High resistance of Panicum miliaceum L. to phenanthrene toxicity based on growth response and antioxidant system assessment

Abstract

Polycyclic aromatic hydrocarbons are a group of organic pollutants influencing different aspects of plants physiology. Physiological responses associated with the impact of phenanthrene (500, 1000, 1500, 2000 ppm) were analysed on Panicum miliaceum L. Seed germination was delayed in all treatments and 2000 ppm of phenanthrene (PHE) significantly retarded the germination rate (28 %) compared to control. The results revealed after 30 day of cultivation, only 1500 and 2000 ppm of PHE had negative impacts on growth parameters as well as photosynthetic pigment contents. Plants exposed to 500 and 1000 ppm of PHE showed an increase in the growth parameters without any symptoms of toxicity, indicating the high tolerance of seedlings to PHE. The activities of antioxidant enzymes were elevated in treated plants. In higher concentrations, H2O2 content also increased despite a reduction in malondialdehyde content. Furthermore, PHE had no effect on root phenol and shoot flavonoid contents and on shoot and root protein contents. Taken together, only higher concentrations of PHE triggered oxidative stress. It can be concluded PHE was not very toxic to P. miliaceum probably because of higher activity of antioxidant system involving in elimination of produced ROS even in plants treated by PHE higher concentrations.

Keywords

• polycyclic aromatic hydrocarbons
• Panicum miliaceum
• phenanthrene
• physiological responses
• toxicity