Bittersweet dynamics from flowers to fruits: chemometric molecular networking reveals metabolic changes towards reduced toxicity over ontogeny in above-ground Solanum dulcamara chemotypes

Abstract

Poisonous plants frequently deploy toxic metabolites in an organ- and ontogenetic-specific manner, yet the developmental dynamics of these plant specialised metabolites remain poorly understood. In the Solanaceae, steroidal glycosides (SGs), including steroidal glycoalkaloids (SGAs) and steroidal saponin glycosides (SSGs), are major defence metabolites with potent ecological and pharmacological activities. Here, we investigated how their metabolic profiles are reorganised during flower and fruit development in Solanum dulcamara using untargeted metabolomics and chemometric molecular networking. Non-metric multidimensional scaling (NMDS) using classified metabolite features recovered clear organ-specific and chemotype-specific segregation of samples, which was further strengthened when analyses were restricted to metabolomic features annotated as SGs. In flowers, orthogonal projections to latent structures discriminant analysis (OPLS-DA) separated both floral developmental stage and chemotype, demonstrating that developmental stage and inherited SG polymorphism represent independent axes of chemodiversity in flowers. Chemometric molecular networks showed pronounced diversification of hydroxycinnamate metabolism towards anthesis, including accumulation of caffeoylputrescine in flower buds and progressive acylation of spermidine conjugates across flower development. Upon anthesis, glycosylated hydroxycinnamates and flavonoids, and hydroxycinnamoyl-acylated flavonoid glycosides are accumulated. Fruit ripening followed a contrasting trajectory, in which SGAs were associated with unripe fruit pericarp, whereas ripe pericarp accumulated N- and O-acetylated SGA derivatives, oxidative deamination products, and predicted steroid degradation products, indicating stepwise detoxification of toxic steroidal glycosides during seed maturation. Together, these findings show that the poisonous chemistry in S. dulcamara is highly dynamic and developmentally orchestrated. Flowers accumulate structurally complex metabolites toward anthesis, including conjugates of hydroxycinnamates, whereas fruits metabolise toxic SGAs into less toxic SGs during ripening, linking metabolic remodelling to reproduction and seed dispersal.