Lecture 2 — 43 — Micronutrient Elements 



reduction systems must be less direct. In general, 

 one could conceive that the various metals do not act 

 entirely independently. If they have a role in protein 

 enzyme systems, the metals might compete for re- 

 active groups in the protein molecule, although enzyme 

 activity would be dependent on specific metals. I have 

 already referred to the effect of zinc deficiency on the 

 oxidase and catalase activities of the leaves of tomato 

 plants. It may also be recalled that after increasing 

 the concentration of zinc in a culture solution beyond 

 a certain point, a leaf injury or chlorosis may follow, 

 that suggests an iron deficiency. Another case in 

 point is that of interrelations between iron and man- 

 ganese. 



Minute Amounts of Chemical Elements in Relation 

 to Animal Nutrition : — Before closing I wish to draw 

 your attention to an aspect of the investigation of 

 micronutrients that concerns students of both plant 

 and animal nutrition. The animal depends in part for 

 its supply of inorganic elements effective in minute 

 amount on the plant. What the plant absorbs from 

 its medium is therefore of consequence to the nutrition 

 of the animal consuming the plant. Some micro- 

 nutrient elements needed by plants are also needed by 

 animals. This seems to be true of copper, zinc and 

 manganese. About boron we are uncertain, as I have 

 said. 



A large amount of evidence supports the con- 

 clusion that animals in certain areas can suffer from 

 deficiency diseases because the vegetation consumed 

 does not supply enough of one or more of the elements 

 that function in minute quantities. The requirements 

 of the plant and of the animal are not necessarily 

 coincidental quantitatively, and perhaps not always 

 qualitatively. The element cobalt furnishes an illus- 

 tration of the latter statement. A number of years 

 ago the discovery was made that in some districts in 

 New Zealand and Australia, sheep suffered from a 



