Physical-Clieniical Aspects of Synthetic Auxins 



295 



Table 4. The relationship of biological activity to absorption spectra and water 

 solubility of phenoxyacetic acids. 



the effects of tfie chemical. The exposure period would have to be of 

 sufficiently long duration to assure that adsorption was not a limiting 

 factor; however, this was demonstrated by Blackman (7) and Osborne 

 (25) to be a relatively short period. Such an experiment was per- 

 formed with corn seedlings, exposing them to a concentration of 6.7 

 X lO-'^M of chemical per seedling for varying lengths of time up to 48 

 hrs. Removal of the seedling from an exposure up to 24 hrs. resulted 

 in a complete recovery, indicating that up to this period of time the 

 action of the chemical was reversible. Measurement of the response 

 was made 48 hrs. after the beginning of the exposure. 



A more definitive experiment of this type would be an exposure 

 of subcellular particles from the plant to a chemical such as 2,4-D, 

 removal from exposiue, washing of the particles, and a measurement 

 of enzymatic activity. Mitochondria would seem to be the fraction of 

 choice since isolation of these particulate fractions from plants and 

 measurement of their activity is now a well-established practice. Mi- 

 tochondria were isolated from cabbage in the usual manner, one ali- 

 quot of the preparation being held as a control; another incubated 

 with 2,4-D, followed by washing with the suspending media to remove 

 excess 2,4-D; a third aliquot was washed with the suspending medium 

 to serve as the washed control. Previous experience had demonstrated 

 that a 10 min. exposure to 2,4-D resulted in equally good inhibition 

 as longer exposures. In order to assme complete saturation of the 

 mitochondria with 2,4-D, they were incubated for 30 min. before re- 

 moving by centrifugation and washing. Samples of the control, the 

 washed control, and the 2,4-D treated mitochondria were tested for 

 enzymatic activity in a Warburg apparatus. To aliquots of the latter 



