THE INFLUENCE OF GIBBERELLIN AND AUXIN 

 ON PHOTOPERIODIC INDUCTION ' 



ANTON LANG 



Department of Botany, University of California, Los Angeles 



The influence of auxin and gibberellin on flower formation, specifi- 

 cally on photoinduction, to which this discussion will be limited, has 

 been studied in an attempt to get a toehold on the biochemistry of 

 flowering. It has been somewhat of an act of desperation, for even 

 though auxin and gibberellin control a great number of growth proc- 

 esses in the plant, there is no advance reason to believe that they should 

 control flower formation, too. However, all more direct and more 

 logical attempts to penetrate into the biochemistry of flowering which 

 were made in the past have remained inconclusive. Thus, there is con- 

 siderable physiological evidence for the existence of floral stimuli or 

 flowering hormones, but all attempts at isolating and identifying these 

 materials have been conspicuous by their lack of success, and some 

 investigators — though not myself — are presently inclined to relegate 

 them into the realm of scientific myth. 



Extensive efforts have also been made to discover biochemical 

 differences between induced and noninduced plants and to relate them 

 to the process of flower induction. With respect to the first of these 

 two goals, this work has been quite successful. More plant constituents, 

 sugars, nitrogenous substances, vitamins, etc., are changed, at least 

 quantitatively, after photoinduction than are not. The same is true 

 for enzyme activities and various other processes in the plant. Some 

 of them go up, and others go down; however, the second goal has 

 not been reached; a clear-cut causal relation between these changes 

 and flower induction has not been established. The most promising 



^ The author's personal research, referred to in this paper, has been gener- 

 ously supported by research grants from the National Institutes of Health, 

 U. S. Public Health Service (RG-3939), the National Science Foundation 

 (G-3388), The Lilly Research Laboratories, and the Committee for Research, 

 University of California. 



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