Integrative Analysis of the Transcriptome and Metabolome Reveals the Mechanism of Saline–Alkali Stress Tolerance in Astragalus membranaceus (Fisch) Bge. var. mongholicus (Bge.) Hsiao

Saline–alkali stress is a major abiotic stress affecting the quality and yield of crops. Astragalus membranaceus (Fisch) Bge. var. mongholicus (Bge.) Hsiao (A. mongholicus) is a well-known medicine food homology species with various pharmacological effects and health benefits that can grow well in saline–alkali soil. However, the molecular mechanisms underlying the adaptation of A. mongholicus plants to saline–alkali stress have not yet been clarified. Here, A. mongholicus plants were exposed to long-term saline–alkali stress (200 mmol·L -1 mixed saline–alkali solution), which limited the growth of A. mongholicus. The roots of A. mongholicus could resist long-term saline–alkali stress by increasing the activity of antioxidant enzymes and the content of osmolytes. Transcriptome analysis (via the Illumina platform) and metabolome analysis (via the Nexera UPLC Series QE Liquid Mass Coupling System) revealed that saline–alkali stress altered the activity of various metabolic pathways (e.g., amino acid metabolism, carbohydrate metabolism, lipid metabolism, and biosynthesis of other secondary metabolites). A total of 3,690 differentially expressed genes (DEGs) and 997 differentially accumulated metabolites (DAMs) were identified in A. mongholicus roots under saline–alkali stress, and flavonoid-related DEGs and DAMs were significantly up-regulated. Pearson correlation analysis revealed significant correlations between DEGs and DAMs related to flavonoid metabolism. MYB transcription factors might also contribute to the regulation of flavonoid biosynthesis. Overall, the results indicate that A. mongholicus plants adapt to saline–alkali stress by up-regulating the biosynthesis of flavonoids, which enhances the medicinal value of A. mongholicus.

Ionomic and Metabolomic Analyses Reveal Different Response Mechanisms to Saline–Alkali Stress Between Suaeda salsa Community and Puccinellia tenuiflora Community

Soil salinization imposes severe stress to plants, inhibits plant growth, and severely limits agricultural productivity and land utilization. The response of a single plant to saline-alkali stress has been well investigated. However, the plant community that usually works as a group to defend against saline–alkali stress was neglected. To determine the functions of plant community, in our current work, Suaeda salsa (S. salsa) community and Puccinellia tenuiflora (P. tenuiflora) community, two communities that are widely distributed in Hulun Buir Grassland in Northeastern China, were selected as research objects. Ionomic and metabolomic were applied to compare the differences between S. salsa community and P. tenuiflora community from the aspects of ion transport and phenolic compound accumulation, respectively. Ionomic studies demonstrated that many macroelements, including potassium (K) and calcium (Ca), were highly accumulated in S. salsa community whereas microelement manganese (Mn) was highly accumulated in P. tenuiflora community. In S. salsa community, transportation of K to aboveground parts of plants helps to maintain high K+ and low Na+ concentrations whereas the accumulation of Ca triggers the salt overly sensitive (SOS)-Na+ system to efflux Na+. In P. tenuiflora community, enrichment of Mn in roots elevates the level of Mn-superoxide dismutase (SOD) and increases the resistance to saline–alkali stress. Metabolomic studies revealed the high levels of C6C1-compounds and C6C3C6-compounds in S. salsa community and also the high levels of C6C3-compounds in P. tenuiflora community. C6C1-compounds function as signaling molecules to defend against stress and may stimulate the accumulation of C6C3C6-compounds. C6C3-compounds contribute to the elimination of free radicals and the maintenance of cell morphology. Collectively, our findings determine the abundance of phenolic compounds and various elements in S. salsa community and P. tenuiflora community in Hulun Buir Grassland and we explored different responses of S. salsa community and P. tenuiflora community to cope with saline–alkali stress. Understanding of plant response strategies from the perspective of community teamwork may provide a feasible and novel way to transform salinization land.

Metabolic Differences Between Suaeda Salsa and Puccinellia Tenuiflora Under Saline-alkali Stress

Background: Salinization of soil is an urgent problem that restricts agroforestry production and environment protection. Substantial accumulation of metal ion or high alkaline alters plant metabolites and may even cause plant death. In order to explore the differences in the response strategies between Suaeda salsa (S. salsa) and Puccinellia tenuiflora (P. tenuiflora), two main constructive species that survive in saline-alkali soil, their metabolic differences were characterized.Result: Metabolomics was conducted to study the role of metabolic differences between S. salsa and P. tenuiflora under saline-alkali stress. A total of 68 significantly different metabolites were identified by GC-MS, including 9 sugars, 13 amino acids, 8 alcohols, and 34 acids. A more detailed analysis indicated that P. tenuiflora utilizes sugars more effectively and may be salt-alkali tolerant via sugar consumption while S. salsa mainly utilizes amino acids, alcohols, and acids to resist salt-alkali stress. Measurement of phenolic compounds showed that more C6C3C6-compounds were accumulated in P. tenuiflora while more C6C1-compounds, phenolic compounds that can be used to defense stress as signaling molecules, were accumulated in S. salsa.Conclusion: Our observations suggest that S. salsa resists the toxicity of saline-alkali stress using aboveground organs and P. tenuiflora eliminates the poison of saline-alkali via roots. S. salsa has a stronger ability of habitat transformation and can provide better habitat for other plants.

Exogenous Spermidine Priming Mitigates the Osmotic Damage in Germinating Seeds of Leymus chinensis Under Salt-Alkali Stress

Spermidine (Spd) is known to protect macromolecules involved in physiological and biochemical processes in plants. However, it is possible that Spd also plays an osmotic regulatory role in promoting the seed germination of Leymus chinensis (L. chinensis) under salt-alkali stress. To investigate this further, seeds of L. chinensis were soaked in Spd solution or distilled water, and a culture experiment was performed by sowing the soaked seeds in saline-alkaline soils. The data showed that the Spd priming resulted in an increase of more than 50% in soluble sugar content and an increase of more than 30% in proline content in the germinating seeds. In addition, the Spd priming resulted in an increase of more than 30% in catalase activity and an increase of more than 25% in peroxidase activity in the germinating seeds and effectively mitigated the oxidative damage to the plasma membrane in the germinating seeds under salt-alkali stress. Moreover, the Spd priming of seeds affected the accumulation of polyamine (PA) and maintained the activities of macromolecules involved in physiological metabolism in germinating seeds exposed to salt-alkali stress. Furthermore, the Spd priming treatment increased the hydrogen peroxide (H2O2) level to more than 30% and the Ca2+ concentration to more than 20% in the germinating seeds, thus breaking the dormancy induction pathways in L. chinensis seeds through beneficial hormone enrichment. This study provides an insight into the Spd-mediated regulation pathway during exogenous Spd priming of L. chinensis seeds, which mitigates osmotic and oxidative damage and maintains the integrality of the cell lipid membrane. Thus, exogenous Spd priming increases PA oxidase activity and maintains the accumulation of H2O2. We found that the H2O2 beneficially affected the balance of Ca2+ and hormones, promoting the vigor and germination of L. chinensis in response to salt-alkali stress.

Effects of Water and Salt Movement On Photosynthetic Production Characteristics and Yield Formation of Cotton On Coastal Saline Land

Background In order to study the effects of spatial distribution and yearly migration variations of soil water and salt in coastal saline land on photosynthetic production and yield formation of cotton, spatial distribution characteristics of water content, salinity, and pH in soil at 0–200 cm depths in 3 cotton fields that were similar in locality but differed markedly in degree of salinization were determined in April through October, and photosynthetic characteristics and photosynthate accumulation of cotton were also determined. Results The study shows that, the slightly salinized cotton field had lower soil salinity and pH, where soil water content was lower in rainy season (July–August), and at the late reproductive stage (September–October), soil water content was markedly higher than that in the moderately salinized cotton field, where cotton suffered smaller salt-alkali stress, photosynthetic production matched well with hydrothermal resource, the sink organ had a long photosynthate accumulation time and was at the active material accumulation stage for a long time; salt-alkali stress to the moderately salinized cotton field was relieved in rainy season, but at the early reproductive stage (April–June) and the late reproductive stage of cotton, salt-alkali stress remained evident, and photosynthetic production fit more poorly with the rich photothermal resource stage; the severely salinized cotton field subjected to prolonged high salt-alkali stress resulted in low levels of photosynthetic production capacity and yield. Conclusions For the severely salinized cotton field, salt inhibition and other relevant agronomic actions should be taken with greater efforts; for the moderately salinized cotton field, water and fertilizer management should be tightened at the early reproductive stage of cotton; for the slightly salinized cotton field, high-quality efficient cotton production should be developed.

Uniform Water Potential Induced by Salt, Alkali, and Drought Stresses Has Different Impacts on the Seedling of Hordeum jubatum: From Growth, Photosynthesis, and Chlorophyll Fluorescence

Hordeum jubatum is a halophyte ornamental plant wildly distributed in the Northeast of China, where the low water potential induced by various abiotic stresses is a major factor limiting plant growth and development. However, little is known about the comparative effects of salt, alkali, and drought stresses at uniform water potential on the plants. In the present study, the growth, gas exchange parameters, photosynthetic pigments, and chlorophyll fluorescence in the seedlings of H. jubatum under three low water potentials were measured. The results showed that the growth and photosynthetic parameters under these stresses were all decreased except for carotenoid (Car) with the increasing of stress concentration, and alkali stress caused the most damaging effects on the seedlings. The decreased net photosynthetic rate (Pn), stomatal conductance (Gs), and intercellular CO2 concentrations (Ci) values under salt stress were mainly attributed to stomatal factors, while non-stomatal factors were dominate under drought and alkali stresses. The reduced chlorophyll and slightly increased Car contents occurred under these stresses, and most significant changed under alkali stress. In addition, the maximum photochemical efficiency (Fv/Fm), actual photochemical efficiency (ΦPSII), and photochemical quenching coefficient (qP) under the stresses were all decreased, indicating that salt, alkali, and drought stresses all increased susceptibility of PSII to photoinhibition, reduced the photosynthetic activity by the declined absorption of light for photochemistry, and increased PSII active reaction centers. Moreover, the non-photochemical quenching coefficient (NPQ) of alkali stress was different from salt and drought stresses, showing that the high pH of alkali stress caused more damaging effects on the photoprotection mechanism depending on the xanthophyll cycle. The above results suggest that the H. jubatum has stronger tolerance of salt than drought and alkali stresses, and the negative effects of alkali stress on the growth and photosynthetic performance of this species was most serious.