Severe Salt Stress Research Articles

Heterologous expression of the durum wheat TdHKT1;4-1 partially complements the mutant athkt1 in Arabidopsis thaliana under severe salt stress.

High-affinity K+ (HKT) transporters which mediate Na+-specific transport or Na+-K+ co-transport play a key role in plant salt tolerance. In our previous functional study in Xenopus oocytes, we demonstrated that the durum wheat TdHKT1;4-1 acts as a Na+-selective transporter. Here, we investigated the function of TdHKT1;4-1 and its contribution in salt stress tolerance in the Arabidopsis athkt1 mutant background. Our results revealed that TdHKT1;4-1 partially complements the salt sensitivity phenotype of the athkt1 transgenic lines. Comparative physiological analyses and oxidative stress status under moderate salt stress (50mM NaCl) showed that both transgenic lines SH3 and SH5 restored the salt stress tolerance comparable to the level observed in Wt plants. Whereas, under severe salt stress treatment (100mM NaCl), the athkt1 transgenic lines exhibited an intermediate salt stress tolerance between Wt and athkt1 mutant. Moreover, TdHKT1;4-1 was highly expressed in leaves under moderate and severe salt stress, while in roots, it was largely expressed only under severe salt stress. In addition, antioxidant enzymes such as catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) were significantly expressed in SH3 and SH5 lines compared to athkt1 and Wt under moderate stress. Therefore, TdHKT1;4-1 seems to differ from its Arabidopsis homologous counterpart, as it contributes to salt stress tolerance up to a specific threshold, above which the TdHKT1;4-1 expression may lead to higher root Na+ influx, hence increasing its toxicity during salt stress.

Enhancing soil amendment for salt stress using pretreated rice straw and cellulolytic fungi

Rice straw breakdown is sluggish, which makes agricultural waste management difficult, however pretreatment procedures and cellulolytic fungi can address this issue. Through ITS sequencing, Chaetomium globosum C1, Aspergillus sp. F2, and Ascomycota sp. SM2 were identified from diverse sources. Ascomycota sp. SM2 exhibited the highest carboxymethyl cellulase (CMCase) activity (0.86 IU/mL) and filter-paper cellulase (FPase) activity (1.054 FPU/mL), while Aspergillus sp. F2 showed the highest CMCase activity (0.185 IU/mL) after various pretreatments of rice straw. These fungi thrived across a wide pH range, with Ascomycota sp. SM2 from pH 4 to 9, Aspergillus sp. F2, and Chaetomium globosum C1 thriving in alkaline conditions (pH 9). FTIR spectroscopy revealed significant structural changes in rice straw after enzymatic hydrolysis and solid-state fermentation, indicating lignin, cellulose, and hemicellulose degradation. Soil amendments with pretreated rice straw, cow manure, biochar, and these fungi increased root growth and soil nutrient availability, even under severe salt stress (up to 9.3 dS/m). The study emphasizes the need for a better understanding of Ascomycota sp. degradation capabilities and proposes that using cellulolytic fungus and pretreatment rice straw into soil amendments could mitigate salt-related difficulties and improve nutrient availability in salty soils.

Exploring Natural Variations in Arabidopsis thaliana: Plant Adaptability to Salt Stress.

The increase in soil salinization represents a current challenge for plant productivity, as most plants, including crops, are mainly salt-sensitive species. The identification of molecular traits underpinning salt tolerance represents a primary goal for breeding programs. In this scenario, the study of intraspecific variability represents a valid tool for investigating natural genetic resources evolved by plants in different environmental conditions. As a model system, Arabidopsis thaliana, including over 750 natural accessions, represents a species extensively studied at phenotypic, metabolic, and genomic levels under different environmental conditions. Two haplogroups showing opposite root architecture (shallow or deep roots) in response to auxin flux perturbation were identified and associated with EXO70A3 locus variations. Here, we studied the influence of these genetic backgrounds on plant salt tolerance. Eight accessions belonging to the two haplogroups were tested for salt sensitivity by exposing them to moderate (75 mM NaCl) or severe (150 mM NaCl) salt stress. Salt-tolerant accessions were found in both haplogroups, and all of them showed efficient ROS-scavenging ability. Even if an exclusive relation between salt tolerance and haplogroup membership was not observed, the modulation of root system architecture might also contribute to salt tolerance.

Differential responses of Hollyhock (Alcea rosea L.) varieties to salt stress in relation to physiological and biochemical parameters

The response of 14 Hollyhock (Alcea rosea L.) varieties to salinity were evaluated in a field experiment over two growing seasons. Carotenoid, Chl a, Chl b, total Chl, proline and MDA content, CAT, APX and GPX activity and petal and seeds yields were determined in order to investigate the mechanism of salt tolerance exhibited by Hollyhock, and too identify salt tolerant varieties. Overall, the photosynthetic pigment content,petal and seed yields were reduced by salt stress. Whereas the proline and MDA content, and the CAT, APX and GPX activities increased as salt levels increased. However, the values of the measured traits were dependent upon the on the level of salt stress, the Varietie and the interaction between the two variables. Based upon the smallest reduction in petal yield, the Masouleh variety was shown to be the most salt tolerant, when grown under severe salt stress. However, based upon the smallest reduction in seed yield, Khorrmabad was the most tolerant variety to severe salt stress. These data suggest that the selection of more salt tolerant Hollyhock genotypes may be possible based upon the wide variation in tolerance to salinity exhibited by the varieties tested.

Ácido salicílico reduz os efeitos prejudiciais do estresse salino em Tropaeolum majus

ABSTRACT Salt stress hampers the growth and physiology of nasturtium (Tropaeolum majus), due to biochemical, physiological, and anatomical disruptions. The application of salicylic acid stands as an alternative to alleviate the detrimental effects of salt stress, but studies on nasturtium are scarce. Thus, the aim of present study was to assess the effects of foliar application of salicylic acid on nasturtium cultivated under salt stress. The experiment followed a completely randomized design in a 3 x 3 factorial scheme, with 0 (no stress), 50 (moderate salt stress), and 100 (severe salt stress) mM of NaCl, and application of 0, 0.5, and 1 mM of salicylic acid, each with six replications. Growth (plant height, stem diameter, and number of leaves), gas exchange (stomatal conductance, photosynthesis, transpiration, internal CO2 concentration, intrinsic water use efficiency, instantaneous water use efficiency, and intrinsic carboxylation efficiency), as well as chlorophyll indices and chlorophyll a fluorescence were evaluated. Salt stress affected the variables analyzed in this study. The application of salicylic acid had a positive effect on mitigating the effects of severe salt stress, resulting in a significant increase in the number of leaves. The most effective dose was 1 mM, also leading to notable improvements in water use efficiency and photochemical efficiency. However, other combinations of salinity and salicylic acid reduced growth and gas exchange in nasturtium plants.

Mitigation of salt stress in lettuce by a biostimulant that protects the root absorption zone and improves biochemical responses.

Horticultural crops constantly face abiotic stress factors such as salinity, which have intensified in recent years due to accelerated climate change, significantly affecting their yields and profitability. Under these conditions, it has become necessary to implement effective and sustainable solutions to guarantee agricultural productivity and food security. The influence of BALOX®, a biostimulant of plant origin, was tested on the responses to salinity of Lactuca sativa L. var. longifolia plants exposed to salt concentrations up to 150 mM NaCl, evaluating different biometric and biochemical properties after 25 days of treatment. Control plants were cultivated under the same conditions but without the biostimulant treatment. An in situ analysis of root characteristics using a non-destructive, real-time method was also performed. The salt stress treatments inhibited plant growth, reduced chlorophyll and carotenoid contents, and increased the concentrations of Na+ and Cl- in roots and leaves while reducing those of Ca2+. BALOX® application had a positive effect because it stimulated plant growth and the level of Ca2+ and photosynthetic pigments. In addition, it reduced the content of Na+ and Cl- in the presence and the absence of salt. The biostimulant also reduced the salt-induced accumulation of stress biomarkers, such as proline, malondialdehyde (MDA), and hydrogen peroxide (H2O2). Therefore, BALOX® appears to significantly reduce osmotic, ionic and oxidative stress levels in salt-treated plants. Furthermore, the analysis of the salt treatments' and the biostimulant's direct effects on roots indicated that BALOX®'s primary mechanism of action probably involves improving plant nutrition, even under severe salt stress conditions, by protecting and stimulating the root absorption zone.

Cytokinin deficiency confers enhanced tolerance to mild, but decreased tolerance to severe salinity stress in in vitro grown potato.

Cytokinin (CK) is a plant hormone that plays crucial roles in regulating plant growth and development. CK-deficient plants are widely used as model systems for investigating the numerous physiological roles of CK. Since it was previously shown that transgenic or mutant CK-deficient Arabidopsis and Centaurium plants show superior tolerance to salinity, we examined the tolerance of three CK-deficient potato lines overexpressing the Arabidopsis thaliana CYTOKININ OXIDASE/DEHYDROGENASE2 (AtCKX2) gene to 50 mM, 100 mM, 150 mM, and 200 mM NaCl applied in vitro. Quantification of visible salinity injury, rooting and acclimatization efficiency, shoot growth, water saturation deficit, and chlorophyll content confirmed that the CK-deficient potato plants were more tolerant to low (50 mM) and moderate (100 mM) NaCl concentrations, but exhibited increased sensitivity to severe salinity stress (150 and 200 mM NaCl) compared to non-transformed control plants. These findings were corroborated by the data distribution patterns according to principal component analysis. Quantification of the activity of superoxide dismutases, peroxidases, and catalases revealed an impaired ability of AtCKX2-transgenic lines to upregulate the activity of antioxidant enzymes in response to salinity, which might contribute to the enhanced sensitivity of these potato lines to severe salt stress. Our results add complexity to the existing knowledge on the regulation of salinity tolerance by CK, as we show for the first time that CK-deficient plants can exhibit reduced rather than increased tolerance to severe salt stress.

Fungal epiphytes differentially regulate salt tolerance of invasive Ipomoea cairica according to salt stress levels.

Fungal symbionts can improve plant tolerance to salt stress. However, the interaction of epiphytic Fusarium oxysporum and Fusarium fujikuroi with the tolerance of the invasive plant Ipomoea cairica against saline coastal habitats is largely unknown. This study aimed to investigate the interaction of the mixture of the two epiphytic fungi with salt tolerance of I. cairica. Surface-sterilized I. cairica cuttings inoculated (E+) and non-inoculated (E-) with the fungal mixture were cultivated with 2, 3, and 5 parts per thousand (PPT) of NaCl solutions to simulate mild, moderate, and severe salt stress, respectively. The hydroponic experiment showed that the growth inhibition and peroxidation damages of E+ and E- cuttings were aggravated with salinity. Noteworthily, E+ cuttings had higher peroxidase (POD) and catalase (CAT) activities, chlorophyll content, total biomass, aboveground biomass, total shoot length and secondary shoot number, but lower root-to-shoot ratio than E- cuttings under 2 and 3 PPT NaCl conditions. Moreover, E+ had higher superoxide dismutase (SOD) activity and proline content but lower belowground biomass and malondialdehyde (MDA) content than E- cuttings under 3 PPT NaCl condition. However, lower SOD, POD, and CAT activities, and chlorophyll content, but higher MDA content occurred in E+ cuttings than in E- cuttings under 5 PPT NaCl condition. These findings suggested that the mixture of the two epiphytic fungi increased salt tolerance of I. cairica mainly through increasing its antioxidation ability and chlorophyll stability under mildly and moderately saline conditions, but decreased salt tolerance of this plant in an opposite way under severely saline conditions.

Investigation of the response of Platycodongrandiflorus (Jacq.) A. DC to salt stress using combined transcriptomics and metabolomics

BackgroundPlatycodon grandiflorus (Jacq.) A. DC is a famous traditional Chinese medicine in China and an authentic medicine in Inner Mongolia. It has been traditionally used as an expectorant in cough and also has anti-inflammatory and other pharmacological effects. As a homologous plant of medicine and food, P. grandiflorus is widely planted in Northeast China. Soil salinity isa limiting factor for its cultivation. In this study, we comprehensively described the physiological characteristics of P. grandiflorus and combined transcriptomics and metabolomics to study the response of roots of P. grandiflorus to salt stress.ResultsOverall, 8,988 differentially expressed genes were activated and significantly altered the metabolic processes. In total, 428 differentially abundant metabolites were affected by salt stress. After moderate and severe salt stress, most of the differentially abundant metabolites were enriched in the L-phenylalanine metabolic pathway. Through the comprehensive analysis of the interaction between key genes and metabolites, the main pathways such as lignin compound biosynthesis and triterpene saponin biosynthesis were completed. The relative content of compounds related to lignin biosynthesis, such as caffeic acid, coniferin, and syringing, increased under salt stress, and the related genes such as PAL, C4H, and the key enzyme gene UGT72E2 were activated to adapt to the salt stress. Platycodon saponin is one of the major triterpene saponins in P. grandiflorus, and Platycodin D is its most abundant major bioactive component. Under severe salt stress, Platycodin D level increased by nearly 1.77-fold compared with the control group. Most of the genes involved insynthetic pathway of Platycodin D, such as HMGCR, GGPS, SE, and LUP, were upregulated under salt stress.ConclusionSalt stress led to a decrease in the biomass and affected the activities of antioxidant enzymes and contents of osmotic regulators in the plant. These results provided not only novel insights into the underlying mechanisms of response of P. grandiflorus to salt stress but also a foundation for future studies on the function of genes related to salt tolerance in the triterpenoid saponin biosynthesis pathway.

Deciphering the regulatory networks involved in mild and severe salt stress responses in the roots of wild grapevine Vitis vinifera spp. sylvestris.

Transcriptional regulatory networks are pivotal components of plant's response to salt stress. However, plant adaptation strategies varied as a function of stress intensity, which is mainly modulated by climate change. Here, we determined the gene regulatory networks based on transcription factor (TF) TF_gene co-expression, using two transcriptomic data sets generated from the salt-tolerant "Tebaba" roots either treated with 50mM NaCl (mild stress) or 150mM NaCl (severe stress). The analysis of these regulatory networks identified specific TFs as key regulatory hubs as evidenced by their multiple interactions with different target genes related to stress response. Indeed, under mild stress, NAC and bHLH TFs were identified as central hubs regulating nitrogen storage process. Moreover, HSF TFs were revealed as a regulatory hub regulating various aspects of cellular metabolism including flavonoid biosynthesis, protein processing, phenylpropanoid metabolism, galactose metabolism, and heat shock proteins. These processes are essentially linked to short-term acclimatization under mild salt stress. This was further consolidated by the protein-protein interaction (PPI) network analysis showing structural and plant growth adjustment. Conversely, under severe salt stress, dramatic metabolic changes were observed leading to novel TF members including MYB family as regulatory hubs controlling isoflavonoid biosynthesis, oxidative stress response, abscisic acid signaling pathway, and proteolysis. The PPI network analysis also revealed deeper stress defense changes aiming to restore plant metabolic homeostasis when facing severe salt stress. Overall, both the gene co-expression and PPI network provided valuable insights on key transcription factor hubs that can be employed as candidates for future genetic crop engineering programs.

Niche-dependent microbial assembly in salt-tolerant tall fescue and its contribution to plant biomass

Tall fescue (Festuca arundinacea Schreb.) is promising for biogas production in cold climate zones and displays good performance and high biomass under moderate to severe salt stress. The plant microbiome is crucial for enhancing plant growth and boosting crop yield under salt stress. To determine the variations of microbiome composition and abundance in different plant compartments with salt-tolerant tall fescue cultivars under salt stress, this study performed 16S ribosomal RNA amplicon and internal transcribed spacer (ITS) sequencing. Moreover, the study investigated the effect of enriched bacteria on tall fescue growth and salt tolerance. The aboveground and belowground compartments shaped distinct and overlapping microbial communities, as evidenced by the fact that Proteobacteria and Ascomycota displayed various preferences in inhabiting each compartment. Salt stress drove significant changes in microbiome composition in different compartments. Interestingly, the abundance and diversity of bacteria varied more significantly than those of fungi in response to salt stress. Microbes may enhance the carbon fixation pathways in prokaryotes and flagellar assembly functions to improve the salinity tolerance of tall fescue. Moreover, the inoculation experiment revealed that Halomonas lutescens could promote plant salt tolerance and biomass accumulation. Taken together, this research presents clear insight regarding the dynamics of plant microbiome recruitment in different tall fescue compartments under salt stress and highlights the role of the microbes in regulating plant salt tolerance, thus offering huge potential for increasing the resilience of crop and bioenergy production in agriculture and industry to salt stress.

Calcium nanoparticles mitigate severe salt stress in Solanum lycopersicon by instigating the antioxidant defense system and renovating the protein profile

Due to increasing global climate change problems to biota, salinity has been recognized as a realistic hazard critically affects the sustain agri-food production and crop quality in many regions of the world. Nanotechnology as an innovative approach can effectively improve plant performance under risky conditions such as salinity. Taking in consideration the ameliorative role of nanoparticles such as calcium nanoparticles (Ca-NPs) in enhancing plant growth and tolerance against various abiotic stresses, the present study was undertaken to illuminate the powerful effect and the underlying mechanism of soil-applied Ca-NPs (20 mM) in preventing salt damage at saline conditions (NaCl at 50, 100 and 200 mM) in tomato. Data revealed that NaCl drastically imposed the morphological parameters, primary and secondary metabolism, photosynthesis pigment content, hydrogen peroxide and lipid peroxidation levels, antioxidant enzyme activities, mineral contents, and protein patterns. In contrast, the supplementation of exogenous Ca-NPs modified salinity toxicity effects by improving the survival, growth parameters, anabolic (soluble ions and osmolytes) and defense mechanisms (enzymatic and nonenzymatic antioxidants). Interestingly, under lethal salinity level (200 mM), Ca-NPs was capable of suppressing the excessive damage effect of salinity by up-regulating the performance of the plants when these plants were completely dead in the absence of Ca-NPs. The descriptive cluster analysis separated treatments and characteristics into 3 to elucidate negative and positive correlations. Moreover, Ca-NPs was more efficient than CaCl2 in eliciting salt tolerance under all investigated NaCl levels. Therefore, all these findings together conclude that Ca-NPs have a positive role in motivating resilience strategies in tomato plants toward salt stress via lessening the ROS overproduction, stimulating enzymatic antioxidants, promoting osmolytes accumulation, and renovating protein profile under mild and severe salinity levels.

Salt adaptability of wolfberry (Lycium chinense) in terms of photosystems performance and interaction

At present, photosystems interaction has not been clearly elucidated in halophyte under salt stress. Here, we intended to investigate salt adaptability from photosystems stability and cooperation in a halophytic economic shrub wolfberry (Lycium chinense) by a pot experiment. Under 200 mM NaCl stress, neither PSII nor PSI photoinhibiting occurred according to insignificant changes in Fv/Fm and △MR/MR0, and thus, high tolerance of photosystems was ascertained in wolfberry. Under 300 mM NaCl stress, tremendous increased leaf Na+ content and decreased leaf relative water content induced oxidative stress with significant elevated lipid peroxidation and H2O2 level. Accordingly, PSII and PSI photoinhibition arose upon elevated excitation pressure and declined photosynthetic rate. Earlier PSII photoinhibition restricted electron flow to PSI in line with delayed PSI oxidation in 820 nm reflection transient at day 7. The restricted electron flow helped defend PSI photoihibition, as the simulated interception of electron donation from PSII prevented significant decrease in △MR/MR0. After 12 days of 300 mM NaCl stress, PSI photoinhibition occurred, and PSI damage was more serious than PSII because of significant declined ratio of △MR/MR0 to Fv/Fm. PSI vulnerability was verified by shortened PSI oxidation in 820 nm reflection transient at day 14 upon restricted electron donation from PSII. Considering elevated I step and lowered I2 in prompt and delayed chlorophyll fluorescence transients at day 14, respectively, PQ reoxidation was inhibited, implying greater damage on PSI likewise. PSI photoinhibition could elevate feedback inhibition on electron transport and might aggregate PSII photoinhibition. Consistently, the decrease of Fv/Fm was exacerbated upon the simulated suppression on electron transport beyond primary quinone, so that PSI photoinhibition portended the breakdown of entire photosynthetic apparatus. In conclusion, earlier PSII photoinhibition assisted in protecting PSI under severe salt stress, but this function was limited, as PSI photoinhibition could not be prevented under prolonged stress.

Moderate application of nitrogen augments the growth of Taxodium hybrid ‘Zhongshanshan 406’ plants in coastal soils

In plants, nitrogen (N) is known to affect photosynthesis and induces resistance to abiotic stresses by influencing physiological processes. In this study, we investigated the influence of low (50 kg ha−1), moderate (150 kg N ha−1) and high (250 kg ha−1) N application on the physiology, photosynthesis and mineral element contents of Taxodium hybrid ‘Zhongshanshan 406’ (T. 406) plants grown with salt stress (low, moderate and severe) or without (non-saline control, CK). T. 406 plants showed poor growth and gradually died under severe salt stress (EC=12.3 dS·m−1). The biomass of T. 406 plants was reduced by 44.3%, on average, in low salt (EC=1.99 dS·m−1) treatment compared with plants grown in control conditions. Moderate N application conspicuously improved photosynthesis and growth of plants in the low-salt treatment group, thus alleviating the adverse effects of salt stress compared with low and high N application treatments. The results showed that moderate N increased the contents of N and cations in T. 406 plants, leading to an increased efficiency of photosynthetic N use. These findings indicated that excessive N fertilization did not promote N uptake in reclaimed soils and that moderate N application may be used as a potential tool for the alleviation of salt stress in T. 406 plants in coastal soils.

Asparagine Uptake: a Cellular Strategy of Methylocystis to Combat Severe Salt Stress.

Methylocystis spp. are known to have a low salt tolerance (≤1.0% NaCl). Therefore, we tested various amino acids and other well-known osmolytes for their potential to act as an osmoprotectant under otherwise growth-inhibiting NaCl conditions. Adjustment of the medium to 10 mM asparagine had the greatest osmoprotective effect under severe salinity (1.50% NaCl), leading to partial growth recovery of strain SC2. The intracellular concentration of asparagine increased to 264 ± 57 mM, with a certain portion hydrolyzed to aspartate (4.20 ± 1.41 mM). In addition to general and oxidative stress responses, the uptake of asparagine specifically induced major proteome rearrangements related to the KEGG level 3 categories of "methane metabolism," "pyruvate metabolism," "amino acid turnover," and "cell division." In particular, various proteins involved in cell division (e.g., ChpT, CtrA, PleC, FtsA, FtsH1) and peptidoglycan synthesis showed a positive expression response. Asparagine-derived 13C-carbon was incorporated into nearly all amino acids. Both the exometabolome and the 13C-labeling pattern suggest that in addition to aspartate, the amino acids glutamate, glycine, serine, and alanine, but also pyruvate and malate, were most crucially involved in the osmoprotective effect of asparagine, with glutamate being a major hub between the central carbon and amino acid pathways. In summary, asparagine induced significant proteome rearrangements, leading to major changes in central metabolic pathway activity and the sizes of free amino acid pools. In consequence, asparagine acted, in part, as a carbon source for the growth recovery of strain SC2 under severe salinity. IMPORTANCE Methylocystis spp. play a major role in reducing methane emissions into the atmosphere from methanogenic wetlands. In addition, they contribute to atmospheric methane oxidation in upland soils. Although these bacteria are typical soil inhabitants, Methylocystis spp. are thought to have limited capacity to acclimate to salt stress. This called for a thorough study into potential osmoprotectants, which revealed asparagine as the most promising candidate. Intriguingly, asparagine was taken up quantitatively and acted, at least in part, as an intracellular carbon source under severe salt stress. The effect of asparagine as an osmoprotectant for Methylocystis spp. is an unexpected finding. It may provide Methylocystis spp. with an ecological advantage in wetlands, where these methanotrophs colonize the roots of submerged vascular plants. Collectively, our study offers a new avenue into research on compounds that may increase the resilience of Methylocystis spp. to environmental change.

Differences in Organic Solute and Metabolites of Leymus chinensis in Response to Different Intensities of Salt and Alkali Stress.

To explore differences in the physiological metabolic response mechanisms of grassland perennial plants to different intensities of salt-alkali stress, we employed GC-MS to identify the metabolome of perennial rhizome-saline-tolerant Leymus chinensis (L. chinensis). L. chinensis reduced stress damage by accumulating osmotic solutes during salt-alkali stress, although the types of accumulated solutes varied with stress and concentration gradients. Soluble sugars increased only under mild salt-alkali stress. Under salt and mild alkali stress, amino acids increased. Under severe salt-alkali stress, organic acids increased. Betaine increased as a typical osmolute under salt-alkali stress. Metabolic analysis identified 20 metabolites, including 4 amino acids, 6 sugars, and 10 organic acids. The majority of them increased in response to stress. Under mild salt stress, the metabolites included glycine and proline. Under mild alkali stress, they primarily consisted of sugars such as isomaltose and lactulose, whereas under severe salt-alkali stress, they primarily consisted of organic acids such as citric acid and isocitric acid. Pathway analysis showed that six pathways were affected. Glycine, serine, and threonine metabolism was affected under mild salt stress. Alanine, aspartate, and glutamate metabolism and butanota metabolism were affected under mild alkali stress, while energy metabolism pathways, such as the TCA cycle and glyoxylate and dicarboxylate metabolism, were affected under severe salt-alkali stress. The results indicate the importance of betaine in stress resistance and the significance of organic acid in severe salt stress, and they also demonstrate that energy supply was one of the key mechanisms in response to severe salt-alkali stress.

Effective root responses to salinity stress include maintained cell expansion and carbon allocation.

Acclimation of root growth is vital for plants to survive salt stress. Halophytes are great examples of plants that thrive even under severe salinity, but their salt tolerance mechanisms, especially those mediated by root responses, are still largely unknown. We compared root growth responses of the halophyte Schrenkiella parvula with its glycophytic relative species Arabidopsis thaliana under salt stress and performed transcriptomic analysis of S.parvula roots to identify possible gene regulatory networks underlying their physiological responses. Schrenkiella parvula roots do not avoid salt and experience less growth inhibition under salt stress. Salt-induced abscisic acid levels were higher in S.parvula roots compared with Arabidopsis. Root transcriptomic analysis of S.parvula revealed the induction of sugar transporters and genes regulating cell expansion and suberization under salt stress. 14 C-labeled carbon partitioning analyses showed that S.parvula continued allocating carbon to roots from shoots under salt stress while carbon barely allocated to Arabidopsis roots. Further physiological investigation revealed that S.parvula roots maintained root cell expansion and enhanced suberization under severe salt stress. In summary, roots of S.parvula deploy multiple physiological and developmental adjustments under salt stress to maintain growth, providing new avenues to improve salt tolerance of plants using root-specific strategies.

Alleviating the adverse effects of salinity stress on Salicornia persica using sodium nitroprusside and potassium nitrate

BackgroundGlasswort (Salicornia persica) is identified as a halophyte plant, which is one of the most tolerant plants to salt conditions. The seed oil of the plant contains about 33% oil. In the present study, the effects of sodium nitroprusside (SNP; 0, 0.1, 0.2, and 0.4 mM) and potassium nitrate (KNO3; 0, 0.5, and 1%) were evaluated on several characteristics of glasswort under salinity stress (0, 10, 20, and 40 dS/m).Resultsmorphological features, phenological traits, and yield parameters such as plant height, number of days to flowering, seed oil, biological yield, and seed yield significantly decreased in response to severe salt stress. However, the plants needed an optimal salinity concentration (20 dS/m NaCl) to obtain high amounts of seed oil and seed yield. The results also showed that a high level of salinity (40 dS/m NaCl) caused a decrease in plant oil and yield. In addition, by increasing the exogenous application of SNP and KNO3, the seed oil and seed yield increased.ConclusionsThe application of SNP and KNO3 were effective in protecting S. persica plants from the deleterious effects of severe salt stress (40 dS/m NaCl), thereby restoring the activity of antioxidant enzymes, increasing the proline content, and maintaining cell membrane stability. It seems that both factors, i.e. SNP and KNO3, can be applied as mitigators of salt stress in plants.

Gas exchange and osmotic adjustment in cotton cultivars subjected to severe salt stress.

Salinity is harmful to crops when the concentration of soluble salts overcomes the salinity threshold of the crop, causing osmotic stress and limitations in plant growth. In this scenario, adopting tolerant cultivars is the most adequate strategy to minimize agricultural losses. However, the inheritance of tolerance depends on the genotype. From this perspective, this study assessed the tolerance to severe salt stress in 11 cotton cultivars based on gas exchange parameters and the free proline content. The cultivars were grown in a greenhouse and subjected to 34 days of saline irrigation (10 dS m-1), starting 45 days after seedling emergence (B1 phase). Plant growth was monitored weekly until the end of the salt stress period. The treatments consisted of a combination of two factors: eleven cultivars associated with two electrical conductivity levels of irrigation water (ECw: 0.3 and 10.0 dS m-1). The experimental design was in randomized blocks in a 11 × 2 factorial arrangement with three replications (66 plots), with the experimental unit consisting of one plant per plot. Salinity impacted plant growth, being reflected on the gas exchange and free proline data of most cultivars. However, BRS 286, FMT 705, BRS 416, and BRS Acácia, and CNPA 7MH withstood the effects of stress and osmotically adjusted to the salt stress conditions, thus minimizing the damage to growth. Those cultivars are the most indicated for improvement programs aiming at tolerance to salt stress based on the results found in this research.

Comprehensive Analysis of StSRO Gene Family and Its Expression in Response to Different Abiotic Stresses in Potato.

As a highly conserved family of plant-specific proteins, SIMILAR-TO-RCD-ONE (SROs) play an essential role in plant growth, development and response to abiotic stresses. In this study, six StSRO genes were identified by searching the PARP, RST and WWE domains based on the genome-wide data of potato database DM v6.1, and they were named StSRO1-6 according to their locations on chromosomes. StSRO genes were comprehensively analyzed using bioinformatics methods. The results showed that six StSRO genes were irregularly distributed on five chromosomes. Phylogenetic analysis showed that 30 SRO genes of four species were distributed in three groups, while StSRO genes were distributed in groups II and III. The promoter sequence of StSRO genes contained many cis-acting elements related to hormones and stress responses. In addition, the expression level of StSRO genes in different tissues of doubled monoploid (DM) potato, as well as under salt, drought stresses and hormone treatments, was analyzed by RNA-seq data from the online database and quantitative real-time polymerase chain reaction (qRT-PCR) analysis. Furthermore, the expression level of StSRO genes was analyzed by transcriptome analysis under mild, moderate and severe salt stress. It was concluded that StSRO genes could respond to different abiotic conditions, but their expression level was significantly different. This study lays a foundation for further studies on the biological functions of the StSRO gene family.