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.
Highlights
Polycyclic aromatic hydrocarbons (PAHs) belong to persistent organic pollutants (POPs) consisting of 2–7 condensed aromatic rings that are arranged in various structural configurations
Phenanthrene (PHE), as one of the priority compounds presented in US-EPA list, represents a typical low molecular weight (LMW) PAH with three fused benzene rings that exists at high levels in PAH polluted environments (Fu et al, 2018)
The analysis of correlation showed negative correlation coefficient between MDA content and antioxidant enzyme activities in shoot (SOD r2 = -0.893, POD r2 = -0.590, CAT r2 = -0.705, Ascorbate peroxidase (APX) r2 = -0.740) and root (SOD r2 = -0.771, POD r2 = -0.717, CAT r2 = -0.451, APX r2 = -0.688) (Table 1). These findings indicate that antioxidant enzymes involved in ROS detoxification and plants resistance to oxidative stress are induced by PHE toxicity
Summary
Polycyclic aromatic hydrocarbons (PAHs) belong to persistent organic pollutants (POPs) consisting of 2–7 condensed aromatic rings that are arranged in various structural configurations. They have been detected in various concentrations in different environments. PAHs hydrophobic nature leads to their accumulation and enrichment in soils, which is the reason for the necessity of the remediation of contaminated sites (Pretorius et al, 2018). Their physicochemical characteristics are low solubility in water, low vapour pressure, and highly lipophilicity which results in their high mobility in environment (IARC, 1983). Increased environmental pollution and anthropological disturbances to ecosystems led to the study of abiotic stress responses in plants and subsequent concern about remediation of PAHs and ecosystem restoration strategies (Alkio et al, 2005)
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