Gibberellins, Cell Division, and Plant Flowering 



525 



cation of sugar content (5, 30, 40), reduced nicotine content in tobacco 

 (45), increased ascorbic acid levels in clover (30), action on chloroplast 

 pigments (5, 14, 30), etc., have been reported to occur after treatment 

 by GA. In many species the effect on the pigments is grossly evident, 

 but it is rather complex. Without a supplementary supply of mineral 

 nutrients, as in a normal garden soil, there is generally a lowering of 

 the pigment content. Table 1 lists nine species we have studied. In 

 some cases the anthocyanin content is also modified. When mineral 

 fertilizers are added in the presence of GA, the chlorophyll content 

 does not drop much or does not drop at all. However, the drop re- 

 mains evident when the treated plant flowers (30). As shown by Moso- 

 lov and Mosolova (30), redox processes are strongly enhanced in the 

 leaves of GA-treated clover plants, and the sugar content of the leaves 

 increases. The assimilation of mineral nutrients also increases. 



All these facts show that GA profoundly affiects the metabolism of 

 plants. In spite of the fragmentary data, some of these facts clearly 

 indicate that under adequate cultural conditions in which mineral 

 nutrition is not limiting, GA enhances certain essential metabolic 

 processes and increases the availability of some important metabolites. 

 This is likely to be very favorable for protein synthesis inside the 

 meristem and in the young tissues of the treated plants. 



Another argument supports this conclusion. Photoperiodic induc- 

 tion of flowering, which can be replaced by the application of GA to 

 LD plants grown in short days, seems to induce an immediate change 

 in the capacity of meristematic cells to synthesize proteins. This ap- 

 pears from the following facts: 



(a) Metzner (27, 28) reported that the proportion of amino acids 

 in the protein fraction of the meristems of Kalanchoe blossfeldiana 



Table L Effect of 100 p. p.m. of gibberellic acid on pigment content of plants. 



