The role of redox state in regulating plant secondary metabolism under stress

Cell redox state serves as an indicator of plant health and plays a central role in maintaining vital functions across all living organisms. Various redox couples, such as glutathione (GSH)/glutathione disulfide (GSSG), reduced nicotinamide adenine dinucleotide (NADH)/nicotinamide adenine dinucleotide (NAD+), and reduced nicotinamide adenine dinucleotide phosphate (NADPH)/nicotinamide adenine dinucleotide phosphate (NADP+), are essential for maintaining redox homeostasis, which is necessary for plants to smoothly perform many biological functions, including secondary metabolism. Plant secondary metabolites are a group of non-essential metabolites during growth and development, including phenolic compounds, terpenoids, and nitrogen-containing compounds. These low-molecular-weight compounds act as defenders under environmental stress. Redox state can dynamically regulate plant secondary metabolism by modulating transcription factors, enzymes, and cross-talk with signal molecules involved in metabolic pathways, thereby prompting plant adaptation to environmental stress through fine-tuned secondary metabolism. In this review, we provided an overview of major redox couples, key classes of secondary metabolites, and how redox state regulates secondary metabolism under stress.