Softwood lignin precursor

The role of coniferyl alcohol as the immediate precursor of softwood lignin has been demonstrated by using 14C labeling. Administration of labeled coniferyl alcohol as /3-glucoside (coniferin) to seedlings of spruce results in the exclusive formation of radioactive lignin. 

The building blocks of wood lignin are derived from carbohydrates metabolized via a so-called shikimic acid pathway and converted to phenylpropane amino acids (Figure 6.6). These amino acids supply precursors for the s Tithesis of lignin, plant proteins and flavonoids. The first step is the -elimination of ammonia from L-phenylalanine to form fra 5-cinnamic acid. Successive hydroxylation and methylation reactions convert cinnamic acid to />-coumaryl alcohol, caffeyl alcohol, coniferyl alcohol, 5-hydroxyconiferyl alcohol and sinapyl alcohol. Softwood mainly uses coniferyl alcohol with a small amount of p-cou-maryl alcohol. 

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