|Grabber, John - PROTIVA-MONSANTO CORP.|
Submitted to: Gordon Research Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: August 22, 1997
Publication Date: N/A
Technical Abstract: The role of ferulate xylan esters as intermediaries in cell wall cross- linking and lignin formation in grasses was investigated using nonlignified walls from maize cell suspensions and lignins isolated from stems of ryegrass. Hydrogen peroxide treatment of maize walls containing 18 mg g-1 of ferulates increased peroxidase-mediated coupling of ferulate monomers into dehydrodimers from 15 to 55%, with 8-5 couplings being the predominan 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%). Structural analysis of ferulate-lignin cross-products isolated from maize walls and ryegrass stems revealed that the initial coupling of ferulates was almost exclusively to the beta-position of monolignols, providing compelling evidence that ferulates act as nucleation sites for lignification. About 40% of the ferulate monomers and 30% to 90% 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, ferulate esters also enhanced the polymerization of monolignols, particularly sinapyl alcohol, into maize walls. Overall, these studies show that ferulate esters play an integral role in xylan-xylan and xylan-lignin cross-linking and lignin formation in grasses.