Biosynthesis of secondary metabolites in aromatic and medicinal plants in response to abiotic stresses: A review

Abstract

Climate change has massive consequences on non-living factors in the environment, resulting in irregular precipitation, fluctuating atmospheric temperature, and variations in humidity. These changes cause biotic and abiotic stresses; plants must have defense mechanisms to survive. Therefore, plants divert some synthesized energy towards producing numerous plant secondary metabolites (PSMs), viz., flavonoids, alkaloids, and essential oils. These compounds act as protections for the plants, helping them to survive under stressful conditions. Medicinal and aromatic plants (MAPs) are sessile organisms that are not immune to harmful consequences of various abiotic stresses in which the PSMs have an important role in acting against the adverse effects. In this regard, the MAPs have a coherent defense mechanism for abiotic stresses. The secondary metabolites produced by these plants are useful as medicines and aromatic products for humans. However, not all stresses produce high secondary metabolites, as their production is highly specific to certain stresses. This review provides a comprehensive understanding of secondary metabolite production under various stressful conditions, including extreme temperature, drought, water logging, salinity, harmful radiation, elevated levels of ozone and CO2, heavy metals, and agrochemicals on MAPs. Additionally, the production of these compounds can be modified by subjecting plants to various stressors. Many authors have reported on PSMs in MAPs, which need to be well documented and exploited for humankind.