|Jung, Hans Joachim|
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2006
Publication Date: 6/1/2006
Citation: Jung, H.G., Casler, M.D. 2006. Maize stem tissues: cell wall concentration and composition during development. Crop Science. 46:1793-1800. Interpretive Summary: Corn silage and other grass crops are among the most important feed resources for beef, milk, and wool production. It is well known that as grasses become more mature, they accumulate higher concentrations of dietary fiber and this fiber becomes progressively less digestible. Only limited information is available on how the various tissues in grass develop and mature, and how the fiber concentration and digestibility of these tissues change during development. Future efforts to improve the feeding value of grasses using biotechnology will require detailed information of tissue development in order to accurately target gene manipulation. A study was done with corn stem segments to characterize the process of tissue development, and the alterations that occur during development in the concentration and composition of fiber. It was found that while corn stem segments are still growing in length and diameter, the concentration of fiber increases very little and the presence of lignin, a chemical that limits digestibility, actually declines in concentration. Once corn stem segments have reached their maximum size, maturation of tissues begins and fiber concentration of some tissues increased dramatically. More importantly, lignin was added to the fiber of all tissues except for one minor tissue. The impact of maturation was most pronounced in tissues near the outside edge (rind) of the stem segments. These results indicate that biotechnologists will need to target gene manipulation to rind tissues and delay or reduce the amount of lignin incorporated into grass fiber in order to improve the feeding value of corn silage and other grasses for livestock production.
Technical Abstract: Maturation of grasses results in reduced cell wall degradability of these forages by ruminant livestock. Using a specific internode of maize (Zea mays L.) stems as a model, the pattern of tissue development and maturation of grass cell walls was characterized. The fourth above-ground, elongated internode from three maize hybrids was harvested at 10 stages of maturity beginning when the internode was ~ 10 mm in length through physiological maturity from a two-year, replicated field trial in St. Paul, MN. Stem tissue development was characterized by light microscopy. Cell wall concentration and composition (polysaccharide sugar residues, Klason lignin, monolignols, ester- and ether-linked ferulates, and esterified p-coumarates) were determined. Growth of internode length and cross-sectional area occurred from the first harvest until the harvest five to six interval. During internode elongation only protoxylem vessels stained for the presence of lignin. After elongation was complete, lignified parenchyma, sclerenchyma, and metaxylem tissues developed while phloem never lignified. Associated with changes in tissue development was an increase in cell wall concentration until shortly after elongation ended. Lignin concentration of the cell wall declined over the first four maturity stages, with an associated increase in glucose and xylose polysaccharide residues, before rising sharply until after elongation was complete. Ferulate cross-links of lignin to arabinoxylan increased 12-fold during elongation and early maturation. Patterns of tissue and cell wall development indicated that maturation of sclerenchyma and rind-region parenchyma accounted for the majority of cell wall accumulation and lignification in grass stems.