Influence of GibbereUic Acid on lAA Disappearance 637 



GA 



I 



I RED 



NEAR INFRA-RED 



f^E >E/ 



RED 



^/ 



NEAR INFRA-RED 



I^E >E/ 



Fig. 5. Hypothetical schemes showing possible relationships between gibberellic acid 

 (GA) above and gibberellins (G) below and the inhibitor (I) of the indoleacetic 

 acid oxidase enzymes (E). 



In dwarf 'Laurel' peas, less inhibitor is found when corresponding 

 parts with tall types, e.g., 'Alaska,' are examined (8). 



To construct a scheme as in Figure 5 (top) one may imagine that 

 when lAA-oxidase inhibitor (/) associates with the lAA-oxidase en- 

 zyme (£), an inactive complex {EI) is formed which will not destroy 

 lAA; the kinetics of the reaction, however, need not concern us. The 

 level of / in a given plant part is influenced by a number of factors. 

 Galston (8) states that GA raises the level of / in the youngest leaves, 

 and we shall assume that this generally holds in other plant parts, in 

 particular the stem. Red light is thought to raise the level of / also, 

 and near infrared radiation to oppose the reaction. These points, 

 shown diagramatically in Figure 5 (top), are linked as follows. X is 

 a precursor of / and does not inhibit E. The reaction X-^I does 

 not take place in a single step but passes through at least one inter- 

 mediate compound, Y. Y but not / can be changed back to X by 

 near infrared radiation, while in the absence of this radiation Y is 

 slowly changed to / by an unknown process. It is necessary to postu- 

 late the intermediate compound, Y, to account for the negative effect 

 of near infrared radiation when applied 1 hr. after red light. 



