Effects of naphthalene, an aromatic hydrocarbon on the molecular and anatomical characteristics of the Portulaca oleracea plant

Polycyclic aromatic hydrocarbons (PAHs) induce oxidative stress in plant cells. Naphthalene is a well-known low molecular weight hydrocarbon. This compound elevates the levels of reactive oxygen species and malondialdehyde in plants. The aim of this study is to investigate the expression of antioxidant enzymes, including glutathione S-transferase, as well as and the anatomical changes in purslane plants in response to naphthalene stress, and to assess their role in mitigating the harmful effects of this substance and its absorption. Four concentrations of naphthalene (0, 15, 30, and 60 ppm) were tested in quadruplicate across 16 hydroponic containers. The gene expression of all four enzymes significantly increased in both roots and shoots under moderate and severe stress conditions. Specifically, the expression of glutathione S-transferase in roots and shoots significantly increased by 80.85 and 78.59%, respectively in response to severe stress compared to the control group. Furthermore, the gene expressions of catalase, superoxide dismutase, and ascorbate peroxidase in roots significantly increased by 64.53, 82.87, and 70.23%, respectively under severe stress conditions. In the shoots, the corresponding increases in expression were 72.14, 71.42 and 78.81%. Furthermore, exposure to naphthalene resulted in distinct anatomical changes in both roots and shoots. The epidermal and parenchyma cells in both structures exhibited a reduction in size and increased sinuosity. Moreover, the number of vascular bundles in the shoots increased. These findings underscore the robust antioxidant defense system and anatomical adaptability of purslane, enabling it to thrive in environments contaminated with naphthalene. This resilience highlights the potential application of purslane in the phytoremediation of naphthalene- polluted ecosystems.