Biosynthesis of phenolic compounds in first internodes of sorghum: lignin and related products

Lignin biosynthesis in excised tissues of Sorghum vulgare variety Wheatland milo incubated in air with and without prior infiltration with H₂O was presumably limited by H₂O₂ production and was dependent upon an endogenous substrate, probably starch. In solution culture without shaking, this conversion of endogenous material was partially blocked at some step prior to p-hydroxycinnamic acid. The synthesis was light independent and continued protein synthesis was not required. The accumulation of lignin products was paralleled by an increase in dhurrin, alkaline sensitive esters of p-hydroxycinnamic, ferulic and sinapic acids, and flavin coenzymes, especially flavin-adenine dinucleotide. There was no detectable evidence of competition for substrates with other phenols such as anthocyanins or with the growth of adventitious roots. There was evidence, however, of mechanisms limiting lignification in the first internode in the intact seedling. Comparisons are made with lignin production in comparable tissues of Phleum.