Maize Stem Tissues: Impact of Development on Cell Wall Degradability

Abstract

Grass degradability declines as cell wall and lignin concentrations increase during maturation. The role of tissue development and lignification in decline of stem degradability was examined in maize (Zea mays L.) internodes sampled at 10 stages of growth from early elongation through plant physiological maturity. The fourth elongated internode above ground level was collected from three maize hybrids grown in a 2‐yr, replicated field trial at St. Paul, MN. Internode cross‐sections and ground samples were incubated in vitro for 24‐ and 96‐h with rumen microbes. Tissue degradation was examined by light microscopy and degradability of cell wall polysaccharide components from ground internodes was determined. All tissues in elongating internodes were completely degradable except for protoxylem vessels, which was the only lignified tissue. After elongation, degradability of all tissues declined markedly except for phloem, which never lignified. Tissues with thick, lignified secondary walls (sclerenchyma and rind‐region parenchyma) required longer incubation times for observable degradation. Cell wall polysaccharide components were highly degradable in immature internodes, but degradability declined after elongation and reached a minimum by Sampling Date 8, with glucose and xylose residues having the greatest reductions in degradability. Cell wall polysaccharide degradation was related to lignin concentration and ferulate cross‐linking in a complex manner.