CELL WALL DYNAMICS 61 



formation in our model, is but one of the requisite parts of the 

 signifying system. We may formulate this in the following manner: 



peroxidase cell wall 



eugenol — > intermediate — > lignin 



H2 O2 reaction 



Perhaps several steps intervene between eugenol and lignin, 

 the formation of native precursors such as coniferaldehyde, for 

 example, and the generation of radicals from this molecule. Such 

 intermediary steps could be effected by peroxidase together with 

 non-enzymic reactions. Thus eugenol would not itself be rigor- 

 ously a monomer in lignin formation althoug still a precursor. 



In somewhat broader terms, we may reformulate our equation as : 



peroxidation peroxidation 



precursor ("premonomer") ► monomer — " 



etc. 



cell wall 



monomer radical ► polymer. 



reaction 



The notion that a derivative of eugenol which serves as the 

 monomer is "activated" by being further oxidized to a radical is 

 in keeping with the evidence for a free radical mechanism in lignin 

 formation discussed earlier and with general concepts of free 

 radical-induced polymerization. The above formulation suggests 

 that the cell wall reaction is, in part, the combination of radicals 

 to yield a polymer. 



Now, it is in order to inquire into the processes underlying 

 our so-called cell wall reaction. It is possible, for example, that 

 the wall is the repository for a polymerizing enzyme. On the 

 other hand, the wall may serve in some physical capacity to bring 

 together the reactive intermediate species. 



The experimental search for a distinction between these pos- 

 sible alternatives led into unexpected avenues of cellular biology 

 and made possible in turn an appreciation of the great controlling 

 forces for chemical reactions which reside in organized macro- 

 molecules themselves. 



If lignin synthesis is limited by an enzymic cell wall reaction 

 the overall process should be sensitive to typical protein-inactiv- 

 ating agents such as heat or urea. Unfortunately, such treatments 

 also destroy the catalytic activity of cell wall peroxidase, which 



