Abstract: A hydroponics experiment was conducted to study the Cd accumulation in Lolium perenne and the effects of the accumulated Cd on the activities of antioxidative enzymes and the concentrations of phytochelatins under Cd²⁺ stress. The ^{L. perenne} plants with three fully expanded leaves were cultured in 1/2 Hoagland’s nutrient solution for 2 weeks, and then treated with 5 mg·L^-1 of Cd²⁺. The Cd concentration, antioxidative enzymes activities, and thiol compounds concentrations in both roots and leaves were measured on the day 0, 0.25, 1, 3, and 6 after treatment. After 6 days, the Cd concentration was 2588 mg·kg^-1 in roots and 240 mg·kg^-1 in leaves. The Cd transport index from root to leaf was 0.093, and the Cd bioconcentration index of leaf was 48, indicating that L. perenne had a high Cd accumulation capacity, and could be applied in phytoremediation. After exposed to Cd²⁺ stress, the MDA content in L. perenne leaves and roots and the SOD and CAT activities in L. perenne roots had less change, but the root APX was highly sensitive to Cd²⁺, with the activity on day 6 decreased significantly by 67%, as compared with that on 0 day. Within 1 day Cd²⁺ exposure, the SOD, APX and CAT activities in leaves decreased significantly. On day 3, the antioxidative enzyme system in leaves had a positive feedback to the increase of leaf Cd content, and the SOD, APX, and CAT activities increased significantly by 14%, 77%, and 99%, respectively, as compared with day 1. On day 6, the SOD activity decreased significantly by 19%, as compared with day 3, but the APX and CAT activities had no significant change. On day 6, the concentrations of Cys, GSH, PC₂, PC₃, PC₄, PC₅, and PC₆ in roots were 2.19, 1.57, 2.06, 16.08, 5.73, 6.03, and 4.31 times higher, and the concentrations of Cys, GSH, PC₂, PC₃, and PC₄ in leaves were 0.69, 3.21, 1.64, 5.73, and 0.27 times higher than those on day 0, respectively. PC₃ thiol had the greatest proportion to total thiol in roots, whereas GSH thiol had the greatest proportion to total thiol in leaves, suggesting that PC₃ thiol and GSH thiol were the main existence forms of thiol in roots and leaves, respectively. With the increasing time of Cd²⁺ treatment, the total thiol concentration both in roots and in leaves increased significantly, and the total PCs-SH concentration in roots and leaves was significantly positively correlated with the Cd concentration in roots and leaves. It was suggested that L. perenne could rapidly synthesize thiol compounds to decrease the proportion of Cd²⁺ to total Cd in leaves and roots, which played a key role in protecting the antioxidative enzymes in roots and leaves, and indirectly maintained the balance of reactive oxygen metabolism.

Key words: copepod, desiccation., resting eggs, potential recruitment, aquaculture ponds