THE DEGRADATION OF CERTAIN 



PHENOXY ACIDS, AMIDES, AND NITRILES 



WITHIN PLANT TISSUESf 



C. H. Fawcett, H. F. Taylor, R. L. Wain, and F, Wightman 

 Agricultural Research Council Unit on Plant Growth Substances and Systemic Fungicides, 



Wye College, University of London 



Recent work at Wye has been concerned with the /3-oxidation of oj-phenoxy- 

 alkanecarboxyhc acids within plant tissues. It had previously been shown 

 that an alternation in growth-regulating activity might operate in an homo- 

 logous series of oj-aryl- or oj-aryloxy-alkanecarboxylic acids as the side-chain 

 length increased (Grace, 1939; Synerholm and Zimmerman, 1947). Such 

 behaviour was ascribed by Synerholm and Zimmerman to the degradation of 

 the side-chain by /j-oxidation. On this basis, only the acetic derivative and 

 its alternate homologues would be expected to show activity. Further 

 biological evidence for the /i-oxidation hypothesis was provided by Fawcett, 

 Ingram, and Wain (1954) and by Wain and Wightman (1954), who showed 

 that only alternate members of the oj-(4-chlorophenoxy)alkanecarboxylic 

 acids were active in the pea curvature and wheat cylinder tests. Again, 

 Luckwill and Woodcock (1955) have recently shown that a similar alterna- 

 tion operates in regard to the capacity of ft>-(2-naphthoxy)alkanecarboxylic 

 acids to induce parthenocarpic development of tomato ovaries. 



Chemical evidence that ^-oxidation can occur within plant tissues has 

 been obtained at Wye. In our first experiments using flax seedlings, 

 members of the homologous series of a>-phenoxyalkanecarboxylic 

 acids, CgH50(CH2) „COOH with n = \ to 10, were supplied to flax seedlings 

 through their roots. After a suitable interval to allow breakdown of the acids 

 to occur, the plants were steam distilled and phenol in the steam distillate 

 estimated colorimetrically. It was found that those acids with an even 

 number of side-chain methylene groups {n = 2, 4, 6, 8, and 10) gave rise to 

 appreciable quantities of phenol, e.g. 



C6H50CH,CH2COOH->[C6H50COCH2COOHl-> 



«"=2 [CeHsOCOOHJ^CeH^OH 



phenol 



The alternate higher homologues (n = 4, 6, 8, 10) could also yield phenol by 

 repeated /^-oxidation. 



The acids with n = 1,3,5, and 7, on the other hand, yielded only traces of 

 phenol, which is in agreement with the fact that phenoxyacetic acid is the 

 expected end product from these compounds (Fawcett et al., 1954), e.g. 



C6H50CH2CHoCH2COOH->[C6H50CH2COCH2COOH]^ 



n=^S C6H5OCH2COOH 



phenoxyacetic acid 



■[" This paper was read at the Conference by R. L. Wain. 



187 



