Seasonal low temperature plays an important role in increasing metabolic content of secondary metabolites in Withania somnifera (L.) Dunal and affects the time of harvesting

Abstract

Withania somnifera (L.) Dunal is a subtropical crop which is widely used in traditional medicine owing to the presence of root bioactives called withanolides. In the present study, phenological variation in withanolide content in roots and leaves was determined at various days after plantation (DAP). Results showed that during the full vegetative state, the amount of marker secondary metabolites viz., withanolide A (Wd-A) and withanone (Wn), increased significantly (p ≤ 0.05) more than early vegetative state (8.16 and 3.2 times, respectively) and maturity stage (54 and 1.33 times, respectively). To qualify the role of temperature per se in enhancing secondary metabolite content, plants during full vegetative stage were exposed to temperature similar to lowest minimum temperature found during the growing period (8°C). During recovery, the metabolic content of secondary metabolites again fell to the level of plants growing at 25°C. This indicated that seasonal temperature played a key role in increasing secondary metabolites rather than the phenological stage of the plant. The physiological importance of this increase in harvesting and its balance with biomass yield has further been discussed.