Effects of the Nitric Oxide Donor Sodium Nitroprusside on Antioxidant Enzymes in Wheat Seedling Roots under Nickel Stress

The inhibitory effect of nickel on the growth of wheat (Triticum aestivum L.) seedlings and the alleviation of nickel toxicity by nitric oxide (NO) were investigated. Nickel (Ni) at 100 mu M caused striking reduction in seedling growth and significant overproduction of MDA and H2O2 in the roots. Supplementation with NO donor sodium nitroprusside (SNP) could significantly reverse the inhibitory effect of nickel in a dose-dependent manner. K3Fe(CN)6, a SNP analogue, which does not release NO, had no ameliorative effect on Ni toxicity in wheat.. In addition, application of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), a NO scavenger, could dramatically counteract the stimulatory effects of SNP on the growth of wheat seedling roots under Ni stress, confirming that NO rather than other compounds derived from SNP was responsible for the alleviating effect of Ni toxicity. Further results showed that SNP enhanced the activities of guaiacol peroxidase (POD, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.11), superoxide dismutase (SOD, EC 1..1..5.1..1), glutathione reductase (GR, EC 1.6.4.2), and glutathione S-transferase (GST, EC 2.5.1.18) in wheat seedling roots under nickel stress, while no significant difference in the activity of catalase (CAT, EC 1.11.1.6) in wheat roots supplemented with SNP or without it was observed. These results clearly indicate that NO has a protective role in Ni-induced oxidative damage through modulation of antioxidant enzymes.