Inhibition of Gibherellin Action by Auxin 



661 



15 - 



50 HOURS 



BUFFER 



lAA 



0.01 

 GA. PRM. 



0.1 



Fis. 4. Interaction of hormones demonstrated in the Avena leaf section test. Aver- 

 ages of 7 tests comprising 150 sections for each value plotted. Vertical lines: 

 magnitude of error. Duration: 50 hrs. Gibberellic acid (GA, 0.01 and 0.1 p.p.m.) 

 promoted leaf growth. The addition of kinetin (K, 0.1 p.p.m.) and of indoleacetic 

 acid (lAA, 0.1 p.p.m.) suppressed the GA-induced growth. Addition of a mixture 

 of lAA and K (both at 0.1 p.p.m.) suppressed the GA effect even more, so that 

 growth in a solution with all three regulators was nearly identical to that of the 

 buffer in sugar solution without regulators. 



hibition of gibberellin by auxin has been found in a large number of 

 tests, although the magnitude of the inhibition was variable. If this 

 phenomenon of gibberellin action inhibited by auxin is a general one, 

 it has some interesting consequences (2). 



Bud Inhibition 



The promoting agent here is gibberellin and the inhibiting agent, 

 auxin. This was proven by the work of Kato (1). 



Fruit Drop 



If one assumes that certain stages of fruit growth are gibberellin 

 dependent, it follows that auxins will inhibit this. This interrelation 

 was demonstrated on cotton by Walhood (4). It also explains why 

 auxin enhances the June drop of apples. 



Root Growth 



In the past it had been assumed that elongation of roots is auxin 

 dependent (2). Suppose it were gibberellin dependent — and there is 



