Peroxidase like Zn doped Prussian blue facilitates salinity tolerance in winter wheat through seed dressing

Salt stress severely limits the growth and yield of wheat in saline-alkali soil. While nanozymes have shown promise in mitigating abiotic stress by scavenging reactive oxygen species (ROS) in plants, their application in alleviating salt stress for wheat is still limited. This study synthesized a highly active nanozyme catalyst known as ZnPB (Zn-modified Prussian blue) to improve the yield and quality of wheat in saline soil. According to the Michaelis-Menten equation, ZnPB demonstrates exceptional peroxidase-like enzymatic activity, thereby mitigating oxidative damage caused by salt stress. Additionally, studies have shown that the ZnPB nanozyme is capable of regulating intracellular Na+ efflux and K+ retention in wheat, resulting in a decrease in proline and soluble protein levels while maintaining the integrity of macromolecules within the cell. Consequently, field experiments demonstrated that the ZnPB nanozyme increased winter wheat yield by 12.15 %, while also significantly enhancing its nutritional quality. This research offers a promising approach to improving the salinity tolerance of wheat, while also providing insights into its practical application.

Metabolomic and physiological analysis of alfalfa (Medicago sativa L.) in response to saline and alkaline stress

Alfalfa (Medicago sativa L.) is a leguminous forage widely grown worldwide. Saline and alkaline stress can affect its development and yield. To elucidate the physiological mechanisms of alfalfa in response to saline and alkaline stress, we investigated the growth and physiological and metabolomic changes in alfalfa under saline (100 mM NaCl) and alkaline (100 mM Na2CO3, NaHCO3) stress. At the same Na+ concentration, alkaline stress caused more damage than that caused by saline stress. A total of 65 and 124 metabolites were identified in response to saline and alkaline stress, respectively. Determination of gene expression, enzyme activity, substance content, and KEGG enrichment analysis in key pathways revealed that alfalfa responded to saline stress primarily by osmoregulation and TCA cycle enhancement. Flavonoid synthesis, TCA cycle, glutamate anabolism, jasmonate synthesis, and cell wall component synthesis increased as responses to alkaline stress. This study provides important resources for breeding saline-alkaline-resistant alfalfa.

Salt stress-induced changes in soil metabolites promote cadmium transport into wheat tissues

Soil salinity is known to improve cadmium (Cd) mobility, especially in arid soils. However, the mechanisms involved in how salt stress-associated metabolic profiles participate in mediating Cd transport in the soil-plant system remain poorly understood. This study was designed to investigate the effects of salinity-induced changes in soil metabolites on Cd bioavailability. Sodium salts in different combinations according to molar ratio (NaCl:Na₂SO₄=1:1; NaCl:Na₂SO₄:NaHCO₃=1:2:1; NaCl:Na₂SO₄:NaHCO₃:Na₂CO₃=1:9:9:1; NaCl:Na₂SO₄:NaHCO₃:Na₂CO₃=1:1:1:1) were applied to the Cd-contaminated soils, which increased soil Cd availability by 22.36% and the Cd content in wheat grains by 36.61%, compared to the control. Salt stress resulted in soil metabolic reprogramming, which might explain the decreased growth of wheat plants and increased Cd transport from the soil into wheat tissues. For example, down-regulation of starch and sucrose metabolism reduced the production of sugars, which adversely affected growth; up-regulation of fatty acid metabolism allowed wheat plants to maintain a normal intracellular environment under saline conditions; up-regulation of the tricarboxylic acid (TCA) cycle was triggered, causing an increase in organic acid synthesis and the accumulation of organic acids, which facilitated the migration of soil Cd into wheat tissues. In summary, salt stress can facilitate Cd transport into wheat tissues by the direct effect of salt-based ions and the combined effect of altered soil physicochemical properties and soil metabolic profiles in Cd-contaminated soils.

Advances in understanding multilevel responses of seagrasses to hypersalinity

Human- and nature-induced hypersaline conditions in coastal systems can lead to profound alterations of the structure and vitality of seagrass meadows and their socio-ecological benefits. In the last two decades, recent research efforts (>50 publications) have contributed significantly to unravel the physiological basis underlying the seagrass-hypersalinity interactions, although most (∼70%) are limited to few species (e.g. Posidonia oceanica, Zostera marina, Thalassia testudinum, Cymodocea nodosa). Variables related to photosynthesis and carbon metabolism are among the most prevalent in the literature, although other key metabolic processes such as plant water relations and responses at molecular (i.e. gene expression) and ultrastructure level are attracting attention. This review emphasises all these latest insights, offering an integrative perspective on the interplay among biological responses across different functional levels (from molecular to clonal structure), and their interaction with biotic/abiotic factors including those related to climate change. Other issues such as the role of salinity in driving the evolutionary trajectory of seagrasses, their acclimation mechanisms to withstand salinity increases or even the adaptive properties of populations that have historically lived under hypersaline conditions are also included. The pivotal role of the costs and limits of phenotypic plasticity in the successful acclimation of marine plants to hypersalinity is also discussed. Finally, some lines of research are proposed to fill the remaining knowledge gaps.

Alhagi sparsifolia acclimatizes to saline stress by regulating its osmotic, antioxidant, and nitrogen assimilation potential

BACKGROUND

Alhagi sparsifolia (Camelthorn) is a leguminous shrub species that dominates the Taklimakan desert's salty, hyperarid, and infertile landscapes in northwest China. Although this plant can colonize and spread in very saline soils, how it adapts to saline stress in the seedling stage remains unclear so a pot-based experiment was carried out to evaluate the effects of four different saline stress levels (0, 50, 150, and 300 mM) on the morphological and physio-biochemical responses in A. sparsifolia seedlings.

RESULTS

Our results revealed that N-fixing A. sparsifolia has a variety of physio-biochemical anti-saline stress acclimations, including osmotic adjustments, enzymatic mechanisms, and the allocation of metabolic resources. Shoot-root growth and chlorophyll pigments significantly decreased under intermediate and high saline stress. Additionally, increasing levels of saline stress significantly increased Na⁺ but decreased K⁺ concentrations in roots and leaves, resulting in a decreased K⁺/Na⁺ ratio and leaves accumulated more Na + and K + ions than roots, highlighting their ability to increase cellular osmolarity, favouring water fluxes from soil to leaves. Salt-induced higher lipid peroxidation significantly triggered antioxidant enzymes, both for mass-scavenging (catalase) and cytosolic fine-regulation (superoxide dismutase and peroxidase) of H₂O₂. Nitrate reductase and glutamine synthetase/glutamate synthase also increased at low and intermediate saline stress levels but decreased under higher stress levels. Soluble proteins and proline rose at all salt levels, whereas soluble sugars increased only at low and medium stress. The results show that when under low-to-intermediate saline stress, seedlings invest more energy in osmotic adjustments but shift their investment towards antioxidant defense mechanisms under high levels of saline stress.

CONCLUSIONS

Overall, our results suggest that A. sparsifolia seedlings tolerate low, intermediate, and high salt stress by promoting high antioxidant mechanisms, osmolytes accumulations, and the maintenance of mineral N assimilation. However, a gradual decline in growth with increasing salt levels could be attributed to the diversion of energy from growth to maintain salinity homeostasis and anti-stress oxidative mechanisms.

Autophagy and Programmed Cell Death Are Critical Pathways in Jasmonic Acid Mediated Saline Stress Tolerance in Oryza sativa

Saline stress is the most limiting condition impacting the plant growth, development, and productivity. In this present study, jasmonic acid (JA) was used as a foliar spray on the rice seedlings grown under saline stress. Increase in photosynthetic pigments, anthocyanin, and total protein content was observed with JA treatment while NaCl showed reduction in biochemical constituents and enhanced antioxidant enzyme activity. The leaf cells of NaCl-treated seedlings accumulated more ROS and had more fragmented nuclei, whereas JA decreased the accumulation and fragmentation during saline stress. In NaCl treatment, gene expression analysis showed many fold upregulation in comparison with other treatments. The results suggest that JA acts as a promoter for growth, physiological, biochemical, and cellular contents, as well as ameliorate the effects of saline stress. The expression of genes demonstrated that saline stress may promote autophagy, which leads to autophagic cell death, and improve tolerance to saline stress in rice seedlings via the jasmonic acid signaling pathway. However, the mechanism by which jasmonate signaling induces autophagy and cell death is unknown and requires further exploration.

Halotolerant bacteria isolated from extreme environments induce seed germination and growth of chia (Salvia hispanica L.) and quinoa (Chenopodium quinoa Willd.) under saline stress

The aim of the study was to characterize halotolerant bacteria and to evaluate their plant growth promotion potential on chia and quinoa seedlings under saline stress. Isolated microorganisms were evaluated for nitrogen fixation, phosphate solubilization, and production of siderophores and indole acetic acid. Three strains and two consortia were selected: Halomonas sp. (SFS), Micrococcus luteus (SA211), Bacillus sp. (HX11), C1 (SA211 + SFS), and C2 (SA211 + HX11). In vitro assays using water agar and half-strength Murashige-Skoog plates showed that an increase in salinity led to an increased seedlings mortality and a decrease in germination (lower than 40%), in total length (varying between 16% and 87% decreases), root length (from 60% to 92% lesser length) and dry weight (from 7% to 86% lower weight). Also, the relative growth index (RGI) decreased for both crops in most treatments, except those with HX11 and C2. These treatments had the highest growth parameters and RGI values in presence of high salinity in chia (50 and 100 mmol/L NaCl) and quinoa (200 and 400 mmol/L NaCl). SA211, the highest producer of indole acetic acid, showed a detrimental effect and anomalous phenotype on plants. Our results suggest that Bacillus sp. HX11, with multiple plant growth promotion traits and tolerance to saline stress, has a great potential as a bioinoculant in saline conditions and could be used as a biofertilizer for crop production.

Remobilization of leaf Na+ content and use of nonstructural carbohydrates vary depending on the time when salt stress begins in woody species

Basic mechanisms are known to promote salt tolerance in plants: a delay in Na⁺ uptake or rapid Na⁺ remobilization from leaf tissue. We measured dynamics of the Na⁺/K⁺ ratio and components of carbon metabolism during the first 72 h after saline stress (200 mM NaCl) began in Cenostigma pyramidale, a woody species, under controlled conditions. Saline stress at two times: one plant group at the beginning of the morning and the other in the evening. Stressed plants had three times more Na⁺ in leaves than did control plants in the first 24 h. However, in the next few hours, despite new applications of saline solution, the Na⁺/K⁺ ratio continued to decline. Several samples, including night treatments, provided evidence that this species uses Na⁺ recirculation mechanisms to endure salt stress. Effects of salt on the traits evaluated differed depending on the time when stress began. Between the two saline treatments, in the first 24 h after saline stress, gas exchange decreased more strongly in morning-stressed plants, when large amounts of Na⁺ reached the leaf and K⁺ left this organ. Nevertheless, when stress was applied in the evening, leaf Na⁺ remobilization was faster, and the soluble sugar/starch ratio remained greater than did the control. Our data suggested that time of the beginning of salt stress could change the level of damage. Morning-stressed plants synthesized greater amounts of proline, H₂O₂, and malondialdehyde than did night-stressed plants. We recommend that details regarding the time of stress be taken into consideration in physiological studies.

Phytobeneficial bacteria improve saline stress tolerance in Vicia faba and modulate microbial interaction network

Increased global warming, caused by climate change and human activities, will seriously hinder plant development, such as increasing salt concentrations in soils, which will limit water availability for plants. To ensure optimal plant growth under such changing conditions, microorganisms that improve plant growth and health must be integrated into agricultural practices. In the present work, we examined the fate of Vicia faba microbiota structure and interaction network upon inoculation with plant-nodulating rhizobia (Rhizobium leguminosarum RhOF125) and non-nodulating strains (Paenibacillus mucilaginosus BLA7 and Ensifer meliloti RhOL1) in the presence (or absence) of saline stress. Inoculated strains significantly improved plant tolerance to saline stress, suggesting either a direct or indirect effect on the plant response to such stress. To determine the structure of microbiota associated with V. faba, samples of the root-adhering soil (RAS), and the root tissues (RT) of seedlings inoculated (or not) with equal population size of RhOF125, BLA7 and RhOL1 strains and grown in the presence (or absence) of salt, were used to profile the microbial composition by 16S rRNA gene sequencing. The inoculation did not show a significant impact on the composition of the RT microbiota or RAS microbiota. The saline stress shifted the RAS microbiota composition, which correlated with a decrease in Enterobacteriaceae and an increase in Sphingobacterium, Chryseobacterium, Stenotrophomonas, Agrobacterium and Sinorhizobium. When the microbiota of roots and RAS are considered together, the interaction networks for each treatment are quite different and display different key populations involved in community assembly. These findings indicate that upon seed inoculation, community interaction networks rather than their composition may contribute to helping plants to better tolerate environmental stresses. The way microbial populations interfere with each other can have an impact on their functions and thus on their ability to express the genes required to help plants tolerate stresses.

Plant growth promotion by Pseudomonas putida KT2440 under saline stress: role of eptA

New strategies to improve crop yield include the incorporation of plant growth-promoting bacteria in agricultural practices. The non-pathogenic bacterium Pseudomonas putida KT2440 is an excellent root colonizer of crops of agronomical importance and has been shown to activate the induced systemic resistance of plants in response to certain foliar pathogens. In this work, we have analyzed additional plant growth promotion features of this strain. We show it can tolerate high NaCl concentrations and determine how salinity influences traits such as the production of indole compounds, siderophore synthesis, and phosphate solubilization. Inoculation with P. putida KT2440 significantly improved seed germination and root and stem length of soybean and corn plants under saline conditions compared to uninoculated plants, whereas the effects were minor under non-saline conditions. Also, random transposon mutagenesis was used for preliminary identification of KT2440 genes involved in bacterial tolerance to saline stress. One of the obtained mutants was analyzed in detail. The disrupted gene encodes a predicted phosphoethanolamine-lipid A transferase (EptA), an enzyme described to be involved in the modification of lipid A during lipopolysaccharide (LPS) biosynthesis. This mutant showed changes in exopolysaccharide (EPS) production, low salinity tolerance, and reduced competitive fitness in the rhizosphere.

The bHLH gene family and its response to saline stress in Jilin ginseng, Panax ginseng C.A. Meyer

Basic helix-loop-helix (bHLH) gene family is a gene family of transcription factors that plays essential roles in plant growth and development, secondary metabolism and response to biotic and abiotic stresses. Therefore, a comprehensive knowledge of the bHLH gene family is paramount to understand the molecular mechanisms underlying these processes and develop advanced technologies to manipulate the processes efficiently. Ginseng, Panax ginseng C.A. Meyer, is a well-known medicinal herb; however, little is known  about the bHLH genes (PgbHLH) in the species. Here, we identified 137 PgbHLH genes from Jilin ginseng cultivar, Damaya, widely cultivated in Jilin, China, of which 50 are newly identified by pan-genome analysis. These 137 PgbHLH genes were phylogenetically classified into 26 subfamilies, suggesting their sequence diversification. They are alternatively spliced into 366 transcripts in a 4-year-old plant and involved in 11 functional subcategories of the gene ontology, indicating their functional differentiation in ginseng. The expressions of the PgbHLH genes dramatically vary spatio-temporally and across 42 genotypes, but they are still somehow functionally correlated. Moreover, the PgbHLH gene family, at least some of its genes, is shown to have roles in plant response to the abiotic stress of saline. These results provide a new insight into the evolution and functional differentiation of the bHLH gene family in plants, new bHLH genes to the PgbHLH gene family, and saline stress-responsive genes for genetic improvement in ginseng and other plant species.

The responses of a soil bacterial community under saline stress are associated with Cd availability in long-term wastewater-irrigated field soil

Long-term wastewater irrigation impacts soil geochemical properties (salinity, pH and soil aggregates) and promotes the bioaccumulation of heavy metals to plants, which may change soil function, decrease soil health, decrease the productivity of farmland, and even cause land degradation. In this study, we explored the impact of saline stress on soil bacterial communities and Cd availability in long-term wastewater-irrigated field soil. Different amounts of saline stress by adding 0.1, 0.3 and 0.5% salts in a fixed proportion (NaCl: Na₂SO₄: NaHCO₃: Na₂CO₃ = 1:9:9:1) were applied in a 1-year, multiple cropping system with winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) in wastewater-polluted soil. Increased salinity in the soil increased Cd availability: compared with CK (no extra salts addition), addition of 0.5% mixed salts significantly increased soil available Cd up by 67.5% and grain Cd concentration by 43.7%, and adding 0.5% salts also resulted in the increases of soil pH (∼0.5 unit) and electric conductivity (97.4%). Soil saline stress significantly changed major soil microbes in Cd-contaminated soil. Increased saline stress enriched taxa in the Bacillaceae, Staphylococcaceae and Pseudomonadaceae bacterial families, while one family within Proteobacteria (Sphingomonadaceae) was the most sensitive biomarker, based on Cd contamination without saline stress in CK-treated soils. Structural equation modeling (SEM) analysis revealed that soil saline stress induced an increase in soil Cd availability that was regulated by the bacterial community.

An insight from tolerance to salinity stress in halophyte Portulaca oleracea L.: Physio-morphological, biochemical and molecular responses

Salinity represents one of the environmental conditions with adverse effects on the productivity of most crops throughout the world. The response of plants to salt stress is of great interest for research to understand the mechanism involved in tolerance to salinity and highlight insights into the improvement of salt tolerance-crops of importance. In this study, the effect of salt stress was observed in wild and cultivated populations of P. oleracea originated from Tunisia and Italy. The results showed that at various concentrations of NaCl (0 mM, 50 mM, 100 mM and 150 mM), salinity has led to changes in growth parameters marked mainly by an increase in fresh and dry biomass. Beside, one of the salinity-induced side effects corresponds to the competition of Na⁺ and K⁺ ions for potassium root transporters. Our results suggested that purslane deployed an important element of tolerance such as the transporters ability to discriminate cations. In addition, the variation of PC5S gene expression tested by semi-quantitative RT-PCR revealed that proline synthesis is important in plants adaptation in saline conditions. A correlation between the gene expression varying by population and saline concentration and the level of proline assayed on the leaves of P. oleracea was highlighted.

The effect of saline-alkaline and water stresses on water use efficiency and standing biomass of Phragmites australis and Bolboschoenus planiculmis

Salt marsh plants in the West Songnen Plain, northern China, are threatened by increasing soil salinity and alkalinity since the late 20th century. To explore how these wetland ecosystems respond to such environmental changes, we examined the effect of saline-alkaline stresses and water stress (flooding/drought) on water use efficiency (WUE, assessed with stable carbon isotopes) and standing biomass of Phragmites australis and Bolboschoenus planiculmis under both greenhouse and field conditions. In the field, sodium bicarbonate (NaHCO₃) was the main saline-alkaline component, and the soil total ion content was negatively related to water level. Higher soil ion content decreased standing biomass of P. australis and B. planiculmis in the field and greenhouse, and increased WUE in the greenhouse. With higher water level, standing biomass of P. australis increased, while that of B. planiculmis decreased in both the field and greenhouse. Alkaline stress exerted the greatest negative influence on growth of P. australis, but only under high ion content. Low alkaline ion content promoted growth of B. planiculmis. Soil ion content exerted the strongest influence on foliar δ¹³C (and thus WUE) and standing biomass of both species compared to water level and stress type. Our findings suggest that under high ion contents, P. australis is more tolerant to flooding stress while B. planiculmis is more tolerant to drought stress. Moreover, P. australis has a high ability to modulate and increase WUE to resist its adverse environment. Our study will contribute to a better understanding of the influence of climate change and increasingly serious human disturbances on the distribution and productivity of these two important wetland species.

Characterization of the responses to saline stress in the symbiotic green microalga Trebouxia sp. TR9

For the first time we provide a study on the physiological, ultrastructural and molecular effects of salt stress on a terrestrial symbiotic green microalga, Trebouxia sp. TR9. Although tolerance to saline conditions has been thoroughly studied in plants and, to an extent, free-living microalgae, scientific data regarding salt stress on symbiotic lichen microalgae is scarce to non-existent. Since lichen phycobionts are capable of enduring harsh, restrictive and rapidly changing environments, it is interesting to study the metabolic machinery operating under these extreme conditions. We aim to determine the effects of prolonged exposure to high salt concentrations on the symbiotic phycobiont Trebouxia sp. TR9, isolated from the lichen Ramalina farinacea. Our results suggest that, when this alga is confronted with extreme saline conditions, the cellular structures are affected to an extent, with limited chlorophyll content loss and photosynthetic activity remaining after 72 h of exposure to 5 M NaCl. Furthermore, this organism displays a rather different molecular response compared to land plants and free-living halophile microalgae, with no noticeable increase in ABA levels and ABA-related gene expression until the external NaCl concentration is raised to 3 M NaCl. Despite this, the ABA transduction pathway seems functional, since the ABA-related genes tested are responsive to exogenous ABA. These observations could suggest that this symbiotic green alga may have developed alternative molecular pathways to cope with highly saline environments.

Plant growth promoting bacteria as an alternative strategy for salt tolerance in plants: A review

Approximately 5.2 billion hectare agriculture land are affected by erosion, salinity and soil degradation. Salinity stress has significantly affecting the fertile lands, and therefore possesses a huge impact on the agriculture and economy of a country. Salt stress has severe effects on the growth and development of plants as well as reducing its yield. Plants are inherently equipped with stress tolerance ability to responds the specific type of stress. Plants retained specific mechanisms for salt stress mitigation, such as hormonal stimulation, ion exchange, antioxidant enzymes and activation of signaling cascades on their metabolic and genetic frontiers that sooth the stressed condition. Additional to the plant inherent mechanisms, certain plant growth promoting bacteria (PGPB) also have specialized mechanism that play key role for salt stress tolerance and plant growth promotion. These bacteria triggers plants to produce different plant growth hormones like auxin, cytokinine and gibberellin as well as volatile organic compounds. These bacteria also produces growth regulators like siderophore, which fix nitrogen, solubilize organic and inorganic phosphate. Considering the importance of PGPB in compensation of salt tolerance in plants, the present study has reviewed the different aspect and mechanism of bacteria that play key role in promoting plants growth and yield. It can be concluded that PGPB can be used as a cost effective and economical tool for salinity tolerance and growth promotion in plants.

Surface display of ACC deaminase on endophytic Enterobacteriaceae strains to increase saline resistance of host rice sprouts by regulating plant ethylene synthesis

Background

Most endophytic bacteria in consortia, which provide robust and broad metabolic capacity, are attractive for applications in plant metabolic engineering. The aim of this study was to investigate the effects of engineered endophytic bacterial strains on rice sprout ethylene level and growth under saline stress. A protocol was developed to synthesize engineered strains by expressing bacterial 1-aminocyclopropane-1-carboxylate (ACC) deaminase gene on cells of endophytic Enterobacter sp. E5 and Kosakonia sp. S1 (denoted as E5P and S1P, respectively).

Results

Results showed that ACC deaminase activities of the engineered strains E5P and S1P were significantly higher than those of the wild strains E5 and S1. About 32–41% deaminase was expressed on the surface of the engineered strains. Compared with the controls without inoculation, inoculation with the wild and engineered strains increased the deaminase activities of sprouts. Inoculation with the engineered strains increased 15–21% more deaminase activities of sprouts than with the wild strains, and reduced the ethylene concentrations of sprouts more significantly than with wild strains (P < 0.05). Inoculation with the wild and engineered strains promoted the growth of sprouts, while the promoting effects were more profound with the engineered strains than with the wild strains. The engineered strains improved saline resistance of sprouts under salt concentrations from 10 to 25 g L⁻¹. The engineered strains promoted longer roots and shoots than the wild strains under the salt stresses, indicating that the ACC deaminases on the endophytic bacterial cells could result in plant-produced ACC degradation and inhibit plant ethylene formation.

Conclusions

The protocols of expressing enzymes on endophytic bacterial cells showed greater potentials than those of plant over-expressed enzymes to increase the efficiency of plant metabolic pathways.

Electronic supplementary material

The online version of this article (10.1186/s12934-017-0831-5) contains supplementary material, which is available to authorized users.

Comparative transcriptomics of rice plants under cold, iron, and salt stresses

Abiotic stresses such as salinity, iron toxicity, and low temperatures are the main limiting factors of rice (Oryza sativa L.) yield. The elucidation of the genes involved in responses to these stresses is extremely important to understand the mechanisms that confer tolerance, as well as for the development of cultivars adapted to these conditions. In this study, the RNA-seq technique was used to compare the transcriptional profile of rice leaves (cv. BRS Querência) in stage V3, exposed to cold, iron, and salt stresses for 24 h. A range of 41 to 51 million reads was aligned, in which a total range of 88.47 to 89.21 % was mapped in the reference genome. For cold stress, 7905 differentially expressed genes (DEGs) were observed, 2092 for salt and 681 for iron stress; 370 of these were common to the three DEG stresses. Functional annotation by software MapMan demonstrated that cold stress usually promoted the greatest changes in the overall metabolism, and an enrichment analysis of overrepresented gene ontology (GO) terms showed that most of them are contained in plastids, ribosome, and chloroplasts. Saline stress induced a more complex interaction network of upregulated overrepresented GO terms with a relatively low number of genes compared with cold stress. Our study demonstrated a high number of differentially expressed genes under cold stress and a greater relationship between salt and iron stress levels. The physiological process most affected at the molecular level by the three stresses seems to be photosynthesis.

Pathogenic ability and saline stress tolerance of two Fusarium isolates from Odontesthes bonariensis eggs

BACKGROUND

Several fungal species represent a potential risk to embryos of Odontesthes bonariensis (Cuvier and Valenciennes, 1835), a euryhaline freshwater fish that lives in the Pampean inland waters and has potential economic relevance.

AIMS

To identify two fungi isolated from O. bonariensis eggs exposed to saline conditions and to characterize their pathogenicity and tolerance to sodium chloride solutions.

METHODS

The isolates were identified by morphological features, and a preliminar phylogenetic analysis using sequences of translation elongation factor 1-alpha (EF-1α) and calmodulin (CAM) was performed. Koch's postulates were tested to identify the causative agent of fungal infection. The influence of NaCl on the fungal growth was evaluated in in vitro assays.

RESULTS

The isolates LPSC 1001 and 1002 were identified as representatives of the genus Fusarium, and belonging to the Fusarium incarnatum-Fusarium equiseti species complex (FIESC) and the Fusarium solani species complex (FSSC), respectively. Histological observations on eggs exposed in vitro to both isolates in infectivity assays confirmed the ability of the fungal isolates to penetrate to egg's chorionic membrane, leading to the death of embryos. Increasing NaCl concentration in the culture medium reduced the growth of the isolates LPSC 1001 and 1002, being completely inhibited at 160 and 120g/l NaCl respectively.

CONCLUSIONS

The isolates LPSC 1001 (FIESC) and 1002 (FSSC) were identified as fungal pathogens to O. bonariensis eggs. The use of NaCl solutions as antifungal treatment was not effective to control the infection with these strains.

24-epibrassinolide restores nitrogen metabolism of pigeon pea under saline stress

BACKGROUND

Several studies have shown that brassinosteroids attenuate the effects of salt stress. However, nothing is known about their effects on amino acid transport, nor the effects of these hormones on nitrate uptake under saline conditions. This study set out to determine the effects of 24-epibrassinolide, at concentrations of 10-7 M and 0.5 × 10-9 M, and clotrimazole (inhibitor of brassinosteroid synthesis), at 10-4 M, on nitrate uptake and metabolism in plants of C. cajan (L.) Millsp, cultivar C11, growing under salinity. The following aspects were analyzed: levels of proteins, amino acids, nitrate, nitrate reductase of roots and the composition of xylem sap amino acids.

RESULTS

Salinity reduced the proportion of N-transport amino acids ASN (the major component), GLU, ASP and GLN. The effect of the hormone in reducing the adverse effects of salt was related to the reestablishment (totally or partially) of the proportions of GLU, ASN and GLN, transported in the xylem and to the small but significant increase in uptake of nitrate. Increased nitrate uptake, induced by 24- epibrassinolide, was associated with a higher activity of nitrate reductase together with greater levels of free amino acids and soluble proteins in roots of plants cultivated under saline conditions.

CONCLUSION

The decline in several components of nitrogen metabolism, induced by salt, was attenuated by 24-epibrassinolide application and accentuated by clotrimazole, indicating the importance of brassinosteroid synthesis for plants growing under salinity.