Soil water stress attenuate the growth and development but enhance the saponin synthesis of Panax notogesing during flowering stage

Water stress can affect the growth and secondary metabolites of plants. Thus, this study identified the effects of soil water conditions on the growth and development of Panax notoginseng, especially saponin synthesis. Panax notoginseng was grown in different soil water conditions (0.40, 0.55, 0.70, 0.85, 1.00 field capacity) for 30 days, and related indicators were determined every 10 days. Panax notoginseng could not survive under the content of 0.40 and 1.00 field capacity. Thus, their cultures were set at 0.55, 0.70, and 0.85 field capacity for experimental purposes. The results showed that agronomic traits, leaf water contents, chlorophyll contents, and photosynthetic efficiency in 0.70 field capacity were significantly higher than in 0.55 and 0.85 field capacity. In addition to flowers, contents of soluble total sugars and proteins increased significantly in all the parts under 0.55 and 0.85 field capacity. Compared with 0.70 field capacity treatment, total saponin content of aboveground organs increased significantly under 0.55 and 0.85 field capacity. And 18 key genes increased significantly but 2 key genes changed insignificantly in saponin synthesis pathway. These results suggested that 0.70 field capacity was the most suitable soil water condition for flowering stage Panax notoginseng and produced the best agronomic traits, while water stress (0.55 and 0.85 field capacity) produce more saponin contents by improving the expression of key genes in saponin synthesis pathway.