Salt Treatment Research Articles

The effect of soil salt content and ionic composition on nitrification in a Fluvisol of the Yellow River Delta

Soil salinization is a common cause of land degradation and a major constraint on global food production. However, the effects that different salts have on soil biogeochemical processes such as nitrification are not fully understood. An incubation experiment was conducted with two different salt treatments applied at varying concentrations (sodium chloride addition, NaCl1: 2.06, NaCl2: 4.12, NaCl3: 5.00 g kg−1; sodium sulphate addition, NaS1: 5.00, NaS2: 6.07, NaS3:12.14 g kg−1). A Fluvisol soil was used as incubation medium and urea was supplied as the nitrogen source. Results showed that urease activities were reduced (28–76%) in salt treated soils on day 1, but recovered over time and finally surpassed that of the control on day 56. Moreover, the average urease activity of Na2SO4 treatments was 1.26 times higher than that of NaCl treatments on day 56. In addition, increasing soil salinity levels simultaneously reduced hydrolysis and nitrification rates, which led to the temporary accumulation of ammonium (NH4+-N) in soils for up to 14 days. The maximum contents of NH4+-N accumulation in NaCl3 and NaS3 were 1.64 and 1.48 times higher than those of NaCl1 and NaS1, respectively. Nitrification rates were inhibited more severely in soils dominated by Cl-. Low soil salt contents (less than 7.79 g kg−1) only delayed nitrification without reducing the total amount of nitrate (NO3--N) produced during the incubation. However, high salt contents (NaS3) significantly decreased the total NO3--N production. Our results indicate that nitrite oxidation process may also limit the speed of nitrification in salt-affected soils. Additionally, a new model is introduced to better simulate the dynamics of nitrification in salt-affected soils. In conclusion, soil salt content is the primary factor that inhibits nitrification. Anions affect the inhibitory strength of salinity on nitrification in soils with similar salinity levels, where Cl- is more suppressive than SO42-.

Transcriptome profiles reveal NF-YC1-regulated pathways in adaption to salt stress in Arabidopsis thaliana

Salt stress is a major abiotic stress affecting plant growth and development. Identification and characterization of genes, especially for transcription factors (TFs), can provide us a comprehensive understanding of the regulatory mechanisms of transcriptional pathways in response to salt stress. Here, we first showed that nuclear-localized transcription factor nuclear factor-Y subunit C1 (NF-YC1) was required for the salt tolerance response in Arabidopsis. Loss of function of NF-YC1 resulted in a salt-sensitive phenotype together with increased sodium (Na) content in roots and shoots, while the overexpression line could complement this phenotype. Subsequent transcriptome analysis revealed differentially expressed genes (DEGs) in WT plants and nf-yc1 mutant, independent of salt treatment. Further analysis identified two positive downstream target genes AOX3 and BGLU47, involved in the cyanide-resistant alternative respiration and lignin biosynthesis, respectively, and a negative downstream target gene, MLS, which is related to malate synthase, as being involved in these regulatory cascades controlling the salt tolerance, and these results were further confirmed by CHIP-qPCR in vivo. In conclusion, several novel pathways have been elucidated, demonstrating that NF-YC1-dependent transcriptional regulation in salt-treated Arabidopsis thaliana.

Combined transcriptomic and metabolomic analysis of alginate oligosaccharides alleviating salt stress in rice seedlings

BackgroundSalt stress is one of the key factors limiting rice production. Alginate oligosaccharides (AOS) enhance plant stress resistance. However, the molecular mechanism underlying salt tolerance in rice induced by AOS remains unclear. FL478, which is a salt-tolerant indica recombinant inbred line and IR29, a salt-sensitive rice cultivar, were used to comprehensively analyze the effects of AOS sprayed on leaves in terms of transcriptomic and metabolite profiles of rice seedlings under salt stress.ResultsIn this experiment, exogenous application of AOS increased SOD, CAT and APX activities, as well as GSH and ASA levels to reduce the damage to leaf membrane, increased rice stem diameter, the number of root tips, aboveground and subterranean biomass, and improved rice salt tolerance. Comparative transcriptomic analyses showed that the regulation of AOS combined with salt treatment induced the differential expression of 305 and 1030 genes in FL478 and IR29. The expressed genes enriched in KEGG pathway analysis were associated with antioxidant levels, photosynthesis, cell wall synthesis, and signal transduction. The genes associated with light-trapping proteins and RLCK receptor cytoplasmic kinases, including CBA, LHCB, and Lhcp genes, were fregulated in response to salt stress. Treatment with AOS combined with salt induced the differential expression of 22 and 50 metabolites in FL478 and IR29. These metabolites were mainly related to the metabolism of amino and nucleotide sugars, tryptophan, histidine, and β -alanine. The abundance of metabolites associated with antioxidant activity, such as 6-hydroxymelatonin, wedelolactone and L-histidine increased significantly. Combined transcriptomic and metabolomic analyses revealed that dehydroascorbic acid in the glutathione and ascorbic acid cycles plays a vital role in salt tolerance mediated by AOS.ConclusionAOS activate signal transduction, regulate photosynthesis, cell wall formation, and multiple antioxidant pathways in response to salt stress. This study provides a molecular basis for the alleviation of salt stress-induced damage by AOS in rice.

Tetracosanoic acids produced by 3-ketoacyl-CoA synthase 17 are required for synthesizing seed coat suberin in Arabidopsis.

Very long-chain fatty acids (VLCFAs) are precursors for the synthesis of membrane lipids, cuticular waxes, suberins, and storage oils in plants. 3-Ketoacyl CoA synthase (KCS) catalyzes the condensation of C2 units from malonyl-CoA to acyl-CoA, the first rate-limiting step in VLCFA synthesis. In this study, we revealed that Arabidopsis KCS17 catalyzes the elongation of C22-C24 VLCFAs required for synthesizing seed coat suberin. Histochemical analysis of Arabidopsis plants expressing GUS (β-glucuronidase) under the control of the KCS17 promoter revealed predominant GUS expression in seed coats, petals, stigma, and developing pollen. The expression of KCS17:eYFP (enhanced yellow fluorescent protein) driven by the KCS17 promoter was observed in the outer integument1 of Arabidopsis seed coats. The KCS17:eYFP signal was detected in the endoplasmic reticulum of tobacco epidermal cells. The levels of C22 VLCFAs and their derivatives, primary alcohols, α,ω-alkane diols, ω-hydroxy fatty acids, and α,ω-dicarboxylic acids increased by ~2-fold, but those of C24 VLCFAs, ω-hydroxy fatty acids, and α,ω-dicarboxylic acids were reduced by half in kcs17-1 and kcs17-2 seed coats relative to the wild type (WT). The seed coat of kcs17 displayed decreased autofluorescence under UV and increased permeability to tetrazolium salt compared with the WT. Seed germination and seedling establishment of kcs17 were more delayed by salt and osmotic stress treatments than the WT. KCS17 formed homo- and hetero-interactions with KCR1, PAS2, and ECR, but not with PAS1. Therefore, KCS17-mediated VLCFA synthesis is required for suberin layer formation in Arabidopsis seed coats.

Short-term changes in antioxidant response of Eutrema salsugineum exposed to severe salinity

Salinity is one of the major constraints limiting plant productivity. Understanding the mechanism of salinity tolerance is a necessary step for improving crops yield in saline conditions. Eutrema salsugineum is a halophyte species and plant model for salinity tolerance mechanism study. Therefore, we studied the ability of E. salsugineum plants for their antioxidant response to 400 mM NaCl treatment. Changes in hydrogen peroxide (H2O2), malondialdehyde (MDA) and tocopherol contents, and kinetics of catalase, superoxide dismutase and peroxidase enzyme activities were investigated. Results shows that, although increasing in the beginning of the salt treatment, the fast decrease in H2O2 and MDA levels afterwhile indicates the ability of E. salsugineum to alleviate oxidative damage and to maintain membrane integrity. Together, with the increase of tocopherol contents, the high enzymatic activity of CAT, SOD and POD reflect the highly efficient antioxidant response of E. salsugineum.

PHT1;5 Repressed by ANT Mediates Pi Acquisition andDistribution under Low Pi andSalinity inSalt Cress.

Salinity and phosphate (Pi) starvation are the most common abiotic stresses that threaten crop productivity. Salt cress (Eutrema salsugineum) displays good tolerance to both salinity and Pi limitation. Previously, we found several Phosphate Transporter (PHT) genes in salt cress upregulated under salinity. Here, EsPHT1;5 induced by both low Pi (LP) and salinity was further characterized. Overexpression of EsPHT1;5 in salt cress enhanced plant tolerance to LP and salinity, while the knock-down lines exhibited growth retardation. The analysis of phosphorus (P) content and shoot/root ratio of total P in EsPHT1;5-overexpressing salt cress seedlings and the knock-down lines as well as arsenate uptake assays suggested the role of EsPHT1;5 in Pi acquisition and root-shoot translocation under Pi limitation. In addition, overexpression of EsPHT1;5 driven by the native promoter in salt cress enhanced Pi mobilization from rosettes to siliques upon a long-term salt treatment. Particularly, the promoter of EsPHT1;5 outperformed that of AtPHT1;5 in driving gene expression under salinity. We further identified a transcription factor EsANT, which negatively regulated EsPHT1;5 expression and plant tolerance to LP and salinity. Taken together, EsPHT1;5 plays an integral role in Pi acquisition and distribution in plant response to LP and salt stress. Further, EsANT may be involved in the cross-talk between Pi starvation and salinity signaling pathways. This work provides further insight into the mechanism underlying high P use efficiency in salt cress in its natural habitat, and evidence for a link between Pi and salt signaling.

Biochemical responses of Silybum marianum seedlings to independent and combined salt and SiO2 treatments

In recent years, silicon dioxide (SiO2) particles have drawn increasing attention due to their potential to enhance plant tolerance to various stresses by modulating physiological and biochemical processes. Salinity is an important abiotic stress with a harmful impact on crop growth and productivity. In this context, the aim of this study was to investigate the influence of silicon dioxide (SiO2) addition on milk thistle (Silybum marianum (L.) Gaertn.) under salinity stress. Thus, individual and combined effects of the application of sodium chloride (NaCl, 50 and 100 mM) and SiO2 particles (0.1 mM) on some physiological and oxidative stress parameters, such as growth variables, photosynthetic pigments and soluble protein contents, the levels of an oxidative stress biomarker (malondialdehyde), and the specific activity of several antioxidant enzymes (superoxide dismutase, catalase and peroxidase) were evaluated. The results revealed that salt stress (100 mM) inhibited plant growth and decreased chlorophyll and carotenoid levels, whereas the added SiO2 partially mitigated these negative effects. In addition, the 100 mM NaCl treatment significantly increased peroxidise (POD) activity and decreased soluble protein content after 22 days, while no significant differences were found for group subjected to salt stress in the presence of SiO2. Results suggest that application of SiO2 on salt-stressed milk thistle may modify the seedling metabolism and increase the plant salt tolerance capacity.

Genome-wide analysis of the heat shock transcription factor family reveals saline-alkali stress responses in Xanthoceras sorbifolium.

The heat shock transcription factor (HSF) family is involved in regulating growth, development, and abiotic stress. The characteristics and biological functions of HSF family member in X. sorbifolium, an important oil and ornamental plant, have never been reported. In this study, 21 XsHSF genes were identified from the genome of X. sorbifolium and named XsHSF1-XsHSF21 based on their chromosomal positions. Those genes were divided into three groups, A, B, and C, containing 12, one, and eight genes, respectively. Among them, 20 XsHSF genes are located on 11 chromosomes. Protein structure analysis suggested that XsHSF proteins were conserved, displaying typical DNA binding domains (DBD) and oligomerization domains (OD). Moreover, HSF proteins within the same group contain specific motifs, such as motif 5 in the HSFC group. All XsHSF genes have one intron in the CDS region, except XsHSF1 which has two introns. Promoter analysis revealed that in addition to defense and stress responsiveness elements, some promoters also contained a MYB binding site and elements involved in multiple hormones responsiveness and anaerobic induction. Duplication analysis revealed that XsHSF1 and XsHSF4 genes were segmentally duplicated while XsHSF2, XsHSF9, and XsHSF13 genes might have arisen from transposition. Expression pattern analysis of leaves and roots following salt-alkali treatment using qRT-PCR indicated that five XsHSF genes were upregulated and one XsHSF gene was downregulated in leaves upon NaCl treatment suggesting these genes may play important roles in salt response. Additionally, the expression levels of most XsHSFs were decreased in leaves and roots following alkali-induced stress, indicating that those XsHSFs may function as negative regulators in alkali tolerance. MicroRNA target site prediction indicated that 16 of the XsHSF genes may be regulated by multiple microRNAs, for example XsHSF2 might be regulated by miR156, miR394, miR395, miR408, miR7129, and miR854. And miR164 may effect the mRNA levels of XsHSF3 and XsHSF17, XsHSF9 gene may be regulated by miR172. The expression trends of miR172 and miR164 in leaves and roots on salt treatments were opposite to the expression trend of XsHSF9 and XsHSF3 genes, respectively. Promoter analysis showed that XsHSFs might be involved in light and hormone responses, plant development, as well as abiotic stress responses. Our results thus provide an overview of the HSF family in X. sorbifolium and lay a foundation for future functional studies to reveal its roles in saline-alkali response.

The removal of organic contaminants from industrial waste salts by pyrolysis and potential use for energy storage

Industrial waste salt (IWS) treatment is a significant technology for current environmental protection and resource utilization, and the complex organic pollutants in waste salts seriously hamper the development of cleaner production. In this work, the kinetic mechanism of the organic pollutant removal by pyrolysis is investigated, and the energy storage performance of the recovered products is studied, which provides a new idea for the coupling of waste salt resource treatment and energy storage utilization. Experimental results and pyrolysis kinetic analysis show that high temperature pyrolysis can deeply remove the organic pollutants in IWS, and the total organic carbon (TOC) removal rate can reach more than 99%. The high temperature pyrolysis of waste salt is mainly divided into two stages, and the pyrolysis reaction mainly occurs in the high temperature section (270°C–330 °C) with lower activation energy. The obtained salt containing carbon material exhibits high light absorptance of about 82%, enhanced thermal conductivity of 0.39 W/(m·K) and specific heat of 1.49 J/(g·K), which can be employed as the low-cost and high-performance photothermal absorption and thermal storage material.

TaBZR1 enhances wheat salt tolerance via promoting ABA biosynthesis and ROS scavenging

Brassinosteroids (BRs) are vital plant steroid hormones involved in numerous aspects of plant life including growth, development, and responses to various stresses. However, the underlying mechanisms of how BR regulates abiotic stress responses in wheat (Triticum aestivum L.) remain to be elucidated. Here, we find that BR signal core transcription factor BRASSINAZOLE-RESISTANT1 (TaBZR1) is significantly up-regulated by salt treatment. Overexpression of Tabzr1-1D (a gain-of-function TaBZR1 mutant protein) improves wheat salt tolerance. Furthermore, we show that TaBZR1 binds directly to the G-box motif in the promoter of ABA biosynthesis gene TaNCED3 to activate its expression and promotes ABA accumulation. Moreover, TaBZR1 associates with the promoters of ROS-scavenging genes TaGPX2 and TaGPX3 to activate their expression. Taken together, our results elucidate that TaBZR1 improves salt-stress tolerance by activating some genes involved in the biosynthesis of ABA and ROS scavenging in wheat, which gives us a new strategy to improve the salt tolerance of wheat.

Evaluation of Lipid Profile of High Salt fed Rats treated with L-Arginine

There is a global concern on salt consumption above the dietary guideline; salt consumption evokes physiological responses with cardiovascular risks associated with dyslipidemia other than increased blood pressure as numerous studies have pointed out. This study aimed at evaluating the effect of L-Arginine on lipid profile of rats fed high salt diet. Forty Male Albino Wister rats weighing between 70-120g were randomly selected assigned into four groups of 10 rats each. Group 1 served as the control and was given distilled water and normal rat chow. Group 2 was fed with high salt diet (8% Nacl in feed, and 1% Nacl in drinking water) Group 3 was treated as group 2 with the introduction of L-Arginine on the 43rd day of the experiment. Group 4 was treated as group 2 with the introduction of losartan administration on the 43rd day of the experiment. Administration of L-Arginine and losartan lasted for 14 days, making a total duration of feeding and drugs administration 56 days. At the end of the 56th day, the rats were fasted overnight for 12 hours and sacrificed under anaesthesia using sodium pentobarbitone. Blood samples were then collected from each animal via cardiac puncture into heparinized tubes and centrifuged at 3500rpm for a period of 15 min, and the clear supernatant plasma were collected and stored at -20°C for biochemical analyses of lipid profile. The results showed a significant increase in TG, LDL-C, TC, VLDL-C and a reduction of HDL-C in the salt fed group. Conversely, a significant reduction in TG, LDL-C, TC, VLDL-C and an increase in HDL-C was shown in the salt + L-Arginine treated group when compared to the control. The changes observed in the L-Arginine treated groups reversed the hyperlipidemia in the salt treated group which indicates L-Arginine is beneficial in treatment of salt induced dyslipidemia and cardiovascular diseases. Keywords: cardiovascular risks, dyslipidemia, L-Arginine, rats fed high salt diet

Vitis Myb14 confer cold and drought tolerance by activating lipid transfer protein genes expression and reactive oxygen species scavenge

The R2R3 Myb transcription factor exhibits a wide range of functions and participates in various biological processes in plant development, secondary metabolism, and abiotic stress tolerance, among others. Vitis Myb14 initially identified for its involvement in resveratrol synthesis in grapevines. In this study, we investigate its role in abiotic stress tolerance. Significant differences in expression were observed between two grape varieties, Vitis amurensis (Cold-hardy) and V. vinifera (Cold-sentitive), under abiotic and hormone treatments. Both VvMyb14 and VaMyb14 demonstrated responsiveness to cold, drought and high salt treatment, but VaMyb14 exhibited a quicker and more pronounced response. To investigate further, we overexpressed VaMyb14 in A. thalina and found that VaMyb14 OE plants showed significantly enhanced cold and drought tolerance compared to wild-type plants. Additionally, the transgenic lines exhibited increased antioxidant enzyme activity, particularly POD activity, and reduced MDA content. Microarray analysis of VaMyb14 OE plants revealed up-regulation of several ABA metabolism and signal transduction genes, including several LTPs, PP2Cs, RD29B, COR78 and other structural genes, indicating that VaMyb14 has the capacity to reprogram a significant signaling pathway. Furthermore, comparative mRNA sequencing profiling of 35S:VaMyb14 grapevine callus indicated its involvement its function involved in ROS scavenging and ABA signaling. These findings collectively demonstrate that Vitis Myb14 serves as a critical regulator in grapevine stress responses, contributing to improved defense against necrotrophic pathogens, enhanced phytoalexin resveratrol production, and increased drought or cold tolerance.

Desalination brine effects beyond excess salinity: Unravelling specific stress signaling and tolerance responses in the seagrass Posidonia oceanica.

Desalination has been proposed as a global strategy for tackling freshwater shortage in the climate change era. However, there is a concern regarding the environmental effects of high salinity brines discharged from desalination plants on benthic communities. In this context, seagrasses such as the Mediterranean endemic and ecologically important Posidonia oceanica have shown high vulnerability to elevated salinities. Most ecotoxicological studies regarding desalination effects are based on salinity increments using artificial sea salts, although it has been postulated that certain additives within the industrial process of desalination may exacerbate a negative impact beyond just the increased salinities of the brine. To assess the potential effect of whole effluent brines on P. oceanica, mesocosm experiments were conducted within 10 days, simulating salinity increment with either artificial sea salts or brines from a desalination plant (at 43 psμ, 6 psμ over the natural 37 psμ). Morphometrical (growth and necrosis), photochemical (PSII chlorophyll a fluorometry), metabolic, such as hydrogen peroxide (H2O2), thiobarbituric reactive substances (TBARS) and ascorbate/dehydroascorbate (ASC/DHA), and molecular (expression of key tolerance genes) responses were analyzed in each different treatment. Although with a still positive leaf growth, associated parameters decreased similarly for both artificial sea salt and brine treatments. Photochemical parameters did not show general patterns, although only P. oceanica under brines demonstrated greater energy release through heat (NPQ). Lipid peroxidation and upregulation of genes related to oxidative stress (GR, MnSOD, and FeSOD) or ion exclusion (SOS3 and AKT2/3) were similarly incremented on both hypersalinity treatments. Conversely, the ASC/DHA ratio was significantly lower, and the expression of SOS1, CAT, and STRK1 was increased under brine influence. This study revealed that although metabolic and photochemical differences occurred under both hypersalinity treatments, growth (the last sign of physiological detriment) was similarly compromised, suggesting that the potential effects of desalination are mainly caused by brine-associated salinities and are not particularly related to other industrial additives.

Treatment of salt from hides curing stage by electrocoagulation for use in the pickling stage of the tanning industry

The raw materials for the tanning industry, namely hides and skins, are preserved (curing stage) and carried with common salt, i.e., sodium chloride (NaCl). Proceeding to conversion into leather, pickling is a key stage of the tannery process, which entails high demand of water and salt. In this work, the salt-derived brine (SdB) generated from the curing of hides was treated by iron-driven electrocoagulation (EC), aiming at its later application in the pickling stage of the tanning industry, promoting a transition to zero waste emission policy. Focusing on reducing the brine's total organic carbon (TOC), central composite rotational design and response surface methodology were adopted to study the effect of electrolysis time (6.2–14.2 min) and current density (74–431 A·m−2) on the treatment of the SdB (≅ 7.5 % wt. NaCl). The quality of the treated brines was then assessed in pickling trials and compared with virgin brine. 68–83 % removal of TOC from the SdB were achieved under electrolysis time ranging 6.2–14.2 min and current density ranging 126–252 A·m−2. Under these operating ranges the quality of the wet-blue leathers was guaranteed. Lowest power consumption (0.44 kWh·m−3) was achieved under electrolysis time of 6 min and current density of 126 A·m−2, yielding 68 % removal of TOC. Moreover, the shrinkage temperature of the hides was improved with treated brine (103.5 °C–110.5 °C) compared to virgin brine (103.0 °C). The present study provides strong evidence that contaminated salt from the curing stage can be valorised within the tanning industry through electrocoagulation treatment and then used in another production stage, instead of being landfilled.

Decoupling of nutrient stoichiometry in Suaeda glauca (Bunge) senesced leaves under salt treatment.

The stoichiometry of senesced leaves is pivotal in nutrient cycling and can be significantly influenced by soil salinization, a rising global issue threatening the functionality of ecosystems. However, the impacts of soil salinization on senesced leaf stoichiometry are not fully understood. In this study, we conducted a pot experiment with varying soil salt concentrations to examine their influence on the concentrations and stoichiometric ratios of nitrogen (N), phosphorus (P), sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), and zinc (Zn) in the senesced leaves of Suaeda glauca (Bunge). Compared to the control group, salt treatments significantly enhanced Na concentration while diminishing the concentrations of K, Ca, Mg, Zn, N, and P. Interestingly, as salinity levels escalated, N concentration maintained stability, whereas P concentration exhibited an increasing trend. Moreover, K, Ca, and Mg significantly declined as salt levels rose. Salt treatments brought about significant changes in stoichiometric ratios, with the N:P, K:Na, N:Na, N:Mg, and Ca : Mg ratios dropping and the N:Ca and N:K ratios rising, illustrating the varying nutrient coupling cycles under different salt conditions. These findings shed light on the plasticity of stoichiometric traits in S. glauca senesced leaves in response to soil salinization shifts, which could potentially offer insights into nutrient cycling reactions to soil salinization.

Promotion effects of salt-alkali on ammonia volatilization in a coastal soil

Coastal ecosystems are highly susceptible to salt-related problems due to their formation process and geographical location. As such ecosystems are the most accessible land resources on Earth, clarifying and quantifying the effects of salt-alkali conditions on N concentration and ammonia (NH3) volatilization are pivotal for promoting coastal agricultural productivity. The challenge in establishing this effect is to determine how salt-alkali conditions impact NH3 volatilization through direct or indirect interactions. An incubation experiment using a coastal soil from a paddy farmland, combined with the structural equation modeling (SEM) method, was conducted to reveal the net effects of salt-alkali on NH3 volatilization and the role of environmental and microbial factors in mutual interaction networks. The specific experimental design consisted of four salt treatments (S1, S2, S3, and S4: 1‰, 3‰, 8‰, and 15‰ NaCl by mass of soil, respectively), four alkaline treatments (A1, A2, A3, and A4: 0.5‰, 1‰, 3‰, and 8‰ NaHCO3 by mass of soil, respectively) and a control without NaCl or NaHCO3 addition (CK), and each treatment had three urea concentrations (N1, N2, and N3: 0.05, 0.10, and 0.15 g N kg-1 soil, respectively) and three replicates. At the N1, N2, and N3 levels, NH3 volatilization increased by 9.31%–34.98%, 3.07%–26.92%, and 2.99%–43.61% as the NaCl concentration increased from 1‰ to 15‰, respectively, compared with CK. With an increase in the NaHCO3 concentration from 0.5‰ to 8‰, NH3 volatilization increased by 8.36%–56.46%, 5.49%–30.10%, and 30.72%–73.18% at the N1, N2, and N3 levels, respectively, compared with CK. According to the SEM method, salinity and alkalinity had positive direct effects on NH3 volatilization, with standardized path coefficients of 0.40 and 0.19, respectively. Considering the total effects (net positive and negative effects) in the SEM results, alkalinity had a greater influence than salinity (total standardized coefficient 0.104 > 0.086). Nitrogen concentrations in the incubation system showed a direct positive effect on NH3 volatilization (standardized path coefficient = 0.78), with an obvious decrease under elevated salinity and alkalinity levels. Additionally, gene abundances of nitrogen-transforming microbes indirectly increased NH3 volatilization (total indirect standardized coefficient = 0.31). Our results indicated that potential NH3 emissions from coastal saline areas could be enhanced more by soil alkalization than by salinization.

Abstract 012: Diagnosis Of Salt Sensitivity Of Blood Pressure Using Circulating Monocyte Isolevuglandin-CXCL/CCL Signaling In Response To Elevated Sodium In Vitro

Salt sensitivity of blood pressure (SSBP) is when blood pressure changes parallel to salt loading/ depletion and is an independent risk factor for cardiovascular disease. Despite its importance, there is no feasible diagnosis, which limits investigational studies to identify therapeutic targets. Our studies indicate that changes in production of isolevuglandins (IsoLGs) in antigen presenting cells (APCs) parallel changes in blood pressure following salt-loading and depletion in humans and this is associated with chemokine signaling. We hypothesized that in vivo responses to salt-loading/depletion leading to IsoLG production in APCs are mirrored in vitro . To test this hypothesis, we isolated peripheral blood mononuclear cells from known salt-sensitive and salt-resistant people and treated them with either normal salt (140 mmoL) or high salt (190 mmoL) for 24 hours in vitro . Using flow cytometry, we found that classical monocytes from salt sensitive but not salt resistant people had a significant increase in IsoLGs (25.15 ± 7.41 vs 14.52 ± 8.60, p = 0.0022) after 24 hours of high salt treatment. To determine mechanisms, we also performed bulk RNAseq on in vitro high salt treated monocytes and CITEseq on PBMCs following the salt-loading/depletion protocol. We found that salt-loading/depletion was associated with parallel changes in the expression of various chemokines in the CXCL and CC families both in vitro and in vivo . Specifically, the changes in levels of CXCL8 (p = 0.01553, r = 0.8067) , CXCL16 (p = 0.004697, r = -0.8725), and CCL2 (p = 0.002292, r = -0.9004) correlated with changes in diastolic and systolic blood pressure from salt loading to depletion. Moreover, changes in systolic blood pressure significantly correlated with changes in CCL2 (p= 0.008878, r= -0.6302) and CCL4 (p= 0.03209, r = -0.5367) from salt loading to salt depletion. These data suggest that in vitro responses of IsoLGs and chemokine production to salt treatment could serve as a feasible diagnosis for salt sensitivity of blood pressure in the clinic.

Abstract P177: Antigen-presenting Cell Vitamin D3 Modulates Salt-sensitive Hypertension In Humans

Salt-sensitivity of blood pressure (SSBP) is a condition in which high sodium intake causes shifts in blood pressure that are associated with cardiovascular disease and mortality. Recent studies from our lab indicate that increased sodium concentrations activate antigen-presenting cells (APCs), leading to SSBP. Vitamin D3 has been shown to attenuate inflammation, but its mechanisms and contribution to SSBP remain unknown. We hypothesized that vitamin D anti-inflammatory signaling in immune cells attenuates SSBP. To test this hypothesis, we performed bulk-RNA sequencing on monocytes after high-salt exposure and noticed an increase in vitamin D receptor (VDR) expression (NS: 1781.18 ± 222.33; HS: 2922.18 ± 371.65). Additionally, we performed single-cell CITE-Seq analysis on peripheral blood mononuclear cells isolated from hypertensive individuals after a rigorous inpatient salt-loading and salt-depletion protocol over a three-day period. On the second day when salt treatment was introduced, we observed an increase in VDR expression within APCs. Conversely, we observed a drop in VDR expression on the third day when salt was depleted from the APCs in salt-sensitive but not salt-resistant individuals. These results suggest that VDRs play an important role in modulating SSBP.

Abstract P302: EFFECTS OF FINERENONE ON MYOCARDIAL INJURY AND SODIUM ACCUMULATION IN ALDOSTERONE-INFUSED RATS

The aim of this study was to examine the effects of finerenone, a nonsteroidal mineralocorticoid receptor (MR) antagonist, on myocardial injury and sodium accumulation in rats subjected to aldosterone and salt treatment. Finerenone was administered orally at a dose of 10 mg/kg body weight, while aldosterone was given subcutaneously at a rate of 0.75 μg/hr and salt was provided in drinking water at a concentration of 1% NaCl. Aldosterone-infused rats experienced mortality within 30 days, while finerenone-treated rats did not. Echocardiography and gene expression analyses were conducted to evaluate cardiac remodeling and function in rats exposed to salt/aldosterone loading for 4 weeks. The results showed adverse cardiac remodeling and cardiac dysfunction with preserved ejection fraction in these rats. However, finerenone treatment completely prevented cardiac dysfunction and improved cardiac remodeling. Sodium accumulation in the left ventricular tissues was markedly elevated in salt/aldosterone-loaded rats, but significantly reduced in rats treated with finerenone. Furthermore, finerenone treatment significantly reduced gene expression of F4/80, a macrophage marker. In vitro studies with RAW 264.7 cells showed that sodium treatment increased mRNA expression of pro-inflammatory markers and upregulated NFAT5, a transcription factor that regulates genes involved in osmotic stress, while reducing the expression of anti-inflammatory markers. Finerenone treatment suppressed the elevation of pro-inflammatory markers and NFAT5, but did not affect anti-inflammatory gene levels. These findings suggest that finerenone protects against aldosterone-induced myocardial injury by suppressing sodium accumulation and subsequent inflammation, as well as adverse cardiovascular remodeling.

On salt stress, PLETHORA signaling maintains root meristems.

Salt stress is one of the unfavorable environmental factors to affect plants. Salinity represses root growth, resulting in reduced biomass of agricultural plants. Little is known about how plants maintain root growth to counteract salt stress. The AP2-domain transcription factors PLETHORA1/2 (PLT1/2) act as master regulators in root meristem maintenance in Arabidopsis. In this study, we report that the salt overly sensitive (SOS) pathway component SOS2 regulates PLT1/2 at the post-transcriptional level. Salt-activated SOS2 interacts and phosphorylates PLT1/2 through their conserved C-terminal motifs to stabilize PLT1/2, critical for root apical meristem maintenance under salt stress. The phospho-mimetic version of PLT1/2 restored meristem and primary root length reduction of sos2-2 and plt1-4 plt2-2 mutants on salt treatment. Moreover, SOS2-mediated PLT1/2 phosphorylation improves root growth recovery after salt stress alleviation. We identify a SOS2-PLT1/2 core protein module that is required for protecting primary root growth and meristem maintenance from salt stress.