Relative effectiveness of certain heavy metals in producing toxicity and symptoms of iron deficiency in barley

Abstract

Excess supply of the heavy metals Mn, Cu, Zn, Co, and Ni to barley caused their accumulation in shoots and specially in roots and induced symptoms characteristic of the particular heavy metal involved, the syndrome of which varied with the different treatments. The effectiveness of the heavy metals in inducing visual symptoms was in the order of Ni²⁺ > Co²⁺ > Cu²⁺ > Mn²⁺ > Zn²⁺. These treatments caused a decrease in dry matter yield of plants in the order Ni²⁺ > Co²⁺ > Zn²⁺ > Mn²⁺ > Cu²⁺.Studies using ⁵⁹Fe indicated that an excess supply of each of the heavy metals reduced iron absorption by plants and affected its distribution in roots and shoots. Excess of Co²⁺, Cu²⁺, Mn²⁺, and Zn²⁺ reduced iron translocation to shoots, induced chlorosis, and decreased catalase activity of young leaves. Excess nickel, which was most active in producing toxic effects, did not inhibit translocation of iron to young leaves. Unlike iron deficiency, an excess of Ni²⁺ did not decrease the activity of catalase and stimulated the activity of peroxidase. Excess supply of each of the heavy metals increased the concentration of non-reducing sugars. Observations suggest that toxicity to heavy metals does not necessarily involve induction of iron deficiency, their redox potentials, or the stability of their organometal complexes.