The biogenesis of natural auxins 



vacuum infiltration of tryptophan {Figures 3 and 4) or in vitro by the use of 

 cell-free enzyme preparations {Figure 5). The vertical broken lines indicate 

 the incubation times used in examining the effect of X-radiation on the 

 activity of the tryptophan to lAA enzyme system. 



Figure 6. The in vitro conversion of 

 tryptophan to auxin by cell-free homogenates 

 made from rnung bean seedlings immediately 

 after X-irradiation. The lower curve gives the 

 relative amounts of lAA formed, the upper curve 

 indoleacetaldehyde . 



¥ 5 



rbntgens xlO^ 



The radiation sensitivity in vivo of the tryptophan-I AA enzyme is shown in 

 Figure 6. Unusually low doses of X-rays inhibited the conversion of tryptophan 

 to lAA. An almost identical response to irradiation was shown using the 



6 8 10 



Time after irradiation 



12 



IV- 

 days 



Figure 7. Relative ability of irradiated mung bean seedlings to convert infiltrated tryptophan to auxin at 

 various times after irradiation. 



vacuum-infiltration technique. The order of dosage required for inhibition 

 of enzyme activity is similar to that shown in Figure 2 for the reduction in vivo 

 of free auxin level by X-radiation. 



Figure 7 describes the post-irradiation responses of the enzyme system. 

 Represented are the inhibitions and recoveries in the rates of tryptophan 

 conversion relative to non-irradiated controls. It can be seen that the extent 

 of inhibition following irradiation increases as the dose becomes larger. A 



69 



