Influence of Gibberellic Acid on lAA Disappearance 641 



AVilh stem sections taken from just below the first node of dark- 

 grown plants, rate of lAA destruction in darkness and in light was 

 decreased by GA. The sparing actions obtained varied in size as 

 for apical tissues. The lAA sparing action is discussed in terms of 

 current theories on the mechanism of action of GA-induced growth. 

 The data are consistent with the hypothesis that GA leads to the 

 production of an inhibitor which retards an auxin-destroying sys- 

 tem. Evidence from the literature that this inhibitor could be an 

 inhibitor of the lAA-oxidase enzyme system is considered. The pos- 

 sibility that the effect of red and near infrared (far-red) radiations on 

 growth could be brought about through an inhibitor/gibberellin- 

 mediated system is pointed out. 



ACKNOWLEDGMENTS 



The authors wish to thank the Directors of Unilever Ltd. for 

 permission to publish this work, and to thank Mr. N. E. Wynn for 

 assistance with the experiments and preparation of the manuscript. 



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