Abstract:Seeds of Medicago sativa L.cv.‘Gannong No.3’ were used as test material to study the effects of different cadmium concentrations on seed germination and physiological and biochemical characteristics.The results showed that:(1)Cadmium significantly inhibited seed generation and bud growth.The germination energy,germination rate,bud and hypocotyl lengths,and dry weight decreased significantly.The inhibition effect on germination energy was found stronger than that on germination rate,and on hypocotyl length was found stronger than that on bud.(2)On the 4th day of germination,proteolytic enzyme activity in seeds was significantly inhibited,together with the significant decrease of soluble protein and soluble sugar contents(P<0.05).(3)On the 10th day of germination,the activities of SOD,APX and GPX increased firstly and then decreased,CAT activity decreased continuously,while superoxide radical generation rate,H2O2 and MDA contents increased significantly,indicating that low cadmium concentration promoted the scavenging capacity of anti-oxidative system in seedlings while under high cadmium concentration,the anti-oxidative system activity decreased,and lipid peroxidation accelerated.The excessive accumulation of reactive oxygen was the main reason for seedling damage and biomass decrease.