Physiological Action of Gibberellin 



603 



Table 3. Eflfect of gibberellin A on coumarin-induced growth inhibition of cu- 

 cumber seedling (H). 



* In each column, differences among the values are not significant at the 5 per cent 

 level . 



t In each column, differences among the values are significant at the 5 per cent 

 level. 



(4-CIBA), 3-chlorophenoxyisobutyric acid (3-CIBA), 2,4,6-trichloro- 

 phenoxyacetic acid (2,4,6-T), and 2-methyl-l,4-dihydronaphthoquinone 

 (Kg) reduce the effect of auxin when the auxin concentration is low, 

 but not when it is high enough. Hence they seem to be competitive 

 with auxin, as already pointed out by McRae and Bonner (16), In- 

 gestad (10), and Fransson (7). In contrast, the anti-auxins used made 

 GA completely ineffective even up to a high concentration, 300 mg/1. 

 The inhibition of GA effect by anti-auxins shall be considered later. 

 Here it is to be noted that anti-auxins are not competitive with GA, 

 while they are comj^etitive with auxin. 



140 



0.001 0.01 0.1 10 1 10 100 



CONCN., lAA.MG./L. CONCN., GA, MG./L. 



Fig. 1. Interaction of 15 mg/1 of 4-chlorophenoxyisobutyric acid (4-CIBA) with 

 lAA and gibberellic acid in the elongation of pea stem sections (13). 



