Negative Effects Of Salt Stress Research Articles

Metabolomic analysis of date palm seedlings exposed to salinity and silicon treatments

ABSTRACTSilicon is known to promote plant growth as well as stress tolerance of plants. The current study was undertaken to assess the growth promoting effect of silicon on date palm seedling development as well as its ability to abate some of the negative effects of salinity. In this study, date palm seedlings were treated with silicon and sodium chloride salts, and the effect of these salts on some physiological parameters of the plants was determined. In addition, a global nontargeted metabolomics analysis was performed for the leaf and root tissues using liquid chromatography-mass spectrometry (LC-MS). The results showed that under non-stress conditions, silicon treatment enhanced the growth of the date palm seedlings, however, under salinity, silicon slightly mitigates the negative effects of salt stress on the date palm seedlings although it enhances the potassium accumulation under this condition. The global metabolomics analysis has identified a total of 1,101 significant differentially accumulated (p, q ≤ 0.05) metabolites in leaves and roots under silicon, salinity or their combination. A differential pairwise metabolic profile comparison revealed the accumulation of distinct metabolites in response to silicon and salinity treatments such as antioxidant compounds pyridoxine, cepharanthine, allithiamine, myristic acid and boldine; osmoregulators such as mucic acid; along with the accumulation of detoxification intermediates such as S-D-lactoylglutathione, beta-cyano-L-alanine and gamma-glutamyl-conjugates. In addition, histochemical analyses revealed that application of silicon significantly (p ≤ 0.05) enhanced the formation of the Casparian strip. Identification of the differentially accumulated metabolites could offer an insight into how silicon is able to promote growth and salinity tolerance in date palms.

AMF and Bacillus megaterium Neutralize the Harmful Effects of Salt Stress On Bean Plants

Two pot experiments were directed under open field conditions where green bean (Phaseolus vulgaris L.) plants cv. Valentino were irrigated with four levels of salinity (1000, 2000, 3000 and 4000 ppm) combined with two anti-salinity agents (Arbuscular Mycorrhizal fungi [AMF] Glomus irradicans 10% w/w, Bacillus megaterium [10 ml/pot] and non-inoculated plants as control) to counteract the negative effect of salt stress, improve the growth, yield, enzymes activity and chemical composition of green bean plants during 2017and 2018 growing seasons. All salinity amelioration treatments (AMF and Bacillus megaterium) significantly improved vegetative growth, shoots biomass (total fresh and dry weight per plant), chlorophyll and antioxidant enzymatic activity at all verified salinity levels compared with non-inoculated plants (control) which showed severe growth retardation especially under the higher salt concentration (4000 ppm). The lowest values of membrane permeability and maximum leaf relative water content were significantly obtained with AMF and B. megaterium. Plants irrigated with lower concentrated saline water (1000 ppm) significantly accumulated lower Na and Cl and higher K than plants irrigated with higher concentrated salinity irrigation water (4000 ppm). The anti-salinity application increased green bean pod yield under all salinity stress levels particularly with AMF followed by B. megaterium compared with non-inoculated plants.

Exogenous spermidine enhances expression of Calvin cycle genes andphotosynthetic efficiency in sweet sorghum seedlings under salt stress

Salinity adversely affects plants resulting in disruption to plant growth and physiology. Previously, it has been shown that these negative effects can be alleviated by various exogenous polyamines. However, the role of spermidine (Spd) in conferring salinity tolerance in sorghum is not well documented. The effect of exogenous Spd on the responses of sweet sorghum (Sorghum bicolor L.) seedlings to salt stress (150 mM NaCl) was investigated by measuring photosynthetic carbon assimilation, Calvin cycle enzyme activities, and the the expression of respective genes. Application of 0.25 mM Spd alleviated the negative effects of salt stress on efficiency of photosystem II and CO2 assimilation and increased the activities of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) and aldolase. Salt stress significantly lowered the transcriptions of genes encoding Rubisco large subunit, Rubisco small subunit, 3-phosphoglyceric acid kinase, glyceraldehyde-3-phosphate dehydrogenase, triose-3-phosphate isomerase, fructose-1,6-bisphosphate aldolase, fructose-1,6-bisphosphate phosphatase, and sedoheptulose-1,7-bisphosphatase. However, transcriptions of genes encoding phosphoribokinase and Rubisco were up-regulated. The Spd application enhanced expressions of most of these genes. It appears Spd conferred salinity tolerance to sweet sorghum seedlings by enhancing photosynthetic efficiency through regulation of gene expressions and activities of key CO2 assimilation enzymes.

Adaptive mechanism of stress tolerance in Urochondra (grass halophyte) using roots study

An experiment was conducted on Urochondra setulosa (grass halophyte) to explore its survival mechanism under stress conditions. For this, different treatments of salinity/sodicity (pH ~ 9.5, pH ~ 10, ECe ~ 30 dS/m, ECe ~ 40 dS/m and ECe ~ 50 dS/m) were created in micro-plots. Roots are the primary structure that first senses the negative effects of salt stress. So, roots were selected to study the tolerance mechanism. Salinity stress caused higher Na+ accumulation and less reduction in K+ content in comparison to sodic stress. Roots accumulated 4.57 folds higher proline at ECe ~ 50 dS/m, whereas under pH ~ 10.0, 3.11 fold higher accumulations than the control roots were observed. Higher reduction in protein content was observed under sodicity stress than salinity stress. In control roots, a total of 26 polypeptide bands were expressed ranging from 12.43 kDa to 81.3 kDa. Under high salinity stress, number of polypeptide bands increased to 31 at ECe ~ 50 dS/m that might be responsible for their survival and growth while sodic stress led to disappearance of more number of polypeptides with a total number of 23 polypeptides at pH ~ 10.0. Interestingly, it was also found that sodic stress had higher damaging affect on Urochondra metabolism in comparison to salinity stress which makes it salinity tolerant grass.

Exogenous melatonin stimulated Amaryllidaceae alkaloid biosynthesis in in vitro cultures of Leucojum aestivum L

Leucojum aestivum L. is a highly demanding pharmaceutical plant which is a natural source of pharmacologically active Amaryllidaceae alkaloids, especially galanthamine and lycorine. To establish an efficient method for the production of these alkaloids Leucojum aestivum plants derived from somatic embryos were subjected to various concentrations of melatonin (N-acetyl-5-methoxy tryptamine), NaCl and melatonin combined with NaCl. The maximum L. aestivum plant biomass was obtained when 10 μM of melatonin was applied to the medium. These plants were characterised by normal growth and did not reveal signs of browning. Enrichment of the medium with NaCl caused a reduction in plant biomass, plant pigment contents (chlorophyll a, chlorophyll b and carotenoids) and an increase in the activities of antioxidant enzymes catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD). The addition of melatonin to the medium containing NaCl neutralised the negative effect of salt stress. Moreover, the stimulating effect of melatonin on Amaryllidaceae alkaloids biosynthesis was observed. In plants grown in the medium enriched with melatonin the galanthamine content was, on average, 58.6 times higher, and the lycorine content was 1.5 times higher as compared with the control. In vitro plants obtained from the medium supplemented with melatonin also showed the highest distribution of alkaloids. It is noteworthy that only the plants grown in the medium with melatonin showed the presence of tazettine and chlidanthine, 1,2-dihydro-. This study presents a promising biotechnological approach for the commercial production of alkaloids, including galanthamine and lycorine.

Effects of ascorbic acid against salt stress on the morphological and physiological parameters of Solanum melongena (L.)

The recent research was done to find out the role of ascorbic acid on morphological and physiological parameters of Solanum melongena during salt stress. The experiment was carried out in pots in which the effect of salt and ascorbic acid was measured on a range of morphological and physiological parameters. In this study, ascorbic acid was applied in two ways viz. as a foliar spray on leaves or through roots in the soil at two levels 100 ppm and 200 ppm to the plants grown under control, 60mM and 100mM NaCl. After sixty days of treatments it was determined that fresh and dry biomass was decreased considerably under salinity stress. Overall, it was observed that salt stress significantly down effect the morphological and physiological parameters. Decrease in the vegetative and reproductive parameters was improved with the application of ascorbic acid. The best result was obtained with the 200 ppm ascorbic acid which significantly improved the morphological and physiological parameters of plants in both control and salt stress treatments suggesting that ascorbic acid mitigate the negative effects of salt stress. Keywords: Ascorbic acid; Foliar spray; Morphological; Physiological; Salt stress http://dx.doi.org/10.19045/bspab.2019.80083

COINOCULATION WITH Bradyrhizobium AND Trichoderma ALLEVIATES THE EFFECTS OF SALT STRESS IN COWPEA

ABSTRACT The deleterious effects of salt stress can be mitigated by the use of beneficial microorganisms. The aims of this study were to evaluate whether coinoculation with Bradyrhizobium and Trichoderma asperelloides alleviates salt stress in cowpea. The experiment was conducted in a greenhouse using pots filled with sterile soil. Seeds were sown and inoculated with Bradyrhizobium or coinoculated with Bradyrhizobium and T. asperelloides. At 15 days after sowing (DAS), the nitrogen-free nutritive solution was supplemented with 50 or 100 mmol L-1 sodium chloride (NaCl) to induce salinity. Uninoculated plants and irrigated with solution without NaCl were used as absolute control. At 35 DAS, plants were collected, and nodules were excised for use in the determinations. The absolute controls did not show root nodules. Salt stress decreased plant biomass and growth, especially in cowpea inoculated with Bradyrhizobium. The stem diameter increased in cowpea coinoculated with Bradyrhizobium and T. asperelloides, mainly in plants subjected to salt stress at 100 mmol L-1 NaCl. Cowpea coinoculated with Bradyrhizobium and T. asperelloides maintained a higher content of free ammonia and organic compounds in its nodules even under salt stress. We concluded that the coinoculation of cowpea with Bradyrhizobium and T. asperelloides induces an increase in the concentration of organic solutes in the root nodules, especially when cowpeas are cultivated under salinity. Therefore, the use of coinoculation with Bradyrhizobium and T. asperelloides alleviates the negative effects of salt stress in cowpea.

Salicylic Acid Alleviated Salt Damage of Populus euphratica: A Physiological and Transcriptomic Analysis

Populus euphratica Oliv. is a model tree for studying abiotic stress, especially salt stress response. Salt stress is one of the most extensive abiotic stresses, which has an adverse effect on plant growth and development. Salicylic acid (SA) is an important signaling molecule that plays an important role in modulating the plant responses to abiotic stresses. To answer whether the endogenous SA can be induced by salt stress, and whether SA effectively alleviates the negative effects of salt on poplar growth is the main purpose of the study. To elucidate the effects of SA and salt stress on the growth of P. euphratica, we examined the morphological and physiological changes of P. euphratica under 300 mM NaCl after treatment with different concentrations of SA. A pretreatment of P. euphratica with 0.4 mM SA for 3 days effectively improved the growth status of plants under subsequent salt stress. These results indicate that appropriate concentrations of exogenous SA can effectively counteract the negative effect of salt stress on growth and development. Subsequently, transcripts involved in salt stress response via SA signaling were captured by RNA sequencing. The results indicated that numerous specific genes encoding mitogen-activated protein kinase, calcium-dependent protein kinase, and antioxidant enzymes were upregulated. Potassium transporters and Na+/H+ antiporters, which maintain K+/Na+ balance, were also upregulated after SA pretreatment. The transcriptome changes show that the ion transport and antioxidant enzymes were the early enhanced systems in response of P. euphratica to salt via SA, expanding our knowledge about SA function in salt stress defense in P. euphratica. This provides a solid foundation for future study of functional genes controlling effective components in metabolic pathways of trees.

Effects of Some Presowing Treatments on Germination of Eggplant (Solanum melongena L.) Under Salt Stress

This research was carried out to determine effects of gibberellic acid (GA) (25, 50 and 100 ppm), kinetin (K) (10, 25 and 50 ppm), ascorbic acid (AA) (0.50, 0.75 and 1.00 mM) and hydropriming on germination of eggplant under salt stress (0 mM, 60 mM and 120 mM NaCl) in Atatürk University, Faculty of Agriculture, Department of Horticulture. Seeds were kept in distilled water, GA, K and AA solutions for 24 h. Then, 50 seeds were put petri dishes with 0 mM, 60 mM and 120 mM NaCl. In the study, it was determined that salt stress negatively affected germination percentage (GP) and mean germination time (MGT) in eggplant. However, it was found that hormone and water treatments significantly improved GP and MGT compared to control and ameliorated the negative effect of salt stress. The best practice for GP and MGT was hydropriming under salt stress. According to the results obtained from the study, hydropriming and hormone treatments can be used as an alternative method in reducing the negative effects of salt stress in eggplant during germination.

Application of the salt stress to the protoplast cultures of the carrot (Daucus carota L.) and evaluation of the response of regenerants to soil salinity

This is the first study to generate carrot plants for enhanced salinity tolerance using a single-cell in vitro system. Protoplasts of three carrot accessions were exposed to treatment by seven different concentrations of NaCl (10–400 mM). Salt concentrations higher than 50 mM decreased plating efficiency and those of 200–400 mM of NaCl completely arrested mitotic divisions of cultured cells. The protoplast-derived plants from the control and 50–100 mM NaCl treatment were subjected to an 8-week salt stress in greenhouse conditions induced by salinized soil (EC 3 and 6 mS cm−1). 50 mM NaCl stress applied in vitro induced polyploidy among regenerated plants. The regenerants obtained from the 50 and 100 mM NaCl-treated protoplast cultures grown in saline soil had a higher survival rate compared to the regenerants from the control cultures. The salt-stressed plants accumulated anthocyanins in petioles and produced denser hairs on leaves and petioles in comparison to the control plants. Salt stress influenced pollen viability and seed setting of obtained regenerants. The results suggest that salt stress applied in vitro in protoplast cultures creates variation which allows alleviating the negative effects of salt stress on the development and reproduction of the carrot.

The roles of reactive carbonyl species in induction of antioxidant defence and ROS signalling in extreme halophytic model Eutrema parvulum and glycophytic model Arabidopsis thaliana

Breakdown of lipids in cell membranes by reactive oxygen species (ROS) causes production of lipid peroxidation products such as 4-hydroxy-2-nonenal (HNE), 4-hydroxy-2-hexenal (HHE), and acrolein (ACR) which are highly electrophilic due to their α-β-unsaturated carbonyl structures and named as reactive carbonyl species (RCS). The aim of this work was to investigate if RCS can induce antioxidant defence in plants and if there is a differential response in glycophytes and halophytes under non-stress conditions. For this aim, different amount and types of RCS (0.1 μM, 1 μM, 10 μM HNE, HHE and ACR) were exogenously applied to both Arabidopsis thaliana and Eutrema parvulum, and activities of some antioxidant enzymes (SOD, CAT, POX, APX) and their isoenzymes of SOD and CAT were determined. Also, to reveal role of RCS on ROS signal transduction, NADPH oxidase (NOX) activity and expression levels of abiotic stress related RBOH genes (RBOHD, RBOHF) were measured. To further elucidate the role of RCS on regulation of ion transporters in glycophyte and halophyte plants, expressions of Na+/H+ ion exchange channels on tonoplast (Na+/H+ exchanger NHX1, NHX5) and plasma membrane (salt overly sensitive 1, SOS1) were investigated. Overall, data provided in this manuscript provided evidence for regulation of antioxidant defence enzymes and ROS signalling in plants depending on the type and concentration of the RCS. In regards of glycophyte and halophyte comparison, remarkable differences were, (i) response of A. thaliana H2O2 scavenging enzymes (CAT, POX, APX) was stronger to RCS treatment when compared to E. parvulum, (ii) NADPH oxidase mediated ROS signalling was downregulated in A. thaliana, while it was maintained in E. parvulum in response to RCS. In addition, gene expression data demonstrated that RCS treatments can induced SOS1, NHX1 and NHX5 expression depending, again, on type and concentration of RCS in the absence of salt stress. Moreover, growth data indicate that RCS treatments can mitigate negative effects of salt stress in E. parvulum, but not in A. thaliana.

Seed priming improves the germination and growth rate of melon seedlings under saline stress

ABSTRACT: The germination and growth of melon (Cucumis melo L.) plants can be severely affected by excess salts in the soil or irrigation water; however, negative effects of salt stress can be attenuated using appropriate methods of seed priming. Thus, effects of osmopriming as inducer of salt stress tolerance in melon seeds exposed to salinity levels were investigated in this study. Seeds were soaked for 22 h at 25 °C in the dark in distilled water (hydropriming) or 0.5% KNO3 solution (osmopriming), and after drying, were distributed in plastic boxes with blotter paper containing different NaCl solutions prepared with osmotic pressure of 0.0 MPa (control), -0.3 MPa (mild stress), and -0.6 MPa (severe stress). Unprimed dry seeds were taken as control. The plastic boxes were kept into a seed germinator, at 25 °C for 14 days. A completely randomized design in a 3 × 3 factorial schemes with four replicates of 25 seeds was used. Results showed that the seed priming with water and KNO3 may be successfully applied on melon seeds to alleviate the adverse effects of saline stress in initial stages of plant growth. However, under severe salt stress conditions, hydropriming should be used because it results in higher germination and initial growth rate of the seedlings when compared to the osmopriming. Use of unprimed seeds should not be adopted in cultivation areas affected by salinity because they result in low germination rate and reduced initial plant growth.

Mepiquat chloride-priming induced salt tolerance during seed germination of cotton (Gossypium hirsutum L.) through regulating water transport and K+/Na+ homeostasis

The present study aimed to demonstrate the role of mepiquat chloride (MC) on the alleviation of the damaging effects of salinity on the germination of four cotton cultivars. Based on the ecophysiological data, CCRI44, CCRI49, and Z571 were less sensitive to salt stress and relied on a salt tolerance strategy to combat salinity at germination. Contrary to those salt-tolerance cultivars, seed germination of CZ91 was significantly inhibited by salt stress but most un-germinated seeds recovered completely when transferred to distilled water, indicating CZ91 follow a salt-avoiding strategy. Priming seeds with MC resulted in nullifying the negative effects of salt stress in salt-tolerance cultivars (especially in the cultivar Z571), but no significant response was observed in the salt-avoiding cultivar CZ91. At the mechanistic level, three complementary physiological traits are modulated by MC-priming upon exposure to salt stress: (i) better OA via increasing the water permeability and solute (i.e., Na+ or K+) mobility probably by regulating PIPs-regulated water channels; (ii) higher tissue tolerance ability via positively maintaining Na+ and K+ homeostasis by co-ordinated regulation of multiple ion transporters (e.g. SOS, HKT1, NHX1, AKT1 and HAK5); and (iii) further enhance the function of ion transport systems via inducing the gene expression of H+-ATPase. The strength of the three physiological traits varied among the MC pretreated cultivars, conferring differential ameliorating roles. Taken together, our observations confirmed that the effect of MC-priming on the alleviation of salinity stress is quite complex and dependent on the cultivar. It also shed light on transcriptional regulation of water and key ion transport systems involved in the maintenance of water absorption and K+/Na+ homeostasis as a key attribute for inducing salt tolerance by MC-priming in cotton cultivars.

Effect of Irrigation with Diluted Seawater on Coriander Growth and Soil Properties of Sandy Soil Amended by Chicken Manure and Biochar

Salt stress is abiotic stress that limits plant growth, crop productivityas well as the main factor contributing to land degradation. This study was conducted to evaluate the ameliorative effect of chicken manure and biochar applications used as soil amendments inalleviating the adverse effects of saline water irrigation on plant attributes and macro nutrients uptake by coriander (Coriandrum sativum) plant grown on a sandy textured soil. The ameliorative effect of soil amendments was also evaluated on the properties of the soil and nutrients availability for the plant. For this purpose, a pot experiment was conducted on coriander plant at The Experimental Farm of the Faculty of Agriculture, Mansoura University, Dakahlia Governorate, Egypt. A split plot design with three replications was used during the spring season of 2016. Treatments were the combination of two types of organic amendments (chicken manure and biochar) and three saline irrigation water treatments, .i.e. non-saline water (control) (S0 = 0.45 dS m-1) and saline water (S1= 3.12 dS m-1, 5% and S2 = 6.25 dS m-1, 10%) irrigation. Obtained results showed that soil productivity, as indicated by the vegetative growth and physiological aspects (plant height, leaves fresh and dry weight, no. of leaves/plant and total chlorophyll) for coriander plant were adversely and significantly affected by saline water irrigation. Addition of chicken manure and biochar significant increased the vegetative growth and physiological parameters due to their ameliorative effect. It had been observed a significantly increased in plant N, P and K contents and uptake by plant due to the addition of chicken manure and biochar amendments under saline and non-saline water irrigation compared to unamended one. The contents and uptake of N, P and K in coriander leaves decreased significantly as salinity of irrigation water increased from (S0) to (S2). Soil pH and EC values increased significantly in saline water irrigation treatments (S1 and S2) compared to non-saline water (S0). Soil pH and EC values decreased in soil amended with chicken manure and biochar application under three water types. The reduction in EC values in soil amended with biochar was higher than those in soil amended with chicken manure under all salinity levels. While, the reduction in soil pH values in soil amended with chicken manure was higher than those in soil amended with biochar. Soil available Na+, K+, Ca2+ and Mg2+ concentrations increased with increases in irrigation water salinity, while available P and Zn concentrations were decreased. Soluble Na+ significantly decreased but K+, Ca2+ and Mg2+ increased as a result of amendments application under three water types used. Soil P and Zn availability increased after applying different soil amendments, the concentration of available P in chicken manure amended soil was higher than those in biochar amended soil. While, available Zn concentration in biochar amended soil was higher than unamended one. In conclusion, chicken manure and biochar added to soil as amendments have the potential to mitigate the negative effects of salt stress mainly related to their ability to improve soil physio-chemical properties, promote vegetative growth of coriander plant, increases soil content of organic matter and available nutrient uptake.

Role of foliar application of sulfur-containing compounds on maize (Zea mays L. var. Malka and hybrid DTC) under salt stress

Soil salinity is one of the major abiotic stresses that drastically reduce crop yield worldwide. The problem of soil salinity is further aggravated when soil is depleted of essential major nutrients such as sulfur. Exogenous application of sulfur can ameliorate negative effects of salt stress on plants. Keeping this in view, a pot experiment was conducted to assess the effect of different sulfur-containing (SC) compounds on maize (Zea mays L. var. Malka and hybrid DTC) under salt stress. Two-week-old maize plants were subjected to two levels of salt (i.e., 0 and 90 mM NaCl) stress. After 2 weeks of salt stress application, plants were foliarly sprayed with different levels of SC compounds, i.e., control (non-spray), FeSO4 (10 mM), LiSO4 (10 mM), cysteine (20 mM) and mixture (in 1:1:2 ratio). Foliar application of SC compounds was performed twice (30 ml per pot each time) at 1-week-interval after salt stress application. Data of 7-week-old maize plants were collected for the determination of various growth and physicochemical parameters. Salt stress significantly decreased the growth of both maize genotypes. However, foliar application of different SC compounds significantly increased root and shoot biomass, length of root and shoot, relative water content (RWC% sprayed with mixture), total soluble proteins, total soluble sugars, ascorbic acid contents and total phenolics, while it (cysteine) decreased RWC (%) (in var. Malka), free proline, glycinebetaine (GB) and flavonoid contents. A differential response among the used SC compounds was observed in increasing the growth parameters of both maize genotypes. Overall, FeSO4 (10 mM), LiSO4 (10 mM) and mixture (in 1:1:2 ratio) were better than cysteine (20 mM) alone.

Nitrogen Fixation Does Not Alter the Effects of Salinity on Soybean Resistance to a Generalist Caterpillar

Premise of research. Nitrogen deficiency, salinity, and herbivory are common stress factors faced by plants, but their simultaneous effects have been overlooked. The goal of our study was to test whether plant resistance to a generalist herbivore was altered by salt stress or symbiotic nitrogen fixation, or both.Methodology. We grew Bradyrhizobium-inoculated and noninoculated soybean plants under two salinity levels, subjected half of them to herbivory by cabbage looper larvae, and measured plant performance and resistance to herbivory.Pivotal results. Prior to herbivory, NaCl-treated plants had lower biomass, chlorophyll content, leaf trichome density, whole-plant fixed nitrogen, and biomass allocation to roots, while the levels of N, K, Ca, Mn, B, and Cl in shoot tissues were higher than in control plants. Most salt-stressed plants produced no seeds. Without salt stress, herbivory reduced plant growth by 25% and seed production by 13%. Constitutive and induced resistance decreased with salt stress but were not affected by inoculation.Conclusions. Nodule formation did not alter the negative effects of salinity on seed production or resistance to herbivory, suggesting that the benefits of biological nitrogen fixation are modest compared with the overwhelming negative effects of salt stress on soybean growth, reproduction, and ability to defend from herbivores.

Plant growth promotion and alleviation of salinity stress in Capsicum annuum L. by Bacillus isolated from saline soil in Xinjiang

To maintain the growth and development of pepper in saline condition, candidates of plant growth promoting rhizobacteria (PGPR) were isolated, and detected to plant growth promoting (PGP) potential under salt stress was investigated. Thirteen bacterial strains with 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, WU-1–13, were isolated from saline soil in Xinjiang, China. The isolates were shown to belong to the genera Bacillus by partial sequencing analysis of their respective 16 S rRNA genes. Seven isolates had the ability to solubilize phosphate. Moreover, the amount of solubilized phosphate was significantly high (P < 0.05), which ranged from 157.33 μg/mL to 922.41 μg/mL. All tested bacterial strains were shown to produce a large amount of ACC deaminase and NH3. Furthermore, nine strains were detected for siderophore production. On the aspect of extracellular enzyme, all bacterial isolates produced lipase, amylase and cellulose, whereas only a minority produced chitinase (15.4%) and 10 isolates produced β-glucanase or protease. In growth room experiments, the results showed that the strain WU-5 exhibited better growth promotion of pepper seedlings in terms of fresh weight (75.60%), dry weight (86.68%), shoot length (12.12%) and root length (146.52%) over the control under saline stress followed by WU-13. Furthermore, seedlings accumulated high amounts of proline induced by the different PGPR inoculation treatments to alleviate the negative effects of salt stress. Further growth-promoting assays under different salt stress were set up to confirm that the fresh and dry weight, shoot and root length of pepper plants inoculated by three strains all were significantly higher than non-inoculated control under different saline stress. In summary, the results demonstrated that WU-9, which induced high levels of proline production and antioxidant enzyme activities, and three strains (WU-5, WU-9 and WU-13) can be of great value in maintaining the growth and development of seedlings on saline lands.

Infection by the fungal endophyte Epichloë bromicola enhances the tolerance of wild barley (Hordeum brevisubulatum) to salt and alkali stresses

Salinization is considered as a major environmental threat to agricultural systems. Infection with Epichloe fungal endophytes has been shown to increase tolerance to NaCl stress for several host grass species, but limited information is available regarding the effects of these endophytes under mixed salt (NaCl and Na2SO4) and mixed alkali (NaHCO3 and Na2CO3) stresses. Since these four compounds are considered very harmful to many inland areas in China, we conducted a study to determine the impact of Epichloe fungal endophyte infection on wild barley (Hordeum brevisubulatum) under both salt stress (SS) and alkali stress (AS). Wild barley with (E+) and without (E-) Epichloe endophyte was subjected to mixed salt (molar ratio of NaCl:Na2SO4 = 1:1) and mixed alkali (molar ratio of NaHCO3:Na2CO3 = 1:1) treatments (0, 100, 200, 300 and 400 mM). Photosynthetic parameters and chlorophyll content were measured after 21 days exposure to stress, and growth parameters, physiological indexes, sodium (Na+), potassium (K+), calcium (Ca2+), nitrogen (N), phosphorus (P) and carbon (C) contents were determined after 22 days exposure to stress. The harmful effect of alkali stress on the growth of wild barley was stronger than those of salt stress, irrespective of endophyte infection. Alkali stress had a greater impact on photosynthesis and chlorophyll content compared to salt stress and also accumulated more of the osmoprotectant glycine betaine. However, salt stress appeared to increase total antioxidant capacity as well as increasing K+ content (resulting in a relative low Na+/K+ ratio). Under alkali stress, Ca2+ content sharply increased in roots as opposed to a decrease under salt stress. In roots, the C, N, P contents and the C:N ratio was higher under salt stress compared to alkali stress whereas the C:P and N:P ratios were lower. In shoots, the N and P contents were higher under salt stress compared to alkali stress whereas the C content and the C:P and C:N ratios were lower. Interestingly, the presence of Epichloe endophyte infection on wild barley under both salt stress and alkali stress led to significant amelioration of both stresses. Epichloe infection significantly increased photosynthesis, chlorophyll content, total antioxidant capacity and glycine betaine content, whilst lowering leaf malondialdehyde content. Furthermore, Epichloe infection reduced Na+ content, the Na+/K+ ratio and shoot Ca2+ content but increased K+ content and the root Ca2+ content. Epichloe infected plants also had higher C, N and P contents but lower ratios of C:N, C:P and N:P than uninfected plants. The presence of the Epichloe endophyte suppresses the negative effect of salt stress and alkali stress on wild barley seedling growth. The possible mechanisms by which the presence of Epichloe endophyte enhances growth of plants exposed to those two stresses include improved photosynthetic ability, increased antioxidant potential, increased nutrient absorption, and osmotic and ionic adjustment. The study also found that alkali stress is more harmful to wild barley than salt stress.

The combination of arbuscular mycorrhizal fungi inoculation (Glomus versiforme) and 28-homobrassinolide spraying intervals improves growth by enhancing photosynthesis, nutrient absorption, and antioxidant system in cucumber (Cucumis sativus L.) under salinity.

Salinity is one of the major obstacles in the agriculture industry causing huge losses in productivity. Several strategies such as plant growth regulators with arbuscular mycorrhizal fungi (AMF) have been used to decrease the negative effects of salt stress. In our experiment, 28‐homobrassinolide (HBL) with spraying intervals was combined with AMF (Glomus versiforme) in cucumber cultivars Jinyou 1# (salt sensitive) and (Changchun mici, in short, CCMC, salt tolerant) under NaCl (100 mmol/L). Studies have documented that the foliar application of HBL and AMF colonization can enhance tolerance to plants under stress conditions. However, the mechanism of the HBL spraying intervals after 15 and 30 days in combination with AMF in cucumber under salt stress is still unknown. Our results revealed that the HBL spraying interval after 15 days in combination with AMF resulted in improved growth, photosynthesis, and decreased sodium toxicity under NaCl. Moreover, the antioxidant enzymes SOD (superoxide dismutase; EC 1.15.1.1) and POD activity (peroxidase; EC 1.11.1.7) showed a gradual increase after every 10 days, while the CAT (catalase; EC 1.11.1.6) increased after 30 days of salt treatments in both cultivars. This research suggests that the enhanced tolerance to salinity was mainly related to elevated levels of antioxidant enzymes and lower uptake of Na+, which lowers the risk of ion toxicity and decreases cell membrane damage.

Foliar or subirrigational silicon supply modulates salt stress in strawberry during vegetative propagation

Availability of silicon (Si) to the plant as a silicic acid could be a limiting factor for crop productivity. Although the effect of Si has been shown to vary by plant species, Si has been shown to improve photosynthesis, and to remediate nutrient imbalances and abiotic stresses in plants. Plants of two Korean strawberry cultivars ‘Seolhyang’ and ‘Maehyang’ at a propagation stage was grown for 58 days with a complete nutrient solution (EC of 0.8 dS m−1) and also with supplementation of either 0, 35, or 70 mg L−1 Si from either potassium silicate (K2SiO3), sodium silicate (Na2SiO3), or calcium silicate (CaSiO3). The Si in solution was supplied to the roots through subirrigational nutrient solution or to the leaves by daily foliar applications. The growth and development of the plants were assessed after this period. Then the plants were subjected to one of different salt stress conditions (EC of either 0.0, 0.8, 1.6, or 2.4 dS m−1) for 14 days. The high EC (2.4 dS m−1) resulted in oxidative stress in the form of H2O2 and O 2 −1 in the leaves of the Si-non-treated plants as compared to Si-treated plants, and no or less stress was observed in the 0.0, and 0.8 or 1.6 dS m−1, respectively. However, Si, especially supplied from K2SiO3, relieved the stress level. Interestingly, the isozyme activities of three important antioxidant enzymes, superoxide dismutase, catalase and guaiacol peroxidase, were abundantly increased in the Si-treated plants, particularly with K2SiO3, even under the high EC (2.4 dS m−1) treatment and decreased in the Si-non-treated plants. The observed responses to Si supply in high salt-stressed plants indicate that Si, particularly supplied from K2SiO3, has a significant role in limiting the negative effects of salt stress by maintaining antioxidative enzymes during the vegetative propagation.