The Effects of Iron Deficiency on Lead Accumulation in Ailanthus altissima (Mill.) Swingle Seedlings

Abstract

Understanding the effects of root Fe deficiency on the uptake and translocation of toxic metals can be important for improving the phytoremediation strategies of polluted soils. The present study investigated how Fe nutritional status affects the uptake and root-to-shoot-translocation of Pb in hydroponically grown seedlings of Ailanthus altissima (Mill.) Swingle. The interactions of Fe deficiency and Pb were assessed by measuring the root Fe(III) reductase activity, carboxylic acids concentration in root exudates, root and shoot biomass, and accumulation of Pb and other metals (Fe, Zn, Mn, and Cu) in roots and leaves of Fe-sufficient (+Fe) and Fe-deficient (-Fe) A. altissima plants. The results indicate that Fe deficiency induced 18-fold higher Fe(III) reductase activity in roots compared with +Fe plants, which was followed by increased root exudation of citric acid (28.2 +/- 1.39 in +Fe and 498 +/- 256.4 mu mol g DW-1 2 h(-1) in -Fe plants). Iron deficiency also induces a significant decrease of root and shoot dry weight compared with the control +Fe plants, whereas 2-wk Pb (20 mu M) treatment did not influence root and shoot growth. Iron-sufficient plants accumulated more Pb (56.8 +/- 17.29 mu g g(-1)) in leaves than -Fe plants (21.5 +/- 8.10 mu g g(-1)). Two weeks of exposure to Pb significantly decreased Fe(III) reductase activity and accumulation of Fe, Zn, and Mn in the roots of -Fe plants. It is hypothesized that 2 wk of root exposure to Pb blocks functioning of a specific Fe transport system activated under Fe deficiency.