Enzymes in Irradiated Tissues 51 



having recourse to an oxygen effect to explain this. This 

 problem needs a great deal more work but seems an example 

 of a rapid effect of X-rays on an enzyme system containing 

 at least 11 enzymes. No individual enzyme was studied, but 

 there is a certain specificity since the respiratory mechanism 

 is unaltered. 



Auxin 



A third instance where radiation is thought to have a 

 direct or indirect effect on a cytoplasmic enzyme is the in- 

 hibition of auxin synthesis in the plant by very low doses of 

 X-rays. Skoog (1935) first investigated the effect of radiation 

 on auxin and thought that auxin itself was inactivated rather 

 than that its synthesis was affected. Later, Gordon and 

 Weber (1955) have concluded that auxin is not particularly 

 sensitive to radiation, but that the synthesis is easily inhibited 

 (Weber and Gordon, 1951a, b and c; 1952a, b and c; Gordon, 

 1956). The effect was first described by Weber and Gordon 

 (1951a) in an Argonne National Laboratory report. Since 

 that time there have been many brief reports in ANL publica- 

 tions and Gordon gave a brief paper at Cambridge in 1955, 

 but, as far as I am aware, no details of the methods used and 

 the results obtained have ever been published and though one 

 can get some notion of the methods from others of Gordon's 

 papers not concerned with radiation, I have yet found it 

 difficult to assess the work. I feel a protest must be made 

 against this habit of publication of brief reports in laboratory 

 journals which are not available to most scientists. The 

 subject deserves more serious treatment. 



Now, to summarize as critically as possible the ANL reports 

 on the inhibition of auxin synthesis by X-rays. Weber and 

 Gordon (1951a) find, first, that low doses of X-rays cause an 

 immediate drop in the auxin content of the young mung bean 

 plant; second (Weber and Gordon 19516), that shoots of the 

 mung bean infiltrated with tryptophan, and then irradiated, 

 form less auxin than similar non-irradiated shoots: third 



