Impact of Salinity Stress on Secondary Metabolite Production in Plants: A Comprehensive Review

Salinity stress is one of the major abiotic constraints limiting plant growth, productivity, and geographical distribution, particularly in arid and semi-arid regions. Increasing soil salinization because of irrigation practices, climate change, and seawater intrusion has intensified interest in understanding plant adaptive mechanisms under salt stress. Medicinal plants, valued for their bioactive secondary metabolites (SMs), exhibit diverse physiological and biochemical responses to salinity. Alkaloids, terpenoids, phenolics, flavonoids, glycosides, and other (SMs) are essential for plant defense and adaptability, and their production is often significantly altered under saline conditions. When oxidative stress, ion toxicity, osmotic stress, and nutritional imbalance are caused by salt stress, reactive oxygen species (ROS) are produced. In response, medicinal plants activate antioxidant defense systems and secondary metabolic pathways as protective strategies. The moderate salinity level has been noted to boost production of some (SMs), thus boosting the medicinal value. Nevertheless, severe salinity stress may have an adverse impact on plant development and metabolic output because of metabolic disruption and cellular damage. The response to salinity is very species specific, and it varies with stress intensity, length of time, stage of development, and genotype. Further research integrating molecular, physiological, and metabolic approaches is important for sustainable employment of medicinal plants under saline conditions.