Short-duration UV-B exposure mitigates salinity stress in Withania somnifera (L.) Dunal and boosts secondary metabolite production

Withania somnifera is a widely valued medicinal plant traditionally cultivated in arid and semi-arid regions of India, where salt stress and rising UV-B radiation pose growing threats to its productivity and pharmacological quality of different metabolites. While the individual impacts of salinity and UV-B stress have been extensively studied, their interactive effects and potential for cross-tolerance in W. somnifera remain unexplored. In this study, we investigated the morphophysiological, biochemical, and metabolic responses of W. somnifera under salt (50–200 mM NaCl), UV-B (1–4 h), and combined exposure. Salt stress significantly reduced plant height, shoot biomass, photosynthetic efficiency (Fv/fm), and pigment content, while inducing oxidative damage. UV-B exposure alone enhanced relative water content, stimulated antioxidant enzyme activities (SOD, CAT, APX, and GR), and promoted the accumulation of secondary metabolites. Under combined salt and UV-B exposure, plants exhibited further amplified responses wherein antioxidant enzyme activities remained elevated while lipid peroxidation levels decreased compared to salt stress alone, suggesting reduced oxidative damage. Due to short-term UV-B exposure, metabolite profiling via high-resolution mass spectrometry revealed a synergistic enhancement in the accumulation of key secondary metabolites, particularly withanolides, flavonoids and triterpenoids, alongside the unique induction of stress-responsive compounds such as betaine and arjungenin. These findings suggest that short-duration UV-B exposure synergistically interacts with salt stress, intensifying redox activity and metabolic reprogramming to reinforce the plant's adaptive capacity. This work provides a foundation for integrating UV-B-based agronomic strategies in saline-prone regions to boost both stress resilience and the commercial phytochemical yield of W. somnifera.