62 THE PLANT CELL WALL 



is recognized as an essential participant in the lignin polymer 

 formation. In contrast to a direct test of the proposition which 

 implicates a specific enzyme, the possible physical participation of 

 the cell wall can be tested more directly, by recourse to a suitable 

 model for cell wall substance. Logically, attention was first focused 

 upon the major frame substance, cellulose, which is also known 

 to be an active adsorbent. 



The general scheme for the conversion of precursors to polymer 

 calls for the participation of peroxidase. Accordingly, the simplest 

 cell wall model system to be devised included eugenol, peroxidase, 

 hydrogen peroxide and cellulose which was supplied as filter paper. 



In practice, filter paper was simply immersed in an aqueous 

 solution of the reactants for a suitable time and then tested for 

 the presence of lignin. This kind of experiment revealed that traces 

 of lignin-like materials were indeed deposited in the paper. Al- 

 though the yield was disappointingly small the general scheme 

 received sufficient support to call for further study. 



It will be recalled that a small but significant proportion of 

 the tissue peroxidase was retained in the wall after destruction 

 of the cells. Thus, the active cell wall preparations studied actually 

 contained peroxidase when they were placed in eugenol-peroxide 

 solutions. This condition was not met by the first filter paper 

 model, but was mimicked by permeating pure filter papers with 

 crystalline horseradish peroxidase and allowing them to dry in 

 the cold. When such treated papers were immersed in eugenol- 

 peroxide solutions, that is, handled as if they were washed cell 

 wall isolates, yields of lignin ranging from 12-25 mg per gram 

 of paper were obtained. The soluble product isolated from the 

 filter paper yielded on analysis, 63-64 per cent C, 6-7 per cent 

 H, and 15-16 per cent OCH 3 . From such analytical values, ultra- 

 violet absorption spectra, color reactions, and solubility, it was 

 ascertained that a material very much like gymnosperm lignin had 

 been formed. Other celluloses, including cotton and milkweed fibers 

 (seed hairs of Asdepias sp.) are similar in behavior to filter paper. 



Such experiments indicate the value of highly simplified model 

 systems in the study of lignification, and perhaps, other processes 

 as well. They follow the reaction schemes which have been proposed 



