516 



M. /. Bukovac and S. H. Wittwer 



COMPOUND 



BIOLOGICAL ASSAY 



^•^3 ^ COOH 



BEAN EPICOTYL TOMATO OVARY 

 5\. ELONGATION GROWTH 



6 



Active 



Active 



n 



^^3 " COOH 



Slightly 

 Active 



Slightly 

 Active 



IE 



^"'H c^oH " 



COOH 



Not 

 Active 



Not 

 Active 



Fig. 8. Relative activity of gibberellin A, derivatives in elongation of llie bean 

 cpicotyl and growth of tomato ovaries. 



was ruptured and a keto group substituted for the hydrogen (carbon 

 7) the compound was inactive (Figure 8, III). 



DISCUSSION 



The diversity of alterable responses following ajiplicaiion of the 

 gibberellins and their derivatives to the intact plant presents unlim- 

 ited possibilities for assessing comparative biological activity. Only a 

 few representative areas of plant behavior — vegetative extension, 

 (lowering, dormancy, and fruit growth — were selected for assay in 

 these studies. As might be anticipated, the biological activities of the 

 four fungal gibberellins and their derivatives varied with the assay, 

 the site of treatment, and the quantity applied. 



AVitli stem elongation in the bean, terminal bud applications (10 



