Natural auxins 



So far, we have studied the effect of lAA only. But, in extracts of plants 

 there are other auxins, such as IAN or lAE. The effect of these substances 

 on the growth of coleoptiles and internodes of Brighton oats under the 

 conditions defined above (presoaking, buffer, 2 per cent sucrose, 0-5 ex. 

 volumes, etc., plus 0-1 per cent Tween 80 to help dissolve substances which 

 are poorly soluble in water), can be seen in Figures 19 and 20. On the whole. 



i 5-0 ~ 



f-0 



I 



^ 3-0 



8-0 



120 



60 



1 



3000 



Concentration of auxins (xSxIO V\) 



Figure 19. Growth curves of oat coleoptile sections {var. Brighton) in buffer '\- sucrose + Tween 80 (0-1 

 per cent) and various molar concentrations of I A A. IAN. and lAE. Pretreatment of sections and scales 

 are as in Fimre 18. 



^ 70- 



e-0 



5-0 



lAE h 

 /lAN/ 



\ 



i^-O 



3-0 



2-0 



1-0 



m 



160 



110 



m 



100 





80 



60 





VO 



Figure 20. Growth curves of 

 oat internode sections in conditions 

 similar to those of Figure 19. 



1 3 10 30 100 300 JOOO 3000 



Concentration of auxins (x5xf0'^V\) 



at equal molar concentrations, the three substances have about the same 

 activity, especially at low concentrations. At higher concentrations, IAN and 

 especially lAE tend to be more active than lAA, but the difference is not a 

 ten-fold one such as can be obtained in the case of IAN with Victory oats 

 under different experimental conditions. 



The following examples show how this more sensitive first internode test 



24 



