Exploring foliar secretion sites and composition in the Legume tree Swartzia flaemingii as an alternative saponin source

Swartzia flaemingii is a legume tree (Fabaceae) from Atlantic Forest, belonging to the infrageneric section Acutifoliae, which includes only Brazilian especies. The species in the Swartzia genus have recognized medicinal and food-related potential. Saponins stand out among the compounds produced by Swartzia spp., with several biological activities. This study aims to investigate S. flaemingii as a model, exploring it as a potential saponin source, locating saponin-containing structures on the leaves, and evaluating the hemolytic (erythrocytes) and cytotoxic (RAW 264.7 macrophages) potential of leaflet extracts. Samples of S. flaemingii leaves underwent anatomical characterization, ultrastructural analyses, saponin histolocalization, phytochemical analysis, hemolytic activity, and cytotoxicity assay. The leaflet of S. flaemingii is dorsiventral, with a uniseriate epidermis. The midrib contains vascular bundles with associated fibers. The identified secretory structures include laticifers, mucilaginous cells, and phenolic idioblasts. Saponins are localizated on the laticifers, in the cuticle above the epidermal cells, inside the fibers and tector trichomes. Phytochemical analysis identified oleonane-type saponins, marking the first report of these compounds in this species. The crude extract of S. flaemingii displayed low hemolytic and cytotoxic activities, with HC50 and CC50 values of 1387.6 ± 14.84 and 963.4 ± 133.26 µg/mL. Further investigation is needed in order to isolate the identified saponins and explore their bioactivity potential. This study underscores the S. flaemingii potential as an alternative saponin source and emphasizes the importance of conserving Atlantic Forest biodiversity.