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Paper mulberry is a high-quality woody feed resource plant with high crude protein content. It is widely distributed in China and has excellent characteristics of salt and alkali tolerance. Paper mulberry has ecological and economic importance. Salt stress has become a critical factor with the increasing degree of soil salinity that restricts plant growth. In the saline-alkali environments, transcriptome expression is altered leading to phenotypic defects in most plants. However, the regulatory mechanism related to paper mulberry's salt-stress (SS) response is not clearly understood. In the present study de novo transcriptomic assembly was performed, and gene expression levels were measured between different SS and natural conditions (25°C) as a control for paper mulberry plants. According to the results of our study, under NaCl stress conditions, the differential gene expression was observed in the leaves of paper mulberry compared with the control. A total of 2126 differentially expressed unigenes were observed. Among these unigenes the expression of 812 DEGs was up-regulated and the expression of 1,314 DEGs was down-regulated. Additionally, The GO and KEGG analyses regarding differentially expressed unigenes (DEUs) revealed that the observed critical transcriptomic alterations under salt stress (SS) conditions were associated with primary and secondary metabolism, photosynthesis, and plant hormone signaling pathways. Further investigations such as gene function studies regarding the unigenes depicting altered expression under salt stress conditions in paper mulberry will help understand the mechanism of salt tolerance, and this information can be utilized in paper mulberry breeding and improvement programs. [ABSTRACT FROM AUTHOR]

Freshwater resources are becoming increasingly scarce in coastal areas, limiting crop productivity in coastal farmlands. Although the characteristic of crop water use is an important factor for water conservation in coastal farmlands, it has not been studied extensively. This study aimed to depict the water use process of soil–plant systems under saline stress in coastal ecosystems and optimize water management. An intensive observation experiment was performed within China's Yellow River Delta to identify the water use processes and crop coefficients (KC) and also quantify the impacts of salt stress on crop water use. The results show that shallow groundwater did not contribute to soil water in the whole rotation; KC values for wheat–maize, wheat–sorghum, and wheat–soybean rotation systems were 45.0, 58.4, and 57% less, respectively, than the FAO values. The water use efficiency of the maize (8.70) and sorghum (9.00) in coastal farmlands was higher than that of the soybean (4.37). By identifying the critical periods of water and salt stress, this paper provides suggestions for water-saving and salinity control in coastal farmlands. Our findings can inform the sustainable development of coastal farmlands and provide new insights to cope with aspects of the global food crisis. [ABSTRACT FROM AUTHOR]

Sweet basil (Ocimum basilicum L.) is an important aromatic plant with high edibility and economic value, widely distributed in many regions of the tropics including the south of China. In recent years, environmental problems, especially soil salinization, have seriously restricted the planting and spread of sweet basil. However, the molecular mechanism of the salt stress response in sweet basil is still largely unknown. In this study, seed germination, seedling growth, and chlorophyll synthesis in sweet basil were inhibited under salt stress conditions. Through comparative transcriptome analysis, the gene modules involved in the metabolic processes, oxidative response, phytohormone signaling, cytoskeleton, and photosynthesis were screened out. In addition, the landscape of transcription factors during salt treatment in sweet basil was displayed as well. Moreover, the overexpression of the WRKY transcription factor-encoding gene, ObWRKY16, and the phenylalanine ammonia-lyase-encoding gene, ObPAL2, enhanced the seed germination, seedling growth, and survival rate, respectively, of transgenic Arabidopsis, suggesting that they might be important candidates for the creation of salt-tolerant sweet basil cultivars. Our data enrich the study on salt responses in sweet basil and provide essential gene resources for genetic improvements in sweet basil in the future. [ABSTRACT FROM AUTHOR]

Seed propagation is the main method of mulberry expansion in China, an important economic forest species. However, seed germination is the most sensitive stage to various abiotic stresses, especially salinity stress. To reveal the molecular regulatory mechanism of mulberry seed germination under salt stress, flavonoid metabolomics and transcriptomics analyses were performed on mulberry seeds germinated under 50 and 100 mmol/L NaCl stress. Analysis of the flavonoid metabolome revealed that a total of 145 differential flavonoid metabolites (DFMs) were classified into 9 groups, 40 flavonols, 32 flavones, 16 chalcones and 14 flavanones. Among them, 61.4% (89) of the DFMs accumulated continuously with increasing salt concentration, reaching the highest level at a 100 mmol/L salt concentration; these DFMs included quercetin-3-O-glucoside (isoquercitrin), kaempferol (3,5,7,4'-tetrahydroxyflavone), quercetin-7-O-glucoside, taxifolin (dihydroquercetin) and apigenin (4',5,7-trihydroxyflavone), indicating that these flavonoids may be key metabolites involved in the response to salt stress. Transcriptional analysis identified a total of 3055 differentially expressed genes (DEGs), most of which were enriched in flavonoid biosynthesis (ko00941), phenylpropanoid biosynthesis (ko00940) and biosynthesis of secondary metabolites (ko01110). Combined analysis of flavonoid metabolomic and transcriptomic data indicated that phenylalanine ammonia-lyase (PAL), 4-coumarate-CoA ligase (4CL), chalcone synthase (CHS), flavonol synthase (FLS), bifunctional dihydroflavonol 4-reductase/flavanone 4-reductase (DFR) and anthocyanidin reductase (ANR) were the key genes involved in flavonoid accumulation during mulberry seed germination under 50 and 100 mmol/L NaCl stress. In addition, three transcription factors, MYB, bHLH and NAC, were involved in the regulation of flavonoid accumulation under salt stress. The results of quantitative real-time PCR (qRT‒PCR) validation showed that the expression levels of 11 DEGs, including 7 genes involved in flavonoid biosynthesis, under different salt concentrations were consistent with the transcriptomic data, and parallel reaction monitoring (PRM) results showed that the expression levels of 6 key enzymes (proteins) involved in flavonoid synthesis were consistent with the accumulation of flavonoids. This study provides a new perspective for investigating the regulatory role of flavonoid biosynthesis in the regulation of mulberry seed germination under salt stress at different concentrations. [ABSTRACT FROM AUTHOR]

Soil salinization is a significant obstacle to improving natural grasslands, also affecting farmland productivity. The main distribution area of high salinity soils is primarily located in western China, with a significant presence in the Qinghai–Tibet Plateau (QTP). Siberian wildrye (Elymus sibiricus L.) has been widely used in ecological restoration and reseeding in the QTP, due to its strong salt and alkali resistance. To comprehensively evaluate its salt tolerance and to screen salt-tolerant and salt-sensitive germplasm resources, 50 wild E. sibiricus accessions were assessed through the measurement of several physiological parameters. These included the relative water content (RWC); relative electrical conductivity (REC); malondialdehyde content (MDA); proline content (Pro); and Na+/K+ ratio after 14 days of salt stress treatment (200 mmol L−1 NaCl). Through principal component analysis (PCA) based on both material sources and physiological indexing, it was found that the salt damage score (SDS) and RWC had a strong positive correlation (p < 0.05), in opposition to other indices. The positive indicators were REC, Pro, Na+/K+, and MDA, and the negative indicators were RWC and SDS. Ultimately, by combining the results of the conventional membership function analysis and the weighted membership function analysis based on major components, three salt-tolerant accessions—including XJ013-28, NM021-13 and XJ012-17—and four salt-sensitive accessions, including XZ008-20, QH013-8, XZ009-20, and QH005-35, were screened out. These results could be effectively used to assess the effects of salt stress on Siberian wildrye and its related species. This study provides a reference for the discovery and breeding of salt-tolerant cultivars among the Elymus species. [ABSTRACT FROM AUTHOR]

Simple Summary: Volunteer wheat is commonly found in the main wheat-producing areas of China and impacts cultivated wheat production. This study's aim was evaluating the effects of environmental conditions on the adaptability and germination of volunteer wheat grains. Our results showed that volunteer wheat was more adaptable to low temperatures of 5 °C and was poorly adaptable to high temperatures of above 30 °C. Volunteer wheat was more adaptable to higher salinity and lower osmotic potential than cultivated wheat. The secondary germination ability of volunteer wheat was also higher than that of cultivated wheat after water immersion. The deep tillage of cultivated land could effectively prevent the spread of volunteer wheat. Our study provides a basis for future studies concerning the control of volunteer wheat. Volunteer wheat commonly occurs and spreads rapidly in the main wheat-producing areas of China, seriously impacting cultivated wheat production. Limited information is currently available regarding the adaptability and germination traits of volunteer wheat. Therefore, this study's aim was to evaluate the effects of environmental conditions on the germination and emergence of volunteer wheat seeds through laboratory experiments. The results showed that the germination percentages and viability of volunteer wheat were significantly higher than those of cultivated wheat at a low temperature of 5 °C, and they were lower than those of cultivated wheat at high temperatures of above 30 °C. Compared to cultivated wheat, volunteer wheat was able to tolerate higher salinity and lower osmotic potential, especially long-dormancy volunteer wheat. The secondary germination ability of volunteer wheat was higher than that of cultivated wheat after water immersion. Furthermore, volunteer wheat could not emerge normally when the seeding depth was greater than 8 cm, and the emergence ability of the volunteer wheat was weaker than that of the cultivated wheats when the seeding depth was 4–8 cm, which indicates that the deep tillage of cultivated land could effectively prevent the spread of volunteer wheat. This study revealed differences in the germination characteristics of volunteer wheat and cultivated wheat under the influence of different environmental factors, which provides a basis for future studies concerning the control of volunteer wheat. [ABSTRACT FROM AUTHOR]

Salt damage is a major threat to sustainable cotton production owing to the limited arable land in China, which is mainly occupied by the production of staple food crops. Salt-stress-tolerant cotton varieties are lacking in production, and the mechanisms underpinning salt stress tolerance in cotton remain enigmatic. Here, DM37, an intraspecific introgression line from Gossypium hirsutum race yucatanense acc TX-1046 into the G. hirsutum acc TM-1 background, was found to be highly tolerant to salt stress. Its seed germination rate and germination potential were significantly higher than those of the recipient TM-1 under salt stress. Physiological analysis showed that DM37 had a higher proline content and peroxidase activity and lower Na+/K+ ratios at the seedling stage, which is consistent with a higher seedling survival rate after durable salt stress. Furthermore, comparative transcriptome analysis revealed that responsive patterns to salt stress in DM37 were different from those in TM-1. Weighted correlation network analysis demonstrated that co-expression modules associated with salt stress in DM37 also differed from those in TM-1. From this analysis, GhPP2C43-A , a phosphatase gene, was found to exhibit negative regulation of salt stress tolerance verified by virus-induced gene silencing and the genration of transgenic Arabidopsis. Gene expression showed that GhPP2C43-A in TM-1 was induced by durable salt stress but not in DM37, probably attributable to a variation in the cis -element in its promoter, thereby conferring different salt stress tolerance. These results provide new genes/germplasms from semi-wild cotton in salt-stress-tolerant cotton breeding, as well as new insight into the mechanisms underpinning salt stress tolerance in cotton. [ABSTRACT FROM AUTHOR]

We conducted a study to examine the growth and physiological changes in 12 different ecotypes of Sesuvium portulacastrum collected from Hainan Island in China. These ecotypes were subjected to different concentrations (0, 200, 400, and 600 mmol/L) of sodium chloride (NaCl) salt stress for 14 days. We also analyzed the expression of metabolic genes related to stress response. Under low salt stress, indicators such as plant height in region K (0 mmol/L: 45% and highest at 200 mmol/L: 80%), internode length (0 mmol/L: 0.38, 200 mmol/L: 0.87, 400 mmol/L: 0.25, and 600 mmol/L: 1.35), as well as leaf area, relative water content, fresh weight, and dry weight exhibited an overall increasing trend with the increase in salt concentration. However, as the salt concentration increased, these indicators showed a decreasing trend. Proline and malondialdehyde contents increased with higher salt concentrations. When the NaCl concentration was 400 mmol/L, MDA content in the leaves was highest in the regions E (196.23%), F (94.28%), J (170.10%), and K (136.08%) as compared to the control group, respectively. Most materials demonstrated a significant decrease in chlorophyll a, chlorophyll b, and total chlorophyll content compared to the control group. Furthermore, the ratio of chlorophyll a to chlorophyll b (Rab) varied among different materials. Using principal component analysis, we identified three ecotypes (L from Xinglong Village, Danzhou City; B from Shuigoupo Village, Lingshui County; and J from Haidongfang Park, Dongfang City) that represented high, medium, and low salt tolerance levels, respectively, based on the above growth and physiological indexes. To further investigate the expression changes of related genes at the transcriptional level, we employed qRT-PCR. The results showed that the relative expression of SpP5CS1, SpLOX1, and SpLOX1 genes increased with higher salt concentrations, which corresponded to the accumulation of proline and malondialdehyde content, respectively. However, the relative expression of SpCHL1a and SpCHL1b did not exhibit a consistent pattern. This study contributes to our understanding of the salt tolerance mechanism in the true halophyte S. portulacastrum, providing a solid theoretical foundation for further research in this field. [ABSTRACT FROM AUTHOR]

Since 2007, Ulva prolifera, a green macroalgal species that blooms periodically in the Yellow Sea of China, has caused the world's biggest green tide, which induced harmful ecological impacts and economic losses. When the alga is subject to prolonged exposure to air, it suffers abiotic stresses. To explore the physiological and molecular mechanisms of salt stress, the transcriptome data of U. prolifera at different salinities (30, 50, and 90 psu) were obtained by high-throughput sequencing using the Illumina HiSeq platform, and photosynthetic physiological parameters were also measured. The results showed that a total of 89,626 unigenes were obtained after de novo assembly, of which 60,441 unigenes were annotated in the databases (NR, NT, KO, SWISS-PROT, PFAM, GO, and KOG). GO functional enrichment analysis revealed that the enrichment of differentially expressed genes (DEGs) was mainly in cellular, cell, and binding processes. KEGG metabolic pathway enrichment analysis showed that the most frequently enriched pathways of DEGs included glycolysis, pyruvate metabolism, peroxisome, and fatty acid biosynthesis. In addition, resistance-associated proteins, such as heat-shock proteins, microtubule-associated proteins, ubiquitin-associated proteins, abscisic-acid-signaling-pathway-associated proteins, and antioxidant-related proteins are upregulated under salt stress. Genes associated with photosynthesis and carbon fixation pathways are also upregulated, accompanied by an increase in photosynthetic oxygen release rates. These findings provide a basis for understanding the molecular mechanisms of the response of U. prolifera to salinity change, thus providing a theoretical basis for the analysis of the green tide outbreak mechanism. [ABSTRACT FROM AUTHOR]

Alfalfa (Medicago sativa L.) is an important source of livestock feed used to address the imbalance between livestock and forage production in China. However, much of the grasslands have a high salt content, which seriously affects the quality and yield of alfalfa. There are many kinds of fungi that play an important role in alfalfa growth and nutrient synthesis. The response of the fungi of alfalfa to salinity is poorly understood. In this study, the physiological characteristics and the fungal community composition of alfalfa under different salt stress conditions were investigated. Salt stress had a great impact on the physiological characteristics and the fungal community composition of alfalfa. The activity of invertase increased significantly under salt stress; the content of water and starch decreased; and the content of crude protein (CP) and soluble sugar increased under mild salt stress. With the increase in salt stress, the relative abundance of Ascomycetes increased, while the relative abundance of basidiomycetes decreased. This showed that the changes in the fungal community may be related to the adaptability of alfalfa plants to salt stress. These findings contribute to a better understanding of alfalfa physiological characteristics and nutrient synthesis under salt stress and deepen our understanding of alfalfa–fungi interactions in the saline soil environment of grasslands. [ABSTRACT FROM AUTHOR]

Vicia villosa Roth is an annual cover crop that is widely grown in orchards in China. Information on seed ecology is valuable as it helps famers to plant cover crops and manage other weed species in agricultural practice; however, information on V. villosa seed-germination ecology is limited. Thus, this study investigated the seed germination and seedling emergence of V. villosa under various temperatures, photoperiods, levels of salt stress, pH, levels of osmotic stress, and burial depths. The results showed that the germination values of the V. villosa seeds were greater than 93% at the constant temperature range of 5–30 °C and fluctuating temperatures of 5/15 °C–20/30 °C; in particular, the germination of the seeds peaked 20 °C and 15/25 °C, with germination values of 95% and 94.5%, respectively. Light was not necessary for the V. villosa seeds' germination. When the pH was in the range of 5–10, the germination values of the V. villosa seeds fluctuated between 85% and 94%, and obvious inhibition of germination was observed at pH = 4, with a germination value of 15%. The Vicia villosa seeds exhibited obvious salt tolerance, and the seed-germination value was still greater than 50% when the salt concentration reached 280 mM. The seeds were relatively sensitive to osmotic stress, and the germination value was lower than 50% when the osmotic potential was −0.5 MPa. In addition, the germination value of the seeds peaked when the seeds were 1–2 cm underneath the ground; in particular, the seeds still germinated and emerged when the seeds were buried in soli at a depth of 10 cm. These results confirmed that V. villosa, as a cover crop, has considerable potential to be planted and grown in orchards in China and, furthermore, that it may contribute to early weed management in fields, supporting the establishment of V. villosa populations. [ABSTRACT FROM AUTHOR]

Understanding salinity and fertilizer interaction is of great importance to improve crop production and fertilizer use efficiency in saline areas. To evaluate the interactive effects of different soil salinity levels and nitrogen (N) applications rates on the sunflower photosynthetic characteristics of N uptake and N use efficiency, a two-year field experiment was conducted in Hetao Irrigation District, China. The experiment consisted of three initial salinity (IS) levels expressed as the electrical conductivity of a saturated soil extract (ECe) (S0: 1.72–2.61 dS/m; S1: 4.73–5.90 dS/m; S2: 6.85–9.04 dS/m) and four N rates (45, 90, 135, and 180 kg/ha), referred as N0–N3, respectively. The results indicated that the net photosynthetic rate (Pn) of sunflowers treated with S0 and S1 levels both had a significant decrease in the bud stage, and then reached their maximum at anthesis. However, during the crop cycle, the Pn at S2 level only had small fluctuations and still remained at a high level (>40 μmol CO2/(m2 s)) at the early mature stage. When increasing IS levels from S0 to S1, the plant N uptake (PNU) under the same N rates were only decreased by less than 10% at maturity, whereas the decline was expanded to 17.2–45.7% from S1 to S2. Additionally, though applying the N2 rate could not increase sunflower PNU at the S0 and S1 levels, its N use efficiency was better than those under N3. Meanwhile, at the S2 level, the application of the N0 rate produced a higher N productive efficiency (NPE) and N uptake efficiency (NUPE) than the other N rates. Therefore, our study proposed recommended rates of N fertilizer (S0 and S1: 135 kg/ha, S2: 45 kg/ha) for sunflowers under different saline conditions. [ABSTRACT FROM AUTHOR]

Fraxinus velutina Torr with high salt tolerance has been widely grown in saline lands in the Yellow River Delta, China. However, the salt-tolerant mechanisms of F. velutina remain largely elusive. Here, we identified two contrasting cutting clones of F. velutina , R7 (salt-tolerant), and S4 (salt-sensitive) by measuring chlorophyll fluorescence characteristics (Fv/Fm ratio) in the excised leaves and physiological indexes in roots or leaves under salt treatment. To further explore the salt resistance mechanisms, we compared the transcriptomes of R7 and S4 from leaf and root tissues exposed to salt stress. The results showed that when the excised leaves of S4 and R7 were, respectively, exposed to 250 mM NaCl for 48 h, Fv / Fm ratio decreased significantly in S4 compared with R7, confirming that R7 is more tolerant to salt stress. Comparative transcriptome analysis showed that salt stress induced the significant upregulation of stress-responsive genes in R7, making important contributions to the high salt tolerance. Specifically, in the R7 leaves, salt stress markedly upregulated key genes involved in plant hormone signaling and mitogen-activated protein kinase signaling pathways; in the R7 roots, salt stress induced the upregulation of main genes involved in proline biosynthesis and starch and sucrose metabolism. In addition, 12 genes encoding antioxidant enzyme peroxidase were all significantly upregulated in both leaves and roots. Collectively, our findings revealed the crucial defense pathways underlying high salt tolerance of R7 through significant upregulation of some key genes involving metabolism and hub signaling pathways, thus providing novel insights into salt-tolerant F. velutina breeding. [ABSTRACT FROM AUTHOR]

Aquaporins are a specific type of membrane channel proteins that efficiently transport water molecules and other small molecular substrates in plants. In this study, we isolated the plasma membrane aquaporin gene EuPIP1;2 from Eucommia ulmoides, an important medicinal plant in China. The EuPIP1;2 protein was localized on the plasma membrane. Quantitative RT-PCR analysis revealed that EuPIP1;2 was constitutively expressed in all analyzed tissues, with the highest expression levels detected in the fruit and root. Overexpression of EuPIP1;2 in transgenic tobacco enhanced plant tolerance of drought and salinity. Under drought and salt stress, the transgenic lines exhibited higher percentage germination, longer roots, and enhanced percentage survival compared with wild-type plants. The contents of malonaldehyde and proline suggested that EuPIP1;2 improved drought and salt tolerance in transgenic lines by reducing damage to membranes and improving osmotic adjustment. We predict that EuPIP1;2 could be applied to improve drought and salt tolerance in transgenic plants. [ABSTRACT FROM AUTHOR]

Soil salinization is the main abiotic stress factor affecting agricultural production worldwide, and salt stress has a significant impact on plant growth and development. Cotton is one of the most salt-tolerant crops. Therefore, the selection and utilization of salt-tolerant germplasm resources and the excavation of salt resistance genes play important roles in improving cotton production in saline–alkali soils. In this study, we analysed the population structure and genetic diversity of a total 149 cotton plant materials including 137 elite Gossypium hirsutum cultivar accessions collected from China and 12 elite Gossypium hirsutum cultivar accessions collected from around the world. Illumina Cotton SNP 70 K was used to obtain genome-wide single-nucleotide polymorphism (SNP) data for 149 elite Gossypium hirsutum cultivar accessions, and 18,430 highly consistent SNP loci were obtained by filtering. It was assessed by using PCA principal component analysis so that the 149 elite Gossypium hirsutum cultivar accessions could be divided into two subgroups, including subgroup 1 with 78 materials and subgroup 2 with 71 materials. Using the obtained SNP and other marker genotype test results, under salt stress, the salt tolerance traits 3d Germination potential, 3d Radicle length drop rate, 7d Germination rate, 7d Radicle length drop rate, 7d Germination weight, 3d Radicle length, 7d Radicle length, Relative Germination potential, Relative Germination rate, 7d Radicle weight drop rate, Salt tolerance index 3d Germination potential index, 3d Radicle length index, 7d Radicle length index, 7d Radicle weight index and 7d Germination rate index were evaluated by GWAS (genome-wide association analysis). A total of 27 SNP markers closely related to the salt tolerance traits and 15 SNP markers closely related to the salt tolerance index were detected. At the SNP locus associated with phenotyping, Gh_D01G0943, Gh_D01G0945, Gh_A01G0906, Gh_A01G0908, Gh_D08G1308 and Gh_D08G1309 related to plant salt tolerance were detected, and they were found to be involved in intracellular transport, sucrose synthesis, osmotic pressure balance, transmembrane transport, N-glycosylation, auxin response and cell amplification. This study provides a theoretical basis for the selection and breeding of salt-tolerant upland cotton varieties. [ABSTRACT FROM AUTHOR]