<p>Polycyclic aromatic hydrocarbons (PAHs) are a class of organic pollutants effecting different aspects of plants physiology. To assess the physiological responses of plants to PAHs, maize (<em>Zea mays</em>)<em> </em>was treated with 25, 50, 75, and 100 ppm of pyrene and after 21 days, the activity of some antioxidant enzymes, malondialdehyde (MDA), total flavonoid, total anthocyanin, and soluble sugar contents were measured in shoots and roots of plants. Pyrene led to increase MDA content as well as CAT, POD, and SOD activities. Increase in pyrene concentration reduced all studied growth variables and significantly increased photosynthetic pigments contents of plants. Soluble sugar content was significantly higher in the shoot, while that was reduced in the roots through increasing of pyrene concentration (<em>p <</em> 0.05). Also, the increase of pyrene concentration decreased total flavonoid content compared to anthocyanin content. In conclusion, these findings supported the hypothesis that pyrene toxicity induces oxidative stress in the maize plant and it also increases the antioxidant systems in order to moderating stress condition. However, the antioxidant system of maize was not strong enough to eliminate all produced ROS at high concentrations, thus this caused oxidative damage to the plant and decreased its growth variables.</p>
Polycyclic aromatic hydrocarbons (PAHs) are widespread organic pollutants which are persistent in the environment. Biodegradation of PAHs is one of the major mechanisms for their removal from environment. However, unlike microorganisms such as fungi and bacteria, the degradation pathways of organic pollutants in plant systems are not completely clear. This paper displays the possible pathways for the degradation of phenanthrene and pyrene (as two abundant PAHs in the environment) in maize plant. Maize plants were treated by phenanthrene and pyrene and after 7, 14, and 21 days, a number of intermediate compounds were identified using gas chromatography–mass spectroscopy (GC–MS) analysis. The obtained results showed that although maize plant can metabolize both compounds, but the degradation rate of phenanthrene was faster and higher than that of pyrene. The degradation of phenanthrene occurred mainly in the second week, whereas the degradation of pyrene was slower and mostly happened after the third week. Intriguingly, the degradation of both compounds was primarily observed in the roots. The number of identified intermediate compounds was different in the shoot and root and depends on the type of contaminant and treatment time. The most outstanding identified intermediates were quinones, dihydrodiols, phthalate and phenolic compounds which were formed through the cleavage of phenanthrene and pyrene. Accordingly, the probable degradation pathways of phenanthrene and pyrene in maize plants were proposed.
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