70 



RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



tration of 2 X 10~^ M . In contrast to other work mentioned, no changes 

 were found in the absorption of phosphate from solution. 



Bould, Nicholas, and Thomas (33) and Blume (34) have reported fur- 

 ther observations of the effects of P^- on plants grown in soil. It was the 

 consensus that the intake of phosphorus and the radiation effects are not 

 large enough to preclude radiotracer fertilizer studies, provided that 

 reasonable concentrations of P^- are used. Blume found no significant 

 changes in plants grown in soils receiving surface applications of KH2PO4 

 containing up to 12,500 nc P^- per gram of total phosphorus. 



Table 2-2. Shoot-tip Cell Lengths as Related to Specific Activity 



" Arbitrary units plus or minus standard error. 



[From Ruth W. Mackie, James M. Blume, and C. E. Hagen, Histological Changes 

 Induced in Barley Plants by Radiation from P^^, Am. J. Botany, 39: 229-237 (1952).] 



Goring and Clark (35) have reported that the levels of P'*' necessary to 

 effect changes in the soil bacterial population are above those normally 

 used in fertilizer studies. If high levels of P'^'- are to be used, then the 

 specific activity should not exceed 50 /jlc P^' per milligram of total phos- 

 phorus. Clark and Goring (36) grew bacteria in a broth containing 

 0.2 ppm inorganic P and 0.6 ppm organic P, which was enriched with 

 4 ppm P as KH2PO4 at levels of to 5000 fic P^'- per milligram of total 

 phosphorus. Deleterious effects were observed at levels higher than 

 100 fiC. It was pointed out that, although individual cells were affected 

 by the P^-, the surviving cells continued to multiply, so that there 

 were no differences in such measurements as turbidity and substrate 

 transformation. 



