Plant defense mechanisms against ozone stress: Insights from secondary metabolism

Ozone pollution is a serious global environmental problem, with surface ozone concentrations consistently ranking among the top air pollutants. In response to ozone stress, plants activate various defense mechanisms, including secondary metabolism. Secondary metabolites are organic compounds that are not directly involved in plant growth and development but serve multiple functions, such as defense against herbivores, pathogens, and protection against abiotic stresses. This review aims to accomplish the following objectives: (i) comprehensively understand the physiological functions, significance, and interconnections between plant secondary metabolism and environmental factors; (ii) analyze the impact of ozone stress on both volatile and non-volatile secondary metabolites in plants; and (iii) explore the defense mechanisms of plant non-volatile secondary metabolites against ozone stress, focusing on plant pigments, hormones, and active ingredients. Furthermore, we summarize the severity of ozone pollution and the role of plant secondary metabolism in alleviating ozone toxicity and facilitating plant adaptation to ozone-polluted environments. Additionally, we review relevant studies on the effects of ozone stress on plant secondary metabolism and investigate the protective mechanisms of plant secondary metabolites in response to ozone stress. Gaining insights into the synthesis and regulation mechanisms of specific metabolites in plants under ozone stress is vital for comprehending the protective and defensive effects of plant secondary metabolism. The examination of protective mechanisms utilized by plant secondary metabolism under ozone stress is an essential aspect of ecological research.