Preliminary Study on the Mechanism of Foliar Spraying of Serine to Alleviate Heat Stress in Panax notoginseng

Purpose To explore the alleviating effect and potential mechanism of foliar spraying serine on heat stress of Panax notoginseng.

Methods Indoor potted P. notoginseng plants were subjected to a 36 ℃ high-temperature treatment for 15 days using a light incubator. During the treatment period, serine solutions with concentrations of 1, 3 and 5 mmol/L were sprayed every two days, and the rate of diseased leaves of P. notoginseng was investigated at the end of treatment. In the field, P. notoginseng was exposed to natural high-temperature conditions, and serine solution with the same concentrations as used indoors were sprayed every three days. The duration of the heat stress treatment was extended to 30 days, the rate of diseased leaves of P. notoginseng and the effects of high temperature on the biomass and saponin content of P. notoginseng were examined. Antioxidant enzyme activity and metabolite changes in indoor potted P. notoginseng plants were measured to elucidate the preliminary mechanism by which serine alleviates heat stress in P. notoginseng.

Results Spraying serine at concentrations of 3 and 5 mmol/L significantly reduced the rate of diseased leaves in potted P. notoginseng (P<0.05). Spraying 1, 3, and 5 mmol/L serine significantly reduced the rate of diseased leaves in field-grown P. notoginseng plants (P<0.05), and increased the dry weight of per plant as well as the content of ginsenosides Rg₁, Re, Rb₁, and Rd. Spraying 1 and 3 mmol/L serine significantly increased the activity of superoxide dismutase (SOD) in potted P. notoginseng leaves (P<0.05), while spraying 3 mmol/L serine significantly increased peroxidase (POD) activity (P<0.05). KEGG enrichment analysis showed that non-enzymatic antioxidant metabolites such as sugar alcohols and amino acids accumulated in large amounts in the leaves after serine treatment. The accumulation of heat stress-related carbohydrates such as sucrose and trehalose also increased. In addition, important metabolites in the tricarboxylic acid cycle such as citric acid, aconitic acid, and succinic acid showed increased accumulation, which contributed to improve energy supply in P. notoginseng.

Conclusion Exogenous foliar application of serine reduces the incidence of diseased leaves, increases biomass, and enhances saponin accumulation in P. notoginseng under heat stress. These effects are likely associated with improved antioxidant capacity and enhanced carbohydrate metabolism in P. notoginseng.