Ferulic acid (FA), tetradeuteroferulic acid (DFA), sinapic acid (SA), or heptadeuterosinapic acid (DSA) was exogenously supplied to poplar (Populus alba L.) callus. Administration of FA or SA increased the lignin content of the callus to about twice that of the control callus. Gas chromatographic analysis of the alkali hydrolysate of the cell wall residue revealed that only a trace amount of SA was bound to the cell wall, and the amount of FA was less than 2% of the total callus lignin. Thioacidolysis of the DFA-treated callus indicated that DFA is effectively converted to both coniferyl and sinapyl alcohols and then incorporated into the corresponding lignin. Incorporation of DSA into syringyl lignin or guaiacyl lignin was not observed, but yields of syringyl lignin thioacidolysis products were markedly increased by DSA treatment of the callus. These results suggest that SA may not be a precursor of sinapyl alcohol and syringyl lignin per se, but it may induce or enhance the biosynthesis of syringyl lignin in poplar callus.
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