KENNETH V. THIMANN 



and 

 NORIKO TAKAHASHI' 



Harvard University 



Inter relationships Between Metallic Ions and 

 Auxin Action, and the Growth Promoting 



Action of Chelating Agents 



The part played by metallic ions in growth processes has gradually 

 become more prominent in recent years. It is now clear that the 

 ions of calcium, potassium, manganese, iron, and cobalt greatly modify 

 the growth of plant sections. In addition it has been reported by 

 Heath and Clark (10) that ethylenediaminetetraacetic acid (EDTA), 

 8-hydroxyquinoline, and other chelating agents have a small but 

 definite growth promoting effect on wheat (Triticum) coleoptile 

 sections and a growth inhibiting effect on wheat roots. The parallel- 

 ism between the action of indole-3-acetic acid (lAA) and EDTA 

 suggested to them that the two substances might act in a similar way, 

 though it was stressed that their actions could not be identical. Since 

 subsequent workers could find no real effect of EDTA on roots, all 

 of what follows is restricted to shoot tissue. 



As an explanation of the effect of chelating agents on growth, it 

 was proposed (10) that growth is normally restrained in some way 

 by a metal, and that growth promoting substances in general act by 

 chelating this metal. In the case of lAA, a comparison was drawn 

 between the nitrogen atom adjacent to the 6-membered ring and 

 that in the chelating agent 8-hydroxyquinoline. However, this ex- 

 planation is evidently most improbable, for several auxins, such as 

 1-naphthaleneacetic and 2,3,6-trichlorobenzoic acids, could have only 

 very weak chelating ability, yet their growth promoting action is 

 very strong and on some plant material stronger than that of lAA; 

 while on the other hand EDTA and 8-hydroxyquinoline are extremely 

 powerful chelators, yet their growth promoting activities are rela- 

 tively small. In Heath and Clark's 10 mm. wheat coleoptile sections 



^Subsequently: Japan Women's University, Bunkyo-Ku, Tokyo, Japan. 



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