CELL WALL DYNAMICS 47 



(d) Aldehyde reduction as in 



alcohol 

 coniferaldehyde+DPNH — coniferyl alcohol+ 



dehydrogenase 

 DPN. 



(c) Transmethylation as in 



methionine 



3,4-dihydroxyphcnylpyruvic acid 



methyltransferase 



3-methoxy-4-hydroxyphenyl (giiaiacyl) pyruvic acid. 



(f) Side chain lengthening as in 



carboligase 

 vanillin +acetaldehyde - guaiacylacetyl carbinol 



carboxylase 

 vanillin+pyruvate — guaiacylacetyl carbinol+C0 2 . 



(g) Side chain oxidation as in 



2 



woeugenol (eugenol) — » coniferaldehyde. 



Obviously, a number of the foregoing reactions must fall into 

 appropriate sequential arrangements if certain potential precursors 

 are to be converted into lignin. Thus, phenylalanine would be 

 transformed into guaiacylpyruvic acid via hydroxylase, tyrosinase, 

 transmethylation, and transaminase or amino acid oxidase. The 

 successive intermediates here would be tyrosine, DOPA, and 

 guaiacylalanine. 



Glucovanillin would be subjected to (3-glucosidase, carboligase 

 (or carboxylase), and alcohol dehydrogenase to yield guaiacyl 

 methyl ethylene glycol. 



In short term, "forced" peroxidation with high levels of pre- 

 cursor and peroxide, eugenol is converted into lignin via coniferal- 

 dehyde. Coniferaldehyde or its alcohol are converted directly to 

 lignins, and ferulic acid is polymerized directly to a low-aldehyde 

 lignin. On the other hand, phenylalanine is inactive and tyrosine and 

 DOPA are transformed into quinonoid polymers rather than 



