61 Erkama: Copper, Manganese and Iron 



one on the ahsoT'ption of another and second, the interrelation of 

 two or more metals within the cell. As for the latter it would be 

 useful to interpret the observed effects, wherever applicable in 

 terms of enzyme systems known to be functioning in the plant 

 cell. For example, can the "antagonistic" effects of Mn and Fe be 

 possibly due to the displacement of Fe by Mn when in high con- 

 centration in the porphyrins involved in the cytochrome or cata- 

 lase system^ 



Prof. Burstrom:— 



You have found an inverse relationship to exist between the 

 contents of Mn, Fe and Cu. As far as I am aware it was shown 

 more than ten years ago that such an inverse relationship generally 

 exists between all cations, alkali— earth, alkali and heavy metals, 

 according to their simple physical properties. Thus I do not quite 

 believe that you are entitled, from only the concentrations of the 

 heavy metals, to conclude as to the redox-conditions. 



Prof. Burstrom's answer to Prof. Arnon concerning heavy 

 metals: I think that Dr. Arnon is right; the heavy metals, espe- 

 cially Fe and Mn, are so similar in all respects that they must 

 compete in every reaction and on every point, where they meet 

 in the cell. 



Dr. Erkama:— 



My conclusions of the oxidation-reduction conditions in plant 

 are hypothetical. On the basis of the analytical data we can, 

 however, notice regular relations between some elements, which 

 very probably determine these conditions. 



Dr. Hewitt:— 



It is necessary to be cautious in interpreting the effects of cop- 

 per or manganese or of other metals on oxidation reduction reac- 

 tions in which the equilibrium between ferrous and ferric iron 

 compounds is involved. The need for such caution is evident 

 when the oxidation-reduction potentials (Eq values) of the follow- 

 ing reactions are considered: — 



Cu+ = Cu++ -I- e- Eo = -0.17V. 



Mn++ = Mn+++ + 6" Eo = -1.51V. 



Co++ = Co+++ -f e- Eo = -1.84V. 



Fe++ = Fe-*-^ -f e" Eo = -0.77V. 



