LIGNIN IN WHEAT INTERNODES - LINKAGES BETWEEN PHENYLPROPANE UNITS

An ozonolysis procedure was used to compare the types of linkage between phenylpropane units in lignin from wheat Triticum aestivum L internodes with those in lignins from gymnosperm and angiosperm woods. The ratios of erythro- to threo-type beta-O-4 linkages (E/T = 2.35) and phenylcoumaran to beta-O-4 linkages (PC/beta-O-4 = 0.07) for mature wheat internode lignin, lie between those for gymnosperm (spruce wood, Picea jezoensis Carr: E/T = 1.78; PC/beta-O-4 = 0.10) and angiosperm (beech. Fagus crenata Bl: E/T = 3.87; PC/beta-O-4 = 0.05) wood lignins whose ratios of syringyl to guaiacyl nuclei (S/V) were similar to those reported previously. The value of PC beta-O-4 for wheat internode lignin decreased as the internodes matured, indicating differences in the nature of linkages formed at different stages of maturation. No significant differences in the proportion of the different aromatic nuclei or linkage types were observed in the lignin-containing fractions obtained during the preparation of Bjorkman lignin from mature wheat internodes. This fractionation is apparently dependent largely on the characteristics of the polysaccharides bound to lignin. The carbon-13 NMR spectra and molecular weight distribution for Bjorkman lignins from maturing wheat internode and woods were also determined and compared.