A^cio Theory on Primary Mode of Auxin Action 



459 



Fi£. :!. A. Model ot li,:! dichluiubcnzoic acid about to be lowered into a 3-dimen- 

 sional liole. The 3 cylinders are imagined to be 3 molecules of the cytoskeleton. 

 The white pieces of foam rubber indicate part of the hydrogen network on the 

 surface of the cytoskeleton. B. Model of 2,3-dichlorobenzoic acid fits tightly into 

 the hole of the cytoskeleton so that it anchors the polar group in position in the 

 hydrogen bond network. C. Model of 2-heptadecanol fitting into the 3-dimensional 

 hole of the cytoskeleton. Note how the -OH group is held into place for partici- 

 pation in the H-bond network. D. Model of indole-3-acetic acid fitting into a hole 

 in the cytoskeleton. An arrangement of this sort, because of the uniformity of the 

 cylinders (molecules that make up the cytoskeleton) may give the false impression 

 that all holes are of uniform size. This is not intended as the holes into which the 

 auxins fit must be specific (see F. H. Dickey, Jour. Phys. Chem. 59: 695. 1955). 



day he has isolated from tobacco tissue. If, indeed, as I am proposing, 

 the primary function of an auxin is the participation of the undissoci- 

 ated acid group in a hydrogen bond system, then there is no physico- 

 chemical reason why another polar group, such as the -OH of an 

 alcohol, could not serve equally well. The discovery by Crosby and 

 Vlitos of the alcohol auxin, therefore, supports my views. It will be 

 noted that the -OH group of this alcohol is on the second carbon. 

 Therefore, it is in a lateral position quite comparable to that of a 

 hindered carboxyl group of a benzoic acid. The long hydrocarbon 

 chain fits the auxin binding site in the cytoskeleton (Figure 3C) and is 

 held in position by van der Waals forces. 



