|Grabber, John - MONSANTO-PROTIVA|
Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: July 11, 1998
Publication Date: N/A
Technical Abstract: The role of ferulate xylan esters as intermediaries in cell wall cross- linking and lignin formation and as barriers of cell wall hydrolysis were investigated with nonlignified cell suspensions of maize. Hydrogen peroxide treatment of maize walls containing 18 mg/g of ferulates increased coupling of ferulate monomers into dehydrodimers from 15 to 55%, with 8-5 couplings being the predominant type. Oxidative coupling of ferulate esters in maize walls with synthetic lignins was greater for ferulate monomers and 5-5- coupled diferulate (ca 95%) than for 8-O-4, 8-5 and 8-8-coupled diferulates (ca 75%). Ferulates coupled primarily to the beta-position of monolignols during gradual "end-wise" polymerization indicating that ferulates can act as nucleation sites for lignification. This role was diminished under rapid "bulk" lignification conditions where ferulates coupled extensively to dilignols or lignin oligomers. Depending on lignification conditions, 14- 25% of the ferulate monomers and 5% to 55% of the ferulate dimers incorporated into lignin were released by high-temperature alkaline hydrolysis, indicating that ferulates differed substantially in their propensity to form 4-O-beta' linked structures with lignin. Due to their ability to transfer radicals, ferulates enhanced the polymerization of monolignols, particularly sinapyl alcohol. Solvent extractability of lignins was enhanced in walls with low ferulation suggesting that ferulates help to anchor lignins within cell walls. Diferulate and ferulate-lignin cross-links also limited the rate and, to a lesser degree, the extent of cell wall degradation by fungal enzymes and rumen bacteria. These studies show that ferulates play an integral role in the cross-linking and lignification of grass walls and their resistance to hydrolytic enzymes.