Abstract
The role of exogenous cysteine (cys) and hydrogen sulfide (supplied as sodium hydrosulfide, NaHS) in the amelioration of Ni toxicity in wheat plants was evaluated in a hydroponic culture system. Exposure of wheat plants to 100 and 200 μM Ni inhibited biomass production, decreased chlorophyll concentration and intensively increased accumulation of Ni in both roots and leaves. Concomitantly, Ni enhanced H2O2 formation, lipid peroxidation (as indicated by malondialdehyde (MDA) accumulation) and the activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and glutathione reductase (GR) while it decreased the contents of cellular ascorbate and glutathione. Exogenous application of 2 mM NaHS and 50 µM cys separately to Ni solution significantly improved wheat growth but had a slight effect on the reversal of chlorophyll loss caused by Ni stress. NaHS significantly decreased the Ni accumulation in both studied wheat organs whereas cys has a slight effect. Application of NaHS and cys alleviated the oxidative damages as evidenced by the lowered hydrogen peroxide (H2O2) and malondialdhyde (MDA) contents. Exogenous sulpher, particularly NaHS, induced increases in the activities of CAT and GPX and the contents of cellular ascorbate and glutathione which was accompanied by a significant reduction in SOD, APX and GR activities in the in both wheat organs. These results reveal the potentiating effect of NaHS and cys in regulating Ni- induced oxidative stress in wheat plants.

Key words: Nickel, Sodium hydrosulfide, Cysteine, Oxidative damage, Antioxidants, Triticum aestivum