Author
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Jung, Hans Joachim |
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Submitted to: Phytochemistry
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/15/2003 Publication Date: 7/1/2003 Citation: JUNG, H.G. MAIZE STEM TISSUES: FERULATE DEPOSITION IN DEVELOPING INTERNODE CELL WALLS. PHYTOCHEMISTRY. 2003. V. 63. P. 543-549. Interpretive Summary: Grass forages provide a major feed resource for dairy, beef, and sheep production. Performance of livestock when fed grasses is often limited by the high fiber content and the low digestibility of fiber in grasses. Ferulate is a component of grass fiber that ties the potentially digestible carbohydrates in fiber to lignin, a compound that blocks digestion. It has been suggested that if ferulate could be reduced in grasses, fiber digestibility would be improved because the carbohydrates would no longer be tied to lignin. However, our understanding of how ferulate is added to fiber during grass growth and development is limited. A study was conducted using the stem of corn plants to determine where and when ferulate is added to fiber during growth and development of grasses. It was observed that contrary to a previous hypothesis, ferulate is added to corn stem fiber throughout the development of grass. Previously it had been suggested that ferulate was only added to the fiber laid down early in grass development. This result puts in question previous explanations for how ferulate affects fiber digestibility. Fiber laid down late in grass development is more digestible than fiber laid down early in development, but apparently both fiber fractions have ferulate. These results will be of value to scientists who are conducting research on limitations to fiber digestibility and for devising strategies for improving grass fiber digestibility. Technical Abstract: It has been hypothesized that ferulates are only deposited in the primary cell wall of grasses. To test this hypothesis, the fourth elongating, above-ground internode of maize (Zea mays L.) was sampled from three maize hybrids throughout development. Cell wall composition was determined by the Uppsala Dietary Fibre method. Ester- and ether-linked ferulates were determined by high-pressure liquid chromatography of ferulic acid released from the internodes by low and high temperature alkaline treatments. Internode length increased from 9 to 152 mm over 96 d of growth, with elongation being complete in the first 12 d. More than half of the cell wall material in the maize internodes accumulated after elongation had ended. Deposition of cell wall material appeared to reach its maximum extent 40 d after sampling began, well before physiological maturity of the maize plants. Galactose and arabinose began to accumulate early in cell wall development which was presumed to be associated with primary wall growth during internode elongation. The major secondary wall constituents (analyzed as glucose, xylose, and Klason lignin) did not begin to accumulate rapidly until shortly before internode elongation ended. Ferulate ester deposition began before ferulate ethers were observed in the cell wall, but both forms of ferulate continued to accumulate in secondary cell walls, long after internode elongation had ceased. These data clearly show that contrary to the hypothesis, ferulate deposition was not restricted to the primary wall and that active lignin/polysaccharide cross-linking mediated by ferulates occurs in the secondary wall. |
