STRUCTURAL FACTORS IN POLVMI- RIZATION 43 



substrates, Hgnin precursors included, begins, leading to lignification and other 

 oxidative changes characteristic of cellular differentiation and senescence. 



Capacity for induction of peroxidase by indoleacetic acid is not uniformly dis- 

 tributed among tissues, but is greatest in the region in which vascular differentia- 

 tion begins. In young apical tissues, therefore, a high level of hormone would 

 serve only to inhibit peroxidation, hence to maintain the relatively undifferentiated 

 condition characteristic ot immature cells. 



When Elodea internode sections were lignified in eugenol-peroxide media, 

 both walls and protoplast of stem cells accumulated a brown coloration; extrac- 

 tion with organic solvents removed most of the protoplast pigmentation. Color 

 tests for lignin applied were positive only in cell walls, although tests for 

 peroxidase showed that enzyme to be of general cellular distribution (29). These 

 findings prompted an examination of the distribution of peroxidase and lignifying 

 ability among cellular constituents, and the fractionation which was subsequently 

 carried out with chloroplast-free pea root tissue yielded the following pattern: 



ACTIVITY, % 



Peroxidative 

 Lignifying 



Save for treatments destroying its activity (8m urea, for example) the wall per- 

 oxidase was firmly bound and could not be eluted by ordinary salt, buffer, or 

 organic acid solutions. Hence, although the oxidative polymerization of eugenol 

 to lignin was clearly established as a peroxidase-dependent process, it did not 

 depend upon this enzyme alone, but upon a cell wall system of which per- 

 oxidase was only a part. It was surmised that the peroxidative step in con- 

 version of eugenol to lignin might be of a 'preparative' nature, transforming 

 premonomer into monomer and presumably monomer radical. There remained 

 then the question as to the exact role of the cell wall in completion of the poly- 

 merization. Two experimentally verifiable possibilities presented themselves: 

 a) a specific polymerase or polymerase system is localized in the wall, a not 

 unreasonable premise when the importance of lignin in the vascular plant is 

 considered; and b) polymerization of peroxidized eugenol involves ordering of 

 activated monomer on cell wall macromolecules without participation of addi- 

 tional enzymes. The probability that activated monomer units will build up a 

 polymer would be increased it they were oriented along wall polysaccharide 

 chains; activated monomer released onto an aqueous medium high in eugenol 

 concentration would be more likely to undergo terminal tlimerization reactions 

 with the more reduced precursor. A test for the second premise was devised that 

 would, if positive, eliminate the need for a wall polymerizing enzyme, and it 



