Monday, May 2, 2011
Grand Ballroom C-D, 2nd fl (Sheraton Seattle)
Lignin is an integral part of plant cell walls and is produced by the oxidative polymerization of syringyl (S), guaiacyl (G) and p-hydroxyphenyl (H) phenylpropanoid units during cell wall biosynthesis. Lignin composition in relation to its basic phenylpropanoid units, particularly the S/G ratio, is an important property for biomass characterization and varies greatly as a function of species, genotype and environment. To understand the natural variation of lignin composition, to evaluate genetic modification upon plant cell walls, and to investigate the inhibitory effects of lignin composition on cell wall deconstruction, a tremendous number of samples need to be analyzed and necessitate a simple and reliable fast screening method. We developed a nondestructive and label-free Raman spectroscopic method to assess S/G ratio rapidly and quantitatively with minimal sample preparation. By characterizing a library of model compounds with FT-Raman spectroscopy, exclusive marker bands for each basic phenylpropanoid unit were identified. A variety of biomass including hardwood (Eucalyptus globulus), softwood (Pinus radiata), herbaceous plants (Zea mays, Panicum virgatum and Sorghum bicolor), and a model dicot (Arabidopsis thaliana) was then measured and the corresponding S/G ratio was calculated after spectral deconvolution. The S/G ratio was also determined by pyro-GC/MS and a linear relationship was established between the Raman and pyro-GC/MS results. The model was used to estimate S/G ratios of a set of Arabidopsis mutants/ecotypes by their Raman spectra successfully. In addition, the distribution of S and G units within the cell walls of corn stover was acquired by Raman imaging.