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Panax notoginseng often faces varying levels of light stress during its growth, which can hinder efforts to improve its yield and quality. Nitrogen (N) and potassium (K) are known play important role in photosynthesis, while the synergistic effect and mechanism in enhancing the resistance to light stress of P. notoginseng have yet to be well understood. In this study, field experiments and pot trials were conducted to investigate the regulatory effects of the combined application of N and K on N allocation in P. notoginseng leaves under light stress, as well as on metabolic products of photosynthesis and the accumulation of saponin. Results showed that compared with medium light (ML: optimal light intensity, 450 μmol/m2/s), both low light (LL: 60 μmol/m2/s) and high light (HL: 800 μmol/m2/s) stress significantly reduced the net photosynthetic rate (Pn) (32.45% and 12.23%, respectively) and photosynthetic nitrogen use efficiency (PNUE) (10.01% and 19.21%, respectively) of P. notoginseng leaves. Compared with N0K0 (N: K=0.0045:0.0045 kg/m2), N1K2 (N: K=0.0225:0.045 kg/m2) treatment significantly increased Pn and PNUE under LL or HL stress in P. notoginseng , with an average increase of 52.80% and 31.61%, respectively. The allocation of carboxylation nitrogen (Ncb) and electron transport nitrogen (Net) were identified as the main limiting factors for PNUE under light stress. However, compared with N0K0, N1K2 treatment mitigated these limitations by increasing Rubisco content at an average of 0.29 ng/g FW, and adjusting the Ncb ratio by 7.31% to 21.11%, primarily through conversion of non-protein nitrogen (N np) to photosynthetic nitrogen (N psn). In addition, compared with N0K0, N1K2 regulated the activity of carbohydrate metabolism enzymes, resulting in an average increase of 25.72% in starch content and a mean decrease of 6.48% in sucrose content under LL or HL stress, ultimately promoting the accumulation of total saponins in P. notoginseng (11.95% to 29.67%). In summary, under light stress, N1K2 synergy improves LL or HL stress resistance of P. notoginseng by expanding and supplementing the N psn pool in its leaves, thereby promoting the accumulation of carbohydrate and saponins. [Display omitted] • N1K2 mitigates Pn, WUE, and Rubisco decline in light-stressed P. notoginseng. • N1K2 increases the capacity and proportion of N psn in P. notoginseng. • N1K2 promotes the conversion of N np to N psn in P. notoginseng. • There is a significant correlation between PNpsn and PNUE. • N1K2 improves P. notoginseng 's stress resistance, enhancing yield and quality. [ABSTRACT FROM AUTHOR]

The high background value of cadmium (Cd) in the Panax notoginseng planting soil is the main reason for the Cd content in P. notoginseng exceeding the limit standards. The main goal of this study was to reveal the mechanism by which potassium (K) reduces Cd accumulation in P. notoginseng from the perspective of the influences of soil microbial communities on soil pH, total organic matter (TOM) and cation exchange capacity (CEC). Pot experiments were conducted to study the effects of different types and amounts of applied K on the Cd content in P. notoginseng , and on the soil pH, TOM, CEC, and bioavailable Cd (bio-Cd) content in soil. Field experiments were conducted to study the effects of K2SO4 fertilizer on the microbial community, and its correlations with the soil pH, TOM and CEC were analyzed. A moderate application of K2SO4 (0.6 g⋅kg–1) was found to be the most optimal treatment for the reduction of Cd in the pot experiments. The field experiments proved that K fertilizer (K2SO4) alleviated the decreases in pH, TOM and CEC, and reduced the content of bio-Cd in the soil. The application of K fertilizer inhibited the growth of Acidobacteria, but the abundances of Mortierellomycota, Proteobacteria and Bacteroidetes were promoted. The relative abundances of Acidobacteria and Proteobacteria in the soil bacteria exhibited significant negative and positive correlations with pH and CEC, respectively. In contrast, the relative abundance of Mortierellomycota was found to be positively correlated with the pH, TOM and CEC. The bio-Cd content was also found to be positively correlated with the relative abundance of Acidobacteriia but negatively correlated with the relative abundances of Proteobacteria and Mortierellomycota. The application of K fertilizer inhibited the abundance of Acidobacteria, which alleviated the acidification of the soil pH and CEC, and promoted increase in the abundances of Mortierellomycota, Proteobacteria and Bacteroidetes, which ultimately increased the soil TOM and CEC. Soil microorganisms were found to mitigated decreases in the soil pH, TOM, and CEC and reduced the bio-Cd content in the soil, which significantly reduced the accumulation of Cd in P. notoginseng. [ABSTRACT FROM AUTHOR]

This study investigated the effect of nitrogen (N) and potassium (K) formula fertilization on cadmium (Cd) accumulation in P. notoginseng. Field investigations as well as formulated N and K fertilizers application experiments were conducted. Field investigations showed that Cd accumulation decreased PNS content in the main roots of P. notoginseng, while PNS content was promoted by soil available potassium (AK) and K in the main roots. The Cd content in P. notoginseng and the bioavailable Cd content in the soil decreased with the increasing of total K (TK) and AK in the soil. The increase of soil pH, total organic matter (TOM) and cation exchange capacity (CEC) values can reduce the bioavailable Cd content in soil, thus reducing the Cd accumulation in P. notoginseng. Under current fertilization in P. notoginseng cultivation, decreased N fertilization can alleviate the deterioration of soil physical and chemical properties. Under identical N fertilization, increasing K fertilization promoted the PNS accumulation (0.3–38.3%), also improved soil physical and chemical properties. Formulated N and K fertilizers application (1:2) experiments showed that reducing application of N and increasing K fertilization could reduce the bioavailable Cd content in soil, and the Cd content also decreased by 0.5–69.6% in P. notoginseng. Abbreviation: PNS: P. notoginseng saponins; F(EXC): Exchangeable fraction; F(Carb): Bound to carbonates fraction; F(Fe-MnOX): Bound to iron and manganese oxides fraction; F(OM): Bound to organic matter fraction; F(RES): Residual fraction; AK: Available potassium; TK: Total potassium; CEC: Cation exchange capacity; TOM: Total organic matter [ABSTRACT FROM AUTHOR]

Aims: Determine whether salicylic acid (SA) can alleviate the inhibitory effects of Al stress on dry matter accumulation in Panax notoginseng, and to investigate the mechanism by which the SA regulates photosynthesis and carbohydrate metabolism. Methods: Effects of SA on the biomass of P. notoginseng and the concentration of Al in leaves under Al stress were evaluated. SA and the scavenger paclobutrazol (PAC, SA synthetic inhibitor) were used to assess the effects of SA on photosynthesis and the metabolism of total nonstructural carbohydrates (TNC) in P. notoginseng. Results: SA reduced Al by 13.23% in the leaves of P. notoginseng under Al stress. It also promoted the synthesis of carbohydrates in the leaves and their transport to the roots. Additionally, SA alleviated the Al-induced reduction of chlorophyll (Chl) by upregulating the expression of Chl synthesis genes (CHLM, CHLG, HEMB1, HEMC, and HEME) and downregulating the degradation genes (CLH2 and PPH1). Concomitantly, the rubisco activase (RCA) and rubisco enzyme activities were promoted by upregulating the expressions of the RCA, rbcL, and rbcS genes via treatment with SA, thereby restoring the synthesis and metabolism of TNC. Furthermore, SA attenuated the decrease in photosynthetic capacity and photosynthesis system II photochemistry efficiency in Al-stressed plants. Furthermore, SA significantly reduced the H2O2 concentration by 12.22% under Al stress. Conclusions: By regulating photosynthesis-related genes and photochemical processes, SA promoted photosynthesis and enhanced leaf carbohydrate synthesis under Al stress. Thus, SA enhanced the production of P. notoginseng biomass, ultimately reducing the inhibitory effects of Al. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Dencichine is significantly correlated with the selenium content in P. notoginseng. • There is a significant correlation between dencichine and selenium content in soil. • Selenium promotes the accumulation of dencichine in P. notoginseng. • Dencichine increases the antioxidant capacity of P. notoginseng. • Dencichine improves the stress resistance of P. notoginseng. Abstract Dencichine is the main ingredient in Panax notoginseng, which is an herb that plays a key role in hemostasis. The biosynthesis of dencichine requires the participation of sulfur. Selenium and sulfur are congeners. The purpose of this study was to reveal if selenium participates in the synthesis of dencichine, and to determine whether dencichine plays a role in anti-stress effects. P. notoginseng and planting soil were sampled from different sites and subjected to selenium and dencichine determinations. Biosynthesis of dencichine was investigated by exposing the seedlings to different selenium concentrations in pot and hydroponic experiments. The effects of dencichine on the regulation of the antioxidant enzyme system and reactive oxygen species (ROS) were also tested in hydroponic experiments. The results indicated that the selenium and dencichine contents of roots were 0.69-0.98% and 0.21–1.18 mg kg−1, respectively, and the soil selenium content in 18 planting areas in Yunnan Province was 0.16-0.32 mg kg−1. Dencichine and selenium contents in soil or plants were positively correlated (R2 = 0.1643***, R2 = 0.3084***, respectively). Selenium treatment increased the dencichine content by 69–111% in pot experiments using 5 mg kg−1 and by 23–33% in hydroponic experiments using 2 μM. The key genes in the dencichine biosynthetic pathway, such as β-cyanoalanine synthase and serine acetyltransferase , were significantly upregulated by the 2 μM selenium treatment. Dencichine treatment (30 μM) significantly enhanced root activity, increased antioxidant capacity, decreased ROS content, and reduced lipid peroxidation of the cell membranes. Therefore, selenium promoted the synthesis of dencichine, which acted as an anti-stress agent in P. notoginseng. However, the selenium content was deficient in the P. notoginseng planting soil from Yunnan Province. These results suggest that appropriate selenium supplementation is beneficial for the growth and development of P. notoginseng and the accumulation of dencichine. [ABSTRACT FROM AUTHOR]

The mechanism of how potassium (K) attenuates cadmium (Cd)-induced demethylation and anabolism of cell wall (CW) pectin through the brassinolide (BR) signaling pathway was verified in Panax notoginseng (Burk.). The P. notoginseng pectin methylesterase gene (PnPME1) was cloned and functionally verified in tobacco. Pectin and BR metabolism, Cd content and the pectin methylation degree (PMD) were detected in response to K, 2,4-epibrassinolide (EBL), and brassinazole treatments of P. notoginseng and tobacco under Cd stress. Activity of the main root pectin methylesterase enzyme (PME) was promoted by 22.29% under the EBL treatment, and Cd content increased by 29.03% under Cd stress. Potassium reduced PME activity and Cd content in main root pectin by 61.03% and 50.73%, respectively, under the EBL and Cd co-treatment. Potassium inhibited the promoting effects of Cd stress on the expression of PnPME1 by 57.04%. Potassium also inhibited expression of BR synthesis genes PnDET2 , PnROT3 , PnCYP90A1 , and PnBR6OX1 by 65.61%, 52.02%, 47.36%, and 55.16%, respectively, and reduced the accumulation of Cd. The PnPME1 was located in the CW. The activity of transgenic tobacco root PME was higher than that of the wild-type, while the PMD was significantly lower. The regulatory effects of K and EBL on tobacco root pectin metabolism were consistent with those in P. notoginseng. In conclusion, K downregulated the expression of BR synthesis genes in P. notoginseng roots under Cd stress and reduced the production of BRs, which inhibited PnPME1 expression. The reduction in PME activity increased the PMD, which reduced the accumulation of Cd. [Display omitted] • Pectin with low degree of methylesterification is easier to bind cadmium. • Brassinosteroid regulates pectin methylesterase activity under cadmium stress. • Potassium reduces the accumulation of cadmium in the Panax notoginseng roots pectin. [ABSTRACT FROM AUTHOR]