83 Burstrom: Manganese and Roots 



in roots catalyzed by manganese which you have earher reported 

 together with Prof. Lundegardh, are acting in the same way in 

 the roots of the green, assimilating plants? 



2) What is your opinion of the relations between the respira- 

 tion catalyzed by manganese and the respiration catalyzed by iron 

 in the green, assimilating plants? 



Prof. Burstrom:— 



1) We do not know in what respects the metabolism of excised 

 roots diflfers from that of attached roots. It must be dissimilar in 

 part, since attached roots obtain their carbohydrates from within, 

 whereas excised roots obtain theirs from the external solution. At- 

 tached roots have the power of performing the same reactions as 

 excised, but we cannot evaluate their quantitative importance in 

 complete plants. The same holds true for all reactions studied in 

 isolated enzyme systems, a fact which is usually overlooked. 



2) I have never studied the respiration in excised roots. How- 

 ever, if nitrate is reduced, something must be oxidized, i.e. carbo- 

 hydrates, and it implies respiration. In physiological experiments 

 we cannot separate the reduction from the oxidation; they are two 

 sides of one redox-system. Neither can we decide whether a 

 heavy metal acts on the oxidation or the reduction side of the 

 system. 



Prof. Amon:— 



In comparing the effects of NO3 and NH4 on the plant cells 

 it would be helpful to regard the NO3 not only as a source of N 

 but also as a source of oxygen when the NO3 is reduced in the 

 plant. This oxidizing function of nitrate may be important since 

 the NO3 can be transported within the plant and reach regions 

 where the oxidation-reduction reaction involving NO3 can be 

 particularly significant. 



Prof. Burstrom:— 



It cannot be denied that a certain amount of oxygen is brought 

 into the cells with the nitrate, but the amount of reduced nitrate 

 is small as compared with the normal respiration. Nitrate is re- 

 duced in the roots where lack of oxygen may occur, and in the 

 leaves where oxygen deficiency is scarcely probable. Roots need 

 oxygen even in the presence of nitrate. It is not known that 



