Negative Effects Of Salt Stress Research Articles

Effects of Melatonin Priming on Seed Germination of Wheat under Salt Stress

Melatonin (N-acetyl-5-methoxytryptamine) has been identified as a new growth regulator in plants due to its beneficial effect in abiotic stress reduction. The experiment was conducted at the Wheat Cultivation Department Laboratory, Gezira Scheme, Sudan. To investigate the effects of melatonin priming in alleviating the negative effect of salt stress on seed germination of winter wheat (Triticum aestivum L. cv Elnilein and Imam). Six concentrations were used: control, salt (300 mM NaCl) and four concentrations of melatonin (M) 10, 100, 500 and 1000 μM with salt (300 mM NaCl) add to each concentration: CT, ST, M1+ST, M2+ST, M3+ST, M4+ST. The treatments were arranged in a Randomized Complete Block Design with three replications. The parameters studied included: seed germination rate (%), germination index, mean germination time (d), lengths (cm) and dry weight (mg) of coleoptile and radicle, starch, soluble sugar, and sucrose concentrations, amylase activities, activities of the antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX) and catalase (CAT), reactive oxygen species (ROS) including malondialdehyde (MDA), Hydrogen peroxide (H2O2) contents and superoxide (O2-) production rate, abscisic acid (ABA). The parameters of seedling establishment were: Shoot height, root length, fresh and dry weight of shoot and root. The treatment M3+ST (500 μM Melatonin + 300 mM NaCl) had the highest seed germination rate, germination index lengths and dry weights of coleoptile and radicle, soluble sugar, sucrose concentrations, amylase and antioxidant enzymes activities, and ABA concentration, seedling shoot and root length, and fresh and dry weight of shoot and root in Imam and Elnilein cultivars, respectively.
 The study revealed that melatonin priming effectively alleviates salt stress during seed germination and seedling establishment in winter wheat.

Improving the Tolerance to Salinity Stress in Lettuce Plants (Lactuca sativa L.) Using Exogenous Application of Salicylic Acid, Yeast, and Zeolite.

Salinity is among the most limiting factors of crop production worldwide. This study aims to investigate the influence of the exogenous application of zeolite, yeast, and salicylic acid in alleviating the negative effect of salt stress under field conditions. Lettuce plants (Lactuca sativa L. cv. Batavia) were tested in a split-plot arrangement replicated three times. The salt stress was applied as a whole-plot factor in the concentrations (0 mM, 50 mM, 100 mM, and 150 mM NaCl). After 28 days of sowing, the plants were sprayed twice during the foliage growth with (control, salicylic acid 0.02%, yeast extract 3%, and zeolite 0.5%) as a split-plot factor. The length of roots and shoots, the number and area of leaves, and the biomass accumulation (dry and fresh weights) were measured 50 days after sowing. The concentrations of total soluble sugars, proline, Chlorophylls a and b in leaves have also been quantified. Salt stress significantly reduced the growth and the total chlorophyll of the lettuce plants (p < 0.05) and increased their proline and sugar contents’. Zeolite application improved the growth of lettuce at 0 and 50 mM NaCl, but at the highest salinity level only the number of leaves was improved by 15%. At a mild salinity stress, the application of salicylic acid has significantly (p < 0.05) increased the root length, height of plant, chlorophyll, and proline contents. Regarding the high stress levels (100 and 150 mM NaCl), yeast application showed the best tolerance to salinity stress by improving significantly most of the growth parameters (p < 0.05) but with lower proline, sugar, and chlorophyll contents. In general, foliar spray of yeast extract may offer a good alternative source of nutrients through leaves, leading to a better tolerance of the high salt stress exerted on roots.

Silicon Supplementation Alleviates the Salinity Stress in Wheat Plants by Enhancing the Plant Water Status, Photosynthetic Pigments, Proline Content and Antioxidant Enzyme Activities.

Silicon (Si) is the most abundant element on earth after oxygen and is very important for plant growth under stress conditions. In the present study, we inspected the role of Si in the mitigation of the negative effect of salt stress at three concentrations (40 mM, 80 mM, and 120 mM NaCl) in two wheat varieties (KRL-210 and WH-1105) with or without Si (0 mM and 2 mM) treatment. Our results showed that photosynthetic pigments, chlorophyll stability index, relative water content, protein content, and carbohydrate content were reduced at all three salt stress concentrations in both wheat varieties. Moreover, lipid peroxidation, proline content, phenol content, and electrolyte leakage significantly increased under salinity stress. The antioxidant enzyme activities, like catalase and peroxidase, were significantly enhanced under salinity in both leaves and roots; however, SOD activity was drastically decreased under salt stress in both leaves and roots. These negative effects of salinity were more pronounced in WH-1105, as KRL-210 is a salt-tolerant wheat variety. On the other hand, supplementation of Si improved the photosynthetic pigments, relative water, protein, and carbohydrate contents in both varieties. In addition, proline content, MDA content, and electrolyte leakage were shown to decline following Si application under salt stress. It was found that applying Si enhanced the antioxidant enzyme activities under stress conditions. Si showed better results in WH-1105 than in KRL-210. Furthermore, Si was found to be more effective at a salt concentration of 120 mM compared to low salt concentrations (40 mM, 80 mM), indicating that it significantly improved plant growth under stressed conditions. Our experimental findings will open a new area of research in Si application for the identification and implication of novel genes involved in enhancing salinity tolerance.

Mitigation negative effects of salt stress on common bean (Phaseolus vulgaris) using seaweed extracts

Mitigation negative effects of salt stress on common bean (Phaseolus vulgaris) using seaweed extracts

Melatonin confers fenugreek tolerance to salinity stress by stimulating the biosynthesis processes of enzymatic, non-enzymatic antioxidants, and diosgenin content.

Salinity-induced stress is widely considered a main plant-growth-limiting factor. The positive effects of melatonin in modulating abiotic stresses have led this hormone to be referred to as a growth regulator in plants. This study aims to show how melatonin protects fenugreek against the negative effects of salt stress. Different amounts of melatonin (30, 60, and 90 ppm), salinity stress (150 mM and 300 mM), and the use of both salinity and melatonin were used as treatments. The results showed that applying different melatonin levels to salinity-treated fenugreek plants effectively prevented the degradation of chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid contents compared with salinity treatment without melatonin application. Besides, melatonin increases the biosynthesis of enzymatic and non-enzymatic antioxidants, thereby adjusting the content of reactive oxygen species, free radicals, electrolyte leakage, and malondialdehyde content. It was observed that applying melatonin increased the activity of potassium-carrying channels leading to the maintenance of ionic homeostasis and increased intracellular water content under salinity stress. The results revealed that melatonin activates the defense signaling pathways in fenugreek through the nitric oxide, auxin, and abscisic acid-dependent pathways. Melatonin, in a similar vein, increased the expression of genes involved in the biosynthesis pathway of diosgenin, a highly important steroidal sapogenin in medical and food industries, and hence the diosgenin content. When 150 mM salinity stress and 60 ppm melatonin were coupled, the diosgenin concentration rose by more than 5.5 times compared to the control condition. In conclusion, our findings demonstrate the potential of melatonin to enhance the plant tolerance to salinity stress by stimulating biochemical and physiological changes.

Assessing Silicon-Mediated Growth Performances in Contrasting Rice Cultivars under Salt Stress.

Silicon (Si) application has great potential to improve salt tolerance in a variety of crop plants. However, it is unclear how Si influences the responses of contrasting rice cultivars when exposed to excessive salt. Here, we investigated the functions of Si in alleviating the negative effects of salt stress on two contrasting rice cultivars, namely BRRI dhan48 (salt-sensitive) and Binadhan-10 (salt-tolerant). Rice seedlings was pre-treated with three doses of Si (as silicic acid; 0, 1 and 2 mM) for 14 days at one-day interval before being exposed to salt stress (10 dSm−1) in a sustained water bath system. The results demonstrated that the seedlings of BRRI dhan48 and Binadhan-10, respectively exhibited substantial reductions in shoot height (16 and 9%), shoot fresh weight (64 and 43%) and shoot dry weight (50 and 39%) under salinity. Intriguingly, BRRI dhan48 pre-treated with 1 and 2 mM Si, respectively, showed a higher increase in shoot height (SH) (by 25.90 and 26.08%) as compared with Binadhan-10 (by 3 and 8%) under salt stress compared with their respective controls. Data revealed that a comparatively higher improvement in the growth performances of the salt-induced Si pre-treated BRRI dhan48 than that of Binadhan-10. For example, 1 and 2 mM of Si treatments significantly attributed to elevated leaf relative water content (RWC) (13 and 22%), proline (138 and 165%), chlorophyll a (42 and 44%), chlorophyll b (91 and 72%), total chlorophyll (58 and 53%) and carotenoids (33 and 29%), and recovery in the reductions of electrolyte leakage (13 and 21%), malondialdehyde content (23 and 30%) and shoot Na+/K+ ratio (22 and 52%) in BRRI dhan48 compared with Si-untreated control plants under salt stress. In addition, we found salt-tolerant Binadhan-10 also had enhanced RWC (9 and 19%), proline (12 and 26%) with pre-treatment with 1 and 2 mM of Si, respectively, under salt stress, while no significant differences were noticed in the case of photosynthetic pigments and Na+/K+ ratio. Our results showed that Si supplementation potentiated higher salt-tolerance ability in the salt-sensitive BRRI dhan48 as compared with salt-tolerant Binadhan-10. Thus, Si application could be highly beneficial in the growth recovery of the salinity-affected salt-sensitive high yielding rice cultivars in the saline-prone areas.

Basil (Ocimum basilicum) growth under saline stress and salicylic acid

Basil (Ocimum basilicum L.) is an aromatic and spice plant used around the world in cooking, in the pharmaceutical, cosmetic and flavoring industries. Salicylic acid has been used to mitigate the deleterious effects of salinity on plants. The objective of this work was to evaluate the growth of basil under saline stress and salicylic acid. The experimental design was in randomized blocks. Five electrical conductivities of irrigation water (ECw - 0.5, 1.3; 3.25; 5.2 and 6.0 dS m-1) and five salicylic acid doses (SA - 0.0, 0.29, 1.0, 1.71 and 2.0 mM) was used. Plant height, number of leaves, stem diameter, leaf area, specific leaf area, relative growth rate, leaf area ratio, leaf mass ratio, relative leaf growth rate and chlorophyll a, b and total indices were evaluated at 32, 39, 46, 53 and 60 days after irrigation with saline water (DAI). The increase in the electrical conductivity of irrigation water (ECw) negatively affected growth and increased the basil chlorophyll index. The application of salicylic acid attenuated the negative effects of salt stress on the number of leaves and leaf area and had negative effects on the stem diameter, but did not affect the other growth variables and chlorophyll indices.

Nitric Oxide Improves Salt Tolerance of Cyclocarya paliurus by Regulating Endogenous Glutathione Level and Antioxidant Capacity.

Cyclocarya paliurus is commonly used to treat diabetes in China. However, the natural habitats of C. paliurus are typically affected by salt stress. Previous studies showed that nitric oxide (NO) level was related to salt tolerance of C. paliurus, and its synthesis was induced by exogenous hydrogen sulfide. However, the effects of different NO donors in alleviating the negative effect of salt stress are still unclear. In the present study, C. paliurus seedlings pretreated with three NO donors (S-nitroso-N-acetylpenicillamine, SNAP and S-nitrosoglutathione, GSNO and sodium nitroprusside, SNP) were exposed to salt stress, and then, the total biomass, chlorophyll fluorescence parameters, NO and glutathione levels, oxidative damage, and antioxidant enzyme activities were investigated. The results showed that pretreatment of NO donors maintained chlorophyll fluorescence and attenuated the loss of plant biomass under salt stress, and the best performance was observed in C. paliurus under SNP treatment. We also found that pretreatment of NO donors further increased the endogenous NO content and nitrate reductase (NR) activity compared with salt treatment. Moreover, pretreatment with NO donors, especially SNP, alleviated salt-induced oxidative damage, as indicated by lowered lipid peroxidation, through an enhanced antioxidant system including glutathione accumulation and increased antioxidant enzyme activities. The supply of NO donors is an interesting strategy for alleviating the negative effect of salt on C. paliurus. Our data provide new evidence contributing to the current understanding of NO-induced salt stress tolerance.

Role of Biostimulant Priming Applications on Germination, Growth and Chlorophyll Content of Sunflower (Helianthus annuus L.) Cultivars under Salinity Stress

Salinity, which is one of the abiotic stresses, has become an important obstacle in agricultural areas. The use of humic acids (HA) as a biostimulant is increasing day by day and it is tried to increase the resistance of plants against stress. In this study, the effects of HA application of 0-15ml L-1 (4 concentrations) on the resistance to salt (S) 0-150 mM L-1 (4 concentrations) stress in 3 sunflower cultivars (Maximus (C1), Sirena (C2), Reyna (C3) were investigated under laboratory conditions. In the study; germination percentage (GP), mean germination time (MGT), salt tolerance percentage (STP), seeding length (SL), root length (RL), relative water content (RWC), real water content (GSI), total chlorophyll (Chl), chlorophyll stability index (CSI) parameters were examined. As a result of the study, HA applications played a role in reducing the negative effects of salt stress on the examined parameters. It was concluded that HA can be evaluated as an effective material that can be used to increase resistance and tolerance of plants against salt stress.

Foliar Application of Spermidine Reduced the Negative Effects of Salt Stress on Oat Seedlings.

The effects of foliar application of spermidine (Spd) on the physiological aspects of salt-stressed oat seedlings were studied under greenhouse conditions. At the seedling stage, the salt-sensitive variety, namely, Caoyou 1 and the salt-tolerant variety, namely, Baiyan 2 were treated with 70 and 100 mM of salt, followed by the foliar application of 0.75 mM Spd or distilled water. Results showed that Spd application increased the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX), and reduced the rate of O2⋅– production and the accumulation of H2O2 and malondialdehyde (MDA). In addition, it increased the level of zeatin riboside (ZR) and the content of endogenous polyamines. The application of Spd increased the contents of soluble sugar, soluble protein, and free proline and helped maintain the osmotic balance of oat leaves. At the same time, foliar Spd treatment helped in maintaining the ion nutrition balance. Specifically, it reduced the content of Na+ and thereby stabilized the ratio of Na+/K+, Na+/Ca2+, and Na+/Mg2+. The effects of Spd application were more obvious for the salt-sensitive cultivar Caoyou 1 and under the lighter 70 mM salt stress.

Determination of the alleviating effect of liquid vermicompost on germination and seedling development of Hungarian Vetch (Vicia pannonica Crantz.) under salt stress

Aims: The alleviating aspects of liquid vermicompost (VCL) on the seed germination and juvenile seedling growth of Hungarian vetch, which is an important fodder plant in Turkey and in the world, under salt stress were evaluated.Methods and Results: Two experiments in laboratory and greenhouse conditions were established according to a randomized plot design with three replications. In the experiments, liquid vermicompost levels were applied as control (0%) - 1% - 2.5% - 5% and 10% and salt solutions were prepared with control (pure water), 30 mM, 60 mM and 90 mM NaCl doses. At the end of the laboratory experiment, germination rate and index of Hungarian vetch seeds, length, fresh and dry weights of plumule, and length, fresh and dry weights of radicle were examined. In the greenhouse experiment, the emergence ratio, seedling height, seedling fresh and dry weights, root length, root fresh and dry weights of Hungarian vetch were investigated.Conclusions: It was observed that the parameters measured in the germination and seedling period of Hungarian vetch were negatively affected by salt stress, but the negative effects of salt stress decreased due to the increase in the amount of liquid vermicompost applied.Significance and Impact of the Study: The present study can be an important reference in terms of revealing the stimulating attribute of VCL and inhibiting attribute of salinity on the germination and various parameters of Hungarian vetch plant. The alleviative and regulatory effect of VCL appeared mostly in its 5% and 10% dose applications during the germination and juvenile seedling of Hungarian vetch, moderately sensitive to salt stress.

Silicon improves ion homeostasis and growth of liquorice under salt stress by reducing plant Na+ uptake

Silicon (Si) effectively alleviates the effects of salt stress in plants and can enhance salt tolerance in liquorice. However, the mechanisms by which Si improved salt tolerance in liquorice and the effects of foliar application of Si on different liquorice species under salt stress are not fully understood. We investigated the effects of foliar application of Si on the growth, physiological and biochemical characteristics, and ion balance of two liquorice species, Glycyrrhiza uralensis and G. inflata. High salt stress resulted in the accumulation of a large amount of Na+, decreased photosynthetic pigment concentrations, perturbed ion homeostasis, and eventually inhibited both liquorice species growth. These effects were more pronounced in G. uralensis, as G. inflata is more salt tolerant than G. uralensis. Foliar application of Si effectively reduced the decomposition of photosynthetic pigments and improved gas exchange parameters, thereby promoting photosynthesis. It also effectively inhibited lipid peroxidation and leaf electrolyte leakage and enhanced osmotic adjustment of the plants. Furthermore, Si application increased the K+ concentration and reduced Na+ absorption, transport, and accumulation in the plants. The protective effects of Si were more pronounced in G. uralensis than in G. inflata. In conclusion, Si reduces Na+ absorption, improves ion balance, and alleviates the negative effects of salt stress in the two liquorice species studied, but the effect is species dependent. These findings may help to develop novel strategies for protecting liquorice plants against salt stress and provide a theoretical basis for the evaluation of salt tolerance and the scientific cultivation of liquorice.

Hydrogen peroxide and saline nutrient solution in hydroponic zucchini culture

Saline water has been used in irrigation due to the limited availability of fresh water, especially in arid and semi-arid regions. However, the use of this type of water can affect crop growth and development. Studies have tested the use of chemical conditioners to minimize the negative effects of salinity on plants. In this scenario, the present study examined the role of hydrogen peroxide in mitigating the negative effects of salt stress on zucchini plants grown in a hydroponic system. The study was carried out in a greenhouse in Pombal - PB, Brazil. The NFT (nutrient film technique) hydroponic system was employed. A randomized complete experimental design was set up with a 4 × 4 factorial arrangement consisting of four levels of electrical conductivity in the nutrient solution (ECns: 2.1 [control], 3.6, 5.1, and 6.6 dS m-1) and four concentrations of hydrogen peroxide (H2O2: 0, 20, 40, and 60 μM), in three replicates. Foliar spraying with H2O2 at 60 and 40 μM associated with the nutrient solution of 2.1 dS m-1 increased stem diameter and root length, respectively, at 47 days after transplanting. However, at ECns higher than 2.1 dS m-1, the application of H2O2 at the concentrations of 60 and 40 μM intensified salt stress, reducing stem diameter and root length. Nutrient solution salinity levels above 2.1 dS m-1 reduce photosynthetic pigments; the number of leaves; leaf area; the length of the main branch; and the dry biomass of stems, leaves, and roots of zucchini plants. Chlorophyll b and carotenoid contents are the variables most sensitive to changes in salinity levels.

Trehalose Alleviated Salt Stress in Tomato by Regulating ROS Metabolism, Photosynthesis, Osmolyte Synthesis, and Trehalose Metabolic Pathways.

Trehalose plays a critical role in plant response to salinity but the involved regulatory mechanisms remain obscure. Here, this study explored the mechanism of exogenous trehalose-induced salt tolerance in tomato plants by the hydroponic test method. Our results indicated that 10 mM trehalose displayed remarkable plant biomass by improving growth physiology, which were supported by the results of chlorophyll fluorescence and rapid light–response curve. In the salinity environment, trehalose + NaCl treatment could greatly inhibit the decrease of malondialdehyde level, and it increases the contents of other osmotic substances, carbohydrates, K+, and K+/Na+ ratio. Meanwhile, trehalose still had similar effects after recovery from salt stress. Furthermore, trehalose pretreatment promoted trehalose metabolism; significantly increased the enzymatic activity of the trehalose metabolic pathway, including trehalose-6-phosphate synthase (TPS), trehalose-6-phosphate phosphatase (TPP), and trehalase (TRE); and upregulated the expression of SlTPS1, SlTPS5, SlTPS7, SlTPPJ, SlTPPH, and SlTRE under saline conditions. However, the transcriptional levels of SlTPS1, SlTPS5, and SlTPS7 genes and the activity of TPS enzyme were reversed after recovery. In addition, we found that hydrogen peroxide (H2O2) and superoxide anion (O2−) were accumulated in tomato leaves because of salt stress, but these parameters were all recovered by foliar-applied trehalose, and its visualization degree was correspondingly reduced. Antioxidant enzyme activities (SOD, POD, and CAT) and related gene expression (SlCu/Zn-SOD, SlFe-SOD, SlMn-SOD, SlPOD, and SlCAT) in salt-stressed tomato leaves were also elevated by trehalose to counteract salt stress. Collectively, exogenous trehalose appeared to be the effective treatment in counteracting the negative effects of salt stress.

Alleviation of the Germination Inhibitory Effect of Salt Stress in Pepper (Capsicum annuum L.) Seeds by Serotonin

Salinity stress is one of the important factors affecting all growth processes, from seed germination to seedling development, plant growth, yield and quality. In this study, the effects of serotonin treatments on the germination of pepper seeds (Capsicum annum L.) under salt stress were investigated. Different doses of salt (0, 75 and 150 mM NaCl) and serotonin (S0:0 µM, S1:5 µM, S2:10 µM, S3:15 µM, S4: 20 µM) were used. The applied seeds were placed between the papers in petri dishes, watered with the prepared salt solutions and left to germinate at 25 °C. In the study, parameters related to germination percentage, germination speed, mean germination time, daily mean germination time, peak value and germination value were investigated. As a result of the research, it was determined that the germination of pepper seeds decreased in parallel with increasing salt concentrations, and this negative effect of salt stress decreased with serotonin applications. Although it changes depending on the serotonin doses, it has been observed that significant effects occur on the measured germination parameters, and the best germination was observed at S1 and S2 doses. It is thought that the application of serotonin will have positive effects on the germination of pepper seeds under salt stress, and these effects may also occur during the plant growth period.

Role of Exogenous Melatonin, Hydrogen Sulfide and Nitric Oxide on Organic Acid Content of Eruca sativa L. under Salt Stress

Salt stress affects agricultural output by influencing numerous internal metabolisms in plants and disrupting physiological and biochemical activities such as photosynthesis, translocation, respiration, and growth stimulants. The role of exogenous melatonin, hydrogen sulfide and nitric oxide application on the organic acid contents of rocket plants under salt stress was examined in this study. Different salt doses (0, 150 and 250 mM NaCl) and exogenous applications (0, 50 and100 µM) were made to rocket plants under the greenhouse conditions. Plants leaves and roots exhibited a decline in the organic acid contents under salinity stress. Application of the amendments, however, was found significant in mitigating the negative effect of salt stress. Melatonin and hydrogen sulfide treatments had a stronger anti-salt action in the leaves. On the other hand, nitrous oxide role was more obvious in the roots followed by melatonin. With this, exogenous applications to the plant mitigated the harmful effects of salt stress on organic acid contents depending on the dose.

Potassium silicate combined with glycine betaine improved salt tolerance in Dalbergia odorifera

Salinity has a huge negative impact on plant growth and development by increasing sodium ions accumulation and potassium ions loss that deeply disturbs the plant cell homeostasis and can lead to plant cell death. The imbalance between Na+ and K+ could be solved by applying potassium silicate (K2SiO3). The glycine betaine (GB) is well-known to play a crucial role against oxidative stress in plants by improving the antioxidant machinery. Thus, this research aimed to apply K2SiO3 (1 mM) and GB (10 mM) alone or in combination against 200 mM NaCl-induced damages in Dalbergia odorifera. The results showed a significant amelioration of negative effects of salt stress on the phenotypic traits, chlorophyll content, net photosynthetic rate, stomatal conductance, transpiration rate, and water use efficiency by applied substances. The contents of saccharides and proline were down-regulated by K2SiO3, GB, and K2SiO3-GB, whereas the proteins content was increased by these treatments. The contents of lipid peroxidation, superoxide anion, hydrogen peroxide were reduced by exogenous substances under stress. The activities of antioxidant enzymes (superoxide dismutase, peroxidase, and catalase) and the accumulation of antioxidants (glutathione and ascorbate) were enhanced by exogenous substances. The K2SiO3-GB combination mostly showed better effects on antioxidant machinery compared to a single treatment.

Potassium application alleviates the negative effects of salt stress on cotton (Gossypium hirsutum L.) yield by improving the ionic homeostasis, photosynthetic capacity and carbohydrate metabolism of the leaf subtending the cotton boll

• Potassium (K) application alleviated the salt stress damage and improved cotton yield. • K application in saline alkali soil maintained the ionic homeostasis of LSCB (leaf subtending the cotton boll). • Under salt stress, K application improved LSCB photosynthetic capacity. • Under salt stress, K application enhanced the carbon metabolism of LSCB. Field experiments were conducted in 2017 and 2018, in order to investigate the effects of potassium (K) application on photosynthetic capacity and carbohydrate metabolism of the leaf subtending the cotton boll (LSCB) under salt stress. Three salinity treatments (EC = 1.68∼1.78, 6.21∼6.42 and 10.59∼11.08 dS m −1 ) with three K levels (0, 150, 300 kg K 2 O ha -1 ) applied in each salinity treatment, were imposed on two cotton ( Gossypium hirsutum L.) cultivars differing in salt sensitivity (CCRI-79, salt tolerant and Simian 3, salt sensitive). The results indicated that under salt stress: (1) K application increased LSCB K + /Na + ratio since Na + concentration decreased and K + concentration increased. Cotton boll (capsule wall, seed and lint) biomass, total boll number, boll weight and seed cotton yield were also increased; (2) K application improved net photosynthetic rates ( Pn ) of LSCB by increasing stomatal conductance rates ( Gs ), chlorophyll a and b concentrations and chlorophyll a / b ratio; (3) K application decreased soluble sugar, sucrose and starch concentrations of LSCB through increases in sucrose phosphate synthase (SPS) and sucrose synthase (SuSy) activities and decreases in sucrose acid invertase (SAI) activity. The results of this study indicated that K fertilizer application rates have a regulating effect on LSCB’s photosynthetic properties and carbohydrate metabolism under salt stress, thus providing a theoretical foundation for increasing cotton yield under salt stress.

Salicylic acid and thiourea ameliorate the negative impact of salt stress in wheat (Triticum aestivum L.) seedlings by up-regulating photosynthetic pigments, leaf water status, and antioxidant defense system

Salinity is one of the most important abiotic stress inhibiting wheat (Triticum aestivum L.) growth and development. Therefore, finding efficient strategies to prevent salt-induced growth retardation and yield loss is critical for modern agriculture to sustain production. The role of exogenous salicylic acid (SA) and thiourea (TU) in regulating salt tolerance was investigated by evaluating morpho-physiological characteristics and antioxidant response in two wheat genotypes at the seedling stage. In both wheat genotypes, salt stress reduced growth characteristics and leaf water status, photosynthetic pigments, while simultaneously increasing the Na+/K+ ratio, hydrogen peroxide (H2O2), and malondialdehyde (MDA). In contrast, exogenous application of SA and/or TU alone in the salt-stressed plants significantly reduced the negative effects of salt stress and improved the growth performance by up-regulating photosynthetic pigments, leaf water status, and proline content in both genotypes. Besides, when compared to seedlings treated only with salt stress, SA and TU played an important role in maintaining lower Na+/K+ levels and reducing oxidative stress by lowering MDA and H2O2 levels in salt-stressed plants through boosting the activities of antioxidant enzymes such as catalase, ascorbate peroxidase, and peroxidase. In addition, hierarchical clustering and principal component analysis revealed a significant interaction among growth characteristics, chlorophyll content, carotenoid content and antioxidant activity with the salt, SA, and/or TU treatments. The findings suggested that exogenous application of SA or TU could be a useful technique for reducing the negative effects of salinity on wheat growth and development.

Nitrogen Nutrition and Adaptation of Halophyte Chenopodium quinoa to Salt Stress

There is little evidence that the nitrogen nu-trition supply at rates above or less than what is considered optimal in non-saline conditions improves growth and yield of halophyte crop cultivated under salt stress. Therefore, hypoth-esize of the present work was to find out the magnitude to which N could restore the harm-ful effects of salt stress on quinoa plants. A pot experiment was performed in greenhouse con-ditions to evaluate quinoa's response grown under water salinity treatments (0.0 & 200 mM NaCl) when nitrogen nutrition rates were limiting (50ppm), adequate (250 ppm), and ex-cess (450 ppm) to guide proper application rate of nitrogen fertilizer under salinity stress. The results indicated that, salinity caused a signifi-cant decrease in the vegetative growth of the plant. Consequently, all vegetative measure-ments were negatively affected. As a result, the seed yield decreased to more than 50%. The application of a moderate level of nitrogen (250 ppm) caused a significant ameliorative effect on seed yield by 126% under non saline conditions and 34.5 % under saline conditions compared to the low nitrogen level. The results did not improve any further with the applica-tion of a higher level of nitrogen. These results indicate that applying (N) in adequate may im-prove most traits and prove to be a physiolog-ical treatment to increase resistance against the negative effects of salt stress in quinoa.