|Jung, Hans Joachim|
Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/18/1998
Publication Date: N/A
Interpretive Summary: Forage crops are the primary feed resource for dairy and beef production systems. Growth and milk production on forage diets is limited by the often low digestibility of the fiber present in forages. Lignin, a component of fiber, has been identified as the factor responsible for poor fiber digestibility by cattle. It has been suggested that the mix of the two chemical building blocks from which lignin is constructed will influence how severely lignin limits fiber digestion. A mutant form of Arabidopsis, a small weedy plant useful in genetic studies, which does not produce one of the lignin building blocks was used to test if lignin composition does alter the inhibitory effects of lignin on fiber digestion. Although the mutant plants produced a very different type of lignin than normal, digestibility of fiber was still reduced by accumulation of lignin just as seen in normal Arabidopsis plants. It was concluded that changes in lignin composition will have little impact on improving forage fiber digestibility. This result will be of interest to biotechnologists who are attempting to modify lignin in plants and suggests that the current goal of altering lignin composition via biotechnology is unlikely to increase fiber digestibility.
Technical Abstract: An Arabidopsis mutant that does not deposit syringyl type lignin was used to test the hypothesis that lignin composition impacts cell wall degradability. Two lines of the ferulate-5-hydroxylase deficient fah1 mutant and the wild-type control line were grown in the greenhouse. In Exp. 1, the plants were harvested at the mature seed stage. For Exp. 2 plants were harvested 5, 6, 7, and 8 wk after sowing. In both experiments stems were analyzed for cell wall concentration and composition and for in vitro degradability of cell wall polysaccharide components by rumen microorganisms. Lignin concentration was the same for all three Arabidopsis lines. Cell wall polysaccharide degradability did not differ among the Arabidopsis lines in the first experiment after 24-h fermentations, but the cell-wall polysaccharides of the fah1-2 mutant line were less degradable after 96-h than either the wild-type or the fah1-5 mutant. In Exp. 2 no differences among lines were found for cell-wall polysaccharide degradability after either 24- or 96-h fermentations; however, significantly higher levels of ester-bound ferulic acid was found in the walls of the fah1 mutant lines. Increasing stem maturity was correlated with reduced degradation of cell wall polysaccharides. These experiments indicate that lignin composition, as measured by syringyl-to- guaiacyl ratio, does not alter cell wall degradability in Arabidopsis.