Table 1.
Demands and toxicity of Zn, Cd, and Fe for plants and impacts of their dietary deficiency or excess on humans.
| Metal | Demands/Toxicity for Plants | Deficiency Diseases/Excess Toxicity for Humans |
|---|---|---|
| Zn | Demand: Cofactor of over 300 enzymes including DNA- and RNA-polymerases; Excess toxicity: Unregulated binding of Zn to S-, N- and O-containing molecules | Deficiency: Stunting, diarrhea, pneumonia; Excess toxicity: Interference of Fe and Cu uptake in the intestines |
| Cd | Toxicity: Binding to protein SH-residues, exchanges with divalent cations such as Zn2+ and Ca2+, and excessive production of reactive oxygen species | Excess toxicity: Itai-itai disease (spinal and leg bone pain) caused by Cd accumulation in the liver and kidneys resulting in tubular renal dysfunction, osteoporosis, cancer, and cardiovascular diseases |
| Fe | Demand: Proteins involved in redox and electron transport. Leaf pigment formation; Toxicity: Free Fe can generate toxic levels of oxygen and hydroxyl free radicals through the Fenton reaction | Deficiency: Anemia, impaired mental development; Iron overload: Excessive accumulation of Fe in the liver, heart, and pancreas. Hemosiderosis; Hemochromatosis |