Maize development: Cell wall changes in leaves and sheaths

Authors: Hatfield, Ronald; Marita, Jane

Submitted to: American Journal of Plant Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2017
Publication Date: 5/22/2017
Citation: Hatfield, R.D., Marita, J.M. 2017. Maize development: Cell wall changes in leaves and sheaths. American Journal of Plant Sciences. 8:1248-1263.

Interpretive Summary: Maize is a prominent grain and forage crop in the United States and other countries throughout the world. It is an important nutritional forage for animal production being preserved primarily as corn silage. In order for ruminants such as dairy cows to take advantage of the energy stored in the fiber fraction of forages, the plant cell walls must be broken down and digested by the animal. This study was undertaken to determine if there are developmental changes that occur in different parts of the corn plant as it matures. Studies like this provide background information for plant breeders or molecular geneticists who select for specific cell wall traits to improve digestibility. We found that structural carbohydrates (fibers) are similar among the different plant part tissues; lignin is highest in the sheath and leaf midrib tissues and lowest in the leaf blades. There was little difference in total lignin within a given tissue when comparing lower nodes to upper nodes, except for the midrib tissues. We also found that the sheath tissue contains two to three times the amount of cross-linking compared to other tissues; cross-linking increases the strength of this tissue and results in less digestible cell walls. Our findings would suggest that cross-linking cell wall components could be a target for plant breeders in order to improve the digestibility of corn plants. It is estimated that increasing the digestibility of forage cell walls by 10% would mean increased milk and meat production worth $350 million in the U.S., 2.8 million tons less manure solids, and 2 million tons less in grain supplements.

Technical Abstract: Developmental changes occur in maize (Zea mays L.) as it transitions from juvenile stages to the mature plant. Changes also occur as newly formed cells mature into adult cells. Maize leaf blades, including the midribs and sheaths, undergo cell wall changes as cells transition to fully mature cell types. As is common in grasses during cell wall maturation, the lignin in the plant tissue is acylated with p-coumarates (pCA). This work characterizes cell walls in maize that make up leaf blade, leaf midrib, and sheath tissues corresponding to tissue development. Maize plants grown in the greenhouse were harvested; leaf, leaf midrib, and sheath tissues from nodes 9 through 14 tissues were analyzed for cell wall composition. Cell wall carbohydrates varied with the type of maize tissue, but there was little change within a tissue type among the different nodes. Lignin concentrations were lowest in the leaf blade (70-88 g/Kg cell wall [CW]), followed by the sheath (123-140 g/Kg CW), and highest in the midrib (140-168 g/Kg CW). Incorporation of pCA into cell walls paralleled the lignification. Ferulates (FA) remained relatively constant as a proportion of the cell wall (3.1-6.4 g/Kg CW) across nodes and across all tissue types. The amount of FA was highest in the sheath and midrib tissues compared to leaf blade (3.8 vs 5.7 g/Kg CW averaged over all nodes). Lignin composition did not change significantly with cell wall maturation within a given tissue type. The aerial portions of maize plants, excluding the stem, showed little difference in cell wall composition along the different nodes. Higher levels of ferulates were found in the sheath and leaf midrib compared to the leaf blade tissues. Leaf midribs from the upper nodes of the plant contained the highest levels of lignin. Perhaps this is a reflection of the function to keep leaves extended and in an upword angle to help maximize the photosynthetic capacity.