uptake and Fate of C'-Iabeled 2,4-D in Bean Stems 283 



The Fate of Radioactive 2,4-D in the Stem Sections 



As has been reported by Fang et al. (11), 2,4-D is relatively im- 

 mune to oxidative attack by plant tissues. Accordingly, less than 1 

 per cent of the radioactivity which was taken up by the stems could 

 be recovered as COo in a KOH trap. Thus the activity which is lost 

 from the stems must be presumed to be liberated into the agar me- 

 dium at the basal end of the stems. However, as would be expected 

 from the results shown in Figures 2 and 3, it proved very difficult to 

 demonstrate a diffusion of radioactivity from the stems into the agar. 

 The gradient established in the stems results in very little radioac- 

 tivity near their basal ends. Undoubtedly the concentration in the 

 agar immediately adjacent to the stems cannot exceed the concen- 

 tration in the stems at that point. For technical reasons it has not 

 proved possible to concentrate the radioactivity from sufficiently large 

 volumes of agar to get significant counts, or to identify the com- 

 pounds involved. Experiments which are designed to establish a com- 

 plete balance sheet for the radioactivity applied to the stems are now 

 in progress. 



In agreement with the results of Jaworski et al. (18) , and of Butts 

 and Fang (9) , who used whole plants, we found that the stem sections 

 converted 2,4-D to at least three compounds resolvable by paper chro- 

 matography. One of these, having an Rf of 0.5 in the solvent of Ja- 

 worski et al. (18), was formed in the largest amount, and, after 3 

 days' incubation, comprised up to 60 per cent of the total radio- 

 activity in the extracts. Figure 5 shows the distribution of radioactivity 



.45 .50 .60 .70 .80 



Rj UNITS 



Fig. 5. The resolution of the radioactive products formed from l-C"-2,4-D in 

 beans by paper chromatography. 



