394 Kessler, Moscicki, and Bak 



centrations, the activity of RNase was stimulated. Similar trends, 

 but at different ranges of TIBA, were found at the higher RNase level 

 (2 /i,g/ml). In this case, low TIBA concentrations had no effect. Above 

 30 /Ag/ml TIBA became inhibitory while at 80 /^g/ml it became 

 promotive. It is seen that TIBA has a dual effect on the activity of 

 RNase, but that the effective TIBA concentrations change with the 

 level of the enzyme. 



If we now assume that TIBA has a similar effect in vivo on RNase 

 activity as found in our in vitro experiments, we might consider the 

 following possibility. TIBA, when applied to a plant at the concen- 

 trations employed, will stimidate RNase activity, causing a temporary 

 increase in the destruction of RNA W'hich may free RNA-bound 

 calcium. 



An hypothesis has been put forw'ard that growth regulators pos- 

 sibly function directly through their chelating action on metals, thus 

 acting as carriers, removing functional metal ions, etc. (6). From our 

 results, it seems that even if there are functional relations between 

 growth regulators and metals, the growth regulators might not act 

 simply as chelating agents but through more complex relations, such 

 as those which possibly exist between TIBA, RNase, RNA. and cal- 

 cium translocation. 



LITERATURE CITED 



1. Biddulph, O. The distribution of P, S, Ca and Fe in bean plants as re- 

 vealed by use of radioactive isotopes. 8th Cong. Int. Bot. C.olloq. .\nalyse 

 Plantes et Probl^mes Engrais Mitieraux. 7-17. 1954. 



2. Bledsoe, R. W., Comar, C. L., and Harris, H. C. Absorption of radioactive 

 calcium by the peanut fruit. Science. 109: 329,330. 1949. 



3. Bukovac, M. J., Tukey, H. B., and Wittwer, S. H. Transport of P^- and Ca''' 

 in plants as influenced by giaft unions and scion stock relationship. [ cf . Gauch 



4 , Wittwer, S. H., and Tukey, H. B. Anesthetization by diethyl ether 



and the transport of foliar applied radiocalcium. Plant Physiol. 31: 254,255. 

 1956. 



5. Chasson, R., and Levitt, J. Stimulation of calcium uptake by potato tuijcr in 

 response to 2,4-dinitrophcnol. Plant Physiol. 31 (suppl.): vi. 1956. 



6. Cohen, D., Ginzburg, B.-Z., and Heitner-Wirguin, C. Metal-chelating properties 

 of plant-growth substances. Nature. 181: 686,687. 1958. 



7. Ferrell, W. K., and Johnson, F. D. Mobility of calcium-45 after injection into 

 western white pines. Science. 124: 361, 365. 1956. 



S. Gauch, H. G. Mineral nutrition of plants. .\nn. Rev. Plain Phvsiol. 8: 

 31-64. 1957. 



9. Kessler, B. Effect of mcthyltryptophan and thiouracil upon protein and 

 ril)onucleic acid synthesis in certain iiigher plants. Nature. 178: 1337, 1338. 



1956. 



10. 



. Further evidence on the effect of bicarbonate ions upon nucleic acid 



metabolism and ion uptake in fruit trees susceptible and nonsusccptiblc to lime- 

 induced chlorosis. Ktavim. 8: 287-293. 1958. 



