Biphasic effects of lanthanum on Vicia faba L. seedlings under cadmium stress, implicating finite antioxidation and potential ecological risk

In the present study, lanthanum (La) as a representative REE was used to explore the mechanisms for alleviation of Cd-induced oxidative damage by extraneous La at appropriate concentrations, and to assess ecological risk of combination of Cd and La at higher concentrations in roots of Vicia faba L. seedlings. The seedlings were hydroponically cultured for 15 d under nutrient solution, 6 μmol L−1 CdCl2, and combination of 6 μmol L−1 CdCl2 and increasing concentrations of La, respectively. The results showed that the supplementation with low concentrations of exogenous La (<120 μmol L−1) led to reduced contents of Cd, Ca, Cu, Zn, Mn or Fe element and increased activities of superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX) and ascorbate peroxidase (APX) isozymes as well as heat shock protein 70 (HSP 70) production in the roots. However, the supplementation with higher La (>120 μmol L−1) showed the adverse effects. The contents of Cd elevated above the single Cd treatment in the roots, accompanying with the decline of antioxidant isozyme’s activities and HSP 70, and increment of carbonylated proteins and endoprotease isozyme’s activities. The results also showed that the root growth was not only related to carbonylated proteins, but also to indole acetic acid oxidase activities. Therefore, the supplemented extraneous La contributed to biphasic effects: stimulated antioxidation at lower concentrations and pro-oxidation at higher concentrations against Cd-induced oxidative stress in the roots.

► Cd brings human health risk. How to diminish Cd and reduce its toxicity in crops is very important.
► Low doses of La diminished contents of Cd and other mineral elements in roots.
► Low doses of La led to enhancement of antioxidant isozymes and HSP 70.
► Higher doses of La contributed to prooxidative effects due to Cd stress.
► Seedling growth was influenced not only by damaged protein, but also indole acetic acid oxidase isozymes.