Abstract
Cadmium (Cd) isotopes provide new insights into Cd uptake, transport and storage mechanisms in plants. Therefore, the present study adopted the Cd-tolerant Ricinus communis and Cd-hyperaccumulator Solanum nigrum, which were cultured under controlled conditions in a nutrient solution with variable Cd supply, to test the isotopic fractionation of Cd during plant uptake. The Cd isotope compositions of nutrient solutions and organs of the plants were measured by multiple collector inductively coupled plasma mass spectrometry (MC-ICPMS). The mass balance of Cd isotope yields isotope fractionations between plant and Cd source (δ114/110Cdorgans-solution) of −0.70‰ to −0.22‰ in Ricinus communis and −0.51‰ to −0.33‰ in Solanum nigrum. Moreover, Cd isotope fractionation during Cd transport from stem to leaf differs between the Cd-tolerant and -hyperaccumulator species. Based on these results, the processes (diffusion, adsorption, uptake or complexation), which may induce Cd isotope fractionation in plants, have been discussed. Overall, the present study indicates potential applications of Cd isotopes for investigating plant physiology.
Highlights
Cadmium (Cd) is a highly toxic heavy metal that can be accumulated in the human body through the food chain[1,2]
Some studies reported that anthropogenic processes might lead to Cd isotopic fractionations, suggesting that Cd stable isotopes could be used as tracers for anthropogenic Cd pollution of the environment[27,28,29,30]
Cd concentrations in different organs of R. communis exhibit a significant gradient with a progressive increase from upper to lower organs, by the order of leaf < stem < root, independently of the Cd concentration in the nutrient solution
Summary
Cadmium (Cd) is a highly toxic heavy metal that can be accumulated in the human body through the food chain[1,2]. Some studies have comprehensively investigated the distribution of metal isotopes in plants, including isotopes of Fe9,10, Zn11–13, Cu14,15, Ca16–20, Mg21,22, and Ni23. Overall, these studies suggested that the identification of different isotopes within higher plants had specific mode of transport. Metal isotopes could be used as valuable tracers when researching metal uptake, storage and translocation processes within plants. Some studies reported that anthropogenic processes might lead to Cd isotopic fractionations, suggesting that Cd stable isotopes could be used as tracers for anthropogenic Cd pollution of the environment[27,28,29,30]. We conducted hydroponic culture experiments with these plant species and two nutrient solutions with differing Cd concentrations to 1) characterise the Cd isotope fractionation associated with Cd transfer in the Cd-tolerant and -hyperaccumulator species; and 2) explore possible mechanisms of Cd mobilisation from the solution to various physiological compartments
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