Natural auxins 



{b) There is at the earher sampHng times an inhibitor, an acidic 

 substance with R^ 0-3-0-4, whose concentration decreases during the first 

 3 days of germination. None was detected in the 72- and 96-hour extracts. 

 In the next few days of seedhng growth, however, this inhibitor re-appears. 



(c) In the 7-day-old etiolated pea seedling an appreciable amount of lAA 

 has been built up, and there is also a significant concentration of inhibitor. 



(d) In many instances, there is some stimulatory activity in strips 7 and 8 

 of the chromatogram. This, however, does not appear consistently and it 

 cannot with certainty be attributed to any known hormone. 



^200 



s> 



k^so 



May 1955 



300 Shoots 300 Roofs 300 Cof/ledons 



k ^100 

 b°^ 50 

 ^ June 1955 





200 Shoots 200 Roofs 200 Cotjiedons 



- Rf yalue •- 



Figure 6. Distribution of hormones and inhibitors in ^-day-old etiolated pea seedlings. 



A series of six experiments with peas indicated similar changes in auxin and 

 inhibitor content during germination. There was, however, a considerable 

 variability in the amounts of activity on different occasions and no attempt 

 has been made to relate the results to absolute amounts of lAA present at 

 each sampling time. 



The results of two experiments carried out to show the distribution of 

 auxin and inhibitor in 8-day-old etiolated seedlings are presented in Figure 6. 

 The shoots contain inhibitor and a relatively large amount of lAA. In the 

 root extracts there is a lower auxin and inhibitor activity. Again, calculation 

 of the absolute amounts of lAA in the tissues has not been attempted, but the 

 histograms suggest that in these etiolated seedlings the shoot contains of the 

 order of 10 times as much lAA as the root system. Since the fresh weight of 

 the shoot is only about 25 per cent greater than that of the root, a higher 

 internal I AA concentration is indicated. In the cotyledons there is stimulatory 

 activity in the TAA zone' and in strips 7 and 8 of the chromatogram. 



Chromatograms similar to those used for biological assay were sprayed with 

 Ehrlich reagent and besides the blue spot due to lAA a pink spot of Rf 0- 1 

 developed which has the same Rf and colour reactions as indole-3-carboxylic 

 acid. The possible significance of this is discussed in other papers of this 

 Symposium (Seeley el at., 1956; Fawcett et at., 1956). 



From these investigations on germinating peas it would seem that the 

 disappearance of an inhibitor during the early stages of germination may be 

 of physiological significance. This inhibitor has completely disappeared 

 after 48 hours when the radicles have emerged. The auxin content, however, 

 increases very slowly during germination proper and only builds up to an 



38 



