Degradability of Cell-Wall Polysaccharides in Maize Internodes during Stalk Development
- H. G. Jung ,
- T. A. Morrison and
- D. R. Buxton
- U SDA-ARS, Plant Sciences Res. Unit and U.S. Dairy Forage Res. Center Cluster, and Dep. of Agronomy and Plant Genetics, Univ. of Minnesota, 411 Borlaug Hall, St. Paul, MN 55108
D ep. of Agronomy and Soils, 201 Funchess Hall, Auburn Univ., Auburn, AL 36849
U SDA-ARS-NPS, Bldg. 005 BARC-West, Beltsville, MD 20705
Limitations to degradation of forage cell-wall constituents in maturing plant tissue are not fully understood, which limits progress in developing cultivars with improved digestibility. We determined in vitro degradability of cell-wall components by rumen microorganisms in developing internodes of maize (Zea mays L.). Plants were grown in the growth chamber and harvested at the 15th-leaf stage of development. Individual internodes were divided in half and separated into rind and pith fractions. Cell-wall degradability was measured on the internode samples and correlated with cell-wall degradability. Degradability of all cell-wall polysaccharide components, except galactose and mannose, declined with maturation of maize internodes. Degradabilities of glucose and xylose residues exhibited large differences between 24- and 96-h fermentation intervals (31 to 58% additional degradation in 72 h), whereas the arabinose and uronic acids potentially degradable in 96 h were already almost completely degraded in 24 h. Maize rind, consisting of epidermal and sclerenchyma tissues and many vascular bundles, was less degradable than the pith (736 vs. 811 g kg-−1, respectively), which had thinner-walled parenchyma tissue and fewer vascular bundles. Lower portions of internodes were younger and more degradable than the upper halves (805 vs. 743 g kg−1, respectively). Ferulate ether concentration was negatively correlated with cell-wall polysaccharide degradability in young, elongating internodes but not for internodes in which elongation had ceased to occur. This pattern is in agreement with the hypothesis that ferulate cross-linking limits cell-wall degradation, but that the effect is only observable in young tissues before dilution of ferulate ether concentrations by secondary wall deposition of lignin and polysaccharides obscures the relationship.
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