ARS | Publication request: Analysis of the cell-wall xylan component of brown midrib mutants of Sorghum bicolor L. by LC-MS^n^

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: August 5, 2012
Publication Date: August 10, 2012
Citation: Bowman, M.J., Dien, B.S., Sattler, S.E. 2012. Analysis of the cell-wall xylan component of brown midrib mutants of Sorghum bicolor L. by LC-MS^n^. Gordon Research Conference [abstract].

Technical Abstract: Sorghum stalks and leaves are a potential renewable source of lignocellulosic biomass for conversion to liquid biofuels. The plant cell wall is a composite of primarily cellulose, hemicellulose, and lignin. Lignin poses a particular challenge for enzymatic 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 quickly monitor changes to plant cell wall. In a replicated field trial, a wild-type Sorghum bicolor L. Moench hybrid and 3 corresponding near isogenic brown midrib lines, which are impaired in lignin biosynthesis, were grown and the biomass samples were alkali-extracted to isolate and quantify the xylan component. The intact xylan polysaccharides are too large and heterogeneous to analyze for structure, therefore each xylan component was enzymatically depolymerized under two different conditions. The resulting oligosaccharides were derivatized and analyzed by RP-HPLC-IT-MS/MS^n^. The LC-MS data revealed the presence of 9 compositions (in 17 chromatographic peaks) for condition 1 and 7 compositions (in 11 chromatographic peaks) for condition 2. The dominant compositions present are a d.p. 5 and d.p.4, respectively, for condition 1 and 2 digestions. Larger d.p. oligomers do not co-elute with the corresponding linear xylo-oligosaccharides, indicating that these are likely arabinose-containing oligosaccharides. On-line tandem MS and MS^n^ 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.