72 Fawcett, Wain, and Wightman 



members of the acid series. The nitriles, however, showed exceptional 

 behavior in both the tissues employed. In pea tissue, only the first 

 member of the series (i.e., 2,4-dichlorophenoxyacetonitrile) showed 

 evidence of hydrolysis to the corresponding carboxylic acid, whereas 

 in wheat tissue, all homologues produced not only the corresponding 

 acid, but also the next lower carboxylic acid. In the case of the higher 

 nitriles, subsequent ^-oxidation of one or other of these acids resulted 

 in the production of the highly active 2,4-dichlorophenoxyacetic acid. 

 This behavior of the nitriles in wheat tissue is explicable in terms 

 of an initial modification of the -CHoCN group by two mechanisms, 

 namely, either hydrolysis to the corresponding acid or conversion to 

 the lower carboxylic acid with the loss of a one-carbon fragment. The 

 latter type of breakdown was referred to as a-oxidation of nitriles, 

 and further evidence for this reaction in plant metabolism has been 

 obtained from studies on the degradation of indole-3-acetonitrile in 

 wheat, pea, tomato, maize, and celery tissues (8). a-Oxidation of this 

 nitrile yields indole-3-carboxylic acid as end product, and the occur- 

 rence of indole-3-aldehyde as an intermediate has been established 



(7) . 



In view of the importance of indole compoinids and in particular 



indole-3-acetic acid and indole-3-acetonitrile in relation to the hor- 

 monal control of plant growth, it was logical to extend the above in- 

 vestigations by examining the growth-regulating activity of a homolo- 

 gous series of indole-3-alkanecarboxylic acids together with the cor- 

 responding amides, nitriles, and methyl esters. This has been carried 

 out using the wheat cylinder, pea segment, and pea curvature tests, 

 and a study has been made of the metabolism of these compoimds in 

 pea and wheat tissues. It is with the results from the latter aspect of 

 the work that this paper is mainly concerned. Briefly the metabolism 

 experiments involved exposing solutions of the various indole com- 

 pounds to wheat coleoptile or pea stem tissues with subsequent ex- 

 traction and paper chromatographic separation of the metabolic 

 products present in the tissues and in the residual solution. After de- 

 velopment, the chromatograms were examined by chromogenic and 

 biological methods. 



MATERIALS AND METHODS 



The compounds examined are given in Table 1 together with 

 their uncorrected melting points, Rf values in two different solvent 

 systems, ultraviolet fluorescence characteristics, and chromogenic reac- 

 tions with three reagents. 



The growth-regulating activity of each of these substances was as- 

 sessed in the wheat cylinder, pea segment, and pea curvature tests. 



