Phyto-saponins as a natural adjuvant for delivery of agromaterials through plant cuticle membranes

With growing use of synthetic adjuvants in modern agriculture, their impacts on the environment are being questioned. In a search for an environmentally safe phyto-adjuvant, we have investigated natural glycosidic saponin for delivery of agromaterials through plant cuticle membranes. Four saponin preparations from Quillaja saponaria bark (QE), obtained from Sigma-Aldrich, and Balanites aegyptiaca fruit mesocarp (ME), kernel (KE), and root (RE), isolated and characterized in our laboratory, were used for testing the delivery of [¹⁴C]-2,4-dichlorophenoxyacetic acid (2,4-D) across isolated intact astomatous adaxial Citrus grandis leaf cuticle membranes (CMs). The results showed that both Q. saponaria and B. aegyptiaca saponin preparations enhanced delivery of 2,4-D through CMs. Among the saponin preparations, ME exhibited a significantly higher level of delivery of 2,4-D with a concentration effect (2% being the highest). Transmission electron microscope (TEM) and dynamic light scattering (DLS) characterization of these saponin preparations in aqueous solution clearly demonstrated the formation of nanoscale vesicles. Various possibilities for a natural amphiphatic phyto-saponin as a delivery adjuvZant through CMs are discussed.