This manuscript describes the toxicity of lead in alfalfa plants treated with ethylenediaminetetraacetic acid (EDTA) and the phytohormones indole-3-acetic-acid (IAA), gibberellic acid (GA), and kinetin (KN), on catalase (CAT), ascorbate peroxidase (APOX), and total amylase activity (TAA). In all cases Pb was used at 40 mg/L; EDTA at 0.2 mM (equimolar to Pb); and IAA, GA, and KN at 1, 10, and 100 μM, respectively. An experiment containing Pb at 40 mg/L, 0.2 mM EDTA, and IAA and KN at 100 μM each was performed to determine changes in TAA. A control (plain nutrient solution) also was used for comparison. In all cases the treatments were performed in triplicate. Standard procedures were followed to determine the activity of the respective enzymes. After 10 d of exposure to the treatments, the leaves were harvested, homogenized, and centrifuged, and the supernatants were analyzed for CAT, APOX, and TAA. All determinations were performed in triplicate. The results demonstrated that CAT was reduced significantly (p < 0.05) by all treatments containing Pb, IAA, and GA at 10 and 100 μM. However, only the treatments Pb/EDTA/KN at 1, 10, and 100 μM reduced the APOX. The TAA in leaves of alfalfa plants was increased significantly (p < 0.05) by all treatments. Overall, the results suggest that the CAT tests showed no lead toxicity to the alfalfa seedlings. However IAA at 10 and 100 μM revealed toxicity to the CAT enzyme. In addition, the APOX tests exhibited no toxicity to the peroxidase enzyme with the exception of Pb/EDTA/KN treatments. Finally, the TAA tests showed high Pb/EDTA/phytohormone toxicity to the amylase enzyme in alfalfa seedlings.
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