Rate of Synthesis of Cell Wall Components in Sorghum Leaf Blades1

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Abstract
Cell wall structure is an important characteristic influencing intake and digestibility of forages. Our objective was to examine changes in cell wall composition that occur during leaf development and estimate rates of synthesis of cell wall components in elongating leaf blades of greenhouse‐grown sorghum [Sorghum bicolor (L.) Moench]. The leaf intercalary meristem and segments of the eighth elongating leaf blade, each representing the average daily growth increment of the leaf, were analyzed for neutral detergent fiber (NDF) and lignin, and hemicellulose and cellulose concentrations were calculated. Concentrations of cell wall components on a dry weight basis generally increased acropetally from the leaf intercalary meristem. When expressed on an NDF basis, concentrations of hemicellulose and cellulose decreased and increased, respectively, from the intercalary meristem to the leaf tip. Lignin concentrations on an NDF basis were highest in 1‐day‐old segments and decreased thereafter. Concentrations of arabinose, galactose, and uronic acids were highest in cell walls of leaf intercalary meristems, and decreased acropetally while xylose concentrations in the cell wall increased. Rates of hemicellulose and cellulose synthesis averaged 0.46 and 0.38 mg segment−1 day−1, respectively for 1‐ to 5‐day‐old segments, while lignin synthesis averaged 25 µg segment−1 day−1 in 1‐ to 4‐day‐old segments. The large relative changes in cell wall composition between the intercalary meristem and 2‐day‐old segments of the elongating leaf indicate that the major changes in fiber composition of leaves occurs early during leaf development.

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