Cross-linking of maize walls by ferulate dimerization and incorporation into lignin.
Cross-linking of xylans and lignin by ferulates was investigated with primary maize walls acylated with 2% ferulate and with ferulate ethyl esters. Peroxidase-mediated coupling of wall ferulate and ethyl ferulate yielded mostly 8-coupled products, including three new dehydrodimers. Significant quantities of 5-5-coupled diferulate formed only within walls, suggesting that matrix effects influence dimer formation. Over 60% of wall ferulate dimerized upon H2O2 addition, suggesting that xylan feruloylation is highly regulated during wall biosynthesis to permit extensive dimer formation at the onset of lignification. During lignification, ferulate and 5-5-coupled diferulate copolymerized more rapidly and formed fewer ether-linked structures with coniferyl alcohol than 8-5-, 8-O-4-, and 8-8-coupled diferulates. The potential incorporation of most ferulates and diferulates into lignin exceeded 90%. As a result, xylans become extensively cross-linked by ferulate dimerization and incorporation to lignin, but only a small and variable proportion of these cross-links is measurable by solvolysis of lignified walls.
Grabber
J H
JH
U.S. Dairy Forage Research Center, Agricultural Research Service, U.S. Department of Agriculture, 1925 Linden Drive West, Madison, Wisconsin 53706, USA. jgrabber@facstaff.wisc.edu
Ralph
J
J
Hatfield
R D
RD
D002473:Cell Wall; D003373:Coumaric Acids; D019281:Dimerization; D007202:Indicators and Reagents; D008031:Lignin / Q000378:metabolism*; D003313:Zea mays / Q000737:chemistry*
D003373:Coumaric Acids; D007202:Indicators and Reagents; D008031:Lignin; C004999:ferulic acid