INTERACTION OF GROWTH FACTORS 



211 



RED * KINETIN 



10' 

 CONCENTRATION 



10" 

 (moles/ liter) 



10" 



Fig. 3. Effect of various molar concentrations of kinetin on the open- 

 ing of the bean hook in the dark and on those exposed to 1 /xw/cm- red 

 irradiance (625-700 m/x). lAA curves are also plotted for comparison. 



Cobalt 



Except for red light, cobalt is the only additive we used that had 

 any appreciable positive effect on the opening of the hypocotyl hook. 

 Figure 4 presents typical cobalt responses. The optimum concentration 

 of cobalt is lO'^M, both in hght and dark. The cobalt effect is essen- 

 tially additive to the red light effect in the same manner as reported for 

 leaf expansion (Miller, 1952). Our results also indicate that cobalt 

 can counteract the negative responses induced by kinetin, either with 

 or without red lisht. 



Flavinmononucleotide (FMN), lAA and Blue Irradiance 



Blue radiant energy alone is relatively ineffective in inducing a 

 photomorphogenic response (Withrow et ai, 1957). However, when 

 hooks are presoaked in lO^M FMN for 1 hour and then exposed to 

 blue irradiance, an increased response results; when red radiant energy 

 is used as a treatment, no change is observed. lAA ( 10~ W) produces 

 the normal inhibition of the hook response in the presence of FMN. If 

 FMN-infiltrated hooks are developed in conjunction with lAA and 

 blue radiant energy, an increased response is obtained at the higher 

 energy values. When the control H-O curve values are subtracted from 



