Citric Acid: Improving Plant Metabolism Under Stress

Plants are persistently challenged by abiotic stressors such as drought, salinity, heat, cold, and heavy metals, as well as biotic threats including bacteria, fungi, viruses, and insect pests. These factors impair essential physiological and biochemical processes, causing oxidative damage, disruption in nutrient balance, and reduced productivity. Citric acid (CA), a key intermediate of the tricarboxylic acid (TCA) cycle, plays a central role in maintaining metabolic homeostasis during stress conditions. Beyond its metabolic function, CA acts as a signaling molecule, chelating agent, and precursor for multiple stress-associated compounds. It enhances stress resilience by modulating antioxidant defense, aiding in heavy metal detoxification, improving nutrient uptake, and participating in the synthesis of phytohormones and osmolytes. Moreover, CA influences defense gene activation and strengthens cell walls, aiding in biotic stress mitigation. This chapter offers a comprehensive overview of CA’s biosynthesis, regulation, and multidimensional role in modulating plant responses to abiotic and biotic stress. By dissecting its molecular and physiological effects, we highlight the potential of CA as a metabolic regulator and biostimulant in sustainable agriculture.