M. KH. CHAILAKHIAN 



U.S.S.R. Academy of Sciences 



Effect of Gibberellins and Derivatives of 



Nucleic Acid Metabolism on Plant 



Grov\/th and Flowering' 



The discovery of gibberellins (GA) is an outstanding achievement in 

 research on plant ontogeny, as mankind has now received a new 

 powerful tool for controlling the growth and development of plants 

 (2, 28). On the other hand, it may serve as a crucial test of the cor- 

 rectness of those hypotheses and of theoretical generalizations which 

 at different times have been made regarding the inner causes of plant 

 flowering since, as is usually the case, the appearance of new facts 

 of outstanding importance revolutionize our theoretical conceptions 

 and excite new ideas. 



It is quite evident that the discovery of gibberellins is directly 

 related to the concept of flowering hormones in plants or, as it was 

 called, florigen, which we proposed over 20 years ago (8). This is es- 

 pecially true if it be noted that a comparison of data on the effect of 

 GA on plants and the results of previous grafting experiments show 

 that GA is not a flowering hormone which is essentially the same 

 for long-day and short-day species. 



As may be recalled, the concept of flowering hormones, among 

 others, was based on grafting experiments in which it was shown 

 that flowering of short-day plants under long-day conditions can be 

 induced by substances produced in the leaves of long-day species, 

 and conversely that long-day plants flower under short-day conditions 

 in the presence of substances from the short-day components of the 

 grafts (7, 23, 24, 25, and others). This was the basis for suggesting that 

 in long-day, short-day, and neutral species flowering hormones (flor- 

 igen) are of the same type. 



^ Read at the Conference by Dr. Clark A. Porter, Boyce Thompson Institute. 



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