The effects of methyl jasmonate and salicylic acid on the growth of callus tissue and saponin formation in Panax quinquefolius L. is a perennial herbaceous plant in the family Araliaceae. Its main active ingredients are ginsenosides and saponin compounds, and it is one of the most commonly used Chinese herbs in the world. According to modern research, it has significant effects in lowering blood lipids, improving myocardial ischemia, and preventing cancer, and has extremely high medical and commercial value. At present, China’s American ginseng has long relied on imports and faces the scarcity of wild resources, high production costs, and long growth cycles. In particular, the content of rare saponins in American ginseng is extremely low, making it difficult to meet clinical application needs. By using medicinal plant cell culture technology, without being limited by time, region, and material growth period, a large amount of American ginseng biomass and target secondary metabolites can be obtained in a relatively short period of time. It is worth noting that the established American ginseng callus culture system still has the problem of low ginsenoside production, which affects the rapid development of the American ginseng industry.

With the continuous development and widespread application of inducers, it has become a hot topic to use inducers as a specific signal to induce the expression of target genes in cells, thereby regulating the synthesis of secondary metabolites in plant cells. Therefore, the study of using inducers to promote the accumulation of secondary metabolites in plant tissue culture has become particularly important. Methyl jasmonate (MeJA) and salicylic acid (SA) are commonly used inducers that promote the synthesis of various metabolites. They have been successfully applied in the induction of secondary metabolites in various medicinal plants such as Tripterygium wilfordii, safflower, Scutellaria baicalensis, and Salvia miltiorrhiza. Currently, there are few reports on using MeJA and SA to increase saponin content in American ginseng callus tissue. Therefore, this experiment used American ginseng callus tissue as the material to study the effects of MeJA and SA treatment on the growth, related enzyme activity, and main chemical component ginsenoside content of American ginseng callus tissue, providing theoretical basis for the cultivation of American ginseng callus tissue and the production of secondary metabolites.

 

Although inducers can promote the purposeful secretion of certain secondary products by plant cells to meet the medicinal value required by humans, the generated secondary products may also cause damage to the growth and development of plant cells themselves, reducing the total biomass of plant cells. Mao et al. conducted orthogonal experiments using inducers of different concentrations, and found that different concentrations of MeJA and yeast extract have different physiological effects on the growth of cinnabar callus tissue; In addition, Miao et al. used HPLC to determine the content of coumarin in the experiment, and the results showed that SA and MeJA had a certain promoting effect on the growth of callus tissue and coumarin in Panax ginseng; Wang et al. pointed out in their experiment that MeJA at concentrations of 50-100 μ mol/L promotes the accumulation of flavonoids in Ginkgo biloba suspension cells, while concentrations of 150-200 μ mol/L inhibit their synthesis. The MeJA and SA inducers used in this experiment both had an impact on the biomass of American ginseng callus tissue and hindered its growth. This may be because high concentrations of inducers can trigger various stress responses in plants, causing the cell membrane system to expand, contract, or break, disrupting the normal structure of cells and inhibiting the growth of plant tissues.

When plant cells grown under normal conditions are stimulated by exogenous inducers, the levels of reactive oxygen species inside the cells will show varying degrees of imbalance. Plant cells activate their own antioxidant enzyme system, utilizing the coordinated coordination of enzymes such as SOD, CAT, and POD to eliminate excess free radicals in the body, thereby protecting the plant from damage in adverse environments. MDA, as a product of peroxidation of cell membrane lipids, can indirectly reflect the degree of damage to the plant cell membrane system and the plant’s stress resistance. Li et al. found that SA and MeJA have a promoting effect on the activities of SOD, POD, CAT, MDA content, and the accumulation of syringol III and 3,6 ‘- sinapyrylsucrose. Taimoor et al. found that the activities of POD and SOD in buckwheat callus tissue showed a trend of first increasing and then decreasing with the prolongation of SA treatment time, with the highest activity at week 7. Marziyeh et al. found that 4% and 6% concentrations of polyethylene glycol significantly increased the MDA content in the callus tissue of Taxus chinensis, but 1%, 2%, 3%, and 5% concentrations of polyethylene glycol had no effect on the MDA content. In this study, it was found that both types of inducers can significantly activate the activities of antioxidant enzymes SOD, CAT, POD, and MDA content in the callus tissue of American ginseng at appropriate concentrations. Beyond the concentration range, the related enzyme activities were lower than those in the control group. This may be because inducers have a certain limit on the activity of antioxidant enzymes. If the limit is exceeded, the enzyme activity will be greatly reduced, resulting in a large accumulation of reactive oxygen species in the cells, which will harm the normal growth of plant cells.

Numerous studies have shown that different inducers and concentrations have significant differences in their effects on the same plant material. For example, adding sodium acetate, SA, and Cu2+can effectively increase the yield of adventitious roots of Bupleurum chinense and the content of saikosaponin to varying degrees; Low concentrations of rare earth element Ce3+can increase the production of flavonoids in Ginkgo biloba suspension cells, but high doses of Ce3+can lead to cell death. The optimal concentration of secondary metabolites induced by inducers varies within the same plant. Qi et al. found that the optimal concentrations of MeJA, SA, and yeast extract added to the hairy root culture of Gynostemma pentaphyllum increased the growth and total saponin content of hairy roots to varying degrees. In this experiment, it was found that both types of inducers can significantly promote the accumulation of ginsenosides in the callus tissue of American ginseng. The optimal concentrations of MeJA and SA induced ginsenosides were 100 and 200 μ mol/L, respectively, which were 4.23 and 2.49 times higher than the control group. In addition, it was found that different inducers and concentrations affect the synthesis of monomeric saponins in American ginseng callus tissue, with significant variations in the effects on monomeric saponins Rg1, Re, Rb1, Rd, Rc, and Rb2. From this, it can be concluded that in the callus tissue of American ginseng, the induction effect is MeJA>SA. In the tissue culture of American ginseng, yeast extract, SA, silver nitrate, calcium chloride, MeJA, and fungal inducer can all increase the content of ginsenosides, which is consistent with our results. This result may be caused by a combination of multiple factors, which may be related to the types and quantities of receptors for different inducers. Although low concentrations of inducers cause less damage to cells, they may only partially induce plant cells, resulting in lower levels of secondary metabolites; It may also be related to the different levels of endogenous cytokinins in the callus of American ginseng, resulting in multiple synthetic pathways and reaction steps involved in secondary metabolites in the plant, and different inducers participating in different synthetic pathways. Therefore, it is particularly important to select appropriate inducers and the optimal concentration to promote the growth of American ginseng callus and the accumulation of ginsenosides.

Secondary metabolites are the result of plants’ adaptation to the ecological environment during long-term evolution, and have important significance in plant life activities. They are also an important source of many compounds such as drugs, dyes, and fragrances. Inducers are one of the most effective and widely used biotechnological tools in plant tissue culture for inducing new secondary metabolites or enhancing biosynthesis and accumulation of secondary metabolites. This experiment investigated the effects of MeJA and SA inducers on the growth, enzyme activity, and ginsenoside content of American ginseng callus tissue. The results showed that adding appropriate concentrations of MeJA and SA to American ginseng callus tissue could significantly activate enzyme activity and increase the content of ginsenoside compounds. Although MeJA inhibited growth, the total saponin content and yield in callus tissue reached their maximum values at a MeJA concentration of 100 μ mol/L. The content of ginsenosides Rg1, Re, Rb1, and Rc was the highest, indicating that MeJA had the best effect on inducing total ginsenosides. This article provides a basis for using inducers to promote the synthesis of active ingredients in American ginseng. However, the mechanism by which inducers regulate the accumulation of ginsenosides in American ginseng callus and how to more effectively synergistically utilize inducers to improve the quality of American ginseng callus are issues that need to be addressed in subsequent experiments.