Proline-rich protein PRPL1 enhances Panax notoginseng defence against Fusarium solani by regulating reactive oxygen species balance and strengthening the cell wall barrier.

The root rot mainly caused by Fusarium solani is a bottleneck in the cultivation of Panax notoginseng. In this study, we reported a gene encoding a plant cell wall structural protein, P. notoginseng proline-rich protein (PnPRPL1), whose transcription was upregulated by F. solani and induced by some hormone signals. The PnPRPL1 recombinant protein significantly inhibited the growth and conidial germination of the root rot pathogens. Downregulation of PnPRPL1 by RNA interference (RNAi) in P. notoginseng leaves increased the susceptibility to F. solani, whereas overexpression of PnPRPL1 in tobacco (Nicotiana tabacum) enhanced the resistance to F. solani. Compared with wild-type tobacco, the PnPRPL1-overexpressing transgenic tobacco had higher reactive oxygen species (ROS)-scavenging enzyme activities, lower ROS levels, and more lignin and callose deposition. The opposite results were obtained for the P. notoginseng expressing PnPRPL1 RNAi fragments. Furthermore, the PnPRPL1 promoter transcription activity was induced by several plant hormones and multiple stress stimuli. In addition, the transcription factor PnWRKY27 activated the expression of PnPRPL1 by directly binding to the promoter region. Thus, PnPRPL1, which is positively regulated by a WRKY transcription factor, encodes an antimicrobial protein that also mediates ROS homoeostasis and callose/lignin deposition during the response to F. solani infection.

Effects of different soil moisture on the growth, quality, and root rot disease of organic Panax notoginseng cultivated under pine forests.

The under-forest economy in the agroforestry system can improve land use efficiency, protect ecological environment, and promote arable land sustainable development. However, the effects of soil moisture in the forest and irrigation strategies on the healthy growth of intercropping crops are still incomplete. Here, considering the organic Panax notoginseng cultivated under pine forests (PPF) as the research object, we explored the effects of different soil moisture on the physiological state, yield, quality and disease occurrence of PPF. Our results suggested that 80-85% and 95-100% field capacity (FC) treatments were more conducive to increased photosynthetic rate and biomass accumulation of PPF, but 50-55% and 65-70% FC treatments were more conducive to the accumulation of saponins in PPF leaves. Notably, the root rot index of PPF was highest under 95-100% FC (19.51) treatment, significantly higher than that under 65-70% FC (8.44) and 80-85% FC (10.21) treatments. Further, the rhizosphere microorganisms of PPF under different soil moisture treatments were sequenced, and the sequencing data analysis revealed that high soil moisture (95-100% FC) could destroy the microbial diversity balance and cause the accumulation of pathogens (Fusarium oxysporum and Ilyonectria radicicola), leading to a high incidence of root rot. The incidence of PPF root rot was negatively correlated with rhizosphere microbial diversity. Overall, our results highlight that the quantitative irrigation (80-85% FC) is conducive to maintaining the balance between yield, saponin content and disease occurrence of PPF, providing a practical basis for PPF irrigation strategy and promoting the sustainable development of PPF agroforestry system.

High nitrogen inhibits photosynthetic performance in a shade-tolerant and N-sensitive species Panax notoginseng.

Nitrogen (N) is a primary factor limiting leaf photosynthesis. However, the mechanism of high-N-driven inhibition on photosynthetic efficiency and photoprotection is still unclear in the shade-tolerant and N-sensitive species such as Panax notoginseng. Leaf chlorophyll (Chl) content, Ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco) activity and content, N allocation in the photosynthetic apparatus, photosynthetic performance and Chl fluorescence were comparatively analyzed in a shade-tolerant and N-sensitive species P. notoginseng grown under the levels of moderate nitrogen (MN) and high nitrogen (HN). The results showed that Rubisco content, Chl content and specific leaf nitrogen (SLN) were greater in the HN individuals. Rubisco activity, net photosynthetic rate (Anet), photosynthetic N use efficiency (PNUE), maximum carboxylation rate (Vcmax) and maximum electron transport rate (Jmax) were lower when plants were exposed to HN as compared with ones to MN. A large proportion of leaf N was allocated to the carboxylation component under the levels of MN. More N was only served as a form of N storage and not contributed to photosynthesis in HN individuals. Compared with the MN plants, the maximum quantum yield of photosystem II (Fv/Fm), non-photochemical quenching of PSII (NPQ), effective quantum yield and electron transport rate were obviously reduced in the HN plants. Cycle electron flow (CEF) was considerably enhanced in the MN individuals. There was not a significant difference in maximum photo-oxidation P700+ (Pm) between the HN and MN individuals. Most importantly, the HN individuals showed higher K phase in the fast chlorophyll fluorescence induction kinetic curve (OJIP kinetic curve) than the MN ones. The results obtained suggest that photosynthetic capacity might be primarily inhibited by the inactivated Rubisco in the HN individuals, and HN-induced depression of photoprotection might be caused by the photodamage to the donor side of PSII oxygen-evolving complex.

Photosynthetic performance and photosynthesis-related gene expression coordinated in a shade-tolerant species Panax notoginseng under nitrogen regimes.

BACKGROUND: Nitrogen (N) is an essential component of photosynthetic apparatus. However, the mechanism that photosynthetic capacity is suppressed by N is not completely understood. Photosynthetic capacity and photosynthesis-related genes were comparatively analyzed in a shade-tolerant species Panax notoginseng grown under the levels of low N (LN), moderate N (MN) and high N (HN). RESULTS: Photosynthetic assimilation was significantly suppressed in the LN- and HN-grown plants. Compared with the MN-grown plants, the HN-grown plants showed thicker anatomic structure and larger chloroplast accompanied with decreased ratio of mesophyll conductance (gm) to Rubisco content (gm/Rubisco) and lower Rubisco activity. Meanwhile, LN-grown plants displayed smaller chloroplast and accordingly lower internal conductance (gi). LN- and HN-grown individuals allocated less N to light-harvesting system (NL) and carboxylation system (NC), respectively. N surplus negatively affected the expression of genes in Car biosynthesis (GGPS, DXR, PSY, IPI and DXS). The LN individuals outperformed others with respect to non-photochemical quenching. The expression of genes (FBA, PGK, RAF2, GAPC, CAB, PsbA and PsbH) encoding enzymes of Calvin cycle and structural protein of light reaction were obviously repressed in the LN individuals, accompanying with a reduction in Rubisco content and activity. Correspondingly, the expression of genes encoding RAF2, RPI4, CAB and PetE were repressed in the HN-grown plants. CONCLUSIONS: LN-induced depression of photosynthetic capacity might be caused by the deceleration on Calvin cycle and light reaction of photosynthesis, and HN-induced depression of ones might derive from an increase in the form of inactivated Rubisco.

Pesticide residues in soils planted with Panax notoginseng in south China, and their relationships in Panax notoginseng and soil.

In this study, 73 samples from soils planted with Panax notoginseng and six P. notoginseng samples were collected in Yunnan Province to investigate the residual levels of six pesticides and their relationships with P. notoginseng and soil. All six pesticides were detected in the soils planted with P. notoginseng located in three regions of Shilin, Kaiyuan, and Yanshan. The detection frequencies of the pesticides in the soils followed the order: quintozene (100%) > iprodione (96%) > procymidone (69%) > chlorothalonil (51%) > pyrimethanil (49%) > pyraclostrobin (29%). The median concentrations of iprodione, pyraclostrobin, pyrimethanil, quintozene, procymidone, and chlorothalonil were 46.40, 6.4, 3.1, 2.86, 2.69, and 0.24 µg/kg, respectively. The mean concentrations of pesticides in the three regions followed the order: Kaiyuan > Shilin > Yanshan, except for iprodione. Furthermore, the concentrations of pesticide residues in soils in each region followed the order: soils never planted with P. notoginseng < soils previously planted with P. notoginseng < soils currently planted with P. notoginseng. The concentration of chlorothalonil in P. notoginseng followed the order: root > stem > leaf, whereas those of the other five pesticides followed the opposite order: root < stem < leaf. There were significant positive correlations between the mean concentrations of pesticides in P. notoginseng and those in the corresponding soils. These results indicate that the rational application of pesticides in P. notoginseng cultivation would be effective for reducing the accumulation of pesticides in P. notoginseng to protect people from the harmful effects of residual pesticides.

Comparative transcriptome and metabolome analyses provide new insights into the molecular mechanisms underlying taproot thickening in Panax notoginseng.

BACKGROUND: Taproot thickening is a complex biological process that is dependent on the coordinated expression of genes controlled by both environmental and developmental factors. Panax notoginseng is an important Chinese medicinal herb that is characterized by an enlarged taproot as the main organ of saponin accumulation. However, the molecular mechanisms of taproot enlargement are poorly understood. RESULTS: A total of 29,957 differentially expressed genes (DEGs) were identified during the thickening process in the taproots of P. notoginseng. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment revealed that DEGs associated with "plant hormone signal transduction," "starch and sucrose metabolism," and "phenylpropanoid biosynthesis" were predominantly enriched. Further analysis identified some critical genes (e.g., RNase-like major storage protein, DA1-related protein, and Starch branching enzyme I) and metabolites (e.g., sucrose, glucose, fructose, malate, and arginine) that potentially control taproot thickening. Several aspects including hormone crosstalk, transcriptional regulation, homeostatic regulation between sugar and starch, and cell wall metabolism, were identified as important for the thickening process in the taproot of P. notoginseng. CONCLUSION: The results provide a molecular regulatory network of taproot thickening in P. notoginseng and facilitate the further characterization of the genes responsible for taproot formation in root medicinal plants or crops.

Reductive soil disinfestation effectively alleviates the replant failure of Sanqi ginseng through allelochemical degradation and pathogen suppression.

Replant failure has threatened the production of Sanqi ginseng (Panax notoginseng) mainly due to the accumulation of soil-borne pathogens and allelochemicals. Reductive soil disinfestation (RSD) is an effective practice used to eliminate soil-borne pathogens; however, the potential impact of RSD on the degradation of allelochemicals and the growth of replant Sanqi ginseng seedlings remain poorly understood. In this study, RSD was conducted on a Sanqi ginseng monoculture system (SGMS) and a maize-Sanqi ginseng system (MSGS), defined as SGMS_RSD and MSGS_RSD, respectively. The aim was to investigate the impact of RSD on allelochemicals, soil microbiomes, and survival rates of replant seedlings. Both short-term maize planting and RSD treatment significantly degraded the ginsenosides in Sanqi ginseng-cultivated soils, with the degradation rate being higher in the RSD treatment. The population of Fusarium oxysporum and the relative abundance of genus Fusarium were dramatically suppressed by RSD treatment. Furthermore, the RSD treatment, but not maize planting, markedly alleviated the replant failure of Sanqi ginseng, with the seedling survival rate being 52.7-70.7% 6 months after transplanting. Interestingly, RSD followed by short-term maize planting promoted microbial activity restoration, ginsenoside degradation, and ultimately alleviated the replant failure much better than RSD treatment alone (70.7% vs. 52.7%). Collectively, these results indicate that RSD treatment could considerably reduce the obstacles and might also act as a potential agriculture regime for overcoming the replant failure of Sanqi ginseng. Additional practices, such as crop rotation, beneficial microorganism inoculation, etc. may also still be needed to ensure the long-term efficacy of seedling survival.

Role of Phenolic Acids from the Rhizosphere Soils of Panax notoginseng as a Double-Edge Sword in the Occurrence of Root-Rot Disease.

Chemical agents in the rhizosphere soils of plants might have an influence on root-rot disease, which therefore might reveal the mechanism of root rot in Panax notoginseng (P. notoginseng). With this hypothesis the alterations of phenolic acids (PAs) in the rhizosphere soils of P. notoginseng after pathogen infection were determined. The effects of PAs on the growth of Fusarium oxysporum (F. oxysporum), a fungal pathogenic factor for P. notoginseng, as well as production of fusaric acid, a wilting agent for the plants, were also examined. The results indicate the presence of five PAs (ferulic acid, syringic acid, p-hydroxybenzoic acid, p-coumaric acid, and vanillic acid) in the rhizosphere soils of P. notoginseng, whose contents in the rhizosphere soils of healthy plants are higher than those of the diseased ones. Further we found that individual PA could inhibit the mycelium growth and spore production of F. oxysporum, but stimulate fusaric acid production as well, disclosing the double-edge sword role of PAs in the occurrence of root rot of P. notoginseng and paving the way for the intervention of P. notoginseng root rot via balancing PAs.

[Effect of different water conditions on Panax notoginseng seeds after-ripening and germination physiology].

Effect of different water conditions on the physiological indexes (e.g.seed water content, vigor, antioxidase activities)of Panax notoginseng seeds were studied under process of after-ripening and germination.The results showed show that compared with 2.5% treatment, under the treatment of 5%, P.notoginseng seeds possessed stable seed water content, the seed vigor was exceed by 51%,variation of antioxidant enzyme (SOD, POD, CAT) activity and malondialdehyde (MDA) content were small, crude fat and total sugar content decreased significantly.With the increase of PEG 6000 concentration, the germination characteristic indexes obviously decreased, antioxidase activities increased firstly and decreased afterwards, content of MDA, soluble protein and total sugar increased obviously.There were significant positive correlation between germination characteristic indexes and osmotic substance content(r>0.900, P<0.01), and significant negative correlation with MDA (r>0.900, P<0.01).In conclusion, because the characteristic of dehydration intolerance of P.notoginseng seeds, 5% water content of sand burying stratification treatment was the best for after-ripening, 15% concentration of PEG 6000 treatment was the highest tolerance limit of germination process.

[Effect of Panax notoginseng seedlings physiological response under simulated drought stress by polyethylene glycol (PEG 6000)].

The physiological effects of Panax notoginseng seedlings under simulated drought stress by PEG 6000 on antioxidant enzymes, osmotic substances and root activities were studied. The results showed that the activity of POD and APX in roots and leaves kept rising with increasing processing concentration and time. However, on the one hand, at the same processing time, SOD in roots and leaves firstly increased and then decreased with the increase of processing concentration. On the other hand, at the same processing concentration, SOD kept rising with the extension of processing time. In addition, the activity of CAT in roots and leaves tended to increase with the increasing concentration at the same processing time, while it increased at first and then decreased with the extension of time at the same concentration. The activity of SOD and APX in stem did not change obviously, whereas CAT activity in stem increased with the increasing processing time and concentration. With the increase of processing concentration and the extension of processing time, the MDA, soluble protein, proline content and root activity in leaves and roots apparently rose. Moreover, fluorescence signal of H2O2 and NO in root tip enhanced as the processing concentration increased after treated for 1 d. In summary, P. notoginseng seedlings could deal with drought stress by means of adjusting the system of antioxidant enzyme, permeating stress substances and impeded stress signal substances. Thus, when the concentration of PEG 6000 was more than 5%, it would have harm on P. notoginseng seedlings.

[Effects of balanced fertilization and soil amendment on growth and yield of sanqi in continuous cropping].

OBJECTIVE: To explore the solution of continuous cropping obstacle of Panax notoginseng. METHOD: The effects of balanced fertilization and soil amendment on the emergence rate, survival rate, growth and yield of P. notoginseng were studied with a pot culture experiment in 3-year-interval continuous cropping soil. RESULT: The result showed that the content of total N, total P, available N, available P and other available components in continuous cropping soil were higher than those in fresh soil while available K and the rate of K/N were declined, and available Cu and some other micro elements were lack. The way of balanced fertilization "low N + fused calcium-magnesium-phosphate fertilizer + high K + lime + micro elements" would significantly enhance the rate of survival, biomass and yield. It also promoted the growth of P. notoginseng in continuous cropping. The bagasse could relieve the continuous cropping obstacle obviously, the survival rate was improved for 31.6% and the yield of medicinal materials was 19.5%. The fly ash had also some effect in relieving the continuous cropping obstacle. CONCLUSION: The overall results suggested that the adequate fertilization plan is the applying lime, reducing N, applying calcium-magnesium-phosphate fertilizer, improving K and supplying mircoelement as well as applying bagasse to resolve the problem of continuous cropping obstacle of P. notoginseng.

[Breeding strains of Panax notoginseng by using EST-SSR markers].

OBJECTIVE: To comparatively determine the genetic variation and differentiation of different breeding strains of Panax notoginseng for providing the basic information for genetic breeding. METHOD: The genetic diversity and genetic structure of the 17 breeding strains of P. notoginseng were assayed by using EST-SSR molecular marker. RESULT: A total of 136 polymorphic loci of EST-SSR were detected in the 17 breeding strains of P. notoginseng, with the PIC (polymorphism information content) being 0.78, H (the gene diversity within population) being 0.139, the I (the Shannon's information index) being 0.208. Gst (coefficient of gene differentiation) was 0.382 among the 17 strains. The cluster analysis of genetic similarity showed that the 17 strains of P. notoginseng and P. stipuleanatus were classified into 4 groups, while the 17 strains of P. notoginseng were classified into three subgroups. CONCLUSION: The genetic differentiation was detected among the 17 strains of P. notoginseng from the same cultivation population by bulk selecting. And it was feasible to detect the effect of bulk selection by EST-SSR markers.

Effects of calcium application on activities of membrane transporters in Panax notoginseng under cadmium stress.

Pot experiments were conducted to study combined effects of Ca and Cd on contents of Cd and Ca, and membrane transporters activities (CC (calcium channel protein), ATPase and CAXs (cationic/H+ antiporter) of two-year old Panax notoginseng with application of different concentrations of Ca2+ (0, 180 and 360 mgkg-1, prepared by Ca(OH)2 and CaCl2, respectively) under Cd2+ (0, 0.6, 6.0, and 12.0 mgkg-1, prepared by CdCl2•2.5H2O) treatments. The results showed that soil available Cd contents decreased with Ca(OH)2 and CaCl2 application. Soil pH value increased with Ca(OH)2 application. The contents of Cd in all parts of P. notoginseng increased with the increase in Cd treatment concentrations. The Cd content of P. notoginseng decreased with Ca(OH)2 and CaCl2 treatments. The activities of CC and ATPase in the main root of P. notoginseng decreased with the increase in Cd treatment concentrations and application of CaCl2. The activities of CC and ATPase increased with Ca(OH)2application. The activity of CAXs in the main root of P. notoginseng increased with the increase of Cd treatment concentration. The results indicate that Ca and Cd should be both related to membrane transporters activities and activities of CC, ATPase and CAXs are promoted by cooperation of Ca2+and OH+, which suggest the Ca(OH)2 application should be better than application of CaCl2 for Cd detoxification.

[Physiologic characteristics of Panax notoginseng seeds during after-ripening process].

OBJECTIVE: The studies were carried out on the physiologic characteristics of Panax notoginseng seeds during the after--ripening process in order to understand the seed's biochemical and physiological changes and lay the foundation for the germplasm conversation and breeding research of P. notoginseng seeds. METHOD: Dynamic changes of storage material contents, respiratory rate and protective enzymatic activity were determined by normal biochemical and physiological measuring methods. RESULT: The respiratory rate increased continuously during the stratification process, the contents of starch, soluble protein, crude fat decreased and the content of water-soluble saccharide increased with the embryo development, activities of CAT, POD and SOD increased with the raise of MDA content. CONCLUSION: P. notoginseng seed's biochemical and physiological changes interacted with its embryo morphological changes to complete its after-ripening development.

[Effects of light intensity on photosynthetic capacity and light energy allocation in Panax notoginseng.] / å ‰å¼ºå¯¹ä¸‰ä¸ƒå ‰åˆèƒ½åŠ›åŠèƒ½é‡åˆ†é çš„å½±å“.

To explore the effects of light intensity on photosynthetic characteristics and light adaptation of the shade-demanding species Panax notoginseng, the responses of photosynthesis to photosynthetic photon flux density, CO2 and sunflecks in the two-year-old Panax notoginseng were investigated under different levels of light intensity (29.8%, 9.6%, 5.0%, 1.4% and 0.2% of full sunlight). Meanwhile, chlorophyll a fluorescence parameter and light energy partitioning were also recorded and calculated in the responsive process. P. notoginseng grown under 29.8% full sunlight (FL) had a lower apparent quantum yield (AQY), potential photochemical quantum yield (Fv/Fm) and potential photochemical activity (Fv/Fo), however, it had a higher maximum net photosynthetic rate (Pn max), maximum electron transport rate (Jmax), F/Fm', electron transport rate (ETR), photochemical quenching (qP) and the proportion of light energy allocated to photochemistry dissipation (ΦPS2), but the non-photochemical quenching (NPQ) was not the highest. There were no significant differences in Pn max, light compensation point (LCP), light saturation point (LSP), dark respiration rate (Rd) among 9.6%FL and 5.0% FL treatments, but these treatments had relatively higher values of NPQ, AQY, carboxylation efficiency (CE), maximum carboxylation rate (Vc max), Fv/Fm and Fv/Fo. In addition, the Pn max, CE, Vc max, Jmax, ETR,F/Fm', qP, NPQ and ΦPSII decreased with the decrease in light intensity from 5.0%FL to 0.2%FL, and the proportion of light energy allocated to fluorescent dissipation (Φf,d) were increased. Under 500 µmol·m-2·s-1 light-flecks inducting, the ΦPSⅡof P. notoginseng increased slowly with the extension of time except for the treatment of less than 5.0%FL, and under the circumstance of 1.4%FL and 0.2%FL, ΦPSⅡreached significantly a perfect result, moreover, Φf,dincreased rapidly. These results suggested that the enhancement in photosynthetic electron transport to use the light energy and the moderate photoinhibition of PS2 might avoid the irreversible oxidative damage of photosynthetic organization in P. notoginseng under high levels of light intensity. Moderate shading was beneficial to maintain its higher non-photochemical quenching ability. However, its photosynthetic capacity depressed and the proportion of light energy allocated to non-photochemical pathway increased obviously in excessive shading, and it easily caused a light oxidative damage.

[In vitro studies on asexual embryos and regenerated plantlets obtained from leaf organ of Panax notoginseng].

OBJECTIVE: To study and improve the tissue culture technology of Panax notoginseng. METHOD: Using the callus of leaf blade and leafstalk of P. notogingseng as explants, MS + 2, 4-D 1.5 mg x L(-1) as basal medium, the formation of asexual embryos was induced by added LFS, BA, KT or ZT 0.5 mg x L(-1), and cultured in dark. It cultured then in 2000 lx of illumination for 10-12 h x d(-1) to induce the asexual embryos germinating and developing to be the regenerated-plantlet. RESULT AND CONCLUSION: Only the medium added with LFS could induce the formation of asexual embryos, and made it developed to be regenerated-plantlet. The inducing ratio of asexual embryos reached about 85%, and 30% of asexual embryos could grow and develop as robust regenerated-plantlets.

Soil bacterial and fungal community dynamics in relation to Panax notoginseng death rate in a continuous cropping system.

Notoginseng (Panax notoginseng), a valuable herbal medicine, has high death rates in continuous cropping systems. Variation in the soil microbial community is considered the primary cause of notoginseng mortality, although the taxa responsible for crop failure remains unidentified. This study used high-throughput sequencing methods to characterize changes in the microbial community and screen microbial taxa related to the death rate. Fungal diversity significantly decreased in soils cropped with notoginseng for three years. The death rate and the fungal diversity were significantly negatively correlated, suggesting that fungal diversity might be a potential bioindicator of soil health. Positive correlation coefficients revealed that Burkholderiales, Syntrophobacteraceae, Myrmecridium, Phaeosphaeria, Fusarium, and Phoma were better adapted to colonization of diseased plants. The relative abundance of Fusarium oxysporum (R = 0.841, P < 0.05) and Phaeosphaeria rousseliana (R = 0.830, P < 0.05) were positively associated with the death rate. F. oxysporum was a pathogen of notoginseng root-rot that caused seedling death. Negative correlation coefficients indicated that Thermogemmatisporaceae, Actinosynnemataceae, Hydnodontaceae, Herpotrichiellaceae, and Coniosporium might be antagonists of pathogens, and the relative abundance of Coniosporium perforans was negatively correlated with the death rate. Our findings provide a dynamic overview of the microbial community and present a clear scope for screening beneficial microbes and pathogens of notoginseng.

Nitrate reductase-mediated NO production enhances Cd accumulation in Panax notoginseng roots by affecting root cell wall properties.

Panax notoginseng (Burk) F. H. Chen is a traditional medicinal herb in China. However, the high capacity of its roots to accumulate cadmium (Cd) poses a potential risk to human health. Although there is some evidence for the involvement of nitric oxide (NO) in mediating Cd toxicity, the origin of Cd-induced NO and its function in plant responses to Cd remain unknown. In this study, we examined NO synthesis and its role in Cd accumulation in P. notoginseng roots. Cd-induced NO production was significantly decreased by application of the nitrate reductase inhibitor tungstate but not the nitric oxide synthase inhibitor L-NAME (N(G)-methyl-l-arginine acetate), indicating that nitrate reductase is the major contributor to Cd-induced NO production in P. notoginseng roots. Under conditions of Cd stress, sodium nitroprusside (SNP, an NO donor) increased Cd accumulation in root cell walls but decreased Cd translocation to the shoot. In contrast, the NO scavenger cPTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) and tungstate both significantly decreased NO-increased Cd retention in root cell walls. The amounts of hemicellulose 1 and pectin, together with pectin methylesterase activity, were increased with the addition of SNP but were decreased by cPTIO and tungstate. Furthermore, increases or decreases in hemicellulose 1 and pectin contents as well as pectin methylesterase activity fit well with the increased or decreased retention of Cd in the cell walls of P. notoginseng roots. The results suggest that nitrate reductase-mediated NO production enhances Cd retention in P. notoginseng roots by modulating the properties of the cell wall.

Autotoxic ginsenosides in the rhizosphere contribute to the replant failure of Panax notoginseng.

BACKGROUND AND AIMS: Sanqi ginseng (Panax notoginseng) growth is often hampered by replant failure. In this study, we aimed to examine the role of autotoxicity in Sanqi replant failures and assess the role of ginsenosides in autotoxicity. METHODS: The autotoxicities were measured using seedling emergence bioassays and root cell vigor staining. The ginsenosides in the roots, soils, and root exudates were identified with HPLC-MS. RESULTS: The seedling emergence and survival rate decreased significantly with the continuous number of planting years from one to three years. The root exudates, root extracts, and extracts from consecutively cultivated soils also showed significant autotoxicity against seedling emergence and growth. Ginsenosides, including R1, Rg1, Re, Rb1, Rb3, Rg2, and Rd, were identified in the roots and consecutively cultivated soil. The ginsenosides, Rg1, Re, Rg2, and Rd, were identified in the root exudates. Furthermore, the ginsenosides, R1, Rg1, Re, Rg2, and Rd, caused autotoxicity against seedling emergence and growth and root cell vigor at a concentration of 1.0 µg/mL. CONCLUSION: Our results demonstrated that autotoxicity results in replant failure of Sanqi ginseng. While Sanqi ginseng consecutively cultivated, some ginsenosides can accumulate in rhizosphere soils through root exudates or root decomposition, which impedes seedling emergence and growth.