Oxidative Processes and Xenobiotic Metabolism in Plants: Mechanisms of Defense and Potential Therapeutic Implications

Plants are continuously exposed to environmental challenges, including pollutants, pesticides, and heavy metals, collectively termed xenobiotics. These substances induce oxidative stress by generating reactive oxygen species (ROS), which can damage cellular components such as lipids, proteins, and nucleic acids. To counteract this, plants have evolved complex metabolic pathways involving both enzymatic and non-enzymatic mechanisms to detoxify and process these harmful compounds. Oxidative stress in plants primarily arises from the overproduction of ROS, including hydrogen peroxide (H2O2), superoxide anions (O2•−), singlet oxygen (1O2), and hydroxyl radicals (•OH), by-products of metabolic activities such as photosynthesis and respiration. Exposure to xenobiotics significantly elevates ROS levels, causing cellular damage and disrupting metabolism. Plants employ a robust antioxidant defense system featuring enzymatic antioxidants like catalase (CAT), superoxide dismutase (SOD), and various peroxidases (POD). These enzymes collaborate to scavenge ROS, minimizing their detrimental effects. Additionally, plants produce numerous non-enzymatic antioxidants, such as flavonoids, phenolic acids, vitamins C and E, which neutralize ROS and regenerate other antioxidants, providing comprehensive protection against oxidative stress. Xenobiotic metabolism in plants involves three phases: Phase I (modification), Phase II (conjugation), and Phase III (compartmentalization), facilitated by enzymes like cytochrome P450 monooxygenases (CYPs), transferases such as glutathione S-transferases (GSTs), and ATP-binding cassette (ABC) transporters. Plant secondary metabolites, including alkaloids, terpenoids, and flavonoids, significantly contribute to detoxification and antioxidant defense. Understanding these oxidative processes and xenobiotic metabolism pathways in plants is crucial, as it offers insights into developing plant-based strategies to mitigate environmental pollution impacts and improve human health through enhanced detoxification and antioxidant mechanisms, as we discuss in this review.