Rothamsted Symposium on Trace Elements 56 



one plant became available for our analysis. Table 13 illustrates 

 some of its characteristics. 



In addition to a low iron content, Table 13 reports on the ex- 

 ceedingly high content of manganese which shows us an antago- 

 nism between copper and manganese. 



Table 14 gives the effect of additional manganese nutrition on 

 the heavy metal content of peas grown in a nutrient solution 

 deficient in manganese. Manganese was added 35 days after sow- 

 ing, and the plants were analyzed when 60 days old. 



Addition of manganese caused a pronounced decrease of iron 

 content in the green parts of our plants, especially in the chlorotic 

 upper leaves. The decrease of iron content in leaves is probably 

 not affected by the increase in the dry matter after the addition 

 of manganese, because the iron content of leaves, after manga- 



Tablb 13 : Copper-deficient peas from copper-deficient seed: — 



nese addition, was lower than in normal plants. The increase of 

 iron in roots apparently results from precipitation, caused by the 

 oxidizing action of manganese. 



Discussion:— Most factors which have an effect on the uptake 

 and availability of iron regulate its degree of oxidation. Both 

 ferrous and ferric iron are present in the soil, as well as in the 

 plant. The relation between these two forms depends on the 

 metabolism of the plant, and particularly on oxidation-reduction 

 conditions. Thus, the problem of the influence of copper and 

 manganese on the iron status of plants should also be discussed in 

 connection with oxidation-reduction phenomena. 



As early as 1920, Maquenne and Demoussy (16) gave at- 

 tention to the oxidizing effect of copper salts on ferrous ions in 

 nutrient solutions and to their preventive action on iron uptake. 

 Later, many other investigators, e.g. Densch and Hunnius (5), 

 Chapman et aL (3), and Willis (24), reported similar observa- 

 tions. 



