STUDIES ON INTERNODE ELONGATION IN SOYBEAN PLANTS .3. EFFECTS OF GIBBERELLIC-ACID ON INTERNODE ELONGATION

In order to obtain fundamental information on the chemical control of plant structure in soybean (Glycine max Merr. cv. Fukuyutaka), the effects of gibberellic acid (GA3) on the internode elongation were examined. GA3 was sprayed with different concentrations on the pot-grown plants at the different growth stages. The internode length was found to be increased by the application of GA3 at 0.1 ppm and more concentration. The higher the GA3 concentration from 0.1 ppm to 1000 ppm was, the longer the internode elongation was (Table 1, Fig. 1). The reduction in the diameter was observed in the internodes which were elongated by the application of the GA3 (Fig. 1). And further, the GA3 application also promoted elongation of petioles in the similar manner (Table 1). The promotion of internode elongation induced by the GA3 was limited for the internodes that elongated after the GA3 application and was most effective when it was given at the floral differentiation stage (Tables 2, 3, 4, Fig. 2). The GA3 application at the floral differentiation stage increased the number of nodes on the main stem (Table 2). The GA3 application increased vegetative growth, whereas seed weight per plant was not increased. From the results it appears that the GA3 treatment at optimal stage can control the plant height and plant type by increasing the length of internodes and the number of nodes on the stem.