ROS-Dependent Induction of Antioxidant System and Heat Resistance of Wheat Seedlings by Hemin

Effect of 24-h-long treatment with hemin (a donor of carbon monoxide, CO, produced with the participation of heme oxygenase) on heat resistance and the processes of ROS formation and neutralization was investigated in wheat (Triticum aestivum L.) seedlings. It was found that treatment of seedlings with hemin in the concentration range from 0.5 to 10 µM induced an elevation of their resistance to damaging heating (45°C, 10 min). The greatest effect was produced by 5 µM hemin. Hemin treatment was associated with a transient elevation in the roots of extracellular peroxidase activity and a rise in the content of hydrogen peroxide. Elevation of H2O2 content was not observed in the presence of its scavenger dimethyl thiourea (DMTU) and upon treatment of seedlings’ roots with CO absorber hemoglobin and inhibitor of extracellular peroxidase sodium azide; however, this pattern was not followed in the presence of NADPH oxidase inhibitor imidazole. Since decomposition of hemin is associated with the production of redox active Fe2+ ions, the specificity of its action as a CO donor was tested by comparing the effects of hemin and 5 µM FeSO4. At the examined concentration, ferrous sulfate did not affect the generation of hydrogen peroxide in the roots and activity of extracellular peroxidase. In 24 h after the beginning of hemin treatment, activities of superoxide dismutase, catalase, and intracellular peroxidase in the roots rose. Elevation in the activity of antioxidant enzymes induced by hemin was not observed in the presence of DMTU, and treatment of seedling roots with FeSO4 did not modify their activity. Exposure to the CO donor after damaging heating also reduced outflux from the seedling roots of compounds absorbed in the ultraviolet spectral region. Positive influence of hemin on heat resistance of the seedlings was eliminated by CO scavenger hemoglobin and hydrogen peroxide absorber DMTU. Treatment of seedlings with FeSO4 did not alter their survival after heating. Hydrogen peroxide is assumed to participate as a signal mediator in realization of the influence of CO donor on the antioxidant system of wheat seedlings and their heat resistance.