The synthesis of Paris saponin VII mainly occurs in leaves and is promoted by light intensity

Abstract

Unraveling the specific organs and tissues involved in saponin synthesis, as well as the light regulatory mechanisms, is crucial for improving the quality of artificially cultivated medicinal materials of Paris plants. Paris saponin VII (PS VII), a high-value active ingredient, is found in almost all organs of Paris plant species. In this study, we focused on Paris polyphylla var. yunnanensis (Franch.) Hand. - Mzt. (PPY) and found that PS VII synthesis predominantly occurs in leaves and is increased by high light intensity. This intriguing discovery has unveiled the potential for manipulating non-traditional medicinal organ leaves to improve the quality of medicinal organ rhizomes. The analysis of the impact of organ differences on saponin concentration in P. polyphylla var. chinensis (Franch.) Hara (PPC), P. fargesii Franch. (PF), and PPY revealed consistency among the three Paris species and was mainly dominated by PS VII. Notably, the leaves and stems exhibited much higher proportions of PS VII than other organs, accounting for 80–90% of the four main saponins. Among the three Paris species, PPY had the highest concentration of PS VII and was selected for subsequent experiments. Further investigations on saponin subcellular localization, temporal variation, and stem wound fluid composition demonstrated that PS VII is synthesized in mesophyll cells, released into the intercellular space through exocytosis, and then transported to the rhizome via vascular tissue. These findings confirm the significant role of leaves in PS VII synthesis. Additionally, a 13C-glucose feeding to trace PS VII biosynthesis revealed that only PS VII in the leaves exhibited incorporation of the labeled carbon, despite conducting 13C-glucose feeding in leaves, stems, rhizomes, and roots. Thus, the leaves are indeed the primary organ for PS VII synthesis in PPY. Furthermore, compared with plants under 100 μmol m−2 s−1, plants under 400 μmol m−2 s−1 exhibited a higher PS VII concentration, particularly in the upper epidermal cells of the leaves. We propose that high light intensity promotes PS VII synthesis in leaves through three mechanisms: (1) increased availability of substrates for saponin synthesis; (2) protection of leaves from high light damage through enhanced saponin synthesis; and (3) enhanced compartmentalization of saponins within the leaves, which in turn feedback regulates saponin synthesis.

Histochemical and ultrastructural localization of triterpene saponins in Medicago truncatula

“…Organelles such as chloroplasts have finding. More recently, Wen et al (2023) analyzed by TEM the subcellular localization of saponins in Paris polyphylla leaves and showed that saponin are present in various cellular components, including membrane, chloroplasts, mitochondria and cell wall. They also demonstrated that the Paris saponin VII (the predominant Paris saponin in leaves and stems) is synthetized in mesophyll cells and then transported through vascular tissue to the rhizome for storage (Wen et al, 2023).…”

“…More recently, Wen et al (2023) analyzed by TEM the subcellular localization of saponins in Paris polyphylla leaves and showed that saponin are present in various cellular components, including membrane, chloroplasts, mitochondria and cell wall. They also demonstrated that the Paris saponin VII (the predominant Paris saponin in leaves and stems) is synthetized in mesophyll cells and then transported through vascular tissue to the rhizome for storage (Wen et al, 2023). With TEM analysis we found that leaf parenchyma cells' cytosolic compartment, vacuoles and nuclei of M. truncatula are devoid of saponin so these compartments and organelles can be ruled out as synthetic sites for saponins.…”

Response Surface Optimization for Water-Assisted Extraction of Two Saponins from Paris polyphylla var. yunnanensis Leaves

“…Research has shown that the saponins contained in the leaves of P. polyphylla var. yunnanensis are similar to those in the rhizomes, such as polyphyllin II and polyphyllin VIII (Figure 1) [13], and it was even found that the synthesis of polyphyllin VII was mainly in the leaves [14]. Therefore, it is the focus of this study to find an economical and practical extraction method to improve the extraction efficiency of the medicinal components contained in the leaves of P. polyphylla var.…”