COMPARISON OF LEAF AND STEM CELL-WALL COMPONENTS IN BARLEY STRAW BY SOLID-STATE C-13 NMR

Barley straw was separated mechanically into leaf and stem fractions. Their C-13 NMR spectra were recorded at low field (25 MHz) using magic -angle spinning and cross-polarisation (CP-MAS) under conditions optim ised for quantitation of lignin. The stem fraction contained more lign in with a higher proportion of ether-linked syringyl residues. The lea f fraction contained more phenolic acids and cutin. The molecular rigi dity of the components of the stem cell walls was estimated from the C -13 spin-lattice relaxation time T-1, which decreases with thermal mot ion. Crystal-interior cellulose and syringyl lignin were the most rigi d polymeric components. These data have implications for the capacity of the straw to withstand mechanical stress and to resist degradation during digestion by ruminants. (C) 1998 Elsevier Science Ltd. All righ ts reserved.