Carbon-13 enrichment of rice stalk lignin traced by solid state 13C NMR spectroscopy

Carbon-13 enrichment of specific carbon of rice stalk lignin was achieved by feeding conifering-[alpha-C-13] coniferin-[beta-C-13] and coniferin-[gamma-C-13] into an internode cavity of the stalk of a growing rice plant (Oryza sativa L.). The resulting rice stalk tissues were analyzed by high-resolution solid state carbon-13 nuclear magnetic resonance (C-13 NMR) spectroscopy. It was found that the administration did not affect the normal ligninfication of rice plant. It was also proved that beta-O-4, beta-beta, beta-5 and beta-1 were mainly a substructure in protolignin of rice stalk although there were some minor substructures as coniferyl alcohol and ferulic acid unit. Importantly, the result indicated that significant bonding occurred at alpha-position to other constituents, presumed to be mainly of carbohydrates.