Drought stress affecting the production of secondary metabolites in medicinal plants

Due to production of some important biochemicals including secondary metabolites (SM), medicinal plants are of economic and health significance. However, medicinal plants are subjected to different types of stress including drought affecting their growth and biochemical properties including SM production. There is an increasing demand for cultivation of medicinal plants and subsequent production of SM as suitable alternatives for conventional pharmaceuticals. Additionally, although research has indicated drought stress may alter SM production in medicinal plants, affecting their health and economic values, the related mechanisms must be investigated in greater details. This review is about drought stress affecting the production of different types of SM (alkaloids, terpenoids and flavonoids), and so, plant response in drought stress as indicated by omics analyses. Moreover, role of elicitors including plant growth regulators such as plant hormones on SM production in drought stress conditions has also been reviewed. Plant stress tolerance (sensitive or tolerant) is an important factor determining the accumulation of SM and plant response in drought stress conditions. Accumulation of flavonoids including anthocyanins and flavonols may alleviate unfavorable effects of drought stress on plant, though the related mechanisms have yet to be indicated. Finding methods, which enhance tolerance of medicinal plants in stress conditions, and so, improve their quality and quantity, is of significance for innovation in the synthesis of therapeutic drugs. This indicates the applicability of this review including the present research gap. Proper level of drought stress may enhance SM production in medicinal plants, and so, their economic and health significance.