Use of untargeted metabolomics to profile the foliar metabolome of Mitragyna speciosa under varying light and water conditions

We investigated the effects of varying light intensity and water availability on the foliar metabolome of Mitragyna speciosa (kratom) seedlings in a hydroponic settings. Untargeted liquid chromatography-mass spectrometry (LC-MS) metabolomics integrated with hierarchical orthogonal partial least squares discriminant analysis (OPLS-DA) was used to characterise the metabolite profiles. We obtained and annotated a total of 377 metabolites that spanned major ontologies such as alkaloids, flavonoids, terpenoids, phenolics/phenylpropanoids, and lipid derivatives. The highest number of unique metabolites was observed under high light (245), followed by low light (162), and medium light (110). Hierarchical OPLS-DA identified two significant splits within the metabolomic dataset, with light intensity as the primary determinant of metabolome variation (Split 1: Silhouette score = 0.52, P-value = 0.011), followed by water potential under low-light conditions (Split 2: Silhouette score = 0.51, P-value = 0.012). Exposure to high-light intensity lowered the abundance of nitrogen-based alkaloids like hirsuteine, corynoxeine, and ajmalicine, while increasing the abundance of photoprotective compounds like uncarine C, picrotin, and ursolic acid. Conversely, low light and low water availability resulted in a higher abundance of metabolites that included quercetin, alpha-tocopherol, magnoflorine, epigallocatechin, and curcumin, suggestive of a stress-induced antioxidant response. The findings can be used for optimizing bioactive metabolite production under controlled environments for pharmacological applications, though confirmation of certain compounds (e.g. magnoflorine and curcumin) in M. speciosa through future validation with authentic standards remains essential.