Effect of Cadmium on Seed Germination and Antioxidative Enzymes Activities in Cotyledon of Solanum nigrum L.

Hyperaccumulator species of the Solanum nigrum L.can accumulate Cd from soils where the concentrations are relatively low,and are therefore used for phytomining and phytoextraction of Cd contaminated soils.Basic studies on the physiology are needed to increase efficiency and uptake capacity of Cd by hyperaccumulators.The seeds of S.nigrum were germinated on the agar containing CdCl2(0,30,50,100,150,200 μmol·L-1 and 300 μmol·L-1) for 7 days.The results showed that germination rate was dramatically reduced at 200～300 μmol·L-1 Cd as compared to control,while no significant differences were found at 30～150 μmol·L-1 Cd.Additionally,vigor index,germination energy and the growth of seedling were reduced markedly in Cd concentrations exceeding 30 μmol·L-1.Root elongation was declined by 17%～35% at 30～150 μmol·L-1 Cd and by 79%～91% at 200～300 μmol·L-1 Cd,respectively;shoot height showed gradual decrease with the increasing Cd levels.Furthermore,the activities of catalase(CAT) and ascorbate peroxidase(APX) in S.nigrum cotyledon were strongly enhanced at 100～150 μmol·L-1 Cd,whereas superoxide dismutase(SOD) activity decreased,yet maintained a relatively high level.Taken together,these data indicated that S.nigrum might tolerate less than 150 μmol·L-1 of Cd and antioxidant enzymes play an important role in counteracting the deleterious effects of Cd.