5-HYDROXYGUAIACYL NUCLEI AS AROMATIC CONSTITUENTS OF NATIVE LIGNIN

The pathway of lignin biosynthesis has been well documented, However, there are still questions because of the lack of knowledge about. the exact chemical structure of lignin, caused by the restriction of analy tical procedures used and/or the interpretation of analytical results. The presence of 5-hydroxyguaiacyl nuclei in lignin of a brown midrib mutant (bm3) of maize has been, established using a. thioacidolysis. I n this paper, it was confirmed using pyrolysis-gas chromatography-mass spectrometry (PY-GC/MS) that in addition to bmr mutants of some tropi cal grasses, lignins of their normal counterparts and some temperate a nd tropical angiosperms woody plants are composed of 5-hydroxyguaiacyl nuclei, in addition to guaiacyl and syringyl nuclei. Based on the res ults, it is suggested that 3(3,4-dihydroxy-5-methoxyphenyl)-propen-1-o l, which is synthesised from 3(3,4-dihydroxy-5-methoxyphenyl)-propioni c acid (5-hydroxyferulic acid) is also invoked in dehydrogenative poly merisation by perioxidase during the biogenesis of lignin of some spec ies of plants. (C) 1997 Elsevier Science Ltd.