YUSUKE SUMIKI 



and 

 AKIRA KAWARADA 



University of Tokyo 



Relation Between Chemical Structure 

 and Physiological Activity 



For the purpose of elucidating the growth regulating activity of gib- 

 berellins, some 20 derivatives or degradation products were prepared 

 and their physiological activity observed using rice seedlings. 



Gibberellins have recently come to be recognized as important in 

 the growth regulating system of higher plants, and the chemical con- 

 stitutions of gibberellins are almost established (1,2,3,4,5) though 

 much remains to be elucidated about their stereochemistry. The au- 

 thors believe it is of considerable interest to study the relation be- 

 tween the chemical constitution and physiological activity of gibber- 

 ellins. 



Moreover, the authors expect that the determination of the par- 

 tial structures essential for showing growth response will be a guide 

 for the synthesis of new gibberellin-like substances having more 

 simplified structures than the native gibberellins. 



The compounds, i.e., the four gibberellins and their derivatives 

 or degradation products, were examined as to their purity by paper 

 chromatography. The physiological activity was observed by measur- 

 ing the length of the second leaf-sheath of rice seedlings on incuba- 

 tion at a concentration of 10 /xg/ml as described in a previous paper. 



The results are illustrated in Figure 1. The values indicate the 

 relative activity of each compound when that of gibberellin A3 is 

 assumed to be 100. Data in Figure 1 may be summarized as follows: 

 (1) On A-ring — S-lactone ring and secondary hydroxyl group are es- 

 sential, and by the inversion of stereochemical configuration of hy- 

 droxyl activity is lost. On B-ring — physiological activity is much re- 

 duced where the carboxyl group is masked by methylation. On C- and 

 D-rings — (a) exocyclic methylene, or double bond, is not essential 



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