Metabolomic Characterization Reveals Organ-Specific Accumulation of Secondary Metabolites in Petiole Glands of Idesia polycarpa

Background/Objectives: Idesia polycarpa Maxim. possesses conspicuous glandular protuberances on its petioles, but the chemical composition and potential biological significance of these structures remain largely unexplored. This study aimed to characterize the metabolic profile of I. polycarpa petiole glands and to determine their organ-specific accumulation patterns of secondary metabolites compared with leaves and shoot tips. Methods: A widely targeted metabolomics approach based on ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) was applied to analyze petiole glands, leaves, and shoot tips collected from the same I. polycarpa individuals. Multivariate statistical analyses and differential metabolite profiling were performed to compare metabolic characteristics among the three organs. Results: Petiole glands contained 700 detected metabolites, representing the highest metabolic diversity among the three examined organs, and 39 metabolites were exclusively detected in petiole glands. Principal component analysis clearly separated petiole glands from leaves and shoot tips, demonstrating their distinct metabolic profile. Compared with other organs, petiole glands showed preferential accumulation of several secondary metabolite classes, including flavonoids, tannins, alkaloids, and phenolic acids. The gland-exclusive metabolites included flavonoids such as kaempferide, kaempferitrin, and tectoridin, as well as diverse proanthocyanidins and phenolic acid derivatives. Conclusions: This study provides the first systematic metabolomic characterization of I. polycarpa petiole glands and reveals their organ-specific accumulation of secondary metabolites. The unique metabolic profile of petiole glands suggests potential ecological relevance and provides a foundation for further investigations into the biological functions of gland-associated metabolites.