IRON NUTRITION INFLUENCE ON CADMIUM ACCUMULATION BY ARABIDOPSIS-THALIANA (L) HEYNH

Greenhouse experiments were conducted to determine whether Arabidopsis thaliana (L.) Heynh., a putative Fe-efficient species, accumulated higher concentrations of Cd from a sparingly soluble Cd source (cadmium dihydrogen phosphate) when growing in Fe-deficient rather than in Fe-sufficient conditions. The Arabidopsis plants, which were grown in double-container, vermiculite-hydroponic plot culture systems and were provided with nutrient solution containing either sufficient (89.5 mu M) or deficient (0 mu M) Fe supplied as the diethylene triamine pentacetate chelate, were exposed to four levels of Cd (nominally 0, 0.45, 0.89 or 1.78 mmol kg(-1) vermiculite). At each substrate Cd level, rosette Cd concentrations were similar at both Fe levels, but racemes and seeds from the Fe-deficient treatment accumulated significantly higher concentrations of Cd than those from the Fe-sufficient treatment. For example, at the highest substrate Cd concentration, the Cd bioaccumulation factor (tissue Cd concentration predicted from polynomial response surface equations describing the relationship between tissue and substrate Cd concentrations divided by nominal substrate Cd concentration) for rosettes was 3.2 in both Fe treatments, but raceme Cd bioaccumulation factors were 1.7 and 0.9, and seed Cd bioaccumulation factors were 0.4 and 0.2 in the Fe-deficient and Fe-sufficient treatments, respectively. Rosette biomass was largely unaffected by tissue Cd level, but at tissue Cd concentrations of at least 1.26 mmol kg(-1) for recemes and 0.32 mmol kg(-1) for seeds, substantial biomass reductions occurred. Analysis of the uptake of other elements by Arabidopsis suggests that the greater accumulation of Cd by plants in the Fe-deficient treatment may be a consequence of the species' Fe efficiency mechanisms. Our results support the hypothesis that uptake of toxic elements by Fe-efficient species can be enhanced when the plants are growing in Fe-deficient soils.