Understanding and Improving Salt Tolerance in Plants

Oryza sativa, C4HC3-type really interesting new gene (RING), OsRFPv6, is a positive regulator in response to salt stress by regulating Na+ absorption

Salinity negatively affects plant growth, productivity, and metabolism. Therefore, plants have evolved diverse strategies to survive in saline environments. To identify such strategies involving the ubiquitin/26S proteasome system, we characterized molecular functions of a rice C4HC3 really interesting new gene (RING)-type E3-ubiquitin ligase gene. Oryza sativa RING finger protein v6 (OsRFPv6) was highly expressed under conditions of abiotic stress, induced by 100 mM NaCl and 20% PEG. The GFP-OsRFPv6 protein was localized in the plasma membrane and cytosol in rice protoplasts. In vitro ubiquitin assay revealed that OsRFPv6 possessed E3-ubiquitin ligase activity, but its variant OsRFPv6C100A did not. OsRFPv6-overexpressing plants were insensitive to salinity, but their growth was delayed under normal conditions. Under saline conditions, transgenic plants exhibited higher proline, soluble sugar, and chlorophyll content and lower H₂ O₂ accumulation than wild-type plants. Moreover, transgenic plants exhibited lower Na⁺ uptake, lower Na⁺ content, and higher K⁺ content in the xylem sap assay. Under saline conditions, the expression levels of nine Na⁺ /K⁺ transporter genes in roots and leaves were significantly different between transgenic and wild-type plants. Specifically, under both normal and saline conditions, the expression of OsHKT2;1, a Na⁺ transporter, in the roots of transgenic plants was lower than that in the roots of wild-type plants. These results suggest that OsRFPv6 E3-ubiquitin ligase serves as a positive regulator of salinity response via Na⁺ uptake.

Gene Mapping, Cloning and Association Analysis for Salt Tolerance in Rice

Soil salinization caused by the accumulation of sodium can decrease rice yield and quality. Identification of rice salt tolerance genes and their molecular mechanisms could help breeders genetically improve salt tolerance. We studied QTL mapping of populations for rice salt tolerance, period and method of salt tolerance identification, salt tolerance evaluation parameters, identification of salt tolerance QTLs, and fine-mapping and map cloning of salt tolerance QTLs. We discuss our findings as they relate to other genetic studies of salt tolerance association.

Evaluation of the Morpho-Physiological, Biochemical and Molecular Responses of Contrasting Medicago truncatula Lines under Water Deficit Stress

Medicago truncatula is a forage crop of choice for farmers, and it is a model species for molecular research. The growth and development and subsequent yields are limited by water availability mainly in arid and semi-arid regions. Our study aims to evaluate the morpho-physiological, biochemical and molecular responses to water deficit stress in four lines (TN6.18, JA17, TN1.11 and A10) of M. truncatula. The results showed that the treatment factor explained the majority of the variation for the measured traits. It appeared that the line A10 was the most sensitive and therefore adversely affected by water deficit stress, which reduced its growth and yield parameters, whereas the tolerant line TN6.18 exhibited the highest root biomass production, a significantly higher increase in its total protein and soluble sugar contents, and lower levels of lipid peroxidation with greater cell membrane integrity. The expression analysis of the DREB1B gene using RT-qPCR revealed a tissue-differential expression in the four lines under osmotic stress, with a higher induction rate in roots of TN6.18 and JA17 than in A10 roots, suggesting a key role for DREB1B in water deficit tolerance in M. truncatula.

Physiological and photochemical evaluation of pepper methionine sulfoxide reductase B2 (CaMsrB2) expressing transgenic rice in saline habitat

Two pepper methionine sulfoxide reductase B2 (CaMsrB2) gene expressing transgenic rice lines (L-8 and L-23) were interrogated with respect to their physiological and photochemical attributes along with control (WT, Ilmi) as a standard against varying levels of salt concentration which are 75 mM, 150 mM and 225 mM. Against various levels of salt (NaCl) concentration, recurring detrimental effects of extreme salt stress was observed and more pronounced in the wild type plants as compared to our transgenic lines. As the exacerbated effects of salinity is responsible for pushing the plants to their ecological tolerance, our transgenic lines performed well uplifted in different realms of physiology and photochemistry such as relative water content (RWC = 60-75%), stomatal conductance (g_s = 70-190 mmolm^-2s^-1), performance index (PI_ABS = 1.0-4.5), maximal photochemical yield of PSII (F_V/F_M = 0.48-0.72) and chlorophyll content index (CCI = 5-7.2 au) in comparison to the control. Relative gene expression, ion analysis and antioxidants activity were analyzed in all treatments to ensure the hypothesis obtained from data of physiology and photochemistry. Photosynthetic apparatus is known to lose energy in various forms such as NPQ, DI_O/CS, damages of reaction center (F_V/F_O) which are the markers of poor health were clearly decreased in the L-23 line as compared to L-8 and WT. Present study revealed the protruding tolerance of L-23 and L-8 transgenic lines with L-23 line in the lead in comparison to control and L-8 transgenic lines.

Integration of environmental metabolomics and physiological approach for evaluation of saline pollution to rice plant

Salinisation of soil is associated with urban pollution, industrial development and rising sea level. Understanding how high salinity is managed at the plant cellular level is vital to increase sustainable farming output. Previous studies focus on plant stress responses under salinity tolerance. Yet, there is limited knowledge about the mechanisms involved from stress state until the recovery state; our research aims to close this gap. By using the most tolerance genotype (SS1-14) and the most susceptible genotype (SS2-18), comparative physiological, metabolome and post-harvest assessments were performed to identify the underlying mechanisms for salinity stress recovery in plant cells. The up-regulation of glutamine, asparagine and malonic acid were found in recovered-tolerant genotype, suggesting a role in the regulation of panicle branching and spikelet formation for survival. Rice could survive up to 150 mM NaCl (∼15 ds/m) with declined of production rate 5-20% ranged from tolerance to susceptible genotype. This show that rice farming may still be viable on the high saline affected area with the right selection of salt-tolerant species, including glycophytes. The salt recovery biomarkers identified in this study and the adaption underlined could be empowered to address salinity problem in rice field.

Lipidomic metabolism associated with acetic acid priming-induced salt tolerance in Carex rigescens

Acetic acid priming may mitigate salt stress to plants by modulating lipid metabolism. Carex rigescens is a stress-tolerant turfgrass species with a widespread distribution in north China. The objective of this study was to figure out whether modification of lipid profiles, including the contents, compositions and saturation levels of leaf lipids, may contribute to acetic acid modulated salt tolerance in C. rigescens. Plants of C. rigescens were primed with or without acetic acid (30 mM) and subsequently exposed to salt stress (300 mM NaCl) for 15 days. Salt stress affected the physiological performance of C. rigescens, while acetic acid-primed plants showed significantly lower malondialdehyde content, proline content, and electrolyte leakage than non-primed plants under salt stress. Acetic acid priming enhanced the contents of phospholipids and glycolipids involved in membrane stabilization and stress signaling (phosphatidic acid, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, digalactosyl diacylglycerol, monogalactosyl diacylglycerol, and sulfoquinovosyldiacylglycerol), reduced the content of toxic lipid intermediates (free fatty acids) during subsequent exposure to salt stress. Furthermore, expression levels of genes involved in lipid metabolism such as CK and PLDα changed due to acetic acid priming. These results demonstrated that acetic acid priming could enhance salt tolerance of C. rigescens by regulating lipid metabolism. The lipids could be used as biomarkers to select for salt-tolerant grass germplasm.

Transcriptomic analysis of salt tolerance-associated genes and diversity analysis using indel markers in yardlong bean (Vigna unguiculata ssp. sesquipedialis)

BACKGROUND

High salinity is a devastating abiotic stresses for crops. To understand the molecular basis of salinity stress in yardlong bean (Vigna unguiculata ssp. sesquipedalis), and to develop robust markers for improving this trait in germplasm, whole transcriptome RNA sequencing (RNA-seq) was conducted to compare the salt-tolerant variety Suzi 41 and salt-sensitive variety Sujiang 1419 under normal and salt stress conditions.

RESULTS

Compared with controls, 417 differentially expressed genes (DEGs) were identified under exposure to high salinity, including 42 up- and 11 down-regulated DEGs in salt-tolerant Suzi 41 and 186 up- and 197 down-regulated genes in salt-sensitive Sujiang 1419, validated by qRT-PCR. DEGs were enriched in "Glycolysis/Gluconeogenesis" (ko00010), "Cutin, suberine and wax biosynthesis" (ko00073), and "phenylpropanoid biosynthesis" (ko00940) in Sujiang 1419, although "cysteine/methionine metabolism" (ko00270) was the only pathway significantly enriched in salt-tolerant Suzi 41. Notably, AP2/ERF, LR48, WRKY, and bHLH family transcription factors (TFs) were up-regulated under high salt conditions. Genetic diversity analysis of 84 yardlong bean accessions using 26 InDel markers developed here could distinguish salt-tolerant and salt-sensitive varieties.

CONCLUSIONS

These findings show a limited set of DEGs, primarily TFs, respond to salinity stress in V. unguiculata, and that these InDels associated with salt-inducible loci are reliable for diversity analysis.

Development of new high-salt tolerant bread wheat (Triticum aestivum L.) genotypes and insight into the tolerance mechanisms

The loss of cropland soils, climate change, and population growth are directly affecting the food supply. Given the higher incidence of salinity and extreme events, the cereal performance and yield are substantially hampered. Wheat is forecast to decline over the coming years due to the salinization widespread as one of the oldest and most environmental severe constraints facing global cereal production. To increase salinity tolerance of wheat, in this study, we developed two new salt-tolerant bread wheats, named 'Maycan' and 'Yıldız'. The salinity tolerance of these lines, their parents, and a salt-sensitive cultivar has been tested from measurements of physiological, biochemical, and genes associated with osmotic adjustment/plant tolerance in cultures containing 0 and 150 mM NaCl at the seedling stage. Differential growth reductions to increased salinity were observed in the salt-sensitive cultivar, with those newly developed exhibiting significantly greater root length, growth of shoot and water content as salinity tolerances overall than their parents. 'Maycan' and 'Yıldız' had higher osmoregulator proline content and antioxidants enzyme activities under salinity than the other bread wheat tested. Notably, an important upregulation in the expression of genes related to cellular ion balance, osmolytes accumulation, and abscisic acid was observed in both new wheat germplasms, which may improve salt tolerance. These finding revealed that 'Maycan' and 'Yıldız' exhibit high-salt tolerance at the seedling stage and differing in their tolerance mechanisms to the other tested cultivars, thereby providing an opportunity for their exploitation as modern bread wheats.

Mitigation of climate change and environmental hazards in plants: Potential role of the beneficial metalloid silicon

In the last decades, the concentration of atmospheric CO₂ and the average temperature have been increasing, and this trend is expected to become more severe in the near future. Additionally, environmental stresses including drought, salinity, UV-radiation, heavy metals, and toxic elements exposure represent a threat for ecosystems and agriculture. Climate and environmental changes negatively affect plant growth, biomass and yield production, and also enhance plant susceptibility to pests and diseases. Silicon (Si), as a beneficial element for plants, is involved in plant tolerance and/or resistance to various abiotic and biotic stresses. The beneficial role of Si has been shown in various plant species and its accumulation relies on the root's uptake capacity. However, Si uptake in plants depends on many biogeochemical factors that may be substantially altered in the future, affecting its functional role in plant protection. At present, it is not clear whether Si accumulation in plants will be positively or negatively affected by changing climate and environmental conditions. In this review, we focused on Si interaction with the most important factors of global change and environmental hazards in plants, discussing the potential role of its application as an alleviation strategy for climate and environmental hazards based on current knowledge.

Differential Effects of Organic Amendments on Maize Biomass and Nutrient Availability in Upland Calcareous Soil

The current study is focuses on a sustainable agricultural ecosystem for soil fertility and human health improvement. To estimate the effects of applying organic amendments (compost, vermicompost, biochar, organic manure and rapeseed cake) on crop growth of maize and nutrient uptake in calcareous soil, eleven treatments were studied, which included compost (CM), cow manure vermicompost (CMV), pig manure vermicompost (PMV), biochar vermicompost (BCV), biochar (BC), conventional synthetic fertilizers (NPK), CMV in addition to NPK (CMV + NPK), and PMV in addition to NPK (PMV + NPK), organic manure (OM), rapeseed cake (RC) and control without any fertilization (CK). Maize above and belowground biomass were analyzed in glass greenhouse experiments. The results showed that nitrogen and carbon contents showed significant differences among treatments. Vermicompost significantly showed higher biomass as compared to inorganic fertilizers except for RC. All vermicompost treatments also showed better nutrient availability as compared to NPK and CK. In conclusion, vermicompost with all substrates are recommended for application as organic fertilizers. Our study will help promote the application of organic fertilizers alone or in combination with inorganic fertilizers rather than only inorganic fertilizers for environmental health and sustainability.

Plant Parasites under Pressure: Effects of Abiotic Stress on the Interactions between Parasitic Plants and Their Hosts

Parasitic angiosperms, comprising a diverse group of flowering plants, are partially or fully dependent on their hosts to acquire water, mineral nutrients and organic compounds. Some have detrimental effects on agriculturally important crop plants. They are also intriguing model systems to study adaptive mechanisms required for the transition from an autotrophic to a heterotrophic metabolism. No less than any other plant, parasitic plants are affected by abiotic stress factors such as drought and changes in temperature, saline soils or contamination with metals or herbicides. These effects may be attributed to the direct influence of the stress, but also to diminished host availability and suitability. Although several studies on abiotic stress response of parasitic plants are available, still little is known about how abiotic factors affect host preferences, defense mechanisms of both hosts and parasites and the effects of combinations of abiotic and biotic stress experienced by the host plants. The latter effects are of specific interest as parasitic plants pose additional pressure on contemporary agriculture in times of climate change. This review summarizes the existing literature on abiotic stress response of parasitic plants, highlighting knowledge gaps and discussing perspectives for future research and potential agricultural applications.

Transcriptome analysis of bread wheat leaves in response to salt stress

Salinity is one of the main abiotic stresses limiting crop productivity. In the current study, the transcriptome of wheat leaves in an Iranian salt-tolerant cultivar (Arg) was investigated in response to salinity stress to identify salinity stress-responsive genes and mechanisms. More than 114 million reads were generated from leaf tissues by the Illumina HiSeq 2500 platform. An amount of 81.9% to 85.7% of reads could be mapped to the wheat reference genome for different samples. The data analysis led to the identification of 98819 genes, including 26700 novel transcripts. A total of 4290 differentially expressed genes (DEGs) were recognized, comprising 2346 up-regulated genes and 1944 down-regulated genes. Clustering of the DEGs utilizing Kyoto Encyclopedia of Genes and Genomes (KEGG) indicated that transcripts associated with phenylpropanoid biosynthesis, transporters, transcription factors, hormone signal transduction, glycosyltransferases, exosome, and MAPK signaling might be involved in salt tolerance. The expression patterns of nine DEGs were investigated by quantitative real-time PCR in Arg and Moghan3 as the salt-tolerant and susceptible cultivars, respectively. The obtained results were consistent with changes in transcript abundance found by RNA-sequencing in the tolerant cultivar. The results presented here could be utilized for salt tolerance enhancement in wheat through genetic engineering or molecular breeding.

Comparative transcriptome analysis of NaCl and KCl stress response in Malus hupehensis Rehd. Provide insight into the regulation involved in Na+ and K+ homeostasis

BACKGROUND

Apple is among the most widely cultivated perennial fruit crops worldwide. It is sensitive to salt stress, which seriously affects the growth and productivity of apple trees by destroying the homeostasis of Na⁺ and K⁺. Previous studies focused on the molecular mechanism underlying NaCl stress. However, signaling transduction under KCl stress has not been thoroughly studied.

RESULTS

We comprehensively analyzed the salt tolerance of Malus hupehensis Rehd., which is a widely used rootstock in apple orchards, by using RNA-Seq. Roots and leaves were treated with NaCl and KCl. Based on mapping analyses, a total of 762 differentially expressed genes (DEGs) related to NaCl and KCl stress in the roots and leaves were identified. Furthermore, we identified seven hub genes by WGCNA Analysis. The Gene Ontology (GO) terms were enriched in ion transmembrane transporter and oxidoreductase activity under NaCl and KCl stress. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways focused on the plant hormone signal transduction and mitogen-activated protein kinase signaling pathway. We also screened out 28 candidate genes from 762 DEGs and verified their expression by quantitative reverse transcription polymerase chain reaction (qRT-PCR). All of these enriched genes were closely related to NaCl and KCl stress and take part in mediating the Na⁺ and K⁺ homeostasis in M. hupehensis.

CONCLUSIONS

This transcriptome analysis provides a valuable resource for elucidating the signaling pathway of NaCl and KCl stress and is a substantial genetic resource for discovering genes related to the NaCl and KCl stress response.

Growth and Element Uptake by Salt-Sensitive Crops under Combined NaCl and Cd Stresses

To test an assumption that organic soil can ameliorate nutritional disorders associated with metal and salinity stresses, we exposed salt-sensitive strawberry and lettuce to four salinity (0-60 mM NaCl) and three contamination (0.3-5 mg Cd/kg) rates in peat (pH_H2O = 5.5). The results showed that, even at 20 mM NaCl, salinity stress exerted a dominant effect on rhizosphere biogeochemistry and physiological processes, inducing leaf-edge burns, chlorosis/necrosis, reducing vegetative growth in crops; at ≥40 mM, NaCl mortality was induced in strawberry. Signifiacntly decreased K/Na, Ca/Na and Mg/Na concentration ratios with raising salinity were confirmed in all tissues. The combined CdxNaCl stresses (vs. control) increased leaf Cd accumulation (up to 42-fold in lettuce and 23-fold in strawberry), whereas NaCl salinity increased the accumulation of Zn (>1.5-fold) and Cu (up to 1.2-fold) in leaves. Lettuce accumulated the toxic Cd concentration (up to 12.6 mg/kg) in leaves, suggesting the strong root-to-shoot transport of Cd. In strawberry Cd, concentration was similar (and sub-toxic) in fruits and leaves, 2.28 and 1.86 mg/kg, respectively, suggesting lower Cd root-to-shoot translocation, and similar Cd mobility in the xylem and phloem. Additionally, the accumulation of Cd in strawberry fruits was exacerbated at high NaCl exposure (60 mM) compared with lower NaCl concentrations. Thus, in salinized, slightly acidic and organically rich rhizosphere, pronounced organo- and/or chloro-complexation likely shifted metal biogeochemistry toward increased mobility and phytoavailability (with metal adsorption restricted due to Na⁺ oversaturation of the caton exchange complex in the substrate), confirming the importance of quality water and soils in avoiding abiotic stresses and producing non-contaminated food.

Beat the stress: breeding for climate resilience in maize for the tropical rainfed environments

Intensive public sector breeding efforts and public-private partnerships have led to the increase in genetic gains, and deployment of elite climate-resilient maize cultivars for the stress-prone environments in the tropics. Maize (Zea mays L.) plays a critical role in ensuring food and nutritional security, and livelihoods of millions of resource-constrained smallholders. However, maize yields in the tropical rainfed environments are now increasingly vulnerable to various climate-induced stresses, especially drought, heat, waterlogging, salinity, cold, diseases, and insect pests, which often come in combinations to severely impact maize crops. The International Maize and Wheat Improvement Center (CIMMYT), in partnership with several public and private sector institutions, has been intensively engaged over the last four decades in breeding elite tropical maize germplasm with tolerance to key abiotic and biotic stresses, using an extensive managed stress screening network and on-farm testing system. This has led to the successful development and deployment of an array of elite stress-tolerant maize cultivars across sub-Saharan Africa, Asia, and Latin America. Further increasing genetic gains in the tropical maize breeding programs demands judicious integration of doubled haploidy, high-throughput and precise phenotyping, genomics-assisted breeding, breeding data management, and more effective decision support tools. Multi-institutional efforts, especially public-private alliances, are key to ensure that the improved maize varieties effectively reach the climate-vulnerable farming communities in the tropics, including accelerated replacement of old/obsolete varieties.

Exogenous methyl jasmonate promotes salt stress-induced growth inhibition and prioritizes defense response of Nitraria tangutorum Bobr

Jasmonates (JAs) play a key role in the regulation of growth and the defense response to environmental stresses. JAs inhibit plant growth and promote defense response. However, their roles in desert halophyte in the response to salt stress remain poorly understood. The effects of the combination of methyl jasmonate (MeJA) and NaCl treatment (the "MeN" condition) on the growth regulation and defense response of Nitraria tangutorum seedlings were investigated. Compared with NaCl treatment alone, exogenous MeJA aggravated the growth inhibition of seedlings by antagonizing to growth-related hormones and suppressing the transcript levels of these hormones-responsive genes, including gibberellin (GA)-responsive NtPIF3, NtGAST1, NtGSAT4, and cytokinin (CYT)-responsive NtARR1, NtARR11, NtARR12. Meanwhile, exogenous MeJA enhanced defense response and alleviated the stress damage by increasing antioxidase activity and antioxidant content, accumulating more osmolytes, maintaining lower Na⁺ /K⁺ ratios in shoots and higher Na⁺ efflux rates in roots of plants. In addition, exogenous MeJA increased the contents of endogenous JA and ABA, and the transcript levels of genes involved in their biosynthesis and responsiveness, thereby further regulating the transcript levels of defense response genes. These findings suggest that exogenous MeJA increases salt stress-induced growth inhibition and prioritizes the defensive responses (e.g. antioxidant defense, osmotic adjustment, and ion homeostasis) of N. tangutorum. These effects may be related to the amplification of jasmonic acid (JA) and abscisic acid (ABA) signals.

Beneficial Effects of Exogenous Melatonin on Overcoming Salt Stress in Sugar Beets (Beta vulgaris L.)

Melatonin has been regarded as a promising substance that enhances the abiotic stress tolerance of plants. However, few studies have devoted attention to the role of melatonin in improving salt tolerance in sugar beets. Here, the effects of different application methods (foliar application (100 μM), root application (100 μM), and combined foliar and root application) of melatonin on the morphological and physiological traits of sugar beets exposed to salt stress were investigated. The results showed that melatonin improved the growth of sugar beet seedlings, root yield and sugar content, synthesis of chlorophyll, photosystem II (PS II) activity, and gas exchange parameters under salt stress conditions. Moreover, melatonin enhanced the capacity of osmotic adjustment by increasing the accumulation of osmolytes (betaine, proline, and soluble sugar). At the same time, melatonin increased the H⁺-pump activities in the roots, thus promoting Na⁺ efflux and K⁺ influx, which maintained K⁺/Na⁺ homeostasis and mitigated Na⁺ toxicity. In addition, melatonin strengthened the antioxidant defense system by enhancing the activities of antioxidant enzymes, modulating the ASA-GSH cycle, and mediating the phenylalanine pathway, which removed superoxide anions (O₂^•−) and hydrogen peroxide (H₂O₂) and maintained cell membrane integrity. These positive effects were more pronounced when melatonin was applied by combined foliar and root application. To summarize, this study clarifies the potential roles of melatonin in mitigating salt stress in sugar beets by improving photosynthesis, water status, ion homeostasis, and the antioxidant defense system.

Morpho-Physiological, Biochemical, and Genetic Responses to Salinity in Medicago truncatula

We used an integrated morpho-physiological, biochemical, and genetic approach to investigate the salt responses of four lines (TN1.11, TN6.18, JA17, and A10) of Medicago truncatula. Results showed that TN1.11 exhibited a high tolerance to salinity, compared with the other lines, recording a salinity induced an increase in soluble sugars and soluble proteins, a slight decrease in malondialdehyde (MDA) accumulation, and less reduction in plant biomass. TN6.18 was the most susceptible to salinity as it showed less plant weight, had elevated levels of MDA, and lower levels of soluble sugars and soluble proteins under salt stress. As transcription factors of the APETALA2/ethylene responsive factor (AP2/ERF) family play important roles in plant growth, development, and responses to biotic and abiotic stresses, we performed a functional characterization of MtERF1 gene. Real-time PCR analysis revealed that MtERF1 is mainly expressed in roots and is inducible by NaCl and low temperature. Additionally, under salt stress, a greater increase in the expression of MtERF1 was found in TN1.11 plants than that in TN6.18. Therefore, the MtERF1 pattern of expression may provide a useful marker for discriminating among lines of M. truncatula and can be used as a tool in breeding programs aiming at obtaining Medicago lines with improved salt tolerance.

Physiological Responses of Salinized Fenugreek (Trigonellafoenum-graecum L.) Plants to Foliar Application of Salicylic Acid

Considering the detrimental effects of salt stress on the physiological mechanisms of plants in terms of growth, development and productivity, intensive efforts are underway to improve plant tolerance to salinity. Hence, an experiment was conducted to assess the impact of the foliar application of salicylic acid (SA; 0.5 mM) on the physiological traits of fenugreek (Trigonellafoenum-graecum L.) plants grown under three salt concentrations (0, 75, and 150 mM NaCl). An increase in salt concentration generated a decrease in the chlorophyll content index (CCI); however, the foliar application of SA boosted the CCI. The malondialdehyde content increased in salt-stressed fenugreek plants, while a reduction in content was observed with SA. Likewise, SA application induced an accumulation of proline, total phenolics, and flavonoids. Moreover, further increases in total free amino acids and shikimic acid were observed with the foliar application of SA, in either control or salt-treated plants. Similar results were obtained for ascorbate peroxidase, peroxidase, polyphenol oxidase, and catalase with SA application. Hence, we concluded that the foliar application of SA ameliorates salinity, and it is a growth regulator that improves the tolerance of fenugreek plants under salt stress.

Comprehensive Evaluation of Salt Tolerance in Asparagus Germplasm Accessions (Asparagus officinalis L.) at Different Growth Stages

The screening and cultivation of salt-tolerant crops are becoming more and more important owing to the constant increase in the saline soil area worldwide. Asparagus (A. officinalis L.) is a highly nutritious vegetable crop and widely consumed globally for a long time; however, little research has been done on asparagus. In this study, the salt tolerance of 95 asparagus germplasm accessions was evaluated at three growth stages (germination, seedling, and adult stages) under both salt-stressed and control conditions. Results showed that the growth parameters of most germplasm accessions were obviously inhibited by salt stress. The mean value of the seed germination rate at the germination stage decreased by half under salt-stressed conditions, the mean salt-injury index at the seedling stage reached 57.68%, and the fresh weight of the aboveground part (FWA) and the dry weight of the aboveground part (DWA) decreased the most among the traits determined at the adult stage by more than 60%. Our study screened out 30, 19, and 18 tolerant germplasm accessions (including highly salt-tolerant and salt-tolerant germplasm accessions) at the germination stage, seedling stage, and adult stage, respectively. Among them, two germplasm accessions (Ji08-2 and Jx1502) were simultaneously identified to be tolerant in all three growth stages, while other germplasm accessions were tolerant only at one or two stages. Thus, the salt tolerance of asparagus has periodic characteristics and changes throughout the lifecycle, and the identification of salt tolerance at all the main growth stages facilitates adequate assessment and application of tolerant germplasm accessions.

Differential Morphophysiological and Biochemical Responses of Cotton Genotypes Under Various Salinity Stress Levels During Early Growth Stage

Cotton is a primary agriculture product important for fiber use in textiles and the second major oil seed crop. Cotton is considered as moderately tolerant to salt stress with salinity threshold of 7.7 dS/m at seedling stage. Salinity causes reduction in the growth of seedlings and cotton production that limits fiber quality and cotton yield. In this study, initially, 22 cotton genotypes were screened for relative salt tolerance using germination test in Petri plates (growth chamber). Selected 11 genotypes were further tested in pot experiment (sand) with 0, 15, and 20 dS/m NaCl treatments under glass house conditions. At four-leaves stage, different morphological and physiological traits were measured for all genotypes while biochemical analysis was performed on selected seven highly tolerant and sensitive genotypes. NaCl treatment significantly reduced plant biomass in two genotypes IR-NIBGE-13 and BS-2018, while NIAB-135, NIAB-512, and GH-HADI had least difference in fresh weight between the control and NaCl-treated plants. Photosynthetic rate was maintained in all the genotypes with the exception of SITARA-16. In two sensitive genotypes (IR-NIBGE-13 and 6071/16), Na+ ion accumulated more in leaves as compared to K+ ion under stress conditions, and an increase in Na+/K+ ratio was also observed. The lesser accumulation of malondialdehyde (MDA) content and higher activity of enzymatic antioxidants such as superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX) in stressed plants of NIAB-135, NIAB-512, and FH-152 indicated that these genotypes had adaption capacity for salinity stress in comparison with sensitive genotypes, i.e., IR-NIBGE-13 and 6071/16. The observed salt tolerance was corelated with plant biomass maintenance (morphological), photosynthetic rate, and ionic homeostasis (K+/Na+ ratio, physiological) and biochemical stress marker regulations. After a series of experiments, it was concluded that NIAB-135, NIAB-512, and FH-152 could be utilized in breeding programs aimed at improving salinity tolerance in cotton and can expand cotton cultivation in saline area.

Differential response of fragrant rice cultivars to salinity and hydrogen rich water in relation to growth and antioxidative defense mechanisms

Salinity negatively effects the growth and productivity of crop plants; however, the effects of hydrogen rich water (HRW) on the early growth of fragrant rice under salinity stress are rarely investigated. In present study, two HRW treatments: foliar application (F-HRW) and irrigation (I-HRW) were applied on the two fragrant rice cultivars, Yuxiangyouzhan and Xiangyaxiangzhan, grown under normal and salt stress conditions, i.e., 0 and 150 mmol NaCl L^-1, respectively. Plants without HRW application were grown as control (CK). Results showed that the dry weight per unit plant height (mg cm^-1) was increased by 12.6% and 23.0% in F-HRW and I-HRW, respectively under salt stress as compared with CK. Application of HRW, regardless of the application method, modulated the antioxidant activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) while reduced malondialdehyde (MDA) contents under salt stress. Moreover, significant and positive relations were observed among total dry weight and shoot dry weight, dry weight per unit plant height, SOD and CAT activity in root. Overall, F-HRW application modulated the early growth and related physiological attributes in fragrant rice under salt stress whereas I-HRW was found to mitigate salt stress. Novelty statement: Involvement of endogenous H₂ in plants for regulating various physiological functions is of great importance to stimulate and/or activate the antioxidant defense responses against oxidative stress; however, there is a lack of research in this aspect. The present study investigated the effects of hydrogen rich water (HRW) on the growth and physiological attributes of two fragrant rice cultivars grown under salt-stress. It was noteworthy to find that application of HRW either foliar application or irrigation improved the morphological characters, i.e., dry weight per unit plant height and enhanced the activities of antioxidants, i.e., peroxidase, superoxide dismutase and catalase whilst decreased the malonaldehyde content. Overall, the application of HRW modulates plant growth and physiological attributes in fragrant rice cultivars under salt-stress conditions. This study will be helpful in improving the early growth and/or stand establishment of fragrant rice nursery under saline conditions.

Effect of saline irrigation on plant water traits, photosynthesis and ionic balance in durum wheat genotypes

In the era of climate change, decreased precipitation and increased evapo-transpiration hampers the yield of several cereal crops along with the soil salinity and poor ground water resource. Wheat being the moderately tolerant crop face many challenges in the arid and semi-arid regions under irrigated agriculture. In view of this, the study was planned to explore the potential of durum wheat genotypes under salinity on the basis of physiological traits. Experiment was designed as RBD in three replications to evaluate 15 wheat genotypes with moderate saline irrigation (EC_iw – 6 dS m⁻¹) and extreme saline irrigation (EC_iw – 10 dS m⁻¹) along with one set of control (Best available water). Different physiological traits such as water potential (ψ_p), osmotic potential (ψ_s), relative water content (RWC), Na⁺ and K⁺ content were recorded in roots as well as shoots at the reproductive stage whereas photosynthetic rate and chlorophyll content were measured in the flag leaves. A significant variability (p < 0.001) was noted among the genotypes under different stress environments and it was observed that durum genotype HI 8728 and HI 8737 showed less reduction in plant water traits (RWC, ψ_p and ψ_s) than the salinity tolerant checks of bread wheat KRL 99 and KRL 3–4. HD 4728 and HI 8708 maintained higher photosynthetic rate as well as higher chlorophyll content under the extreme salinity level of EC_iw – 10 dSm⁻¹. No significant differences were found in root Na⁺ in genotypes KRL 99 (3.17^g), KRL 3–4 (3.34^g) and HI 8737 (3.41^g) while in shoots, lowest accumulation was seen in KRL 99, MACS 3949 and KRL 3–4 at EC_iw – 10 dSm⁻¹. The mean range of K⁺ content was 7.60–9.74% in roots and 4.21–6.61% in shoots under control environment which decreased to 50.77% in roots and 46.05% in shoots under extreme salinity condition of EC_iw – 10 dSm⁻¹. At EC_iw – 10 dSm⁻¹, KRL 99 maintained highest K^+/Na⁺ in both root and shoot followed by KRL 3–4, HI 8737, MACS 3949, HD 4728 in roots and MACS 3949, KRL 3–4, MACS 4020, HD 4758, MACS 3972 and HI 8713 in shoots. The differential response of durum wheat genotypes under salinity particularly for physiological traits, confer their adaptability towards stress environments and exhibit their potential as genetic sources in breeding programs for improving salt stress tolerance.

Environmental salinization processes: Detection, implications & solutions

A great portion of Earth's freshwater and land resources are salt-affected and thus have restricted use or may become unsuitable for most human activities. Some of the recent scenarios warn that environmental salinization processes will continue to be exacerbated due to global climate change. The most relevant implications and side-effects in ecosystems under excessive salinity are destructive and long lasting (e.g. soil dispersion, water/soil hypersalinity, desertification, ruined biodiversity), often with non-feasible on site remediation, especially at larger scales. Agro-ecosystems are very sensitive to salinization; after a certain threshold is reached, yields and food quality start to deteriorate sharply. Additionally, salinity often coincides with numerous other environmental constrains (drought, waterlogging, pollution, acidity, nutrient deficiency, etc.) that progressively aggravate the threat to food security and general ecosystem resilience. Some well-proven, widely-used and cost-effective traditional ameliorative strategies (e.g. conservation agriculture, application of natural conditioners) help against salinity and other constraints, especially in developing countries. Remotely-sensed and integrated data of salt-affected areas combined with in situ and lab-based observations have never been so easy and rapid to acquire, precise and applicable on huge scales, representing a valuable tool for policy-makers and other stakeholders in implementing targeted measures to control and prevent ecosystem degradation (top-to-bottom approach). Continued progress in biotechnology and ecoengineering offers some of the most advanced and effective solutions against salinity (e.g. nanomaterials, marker-assisted breeding, genome editing, plant-microbial associations), albeit many knowledge gaps and ethical frontiers remain to be overcome before a successful transfer of these potential solutions to the industrial-scale food production can be effective.

Identification and development of novel salt-responsive candidate gene based SSRs (cg-SSRs) and MIR gene based SSRs (mir-SSRs) in bread wheat (Triticum aestivum)

Salt stress adversely affects the global wheat production and productivity. To improve salinity tolerance of crops, identification of robust molecular markers is highly imperative for development of salt-tolerant cultivars to mimic yield losses under saline conditions. In this study, we mined 171 salt-responsive genes (including 10 miRNAs) from bread wheat genome using the sequence information of functionally validated salt-responsive rice genes. Salt-stress, tissue and developmental stage-specific expression analysis of RNA-seq datasets revealed the constitutive as well as the inductive response of salt-responsive genes in different tissues of wheat. Fifty-four genotypes were phenotyped for salt stress tolerance. The stress tolerance index of the genotypes ranged from 0.30 to 3.18. In order to understand the genetic diversity, candidate gene based SSRs (cg-SSRs) and MIR gene based SSRs (miR-SSRs) were mined from 171 members of salt-responsive genes of wheat and validated among the contrasting panels of 54 tolerant as well as susceptible wheat genotypes. Among 53 SSR markers screened, 10 cg-SSRs and 8 miR-SSRs were found to be polymorphic. Polymorphic information content between the wheat genotypes ranged from 0.07 to 0.67, indicating the extant of wide genetic variation among the salt tolerant and susceptible genotypes at the DNA level. The genetic diversity analysis based on the allelic data grouped the wheat genotypes into three separate clusters of which single group encompassing most of the salt susceptible genotypes and two of them containing salt tolerance and moderately salt tolerance wheat genotypes were in congruence with penotypic data. Our study showed that both salt-responsive genes and miRNAs based SSRs were more diverse and can be effectively used for diversity analysis. This study reports the first extensive survey on genome-wide analysis, identification, development and validation of salt-responsive cg-SSRs and miR-SSRs in wheat. The information generated in the present study on genetic divergence among genotypes having a differential response to salt will help in the selection of suitable lines as parents for developing salt tolerant cultivars in wheat.

Transgenic chickpea (Cicer arietinum L.) harbouring AtDREB1a are physiologically better adapted to water deficit

BACKGROUND

Chickpea (Cicer arietinum L.) is the second most widely grown pulse and drought (limiting water) is one of the major constraints leading to about 40-50% yield losses annually. Dehydration responsive element binding proteins (DREBs) are important plant transcription factors that regulate the expression of many stress-inducible genes and play a critical role in improving the abiotic stress tolerance. Transgenic chickpea lines harbouring transcription factor, Dehydration Responsive Element-Binding protein 1A from Arabidopsis thaliana (AtDREB1a gene) driven by stress inducible promoter rd29a were developed, with the intent of enhancing drought tolerance in chickpea. Performance of the progenies of one transgenic event and control were assessed based on key physiological traits imparting drought tolerance such as plant water relation characteristics, chlorophyll retention, photosynthesis, membrane stability and water use efficiency under water stressed conditions.

RESULTS

Four transgenic chickpea lines harbouring stress inducible AtDREB1a were generated with transformation efficiency of 0.1%. The integration, transmission and regulated expression were confirmed by Polymerase Chain Reaction (PCR), Southern Blot hybridization and Reverse Transcriptase polymerase chain reaction (RT-PCR), respectively. Transgenic chickpea lines exhibited higher relative water content, longer chlorophyll retention capacity and higher osmotic adjustment under severe drought stress (stress level 4), as compared to control. The enhanced drought tolerance in transgenic chickpea lines were also manifested by undeterred photosynthesis involving enhanced quantum yield of PSII, electron transport rate at saturated irradiance levels and maintaining higher relative water content in leaves under relatively severe soil water deficit. Further, lower values of carbon isotope discrimination in some transgenic chickpea lines indicated higher water use efficiency. Transgenic chickpea lines exhibiting better OA resulted in higher seed yield, with progressive increase in water stress, as compared to control.

CONCLUSIONS

Based on precise phenotyping, involving non-invasive chlorophyll fluorescence imaging, carbon isotope discrimination, osmotic adjustment, higher chlorophyll retention and membrane stability index, it can be concluded that AtDREB1a transgenic chickpea lines were better adapted to water deficit by modifying important physiological traits. The selected transgenic chickpea event would be a valuable resource that can be used in pre-breeding or directly in varietal development programs for enhanced drought tolerance under parched conditions.

Melatonin improves K+ and Na+ homeostasis in rice under salt stress by mediated nitric oxide

Rice (Oryza sativa L.) productivity is greatly affected by soil salinity and melatonin (MLT) has long been recognized as a positive molecule that can alleviate the damage caused by salt. Here, the role of nitric oxide (NO) in the regulation of salt tolerance by MLT was investigated in rice. MLT pretreatment increased the fresh and dry weight of rice seedlings under salt stress. Its beneficial effects include less relative electrolyte leakage (REL) and better K⁺/Na⁺ homeostasis. MLT increased the activity of nitric oxide synthase (NOS). The polyamines (PAs) content and the utilization of arginine were also increased, thereby increasing NO content in salt-stressed rice seedlings. Pharmacological approach showed that NO, as a necessary downstream signaling molecule, was involved in the regulation of MLT on the K⁺/Na⁺ homeostasis of rice. Under salt stress, MLT improved the H⁺-pumps activities in plasma membrane (PM) and vacuole membrane (VM) in roots, MLT also increased the ATP content of rice roots by increasing the NO content of rice. Thus, the efflux of Na⁺ and the influx of K⁺ were promoted. When endogenous NO was scavenged, the regulation of K⁺/Na⁺ homeostasis by MLT was blocked. Therefore, MLT mediated K⁺/Na⁺ homeostasis of rice under salt stress by mediating NO.

Comparative Transcriptome, Metabolome, and Ionome Analysis of Two Contrasting Common Bean Genotypes in Saline Conditions

Soil salinity is a major abiotic stress factor that limits agricultural productivity worldwide, and this problem is expected to grow in the future. Common bean is an important protein source in developing countries however highly susceptible to salt stress. To understand the underlying mechanism of salt stress responses, transcriptomics, metabolomics, and ion content analysis were performed on both salt-tolerant and susceptible common bean genotypes in saline conditions. Transcriptomics has demonstrated increased photosynthesis in saline conditions for tolerant genotype while the susceptible genotype acted in contrast. Transcriptome also displayed active carbon and amino-acid metabolism for the tolerant genotype. Analysis of metabolites with GC-MS demonstrated the boosted carbohydrate metabolism in the tolerant genotype with increased sugar content as well as better amino-acid metabolism. Accumulation of lysine, valine, and isoleucine in the roots of the susceptible genotype suggested a halted stress response. According to ion content comparison, the tolerant genotype managed to block accumulation of Na⁺ in the leaves while accumulating significantly less Na⁺ in the roots compared to susceptible genotype. K⁺ levels increased in the leaves of both genotype and the roots of the susceptible one but dropped in the roots of the tolerant genotype. Additionally, Zn⁺² and Mn⁺² levels were dropped in the tolerant roots, while Mo⁺² levels were significantly higher in all tissues in both control and saline conditions for tolerant genotype. The results of the presented study have demonstrated the differences in contrasting genotypes and thus provide valuable information on the pivotal molecular mechanisms underlying salt tolerance.

Germination and Growth of Spinach under Potassium Deficiency and Irrigation with High-Salinity Water

Information is scarce on the interaction of mineral deficiency and salinity. We evaluated two salt-tolerant spinach cultivars under potassium (K) doses (0.07, 0.15, 0.3, and 3.0 mmol_c L^-1) and saline irrigation (5, 30, 60, 120, and 160 mmol_c L^-1 NaCl) during germination and growth. There was no interaction between salinity and K. Salinity decreased germination percent (GP), not always significantly, and drastically reduced seedling biomass. 'Raccoon' significantly increased GP at 60 mmol_c L^-1 while 'Gazelle' maintained GP up to 60 or 120 mmol_c L^-1. After 50 days under saline irrigation, shoot biomass increased significantly at 30 and 60 mmol_c L^-1 at the lowest K dose but, in general, neither salinity nor K dose affected shoot biomass, suggesting that salinity supported plant growth at the most K-deficient dose. Salinity did not affect shoot N, P, or K but significantly reduced Ca, Mg, and S, although plants had no symptoms of salt toxicity or mineral deficiency. Although spinach seedlings are more sensitive to salt stress, plants adjusted to salinity with time. Potassium requirement for spinach growth was less than the current crop recommendation, allowing its cultivation with waters of moderate to high salinity without considerable reduction in yield, appearance, or mineral composition.

Advances and Challenges in the Breeding of Salt-Tolerant Rice

Soil salinization and a degraded ecological environment are challenging agricultural productivity and food security. Rice (Oryza sativa), the staple food of much of the world’s population, is categorized as a salt-susceptible crop. Improving the salt tolerance of rice would increase the potential of saline-alkali land and ensure food security. Salt tolerance is a complex quantitative trait. Biotechnological efforts to improve the salt tolerance of rice hinge on a detailed understanding of the molecular mechanisms underlying salt stress tolerance. In this review, we summarize progress in the breeding of salt-tolerant rice and in the mapping and cloning of genes and quantitative trait loci (QTLs) associated with salt tolerance in rice. Furthermore, we describe biotechnological tools that can be used to cultivate salt-tolerant rice, providing a reference for efforts aimed at rapidly and precisely cultivating salt-tolerance rice varieties.

Gamma-aminobutyric acid (GABA) alleviates salt damage in tomato by modulating Na+ uptake, the GAD gene, amino acid synthesis and reactive oxygen species metabolism

BACKGROUND

Salt stress is a serious abiotic stress that caused crop growth inhibition and yield decline. Previous studies have reported on the the synthesis of gamma-aminobutyric acid (GABA) and its relationship with plant resistance under various abiotic stress. However, the relationship between exogenous GABA alleviating plant salt stress damage and ion flux, amino acid synthesis, and key enzyme expression remains largely unclear. We investigated plant growth, Na⁺ transportation and accumulation, reactive oxygen species (ROS) metabolism and evaluated the effect of GABA on amino acids, especially SlGADs gene expression and the endogenous GABA content of tomato (Solanum lycopersicum L.) seedlings treated with or without 5 mmol·L^- 1 GABA under 175 mmol·L^- 1 NaCl stress.

RESULTS

Exogenous application of GABA significantly reduced the salt damage index and increased plant height, chlorophyll content and the dry and fresh weights of tomato plants exposed to NaCl stress. GABA significantly reduced Na⁺ accumulation in leaves and roots by preventing Na⁺ influx in roots and transportation to leaves. The transcriptional expression of SlGAD1-3 genes were induced by NaCl stress especially with GABA application. Among them, SlGAD1 expression was the most sensitive and contributed the most to the increase in glutamate decarboxylase (GAD) activity induced by NaCl and GABA application; Exogenous GABA increased GAD activity and amino acid contents in tomato leaves compared with the levels under NaCl stress alone, especially the levels of endogenous GABA, proline, glutamate and eight other amino acids. These results indicated that SlGADs transcriptional expression played an important role in tomato plant resistance to NaCl stress with GABA application by enhancing GAD activity and amino acid contents. GABA significantly alleviated the active oxygen-related injury of leaves under NaCl stress by increasing the activities of antioxidant enzymes and decreasing the contents of active oxygen species and malondialdehyde.

CONCLUSION

Exogenous GABA had a positive effect on the resistance of tomato seedlings to salt stress, which was closely associated with reducing Na⁺ flux from root to leaves, increasing amino acid content and strengthening antioxidant metabolism. Endogenous GABA content was induced by salt and exogenous GABA at both the transcriptional and metabolic levels.

GhCIPK6a increases salt tolerance in transgenic upland cotton by involving in ROS scavenging and MAPK signaling pathways

BACKGROUND

Salt stress is one of the most damaging abiotic stresses in production of Upland cotton (Gossypium hirsutum). Upland cotton is defined as a medium salt-tolerant crop. Salinity hinders root development, shoots growth, and reduces the fiber quality.

RESULTS

Our previous study verified a GhCIPK6a gene response to salt stress in G. hirsutum. The homologs of GhCIPK6a were analyzed in A₂ (G. arboreum), D₅ (G. raimondii), and AD₁ (G. hirsutum) genomes. GhCIPK6a localized to the vacuole and cell membrane. The GhCBL1-GhCIPK6a and GhCBL8-GhCIPK6a complexes localized to the nucleus and cytomembrane. Overexpression of GhCIPK6a enhanced expression levels of co-expressed genes induced by salt stress, which scavenged ROS and involved in MAPK signaling pathways verified by RNA-seq analysis. Water absorption capacity and cell membrane stability of seeds from GhCIPK6a overexpressed lines was higher than that of wild-type seeds during imbibed germination stage. The seed germination rates and seedling field emergence percentages of GhCIPK6a overexpressed lines were higher than that of control line under salt stress. Moreover, overexpressing of GhCIPK6a in cotton increased lint percentage, and fiber length uniformity under salt stress.

CONCLUSIONS

We verified the function of GhCIPK6a by transformation and RNA-seq analysis. GhCIPK6a overexpressed lines exhibited higher tolerance to abiotic stresses, which functioned by involving in ROS scavenging and MAPK pathways. Therefore, GhCIPK6a has the potential for cotton breeding to improve stress-tolerance.

Enhancing Sustainability by Improving Plant Salt Tolerance through Macro- and Micro-Algal Biostimulants

Algal biomass, extracts, or derivatives have long been considered a valuable material to bring benefits to humans and cultivated plants. In the last decades, it became evident that algal formulations can induce multiple effects on crops (including an increase in biomass, yield, and quality), and that algal extracts contain a series of bioactive compounds and signaling molecules, in addition to mineral and organic nutrients. The need to reduce the non-renewable chemical input in agriculture has recently prompted an increase in the use of algal extracts as a plant biostimulant, also because of their ability to promote plant growth in suboptimal conditions such as saline environments is beneficial. In this article, we discuss some research areas that are critical for the implementation in agriculture of macro- and microalgae extracts as plant biostimulants. Specifically, we provide an overview of current knowledge and achievements about extraction methods, compositions, and action mechanisms of algal extracts, focusing on salt-stress tolerance. We also outline current limitations and possible research avenues. We conclude that the comparison and the integration of knowledge on the molecular and physiological response of plants to salt and to algal extracts should also guide the extraction procedures and application methods. The effects of algal biostimulants have been mainly investigated from an applied perspective, and the exploitation of different scientific disciplines is still much needed for the development of new sustainable strategies to increase crop tolerance to salt stress.

Salicylic acid and thiourea mitigate the salinity and drought stress on physiological traits governing yield in pearl millet- wheat

Plant growth is often affected with hampered physiological and cellular functioning due to salinity and drought stress. To assess the effectiveness of plant bioregulators (PBRs) in mitigating abiotic stresses, a double spilt plot field study was conducted with three replications at ICAR-CSSRI, research farm, Nain, Panipat. The study comprised of three deficit irrigation regimes viz., 100, 80 and 60% of crop evapo-transpiration (ET_c) (I₁, I₂ and I₃), four levels of irrigation water salinity i.e. 2, 4, 8, 12 dS m⁻¹ (S₀, S₁, S₂ and S₃) and two PBRs salicylic acid (SA; G₁) and thiourea (TU; G₂). Irrigations, as per regimes and salinity, were applied at identified critical stages of wheat and if needed in pearl millet. PBRs were applied as seed priming and foliar sprays at two sensitive stages of respective crops. The trend of plant height, and physiological and biochemical traits was similar under different treatments at both stages, but differed significantly only at reproductive stage. Water deficit caused significant reduction in pearl millet (5.1%) and wheat (6.7%) grain yields. The reduction in grain yield under 8 and 12 dS m⁻¹ was 12.90 and 22.43% in pearl millet and 7.68 and 32.93% in wheat, respectively compared to 2 dS m⁻¹. Application of either SA (G₁) or TU (G₂) significantly enhanced plant height and grain yield, but magnitude of the increment was higher with SA in pearl millet and with TU in wheat. Application of SA and TU increased grain yield by 14.42 and 12.98 in pearl millet, and 12.90 and 17.36% in wheat, respectively. The plant height, RWC, TC, MI, LP, proline, Fv/Fm and Na/K ratio significantly reduced by salinity stress in pearl millet and both water and salinity stress in wheat. Application of both PBRs proved beneficial to mitigate adverse effect of water deficit and salt stress by significantly improving physiological traits, biochemical traits and ultimately grain yield in both crops.

Native Arbuscular Mycorrhizal Fungi Characterization from Saline Lands in Arid Oases, Northwest China

Arbuscular mycorrhizal fungi (AMF) colonize land plants in almost every ecosystem, even in extreme conditions, such as saline soils. In the present work, we report the mycorrhizal capacity of rhizosphere soils collected in the dry desert region of the Minqin Oasis, located in the northwest of China (Gansu province), which is characterized by several halophytes. Lycium spp. and Peganum nigellastrum were used as trap plants in a greenhouse experiment to identify autochthonous AMF associated with the halophytes’ rhizospheres. Morphological observations showed the typical AMF structures inside roots. Twenty-six molecularly distinct AMF taxa were recovered from soil and root DNA. The taxonomical diversity mirrors the several AMF adapted to extreme environmental conditions, such as the saline soil of central China. Knowledge of the AMF associated with halophytes may contribute to select specific fungal isolates to set up agriculture strategies for protecting non-halophyte crop plants in saline soils.

Physiological approach to decipher the drought tolerance of a soybean genotype from Brazilian savana

Drought is one of the major constraints for soybean production in Brazil. In this study we investigated the physiological traits of two soybean parental genotypes under progressive soil drying and rewetting. The plants were evaluated under full irrigation (control) conditions and under water deficit imposed by suspending irrigation until the plants reached predawn leaf water potentials (Ψam) of -1.0 MPa (moderate) and -1.5 MPa (severe). Physiological analyses showed that these genotypes exhibit different responses to water deficit. The Embrapa 48 genotype reached moderate and severe water potential two days after the BR16 genotype and was able to maintain higher levels of A, ETR and ΦPSII even under deficit conditions. This result was not related to changes in gs, 13C isotopic composition and presence of a more efficient antioxidant system. In addition, Fv/Fm values did not decrease in Embrapa 48 genotype in relation to irrigated condition showing that stress was not causing photochemical inhibition of photosynthesis. The greater reduction in the relative growth of the shoots, with concomitant greater growth of the root system under drought, indicates that the tolerant genotype is able to preferentially allocated carbon to the roots, presenting less damage to photosynthesis. Therefore, the physiological responses revealed that the tolerant genotype postponed leaf dehydration by a mechanism involving a more efficient use and translocation of water from root to shoot to maintain cell homeostasis and photosynthetic metabolism under stress.

Gene expression studies of Saccharum spontaneum, a wild relative of sugarcane in response to salinity stress

The study is aimed to assess the morphological, physiological, and molecular responses of seven Saccharum spontaneum clones for salinity stress. These clones (IND-07-1462, IND-07-1465, IND-07-1470, IND-07-1471, IND 16-1761, IND 16-1762, and IND 16-1763) were subjected to salinity stress at two different concentrations of electrical conductivity 6 and 8 ds/m after 60 days of planting. All seven genotypes showed a decrease in relative water content and nitrate reductase activity with an increase in severity of salt stress. The effect was more pronounced in IND-07-1471, while IND-16-1762 exhibited only a minimum drop. Similarly we observed an increase in proline content and lipid peroxidation activity for the genotype IND-07-1471, while IND-16-1762 showed minimum increase. Molecular profiling of genes/transcription factors like salt overly sensitive, responsive to abscissic acid, dirigent, myeloblastosis, ethylene responsive factor associated with salinity stress tolerance showed 19-, 18-, 17-, 10-, and 9-fold increased expression at 8 ds/m of salinity stress, respectively, in IND-16-1762 showed. Based on the evidences obtained from expression profiling, we have cloned the conserved regions of RAB and SOS1 genes. The domain of SOS and RAB was identified as a regulatory subunit of cAMP-dependent protein kinases which is involved in a signaling pathway.

GsSnRK1 interplays with transcription factor GsERF7 from wild soybean to regulate soybean stress resistance

Although the function and regulation of SnRK1 have been studied in various plants, its molecular mechanisms in response to abiotic stresses are still elusive. In this work, we identified an AP2/ERF domain-containing protein (designated GsERF7) interacting with GsSnRK1 from a wild soybean cDNA library. GsERF7 gene expressed dominantly in wild soybean roots and was responsive to ethylene, salt, and alkaline. GsERF7 bound GCC cis-acting element and could be phosphorylated on S36 by GsSnRK1. GsERF7 phosphorylation facilitated its translocation from cytoplasm to nucleus and enhanced its transactivation activity. When coexpressed in the hairy roots of soybean seedlings, GsSnRK1(wt) and GsERF7(wt) promoted plants to generate higher tolerance to salt and alkaline stresses than their mutated species, suggesting that GsSnRK1 may function as a biochemical and genetic upstream kinase of GsERF7 to regulate plant adaptation to environmental stresses. Furthermore, the altered expression patterns of representative abiotic stress-responsive and hormone-synthetic genes were determined in transgenic soybean hairy roots after stress treatments. These results will aid our understanding of molecular mechanism of how SnRK1 kinase plays a cardinal role in regulating plant stress resistances through activating the biological functions of downstream factors.

Genetics of yield, abiotic stress tolerance and biofortification in wheat (Triticum aestivum L.)

A review of the available literature on genetics of yield and its component traits, tolerance to abiotic stresses and biofortification should prove useful for future research in wheat in the genomics era. The work reviewed in this article mainly covers the available information on genetics of some important quantitative traits including yield and its components, tolerance to abiotic stresses (heat, drought, salinity and pre-harvest sprouting = PHS) and biofortification (Fe/Zn and phytate contents with HarvestPlus Program) in wheat. Major emphasis is laid on the recent literature on QTL interval mapping and genome-wide association studies, giving lists of known QTL and marker-trait associations. Candidate genes for different traits and the cloned and characterized genes for yield traits along with the molecular mechanism are also described. For each trait, an account of the present status of marker-assisted selection has also been included. The details of available results have largely been presented in the form of tables; some of these tables are included as supplementary files.

Physiological responses and tolerance mechanisms of seashore paspalum and centipedegrass exposed to osmotic and iso-osmotic salt stresses

Osmotic stresses caused by reduced water availability or the accumulation of salts in the soil can be highly damaging to plants. The objective of this study was to investigate physiological responses and tolerance mechanisms of two turfgrass species (seashore paspalum and centipedegrass) with distinct differences in salinity tolerance exposed to osmotic and iso-osmotic salt stresses. Three turfgrass genotypes including seashore paspalums 'Seastar' and 'UGP113', and centipedegrass 'TifBlair' were grown in ½ strength Hoagland's solution with three different treatment conditions; control (no external addition), salt stress (-0.4 MPa by adding NaCl) and osmotic stress [-0.4 MPa by adding polyethylene glycol (PEG)]. Osmotic stress damages were more severe with greater reductions in turf quality, photochemical efficiency (Fv/Fm), relative water content (RWC) and leaf water potential (Ψw) compared to iso-osmotic salt stress in both seashore paspalum and centipedegrass. Greater osmotic adjustment (OA) with greater accumulation of metabolically inexpensive inorganic osmolytes (Na⁺) helped turfgrasses to lessen damages in salt stress compared to osmotic stress. However, such accumulation of Na⁺ resulted ion-toxicity and triggered some damages in terms of increased electrolyte leakage (EL) and reduced total protein in salt-sensitive centipedegrass. Seashore paspalum had better ion regulation and also maintained greater antioxidant enzyme activities compared to centipedegrass; therefore it was able to avoid ion-specific damages under salt stress. Differences in the utilization of specific solutes for osmotic adjustment and antioxidant metabolism are partially responsible for the differences in salt versus osmotic stress responses in these species; the regulation of these defense mechanisms requires further investigation.

Sphingobacterium sp. BHU-AV3 Induces Salt Tolerance in Tomato by Enhancing Antioxidant Activities and Energy Metabolism

Salt tolerant bacteria can be helpful in improving a plant's tolerance to salinity. Although plant-bacteria interactions in response to salt stress have been characterized, the precise molecular mechanisms by which bacterial inoculation alleviates salt stress in plants are still poorly explored. In the present study, we aimed to determine the role of a salt-tolerant plant growth-promoting rhizobacteria (PGPR) Sphingobacterium BHU-AV3 for improving salt tolerance in tomato through investigating the physiological responses of tomato roots and leaves under salinity stress. Tomato plants inoculated with BHU-AV3 and challenged with 200 mM NaCl exhibited less senescence, positively correlated with the maintenance of ion balance, lowered reactive oxygen species (ROS), and increased proline content compared to the non-inoculated plants. BHU-AV3-inoculated plant leaves were less affected by oxidative stress, as evident from a reduction in superoxide contents, cell death, and lipid peroxidation. The reduction in ROS level was associated with the increased antioxidant enzyme activities along with multiple-isoform expression [peroxidase (POD), polyphenol oxidase (PPO), and superoxide dismutase (SOD)] in plant roots. Additionally, BHU-AV3 inoculation induced the expression of proteins involved in (i) energy production [ATP synthase], (ii) carbohydrate metabolism (enolase), (iii) thiamine biosynthesis protein, (iv) translation protein (elongation factor 1 alpha), and the antioxidant defense system (catalase) in tomato roots. These findings have provided insight into the molecular mechanisms of bacteria-mediated alleviation of salt stress in plants. From the study, we can conclude that BHU-AV3 inoculation effectively induces antioxidant systems and energy metabolism in tomato roots, which leads to whole plant protection during salt stress through induced systemic tolerance.

Nitrogen Enhances Salt Tolerance by Modulating the Antioxidant Defense System and Osmoregulation Substance Content in Gossypium hirsutum

Increasing soil salinity suppresses both productivity and fiber quality of cotton, thus, an appropriate management approach needs to be developed to lessen the detrimental effect of salinity stress. This study assessed two cotton genotypes with different salt sensitivities to investigate the possible role of nitrogen supplementation at the seedling stage. Salt stress induced by sodium chloride (NaCl, 200 mmol·L-1) decreased the growth traits and dry mass production of both genotypes. Nitrogen supplementation increased the plant water status, photosynthetic pigment synthesis, and gas exchange attributes. Addition of nitrogen to the saline media significantly decreased the generation of lethal oxidative stress biomarkers such as hydrogen peroxide, lipid peroxidation, and electrolyte leakage ratio. The activity of the antioxidant defense system was upregulated in both saline and non-saline growth media as a result of nitrogen application. Furthermore, nitrogen supplementation enhanced the accumulation of osmolytes, such as soluble sugars, soluble proteins, and free amino acids. This established the beneficial role of nitrogen by retaining additional osmolality to uphold the relative water content and protect the photosynthetic apparatus, particularly in the salt-sensitive genotype. In summary, nitrogen application may represent a potential strategy to overcome the salinity-mediated impairment of cotton to some extent.

Effect of salt stress on in vitro organogenesis from nodal explant of Limnophila aromatica (Lamk.) Merr. and Bacopa monnieri (L.) Wettst. and their physio-morphological and biochemical responses

Salinity is one of the most severe abiotic stress factors that limit crop productivity by affecting the growth of plants. Therefore, it is significant to know the responses of plants against salt stress. In this study, the callus formation capabilities of nodal explants of Limnophila aromatica (Lamk.) Merr. and Bacopa monnieri (L.) Wettst. incubated under different NaCl concentrations (0-100 mM) in in vitro culture conditions were investigated and also the effect of NaCl on the release of regenerated shoots from these calluses was examined. Furthermore, the plants under NaCI stress were evaluated physiologically and biochemically. Callus formation percentages and callus intensities from the nodal explants decreased with increasing NaCl concentrations. In addition, yellowing, browning and even deaths were observed in calluses under salt toxicity. The callus was taken into the subculture, and the increased NaCl concentration in both plant species adversely affected the regeneration ability of the shoots. The number of shoots per callus for L. aromatica and B. monnieri was 6.72-17.49 and 7.42-15.38, respectively. The length of shoots in L. aromatica was between 0.95 and 1.65 cm, and in B. monnieri between 1.17 and 1.81 cm. The lowest number of shoots per callus and the shoot lengths were found in medium containing 100 mM NaCl. Moreover, photosynthetic pigmentation, lipid peroxidation, protein content, and proline content was damaged with increased salinity compared to the control group. This comprehensive study in tissue culture conditions can a be potential contributor to the literature and can help other studies to be carried out in the future.

Comparative Transcriptome Analysis Reveals Molecular Defensive Mechanism of Arachis hypogaea in Response to Salt Stress

Abiotic stresses comprise all nonliving factors, such as soil salinity, drought, extreme temperatures, and metal toxicity, posing a serious threat to agriculture and affecting the plant production around the world. Peanut (Arachis hypogaea L.) is one of the most important crops for vegetable oil, proteins, minerals, and vitamins in the world. Therefore, it is of importance to understand the molecular mechanism of peanut against salt stress. Six transcriptome sequencing libraries including 24-hour salt treatments and control samples were constructed from the young leaves of peanut. A comprehensive analysis between two groups detected 3,425 differentially expressed genes (DEGs) including 2,013 upregulated genes and 1,412 downregulated genes. Of these DEGs, 141 transcription factors (TFs) mainly consisting of MYB, AP2/ERF, WRKY, bHLH, and HSF were identified in response to salinity stress. Further, GO categories of the DEGs highly related to regulation of cell growth, cell periphery, sustained external encapsulating structure, cell wall organization or biogenesis, antioxidant activity, and peroxidase activity were significantly enriched for upregulated DEGs. The function of downregulated DEGs was mainly enriched in regulation of metabolic processes, oxidoreductase activity, and catalytic activity. Fourteen DEGs with response to salt tolerance were validated by real-time PCR. Taken together, the identification of DEGs' response to salt tolerance of cultivated peanut will provide a solid foundation for improving salt-tolerant peanut genetic manipulation in the future.

Salinity tolerance in barley during germination- homologs and potential genes

Salinity affects more than 6% of the world's total land area, causing massive losses in crop yield. Salinity inhibits plant growth and development through osmotic and ionic stresses; however, some plants exhibit adaptations through osmotic regulation, exclusion, and translocation of accumulated Na+ or Cl-. Currently, there are no practical, economically viable methods for managing salinity, so the best practice is to grow crops with improved tolerance. Germination is the stage in a plant's life cycle most adversely affected by salinity. Barley, the fourth most important cereal crop in the world, has outstanding salinity tolerance, relative to other cereal crops. Here, we review the genetics of salinity tolerance in barley during germination by summarizing reported quantitative trait loci (QTLs) and functional genes. The homologs of candidate genes for salinity tolerance in Arabidopsis, soybean, maize, wheat, and rice have been blasted and mapped on the barley reference genome. The genetic diversity of three reported functional gene families for salt tolerance during barley germination, namely dehydration-responsive element-binding (DREB) protein, somatic embryogenesis receptor-like kinase and aquaporin genes, is discussed. While all three gene families show great diversity in most plant species, the DREB gene family is more diverse in barley than in wheat and rice. Further to this review, a convenient method for screening for salinity tolerance at germination is needed, and the mechanisms of action of the genes involved in salt tolerance need to be identified, validated, and transferred to commercial cultivars for field production in saline soil.

The Saltol QTL-localized transcription factor OsGATA8 plays an important role in stress tolerance and seed development in Arabidopsis and rice

GATA represents a highly conserved family of transcription factors reported in organisms ranging from fungi to angiosperms. A member of this family, OsGATA8, localized within the Saltol QTL in rice, has been reported to be induced by salinity, drought, and ABA. However, its precise role in stress tolerance has not yet been elucidated. Using genetic, molecular, and physiological analyses, in this study we show that OsGATA8 increases seed size and tolerance to abiotic stresses in both Arabidopsis and rice. Transgenic lines of rice were generated with 3-fold overexpression of OsGATA8 compared to the wild-type together with knockdown lines with 2-fold lower expression. The overexpressing lines showed higher biomass accumulation and higher photosynthetic efficiency in seedlings compared to the wild-type and knockdown lines under both normal and salinity-stress conditions. OsGATA8 appeared to be an integrator of diverse cellular processes, including K+/Na+ content, photosynthetic efficiency, relative water content, Fv/Fm ratio, and the stability to sub-cellular organelles. It also contributed to maintaining yield under stress, which was ~46% higher in overexpression plants compared with the wild-type. OsGATA8 produced these effects by regulating the expression of critical genes involved in stress tolerance, scavenging of reactive oxygen species, and chlorophyll biosynthesis.

Constitutive Contribution by the Rice OsHKT1;4 Na+ Transporter to Xylem Sap Desalinization and Low Na+ Accumulation in Young Leaves Under Low as High External Na+ Conditions

HKT Na⁺ transporters correspond to major salt tolerance QTLs in different plant species and are targets of great interest for breeders. In rice, the HKT family is composed of seven or eight functional genes depending on cultivars. Three rice HKT genes, OsHKT1;1, OsHKT1;4 and OsHKT1;5, are known to contribute to salt tolerance by reducing Na⁺ accumulation in shoots upon salt stress. Here, we further investigate the mechanisms by which OsHKT1;4 contributes to this process and extend this analysis to the role of this transporter in plants in presence of low Na⁺ concentrations. By analyzing transgenic rice plants expressing a GUS reporter gene construct, we observed that OsHKT1;4 is mainly expressed in xylem parenchyma in both roots and leaves. Using mutant lines expressing artificial microRNA that selectively reduced OsHKT1;4 expression, the involvement of OsHKT1;4 in retrieving Na⁺ from the xylem sap in the roots upon salt stress was evidenced. Since OsHKT1;4 was found to be also well expressed in the roots in absence of salt stress, we extended the analysis of its role when plants were subjected to non-toxic Na⁺ conditions (0.5 and 5 mM). Our finding that the transporter, expressed in Xenopus oocytes, displayed a relatively high affinity for Na⁺, just above 1 mM, provided first support to the hypothesis that OsHKT1;4 could have a physiological role at low Na⁺ concentrations. We observed that progressive desalinization of the xylem sap along its ascent to the leaf blades still occurred in plants grown at submillimolar Na⁺ concentration, and that OsHKT1;4 was involved in reducing xylem sap Na⁺ concentration in roots in these conditions too. Its contribution to tissue desalinization from roots to young mature leaf blades appeared to be rather similar in the whole range of explored external Na⁺ concentrations, from submillimolar to salt stress conditions. Our data therefore indicate that HKT transporters can be involved in controlling Na⁺ translocation from roots to shoots in a much wider range of Na⁺ concentrations than previously thought. This asks questions about the roles of such a transporter-mediated maintaining of tissue Na⁺ content gradients in non-toxic conditions.