Movement of Calcium 



393 



In the course of other studies we recently obtained results which 

 also might have some bearing on the mode of action of growth regu- 

 lators on the translocation of metals in plants. It was found that cal- 

 cium accumulates in tissues which are carrying on net ribonucleic 

 acid (RNA) synthesis (9). It is possible that calcium is bound to ribo- 

 nucleoproteins, which have been suggested to act as ion carriers (10, 

 13, 17), in an immobile form. In such a way the movement of calcium 

 would be limited. Hence, it would accumulate in tissues where an 

 intensive RNA synthesis takes place. A similar situation was found 

 in our results, and in that case, one would expect that any action 

 of ribonuclease (RNase) on RNA should considerably affect the trans- 

 location of calcium. This point is now under experimental test. To 

 date, we have indications that TIBA influences the activity of RNase 

 (11) in vitro, a result which gives some support to our hypothesis as- 

 suming some connection between RNA and the movement of calcium. 

 Typical results of the effect of TIBA on RNase activity are presented 

 in Figure 5. It can be seen that TIBA has a marked effect upon 

 RNase activity but that this effect is somehow dependent on the level 

 of RNase in the reaction mixture. At the low RNase level (1 /xg/ml) 

 there is an increasing inhibition of RNase activity with increasing 

 TIBA concentrations, up to about 50 /xg/ml. At higher TIBA con- 



100 



20 40 60 



TIBA, ^G./ML REACTION MIXTURE 



80 



100 



lig. 5. The effect of TIBA upon the activity of RNase in vitro. 



