The present work investigates the possible protective role of nitric oxide (NO) against heavy metals stress in Lupinus termis L. plants. A greenhouse experiment was conducted as a 2 x 2 factorial design with five replications. Lupine seedlings were treated with two concentrations (0.4 mM and 0.6 mM) of sodium nitroprusside (SNP as an NO donor) and subjected to high levels of nickel (Ni) sulfate (100 and 150 mM). The toxic effects of Ni on L. termis plants were evaluated by measuring the oxidative stress markers such as lipid peroxidation, hydrogen peroxide and electrolyte leakage. In addition, growth parameters, endogenous phytohormones, photosynthetic pigment, calcium, magnesium and Ni accumulation in lupin plants grown under Ni toxicity in the presence or absence of NO were also determined. Carbohydrate, organic acid and proline contents were also measured to determine the possible NO-mediated defense strategies in lupine plants to resist Ni stress. The obtained results proved that, Ni toxicity resulted in significantly elevated levels of oxidative stress markers, as well as abscisic acid, jasmonic acid and proline contents, which are associated with significant reduction in growth parameters, photosynthetic pigments, carbohydrate, indole acetic acid and gibberellic acid contents compared with control plants. SNP treatments significantly alleviated the toxic effect of Ni on Lupinus termis L. and increased the amounts of proline, soluble sugars and polysaccharides in shoots and roots, which could be an induced defensive mechanism against heavy-metal stress. Treatment with 0.4 mM SNP was more effective in increasing lupine plants tolerance to Ni toxicity than the 0.6 mM SNP.

This study was conducted to investigate the effects of sodium nitroprusside (SNP) on antioxidant enzyme activities in <em>Lupinus </em><em>albus </em>subsp. <em>termis </em>(Forssk.) Ponert plants subjected to salt and heavy metal stress. Foliar spray of SNP (0.4 and 0.6 mM) was used as a nitric oxide (NO) donor to treat lupine plants grown under different levels of salinity (0, 75, and 150 mM NaCl) and nickel (Ni) stress (100 and 150 mM Ni sulfate). Growth parameters and yield as well as total phenols, flavonoids, and antioxidant enzyme activities (including those of superoxide dismutase, peroxidase, ascorbate peroxidase, catalase, and glutathione transferase) in NO-treated and untreated plants grown under normal or salt/heavy metal  stress conditions were determined. We found that exogenously applied SNP effectively mitigated the inhibitory effects of salinity and Ni stresses on all measured growth parameters and yield components of lupine plants. In addition, NO downregulated antioxidant enzyme activities, which proved to be a good indicator reflecting changes in the oxidative status of lupine plants in response to SNP, salt, and Ni sulfate treatments.

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