Investigation of natural auxins and growth inhibitors 



identity of these substances. This is much more difficult because, for analytical 

 investigations, the chemist generally needs larger quantities of material than 

 the biologist. However, if we have a set of synthetic auxins, we can try to 

 see if some of the natural compounds are identical with them. For example, 

 we always run control chromatograms with synthetic lAA, IAN, and lAE. 

 If a given substance in an extract runs at the exact location of, let us say, 

 synthetic IAN, we have a first presumption that it could be IAN. If the 

 same substance, chromatographed in a totally different solvent, runs again 

 at the location of synthetic IAN, then the presumption is strengthened. 

 This is not enough to identify a compound, however. We have attempted to 

 identify compounds on the paper by determining their absorption spectra. 



on 



0-12 



Figure 26. Absorption spectrum in 

 ultra-violet light of A y of lAA on 

 unwashed Whatman J\fo. 1 paper 

 observed in a Beckman spectrophoto- 

 meter. The determination was made 20 

 minutes after spraying the chromato- 

 gram with paraffin oil. 



I 



I 



OfO - 



aos 



006- 



00¥ 



002 



260 280 SOO 320 

 Wai^elen^fh 



3f0 



This can be done in two ways. First, if we know the location of the compound 

 on the paper, we can try to obtain its absorption spectrum in the u.v. This 

 cannot be done readily because the paper absorbs the ultra-violet light. 

 To render the paper translucent, we have simply sprayed it with paraffin oil. 

 The readings, taken 20 minutes after spraying, in a Beckman spectro- 

 photometer. Model DU, gave the absorption curve oi Figure 26^ with 4 y of 

 lAA. The fine details of the lAA absorption curve are lost, of course, 

 owing to the paper (unwashed Whatman No. 1), but the general shape and 

 the region of maximum absorption fit reasonably well with those given by 

 lAA in solution. On the other hand, if we do not know where the substance is, 

 but if it appears as a coloured spot upon spraying with a suitable reagent, 

 then we can determine the absorption spectrum of the coloured product (in 

 visible light, this time) and compare it with that of a synthetic auxin. The 

 curves of Figure 27 have been obtained in this manner. The coloured 

 product obtained after spraying 1 y of lAA with the ferric-perchloric acid 

 reagent of Gordon and Weber (1951) (100 c.c. of 35 per cent perchloric 

 acid+270 mg of FeCla . 6H2O+ 100 c.c. of 95 per cent ethanol) had, on the 

 paper, an absorption maximum at 550 m/^ 45 minutes after spraying, while 

 the maximum was at 580 m/i in the case of IAN and around 460 mfx for 



29 



