CELL WALL DYNAMICS 57 



the preexisting layers involves the release of chitin- and protein- 

 hydrolyzing enzymes. In plants, sculpturing of cell walls and 

 dissolution of end walls are an integral part of vascular differen- 

 tiation: The ripening and softening of fruits involves the autolysis 

 of intercellular substance by pectic enzymes; and in the process 

 of abscission a weak end zone is formed, also through the dissolu- 

 tion of the pectic substance. 



(b) Lysis of specialized walls is a part of the process of spore 

 germination in many organisms. 



(c) Invasions of cells or tissues by parasites depends in part 

 on the lysis of host walls or other intercellular materials by the 

 invader. Phytopathogenic bacteria and fungi, particularly "soft rot" 

 organisms, possess a full complement of enzymes for degrading 

 intercellular pectic substances. Animal pathogens frequently 

 release hyaluronidase, an enzyme which hydrolyzes the important 

 connective tissue ground substance, hyaluronic acid. 



(d) Among the factors which influence the survival of indivi- 

 dual species or strains of micro-organisms in mixed populations, 

 the release of various hydrolases must be included as one of consider- 

 able importance. The production and release by specific organisms 

 of wall or capsule-lysing enzymes are assumed to be independent of 

 the presence of "competing" forms, and may sometimes originate 

 in autolysis of individuals, yet could affect the survival of the source 

 organism and the constitution of the associated population. Wall- 

 lysing enzymes in multicellular organisms may serve in a defensive 

 capacity by attacking invading pathogens in susceptible tissues. 

 Such enzymes (lysozyme, for example) may be already present in 

 the inter- or extra-cellular mileau or may be released by host cells 

 which have been lysed by the parasite. 



(e) Finally, wall-lysing enzymes may be of importance at a 

 nutritional level. In herbivorous mammals, the major components 

 of vegetable foodstuff are, of course, cell wall substances. These 

 animals are dependent upon the microflora and fauna of the digestive 

 tract for their cellulolytic activity. In rumen fluid bacteria play a ma- 

 jor role in cellulose digestion, oligotrich flagellates a lesser role. In 

 termites, as in mammals, the ability to digest cellulose depends 

 upon intestinal micro-organisms. Again, both bacteria and flagel- 



