Abstract
It was reported that the administered sinapate was incorporated into syringyl lignin of Robinia pseudoacacia and that 4CL isoenzyme in R. pseudoacacia utilized sinapate unlike other plant 4CLs. These findings are indicative of an alternative route of syringyl lignin biosynthesis where sinapyl alcohol is biosynthesized passing through sinapate and sinapoyl CoA. We therefore examined enzyme activities involved in lignification in the developing xylem of R pseudoacacia. Protein extract from the developing xylem of R pseudoacacia exhibited methylation activities toward 5-hydroxyferulate and 5-hydroxyconiferyl aldehyde when these substrates were mixed. In addition, 5-hydroxylation activity with ferulate was not completely abolished by the presence of coniferyl aldehyde in the reaction. These results suggest the presence of biosynthetic route of syringyl lignin via sinapate in R pseudoacacia and that the syringyl lignin biosynthetic pathway differs among angiosperm species.
