Alleviation of cadmium-induced root growth inhibition in crop seedlings by nanoparticles

The short-term effects of six types of nanoparticles (NPs) (Kaolin, montmorillonite, hydroxyapatite, Fe(3)O(4), α-Fe(2)O(3) and γ-Fe(2)O(3)) on the EC50s (Cd) for root growth of four plant species (i.e. tomato, cucumber, carrot and lettuce) were investigated using standard toxicity testing. NPs and Cd influencing on growth of the plant were as well as tested, respectively. Scanning-electron microscopy (SEM) equipped with the element dispersive spectrometer (EDS) was used to observe the interaction of NPs prepared with EC50s (Cd) as the solvents with the root surface and identify the mechanisms of Cd toxicity reduction to the root growth induced by NPs additives. The results showed that the seedling growth was negatively related to the exposure concentration of Cd, among the tested plants, the sensitive endpoint appeared in the order of tomato>carrot≈lettuce>cucumber according to the ECx measured. The root growth was not significantly inhibited by the presence of NPs except for HAP on tomato, but was noticeably promoted by particular NPs suspensions prepared with EC50s (Cd) as the solvents at higher test concentrations compared with the controls (Cd, EC50s) with one exception for Kaolin. Microscopy images showed roots of tested plants exposed to Cd exhibited a decrease in root diameter and root wilt, and the disintegration of the root epidermis, the clutter root surface showed the evident stress under Cd solution, after the addition of NPs, many root hairs and no disintegration on the surfaces of the root system can be observed, NPs crystal also occurred on the plants root surface. The element dispersive spectrometer (EDS) analysis showed that the precipitation mainly contributed to phytotoxicity reduction by the NPs.