Nitrogen form regulates ginsenoside biosynthesis in Panax ginseng adventitious roots: comparative transcriptomics of...

Panax ginseng C. A. Mey. is a valuable Chinese herbal medicine. Saponins are one of its main active ingredients, possessing various important pharmacological activities and serving as key indicators for evaluating ginseng quality. Due to the depletion of wild ginseng resources, adventitious root culture has emerged as an effective approach for ginsenoside production; however, the ginsenoside content in cultured adventitious roots remains relatively low. Nitrogen, as an essential macronutrient for plant growth and development, plays a vital role in both biomass accumulation and secondary metabolite biosynthesis. Different nitrogen forms exert distinct regulatory effects on the synthesis of triterpenes, but the molecular mechanism of ammonium nitrogen and nitrate nitrogen regulating the accumulation of ginsenosides in ginseng adventitious roots is not clear. In this study, we combined physiological measurements with comparative transcriptomic analysis to investigate the regulatory pathways underlying adventitious root growth and differential ginsenoside accumulation under nitrate-only, ammonium-only, and nitrogen-free conditions at the optimal nitrogen concentration. Physiological results showed that nitrate nitrogen supply significantly increased adventitious root biomass and total ginsenoside content compared with ammonium nitrogen. Functional enrichment analysis of transcriptomic data revealed significant transcriptional remodeling in terpenoid biosynthesis, plant hormone signal transduction, and redox homeostasis pathways. Further analysis showed that the core genes of ginsenoside synthesis pathway were upregulated under nitrate nitrogen conditions. Nitrate treatment also resulted in higher levels of endogenous IAA and CTK and activation of most hormone signaling pathways, whereas ammonium nitrogen induced a significant increase in CAT and POD antioxidant enzyme activities. Nitrate nitrogen can promote endogenous nitric oxide (NO), and further pharmacological experiments suggest that NO likely acts as an important intermediate signal contributing to nitrate-driven promotion of adventitious root growth and ginsenoside synthesis. The results clarify the molecular mechanism of nitrogen form regulating ginseng secondary metabolism and provide a theoretical basis for optimizing the nitrogen strategy of ginseng adventitious root culture and improving the yield of ginsenosides.