Transcriptomic and Metabolomic Profiling Reveals Differential Responses of Soybean Germination to Neutral and Alkaline Salt Stresses

Bermudagrass (Cynodon dactylon), a salt-tolerant species surviving in environments with pH up to 9.3, and it exhibits variable germination responses under salt and alkaline stress. This study evaluates the impact of neutral and alkali salts with varying pH levels on bermudagrass seed germination. Six bermudagrass germplasm accessions were analyzed using neutral (NaCl: Na2SO4 = 1:1, pH 6.12–7.14) and alkali (NaHCO3:Na2CO3 = 1:1, pH 9.62–9.90) salt treatments. Salt concentrations ranged from 0 to 250 mmol/L, with increments of 25 mmol/L. The assessed parameters included seed germination rate, germination potential, germination index, radicle length, plumule length, seedling weight, and radicle and plumule length ratio. The salt tolerance threshold of each germplasm was calculated using a linear regression fitting model. Critical indicators of salt tolerance were selected through stepwise regression, and the salt-alkali tolerance ranking was determined using a combined membership function and discriminant analysis. The results indicated that the total score decreased with increasing salt concentration under neutral salt stress. Alkali salt stress was more damaging to bermudagrass seedlings than neutral salt stress, inhibiting germination at 50 mmol/L. Neutral salt tolerance thresholds ranged from 31.7 to 207.7 mmol/L, while alkaline salt tolerance thresholds ranged from 16.9 to 53.3 mmol/L. The six germplasm accessions exhibited different responses to salt and alkali stress. Key indicators for neutral salt tolerance included plumule length, radicle and plumule length ratio, and seedling weight. For alkali salt tolerance, key indicators were germination potential, radicle length, and seedling weight, which can be used to screen for resistant germplasms. Our study demonstrates that alkaline salts inhibit seed germination and seedling growth more than neutral salts, and pH affects root growth and the radicle-to-plumule length ratio in seedlings. This research has significant ecological implications, providing insights into the adaptation strategies of bermudagrass in salt-affected and alkaline environments, which could aid in the restoration and management of degraded ecosystems.

Differences in growth, ionomic and antioxidative enzymes system responded to neutral and alkali salt exposure in halophyte Haloxylon ammodendron seedlings.

Variable climatic conditions frequently have harmful effects on plants. Reaumuria trigyna, a salt-secreting xerophytic shrub, occurs in Inner Mongolia, which has a poor environment for plant growth. To explore the physiological and molecular mechanisms of R. trigyna in response to environmental stress, this study investigated the abiotic resistance of R. trigyna in terms of growth regulation, antioxidant defense, osmotic regulation, ion transport, and ion homeostasis-related genes. R. trigyna seedlings were treated with 400 mM NaCl, 400 mM neutral salts (NaCl:Na2SO4 = 9:1), 50 mM alkaline salts (NaHCO3:Na2CO3 = 9:1), 10% polyethylene glycol (PEG), and UV-B. Seedlings under 400 mM NaCl and 400 mM neutral salt stress showed less damage. While alkaline salt, PEG, and UV stress caused more damage, specifically in oxidative damage, proline levels, electrolyte leakage, and activation of antioxidant defenses. Furthermore, under the abiotic stress treatments, the accumulation of Na+ increased while the accumulation of K+ decreased. Further analysis showed that the flow rate of Na+ and K+ under alkaline salt stress was higher than under neutral salt stress. Neutral salt induced high expression of RtNHX1 and RtSOS1, while alkaline salt induced high expression of RtHKT1, and alkaline salt stress significantly reduced the activity of root cells. These results indicated that R. trigyna seedlings were more tolerant to neutral than alkaline salts; this might be because root activity decreased at high pH levels, which impaired membrane permeability and the ion transfer system, leading to an imbalance between Na+ and K+, and in turn to excessive accumulation of reactive oxygen species (ROS) and decreased plant stress resistance.

Salinity and alkalinity stress are two major constraints on plant growth and crop production, limiting sustainable agricultural production. Wheat is a vital cereal crop. It is very important to ensure food security; however, its growth and yield are usually adversely affected by salinity and alkalinity stress. To investigate the differential effects of neutral and alkaline salt stress on the seedling growth of wheat, we set wheat hydroponic culture experiment: CK, neutral salt (NaCl:Na2SO4 = 9:1 pH = 6.5), neutral salt with high pH value (NaCl:Na2SO4 = 9:1 pH = 8.9), alkaline salt (NaHCO3:Na2CO3 = 9:1 pH = 8.9), all treatments at the same Na+ concentration. The results indicated alkaline salt inhibited seedling growth more than neutral salt and neutral salt with high pH value. The results showed that the salt and alkali stresses decreased chlorophyll contents in leaves of wheat seedlings, inhibited photosynthesis and induced osmotic stress, oxidative stress and ion toxicity to wheat seedlings and finally inhibited the growth of wheat seedlings, while the alkaline salt caused a stronger injurious effect on wheat seedlings than the neutral salt, neutral salt with high pH value. Our study results demonstrated that alkaline salt inhibited wheat seedlings more significantly than neutral salt and neutral salt with high pH value. And, the main factor affected seedling growth is not pH alone.

Salt stress is a common abiotic stress that negatively affects crop growth and yield. However, there have been significant differences found on the effect degree and management mechanism in plants under neutral salt stress and alkaline stress. In this study, two soybean cultivars, Heihe 49 (HH49, saline-alkali stress tolerant) and Henong 95 (HN95, saline-alkali stress sensitive), were hydroponically cultured and treated with salt solutions of 25, 50, and 75 mM Na+ in the form of NaCl, Na2SO4, NaHCO3, and Na2CO3. Plants treated with alkaline stress (NaHCO3 and Na2CO3) showed a greater decrease in root growth and root activity of both soybean cultivar seedlings than that under neutral salt stresses (NaCl and Na2SO4) with 25–75 mM Na+ concentration. Alkaline stress (25–50 mM Na+ content) activated a higher ability of antioxidant defense (by enhancing the activists of superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX)) and increased the content of soluble sugars to a higher level than that under neutral salt stresses. However, 75 mM Na+ content salt treatments reduced antioxidant enzyme activities and osmotic regulating substance content. Furthermore, alkaline salt and neutral salt stress was able to induce DNA damage and cell cycle arrest in HH49 and HN95 seedling roots. Treatment with Na2CO3 induced the least random amplification polymorphic DNA (RAPD) polymorphism in soybean seedling roots among all salt treatments, which could have been related to the early cell cycle arrest.

BackgroundSoil salinity and alkalinity present a serious threat to global agriculture. However, most of the studies have focused on neutral salt stress, and the information on the metabolic responses of plants to alkaline salt stress is limited. This investigation aimed at determining the influence of neutral salt and alkaline salt stresses on the content of metal elements and metabolites in maize plant tissues, by using mixtures of various proportions of NaCl, NaHCO3, Na2SO4, and Na2CO3.ResultsWe found that alkaline salt stress suppressed more pronouncedly the photosynthesis and growth of maize plants than salinity stress. Under alkaline salt stress conditions, metal ions formed massive precipitates, which ultimately reduced plant nutrient availability. On the other hand, high neutral salt stress induced metabolic changes in the direction of gluconeogenesis leading to the enhanced formation of sugars as a reaction contributing to the mitigation of osmotic stress. Thus, the active synthesis of sugars in shoots was essential to the development of salt tolerance. However, the alkaline salt stress conditions characterized by elevated pH values suppressed substantially the levels of photosynthesis, N metabolism, glycolysis, and the production of sugars and amino acids.ConclusionsThese results indicate the presence of different defensive mechanisms responsible for the plant responses to neutral salt and alkaline salt stresses. In addition, the increased concentration of organic acids and enhanced metabolic energy might be potential major factors that can contribute to the maintenance intracellular ion balance in maize plants and counteract the negative effects of high pH under alkaline salt stress.

The aims of this study were to compare the physiological responses of krishum (Iris lactea Pall. var. chinensis Koidz) to neutral and alkaline salt stress and identify and examine the mechanisms involved in plant response to salt treatments. In this study, biomass, ion accumulation (Na+, K+, Ca2+, Mg2+), organic solute (proline) concentration, rate of membrane electrolyte leakage (REL) and antioxidase activities including those of superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6) and peroxidase (POD, EC 1.11.1.7) were investigated in krishum under different concentrations of NaCl, Na2CO3 and the mixture of the two salts in the same volume. All three treatments caused increases in Na+ concentration, proline content and REL and decreases in root Mg2+ and K+ content. Increased Ca2+ and antioxidase activities were observed at lower external Na+ concentrations. However, at higher external Na+ levels, decreased Ca2+ and antioxidase activities were detected. Alkaline salt resulted in more damage to krishum than neutral salt including lower SOD, POD and CAT activities and decreased proline content, relative to neutral salt. High Na+ and low K+ in krishum intensified ion toxicity under alkaline condition. Alkaline salt caused greater harm to plants than neutral salt, the primary reason of which might be the lower Ca2+ content in the plant under alkaline salt stress.

The knowledge about the genetic basis of alkaline salt stress and neutral salt stress in rice is limited. Here, we located quantitative trait loci (QTL) for seed germination rate (GR) under alkaline salt stress (NaHCO3) and neutral salt stress (NaCl) using backcross inbred lines population, which was derived from a cross between indica cv. Changhui 891 (CH891) and japonica cv. 02428 with 3057 bins markers. A total of ten QTL for five salt stress-related traits were detected. The QTL detected for control condition, NaCl stress, and NaHCO3 stress were quite different, which suggested that the genes controlling the transport of the Na+, in the form of NaCl and the NaHCO3, may be different or induced incoordinately by salt stress. Furthermore, on the basis of the high-density genetic map, the ten QTL were mapped on 40–980 kb chromosomal regions on Nipponbare genome, and 16 candidate genes related to stress or metal transport were found. These results contribute to the fine mapping and use of these GR-related QTL.

Based on Glycine gracilis growth and ion homeostasis testing, neutral salt (NS)and alkaline salt (AS) stress were characterized and the responses of G. gracilis were investigated.The injurious effects of AS on G. gracilis were obviously stronger than those of NS.The effects of both stresses on the Na + content and Na + /K + ratio were similar at low concentrations, but as the stress increased, the effects of a greater Na + content and Na + /K + ratio increased slowly under NS conditions, but sharply under AS.The roots of G. gracilis accumulated NO 3 -and H 2 PO 4 -, while the stems and leaves accumulated C 2 O 4 2 -and H 2 PO 4 -to maintain thein tracellular ion balance.The dominant intracellular anions in the stipes were NO 3 -and C 2 O 4 2 -under control conditions, and NO 3 -and H 2 PO 4 -under salt stress.With the increasing AS, the Cl -, NO 3 -and H 2 PO 4 -concentrations decreased, and G. gracilis might have increased SO 4 2 -and C 2 O 4 2 -levels to compensate for the shortage of inorganic anions.Under NS, the NO 3 -and C 2 O 4 2 -concentrations decreased, and G. gracilis might have increased Cl -, H 2 PO 4 -and SO 4 2-levels to compensate for the shortage of inorganic anions.G. gracilis seedling showed a special nutritional metabolism and some growth adaptability under salt stress.

Salinity is a major constraint to crop growth and productivity, limiting sustainable agriculture production. Planting canola (Brassica napus L.) variety with salinity-alkalinity tolerance as a green manure on the large area of salinity-affected land in Xinjiang could alleviate feed shortage. To investigate the differential effects of neutral and alkaline salt stress on seed germination and seedling growth of canola, we used two salts at varying concentrations, i.e., NaCl (neutral salt at 100, 150, and 200 mM) and Na2CO3 (alkaline salt at 20, 30, and 40 mM). To further explore the effects of Na+ and pH on seed germination, we included combined of NaCl (0, 100, 150, and 200 mM) and pH (7.1, 8.0, 9.0, 10.0, and 11.0). Shoot growth was promoted by low concentrations of NaCl and Na2CO3 but inhibited at high salt concentrations. Given the same Na+ concentration, Na2CO3 inhibited seed germination and seedling growth more than NaCl. The results showed that the main factor affecting seed germination and seedling growth is not pH alone, but the interaction between pH and salt ions. Under NaCl stress, canola increased the absorption of K+, Ca2+, and Mg2+ in roots and K+ in leaves. However, under Na2CO3 stress, canola maintained a high K+ concentration and K+/Na+ ratio in leaves and increased Ca2+ and Mg2+ in roots. Our study showed that alkaline salts inhibit canola seed germination and seedling growth more significantly than neutral salts and salt species, salt concentration, and pH significantly affected on seed germination and seedling growth. However, pH affected seed germination and seedling growth mainly through an interaction with salt ions.

Identification of differentially expressed genes in flax (Linum usitatissimum L.) under saline–alkaline stress by digital gene expression

Bud seedlings were used to study short-term effect of different saline and alkaline concentrations on alfalfa root and stem growth. Two neutral salts (NaCl and Na2 SO4) and 2 alkaline salts (NaHCO3 and Na2 CO3) were mixted at 9:1 mole ratio, respectively, to imitate typical saline and alkaline environments. 8 saline concentrations: 0, 10, 20, 40, 60, 80, 100, 120 mmol/L, and 7 alkaline concentrations: 0, 2, 5, 10, 20, 40, 50 mmol/L were selected to determine the stress effects on 5-day, 2-cm bud seedlings. The results indicated that bud seedlings’ root length increased firstly and then decreased as the increase of stress concentrations. On condition of neutral salt stress, 40 mmol/L treatment showed optimum root length, which was 102% times higher than CK, with significant difference (P<0.05). Under alkaline salt stress, 5 mmol/L treatment showed optimum root length, which was 156% times higher than the CK, with significant difference (P<0.05). The effects of the stresses on stem length surpassed root length. And the inhibitory effect of alkaline salt stress on seedlings’ growth in early stage surpassed neutral salt stress.

H2S pretreatment mitigates the alkaline salt stress on Malus hupehensis roots by regulating Na+/K+ homeostasis and oxidative stress

A comprehensive acquaintance of photosynthesis and ionic homeostasis are essential for improvement of salt tolerance in crops. However, gas exchange, ion homeostasis and their effects on metabolites in soybean under salt stress have not been fully investigated. In this study, wild and cultivated soybeans were used to explore gas exchange and ionomic profile changes in order to reveal the salt tolerance mechanism in wild soybean. Under neutral salt stress (NS), wild soybean increased the net photosynthetic rate (pN) and decreased Na+ and Cl– absorption and accumulated in the roots and reduced content in leaves than in cultivated soybean. Under alkaline salt stress, it inhibited the absorption of Cl– to adapt salt stress. During neutral salt stress in wild soybean, pN and carotenoids in leaves were positively correlated with fatty acid metabolism, but negatively correlated with amino acid, organic acid and antioxidant receiver operating characteristics (ROC) metabolisms in roots and Na+ and Cl– were negatively correlated with fatty acid metabolism in leaves and with TCA cycle in roots. Under alkaline salt stress, gas exchange was negatively correlated with amino acid metabolism in leaves, and with TCA cycle in roots and Na+ was positively correlated with amino acid metabolism. Results indicated the restricted accumulation of toxic ions, regulated absorption of nutrient elements, maintained gas exchange and then caused changes in small molecule metabolites pathway are possible reasons for salt tolerance in wild soybean.

The salinization and alkalization of soil are widespread environmental problems. Sugar beet (B. vulgaris L.) is a moderately salt tolerant glycophyte, but little is known about the different mechanisms of sugar beet response to salt and alkaline stresses. The aim of this study was to investigate the influence of neutral salt (NaCl:Na2SO4, 1:1) and alkaline salt (Na2CO3) treatment on physiological and transcriptome changes in sugar beet. We found that a low level of neutral salt (NaCl:Na2SO4; 1:1, Na+ 25 mM) or alkaline salt (Na2CO3, Na+ 25 mM) significantly enhanced total biomass, leaf area and photosynthesis indictors in sugar beet. Under a high concentration of alkaline salt (Na2CO3, Na+ 100 mM), the growth of plants was not significantly affected compared with the control. But a high level of neutral salt (NaCl: Na2SO4; 1:1, Na+ 100 mM) significantly inhibited plant growth and photosynthesis. Furthermore, sugar beet tends to synthesize higher levels of soluble sugar and reducing sugar to cope with high neutral salt stress, and more drastic changes in indole acetic acid (IAA) and abscisic acid (ABA) contents were detected. We used next-generation RNA-Seq technique to analyze transcriptional changes under neutral salt and alkaline salt treatment in sugar beet. Overall, 4,773 and 2,251 differentially expressed genes (DEGs) were identified in leaves and roots, respectively. Kyoto encyclopedia of genes and genomes (KEGG) analysis showed that genes involving cutin, suberine and wax biosynthesis, sesquiterpenoid and triterpenoid biosynthesis and flavonoid biosynthesis had simultaneously changed expression under low neutral salt or alkaline salt, so these genes may be related to stimulating sugar beet growth in both low salt treatments. Genes enriched in monoterpenoid biosynthesis, amino acids metabolism and starch and sucrose metabolism were specifically regulated to respond to the high alkaline salt. Meanwhile, compared with high alkaline salt, high neutral salt induced the expression change of genes involved in DNA replication, and decreased the expression of genes participating in cutin, suberine and wax biosynthesis, and linoleic acid metabolism. These results indicate the presence of different mechanisms responsible for sugar beet responses to neutral salt and alkaline salt stresses.