Enhanced bacoside synthesis in Bacopa monnieri plants using seed exudates from Tamarindus indica

Diverse allelochemicals are released from different plant parts via leaching, exudation, volatilization, etc., which can induce either stimulatory or inhibitory effects depending on the target plant species. Very few reports provide details about allelopathic interaction through seed exudates. Since Tamarindus indica L. seed exudate (TSE) has been known to exhibit growth stimulatory effect on lettuce, radish, and sesame, in the present study we have evaluated its role in regulating the secondary metabolism of an over-exploited medicinal herb, Bacopa monnieri (L.) Pennel. The bacoside biosynthesis rate of B. monnieri is quite low in comparison to its increasingly high demands in the pharmaceutical industry. Currently, researches are aimed towards enhancing the biosynthesis of this secondary metabolite in planta by utilizing external stress factors. Presently, 7-day-old B. monnieri seedlings were treated with 1:16, 1:8, 1:4, 1:3, and 1:2 (seed weight: water) TSE. Maximum upregulation of secondary metabolite contents was found in the 1:4 (seed weight: water) TSE treatment set. This TSE treatment also enhanced H₂O₂ and salicylic acid production leading to the upregulation of the genes related to the MVA pathway (BmAACT, BmHMGR, BmMDD, BmSQS, and BmBAS) which are responsible for bacoside biosynthesis and 1.7-fold higher bacoside level was found in TSE treated set compared to control. LC-HRMS analysis of TSE confirmed the presence of alkaloid (lupanine), phenol (chlorogenic acid), and organic acid (mucic acid), which are identified as potential allelochemicals responsible for modulating the secondary metabolism of B. monnieri. Thus, this study highlights a sustainable approach towards enhancing bacoside production in planta.