CELL WALL DYNAMICS 63 



and support the notion that lignification is completed by a physical 

 interaction at the cell wall. 



Although cellulose was a reasonable first choice for this study, 

 we know it to be only one among several wall components, including 

 protein, pectic substances, and other polysaccharide derivatives. 

 It is of some importance to know how specific the requirement 

 for cellulose is in model lignification systems. In the absence of 

 cellulose, the otherwise complete system yields simpler products 

 but no lignin polymers. Soluble proteins including gelatin and 

 peroxidase itself, and fibrous proteins such as collagen, hair and 

 fibrin all help to promote the formation of lignin. 



Simple carbohydrates, glucose, sucrose, raffinose, similarly 

 show no activity. In early experimental studies, it was decided 

 to test a substance closely related to cellulose, i.e. chitin. Chitin 

 is the polymer of 2-acetylamino-[3-D-glucopyranoside hence is an 

 analog of cellulose, with similar molecular and crystallographic 

 properties. Native chitin isolated from the egg case of the mollusk 

 Busycon showed only trace activity until deacetylated by alkali 

 treatment, giving thereafter three-fold more lignin than cellulose 

 itself. A consideration of the disaggregating effect of alkali upon 

 chitin led to tests with soluble polysaccharides, starch and methyl 

 cellulose, both highly active in lignin synthesis. These polysaccha- 

 rides were from 50- to 250-fold more active than cellulose. When 

 it was tested subsequently, pectic acid exceeded cellulose in activity 

 by a factor of approximately 100. 



The activities of the several effective substances were compared 

 with cell wall preparations from pea root tissue. Cellulose ex- 

 hibits one-twentieth and chitin one-seventh the activity measured 

 in cell wall systems, whereas pectic acid and methyl cellulose were 

 found to exceed cell wall preparations 2-10-fold. 



Hence, the net activity of the cell wall may involve a comparativ- 

 ely small contribution from cellulose itself together with large 

 contributions from polysaccharides of lower molecular weight 

 such as pectic acid. 



The relative contributions of cellulose and pectic substances 

 to lignifying "capacity" of the cell wall is well illustrated by 

 a different sort of experimental test. Returning to more biological 



