Alleviate Salt Stress Research Articles

Analysis of the Alternative Splicing Events of Exogenous δ-Aminolevulinic Acid under NaCl Stress in Wild Jujube Seedlings

Salt injury, as an abiotic stress factor, seriously affects the quality and yield of crops. This study was conducted by analyzing alternative splicing in the control (CK), δ-aminolevulinic acid (ALA), NaCl, and ALA + NaCl treatments of wild jujube (Zizyphus spinosus (Bunge)Hu) using RNA-seq. It was found that the unique differential alternative splicing is closely related to the alleviation of salt stress and the analyzed intermediates of chlorophyll synthesis and chlorophyll content in the leaves. The results showed that the content and synthesis of chlorophyll were reduced and disrupted in wild jujube leaves under NaCl stress, and the exogenous spraying of ALA could alleviate the effect of NaCl stress on the content of chlorophyll. RNA-seq indicated that the alternative splicing of genes was dominated by exon skipping in all the experimental treatments. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses revealed that the CK and ALA + NaCl comparison groups were primarily enriched in porphyrin and chlorophyll metabolism, chloroplast, and energy metabolism pathways. It is hypothesized that ALA treatment can alleviate the effects of salt stress on chlorophyll by altering the alternative splicing of genes related to photosynthesis, chlorophyll metabolism, and energy metabolism in wild jujube. In addition, the verification of alternative splicing genes related to chlorophyll metabolism in wild jujube revealed that treatment with ALA significantly upregulated the expression of HEMH, UROIII, and ChlD genes in the leaves under salt stress and increased the content of the chlorophyll biosynthetic intermediates endogenous ALA, porphobilinogen, protoporphyrin IX, Mg-protoporphyrin IX, and protochlorophyllide, which served to alleviate the effects of NaCl stress on chlorophyll in wild jujube.

Salt tolerance evolution facilitates antibiotic resistome in soil microbiota: Evidences from dissemination evaluation, hosts identification and co-occurrence exploration

Salinity is considered as one of the vital factors affecting the profiles of antibiotic resistance genes (ARGs) in soils, whereby its roles in shaping the antibiotic resistome were still poorly understood. Here, metagenomic analysis was conducted to track the ARGs distributions and dissemination in soils during salt accumulation and desalinization processes. Neutral-salt accumulation for 45 and 90 days significantly increased the relative abundances of ARGs and mobile genetic elements (MGEs) carrying antibiotic resistance contigs (ARCs). The ARGs within antibiotic efflux and target protection families primarily carried by Streptomyces, Nocardioides, Rhodanobacter and Monashia were largely enriched by salinity. The ARGs subtypes of the resistance-nodulation-division (RND) family, ATP-binding cassette (ABC) family, rRNA methyltransferase and other efflux were closely associated with MGEs, contributing to the enrichment of ARGs. Moreover, the ARGs subtypes and transposons were genetically linked with the salt-tolerance mechanisms of organic osmolyte transporters and K+ uptake proteins on the same ARC, demonstrating the coselection of ARGs and halotolerant genes. Furthermore, the antibiotic resistome could recover to a normal state after the prolonged incubation by alleviating salt stress. Nevertheless, the acquisition of ARGs by opportunistic pathogens after salt treatment was increased, serving to prioritize further efforts on the health risks correlated with resistance propagation and human exposure in saline soils.

Whole-transcriptome analyses of Sorghum leaves identify key mRNAs and ncRNAs associated with GA3-mediated alleviation of salt stress.

Sorghum has recently attracted much attention for its tolerance in high salt environment. However, the effect and regulatory mechanism of the gibberellic acid (GA3)-mediated alleviation of salt stress in sorghum remains unclear. Herein, we reported that a GA3 concentration of 50 mg/L is optimal for sorghum ("Jitian 3") development under salt stress. We conducted a whole-transcriptome analysis between GA3-treated and control sorghum leaves under salt stress, and we identified 1002 differentially expressed (DE)-messenger RNAs (mRNAs), 81 DE-long non-coding RNAs (lncRNAs), 7 DE-circular RNAs (circRNAs), and 26 DE-microRNA (miRNAs) in sorghum following GA3 treatment. We also identified a majority of DE-mRNAs and non-coding RNAs (ncRNAs) targets that serve essential roles in phenylpropanoid biosynthesis and plant hormone networks. In addition, we generated a competitive endogenous RNA (ceRNA)-miRNA-target gene network, and 3 circRNAs (circRNA_2746, circRNA_6515, circRNA_5622), 4 lncRNAs (XR_002450182.1, XR_002452422.1, XR_002448510.1, XR_002448296.1) and 4 genes (LOC8056546, LOC8062245, LOC8061469, LOC8071960) probably act as valuable candidates for the regulation of the GA3-mediated alleviation of salt stress in sorghum. Our findings uncovered potential mRNA and non-coding RNAs that contribute to GA3 regulation, thus offering a basis for the future investigation of underlying mechanisms of salt stress in sorghum.

Increased Leaching Requirements Allow the Use of Source Water High in Salts for Plant Growth

Growers have different capabilities to alleviate salt stress in the growing substrate. One method to reduce substrate salt levels is to increase the volume of water applied during irrigation. This increases the leaching fraction (LF) which is the volume of water that drains from the growing substrate divided by the volume applied during irrigation. We can determine the leaching requirement (the minimum LF to maintain a desired substrate salt level) using the formula LF = ECw/5(ECe − ECw), where ECw is the electrical conductivity (EC) of the water and ECe is the desired EC of the substrate. We tested this formula to see if we could maintain an acceptable substrate EC of 4 dS⋅m−1 by modifying the LF for ‘Hope’ philodendron (Philodendron selloum) and ‘Tineke’ ficus (Ficus elastica) irrigated with tap water (EC 0.17 dS⋅m−1) or reclaimed wastewater (RWW) from Davie, FL, USA (EC 1.66 dS⋅m−1) and RWW from Hollywood, FL, USA (EC 2.93 dS⋅m−1). Shoot and root dry weight was greatest for both species with the tap water applied with a 5% LF. Increasing the LF to 15% for Davie RWW and a 55% for Hollywood RWW, produced acceptable growth for ‘Hope’ philodendron and ‘Tineke’ ficus. In our second experiment, we monitored the growth of ‘Looking Glass’ begonia (Begonia fibrous), ‘Freddie’ calathea (Calathea concinna), and ‘Déjà vu’ philodendron (Philodendron selloum) irrigated with tap water (EC 0.15 dS⋅m−1), salt water (EC 3.49 dS⋅m−1), or RWW (EC 3.48 dS⋅m−1) with LFs of 28%, 50%, or 65%. ‘Looking Glass’ begonia and ‘Freddie’ calathea growth was greater with 65% LF than 28% LF, respectively, for all three water sources. Philodendron growth was not different due to LF. However, philodendron, calathea, and begonia growth was greater with tap water and RWW than with saltwater. Although final leachate EC with saltwater and RWW was around 2 dS⋅m−1 using 50% LF, leachate sodium (Na) levels from salt watered plants was higher than for RWW or tap watered plants. We suspect that high Na levels in combination with lower potassium (K) and calcium (Ca) levels in the saltwater solution resulted in poor plant growth. Although the Na levels in leachate from RWW substrates was higher than tap watered substrates, Ca and K levels also were greater. Although we were able to use the salt equation to maintain substrate EC levels ranging from 2 to 4 dS⋅m−1, volumes of solution applied were two to three times higher when using RWW or salt water compared with tap water. We suspect that a balance between Na, Ca, and K supported better plant growth with RWW than salt water. However, additional work needs to be done on the benefits of supplemental Ca and K when using water high in salts or Na. This works suggests that in addition to monitoring EC, it also is important to monitor Na, Ca, and K concentrations.

Brassinosteroids or proline can alleviate yield inhibition under salt stress via modulating physio-biochemical activities and antioxidant systems in snap bean

ABSTRACT Legumes are sensitive to salt stress, especially in the early phases of growth. Brassinosteroids (BRs) or proline (Pro) have been shown to improve salt stress tolerance in several plant species when given exogenously. Therefore, two pot experiments laid out in 4 × 3 factorial in a completely randomised design, replicated three times were carried out on snap bean (Phaseolus vulgaris L.) cv. Valentino to examine the roles of BRs or Pro in improving the salt tolerance of snap beans. The first factor included four saline irrigation water levels viz. 0.0, 20, 40, and 60 mM sodium chloride (NaCl), while the second factor involved foliar application with 0.1 µM BRs or 30 mM Pro or distilled water as control. The results revealed that saline irrigation water reduced chlorophyll, membrane stability, relative water content, and yield. Exogenous BRs or Pro alleviated salt stress by reducing uptake and translocation of Na+ and Cl− while enhancing plant K+ assimilation. Increased water status, chlorophyll content, and antioxidant enzyme activity (SOD, POD, CAT) in leaves of snap beans may contribute to improved salt tolerance. These findings suggested that foliar treatment of brassinosteroids or proline could be an effective strategy to improve snap bean salt tolerance.

Selenate and selenite transporters in proso millet: Genome extensive detection and expression studies under salt stress and selenium.

Crops are susceptible to a variety of stresses and amongst them salinity of soil is a global agronomic challenge that has a detrimental influence on crop yields, thus posing a severe danger to our food security. Therefore, it becomes imperative to examine how plants respond to salt stress, develop a tolerance that allows them to live through higher salt concentrations and choose species that can endure salt stress. From the perspective of food, security millets can be substituted to avoid hardships because of their efficiency in dealing with salt stress. Besides, this problem can also be tackled by using beneficial exogenous elements. Selenium (Se) which exists as selenate or selenite is one such cardinal element that has been reported to alleviate salt stress. The present study aimed for identification of selenate and selenite transporters in proso millet (Panicum miliaceum L.), their expression under NaCl (salt stress) and Na2SeO3 (sodium selenite)treatments. This study identified eight transporters (RLM65282.1, RLN42222.1, RLN18407.1, RLM74477.1, RLN41904.1, RLN17428.1, RLN17268.1, RLM65753.1) that have a potential role in Se uptake in proso millet. We analyzed physicochemical properties, conserved structures, sub-cellular locations, chromosome location, molecular phylogenetic analysis, promoter regions prediction, protein-protein interactions, three-dimensional structure modeling and evaluation of these transporters. The analysis revealed the chromosome location and the number of amino acids present in these transporters as RLM65282.1 (16/646); RLN42222.1 (1/543); RLN18407.1 (2/483); RLM74477.1 (15/474); RLN41904.1 (1/521); RLN17428.1 (2/522); RLN17268.1(2/537);RLM65753.1 (16/539). The sub-cellular locations revealed that all the selenite transporters are located in plasma membrane whereas among selenate transporters RLM65282.1 and RLM74477.1 are located in mitochondria and RLN42222.1 and RLN18407.1 in chloroplast. The transcriptomic studies revealed that NaCl stress decreased the expression of both selenate and selenite transporters in proso millet and the applications of exogenous 1µM Se (Na2SeO3) increased the expression of these Se transporter genes. It was also revealed that selenate shows similar behavior as sulfate, while selenite transport resembles phosphate. Thus, it can be concluded that phosphate and sulphate transporters in millets are responsible for Se uptake.

Sex-specific photosynthetic capacity and Na+ homeostasis in Populus euphratica exposed to NaCl stress and AMF inoculation.

Soil salinity and associated land degradation are major ecological problems. Excess Na+ ions in soil impede the plant photosynthetic process and Na+ homeostasis status. Arbuscular mycorrhizal fungi (AMF) can alleviate salt stress in host plants. Although a number of studies have demonstrated that Na+ accumulation is decreased by mycorrhizae, the molecular mechanisms involved have received little attention from researchers. Populus euphratica is a typical natural woody tree with excellent salt tolerance. Due to its symbiosis forming capability with AMF, we explored the influence of Funneliformis mosseae on the growth, photosynthesis, and expression of three genes involved in Na+ homeostasis within dioecious P. euphratica under salt stress. The results indicated that salt stress significantly increases Na+ contents and inhibits growth status and photosynthetic capacity, especially in females. However, AMF had positive effects on the growth status, photosynthetic capacity and Na+ homeostasis, especially in males. The expression levels of NHX1 in shoots and HKT1 and SOS1 in roots, all of which are involved in Na+ homeostasis, were upregulated by F. mosseae under salt stress. For males, the beneficial effect of AMF centered on extruding, sequestering and long-distance transporting of Na+ ions . For females, the beneficial effect of AMF centered on extruding excessive Na+.

Physiological mechanism of exogenous brassinolide alleviating salt stress injury in rice seedlings

Brassinolide (BR) is a sterol compound, which can regulate plant seed germination, flowering, senescence, tropism, photosynthesis, stress resistance, and is closely related to other signaling molecules. This study aimed to evaluate the ability of soaking with BR to regulate growth quality at rice seedling stage under salt stress. Results demonstrated that salt stress increases the contents of ROS, MDA, Na+ and ABA, reduces the the SPAD value, net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), maximum fluorescence (Fm), variable fluorescence (Fv), the effective photochemical efficiency of PSII (Fv/Fo) and the maximum photochemical efficiency of PSII (Fv/Fm), reduces the biomass production and inhabits plant growth. All of these responses were effectively alleviated by BR soaking treatment. Soaking with BR could increase the activities of superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, and the contents of ascorbic acid, glutathione as well as soluble protein and proline, while BR soaking treatment inhibited the accumulation of ROS and reduced the content of MDA. BR soaking significantly reduced the contents of Na+ and increased the contents of K+ and Ca2+, indicating that soaking with BR is beneficial to the excretion of Na+, the absorption of K+ and Ca2+ and the maintenance of ion balance in rice seedlings under salt stress. BR also maintained endogenous hormone balance by increasing the contents of indoleacetic acid (IAA), zeatin (ZT), salicylic acid (SA), and decreasing the ABA content. Soaking with BR significantly increased the SPAD value, Pn and Tr and enhanced the Fm, Fv/Fm and Fv/Fo of rice seedlings under NaCl stress, protected the photosythetic system of plants, and improved their biomass. It is suggested that BR was beneficial to protect membrane lipid peroxidation, the modulation of antioxidant defense systems, ion balance and endogenous hormonal balance with imposition to salt stress.

H2S Enhanced the Tolerance of Malus hupehensis to Alkaline Salt Stress through the Expression of Genes Related to Sulfur-Containing Compounds and the Cell Wall in Roots.

Malus is an economically important plant that is widely cultivated worldwide, but it often encounters saline-alkali stress. The composition of saline-alkali land is a variety of salt and alkali mixed with the formation of alkaline salt. Hydrogen sulfide (H2S) has been reported to have positive effects on plant responses to abiotic stresses. Our previous study showed that H2S pretreatment alleviated the damage caused by alkaline salt stress to Malus hupehensis Rehd. var. pingyiensis Jiang (Pingyi Tiancha, PYTC) roots by regulating Na+/K+ homeostasis and oxidative stress. In this study, transcriptome analysis was used to investigate the overall mechanism through which H2S alleviates alkaline salt stress in PYTC roots. Simultaneously, differentially expressed genes (DEGs) were explored. Transcriptional profiling of the Control-H2S, Control-AS, Control-H2S + AS, and AS-H2S + AS comparison groups identified 1618, 18,652, 16,575, and 4314 DEGs, respectively. Further analysis revealed that H2S could alleviate alkaline salt stress by increasing the energy maintenance capacity and cell wall integrity of M. hupehensis roots and by enhancing the capacity for reactive oxygen species (ROS) metabolism because more upregulated genes involved in ROS metabolism and sulfur-containing compounds were identified in M. hupehensis roots after H2S pretreatment. qRT-PCR analysis of H2S-induced and alkaline salt-response genes showed that these genes were consistent with the RNA-seq analysis results, which indicated that H2S alleviation of alkaline salt stress involves the genes of the cell wall and sulfur-containing compounds in PYTC roots.

Chaetomium globosum D5 confers salinity tolerance on Paeonia lactiflora Pall

Plants will interact with beneficial endophytic fungi to increase resistance under environmental stress. Among these stresses, salt stress poses one of the major threats to plant growth worldwide. We have studied the response mechanism of Chaetomium globosum D5, a salt-tolerant fungus isolated from the roots of Paeonia lactiflora under salt stress, and its mechanism of action in helping P. lactiflora alleviate salt stress. In our study, high levels of salt inhibit growth, whereas low levels promote the growth of C. globosum D5, which resists salt stress by forming dense hyphae and producing more pigments, soluble proteins, and antioxidants. Under salt stress, growth and photosynthesis of P. lactiflora are inhibited, and they are subjected to osmotic stress, oxidative stress, and ionic stress. C. globosum D5 could help P. lactiflora promote growth and photosynthesis by increasing the uptake of nitrogen and phosphorus and increasing the accumulation of the carbon and photosynthetic pigments, help P. lactiflora alleviate osmotic stress by increasing the accumulation of proline, help P. lactiflora alleviate ion stress by reducing Na+ and increasing K+/Na+, Ca2+/Na+ and Mg2+/Na + ratios in P. lactiflora roots and leaves. In summary, joint action between P. lactiflora and C. globosum D5 is responsible for mitigating damage caused by P. lactiflora under salt stress. We first investigate the interaction between the fungus and P. lactiflora under salt stress, providing a theoretical basis for further investigations into the mechanisms of P. lactiflora's response to salt stress and its promotion in coastal areas.

Transcriptomic analysis reveals the mechanism of the alleviation of salt stress by salicylic acid in pepper (Capsicum annuum L.)

BackgroundThe growth and yield of pepper (Capsicum annuum L.) is often affected by the critical salt stress. Salicylic acid (SA) can improve plants’ stress tolerance by promoting growth and regulating ion absorption and transportation.Methods and resultsTo uncover the alleviated mechanism of salt stress by SA in pepper, we conducted morphological, physiological, cytological, and transcriptomic analyses under a single SA treatment and NaCl with and without SA pre-treatment for 9 days. Seedlings under NaCl treatment showed yellow shrunken leaves, this tatus were alleviated by NS treatment (NaCl with SA pre-treatment). Compared with plants under NaCl treatment, those in the NS treatment showed reduced lipid peroxidation, and significantly increased contents of chlorophyll and osmotic regulators (proline, soluble sugars). Treatment with SA balanced the Na+/K+ ratio. We conducted transcriptome sequencing and identified differentially expressed genes (DEGs) contributing to alleviation of salt stress by SA in pepper. Besides photosynthesis related genes, GO and KEGG analyses revealed that the DEGs were enriched in ‘sequence-specific DNA binding’, ‘transcription regulator activity’ and ‘DNA binding transcription factor activity’ by GO terms. And our results showed that TFs, such as MYB, bZIP, BBX, AP2/ERF, NAC, etc., probably make a great contribution in the alleviation of salt stress by SA.ConclusionsThese results reveal that SA can improve plants’ stress tolerance by balancing ion absorption, gene expression and transcriptional regulation, which provide new ideas and resources for subsequent research on the mechanism of salt tolerance in pepper.

Relationships between soil biodiversity and multifunctionality in croplands depend on salinity and organic matter

Soil salinization is a widespread environmental problem adversely impacting global food production. Increasing soil organic matter (SOM) could alleviate salt stress, but soil salinity and SOM have differing effects on microbial diversity and activities. We explored how the relationships between soil biodiversity and multifunctionality were altered by soil salinity and SOM. We collected soils from the wheat-maize cropping system in the North China Plain and categorized soils according to salinity and SOM. Soil functions related to carbon, nitrogen, phosphorus, and micronutrient processing were measured as metrics of soil multifunctionality (SMF) characterization. We found significant positive relationships between SMF and bacterial diversity but not fungal diversity in soils with high SOM (>15 mg/kg) and low EC (<4 ds/m). The diversity and abundance of sensitive bacteria were more strongly correlated with SMF than those of non-sensitive bacteria. SOM directly and indirectly impacted SMF through changes in sensitive bacterial abundance, while soil EC impacted SMF via altered sensitive bacterial diversity. With respective to individual soil function, carbon and micronutrient cycling were predominantly determined by bacterial diversity. Our findings suggest coupling decreased salinization with the increase of SOM could increase soil multifunctionality by increasing diversity and abundance of sensitive soil microbes. These findings highlight the importance of sensitive microbial taxa to sustaining soil ecosystem functioning in croplands.

Integrated Metabolomics and Morpho-Biochemical Analyses Reveal a Better Performance of Azospirillum brasilense over Plant-Derived Biostimulants in Counteracting Salt Stress in Tomato.

Increased soil salinity is one of the main concerns in agriculture and food production, and it negatively affects plant growth and crop productivity. In order to mitigate the adverse effects of salinity stress, plant biostimulants (PBs) have been indicated as a promising approach. Indeed, these products have a beneficial effect on plants by acting on primary and secondary metabolism and by inducing the accumulation of protective molecules against oxidative stress. In this context, the present work is aimed at comparatively investigating the effects of microbial (i.e., Azospirillum brasilense) and plant-derived biostimulants in alleviating salt stress in tomato plants by adopting a multidisciplinary approach. To do so, the morphological and biochemical effects were assessed by analyzing the biomass accumulation and root characteristics, the activity of antioxidant enzymes and osmotic stress protection. Furthermore, modifications in the metabolomic profiles of both leaves and root exudates were also investigated by ultra-high performance liquid chromatography/quadrupole time-of-flight mass spectrometry (UHPLC/QTOF-MS). According to the results, biomass accumulation decreased under high salinity. However, the treatment with A. brasilense considerably improved root architecture and increased root biomass by 156% and 118% in non-saline and saline conditions, respectively. The antioxidant enzymes and proline production were enhanced in salinity stress at different levels according to the biostimulant applied. Moreover, the metabolomic analyses pointed out a wide set of processes being affected by salinity and biostimulant interactions. Crucial compounds belonging to secondary metabolism (phenylpropanoids, alkaloids and other N-containing metabolites, and membrane lipids) and phytohormones (brassinosteroids, cytokinins and methylsalicylate) showed the most pronounced modulation. Overall, our results suggest a better performance of A. brasilense in alleviating high salinity than the vegetal-derived protein hydrolysates herein evaluated.

Volatile organic compounds emitted by Burkholderia pyrrocinia CNUC9 trigger induced systemic salt tolerance in Arabidopsis thaliana.

Salinity is among the most significant abiotic stresses that negatively affects plant growth and agricultural productivity worldwide. One ecofriendly tool for broadly improving plant tolerance to salt stress is the use of bio-inoculum with plant growth-promoting rhizobacteria (PGPR). In this study, a bacterium strain CNUC9, which was isolated from maize rhizosphere, showed several plant growth-promoting characteristics including the production of 1-aminocyclopropane-1-carboxylate deaminase, indole acetic acid, siderophore, and phosphate solubilization. Based on 16S rRNA and recA gene sequence analysis, we identified strain CNUC9 as Burkholderia pyrrocinia. Out of bacterial determinants to elicit plant physiological changes, we investigated the effects of volatile organic compounds (VOCs) produced by B. pyrrocinia CNUC9 on growth promotion and salinity tolerance in Arabidopsis thaliana. Higher germination and survival rates were observed after CNUC9 VOCs exposure under 100 mM NaCl stress. CNUC9 VOCs altered the root system architecture and total leaf area of A. thaliana compared to the control. A. thaliana exposed to VOCs induced salt tolerance by increasing its total soluble sugar and chlorophyll content. In addition, lower levels of reactive oxygen species, proline, and malondialdehyde were detected in CNUC9 VOCs-treated A. thaliana seedlings under stress conditions, indicating that VOCs emitted by CNUC9 protected the plant from oxidative damage induced by salt stress. VOC profiles were obtained through solid-phase microextraction and analyzed by gas chromatography coupled with mass spectrometry. Dimethyl disulfide (DMDS), methyl thioacetate, and 2-undecanone were identified as products of CNUC9. Our results indicate that optimal concentrations of DMDS and 2-undecanone promoted growth in A. thaliana seedlings. Our findings provide greater insight into the salt stress alleviation of VOCs produced by B. pyrrocinia CNUC9, as well as potential sustainable agriculture applications.

Co-application of salicylic acid and spermine alleviates salt stress toxicity in wheat: growth, nutrient acquisition, osmolytes accumulation, and antioxidant response

Salicylic acid (SA) and spermine (SPM) elicit particular responses in response to various environmental stressors. However, there is little known about the underlying mechanism of their combination treatments' mediating effect on salt stress tolerance. In this investigation, the potential impact of 100 mg L−1 SA and/or 30 mg L−1 SPM in avoiding salt damage at saline environments of 6.0 and 12.0 dS m–1 in wheat was examined. Results showed that by increasing mineral acquisition, chlorophyll a and b contents, antioxidant enzymes activity, osmolytes accumulation, leaf water content, grains carbohydrate and protein content as well as reducing Na+ accumulation, membrane electrolyte leakage, malondialdehyde and hydrogen peroxide contents, exogenously applied SA and/or SPM significantly reduced the detrimental impacts of soil salinization and increased wheat growth and productivity. The best outcomes came from combining the SA and SPM treatments. Overall, this combined treatment enhanced mineral homeostasis, osmolytes accumulation, and antioxidant response, pointing to a potential role for it in minimizing the negative consequences of salt stress. Therefore, combining SA and SPM in a sustainable agricultural system can be viewed as a successful technique for reducing salt damage.

Plant Growth and Yield Response to Salinity Stress of Rice Grown under the Application of Different Nitrogen Levels and Bacillus pumilus Strain TUAT-1

Rice is an important food crop, and its production is significantly affected by salt stress under the changing climate. Soil-inhabiting microbial inoculants as well as efficient nitrogen (N) nutrition may have ameliorative effects on rice growth and yield under salt stress. However, the effects of the interaction between N application and microbial inoculants on the growth and grain yield of rice under salt stress is not yet fully understood. This study aimed to clarify whether the use of the Bacillus pumilus strain TUAT-1 biofertilizer, along with the right amount of N fertilizer, would alleviate salt stress in lowland rice production. We applied the Bacillus pumilus strain TUAT-1 as a biofertilizer in combination with different rates of N fertilizer: control (0% N), 2.64 g (NH4)2SO4 per nursery tray (100% N: the farmer-recommended amount), and 3.96 g (NH4)2SO4 per nursery tray (150% N). Salinity (100 mM of NaCl) was applied at the heading stage of rice plants in pot culture in the greenhouse, and the growth and yield components were accessed at harvest. In the nursery phase, the application of the biofertilizer TUAT-1 significantly increased seedling vigor and the root development of 21-day-old seedlings. Salinity stress at the heading stage significantly reduced chlorophyll content, panicle number, straw biomass, and grain yield; however, either the application of N alone or in combination with TUAT-1 ameliorated the salinity-related reduction in grain yield and yield component parameters. Plants receiving a high amount of N fertilizer (150% N) showed similar straw biomass and grain yield with or without TUAT-1 inoculation, regardless of saline or non-saline conditions. In both saline and control conditions, straw biomass and grain yield were higher in the plants inoculated with TUAT-1 than in those without TUAT-1. Specifically, the combined application of TUAT-1 and the farmer-recommended N level (100% N) led to an increase of 8% in straw biomass and 15% in grain yield under saline stress when compared with their respective plants without TUAT-1. Straw biomass and grain yield were similar in the (un-inoculated) plants grown under normal conditions and TUAT-1 + 100% N under salinity treatments, because TUAT-1 enhanced root development, which may promote soil nutrient uptake. Our results indicated that combined nursery application of TUAT-1 biofertilizer and 100% N fertilizer rate has the potential to boost the capacity of this bacteria to increase seedling vigor, which subsequently ameliorated the salt-induced reduction in the grain and straw yield.

Abscisic Acid, Paclobutrazol, and Salicylic Acid Alleviate Salt Stress in Populus talassica × Populus euphratica by Modulating Plant Root Architecture, Photosynthesis, and the Antioxidant Defense System

The exogenous plant growth regulators (PGRs) represent a useful strategy for reducing the adverse effects of salt stress in plants. In order to investigate the regulatory effect of exogenous PGRs on the salt tolerance of Populus talassica × Populus euphratica seedlings, in this study, the effects of different foliar spray concentrations of ABA (5 mg·L−1, 15 mg·L−1, 25 mg·L−1), PP333 (300 mg·L−1, 900 mg·L−1, 1500 mg·L−1), and SA (40 mg·L−1, 120 mg·L−1, 200 mg·L−1) on P. talassica × P. euphratica seedlings under salt stress (soil salt concentration of 2%) were determined. The results showed that the dry weight, total root length, root surface area, root volume, total Chl content, and photosynthetic parameters of P. talassica × P. euphratica seedlings significantly decreased under salt stress and increased their contents of malondialdehyde (MDA), hydrogen peroxide (H2O2), superoxide anion (O2−), free proline (Pro), superoxide dismutase (SOD), and peroxidase (POD). However, ABA, PP333, and SA can mitigate the adverse effects of salt stress on these indicators. Especially, the 15 mg·L−1 ABA, 900 mg·L−1 PP333, and 120 mg·L−1 SA treatments had the best effect on alleviating salt stress, with significant increases in dry weight, root parameters, total Chl content, and the photosynthetic parameters of the P. talassica × P. euphratica seedlings, improving their photosynthetic characteristics; meanwhile, increased Pro content and enzyme activity and decreased MDA, H2O2, and O2− content protected the integrity of membrane system and enhanced the salt tolerance of the seedlings. SA resulted in a better ameliorative effect on salt stress compared to ABA and PP333.

Salt-tolerant PGPR strain Priestia endophytica SK1 promotes fenugreek growth under salt stress by inducing nitrogen assimilation and secondary metabolites.

Soil salinity is a huge obstacle in crop production worldwide. Saline soil can reduce active chemical contents in medicinal plants of the Leguminosae family through crippled normal nodule function. Intensive efforts are underway to improve yield and medicinal value of leguminous herbs under salt stress condition by using benign microbes. Here, an attempt was made to explore the salt-tolerant bacteria associated with rhizosphere of fenugreek plant (Trigonella foenum-graecum L.) and to evaluate their impact on host plant growth and metabolite of pharmaceutical importance. A salt-tolerant plant growth promoting rhizobacterial (PGPR) strain Priestia endophytica SK1 isolated from fenugreek rhizospheric soil, which increased biomass and metabolite content in plants grown under saline stress. SK1 bacterial application induced nodule formation and enhanced nitrogen and phosphorus content under salt (100 mM NaCl) stress as compared to control plants. H2 O2 production and lipid peroxidation as a measure of stress were observed high in control plants, while a reduction in these parameters was observed in plants inoculated with SK1. In addition, a significant effect was found on the phenolic compounds and trigonelline content in fenugreek plant inoculated with SK1 bacterium. An increased trigonelline content of about 54% over uninoculated control was recorded under salt stress. The results of this study revealed that the application of salt-tolerant PGPR strain P. endophytica SK1 induced nitrogen fixation machinery that leads to alleviate salt stress and improved the biosynthesis of trigonelline content in fenugreek. This study extends our understanding on the significance of rhizosphere microbiome and their beneficial role in plant health under environmental stress to promote agro-eco-farming practices.

Alleviation of Salt Stress with Chitosan Foliar Application and Its Effects on Growth and Development in Tomato (Solanum lycopersicum L.)

Environmental and climatic fluctuations as well as abiotic stress factors affect agricultural production and cause a loss in quality and yield. It is important to find alternative solutions for the sustainability of agricultural production to feed the increasing population. Salt stress is one of the most devastating abiotic stress factors and tomato (Solanum lycopersicum L.) production is also affected by salt stress since it needs extensive irrigation for high yield. The exogenous application of some plant inducers showed promising results in the induction and improvement of plant tolerance to stress factors. Chitosan (2-amino-2-deoxy-b-D-glucosamine), one of the organic compounds, is getting significant attention in agriculture with its potential. Here, we evaluated the potential of chitosan application for salt stress tolerance on tomato. 0.03% and 0.05% chitosan solutions were applied as a foliar spray to the plant and salt tolerance improvement were investigated under untreated (0 mM NaCl) and 100 mM NaCl conditions. The growth-related (root and shoot diameters, above and below-ground biomass, number of leaves and branches, and plant height), photosynthetic parameters (chlorophyll a, b, total carotenoid content), and ion leakage were investigated. According to the results, chitosan application improves plant development in both untreated and salt-stress conditions and improved plant growth. Also, photosynthetic parameters showed that the application of chitosan increased chlorophyll contents under untreated conditions. Our result suggests that the application of chitosan may have a promising effect on salt stress tolerance and further research may shed light on its molecular mechanisms.

A novel PGPF Penicillium olsonii isolated from the rhizosphere of Aeluropus littoralis promotes plant growth, enhances salt stress tolerance, and reduces chemical fertilizers inputs in hydroponic system.

The hydroponic farming significantly enhances the yield and enables multiple cropping per year. These advantages can be improved by using plant growth-promoting fungi (PGPF) either under normal or stress conditions. In this study, the fungal strain (A3) isolated from the rhizosphere of the halophyte plant Aeluropus littoralis was identified as Penicillium olsonii based on sequence homology of its ITS region. The A3 fungus was shown to be halotolerant (up to 1 M NaCl) and its optimal growth was at 27°C, but inhibited at 40°C. In liquid culture medium, the A3 produced indole acetic acid (IAA) especially in the presence of L-tryptophan. Tobacco plants grown under hydroponic farming system were used to evaluate the promoting activity of the direct effect of A3 mycelium (DE) and the indirect effect (IDE) of its cell-free culture filtrate (A3CFF). The results showed that for the two conditions (DE or IDE) the tobacco seedlings exhibited significant increase in their height, leaf area, dry weight, and total chlorophyll content. Interestingly, the A3CFF (added to the MS liquid medium or to nutrient solution (NS), prepared from commercial fertilizers) induced significantly the growth parameters, the proline concentration, the catalase (CAT) and the superoxide dismutase (SOD) activities of tobacco plants. The A3CFF maintained its activity even after extended storage at 4°C for 1 year. Since the A3 is a halotolerant fungus, we tested its ability to alleviate salt stress effects. Indeed, when added at 1:50 dilution factor to NS in the presence of 250 mM NaCl, the A3CFF enhanced the plant salt tolerance by increasing the levels of total chlorophyll, proline, CAT, and SOD activities. In addition, the treated plants accumulated less Na+ in their roots but more K+ in their leaves. The A3CFF was also found to induce the expression of five salt stress related genes (NtSOS1, NtNHX1, NtHKT1, NtSOD, and NtCAT1). Finally, we proved that the A3CFF can reduce by half the chemical fertilizers inputs. Indeed, the tobacco plants grown in a hydroponic system using 0.5xNS supplemented with A3CFF (1:50) exhibited significantly higher growth than those grown in 0.5xNS or 1xNS. In an attempt to explain this mechanism, the expression profile of some growth related genes (nitrogen metabolism (NR1, NRT1), auxin (TRYP1, YUCCA6-like), and brassinosteroid (DET2, DWF4) biosynthesis) was performed. The results showed that all these genes were up-regulated following plant treatment with A3CFF. In summary the results revealed that the halotolerant fungus P. olsonii can stimulates tobacco plant growth, enhances its salt tolerance, and reduces by half the required chemical fertilizer inputs in a hydroponic farming system.