Comparative Untargeted Metabolomics of Flavonoid- and Phenylpropanoid-Related Differential Metabolites in Different Tissues and Growth Stages of Apocynum venetum and Apocynum pictum

Apocynum venetum and Apocynum pictum are two important medicinal plants of the same genus but distinct species; their flavonoid and phenylpropanoid constituents are closely related to their medicinal value. Untargeted metabolomics was used to compare the flavonoid- and phenylpropanoid-related differential metabolites of roots, stems, and leaves in the two species at the seedling, growth, and mature stages. In total, 568, 560, and 530 differential metabolites were annotated in roots, stems, and leaves, respectively, of which 39 were related to the flavonoid and phenylpropanoid pathways. KEGG enrichment analysis showed that flavonoid and phenylpropanoid biosynthesis were enriched in leaves and flavone and flavonol biosynthesis in stems. Among the annotated metabolites, flavone/flavonol-type compounds (Quercetin and Luteolin) and phenylpropanoid compounds (Sinapic acid, Sinapyl alcohol, Caffeic acid, 5-caffeoylshikimic acid) differed markedly between species and among tissues, whereas flavanones and their derivatives, the flavanonol Taxifolin (Level 2) and naringenin-O-dihexoside (Level 3), were enriched in A. pictum. Overall, species, tissue, and growth stage jointly influence the accumulation of flavonoid- and phenylpropanoid-related metabolites in Apocynum, providing a basis for germplasm evaluation, medicinal-material identification, and the rational utilization of different tissues.