High Salinity Stress Research Articles

The SALT OVERLY SENSITIVE 2-CONSTITUTIVE TRIPLE RESPONSE1 module coordinates plant growth and salt tolerance in Arabidopsis.

High salinity stress promotes plant ethylene biosynthesis and triggers the ethylene signalling response. However, the precise mechanism underlying how plants transduce ethylene signalling in response to salt stress remains largely unknown. In this study, we discovered that SALT OVERLY SENSITIVE 2 (SOS2) inhibits the kinase activity of CONSTITUTIVE TRIPLE RESPONSE1 (CTR1) by phosphorylating the 87th serine (S87). This phosphorylation event activates the ethylene signalling response, leading to enhanced plant salt resistance. Furthermore, through genetic analysis, we determined that the loss of CTR1 or the gain of SOS2-mediated CTR1 phosphorylation both contribute to improved plant salt tolerance. Additionally, in the sos2 mutant, we observed compromised proteolytic processing of ETHYLENE INSENSITIVE 2 (EIN2) and reduced nuclear localization of EIN2 C-terminal fragments (EIN2-C), which correlate with decreased accumulation of ETHYLENE INSENSITIVE 3 (EIN3). Collectively, our findings unveil the role of the SOS2-CTR1 regulatory module in promoting the activation of the ethylene signalling pathway and enhancing plant salt tolerance.

Growth retardation and suppression of ubiquitin-dependent catabolic processes in the brackish water clam Corbicula japonica in response to salinity changes and bioaccumulation of toxic heavy metals

The brackish water clam (Corbicula japonica) is constantly exposed to stressful salinity gradients and high levels of heavy metals in the freshwater-saltwater interface of estuary environments, which are introduced from upstream regions and land. To identify the key molecular pathways involved in the response to salinity changes and heavy metal bioaccumulation, we obtained the transcriptomes of C. japonica inhabiting different salinities and heavy metal distributions in Gwangyang Bay (Korea) using RNA sequencing. Among a total of 404,486 assembled unigenes, 5534 differentially expressed genes were identified in C. japonica inhabiting different conditions, 1549 of which were significantly upregulated and 1355 were significantly downregulated. Correlation analyses revealed distinct gene expression patterns between the low and high conditions of salinity and heavy metal bioaccumulation. Functional annotation revealed significant downregulation of genes involved in “ubiquitin-dependent protein catabolic process,” “tricarboxylic acid cycle,” and “intracellular protein transport” in C. japonica from the high condition compared to the low condition. Transcription and translation pathways were significantly enriched in the high condition. Additionally, upon comparison of the low and high conditions by qRT-PCR and proteasome enzyme activity analyses, our findings demonstrated that environmental stress could suppress the ubiquitin-proteasome complex (UPC). Additionally, transcriptomic changes under high salinity stress conditions may be related to an increase in cellular protection by defense enzymes, which leads to more energy being required and a disruption of energy homeostasis. Ultimately, this could cause growth retardation in the clam C. japonica. In summary, this study provides the first evidence of UPC suppression induced by a combination of high salinity and heavy metal bioaccumulation stress in C. japonica, which could compromise the survival and growth of estuarine bivalves.

Effects of acute salinity stress on physiology and immunoenzymatic activity in juvenile sea cucumber, Stichopus monotuberculatus

To investigate the effects of acute salinity stress on physiology and immunoenzymatic activity in juvenile sea cucumbers, Stichopus monotuberculatus and S. monotuberculatus with body weights of 12.6 ± 3.1 g were selected as study subjects, and a salinity of 30‰ was used as the control, while salinities of 20‰, 25‰, 35‰ and 40‰ were used as acute salinity stress treatment groups. The survival rate of S. monotuberculatus was calculated, histological changes in the intestines were observed, and the activities of superoxide dismutase (SOD), catalase (CAT), and alkaline phosphatase (AKP) in the coelomic fluid, as well as Na+/K+-ATPase in the intestine, were measured and analyzed. The results showed that juvenile S. monotuberculatus could survive at salinities of 20–35‰, and could only survive for 24 h at a salinity of 40‰. Both high and low salinity stress changed the intestinal morphology of S. monotuberculatus, as epithelial cells were damaged and necrotic, vacuolated in the intestinal villi, and had unclear brush border edges. At 6 h after salinity stress, SOD and CAT activities in coelomic fluid increased or decreased rapidly and then adjusted and recovered gradually with the extension of stress time. SOD activity in the low-salinity groups was significantly higher than that in the control group, and CAT activity was significantly higher in the low-salinity groups (20‰ and 25‰) than in the high-salinity groups (35‰ and 40‰). AKP activity in the coelomic fluid was inhibited in the low-salinity groups and showed a gradual increase with increasing salinity. Na+/K+-ATPase activities in intestines showed a slow increase in the 20‰ salinity group and then dropped back to control levels. In the other salinity groups, Na+/K+-ATPase activity was higher at 6 h and 48 h after salinity stress. The results obtained from the present study indicate that salinity stress affected the survival rate and intestinal morphology of S. monotuberculatus, and S. monotuberculatus could respond to external environmental changes by regulating the activities of antioxidant enzymes, Na+/K+-ATPase, and AKP.

How Does Zinc Improve Salinity Tolerance? Mechanisms and Future Prospects.

Salinity stress (SS) is a serious abiotic stress and a major constraint to agricultural productivity across the globe. High SS negatively affects plant growth and yield by altering soil physio-chemical properties and plant physiological, biochemical, and molecular processes. The application of micronutrients is considered an important practice to mitigate the adverse effects of SS. Zinc (Zn) is an important nutrient that plays an imperative role in plant growth, and it could also help alleviate the effects of salt stress. Zn application improves seed germination, seedling growth, water uptake, plant water relations, nutrient uptake, and nutrient homeostasis, therefore improving plant performance and saline conditions. Zn application also protects the photosynthetic apparatus from salinity-induced oxidative stress and improves stomata movement, chlorophyll synthesis, carbon fixation, and osmolytes and hormone accumulation. Moreover, Zn application also increases the synthesis of secondary metabolites and the expression of stress responsive genes and stimulates antioxidant activities to counter the toxic effects of salt stress. Therefore, to better understand the role of Zn in plants under SS, we have discussed the various mechanisms by which Zn induces salinity tolerance in plants. We have also identified diverse research gaps that must be filled in future research programs. The present review article will fill the knowledge gaps on the role of Zn in mitigating salinity stress. This review will also help readers to learn more about the role of Zn and will provide new suggestions on how this knowledge can be used to develop salt tolerance in plants by using Zn.

Comparative studies on the effect of salinity and drought stress on enzymatic antioxidant defense system of two maize (<i>Zea mays</i> l.). varieties

Soil salinization and drought are serious threat to crop productivity and predicted to increase in face of global climate change. Studies have shown that as much as the 12 billion US dollar will be lost globally each year, due to the reduction in agricultural production from drought and salt-affected areas. Maize is an economically important cereal crop affected by high salinity and drought stress, maize seedling was subjected to 50 mM, 100 mM and 150 mM NaCl and 4, 6 and 8 days to emulate high soil salinity and drought stress. Root and mature leaves were harvested after 21 days of sowing. High salinity induced oxidative stress in the root and mature leaves. The root and matured leaves showed increased malondialdehyde (MDA) and the hydrogen peroxide (H2O2) concentration at 50, 100 and 150 mM NaCl and 4, 6, and 8 days of drought strss. Activities of enzymatic antioxidants, Catylase (CAT, E .C 1.11.1.6) increase in all organs of salt treated maize seedling, while superoxide dismutase (SOD, 1.15.1.1) and peroxidase (POX, E.C. 1.11.1.7) increased specifically in mature leaves. This indicates a possible role of reactive oxygen species (ROS) in the systemic signaling from roots to leaves, allowing leaves to activate their defense mechanism for better protection against salt and drought stress.

Soil P solubilization and plant growth promotion by a saline–alkali-tolerant P-solubilizing bacterium, Bacillus sp. DYS211

Abstract High total P content but insufficient available P in soil is an obstacle that restricts the efficient utilization of P in saline–alkali soil regions. Although saline–alkali resistant P-solubilizing bacteria (PSB) solubilize insoluble P, few studies have focused on their application in plant growth. We isolated a PSB strain, identified as Bacillus sp. DYS211, from bird droppings in saline–alkali regions and determined its growth characteristics and resistance to salt and alkalis. To investigate the effect of PSB on the germination and growth of plant seeds, we performed a potting experiment using Suaeda salsa with PSB added. The PSB strain grew rapidly in the first 12 h, and the solubilized P content from PSB reached a maximum of 258.22 mg L−1 at 48 h. Saline–alkali tolerance and P-solubilizing ability tests showed that Bacillus sp. DYS211 preferred to dissolve inorganic P, was halophilic, and had a good P-solubilizing effect at 1%–8% salinity (available P > 150 mg L−1). It exhibited good P solubilization abilities when glucose and sucrose were used as C sources or when ammonium sulfate, ammonium nitrate or yeast extract powder were used as N sources. In the growth promotion test, PSB increased seed germination, particularly under high-salinity stress, with a growth promotion of 8.33%. The PSB also improved the growth of S. salsa, including plant height and biomass (up to three times) under both saline and alkaline conditions, and the stem diameter increased under high-salinity stress. This strain demonstrates potential for vegetation restoration in saline–alkali regions.

Divergent molecular responses of greater amberjack (Seriola dumerili) to acute salinity stress revealed by comparative transcriptome analysis

Greater amberjack (Seriola dumerili) is an important commercial fish for its high growth rate and excellent flesh quality. However, its sensitivity to variations of water salinity poses challenges to the cage culture. In this study, the greater amberjack were reared in the optimum salinity (30 ppt, CK) and undesired regimes (10 and 40 ppt) for 72 hours. The molecular adaptive mechanisms to salinity stress were revealed by the comparative transcriptome analysis for the gills and kidneys. In gills, a total of 445 and 423 differentially expressed genes (DEGs) were identified in 10 and 40 ppt salinity stress groups, respectively. Those DEGs were involved in cartilage and skeletal development, ions transport, and immune response. The major ion secretion and osmoregulation transport proteins gene slc12a2/nkcc1 and cftr expression levels were significantly down-regulated at 10 ppt, but slightly activated at 40 ppt, compared with the control group. The expression changes in response to the Na+, K+ movement, and Cl- ion secretion reduced under the hypo-osmotic exposure and ion excretion boost upon hyper-salinity stress. Meanwhile, the cartilage and skeletal development were enhanced in the gills by hypo- or hyper-salinity stimuli, which is critical for maintaining gill structures and improving respiration and osmoregulation under salinity stress. In kidneys, 600 and 539 DEGs were identified in 10 and 40 ppt groups, respectively. Those DEGs were enriched in oxygen transport, pronephros development, regulation of growth, blood coagulation, ion transmembrane transport, and immune response. While the known renal Na+/Cl– co-transporter gene slc12a3/ncc expression level was significantly down-regulated at 10 ppt, the organic cation transporter 2 gene slc22a2, ammonium transmembrane transport gene rhd and rhag expression levels were overexpressed under the hyper-salinity condition at 40 ppt, contributing to the salts secretion and ammonium transport regulation, to combat the osmotic influx of salts following the drink of seawater and elevated ammonia production upon high salinity stress. These findings advance our knowledge of adaptative mechanisms to the salinity stress and provide theoretical guidance for the optimal breeding mode for the aquaculture of greater amberjack.

Characterization and the comprehensive expression analysis of tobacco valine-glutamine genes in response to trichomes development and stress tolerance

Valine-glutamine genes (VQ) acted as transcription regulators and played the important roles in plant growth and development, and stress tolerance through interacting with transcription factors and other co-regulators. In this study, sixty-one VQ genes containing the FxxxVQxxTG motif were identified and updated in the Nicotiana tobacum genome. Phylogenetic analysis indicated that NtVQ genes were divided into seven groups and genes of each group had highly conserved exon-intron structure. Expression patterns analysis firstly showed that NtVQ genes expressed individually in different tobacco tissues including mixed-trichome (mT), glandular-trichome (gT), and nonglandular-trichome (nT), and the expression levels were also distinguishing in response to methyl jasmonate (MeJA), salicylic acid (SA), gibberellic acid (GA), ethylene (ETH), high salinity and PEG stresses. Besides, only NtVQ17 of its gene family was verified to have acquired autoactivating activity. This work will not only lead a foundation on revealing the functions of NtVQ genes in tobacco trichomes but also provided references to VQ genes related stress tolerance research in more crops.

Bioaccumulation and speciation of arsenic in plankton from tropical soda lakes along a salinity gradient

Uptake and transformation of arsenic (As) by living organisms can alter its distribution and biogeochemical cycles in the environment. Although well known for its toxicity, several aspects of As accumulation and biological transformation by field species are still little explored. In this study, the bioaccumulation and speciation of As in phytoplankton and zooplankton from five soda lakes in the Brazilian Pantanal wetland were studied. Such lakes exhibited contrasting biogeochemical characteristics along an environmental gradient. Additionally, the influence of contrasting climatic events was assessed by collecting samples during an exceptional drought in 2017 and a flood in 2018. Total As (AsTot) content and speciation were determined using spectrometric techniques, while a suspect screening of organoarsenicals in plankton samples was carried out by high-resolution mass spectrometry. Results showed that AsTot content ranged from 16.9 to 62.0 mg kg−1 during the dry period and from 2.4 to 12.3 mg kg−1 during the wet period. The bioconcentration and bioaccumulation factors (BCF and BAF) in phytoplankton and zooplankton were found to be highly dependent on the lake typology, which is influenced by an ongoing evapoconcentration process in the region. Eutrophic and As-enriched lakes exhibited the lowest BCF and BAF values, possibly due to the formation of non-labile As complexes with organic matter or limited uptake of As by plankton caused by high salinity stress. The season played a decisive role in the results, as significantly higher BCF and BAF values were observed during the flooding event when the concentration of dissolved As in water was low. The diversity of As species was found to be dependent on the lake typology and on the resident biological community, cyanobacteria being responsible for a significant portion of As metabolism. Arsenosugars and their degradation products were detected in both phytoplankton and zooplankton, providing evidence for previously reported detoxification pathways. Although no biomagnification pattern was observed, the diet seemed to be an important exposure pathway for zooplankton.

Effects of LPS from Rhodobacter sphaeroides, a Purple Non-Sulfur Bacterium (PNSB), on the Gene Expression of Rice Root.

The effects of lipopolysaccharide (LPS) from Rhodobacter sphaeroides, a purple non-sulfur bacterium (PNSB), on the gene expression of the root of rice (Oryza sativa) were investigated by next generation sequencing (NGS) RNA-seq analysis. The rice seeds were germinated on agar plates containing 10 pg/mL of LPS from Rhodobacter sphaeroides NBRC 12203 (type culture). Three days after germination, RNA samples were extracted from the roots and analyzed by RNA-seq. The effects of dead (killed) PNSB cells of R. sphaeroides NBRC 12203T at the concentration of 101 cfu/mL (ca. 50 pg cell dry weight/mL) were also examined. Clean reads of NGS were mapped to rice genome (number of transcript ID: 44785), and differentially expressed genes were analyzed by DEGs. As a result of DEG analysis, 300 and 128 genes, and 86 and 8 genes were significantly up- and down-regulated by LPS and dead cells of PNSB, respectively. The plot of logFC (fold change) values of the up-regulated genes of LPS and PNSB dead cells showed a significant positive relationship (r2 = 0.6333, p < 0.0001), indicating that most of the effects of dead cell were attributed to those of LPS. Many genes related to tolerance against biotic (fungal and bacterial pathogens) and abiotic (cold, drought, and high salinity) stresses were up-regulated, and the most strikingly up-regulated genes were those involved in the jasmonate signaling pathway, and the genes of chalcone synthase isozymes, indicating that PNSB induced defense response against biotic and abiotic stresses via the jasmonate signaling pathway, despite the non-pathogenicity of PNSB.

Differences in the Physiological Indicators of Seed Germination and Seedling Establishment of Durum Wheat (Triticum durum Desf.) Cultivars Subjected to Salinity Stress

To investigate the effects of salinity stress on durum wheat cultivars at the critical stages of germination and seedling establishment under salinity stress, a study was conducted on eight durum wheat cultivars (Karim, Khiar, Inrat100, Maali, Monastir, Portodur, Razeg, and Salim) subjected to an increasing salinity concentration by using sodium chloride (NaC) (0, 2, 4, 6, and 10 g L−1). Germination and seedling physiological parameters were measured and thoroughly analyzed. Salinity stress significantly decreased germination capacity (GC), germination rate (GR), final germination capacity (FGC), germination index (GI), mean daily germination (MDG), and velocity coefficient (Vc), whereas mean germination time (MGT) and the stress index (SI) increased. Plantlet growth and initial vigor (IV) were also significantly hampered. Regarding all these traits, the cultivars’ differences were revealed: Karim and Salim were the least affected, whereas Razeg and Maali were the most affected, and the other cultivars occupied an intermediate position. Depending on cultivar, salinity stress decreased the germination capacity and delayed its initiation. At low salinity stress (2–4 g L−1 NaCl), the osmotic effect (OE) was the main cause of germination inhibition, whereas at high salinity stress (6–10 g L−1 NaCl), the toxic effect (TE) dominated and irreversibly inhibited the germination process. The initial vigor and the stress index that clearly discriminate among the studied cultivars are useful traits for screening tolerant genotypes. Otherwise, durum wheat showed a higher plasticity with salinity at the germination stage, allowing it to develop better tolerance at this stage, as compared to early stage plantlet growth.

The Sweet Potato K+ Transporter IbHAK11 Regulates K+ Deficiency and High Salinity Stress Tolerance by Maintaining Positive Ion Homeostasis.

The K+ transporter KT/HAK/KUP (K+ transporter/high-affinity K+/K+ uptake) family has a critical effect on K+ uptake and translocation in plants under different environmental conditions. However, the functional analysis of KT/HAK/KUP members in sweet potatoes is still limited. The present work reported the physiological activity of a new gene, IbHAK11, in the KT/HAK/KUP family in sweet potatoes. IbHAK11 expression increased significantly in the low K+-tolerant line compared with the low K+-sensitive line following treatment with low K+ concentrations. IbHAK11 upregulation promoted root growth in Arabidopsis under low K+ conditions. Under high saline stress, transgenic lines had superior growth and photosynthetic characteristics compared with the wild-type (WT). As for IbHAK11-overexpressing plants, activation of both the non-enzymatic and enzymatic reactive oxygen species (ROS) scavenging systems was observed. Therefore, IbHAK11-overexpressing plants had lower malondialdehyde (MDA) and ROS levels (including H2O2 and O2-) compared with WT under salt-induced stress. We also found that under both low K+ and high salinity conditions, overexpression of IbHAK11 enhanced K+ translocation from the root to the shoot and decreased Na+ absorption in Arabidopsis. Consequently, IbHAK11 positively regulated K+ deficiency and high salinity stresses by regulating K+ translocation and Na+ uptake, thus maintaining K+/Na+ homeostasis in plants.

A Preliminary Survey of Transfer RNA Modifications and Modifying Enzymes of the Tropical Plant Cocos nucifera L.

The coconut (Cocos nucifera L.) is a commercial crop widely distributed among coastal tropical regions. It provides millions of farmers with food, fuel, cosmetics, folk medicine, and building materials. Among these, oil and palm sugar are representative extracts. However, this unique living species of Cocos has only been preliminarily studied at molecular levels. Benefiting from the genomic sequence data published in 2017 and 2021, we investigated the transfer RNA (tRNA) modifications and modifying enzymes of the coconut in this survey. An extraction method for the tRNA pool from coconut flesh was built. In total, 33 species of modified nucleosides and 66 homologous genes of modifying enzymes were confirmed using a nucleoside analysis using high-performance liquid chromatography combined with high-resolution mass spectrometry (HPLC-HRMS) and homologous protein sequence alignment. The positions of tRNA modifications, including pseudouridines, were preliminarily mapped using a oligonucleotide analysis, and the features of their modifying enzymes were summarized. Interestingly, we found that the gene encoding the modifying enzyme of 2'-O-ribosyladenosine at the 64th position of tRNA (Ar(p)64) was uniquely overexpressed under high-salinity stress. In contrast, most other tRNA-modifying enzymes were downregulated with mining transcriptomic sequencing data. According to previous physiological studies of Ar(p)64, the coconut appears to enhance the quality control of the translation process when subjected to high-salinity stress. We hope this survey can help advance research on tRNA modification and scientific studies of the coconut, as well as thinking of the safety and nutritional value of naturally modified nucleosides.

Using comparative transcriptome analysis to identify molecular response mechanisms to salinity stress in channel catfish (Ictalurus punctatus)

Channel catfish (Ictalurus punctatus) are an important global aquaculture species. To explore gene expression patterns and identify adaptive molecular mechanisms in catfish during salinity stress, we performed growth comparison and comparative transcriptome sequencing on liver tissue. Our study revealed that salinity stress has a significant impact on the growth, survival, and antioxidant system of channel catfish. 927 and 1356 significant DEGs were identified in L vs. C group and H vs. C group. Gene Ontology (GO) functional annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses suggested that both high and low salinity stress affected gene expression related to oxygen carrier activity, hemoglobin complex, and oxygen transport pathways, and also amino acid metabolism, immune responses, and energy and fatty acid metabolism in catfish. Among mechanisms, amino acid metabolism genes were significantly up-regulated in the low salt stress group, immune response genes were significantly up-regulated in the high salt stress group, and fatty acid metabolism genes were significantly up-regulated in both groups. These results provided a platform for unraveling steady-state regulatory mechanisms in channel catfish under salinity stress, and may limit the impact of extreme salinity changes on catfish during aquaculture practices.

Osmoprotectants play a major role in the Portulaca oleracea resistance to high levels of salinity stress-insights from a metabolomics and proteomics integrated approach.

Purslane (Portulaca oleracea L.) is a non-conventional food plant used extensively in folk medicine and classified as a multipurpose plant species, serving as a source of features of direct importance to the agricultural and agri-industrial sectors. This species is considered a suitable model to study the mechanisms behind resistance to several abiotic stresses including salinity. The recently achieved technological developments in high-throughput biology opened a new window of opportunity to gain additional insights on purslane resistance to salinity stress-a complex, multigenic, and still not well-understood trait. Only a few reports on single-omics analysis (SOA) of purslane are available, and only one multi-omics integration (MOI) analysis exists so far integrating distinct omics platforms (transcriptomics and metabolomics) to characterize the response of purslane plants to salinity stress. The present study is a second step in building a robust database on the morpho-physiological and molecular responses purslane to salinity stress and its subsequent use in attempting to decode the genetics behind its resistance to this abiotic stress. Here, the characterization of the morpho-physiological responses of adult purslane plants to salinity stress and a metabolomics and proteomics integrative approach to study the changes at the molecular level in their leaves and roots is presented. Adult plants of the B1 purslane accession lost approximately 50% of the fresh and dry weight (from shoots and roots) whensubmitted to very high salinity stress (2.0 g of NaCl/100 g of the substrate). The resistance to very high levels of salinity stress increases as the purslane plant matures, and most of the absorbed sodium remains in the roots, with only a part (~12%) reaching the shoots. Crystal-like structures, constituted mainly by Na+, Cl-, and K+, were found in the leaf veins and intercellular space near the stoma, indicating that this species has a mechanism of salt exclusion operating on the leaves, which has its role in salt tolerance. The MOI approach showed that 41 metabolites were statistically significant on the leaves and 65 metabolites on the roots of adult purslane plants. The combination of the mummichog algorithm and metabolomics database comparison revealed that the glycine, serine, and threonine, amino sugar and nucleotide sugar, and glycolysis/gluconeogenesis pathways were the most significantly enriched pathways when considering the total number of occurrences in the leaves (with 14, 13, and 13, respectively) and roots (all with eight) of adult plants; and that purslane plants employ the adaptive mechanism of osmoprotection to mitigate the negative effect of very high levels of salinity stress; and that this mechanism is prevalent in the leaves. The multi-omics database built by our group underwent a screen for salt-responsive genes, which are now under further characterization for their potential to promote resistance to salinity stress when heterologously overexpressed in salt-sensitive plants.

GhPYL9-5D and GhPYR1-3 A positively regulate Arabidopsis and cotton responses to ABA, drought, high salinity and osmotic stress

BackgroundAbscisic acid (ABA) receptor pyrabactin resistance 1/PYR1-like/regulatory components of ABA receptor proteins (PYR/PYL/RCARs) have been demonstrated to play pivotal roles in ABA signaling and in response to diverse environmental stimuli including drought, salinity and osmotic stress in Arabidopsis. However, whether and how GhPYL9-5D and GhPYR1-3A, the homologues of Arabidopsis PYL9 and PYR1 in cotton, function in responding to ABA and abiotic stresses are still unclear.ResultsGhPYL9-5D and GhPYR1-3A were targeted to the cytoplasm and nucleus. Overexpression of GhPYL9-5D and GhPYR1-3A in Arabidopsis wild type and sextuple mutant pyr1pyl1pyl2pyl4pyl5pyl8 plants resulted in ABA hypersensitivity in terms of seed germination, root growth and stomatal closure, as well as seedling tolerance to water deficit, salt and osmotic stress. Moreover, the VIGS (Virus-induced gene silencing) cotton plants, in which GhPYL9-5D or GhPYR1-3A were knocked down, showed clearly reduced tolerance to polyethylene glycol 6000 (PEG)-induced drought, salinity and osmotic stresses compared with the controls. Additionally, transcriptomic data revealed that GhPYL9-5D was highly expressed in the root, and GhPYR1-3A was strongly expressed in the fiber and stem. GhPYL9-5D, GhPYR1-3A and their homologs in cotton were highly expressed after treatment with PEG or NaCl, and the two genes were co-expressed with redox signaling components, transcription factors and auxin signal components. These results suggest that GhPYL9-5D and GhPYR1-3A may serve important roles through interplaying with hormone and other signaling components in cotton adaptation to salt or osmotic stress.ConclusionsGhPYL9-5D and GhPYR1-3A positively regulate ABA-mediated seed germination, primary root growth and stomatal closure, as well as tolerance to drought, salt and osmotic stresses likely through affecting the expression of multiple downstream stress-associated genes in Arabidopsis and cotton.

Differential effect of water salinity levels on gas exchange, chlorophyll fluorescence and antioxidant compounds in ex vitro date palm plants

In this study, the response to salt stress was evaluated in ex vitro acclimated date palm plants, regenerated from in vitro culture multiplication. The plants, eighteen-month-old, were irrigated with 0 (control), 150, 300 or 450 mM NaCl solutions (high to very high-water salinity). Photosynthesis parameters and antioxidant compounds were determined at the end of the experiment in leaves. At 150 mM NaCl, net CO2 assimilation rate and internal CO2 concentration were not impaired; while transpiration and stomatal conductance decreased by 60 and 70%, respectively. By increasing salt concentrations, all gas exchanges parameters were decreased. Measurement of chlorophyll fluorescence and P700 redox state showed that PSII and PSI machineries were significantly enhanced under 150 mM NaCl, conditions. With the 300 mM NaCl, the PSI parameters remained unchanged compared to control, while some of the PSII parameters, such as NPQ and Y (NPQ), were increased. At 450 mM NaCl, photosystems functionality was light intensity (PAR) dependent. Only at low PAR, a significant increase of some PSI and PSII parameters was observed. At the contrary, with high PAR, most of the energy conversion functions were significantly reduced, especially those related to PSI, indicating that PSI was more susceptible for damage by salinity than PSII. To overcome high salinity stress, ex vitro date palm plants mobilized a cascade of physio-biochemical pathways including the antioxidant activity and proline biosynthesis. Overall, the salinity of irrigation water, and up to 150 mM, improves the physiological performance of ex vitro date palm plants, which manage to tolerate very high levels of this stress.

Purslane (Portulaca oleracea L.) salt tolerance assessment

ABSTRACT The present study was aimed to evaluate the effect of irrigation water salinity on some agronomic and physiological attributes of purslane (Portulaca oleracea L.) and its tolerance to salinity stress. The treatments included seven levels of electrical conductivity of irrigation water (0.6 (control), 3, 6, 9, 12, 15, and 18 dSm−1) arranged in the form of a completely randomized design with three replications. The results showed that salinity stress successively decreased agronomic attributes such as root, shoot, and stem dry weight, plant height and leaf area. Physiological attributes such as relative water content as well as ion leakage differently responded to salinity stress. Relative water content response to salinity followed a quadratic regression model with the maximum of 81% at electrical conductivity of 6.87 dSm−1 and the minimum of 65% at highest salinity level of 18 dSm−1. Following an exponential regression model, ion leakage remained relatively the same till irrigation water salinity of 15 dSm−1 and reached to the maximum of 78% at highest irrigation water salinity of 18 dSm−1. In addition, shoot potassium content of purslane under non saline conditions equaled to 11% that was around 10 times more than the typical of potassium sufficient concentration for adequate growth. Moreover, with increasing salinity stress, shoot potassium content decreased to 7% at highest salinity level of 18 dSm−1 of irrigation water. However, with increasing irrigation water salinity, sodium shoot content of purslane was increased from 1.9% at the lowest salinity stress to 6.7% at the highest salinity stress. Based on the linear and nonlinear models, 10% of purslane biomass reduction occurred at soil electrical conductivity of around 10 dSm−1. In addition, 25 and 50% yield reduction observed at 16 and 25 dSm−1 of electrical conductivity of soil saturated paste. Therefore, purslane can be considered as a very salt tolerant plant, halophyte, and can successfully grow in soils with electrical conductivities not suitable for most crops.

Total Phenolic Content and Antioxidant Capacity of &amp;lt;i&amp;gt;Dunaliella salina &amp;lt;/i&amp;gt;Were Cultivated Under Stress Conditions on Salt Field Media

<i>Dunaliella salina</i> (<i>D. salina</i>) is a unicellular green microalga with a high β-carotene content and bioactive compounds that is essential for any study of the application of microalgae. The current research aimed to evaluate total phenolic content, and antioxidant capacity of <i>D. salina</i> CCAP 19/18 strain in RM1 and RM2 salt field media under various stress conditions including natural light, high salinity, and nitrogen starvation. As a result, after 17 days of being enrichment, in the RM1 medium, there was no significant difference in phenolic content under natural light, high salinity, and nitrogen starvation stresses, with p = 0.305. Similarly, the antioxidant capacity had no significant difference, which was p = 0.105 (natural light with high salinity), and p=0.428 (nitrogen starvation with high salinity). While in RM2 medium, the phenolic content and antioxidant capacity under nitrogen starvation stress far exceeded that of natural light and high salinity, with respective figures being 157.147 fg acid gallic/cell and 600.443%/cell and these figures had a significant difference (p<0.05). As a consequence, we could choose an appropriate medium for cultivating and harvesting algae in a large-scale pilot. These true potential extract ingredients in algae are fascinating for cosmetic industries or used for various health benefits such as nutraceuticals and medications against damaging causes, particularly free radicals.

Salinity effect on an anaerobic methane- and ammonium-oxidising consortium: Shifts in activity, morphology, osmoregulation and syntrophic relationship

Nitrate-dependent anaerobic methane oxidation (AOM) is a microbial process of both ecological significance for global methane mitigation and application potential for wastewater treatment. It is mediated by organisms belonging to the archaeal family ‘Candidatus Methanoperedenaceae’, which have so far mainly been found in freshwater environments. Their potential distribution in saline environments and their physiological responses to salinity variation were still poorly understood. In this study, the responses of the freshwater 'Candidatus Methanoperedens nitroreducens’-dominated consortium to different salinities were investigated using short- and long-term setups. Short-term exposure to salt stress significantly affected nitrate reduction and methane oxidation activities over the tested concentration range of 15–200‰ NaCl, and ‘Ca. M. nitroreducens’ showed the higher tolerance to high salinity stress than its partner of anammox bacteria. At high salinity concentration, near marine conditions of 37‰, the target organism ‘Ca. M. nitroreducens’ showed stabilized nitrate reduction activity of 208.5 µmol day−1 gCDW−1 in long-term bioreactors over 300 days, in comparison to 362.9 and 334.3 µmol day−1 gCDW−1 under low-salinity conditions (1.7‰ NaCl) and control conditions (∼15‰ NaCl). Different partners of ‘Ca. M. nitroreducens’ evolved in the consortia with three different salinity conditions, suggesting the different syntrophic mechanisms shaped by changes in salinity. A new syntrophic relationship between ‘Ca. M. nitroreducens’ and Fimicutes and/or Chloroflexi denitrifying populations was identified under the marine salinity condition. Metaproteomic analysis shows that the salinity changes lead to higher expression of response regulators and selective ion (Na+/H+) channeling proteins that can regulate the osmotic pressure between the cell and its environment. The reverse methanogenesis pathway was, however, not impacted. The finding of this study has important implications for the ecological distribution of the nitrate-dependent AOM process in marine environments and the potential of this biotechnological process for the treatment of high-salinity industrial wastewater.