In-vitro Fermentability of Cell Walls as Influenced by Lignin Composition and Cross-Linking.
John H. Grabber1, David R. Mertens1, Carola Funk2, and John Ralph1. (1) U.S. Dairy Forage Research Center, USDA-Agricultural Research Service, 1925 Linden Drive West, Madison, WI 53706, (2) Institute of Biochemistry and Food Chemistry, University of Hamburg, Grindelallee 117, 20146, Hamburg, Germany
We assessed how diverse modifications in lignin composition and reductions in ferulate-lignin cross-linking influence the degradability of cell walls. Cell walls from nonlignified maize cell suspensions were artificially lignified with varying ratios of normal monolignols (coniferyl and sinapyl alcohols) and with monolignols plus unusual lignin precursors identified in some types of normal, mutant, and transgenic plants. Cell walls with normal or reduced feruloylation were also lignified with normal monolignols plus varying levels of sinapyl p-coumarate, the presumed precursor of p-coumaroylated lignins in grasses. Lignified cell walls were incubated in vitro with rumen microflora and then nondegraded structural carbohydrates were determined by acid-solubolization and colorimetric analysis. Shifts in normal monolignol composition or incorporation of coniferaldehyde, gamma-acetylated sinapyl alcohol, dihydroconiferyl alcohol, or sinapyl p-coumarate into lignin did not influence structural carbohydrate degradability. Degradability was, however, enhanced by incorporation of 5-hydroxyconiferyl alcohol into lignin and by reductions in ferulate-lignin cross-linking. In ongoing work, the kinetics of cell wall degradation will be determined by measuring gas production during in vitro fermentation with rumen microflora.