Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 30, 2002
Publication Date: N/A
Interpretive Summary: Fiber makes up 15 to 80% of the dry weight of plants. Fiber is composed primarily of structural polysaccharides, proteins, and an inert substance known as lignin. In grasses and cereal crops, these components are cross-linked (i.e. knit together) by small molecules known as ferulate. Plants may use ferulate cross-linking and lignin to stop the growth of their tissues and to ward off various pests. Ferulate cross-links and lignin also limit the digestibility of feeds consumed by livestock and they influence the physical properties and health benefits of human foods. It extremely difficult to characterize the types of structures formed between ferulate and lignin in mature plants. In a laboratory study, we isolated nonlignified fiber from corn cells and measured the concentration of ferulate and of various dimers it forms. We then formed a small amount of artificial lignin in the corn fiber and characterized the types of structures formed between ferulate and lignin. These experiments revealed that ferulates can play a role in plants as nucleation sites for lignin formation¿sites at which lignification begins in fiber. Our findings will help researchers working in the areas of plant physiology, human nutrition, feed utilization, and food science to better understand and characterize interactions between ferulate and lignin in plants.
Technical Abstract: Ferulate and diferulates mediate cell wall cross-linking in grasses but little is known about their cross-coupling reactions with monolignols and their role in lignin formation in primary cell walls. Feruloylated primary walls of maize were artificially lignified and then saponified to release ferulate and diferulates and their cross-products with coniferyl alcohol for analysis by GC-FID, GC-MS, and NMR. Ferulate and 5¿5-coupled diferulate had a greater propensity than 8-coupled diferulates to copolymerize with coniferyl alcohol, forming mostly 4-O-b', and 8-b' and some 8¿O¿4' and 8¿5' cross-coupled structures. Some 8¿b' structures de-esterified from xylans but these cross-links were subsequently replaced as 8-coupled diferulates formed stable cross-coupled structures with lignin. Based on the incorporation kinetics of ferulate and diferulates and the predicted growth of lignin, cross-products formed at the onset of lignification acted as nucleation sites for lignin polymerization.