[Effect of low light stress on growth and active ingredient content of Pinellia ternata]

Pinellia ternata is a characteristic shade-tolerant plant. In this study, LED light sources were used to investigate the phenotypic, physiological, and molecular responses of P. ternata seedlings under three light intensities: excessively low light(L1, 100 μmol·m~(-2)·s~(-1)), low light(L2, 200 μmol·m~(-2)·s~(-1)), and critical light(L3, 400 μmol·m~(-2)·s~(-1)). The results showed that plant height and chlorophyll content were highest under L2, while leaf area and biomass were highest under L3. The content of bioactive compounds was higher under L2 than under the other two light treatments. In contrast, excessive shading(L1) significantly inhibited seedling height and stem diameter due to a lower net photosynthetic rate and induced higher membrane lipid peroxidation. Additionally, the highest total alkaloid and nucleoside contents were observed under L3, whereas the highest total organic acid content was found under L2. Furthermore, at 5 days of treatment, photosynthetic efficiency and related indicators were highest under L3, whereas at 20 days, photosynthetic parameters increased under L2. Transcriptome analysis revealed that differentially expressed genes(DEGs) in response to different light intensities were significantly enriched in pathways related to photosynthesis, photosynthetic-antenna proteins, phenylpropanoid biosynthesis, and starch and sucrose metabolism. Among these, 42 DEGs were involved in photosynthesis-related pathways, regulating photosynthetic efficiency through photosystem related genes(psa, psb, PNSL), photosynthetic electron transport genes(petA, petC, petD), and adenosine triphosphate(ATP) synthase(atp, ATPC, ATPF2). Most of these genes were upregulated under L3 at 5 days and under L2 at 20 days. Together, these findings elucidate the physiological and molecular mechanisms by which P. ternata seedlings respond to different shading levels, providing a basis for understanding light regulation, cultivation, and ecological adaptation mechanisms in this species.