Characteristics of cadmium translocation and isotope fractionation in Ricinus communis seedlings: Effects from split/cut-root and limited nutrients

Abstract

Studying cadmium (Cd) transport in plants will improve the current understanding of Cd tolerance mechanisms. Due to the influence of analytical techniques, the application of Cd isotopes in plants is still in its early stages. Therefore, the relationships between Cd isotope fractionation and Cd translocation in plants remain unclear. In this study, we cultured Ricinus communis in hydroponic solutions during split/cut-root experiments and limited and infinite nutrient experiments. To understand the Cd transport process, the Cd2+ and other ion concentrations in different tissues (i.e., roots, stems, and leaves) and nutrient solutions, Cd isotope composition and the soluble protein in tissues were measured. The results showed that although significant effects were evident in the top leaves, the principal roots had less pronounced effects on Cd2+ translocation in the stems. Moreover, Cd underwent homolateral transport before it was translocated from the principal roots to the leaves on the side without Cd. It was apparent that the stems were responsible for translocating Cd2+ in plants. In addition, the continuous supply of high Cd2+ concentrations inhibited the growth of the top leaves, while in low Cd2+ concentrations, it was gradually transferred to the top leaves. Moreover, the tissues of R. communis were enriched with lighter Cd isotopes compared with the solutions. The clear differences between the Cd isotope fractionation of leaves under infinite and limited nutrient experiments may be attributed to plant growth and Cd uptake rates. This study provides important information for understanding Cd2+ translocation in R. communis and furthers our understanding of its tolerance and hyperaccumulation.