Effect of Cu2plus concentration on growth, antioxidant enzyme activity and malondialdehyde content in garlic [Allium sativum L.]

The effects of different concentrations (10-5 M, 10-4 M. 10-3 M) of Cu2+ on growth, antioxidant enzyme activity and malondialdehyde (MDA) content were investigated in hydroponically grown Allium sativum L. The results indicated that the growth of garlic seedlings was not inhibited under treatment with 10-5 M Cu2+. Garlic seedlings exposed to 10-4 M and 10-3 M Cu2+ exhibited significant growth reduction. With increasing Cu2+ concentration and treatment time, superoxide dismutase (SOD) activity increased in leaves and roots, and peroxidase (POD) activity increased in leaves. In roots of plants exposed to 10-4 M and 10-3 M Cu2+, POD activity increased within 9 d and then dropped, but was still higher than in the control at the end of the experiment. Catalase (CAT) activity increased in seedlings grown at 10-5 M and l0-4 M, whereas a highly toxic level of Cu2+ (10-3 M) markedly inhibited CAT activity. SOD and POD activity were higher in roots than in leaves, whereas CAT activity was higher in leaves than in roots under both control and Cu2+ treatments. There was no obvious effect on MDA content in the seedlings treated with 10-5 M Cu2+; at 10-4 M and 10-3 M Cu2+ it increased. The mechanisms of Cu2+ toxicity and Cu2+ tolerance in garlic are briefly discussed.