Destructive Effect of Heavy Metals on the Oxidative Defense Mechanism of Some Aromatic Plants

Abstract

Aromatic plants are used in the production of natural medicines, treatment of various diseases, production of essential oils, and as a food source. Many plants are cultivated for their aromatic compounds. The essential oils they produce are used as antibacterial, antifungal, antiviral, and insecticidal agents, and as appetite suppressants against herbivores. Heavy metal pollution, which has become a significant environmental issue, can be highly reactive and toxic to living cells. Aromatic plants may be exposed to heavy metals in both natural and cultivated environments, leading to stress and oxidative damage in the plants. Some heavy metals cannot undergo biological degradation reactions, while others, due to their immobile nature, cannot be removed from the environment, resulting in accumulation. Those that are mobile can enter cells through various transport pathways and negatively affect physiological processes in the plant. The formation of reactive oxygen species (ROS) occurs as a result of these physiological processes. ROS types, such as O2 •-, 1O2, H2O2, and •OH, can be hazardous to cells, cause structural damage, and lead to cell death. The imbalance between the accumulation and removal of these oxidative molecules in the cell causes oxidative stress. The effects of oxidative stress can be observed in enzyme inactivation, disruption of membrane integrity, and inhibition of growth in plants. To mitigate the effects of oxidative stress and defend themselves, plants have antioxidant defense mechanisms. These mechanisms include enzymatic antioxidants such as superoxide dismutase, peroxidase, ascorbate peroxidase, and nonenzymatic antioxidants such as lipid-soluble and water-soluble reducing agents. The type, dose, and duration of heavy metal exposure, as well as the species and developmental stages of the plant, trigger various antioxidant defense mechanisms and responses. In this process, the role of ROS detoxifying enzymes is particularly significant. Due to their various properties, such as metal exclusion, aromatic plants are able to cope with oxidative stress. In conclusion, understanding the factors that affect the antioxidant defense mechanisms and enzyme inhibition in plants under heavy metal stress, and developing strategies to address them, is important for enhancing plant productivity and ensuring adaptation to environmental stress. © 2025 Elsevier Inc. All rights reserved.