Pumpkin (Cucurbita moschata Duch.) tolerates high levels of lead and copper by modulating ecophysiological characteristics and antioxidant defense system

Pollution caused by heavy metals is one of the most prominent environmental challenges, and these pollutants induce various detrimental effects on plants. Copper (Cu) is an essential micronutrient for the normal growth and development of plants in trace amounts, while lead (Pb) causes deleterious effects even at low levels. Although pumpkin is used extensively worldwide for its nutritional and medicinal value, little is known about this plant in the context of heavy metal stress. Therefore, this study investigated the effects of different concentrations of lead (25 mM and 50 mM) and copper (50 mM and 100 mM) on pumpkin at the ecophysiological and molecular levels, focusing on the mechanisms involved in heavy metal tolerance. As a result, both lead and copper stress generally favored stem growth while limiting root growth. Pumpkin accumulated lead and copper mostly in the roots to reduce the hazardous effects of Pb and Cu, as evidenced by higher Pb and Cu content in the roots than in the leaves. Additionally, Pb-treated plants had noticeably higher chlorophyll amounts, whereas Cu-treated plants showed a concentration-dependent response. Pb and Cu stress increased malondialdehyde (MDA) content at higher concentrations, accompanied by a general decline in total protein amounts. Furthermore, Pb and Cu stress increased superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) activities, as well as the gene expression of these enzymes. Overall, this study revealed that pumpkin is highly tolerant to lead and copper and achieves this tolerance by enhancing the activities and gene expressions of antioxidant enzymes.