90 Fawcett, Wain, and IVightman 



bers of this series in pea tissue. The chromatographic (Figure 7) and 

 bioassay results (Figure 8) from metabolism experiments with pea tis- 

 sue sustain this conclusion, only the acetonitrile and heptanonitrile 

 being found to yield acidic compounds with high growth-promoting 

 activity. The metabolized acetonitrile gave rise to three major spots 

 on the chromatogram at Rf 0.21, 0.26, and 0.93 which were identified 

 as indole-3-carboxylic acid, indole-3-acetic acid and indole-3-acetoni- 

 trile respectively. Production of the acetic acid confirms the view that 

 the activity of indole-3-acetonitrile in the pea tests is related to its 

 conversion to this highly active acid, and the appearance of appreci- 

 able quantities of indole-3-carboxylic acid indicates that the conver- 

 sion -CHoCN > -COOH also readily occurs in pea tissue. Of the 



higher nitriles, only the heptanonitrile yielded evidence of acidic 

 degradation products, and from their Rf value, color reaction, and bio- 

 logical activity these compounds were identified as indole-3-acetyl- 

 aspartic acid (Rf 0.05) , indole-3-carboxylic acid (Rf 0.20) , indole-3- 

 acetic acid (Rf 0.25), and y-(indole-3-)butyric acid (Rf 0.38) . The 

 acetic and butyric acids presumably arose by [3-oxidation of <,-(indole- 

 3-)caproic acid produced by a-oxidation of the heptanonitrile. The 

 appearance of indole-3-carboxylic acid may be due to co-oxidation of 

 this nitrile as occurred in wheat tissue. 



SUMMARY 



It would appear from the metabolism experiments that the 

 growth-regulating activity shown by all the higher indole acids in 

 wheat and pea tissue is due to the breakdown of the side-chain of 

 each acid by (5-oxidation to yield either the highly active acetic or 

 propionic acids as end product. The activity shown by the higher 

 amides and methyl esters can be similarly explained, except that ^viih 

 these compountls hydrolysis of the amide or ester grouping to the 

 (orresjionding carboxylic acid precedes the (3-oxidative degradation 

 reactions. The contrasting behavior of the nitrile series in the three 

 standard tests is evidently due primarily to the different abilities of 

 wheat and pea tissue to convert the higher nitriles either by hydroly- 

 sis to the corresponding acid or by a-oxidation to tiie next lower 

 carboxylic acid. Except in the case of the heptanonitrile, neither of 

 these reactions appears to proceed in pea tissue with the higher mem- 

 bers of this series, and in consecjuence further degradation of the 

 side-ciiain does not occur. On the other hand, in wheat tissue the 

 higher nitriles are subject to two and possibly three distinct degrada- 

 tion pathways, namely (a) hydrolysis to the corresponding acid fol- 

 lowed by (3-oxidation, (b) a-oxidation to the next lower carboxylic 

 ;icid followed by ^-oxidation, and (c) co-oxidation to yield in all 

 instances inclole-3-carboxylic acid. 



