy-4-hydroxyphenyl-propanoid) and syringyl (3,5-dimethoxy-4-hydroxyphenyl-propanoid) units whereas coniferyl aldehyde cross-couples only with syringyl units.