Indole-3-acetaldehyde in Plant Extracts 49 



sembles the neutral auxin from Pisum and Vicia faba and the auxin 

 prepared from isatin and tryptophan (21) . 



Synthetic IAN, when tested at low concentrations, proved to have 

 about the same activity per microgram as lAA in the Avena coleoptile 

 curvature test. This confirms the results of Bentley and Bickle (3) . 

 The standard soil treatment (see above) almost completely removed 

 the activity of the preparation. Examples: IAN, 80 jxg/l, 30.4° curv- 

 ature; soil-treated, 0° curvature; IAN, 8 /xg/1, 8.5° curvature; soil- 

 treated, 0° curvature. IAN and lAAld can thus be distinguished by 

 their different reactions to the standard soil treatment. 



Plant Extracts 



Pisum. Samples of neutral, defatted fractions of pea epicotyl ex- 

 tract, each representing 11 to 12 g. of fresh plant material, were evap- 

 orated as spots on the starting line of the chromatographic paper. 

 Samples of synthetic lAAld and IAN (8 to 10 /xg.) were applied at sepa- 

 rate spots to serve as markers. The chromatograms were developed by 

 spraying with DMCA after about 18 hrs. A colored spot at the starting 

 line w-as reddish purple and a 40 mm. long spot around Rf 0.055 

 (lAAld location) was clear blue. Faint blue streaking was visible 

 behind the blue spot at Rf 0.055, both in the pea extract and in the 

 synthetic lAAld preparation. No other coloration was detected on the 

 chromatogram. Suitable zones (see Figure 2) were cut out of two 

 parallel, unsprayed strips of the paper. Each of these zones was cut to 

 smaller pieces and extracted with three changes of ether over a period 

 of 3 days. Each of these eluates was made to a volume of 25 ml. and 

 tested at various concentrations in the Avena coleoptile curvature test. 

 The results are given in Figure 2. Auxin activities are expressed in rela- 

 tive units, based on the amount of plant material needed. The con- 

 centration yielding 10° curvature was interpolated on the ascending 

 part of concentration activity curves (example in Figure 1) . 



The solid lines in Figure 2 represent direct tests without soil treat- 

 ment. By far the highest activity is present in zone III containing the 

 clear blue spot at Rf 0.055. Considerably less was present in zones I 

 and II, and no activity was detected in the other parts of the chroma- 

 togram down to Rf 0.31, although concentrations representing up to 

 110 kg. fresh plant material per liter of agar were tested. 



The broken lines (Figure 2) indicate the activity of the eluates 

 after soil treatment. In zone III the auxin activity was increased 

 several-fold by the soil treatment (see also Figure 1). Also in zone I 

 the activity was increased, but to a smaller extent. The eluate from 

 zone II was not treated with soil. Soil treatment did not produce any 

 activity in zones IV and V. 



