Sodium Nitroprusside Mitigates the Inhibitory Effect of Salt and Heavy Metal Stress on Lupine Yield and Downregulates Antioxidant Enzyme Activities

This study was conducted to investigate the effects of sodium nitroprusside (SNP) on antioxidant enzyme activities in Lupinus albus subsp. termis (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.