Confers Salt Stress Tolerance Research Articles

Salicylic Acid Seed Priming: A Key Frontier in Conferring Salt Stress Tolerance in Barley Seed Germination and Seedling Growth

Salicylic Acid Seed Priming: A Key Frontier in Conferring Salt Stress Tolerance in Barley Seed Germination and Seedling Growth

SlNAC12, a novel NAC-type transcription factor, confers salt stress tolerance in tomato.

SlNAC12 enhances salt stress tolerance of transgenic tomato by regulating ion homeostasis, antioxidant activity and flavonoids biosynthesis Soil salinization is a major environmental factor that adversely affects plant growth and development. NAC (NAM, ATAF1/2, and CUC2) is a large family of plant-specific transcription factors that play crucial roles in stress response. Here, we investigated the role of a novel NAC transcription factor, SlNAC12, in conferring salt stress tolerance in tomato (Solanum lycopersicum). Subcellular localization and yeast assays studies revealed that SlNAC12 is localized in the nucleus with weak transcriptional activity. SlNAC12 transcript was induced by salt stress in the leaves and roots of tomato seedlings. Overexpression of SlNAC12 in tomato led to significantly reduced plant height and root length. Transgenic tomato lines overexpressing of SlNAC12 (OE#1 and OE#3) exhibited enhanced tolerance to salinity, as evidenced by reduced the inhibitory effect of growth parameters under salt stress compared to wild type (WT). Overexpression of SlNAC12 in tomato affected Na+ and K+ homeostasis, leading to reduced Na+/K+ ratio, enhanced activity of antioxidant enzymes and decreased reactive oxygen species (ROS) accumulation under salt stress. Furthermore, the transcript levels of several genes involved in flavonoids metabolism and the levels of flavonoids accumulation were increased in SlNAC12-overexpressing tomato lines. Collectively, this study suggests that SlNAC12 transcription factor enhances salt stress tolerance in tomato is correlated with ion homeostasis, antioxidant enzyme systems, and flavonoids accumulation.

Activation of ABA Signaling Pathway and Up-Regulation of Salt-Responsive Genes Confer Salt Stress Tolerance of Wheat (Triticum aestivum L.) Seedlings

Salt is a potent abiotic stress that arrests plant growth by impairing their physio-biochemical and molecular processes. However, it is unknown how the ABA signaling system and vacuolar-type Na+/H+ antiporter proteins induce stress tolerance in wheat (Triticum aestivum L.) seedlings. The present study aimed to identify salt-responsive proteins and signaling pathways involved in the resistance of wheat to salt stress. We explored the proteome profile, 20 amino acids, 14 carbohydrates, 8 major phytohormones, ion content, and salt tolerance genes in wheat (Triticum aestivum L., cv.) under 200 mM NaCl with control plants for six days. The results showed that amino acids such as alanine, serine, proline, glutamine, and aspartic acid were highly expressed under salt stress compared with control plants, suggesting that amino acids are the main players in salinity tolerance. The ABA signaling system was activated in response to salinity stress through the modulation of protein phosphatase 2C (PP2C) and ABA-responsive element binding factor (ABF), resulting in an ABA-mediated downstream response. Additionally, the vacuolar-type Na+/H+ antiporter was identified as a key protein in salt stress tolerance via compartmentalizing Na+ in the vacuole. Furthermore, a significant increase in the abundance of the 14-3-3 protein was noticed in salt-fed plants, suggesting that this protein plays an important role in Na+ compartmentalization. Moreover, up-regulation of ascorbate peroxidase (APX), glutathione-S-transferase (GST), and thioredoxin-scavenged reactive oxygen species resulted in improved plant growth under salt stress. These data will help to identify salt-responsive proteins that can be used in future breeding programs to develop salt-tolerant varieties.

Functional validation of mungbean LEA protein coding gene in bacterial expression system confers salt stress tolerance

Mungbean (Vigna radiata R. Wilczek) is a major tropical food grain legume that is widely cultivated in tropical part of the world. Mungbean like other plants, tolerate and survive limited water situation owing to expression of stress associated proteins that offers membrane stability and cell protection. Late Embryogenesis Abundant (LEA) proteins are among the group of low molecular weight proteins, that play diverse roles in stress protection in several species of plants and animals. A LEA protein coding gene VrLEA2 was isolated from mungbean and its role in stress tolerance has been demonstrated using a bacterial expression system. VrLEA2 gene isolated was of size 893 bp and characterized as a group 1 LEA protein based on the sequence signature motif with presence of hydrophilic domain and a characteristic 20-mer conserved amino acids motif. VrLEA2 gene was cloned into a bacterial expression vector, pET 28a (+), transformed into the E.coli BL21 (DE3) cells for recombinant protein expression and subsequently subjected to antibiotic selection with kanamycin. Functional validation of the VrLEA2 for salt stress tolerance with varied concentration of NaCl (0 mM to 600 mM) showed alteration in colony morphology and reduction in the number of colonies in control compared to the transformed cells demonstrating the improved survival rate of cells expressing VrLEA2 protein. These findings indicate the best use of bacterial expression system for functional validation of plant proteins under stressed environments.

Boosting Stevia's sweetness: Growth regulators mitigate salt stress and enhance steviol glycosides

Stevia rebaudiana Bertoni is a plant species with sweet-tasting leaves that can be used as a natural, low-calorie sweetener with potential health benefits. Salt stress can reduce plant growth and productivity, but the application of growth regulators like salicylic acid (SA), methyl jasmonate (MeJ), and spermidine (Spd) can manage various plant abiotic stresses and improve plant growth and productivity. In this work, we investigated the role of exogenous SA, MeJ, and Spd in conferring salt stress tolerance in Stevia by analyzing plant growth, chlorophyll (Chl), total phenolic, total carotenoid content, antioxidant defense system and steviol glycosides. The aim of a recent study was to assess the effects of these regulators on Stevia plants under both individual and combined salt stress conditions. Foliar application of these regulators improved plant growth under salt stress, with moderate salinity stress increasing glycoside compounds. SA was most effective in increasing rebaudioside A (Reb A), while MeJ + Spd combination was best for increasing stevioside (Stv) content. Individual applications of Spd, MeJ, and SA significantly impacted plant growth and antioxidant content, although their combined use was less effective. Spd application under salt stress yielded the highest increases in total carotenoid and Chl a content, while MeJ and Spd together significantly boosted Chl b content. The study found that SA enhanced superoxide dismutase (SOD) activity and reduced catalase (CAT) activity under salt stress, whereas MeJ alone increased both CAT and SOD activity. The distinct responses to Spd, SA, and MeJ suggest varied mechanisms in oxidative stress-induced antioxidant production. Overall, the use of these growth regulators can improve the growth, yield, and nutritional value of Stevia under salt stress, offering significant implications for agriculture and food security.

Proteomic analysis of MsFtsH8 overexpression reveals enhanced salt stress response in alfalfa through PSII stability and antioxidant capacity improvement

The FtsH (Filamentous temperature sensitive H) proteases, known for their crucial roles in protein quality control and maintaining the integrity of photosynthetic machinery, have emerged as key regulators of stress responses in plants. Our previous study revealed the overexpression of MsFtsH8, an FtsH gene from alfalfa (Medicago sativa L.), confers salt stress tolerance to the plant. By comparing the proteomic profiles of MsFtsH8-overexpressing alfalfa and wild type under salt stress conditions, we elucidate the molecular pathways underlying MsFtsH8-mediated salt stress resilience. We identified 730 differentially expressed proteins (DEPs) in MsFtsH8-overexpressing alfalfa under salt stress, compared to 498 DEPs in wild type alfalfa under the same growth condition. Our results reveal significant alterations in the expression of proteins involved in the photosynthetic system, consistent with the chloroplast subcellular localization of MsFtsH8. Specifically, MsFtsH8 overexpression stabilizes key components of Photosystem II (PSII) and enhances electron transport processes, leading to increased photosynthetic efficiency and oxidative photodamage repair capacity under salt stress. Moreover, MsFtsH8-overexpressing alfalfa exhibits elevated levels of antioxidative enzymes, further mitigating oxidative damage induced by high salinity. These findings deepen our understanding of the regulatory role of MsFtsH8 in salt stress response and highlight its potential for improving crop resilience under adverse environmental conditions.

Arabidopsis class II TPS controls root development and confers salt stress tolerance through enhanced hydrophobic barrier deposition.

The mechanism of conferring salt tolerance by AtTPS9 involves enhanced deposition of suberin lamellae in the Arabidopsis root endodermis, resulting in reduction of Na+ transported to the leaves. Members of the class I trehalose-6-phosphate synthase (TPS) enzymes are known to play an important role in plant growth and development in Arabidopsis. However, class II TPSs and their functions in salinity stress tolerance are not well studied. We characterized the function of a class II TPS gene, AtTPS9, to understand its role in salt stress response and root development in Arabidopsis. The attps9 mutant exhibited significant reduction of soluble sugar levels in the leaves and formation of suberin lamellae (SL) in the endodermis of roots compared to the wild type (WT). The reduction in SL deposition (hydrophobic barriers) leads to increased apoplastic xylem loading, resulting in enhanced Na+ content in the plants, which explains salt sensitivity of the mutant plants. Conversely, AtTPS9 overexpression lines exhibited increased SL deposition in the root endodermis along with increased salt tolerance, showing that regulation of SL deposition is one of the mechanisms of action of AtTPS9 in conferring salt tolerance to Arabidopsis plants. Our data showed that besides salt tolerance, AtTPS9 also regulates seed germination and root development. qRT-PCR analyses showed significant downregulation of selected SNF1-RELATED PROTEIN KINASE2 genes (SnRK2s) and ABA-responsive genes in the mutant, suggesting that AtTPS9 may regulate the ABA-signaling intermediates as part of the mechanism conferring salinity tolerance.

Isolation and identification of associated endophytic bacteria from barely seeds harbour non-ribosomal peptides and enhance tolerance to salinity stress

BackgroundBarely Hordeum vulgare L. is considered one of the most important cereal crops with economic and industrial importance in the world, but its productivity is affected by climate change and abiotic stresses. One of the most recent and important microbiological promising aspects is the use of associated microorganisms, especially the endophytic bacteria producers for non-ribosomal peptides which play an important role in promoting plant growth, productivity, and tolerance to biotic and abiotic stresses. This work aims to identify vertically transferred or inherited endophytic bacterial communities in barely seeds, detect the presence of non-ribosomal peptides from these isolated endophytic strains and study their effect on protein patterns as a response to salinity stress.ResultsFrom two different tolerant (Giza 126) and sensitive (Giza 123) barely seeds cultivars, six different endophytic bacterial strains were isolated and identified using 16S rRNA. Bacterial strains belonged to Bacillus, Paenibacillus, Staphylococcus and Acinetobacter genera. Three of them have been isolated from both sensitive and tolerant barely cultivar (Uncultured Staphylococcus, Acinetobacter and Priestia endophytica or Bacillus endophyticus), while the other three endophytes have been isolated uniquely from the tolerant barely cultivar (Paenibacillus glucanolyticus, Bacillus cereus and Bacillus sp.). Non-ribosomal peptide synthetases genes NRPs of two lipopeptide families; surfactins and kurstakins have been detected using both bioinformatic analysis and degenerate primers. On the other hand, fragments similar to NRPs genes might be considered new NRPS molecules in Paenibacillus glucanolyticus, Acinetobacter and Priestia endophytica which have been detected using degenerate primers and required whole genome sequencing. The effect of soaking barely seeds exposed to 2.5% NaCl using SDS-PAGE electrophoresis revealed the presence of 24 bands, 10 of them were monomorphic with 41.5%, and 14 were polymorphic with 58.5% polymorphism.ConclusionThe overnight soaking and co-cultivation of isolated endophytic strains with barely seeds before planting proved their capability in conferring salt stress tolerance to barely seedlings which appeared in protein patterns. We could consider these barely seeds endophytic among the PGPR strains promising to improve plant growth during abiotic stresses.

Calcineurin B-like protein ZmCBL8-1 promotes salt stress resistance in Arabidopsis.

ZmCBL8-1 enhances salt stress tolerance in maize by improving the antioxidant system to neutralize ROS homeostasis and inducing Na+/H+ antiporter gene expressions of leaves. Calcineurin B-like proteins (CBLs) as plant-specific calcium sensors have been explored for their roles in the regulation of abiotic stress tolerance. Further, the functional variations in ZmCBL8, encoding a component of the salt overly sensitive pathway, conferred the salt stress tolerance in maize. ZmCBL8-1 is a transcript of ZmCBL8 found in maize, but its function in the salt stress response is still unclear. The present study aimed to characterize the protein ZmCBL8-1 that was determined to be composed of 194 amino acids (aa) with three conserved EF hands responsible for binding Ca2+. However, a 20-aa fragment was found to be missing from its C-terminus relative to another transcript of ZmCBL8. Results indicated that it harbored a dual-lipid modification motif MGCXXS at its N-terminus and was located on the cell membrane. The accumulation of ZmCBL8-1 transcripts was high in the roots but relatively lower in the leaves of maize under normal condition. In contrast, its expression was significantly decreased in the roots, while increased in the leaves under NaCl treatment. The overexpression of ZmCBL8-1 resulted in higher salt stress resistance of transgenic Arabidopsis in a Ca2+-dependent manner relative to that of the wild type (WT). In ZmCBL8-1-overexpressing plants exposed to NaCl, the contents of malondialdehyde and hydrogen peroxide were decreased in comparison with those in the WT, and the expression of key genes involved in the antioxidant defense system and Na+/H+ antiporter were upregulated. These results suggested that ZmCBL8-1 played a positive role in the response of leaves to salt stress by inducing the expression of Na+/H+ antiporter genes and enhancing the antioxidant system to neutralize the accumulation of reactive oxygen species. These observations further indicate that ZmCBL8-1 confers salt stress tolerance, suggesting that transcriptional regulation of the ZmCBL8 gene is important for salt tolerance.

ZmILI1 confers salt stress tolerance by regulating genes of phytohormone response in maize

Salt stress is a major abiotic stress that has severe adverse effects on the growth, development, yield and quality of crop plants. Molecular regulatory mechanisms underlying salt stress response in maize are still elusive. Understanding salt stress tolerance mechanisms is essential for the development of high-yielding maize cultivars with improved salt tolerance. Here, we identified a gene, INCREASED LEAF INCLINATION1 (ZmILI1), encoding a bHLH transcription factor, which positively regulates maize response to salt stress. Salt stress induces the expression of ZmILI1, and the overexpression of ZmILI1 enhances catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) activities, thus enhancing salt stress tolerance. DNA affinity purification sequencing (DAP-Seq), RNA sequencing (RNA-Seq), dual-luciferase (LUC), yeast one hybrid, and Real-time polymerase chain reaction (RT-qPCR) assays revealed that ZmILI1 positively regulates salt stress response in maize by modulating the expression of the transcription factor family genes (ZmAP2–197), hormone-related genes (ZmLOX6, ZmDHN1, ZmCaDK2C) and antioxidant enzyme system-related genes (ZmPOD5), thus maintaining cellular homeostasis. Moreover, ZmILI1 is directly or indirectly implicated in maize response to salt stress by regulating the expression of genes involved in jasmonic acid (JA) biosynthesis, such as ZmLOX6, leading to elevated levels of JA hormone in maize under salt-stressed conditions. Our findings not only provide genetic evidence for the role of the bHLH protein family in agricultural production but also reveal potential regulatory mechanisms for the development of salt-tolerant genetic resources, offering new insights into the breeding of salt-tolerant maize varieties.

Endophytic Fungi from Salt Adapted Plants Confer Salt Tolerance in Barley

Endophytic fungi are known to improve plant tolerance under stressful conditions including salt stress. Considering this, the endophytic fungi, Alternaria chlamydospora, Embellisia phragmospora, Phomabetae, Chaetomium coarctatum, Fusarium equiseti and Fusarium graminearum, was isolated from roots of plants growing in salt environments and then, evaluated for their contribution in conferring salt stress tolerance in barley plants. The influence of inoculation with endophytic fungi, on germination, root and shoot lengths of barley seeds under different NaCl levels (0, 200, 300 and 400 mM) was investigated. Results showed that seed germination and root and shoot lengths were higher in seeds pretreated with endophytic fungi cultures than their controls under saline conditions. This study suggests that the tested endophytic fungi might be applied as a strategy for mitigating the stress-imposed salt in plants and, therefore, improving crop growth and productivity.

The synergy of halotolerant PGPB and mauran mitigates salt stress in tomato (Solanum lycopersicum) via osmoprotectants accumulation.

Salinity stress is one of the major abiotic factors limiting sustainable agriculture. Halotolerant plant growth-promoting bacteria (PGPB) increased salt stress tolerance in plants, but the mechanisms underlying the tolerance are poorly understood. This study investigated the PGP activity of four halotolerant bacteria under salinity stress and the tomato salt-tolerance mechanisms induced by the synergy of these bacteria with the exopolysaccharide (EPS) mauran. All PGPB tested in this study were able to offer a significant improvement of tomato plant biomass under salinity stress; Peribacillus castrilensis N3 being the most efficient one. Tomato plants treated with N3 and the EPS mauran showed greater tolerance to NaCl than the treatment in the absence of EPS and PGPB. The synergy of N3 with mauran confers salt stress tolerance in tomato plants by increasing sodium transporter genes' expression and osmoprotectant content, including soluble sugars, polyols, proline, GABA, phenols and the polyamine putrescine. These osmolytes together with the induction of sodium transporter genes increase the osmotic adjustment capacity to resist water loss and maintain ionic homeostasis. These findings suggest that the synergy of the halotolerant bacterium N3 and the EPS mauran could enhance tomato plant growth by mitigating salt stress and could have great potential as an inductor of salinity tolerance in the agriculture sector.

The Carrot Phytoene Synthase 2 (DcPSY2) Promotes Salt Stress Tolerance through a Positive Regulation of Abscisic Acid and Abiotic-Related Genes in Nicotiana tabacum.

Background: Carotenoids, which are secondary metabolites derived from isoprenoids, play a crucial role in photo-protection and photosynthesis, and act as precursors for abscisic acid, a hormone that plays a significant role in plant abiotic stress responses. The biosynthesis of carotenoids in higher plants initiates with the production of phytoene from two geranylgeranyl pyrophosphate molecules. Phytoene synthase (PSY), an essential catalytic enzyme in the process, regulates this crucial step in the pathway. In Daucus carota L. (carrot), two PSY genes (DcPSY1 and DcPSY2) have been identified but only DcPSY2 expression is induced by ABA. Here we show that the ectopic expression of DcPSY2 in Nicotiana tabacum L. (tobacco) produces in L3 and L6 a significant increase in total carotenoids and chlorophyll a, and a significant increment in phytoene in the T1L6 line. Tobacco transgenic T1L3 and T1L6 lines subjected to chronic NaCl stress showed an increase of between 2 and 3- and 6-fold in survival rate relative to control lines, which correlates directly with an increase in the expression of endogenous carotenogenic and abiotic-related genes, and with ABA levels. Conclusions: These results provide evidence of the functionality of DcPSY2 in conferring salt stress tolerance in transgenic tobacco T1L3 and T1L6 lines.

Overexpression of ThSCL32 confers salt stress tolerance by enhancing ThPHD3 gene expression in Tamarix hispida.

GRAS transcription factors belong to the plant-specific protein family. They are not only involved in plant growth and development but also in plant responses to a variety of abiotic stresses. However, to date, the SCL32(SCARECROW-like 32) gene conferring the desired resistance to salt stresses has not been reported in plants. Here, ThSCL32, a homologous gene of ArabidopsisthalianaAtSCL32, was identified. ThSCL32 was highly induced by salt stress in Tamarix hispida. ThSCL32 overexpression in T. hispida gave rise to improved salt tolerance. ThSCL32-silenced T. hispida plants were more sensitive to salt stress. RNA-seq analysis of transient transgenic T. hispida overexpressing ThSCL32 revealed significantly enhanced ThPHD3 (prolyl-4-hydroxylase domain 3 protein) gene expression. ChIP-PCR further verified that ThSCL32 probably binds to the novel cis-element SBS (ACGTTG) in the promoter of ThPHD3 to activate its expression. In brief, our results suggest that the ThSCL32 transcription factor is involved in salt tolerance in T. hispida by enhancing ThPHD3 expression.

Salt stress-induced chloroplastic hydrogen peroxide stimulates pdTPI sulfenylation and methylglyoxal accumulation.

High salinity, an adverse environmental factor affecting about 20% of irrigated arable land worldwide, inhibits plant growth and development by causing oxidative stress, damaging cellular components, and disturbing global metabolism. However, whether and how reactive oxygen species disturb the metabolism of salt-stressed plants remain elusive. Here, we report that salt-induced hydrogen peroxide (H2O2) inhibits the activity of plastid triose phosphate isomerase (pdTPI) to promote methylglyoxal (MG) accumulation and stimulates the sulfenylation of pdTPI at cysteine 74. We also show that MG is a key factor limiting the plant growth, as a decrease in MG levels completely rescued the stunted growth and repressed salt stress tolerance of the pdtpi mutant. Furthermore, targeting CATALASE 2 into chloroplasts to prevent salt-induced overaccumulation of H2O2 conferred salt stress tolerance, revealing a role for chloroplastic H2O2 in salt-caused plant damage. In addition, we demonstrate that the H2O2-mediated accumulation of MG in turn induces H2O2 production, thus forming a regulatory loop that further inhibits the pdTPI activity in salt-stressed plants. Our findings, therefore, illustrate how salt stress induces MG production to inhibit the plant growth.

Endophytic Fusarium clavum confers growth and salt tolerance in Cucumis melo

In the present study, we investigated the in-vitro and in-vivo effects of root endophytic fungal species isolated from squirting cucumber Ecballium elaterium on morphological, physiological and biochemical mechanisms of muskmelon (Cucumis melo) in response to salt stress. A total of 23 endophytic fungal isolates belonging to nine different genera were initially screened for their salt tolerance potential in saline medium. Endophytic Fusarium clavum EeR24 exhibited maximum salt tolerance in screening studies and was selected for further studies. Seedlings of C. melo were inoculated with F. clavum EeR24 and one week later were subjected to two salt (100 and 200 mM NaCl) and control (no salt) treatments in a growth chamber and greenhouse experiments. In growth chamber assays, seedlings treated with F. clavum EeR24 exhibited significant increase in growth and biomass under both controlled and saline conditions. Under greenhouse conditions, F. clavum EeR24 significantly improved morphological and physiological traits including plant height, weight, number of leaves, membrane stability, electrical conductivity, photosynthesis, stomatal conductance and transpiration, in C. melo in response to salt stress. Endophyte colonization also led to decreased absorption of Na+ (36–42 %) and Cl- (23–33 %) ions and an improved K+ (35 %) absorption. Under saline conditions, endophyte colonization improved catalase (24–37 %), guaiacol peroxidase (31–42 %) and superoxide dismutase (16–22 %), chlorophyll and phenolic content by 30–64 %, compared to non-colonized plants. Lipid peroxidation activities significantly decreased by 45 % and proline accumulation increased by 18 % in endophyte-colonized compared to non-colonized plants. Histochemical analysis indicated that under saline conditions, endophytic colonization reduced levels of H2O2, superoxide ion production and cell mortality and increased lignin deposition. The endophytic isolate F. clavum EeR24 also exhibited plant growth promoting activities by producing hydrolytic enzymes, IAA, and phosphate solubilization. Furthermore, a study on spatial colonization of the endophyte, using either conventional Petri-plate counts or RFP-tagging, indicated that F. clavum was able to penetrate the root tissues of C. melo. Conclusively, the endophyte F. clavum EeR24 is an effective salt stress reducer and melon growth promotor; hence can be further taken into account for development as an eco-friendly bio-fertilizer to confer salt stress tolerance in melon.

Transcriptome Analyses in a Selected Gene Set Indicate Alternative Oxidase (AOX) and Early Enhanced Fermentation as Critical for Salinity Tolerance in Rice.

Plants subjected to stress need to respond rapidly and efficiently to acclimatize and survive. In this paper, we investigated a selected gene set potentially involved in early cell reprogramming in two rice genotypes with contrasting salinity tolerance (Pokkali tolerant and IR29 susceptible) in order to advance knowledge of early molecular mechanisms of rice in dealing with salt stress. Selected genes were evaluated in available transcriptomic data over a short period of 24 h and involved enzymes that avoid ROS formation (AOX, UCP and PTOX), impact ATP production (PFK, ADH and COX) or relate to the antioxidant system. Higher transcript accumulation of AOX (ROS balancing), PFK and ADH (alcohol fermentation) was detected in the tolerant genotype, while the sensitive genotype revealed higher UCP and PTOX transcript levels, indicating a predominant role for early transcription of AOX and fermentation in conferring salt stress tolerance to rice. Antioxidant gene analyses supported higher oxidative stress in IR29, with transcript increases of cytosolic CAT and SOD from all cell compartments (cytoplasm, peroxisome, chloroplast and mitochondria). In contrast, Pokkali increased mRNA levels from the AsA-GSH cycle as cytosolic/mitochondrial DHAR was involved in ascorbate recovery. In addition, these responses occurred from 2 h in IR29 and 10 h in Pokkali, indicating early but ineffective antioxidant activity in the susceptible genotype. Overall, our data suggest that AOX and ADH can play a critical role during early cell reprogramming for improving salt stress tolerance by efficiently controlling ROS formation in mitochondria. We discuss our results in relation to gene engineering and editing approaches to develop salinity-tolerant crops.

Overexpression of the Tectona grandis TgNAC01 regulates growth, leaf senescence and confer salt stress tolerance in transgenic tobacco plants.

NAC transcription factors play critical roles in xylem secondary development and in regulation of stress response in plants. NAC proteins related to secondary cell wall development were recently identified and characterized in Tectona grandis (teak), one of the hardwood trees of highest economic importance in the world. In this work, we characterized the novel TgNAC01 gene, which is involved in signaling pathways that mediate teak response to stress. Abscisic acid (ABA) increases TgNAC01 expression in teak plants. Therefore, this gene may have a role in signaling events that mediate ABA-dependent osmotic stress responsive in this plant species. Stable expression in tobacco plants showed that the TgNAC01 protein is localized in the cell nucleus. Overexpression of TgNAC01 in two out three independent transgenic tobacco lines resulted in increased growth, leaf senescence and salt tolerance compared to wild type (WT) plants. Moreover, the stress tolerance of transgenic plants was affected by levels of TgNAC01 gene expression. Water potential, gas exchange and chlorophyll fluorescence were used to determine salt stress tolerance. The 35S:TgNAC01-6 line under 300 mM NaCl stress responded with a significant increase in photosynthesis rate, stomatal conductance, transpiration and carboxylation efficiency, but lower water potential compared to WT plants. The data indicate that the TgNAC01 transcription factor acts as a transcriptional activator of the ABA-mediated regulation and induces leaf senescence.

MpSnRK2.10 confers salt stress tolerance in apple via the ABA signaling pathway

Sucrose non-fermentation-1 related protein kinase 2 (SnRK2) family members play an important role in the abscisic acid (ABA) signaling pathway and adaptation to various environments in plants. Here, we found that salt stress and ABA treatment induced the expression of MpSnRK2.10, and overexpression of this gene alleviated growth restriction caused by salt stress in apple. After treated with salt stress for 15 d, the relative electrolyte leakage, malondialdehyde content, and reactive oxygen species production were lower in overexpression (OE) lines, and the chlorophyll content, superoxide dismutase activity, photosynthetic capacity, and accumulation of several amino acids were higher in OE lines than in wild-type (WT) plants. OE plants also accumulated less Na+ in response to salt stress, and several genes involved in Na+ balance under salt stress were up-regulated in OE plants compared with WT plants. Overexpression of MpSnRK2.10 altered the role of the ABA pathway in the response to salt stress. We found that the ABA content and stomatal aperture were greater in OE plants than in WT plants. Exogenous ABA and the ABA inhibitor nordihydroguaiaretic acid (NDGA) altered the morphology and physiological status of plants under salt stress, especially OE plants, which became more sensitive to salt stress treatment. The ABA content and stomatal aperture were also altered in response to ABA and NDGA. In sum, our results showed that MpSnRK2.10 alleviated the salt stress inhibition of apple plants by altering the Na+ balance and ABA pathway.

Improvement of salt tolerance in Stevia rebaudiana by co-application of endophytic fungi and exogenous spermidine

Stevia (Stevia rebaudiana Bertoni) is an important and salt-sensitive medicinal plant used as a natural sweetener in food products. In this work, we used a pot experiment to investigate the role of microbial inoculation and exogenous polyamine spermidine (Spd) in conferring salt stress tolerance in stevia by analyzing plant growth, chlorophyll (Chl) content, Chl a fluorescence, antioxidant defense system and steviol glycosides. The inoculated plants with Piriformospora indica (Pi), Tricuderma virens (Trich) or Pi+Trich were grown in optimum conditions. At the late of vegetative stage (BBCH growth stage 47), plants sprayed with different concentrations of Spd (0, 0.75, and 1.5 mM) and then were exposed to salinity stress by irrigation with saline treatments (mix of Caspian Sea and distilled water; 0, 6, and 12 dS m−1). The results revealed that salt stress increased hydrogen peroxide (H2O2) and lipid peroxidation (Malondialdehyde: MDA), and consequently plant growth characteristics and maximum photochemical quantum yield of PSII (Fv/Fm) as well as Chl content decreased, but antioxidant enzymes activity including superoxide (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) increased in the plants. Exposure to moderate salinity increased stevioside (Stv) and rebaudioside A (Reb A) content, while these compounds were decreased in the presence of severe salinity. The endophytic symbiosis and foliar spray of Spd (especially in Pi+Trich and Spd 0.75 mM) mitigated salt stress by significant increases in antioxidant enzymes activity and a decrease in H2O2 content and lipid peroxidation. Inoculation with Pi, Trich, and especially Pi+Trich increased the Chl content, Fv/Fm, shoot dry weight, and Stv and Reb A content at all salinity levels. Consequently, combined inoculation of Pi and Trich and foliar application of Spd can be a good approach to improve tolerance, growth and steviol glycosides production of stevia in salt stress conditions.