1-07: Analysis of the cell-wall xylan component of mutant Sorghum bicolor L. by LC-MSn

Sorghum (Sorghum bicolor L. Moench) is a potential renewable source of lignocellulosic biomass for conversion to liquid biofuels.  The plant cell wall is essentially a composite of cellulose, hemicellulose, and lignin.  Lignin poses a particular challenge for biochemical conversion as it acts as a barrier to hydrolysis and is not easily deconstructed into its components.  Down regulating lignin synthesis has been shown to enhance extraction of sugars by enzyme hydrolysis.  However, lignin modifications will likely to lead to changes in the structure and organization of polysaccharides such as increased quantities, changes to structural elements (i.e. side groups), or carbohydrate-protein/carbohydrate-carbohydrate interactions (i.e. cross-linking).  More informative analytical methods are needed to better monitor structural changes to plant cell walls.

In a replicated field trial, 3 brown midrib near isogenic hybrid lines, which are impaired in lignin biosynthesis, and the corresponding wild-type hybrid were grown and the biomass samples were alkali-extracted to isolate and quantify the xylan components.  The intact xylan polysaccharides are too complex to analyze intact, therefore each xylan component was depolymerized enzymatically under two different conditions.  The resulting oligosaccharides were derivatized and analyzed by LC-MSⁿ.  The LC-MS data revealed 9 compositions (in 17 chromatographic peaks) for digestion with pure endo-xylanase and 7 compositions (in 11 chromatographic peaks) for digestion with a commercial enzyme preparation.  Online tandem MS and MSⁿ allow for distinction and putative identification of the isomeric oligosaccharides.  The analysis of residual oligosaccharide sequences facilitates the identification of structural components from the xylan component from plant cell wall material.