Biological Evaluation of Gihhcrellins 



513 



Table 3. Characterization of several ?i-alkyl esters of gibberellin A3 and their effect 

 on lettuce seed germination in the dark (13). 



Ester 



Control 



H (gibberellin A3 



Methyl 



Ethyl 



n-Propyl 

 w-Butyl . 



H-Amyl. . . 

 f!-Hexyl 



«-Heptyl 



«-Octyl 



?i-Nonyl 



w-Decyl 



Empirical 

 Formula 



CigHosOe 

 C20H24O6 

 C21H26O6 



CaoHogOe 

 C23H30O6 

 C24H32O6 

 C25H34O6 



C2CH36O6 

 C27H38O6 

 C28H40O6 

 C29H42O6 



Melting Point, 

 Degrees Centigrade 



232-35 



202 



155 



138 

 145 



165-66 

 188-89 



181-82 

 157-58 

 131-32 

 102.5-108. 



Germination of 



Lettuce Seed, 



Per Cent 



41.2* 



80.6 



63.5 



78.4 



68.9 

 83.7 

 79.1 

 56.8 



57.2 

 48.0 

 46.7 

 40.0 



L.S.D. at P .05: 11.7; L.S.D. at P .01: 16.4. 



was then assayed in terms of the promotion of lettuce seed germina- 

 tion in the dark, stimulation of bean epicotyl elongation, and growth 

 of tomato ovaries. 



Germination was significantly enhanced by the methyl, ethyl, n- 

 propyl, ??-butyl, w-amyl, n-hexyl, and n-heptyl gibberellates at 3 X 

 10-5 TVf (Table 3). The ?z-octyl, n-nonyl, or n-decyl gibberellates were 

 inactive. Germination from the methyl, ethyl, n-propyl, n-butyl, and n- 

 amyl gibberellates equalled or approached the response from the free 

 acid. By contrast, none of the esters promoted the elongation of bean 

 epicotyls or, over a wide range of concentrations in lanolin (3 X 10"^ 

 to 3 X 10^ M), the growth of tomato ovaries. 



In separate experiments, however, the butyl cellosolve ester of A3 

 (Merck & Co., Inc.) was found equally as effective as the free acid in 

 promoting lettuce seed germination, tomato ovary growth, and elonga- 

 tion of the bean epicotyl. 



COMPARATIVE ACTIVITY OF SEVERAL DERIVATIVES OF 

 GIBBERELLINS Ai, A3, AND A4 



Several derivatives of gibberellins Aj, A3, and A4, procured from 

 Dr. Y. Sumiki, were next assayed for their promotion of epicotyl elon- 

 gation in bean seedlings and growth of tomato ovaries. 



The relative activities of the respective derivatives as related to 

 the parent compounds are given in Figures 6, 7, and 8. Dihydro-gib- 

 berellin Aj (Figure 6, II) and the keto product of dihydro-gibberellin 

 Ai (Figure 6, III) were slightly active. Compound IV, in which the 



