Effect of phenanthrene on physiological parameters and induction of oxidative stress in sunflower plants

Nowadays, one of the environmental problems is the production and release of persistent organic pollutants, including polycyclic aromatic hydrocarbons such as phenanthrene, into the environment. In this study, the effect of different concentrations of phenanthrene (0, 50 and 100 mg/L) on growth parameters, photosynthetic pigments, some antioxidant enzymes, and some biochemical activities of the sunflower plant were investigated. Sunflower seeds were cultivated in pots containing perlite and different concentrations of phenanthrene. The water content of pots was adjusted to field capacity using distilled water and kept in the dark for one week. Seedlings were transferred to growth chambers with controlled conditions (25–30 °C, 16/8 h light/dark photoperiod, and relative humidity of 50-60% and light intensity of 80 μmol/m2/s). After 50 days, plants were harvested and the mentioned parameters were evaluated. Growth parameters of sunflower were decreased at the level of 100 mg/L of phenanthrene. Phenanthrene treatment increased the concentration of chlorophyll a and b as well as carotenoids in sunflower compared to control plants. Concentrations of non-enzymatic antioxidant compounds in treated plants with phenanthrene showed significant changes. The activity of antioxidant enzymes including superoxide dismutase (SOD), ascorbate, peroxidase (APX) and peroxidase (POX) was significantly increased especially in the root. In conclusion, it seems that phenanthrene toxicity induces oxidative stress in the sunflower, and plants improve their enzymatic antioxidant system to moderate the stress condition. In addition, damage of cell membranes by phenanthrene leads to weakening of plants root system as well as disordering in water and nutrient uptake and finally reduction in the plant growth.