Physiological and metabolic responses of Bacopa monnieri to salt-induced stress: implications for secondary metabolite elicitation

Abstract

Bacopa monnieri is a medicinal plant rich in bacoside A, a group of saponins with neuroprotective and therapeutic potential for neurodegenerative conditions. Salt stress, exacerbated by climate change, limits plant growth and productivity but may also trigger phytochemical accumulation. This study aimed to optimize NaCl concentration and exposure duration to enhance bacoside A production in B. monnieri. Plants were grown in pots for four weeks and treated with 0–200 mM NaCl at two-day intervals. Results showed that root length declined with increasing salinity, while shoot length, biomass, and chlorophyll content were influenced by stress duration. Prolonged exposure reduced maximum quantum yield (Fv/Fm), PSII efficiency (Fv’/Fm’), and increased malondialdehyde (MDA) and electrolyte leakage (EL), indicating oxidative stress. Bacopasaponin C and total bacoside A peaked at 2.047 mg/g dry weight (mg/g DW) (200 mM NaCl for 3 weeks) and 3.10 mg/g DW (50 mM NaCl for 4 weeks), with stress duration having a greater impact than salinity level. Compared to the control, bacopasaponin C and total bacoside A increased by 12.07% and 25.36%, respectively. Principal component analysis (PCA) and hierarchical cluster analyses (HCA) grouped treatments primarily by stress duration. This is the first study to systematically compare the combined effects of multiple salinity levels and exposure durations under soil-grown conditions, highlighting the critical role of stress duration in modulating secondary metabolism. Our findings enable optimized stress elicitation protocols to enhance B. monnieri phytochemical production in climate-resilient cultivation systems, advancing sustainable metabolite induction approaches.