Long-distance transport of cadmium from roots to leaves of Solanum melongena

In this study, the characteristics of cadmium (Cd) uptake by roots and translocation from roots to leaves of two eggplant species (Solanum melongena and Solanum torvum) under relatively low Cd concentrations were investigated using stable ¹⁰⁸Cd isotope through a number of hydroponic experiments. The uptake and translocation of ¹⁰⁸Cd was compared with those of ⁷⁰Zn and ¹⁵N. The results showed more ¹⁰⁸Cd was loaded to the vascular channels and translocated upward to the leaves in S. melongena than in S. torvum, while the ¹⁰⁸Cd concentrations were significantly lower in the roots of S. melongena than in S. torvum. When the phloem and xylem were wounded by grafting treatments, the foliar ¹⁰⁸Cd concentrations were decreased by more than 66 % regardless of the rootstock species, whereas the uptake of ¹⁰⁸Cd in the root was not inhibited by grafting. Similar grafting effects were observed for ⁷⁰Zn. Hence, wounding phloem and xylem by grafting disturbed the upward transport of ¹⁰⁸Cd and ⁷⁰Zn to the eggplant leaves. Similarly, interruption of the phloem by the girdling treatment reduced the concentrations of ¹⁰⁸Cd in the leaves of S. melongena by approximately 51 %, though the uptake of ¹⁰⁸Cd by roots was not reduced by the interruption of phloem. In contrast, neither ⁷⁰Zn concentrations nor stable N isotope ratio (δ¹⁵N) values in the roots and leaves of S. melongena were significantly influenced by the interruption of phloem. In conclusion, the phloem played a dominant role in the long-distance transport of Cd from the root to the leaf of S. melongena, whereas the xylem was the main channel for the translocation of Zn and N.