To investigate the effects of Cd on tolerance and antioxidant activities of castor, two different castor(Ricinus communis L.) cultivars(Zibo No. 5 and Zibo No. 8) were used for a hydroponic experiment(0, 1 and 2 mg/L Cd) and a pot experiment using Cd-contaminated soil(34 mg/kg) with the addition of ethylenedinitrilotetraacetic acid(EDTA). The results indicated that there were significant differences between the two cultivars with respect to Cd uptake in shoots(113–248 mg/kg for Zibo No. 5 and 130–288 mg/kg Zibo No. 8), biomass tolerance indexes(64.9%–74.6% for Zibo No. 5 and 80.1%–90.9% for Zibo No. 8) in the hydroponic experiment and survival rates(0% for Zibo No. 5 and 100% for Zibo No. 8)determined by the addition of EDTA in the pot experiment, suggesting that Zibo No. 8 has higher tolerance than Zibo No. 5. Moreover, the castor cultivars have low bioconcentration factors(4.80% for Zibo No. 5 and 5.43% for Zibo No. 8) and low translocation factors(<1%).Consequently, Zibo No. 8 can participate in Cd phytostabilization in highly Cd-polluted areas. The results indicated that glutathione(GSH) as a non-enzymatic antioxidant, and antioxidant enzymes including superoxide dismutase(SOD), catalase(CAT) and guaiacol peroxidase(GPX), were cultivar- and dose-dependent. The higher tolerance of Zibo No. 8compared with Zibo No. 5 can be attributed to the higher GSH levels in the root and higher GPX activity in the leaf.
