SOME ASPECTS OF PHOTOTHERMAL AND 



CHEMICAL CONTROL OF GROWTH 



AND FLOWERING 



FAUSTO LONA 



Institute of Botany, University of Parma, Parma, Italy 



On studying the action of gibberellic acid (GA) on vegetables, we 

 became aware that plants treated with this substance assumed features 

 similar in some respects to those produced by special environmental 

 conditions such as low light intensity, long photoperiod, and relatively 

 high night temperature. With regard to light conditions which possibly 

 should have a similarity of action with that of GA, our attention was 

 focused, of course, on the most noted morphogenetical radiations. 

 Concerning the photoperiodic factor, the action of GA, in this paper, 

 will be considered especially in relation to the quality of light used as a 

 periodic supplement to a basic natural short day. In concluding this 

 principal argument, we shall briefly mention temperature interference. 

 We investigated the possibility of a relationship between GA mor- 

 phogenesis and plants responses to light through the reaction of percep- 

 tive systems and related processes. Our first experiments included 

 rapid tests for the effects of red and far-red light on germination of 

 photoblastic seeds and on shoot lengthening (Lona, 1956a; Lona and 

 Bocchi, 1956). Similarities in the responses of intact plants were found 

 in many instances between the effect of far-red irradiation and that of 

 GA. At the same time we noted that red light frequently had an effect 

 opposite to that of GA. notably in shoot lengthening, chlorophyll pig- 

 mentation, anthocyanin production, and of other secondary products 

 of metabolism (phenol compounds and such). On the other hand, we 

 found that Lactiica seed germination responded in an opposite fashion 

 and that GA promoted germination just as red irradiation does. The 

 same is true of the expansion of excised leaf discs (see Liverman. 

 Section III, pp. 161-180). 



351 



