STUDIES OF LIGNIN BIOSYNTHESIS USING ISOTOPIC CARBON: IV. FORMATION FROM SOME AROMATIC MONOMERS

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Abstract
Studies have been carried out on the transformation of some C14- labelled aromatic monomers into the lignin residues which yield phenolic aldehydes on nitrobenzene oxidation. The dilution of the radioactive carbon during transformation of the administered precursor to the aldehyde-yielding residue has been taken as a criterion of its efficiency as a lignin precursor. In wheat plants, substances with a phenylmethane (C6, C1) skeleton are not, in general, efficient precursors, although the carbon-14 of vanillin and p-hydroxybenzoic acid is incorporated appreciably into parts of the lignin. In contrast, several substances with a phenylpropane (C6, C3) structure—phenylalanine, tyrosine, and cinnamic acid—are readily transformed to two or more of the three lignin residues, and ferulic acid is very efficiently converted to the guaiacyl part of lignin. Degradation experiments indicate that the aromatic ring and at least the adjacent side chain carbon of the C6, C3compounds are incorporated as a unit. Preliminary evidence has been obtained of marked differences in the utilization of lignin precursors by different species. A new procedure is described for the separation of vanillin, syringaldehyde, and p-hydroxybenzaldehyde by partition chromatography on columns of diatomaceous earth.