Metallic Ions, Auxin Action, and Chelating Agents 375 



and conclude that the action is due to inhibition of lAA destruction. 

 However, they also showed that the translocation of botJi lAA and 

 NAA was promoted, and conclude that Fe^^ has two different effects — 

 to inhibit destruction and to promote transport. The parallelism with 

 the action of EDTA is suggestive. The several parallels with the 

 action of cobalt are also notable, for cobalt, like EDTA, shows little 

 or no effect in the absence of auxin, but causes up to 50 per cent 

 increment in presence of optimal auxin; both cobalt and EDTA are 

 somewhat more effective on coleoptiles than on pea stems, and both 

 are considerably more effective in presence of sucrose than in its 

 absence (21). Cobalt differs from EDTA in that it promotes growth 

 in solution equally well with NAA and lAA, but again there is a 

 suggestion of similarity, since when acetate is present cobalt becomes 

 strongly inhibitory but this occurs only with NAA and not with lAA. 



It is worth noting that it is not impossible for a metal ion and 

 a chelating agent to act in the same way, for, if a particular catalyst 

 owes its activity to a metal complex, then an exogenous metallic ion 

 could compete at its site of action, while the chelating agent, by form- 

 ing a chelate in situ, could prevent the metal and its site of action 

 from coming together. 



Such an action need not be in the wall and indeed the possibility 

 should be considered that it occurs in the mitochondria. It is known 

 that the activity of these bodies is strongly influenced by their Ca+2 

 (11) and since the energy for growth of coleoptiles, pea stems, and 

 freshly-cut potato sections is supplied via cytochrome oxidase, which 

 is in the mitochondria, a close relation between metal ions and 

 growth could be suspected here. Further, EDTA, as well as manganese, 

 is known to prevent the swelling of mitochondria which occurs in 

 isotonic solutions (20).2 



It seems a safe prediction that the mode of action of auxin will 

 not be fully understood until the role of the several metal-dependent 

 reactions has been elucidated. 



ACKNOWLEDGMENTS 



This work was supported by a grant from the National Science 

 Foundation. The experiments on potato disks were carried out by 

 Dr. Kenneth Wright while on a leave of absence from Smith College, 

 Northampton, Mass. For skillful technical assistance in the later work 

 the writer is indebted to Mrs. C. ^Vinkler Kurland. 



''The subsequent finding of Whitehouse, Staple, and Kritchevsky (Arch. 

 Biochem. Biophys. 87: 193. 1960) that cobalt activates the oxidation of cholesterol, 

 pyruvate, and octanoate by rat liver mitochondria supports this line of reasoning. 



