CHAPTER 2 



CELL WALL DYNAMICS 



I. Biosynthesis, Growth and Regulation 



Commonly, the cell wall is pictured as something of a final repos- 

 itory for certain products of cellular metabolism. Thus, we see cell 

 wall rudiments laid down during division, increase in extent during 

 growth, and finally undergo thickening and often incrustation 

 with secondary substances such as lignin, suberin, or cutin. Even 

 though the cell wall, once deposited, tends to retain its constitu- 

 ents, its relations to growth and differentiation are not those of 

 a static member in living cells and tissues. The apparently static 

 character of cell walls probably derives from the fact that they 

 commonly outlast the living protoplast. 



During the active life of the cell, the changing pattern of cell 

 wall constitution and organization is a reflection of the changing 

 physiological states and biochemical capacities of the protoplast. 

 Thus, the chemical and physical properties of cell walls provide 

 a measure of protoplast and membrane functions which we now 

 comprehend but vaguely. 



Our present consideration of cell wall dynamics will center 

 about three areas: First, current knowledge as to the biosynthesis 

 of individual cell wall components; second, the patterns of change 

 in constitution and architecture during growth and differentiation; 

 and third, the little knowledge now at hand about chemical 

 regulation of cell wall formation. 



The Biosynthesis of Cell Wall Components 



The overall composition of the cell wall changes during growth. 

 Thus, a sunflower hypocotyl of 5 mm diameter contains 38 per 

 cent cellulose, 46 per cent pectin, and about 8 per cent each of 

 (neutral) non-cellulosic polysaccharide and lignin. A five-fold 



