M. J. BUKOVAC 



and 



S. H. WITTWER 



Michigan State University' 



Biological Evaluation of GibbereUins A, A, A, 

 and A, and Some of Their Derivatives 



Early difficulties experienced by American and British scientists in 

 the production and isolation of gibberellin A,- as announced by 

 Yabuta and Sumiki (20), eventually led to the characterization of 

 several fungal gibberellins. Stodola et al. (14) announced the 

 isolation of gibberellin A and a new gibberellin designated as 

 gibberellin X. Concurrently, Curtis and Cross (7) isolated gibberellic 

 acid, which was found (6) identical to Stodola's gibberellin X, but 

 differed from the Japanese gibberellin A. The Japanese workers then 

 re-examined their product and found a mixture of three gibberellins, 

 which they termed gibberellins Aj, Ao, and A3 (17). Gibberellin A^ 

 was identical to Stodola's A and gibberellin A3 to gibberellin X and 

 gibberellic acid. Takahashi et al. (18) next reported the isolation of 

 gibberellin A4. Henceforth, the four fungal gibberellins will be re- 

 ferred to as gibberellins Aj, A2, A3, and A4. 



Extensive field and greenhouse experiments have now been con- 

 ducted and the results summarized (1, 15, 16, 19) for a wide variety of 

 plant and crop responses produced with commercial gibberellin 

 preparations consisting largely of A3 or undetermined mixtures of 

 Al and A3. Meanwhile, little attention has been devoted to the bio- 

 logical effects of gibberellins Ao and A4. With the exception of some 

 preliminary reports (3, 5, 9, 12), no critical studies of the effects of the 

 four fungal gibberellins and their derivatives on diverse responses 

 of higher plants have appeared. 



'Journal article no. 2445 from the Michigan Agricultural Experiment Station, 

 initially named gibberellin B and changed to gibberellin A (20, 21). 



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