CIS-MONOLIGNOLS IN FAGUS GRANDIFOLIA AND THEIR POSSIBLE INVOLVEMENT IN LIGNIFICATION

Article abstract of DOI:10.1016/S0031-9422(00)81239-X

Lignification in all plant species is assumed to occur exclusively via the dehydrogenative polymerization of the trans (E) monolignols, p-coumaryl, coniferyl and sinapyl alcohols.This assumption may have to be revised somewhat due to the presence of both E (trans) and Z (cis) isomers of p-hydroxy substituted cinnamic acids in grasses, and cis-coniferyl and cis-sinapyl alcohols in beech bark (Fagus grandifolia).This suggests that lignification of these tissues may use either cis- or trans-monolignols.By means of H2O2/peroxidase induction, we have prepared synthetic dehydrogenative polymerized (DHP) lignin from both cis- and trans-coniferyl alcohols.Under the tests employed, the degradation products from both DHPs were identical suggesting that either cis- or trans-monolignols are suitable substrates for this enzyme and, therefore, lignification.An alternative hypothesis is that the cis-monolignols accumulate in beech bark because they are not suitable substrates.Therefore, it would follow that the enzymes involved in lignification in vivo are highly specific. Key Word Index - Fagus grandifolia; Fagaceae; American beech; biosynthesis; cis/trans-monolignols; lignin; p-hydroxycinnamyl alcohols; dehydrogenative polymerized lignin.