Possible reasons for development of iron deficiency were investigated in the plants of Mimulus guttatus Fischer ex DC exposed to separate or joint action of NiSO4 (20 and 80 μM) and ZnSO4 (50, 100, and 200 μM). Six-week-old plants were grown during the next 28 days under controlled-climate conditions in water culture on a modified Rorison’s medium supplemented with or without NiSO4 and/or ZnSO4. It was found that the plants of M. guttatus are very tolerant to joint action of nickel and zinc sulfates. We revealed an antagonism between Ni2+ and Zn2+ in the course of uptake by the roots: Zn2+ impeded Ni2+ uptake by the roots even if concentration of Zn2+ in the medium was 1.6 times lower than the concentration of Ni2+, whereas Ni2+ inhibited uptake of Zn2+ by the roots if concentration of Ni2+ in the medium was 1.6 times higher than the level of Zn2+. The nickel did not affect zinc translocation to the aboveground organs, whereas zinc boosted translocation of nickel from the roots to the leaves. We showed a strong reverse correlation between the content of iron and total content of zinc and nickel in the leaves and a reverse correlation between translocation of iron and nickel. Assay of iron and determination of Fe(III)-chelate reductase activity in the roots showed that development of iron deficit in plants exposed to NiSO4 and ZnSO4 was not associated with inhibition by Ni2+ and Zn2+ of Fe2+ uptake by the roots. It was found that the plants responded to exposure to 50–200 μM ZnSO4 with a manifold rise in the content of free nicotianamine (NA) in the root system, whereas when culture medium was supplemented with 20 or 80 μM NiSO4 in addition to ZnSO4, the level of free NA in the roots became at least three times lower relative to the content of free NA in the roots exposed to ZnSO4 alone. Finally, we revealed a direct correlation between the content of free NA and accumulation of nickel in plant leaves. The data suggest that development of iron deficit in the plants of M. guttatus exposed to joint influence of nickel and zinc sulfates depends on the competition between Ni2+ and Fe2+/Fe3+ for a chelating agent (probably, NA).
Russian Journal of Plant Physiology – Springer Journals
Published: Oct 18, 2015
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