Hydrogen sulfide (H2S) regulates many critical processes of plants. The effect of sodium hydrogen sulfide as H2S agent was investigated in basil plants under cadmium stress. A completely randomized design with three different concentrations (0, 50 and 100 μM) of CdCl2 and two levels of NaHS (0 and 100 μM) was used in this study. Cadmium exposure reduced growth parameters and relative water content. Cd also caused a significant increase in ion leakage and higher oxidative stress in terms of lipid peroxidation and H2O2 production. Although exogenous NaHS used in non-stressed control plants negatively affected growth and physiological parameters, it improved the root/shoot length ratio and fresh weight in basil plants under Cd 50 μM exposure. Moreover, NaHS alleviated deleterious effects of cadmium on ion leakage, relative water content and photosynthetic pigments of leaves. The activity of antioxidant enzymes like catalase, peroxidase and ascorbate peroxidase were also enhanced by NaHS in plants under moderate cadmium stress. Our results show that NaHS 50 μM ameliorates growth retardation induced by cadmium 50 μM stress in basil plants, probably through regulating physiological parameters such as photosynthetic pigments content, relative water content and the activity of antioxidant enzymes.

The study was carried out to investigate the interactive effects of exogenous melatonin and excess amounts of zinc and copper on the growth and physiological parameters, antioxidant defense system and nutritional balance of cannabis seedlings. Cannabis sativa L. plants, grown under a completely randomized design, were irrigated with complete Hoagland’s nutrient solution. CuSO ₄ (0, 50 and 150 µM) and ZnSO ₄ (0, 50 and 100 µM) and their combinations were supplied to 21-day-old seedlings for 2 weeks. During the second week, melatonin was added to the nutrient solution at 100 μM. Zn and Cu stress led to reduced growth and physiological parameters, it promoted oxidative stress, changes in antioxidant enzymes activity and imbalance of mineral nutrients in cannabis seedlings. However, melatonin alleviated the growth retardation and physiological disorders of seedlings under normal conditions and heavy metal stress. The content of reduced glutathione and the activity of antioxidant enzymes such as glutathione reductase and ascorbate peroxidase were improved by melatonin. Excess amounts of zinc and copper changed the pattern of nutritional elements distribution in cannabis seedlings. Cu and Zn caused reduced content of Fe, Ca and K ions in shoots and roots. Melatonin treatment was able to adjust the nutrients content in metal-stressed seedlings up to the level of the control. Exogenous melatonin reduced toxic levels of Cu and Zn in seedlings overloaded with copper and zinc. MT also raised K, Ca and Fe concentrations in roots and shoots of seedlings under stress. Our results support the idea that melatonin acts as a powerful antioxidant, it can also be considered as a potent regulator of ion homeostasis in cannabis seedlings under heavy metal toxicity. Further studies still need to investigate the alleviatory effects of melatonin under field conditions.