Toxicological effects involved in risk assessment of rare earth lanthanum on roots of Vicia faba L.seedlings

Combined chemical analyses and biological measurements were utilized to investigate potential toxicological effects and possible mechanisms involved in risk assessment of rare earth elements （REEs） on Viciafaba L. seedlings, which were hydroponically cultivated and exposed to various concentrations of lanthanum （La） for 15 days. The results showed that La contents in both the solution and roots increased with the increase of extraneous La, contributing to hormetic dose responses of superoxide dismutase （SOD）, catalase （CAT）, guaiacol peroxidase （GPX）, ascorbate peroxidase （APX） and endoprotease （EP） isozymes activities, and HSP 70 production enhanced at low doses but suppressed at higher doses of La. These physiological responses constituted antioxidant and detoxification systems against La-induced oxidative stress. The elevated La levels also contributed to oxidatively modified proteins, which were most responsible for subsequent cell death and growth retardation of the roots. By combination of hormetic and traditional threshold dose levels, the threshold dose range was deduced to be 108-195 μg La/g dry weight in the roots, corresponding to 0.90-3.12 mg/L of soluble La in the culture solution. It suggests that persistent applications of REEs may lead to potential ecological risk in the environment.

Nano-selenium controlled cadmium accumulation and improved photosynthesis in indica rice cultivated in lead and cadmium combined paddy soils

Selenium nanoparticles(Se NPs) are less toxic and more biocompatible than selenite or selenate. However, studies involving spraying with Se NPs for reducing accumulation of cadmium(Cd) and lead(Pb) in rice grains have been rarely reported as yet. Herein, indica rice seedlings cultivated in Cd + Pb-spiked paddy soils(denoted as positive control) were sprayed with Se NPs sols for four times from tillering to booting stage. Compared to positive control, 50–100 μmol/L Se NPs downregulated Cd transporters-related genes such as Os LCT 1, OsH MA 2 and Os CCX2 in leaves and OsLCT1, Os PCR1 and Os CCX2 genes in node I at filling stage. Meanwhile, Se-binding protein 1 was distinctly elevated, involving the repression of Cd and Pb transportation to rice grains. Se NPs also differentially improved RuBP carboxylase and chlorophylls especially some key genes and proteins involving photosynthetic system. Besides, 25–50 μmol/L Se NPs diminished reactive oxygen species overproduction from NADPH oxidases whereas boosted glutathione peroxidase, reducing protein carbonylation in rice seedlings. However, the antioxidant isozymes and oxidatively modified proteins were slightly rebounded at 100 μmol/L. Se contents were noticeably elevated and confirmed to exist as selenomethionine in the rice grains following all the treatments by Se NPs. Thus, the optimal dosage of Se NPs for foliar application is 50 μmol/L, which significantly decreased Cd accumulation, improved photosynthesis and Se enrichment whereas caused no distinct reduction of Pb in the grains. Thus, an appropriate dosage of Se NPs can be conducted to decrease Cd accumulation, improve photosynthesis, and organic Se contents in rice grains.

Mineral nutrient imbalance,DNA lesion and DNA-protein crosslink involved in growth retardation of Vicia faba L.seedlings exposed to lanthanum ions

Effects of mineral nutrient imbalance,DNA lesion and DNA-protein crosslink on growth of Vicia faba L.seedlings hydroponically cultivated in concentrations of extraneous lanthanum（La） for 20 days were investigated in the present experiment.The results showed that contents of La,Cu or K elements in roots generally changed synchronously with those in leaves,while Ca,Fe,Zn,Mg,Mn or P in the roots altered inversely to those in the leaves.Thus,the extraneous La led to redistribution and imbalance of mineral nutrient elements in the roots and leaves.DNA lesion and DNA-protein crosslink were investigated by single cell gel electrophoresis（SCGE） and sodium dodecyl sulfate/potassium（SDS/K＋） precipitation methods,respectively.The results demonstrated that the increasing La induced DNA break and DNA-protein crosslinks（DPCs） in the seedlings.These results suggested that mineral nutrient imbalance,DNA lesion and DNA-protein crosslink were involved in the growth retardation and growth alteration of the seedlings,which may help to understand the mechanisms of rare earth elements（REEs） on plant growth.