180 



Fundamentals of Auxin Action 



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 o 



z 



UJ 

 CD 

 (T 

 O 

 (f) 



m 

 < 



.01 



-.02 



.03 



-.04 



-.05 





_i I I I L. 



10- 



K)- 



10-9 10-8 10-7 10-6 10-5 M. 



CONC. OF ACID 



Fig. 80. The effects of some auxins and related compounds upon the disappear- 

 ance of free sulfhydryls of coenzyme A (Leopold and Guernsey, 1953). 

 2,4,5-T: 2,4,5-trichlorophenoxyacetic acid 

 2,4-D: 2,4-dichlorophenoxyacetic acid 

 lAA: indoleacetic acid 



NAA: naphthaleneacetic acid 

 PCA: p-chlorophenoxyacetic acid 

 DCB: 2,4-dichlorobenzoic acid 

 CHA: cyclohexaneacetic acid 



The suggestion was made that auxin may form a thiol ester with 

 CoA. The proposed reaction might be expected to be as follows: 



CHzCOOH + (Co/i 



CHgC. (CoA) + HjO 



The auxinyl-CoA avouM be expected to be a high-energy bond, just 

 as are the esters of CoA with other organic acids. 



The theory that auxin may act through an ester with CoA is 

 further supported by the findings that CoA and adenosine-triphos- 



