ON THE EFFECTS OF P^T^^-SUBSTITUTION 



IN SOME PLANT GROWTH REGULATORS 



WITH PHENYL NUCLEI 



B. Aberg 

 Institute of Plant Physiology, Royal Agricultural College, Uppsala, Sweden 



INTRODUCTION 



The remarkable effect of introducing 3. para chlorine atom into the phenoxy- 

 acetic acid molecule, thereby changing the physiological character of this 

 substance from weakly anti-auxinic (or better: intermediate) to strongly 

 auxinic, has also been found to have its counterpart among the more typical 

 auxins and anti-auxins. The strong increase in the auxin activity from 

 2-chloro- to 2:4-dichlorophenoxyacetic acid is well known, and among the 

 anti-auxins such a para chlorine effect upon the activity has been found for the 

 phenoxy?jobutyric acids (Burstrom, 1951a) as well as for different types of 

 substituted phenoxyacetic acids (see Aberg, 1954). 



Under the circumstances it was thought pertinent to make a more extensive 

 study of several pairs of substances differing only with respect to a para 

 chlorine substituent. Some insight into the nature of its function could be 

 expected from studies on the effects of other para substituents. A number of 

 phenoxyacetic acids with such substituents have therefore been included in 

 the present connection. 



Most of the substances used have been synthesized by Prof. A. Fredga and 

 Dr. M. Matell of Uppsala, to whom I tender my sincere thanks for their 

 generous and unfailing co-operation. The following abbreviations will be 

 used: 



POA: phenoxyacetic acid, CgHg-O-CHg-COOH; substituents in the 

 phenyl nuclevis are indicated in the usual manner, Me signifying 

 a methyl group, Et an ethyl group, iP an iso-propyl 

 group, and /B a terf.-hutyl group. Some phenoxyacetic 

 derivatives have been further abbreviated, according to 

 common usage: 2:4-D = 2:4-Cl2POA, 2:6-D = 2:6-Cl2POA, 

 2:4:6-T = 2:4:6-Cl3POA. 

 Th : thymoxyacetic acid, 2-?P-5-MePOA. 

 ClTh: chlorothymoxyacetic acid, 2-fP-4-Cl-5-MePOA. 

 POP: a-phenoxy-propionic acid, C6H50CH(CH3)COOH. 

 POi'B: a-phenoxy?>obutyric acid. The 4-chloro derivative, 4-ClPOiB, 

 was originally designated PCIB by Burstrom (1950). 



Tr 



PF 



lAA 



1-NMSA 



transcinnamic acid, CgH5CH:CHCOOH. 



phenyl-formic or benzoic acid, CgH^COOH. 

 3-indolylacetic acid. 

 1 -naphthylmethyl-sulphide-acetic acid, 

 C2qH7-CH2'S-CH2"COOH. 

 1-NMSP: the corresponding a-propionic acid. 



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