THE EFFECTS OF HEAVY METALS ON THE ACTIVITIES OF SOD AND CAT IN LOQUAT LEAF

Changes in superoxide dismutase (SOD) and catalase (CAT) activities after application of Hg²⁺, Cd²⁺ or Cu²⁺ at different concentrations to the potted seedlings of loquat (Eriobotrya japonica Lindl.) at budbreak of spring flush were measured. The results indicated that with the increase of concentrations of heavy metals and with the time exposed to the heavy metals, their inhibitory effect on SOD and CAT activities was strengthened. Low concentrations of Cu²⁺ (20 mg L^-1 and 40 mg L^-1) promoted SOD activity, while low concentration of Hg²⁺ (0.1 mg L^-1 and 0.2 mg L^-1) and Cd²⁺ (0.1 mg L^-1) within 40 days enhanced CAT activity. Excessive heavy metals completely eliminated the CAT activity but not the SOD activity.