630 



5. Housley and B. J. Deverall 



RESULTS 



Experiments With Enzyme Breis 



In pea and other phmts an enzyme system occurs (lAA-oxidase) 

 which destroys lAA (18,27). It was necessary, therefore, to examine 

 whether GA has any sparing action upon rate of lAA destruction 

 when incubated with this enzyme system. The result of one experi- 

 ment is shown in Figure lA. In all experiments, absorption is plotted 

 against time of sampling aliquots from the reaction mixture. It is 

 seen that as the concentration of lAA decreases, GA has no effect 

 upon the rate of lAA destruction. Similar results were obtained 

 when this experiment was repeated, and also when a third experi- 

 ment was carried out with a brei prepared from 'Alaska' peas. 



As the activity of crude preparations of lAA-oxidase of peas can 

 be influenced by light (9), it was decided to examine the effect of GA 

 on rate of lAA destruction when reaction mixtures with enzyme brei 

 were light-irradiated throughout the experimental period. A brei 

 from dark-grown plants was used, as light-grown plants contain an 

 inhibitor of the lAA-oxidase system (9). The experiment was simi- 

 lar to that shown in Figure lA except that it was carried out under 

 fluorescent light tubes. The result was similar to those shown in 

 Figure lA in which GA had no influence on rate of lAA destruction, 

 while another two experiments, one of which is shown in Figme IB, 



0.3 



50 



100 150 50 



TIME IN MINUTES 



150 



Fig. 1. Rate of cicstiuciion of iiulolc-IJadtic acid l)v iiidolc-S-acctic oxidase enzyme 

 in the presence (solid lines) and absence (broken lines) of gibbeiellic acid in dark- 

 ness (A) and in lio;lit (B). 



