INTERACTION OF GROWTH FACTORS 



213 



10 100 1000 



IRRADIANCE. BLUE (mj/cm^) 



Fig. 6. Graph showing the marked similarity of the difference curves 

 between FMN and water and between FMN + lAA and lAA. 



of added lAA. The lAA merely shifts the level of the curve and does 

 not alter its shape, indicating that there is no interaction between FMN 

 and the added lAA. The interaction between FMN, blue irradiance, 

 and the hook opening occurs at relatively high concentrations of FMN 

 (10~^M) and at high levels of irradiance. 



Discussion 



Numerous reports have indicated that gibberellin and kinetin can 

 produce a photomorphogenic response in the absence of light (Miller, 

 1956; Scott and Livenrian, 1956; and Kahn et ah, 1957). The bio- 

 logical assay used in most cases consisted of etiolated bean leaf discs or 

 lettuce seeds. In either of these assays, KNOs causes an increase in 

 diameter of the leaf discs and increased germination in lettuce seeds 

 (Toole et ai, 1956), as compared to a H2O control. This would indi- 

 cate that any additive which produces a more nearly optimal condition 

 for growth would act in a positive manner. While the above positive 

 influence does not invalidate the use of seeds and leaves as test objects, 

 it makes more difficult the evaluation of a light effect. On the other 

 hand, the bean hook test has a more specific requirement for light. 

 Indoleacetic acid, gibberellin, and kinetin all produce a negative curva- 

 ture in darkness and oppose the light response. The outer (convex) 

 cells of the bean hook respond in a manner similar to leaf discs upon 

 addition of growth regulators, but the inner (concave) cells do not 

 respond until application of a light treatment. In general, most of the 

 additives produce a growth response that is kinetically separable from 



