Impact of salicylic acid elicitation on the growth, photosynthesis, and metabolites of Bacopa monnieri (L.) Pennell growing in a hydroponic control system

Bacopa monnieri (L.) Pennell is a nootropic herb used as a memory enhancer in Ayurveda, an Indian system of medicine. Owing to the surplus demand for B. monnieri in international markets, there is a threat of overharvesting. Many medicinal plant species cultivated in soil often contain lower levels of medicinal compounds than wild-harvested plants do. The hydroponic cultivation of medicinal plants may provide sustainable access to increase secondary metabolite contents under abiotic and biotic stress conditions. The present study aimed to evaluate the growth parameters, photosynthetic rates, and phytoconstituents of B. monnieri grown in soil, hydroponic control, and salicylic acid-treated hydroponic systems. The plant growth parameters, such as plant height, number of shootlets, dry weight, and photosynthetic rate, were evaluated at two-week time intervals in different cultivation systems. In addition, a comparison of metabolites from different cultivation systems was performed after six weeks via ultra-performance high-resolution liquid chromatography-mass spectrometry. Compared with those in the soil and hydroponic control systems, the plant height (180.1±2.149419 cm), number of shootlets (185.8±7.596052), and dry weight (4.0329±0.0732 g/plant) were greater in the SA-treated hydroponic system. Metabolite profiling of B. monnieri revealed that a total of 312 metabolites and 134 metabolites were significantly different between the soil and hydroponic control systems and between the hydroponic control and salicylic acid-treated hydroponic systems, respectively. The levels of primary and secondary metabolites, such as geniposidic acid, Arg-Ile, sucrose, alpha, alpha-trehalose, Lys-Leu, uridine-5′-monophosphate, and aucubin, were 5–7-fold variation in the SA-treated hydroponic system than in the hydroponic control system. Hence, a salicylic acid-treated hydroponic system can provide higher quality and better yield of B. monnieri along with enhanced bioactive compounds to meet pharmaceutical demands than a controlled hydroponic system.