Comparing Corn Types for Differences in Cell Wall Characteristics and p-Coumaroylation of Lignin

Authors: Hatfield, Ronald; Chaptman, Ann

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2009
Publication Date: 4/10/2009
Citation: Hatfield, R.D., Chaptman, A.K. 2009. Comparing Corn Types for Differences in Cell Wall Characteristics and p-Coumaroylation of Lignin. Journal of Agricultural and Food Chemistry. 57(10):4243-4249.

Interpretive Summary: Corn silage is a popular component of dairy cow diets, mostly for economic reasons associated with a one-time harvest that produces sufficient yields to meet year-around feed requirements. Fiber (cell walls) is a major component of corn silage and is mainly made up of carbohydrates, protein, and an indigestible component called lignin. Fiber provides a source of nutritional energy for dairy cows and is critical for maintaining good animal health. However, only about 40% of the fiber is digested by the animal due to the binding of lignin to the fiber carbohydrates. We have found that corn lignin is unique in that it contains high amounts of p-coumaric acid (pCA). Our studies indicate that pCA does not have a structural role, but is important in helping the plant to form lignin within the cell wall. There are several types of corn that are commercially available, ranging from uses as decorative to human consumption in the form of sweet corn. This study was undertaken to determine if there were major differences in the building blocks (structural carbohydrates, pCA, and lignin) that make up the cell walls of corn stem and root tissues. Five different corn varieties were grown, and stem and root cell walls were analyzed. Stem materials from the five corn varieties had similar patterns of cell wall composition. Only the roots had consistently different cell walls. There was some variation in the amounts of lignin and pCA levels, suggesting that selection could be used to decrease the negative impact of lignin upon fiber digestion in corn silage. This information is important to corn geneticists that are interested in development of corn silage varieties with better digestibility. Improving corn silage digestibility would lead to better-feed utilization in dairy farming, improved economic returns to the farmer, and decreased environmental impacts due to reduced manure wastes. It is estimated that relative small changes (10%) in fiber digestibility would generate economic returns of greater than $350 million for dairy farmers from increased milk and meat production. There is an added benefit of decrease manure solids and less need for grain supplements.

Technical Abstract: This study was undertaken to compare cell wall characteristics, including levels of pCA and lignin in diverse corn (Zea mays L.) germplasm. Five different types of corn (Zea mays L.) germplasm (four commercial and Teosinte) were grown in the greenhouse in individual pots. For each corn type, replicate stems were harvested at tassel emergence. Lower internodes were separated into rind and pith tissues, and roots were collected for cell walls analysis. Stem cell wall characteristics of the different corn germplasm were similar for total neutral sugars, total uronosyls, lignin, and phenolic acids. However, the neutral sugar composition of root cell walls was markedly different with high levels of galactose and arabinose. Levels of pCA in the different tissues ranged from 13.8 mg/gCW to 33.1 mg/gCW without any clear patterns with respect to the tissue type. There was no evidence that pCA was incorporated into cell walls attached to arabinoxylans.