Zinc and copper toxicity in basil (Ocimum basilicum L.) seedlings: Role of melatonin in mitigating stress

The effects of melatonin (MT) on the growth and antioxidant responses of basil (Ocimum basilicum L.) exposed to copper and zinc excess stress are investigated. For this purpose, seedlings were exposed to different concentrations of copper oxide (0, 50 and 150 mu M), zinc oxide (0, 50 and 100 mu M) and melatonin (0 and 100 mu M) for 14 days. Growth and biochemical parameters, the activity of some antioxidant enzymes, and phenylalanine ammonia lyase (PAL) and some of the main nutritional elements in the shoot and root of seedlings were measured. The results of this study showed that the excess of copper (Cu 50 and 150 mu M) and zinc (Zn 50 and 100 mu M) causes a decrease in growth, and a higher oxidative stress indicator such as hydrogen peroxide and malondialdehyde (MDA) content. The homeostasis balance of mineral nutrition of basil seedlings was also disrupted under copper and zinc stress. Melatonin treatment in Cu, Zn stressed seedlings improved growth parameters by reducing the levels of hydrogen peroxide (H2O2) and malondialdehyde (MDA) and increasing the activity of PAL and antioxidant enzymes. Melatonin also regulated the distribution of minerals in basil seedlings under Cu and Zn stress conditions. The results of this research showed that MT can improve the tolerance of basil seedlings against copper and zinc stress by modulate growth and antioxidant responses and regulating mineral nutrition.