Maize stem tissues: Cell wall concentration and composition during development

Grass maturation results in reduced cell wall degradability by ruminant livestock. Using a specific internode of maize (Zea mays L.) stems as a model, the pattern of grass stem tissue and cell wall development was characterized. The fourth elongated internode above ground level from three maize hybrids was sampled at 10 stages of development beginning when the internode was about 10 mm in length through physiological maturity from a 2-yr, replicated field trial at St. Paul, MN. Tissue development was characterized by light microscopy. Cell wall concentration and composition (polysaccharide sugar residues, lignin, ferulates, and p-coumarates) were determined. Internode length and cross-sectional area increased from Sampling Date I until the interval between Sampling Dates 5 and 6. During elongation only protoxylem vessels stained positive for lignin. After elongation, parenchyma, sclerenchyma, and metaxylem tissues lignified, but phloem did not. Cell wall concentration increased until shortly after elongation ended. Cell wall lignin concentration declined over the first four samples, with an increase in glucose and xylose polysaccharide residues, before rising sharply until after elongation was complete. Ferulate cross-tinks of lignin to arabinoxylan increased 12-fold during elongation. Our results indicated that post-elongation development of sclerenchyma and rind-region parenchyma accounted for the majority of cell wall accumulation and lignification in maize stems.