Viciafaba L. seedlings were hydroponically cultivated in 0-12 mg/L of extraneous lanthanum （La） for 15 d to investigate ecotoxicological effects and risk assessment of rare earth elements （REEs）. The results showed that reactive oxygen species （ROS） production such as superoxide radical （O2） and hydrogen peroxide （H202） were overproduced at higher concentrations of La, resulting in oxidatively modi- fied proteins and shoot growth retardation. While, superoxide dismutase （SOD）, catalase （CAT）, ascorbate peroxidase （APX） and guaiacol peroxidase （GPX） isoenzymes were elevated to some extent to eliminate excess of ROS. HSP70 production and endopeptidase isoenzymes were also enhanced, which were involved in repairing or degradation of the oxidatively modified proteins due to La. Thus, the antioxidant isoenzymes, endoprotease isoenzymes and HSP70 worked cooperatively to alleviate the La-induced oxidative damage. The significant en- hancement of CAT and APX isoenzymes and HSP70 could also be used as early bioindicators of La-polluted solution. The threshold dose range was firstly delimited as 1-2 mg/L of extraneous La, corresponding to 7.34-9.37 μg/g dry weight in the leaves. These results would be helpful to further understand the toxicological effects and possible mechanisms of REE（s） on crop seedlings.
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.
