Degradability of Cell‐Wall Polysaccharides in Maize Internodes during Stalk Development

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.