Hormones and hormone precursors 



fraction (e.g. Figures l{a), 2{c), 2{e)) and also in the acid and neutral ethereal 

 fractions (results of these fractions are published in detail elsewhere). It was 

 therefore decided to examine synthetic IPyA to determine whether, in fact, 

 it could be responsible for the activity in this region. 



3-Indolylpyriivic acid 



IPyA has been synthesized and fully characterized by Dr. G. F. Smith, 

 Dr. K. R. Farrar, and Mr. W. Taylor of the Chemistry Department, 

 Manchester University. Its behaviour under the conditions of chromato- 

 graphy used by Stowe and Thimann to demonstrate its presence in maize 

 endosperms, and also its growth-promoting activity, have been investigated. 



In order to permit a detailed account of this work to appear elsewhere 

 (Bentley, Farrar, Housley, Smith, and Taylor, 1956), the remainder of the 

 lecture which dealt with the results of these investigations is not reported 

 here. It may be briefly stated, however, that work on synthetic IPyA has 

 shown that it breaks down completely to form lAA, together with other 

 substances, under the conditions of ammoniacal chromotography used in 

 the studies of Stowe and Thimann. The presence of IPyA itself cannot be 

 demonstrated using the solvent system employed by these authors. 



Chromogenic studies of chromatograms of the aqueous extract of maize 

 {Figure 6) have shown that lAA is not present on these chromatograms. 

 It appears improbable, therefore, that the activity near the starting line in 

 Figure 6 is due to IPyA, suggesting that there is yet another unknown auxin 

 in this region. 



It has also been suggested by Stowe and Thimann that the ether-soluble 

 acidic substance called accelerator-a (Bennet-Clark and Kefford, 1953) which 

 runs between lAA and the starting line under conditions of ammoniacal 

 chromatography is probably IPyA. Bennet-Clark and Kefford have 

 demonstrated that accelerator-a promotes root-growth, whereas we find 

 that synthetic IPyA causes only inhibition of root-growth (cress assay 

 method), with an activity approximately one-tenth that of lAA. The zone 

 of activity between the starting line and lAA in Figure 6 has not yet been 

 tested for its effect on root growth. 



DISCUSSION 



Examination of the aqueovis, ether-insohible portion of cabbage, tomato, and 

 maize extracts has shown that this fraction has auxin activity which is 

 usually considerably greater than that obtained in ether extracts. Only low 

 activity is obtained in acid ether extracts, and this largely follows the same 

 pattern as the aqvieous extracts. Two clear-cut peaks are obtained in 

 cabbage with both ammoniacal /^opropanol and «-bvitanol ; in tomato, there 

 are three clear-cut peaks with ammoniacal «-butanol. 



The growth promoter near the solvent front in cabbage is neutral, ether- 

 soluble, and has the Rp fluorescence, and chromogenic reactions of IAN, 

 with which it is believed to be identical. On the other hand, the hormone 

 near the solvent front in tomato has been similarly examined, and, apart from 

 Rf value, no convincing evidence has been obtained that this zone is due to 

 the nitrile. It has not been possible to obtain even a transient reaction with 

 HNO2/HNO3 at this position. 



49 



