68 



THE PLANT CELL WALL 



LIGNIN CONTENT - % OF DRY MATTER 

 5 10 15 



2 3 4 5 6 



PRESSURE - DYNES/CM 2 



20 



7 xlO* 



Fig. 1. Pressure-lignification diagram for Euphorbia. (From Siegel, S.M., 

 The biochemistry of lignin formation. Physiol. Plantation 8, 20, 1955.) 



Tissues from seven angiosperms and fifteen other plants have 

 been used in the comparative study of lignification (Table 1). 



Among these species, thirteen contain lignin, although several 

 have only trace quantities and several show typical lignin color 

 reactions in atypical tissues. Thus lignin is conventionally located 

 in vascular tissues, but occurs only in the rhizophore in Selaginella, 

 in the peristome teeth of the Polytrichum (sporophyte) capsule, 

 and in the sporophore of Polyporus. Among the vascular plants, 

 the aquatic form Elodea is conspicuous for its virtual lack of 

 lignin. 



The oxidases of importance in the lignification process include 

 both the hemoprotein peroxidase (Px) and the copper-containing 

 phenolases (Ph). Their most important physiological distinction 

 lies perhaps in the electron acceptor (oxidant) involved— W 2 Oi 

 or 2 . Some of the copper oxidases, potato tyrosinase for example, 

 cannot convert eugenol into lignins. 



All of the chlorophyllous forms contain peroxidase alone 

 (9 spp.) or both types of oxidizing enzymes (6 spp.). Two fungi 

 contain traces of peroxidase; five fungi contain phenolases only. 



