Auxins and the Process of Aging in Root Cells 179 



4 8 12 16 Standard 



HOURS 



Fig. 1. Chromatogram of the Ehrlich-positive substances extracted by ethanol 

 from pea root tips following incubation in auxin for different periods of time. 

 Five mm. root tips from 2-day-old seedlings incubated in solution containing lAA, 

 1 X 10"* ^t] sucrose, 0.5 per cent; Ca(N03)2, 1 x 10"^M; potassium phosphate, 5 x 

 10-^ M; streptomycin, 30 p.p.m.; penicillin, 15 p.p.m.; pH 5.2. 



was chromatographed in wo-propanol-ammonia-water (80:10:15). 

 Three phases can be differentiated. During the initial phase, lasting 

 about two hours, free lAA rapidly accumulates in the tissues. Quan- 

 titively, it has been found that the initial concentration of lAA 

 reaches ten times that of the external solution and that during this 

 time all the lAA lost from solution can be accounted for as accumu- 

 lated lAA. During the second phase, lasting from about the second 

 to the twelfth hour, the lAA content declines and conjugation com- 

 mences. In the third phase, free lAA is no longer detectable in the 

 tissues, while the indoleacetylaspartic acid content continues to in- 

 crease. The formation of indoleacetylaspartic acid appears to be a 

 detoxication process and not a physiological activation of the lAA 

 molecule. 



