Abstract
The cross-linked nature of plant cell walls provides structural integrity for continued growth and development, but limits degradation and utilization by ruminants. In grasses a major cross-linking component is ferulic acid that is incorporated into cell walls as an ester linked residue on arabinoxylans. Ferulates can become coupled to each other and to lignin forming a highly cross-linked matrix of carbohydrates and lignin. Seedling ferulate ester mutants (sfe) were produced in maize using the transposon system and evaluated in feeding trials. The work described here was undertaken to characterize changes in the ferulate cross-linked nature as well as other components of the corn cell wall matrix in leaf, sheath and stem tissues. Total ferulates decreased modestly due to the mutation and were more apparent in leaf tissue (16% - 18%) compared to sheath (+5 to -6% change) and stem (8% - 9% decrease). The most significant changes were in the ether linked ferulates to lignin, both monomer and dehydrodiferulates (14% to 38% decrease). Other characteristics of the cell wall (lignin, neutral sugar composition) also showed modest changes. The change in total ferulates was modest, but led to improved animal performance. These findings suggest that relatively small changes can have a significant impact upon how well plant materials can be broken down and utilized by ruminants such as dairy cows.
Highlights
It is well established that ferulates play a pivotal role in cross-linking the cell wall matrix
Decreasing the level of ferulates incorporated into the cell wall matrix would theoretically decrease the amount of cross-coupling mediated by ferulates and increase cell wall digestibility
The maize sfe mutants resulted in changes within the cell wall matrices including a reduction in total ferulate cross-linking within the cell walls and reductions in lignin
Summary
There is a renewed interest in forages especially in energy dense diets such as those required for high producing dairy cows This is primarily due to the increase in grain prices partially driven by the creation of new markets especially for corn grain as a primary feedstock for ethanol production. With increasing demands for bioenergy liquid fuels either from grain or from plant vegetative biomass there is competition for productive land areas among needs for human food and fiber, animal feed needs, and biomass for bioenergy. Once incorporated in the cell wall, FA can undergo radical mediated cross-coupling reactions [4] [5] to form an array of dehydrodiferulates (dimers DFA). Ferulates can undergo further radical mediated cross-coupling reactions with growing lignin polymers [8] [9] [10]. Because of the direct impact of ferulate cross-linking on cell wall degradation, limiting the degree of ferulate incorporation should result in increased wall degradation
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