Mechanics of Auxin-induced Grozuth 



319 



Table 3. Characteristics of the pectic materials of the cell walls of Avena coleoptile 

 sections. After Jansen f/ a/. (16). 



Fraction 



Whole cell walls 



Cold H2O soluble, 70 per cent 



EtOH insol 



Hot HP soluble 



Residual 



Per Cent 



AUA* 



in Fraction 



5.3 



4.0 

 23 

 43 



Per Cent 

 of Total 



AUA 



91 



5 

 14 

 78 



Per Cent 



Methyl 

 Esterified 



40 



ca 100 

 90 

 31 



* AUA = Anhydrouronic (galacturonic) acid. 



It makes up some 80 per cent of the total, is roughly 30 per cent ester- 

 ified, and contains essentially all of the free pectic carboxyl groups 

 which contribute to the cation exchange capacity of the wall. This 

 residual pectin may be solubilized by hot water in the presence of 

 the chelating agent ethylenediaminetetraacetic acid (EDTA). 



The effects of lAA, so far as pectic material is concerned, are con- 

 centrated in the hot and cold water soluble pectic fractions. Informa- 

 tion bearing on this point is summarized in Table 4 for two types of 

 experiments. In the one type of experiment, sections were merely in- 

 cubated for 15 hrs. in the presence of glucose and in the presence or 



Table 4. Cell wall pectic synthesis during the growth of Avena coleoptile sections. 

 Summarized after Albersheim and Bonner (1). 



* AUA = Anhydrouronic (galacturonic) acid. 



** Sections incubated 5 hrs. in uniformly labeled C"-glucose, 2.5 X 10~*M, 1.9 

 mc/millimole. 



