Salt Stress Damage Research Articles

Low-Molecular-Weightt Polysaccharides From Pyropia yezoensis Enhance Tolerance of Wheat Seedlings (Triticum aestivum L.) to Salt Stress.

Soil salinity is one of the major issues worldwide that affects plant growth and reduces agricultural productivity. Seaweed polysaccharides have been shown to promote crop growth and improve the resistance of plant to abiotic stresses. Pyropia yezoensis is a commercially important edible red alga in Southeast Asia. However, there is little research on the application of polysaccharides from P. yezoensis in agriculture. The molecular weight (MW) of polysaccharides influences their properties. Therefore, in this study, four representative polysaccharides from P. yezoensis (PP) with different MWs (MW: 3.2, 10.5, 29.0, and 48.8 kDa) were prepared by microwave-assisted acid hydrolysis. The relationship between the degradation of polysaccharides from P. yezoensis (DPP) and their effects on plant salt tolerance was investigated. The results showed that exogenous PP and DPPs increased wheat seedling shoot and root lengths, and fresh and dry weights, alleviated membrane lipid peroxidation, increased the chlorophyll content and enhanced antioxidant activities. The expression level examination analysis of several Na+/K+ transporter genes suggested that DPPs could protect plants from the damage of salt stress by coordinating the efflux and compartmentation of Na+. The results demonstrated that polysaccharides could regulate antioxidant enzyme activities and modulate intracellular ion concentration, thereby to protect plants from salt stress damage. Furthermore, there was a significant correlation between the tolerance of wheat seedlings to salt stress and MW of polysaccharides. The results suggested that the lower-MW samples (DPP1, 3.2 kDa) most effectively protect wheat seedlings against salt stress.

Alleviation of NaCl toxicity in the cyanobacterium Synechococcus sp. PCC 7942 by exogenous calcium supplementation

Salinity (NaCl) is one of the major problems associated with irrigated agricultural lands, especially rice fields. Being the common inhabitants of rice fields, cyanobacteria frequently experience high concentration of NaCl which in turn causes cellular damage. Therefore, mitigation of NaCl stress in cyanobacteria, plant growth-promoting microorganisms, is of utmost importance. The present study was designed to investigate the role of calcium in the alleviation of NaCl stress-induced cellular in Synechococcus sp. PCC 7942. The cyanobacterium was subjected to sub-lethal concentration of NaCl (800 mM) with and without the supplementation of calcium (1 mM CaCl2) for 8 days. The results showed a drastic reduction in growth due to excess NaCl, but supplementation of CaCl2 reduced the salt stress damage and partially restored growth. Application of calcium increased pigment contents, photosynthetic efficiency, antioxidative enzyme activity, osmolyte contents and reduced the intracellular sodium ion concentration, MDA content, electrolyte leakage and free oxygen radical generation. Furthermore, proteins involved in photosynthesis, respiration, ATP synthesis and protein synthesis along with two hypothetical proteins were also observed to be upregulated in the cyanobacterium in presence of calcium. Furthermore, proteins related to oxidative stress defence, nitrogen metabolism, carbohydrate metabolism, fatty acid metabolism and secondary metabolism were found to be upregulated by several fold. Therefore, our study suggests that calcium suppresses salt toxicity in Synechococcus sp. PCC 7942 by restricting the entry of Na+ into the cell, increasing osmolyte production and upregulating defence-related proteins.

Exogenous application of a low concentration of melatonin enhances salt tolerance in rapeseed (Brassica napus L.) seedlings

Melatonin is a naturally occurring compound in plants. Here, we tested the effect of exogenous melatonin on rapeseed (Brassica napus L.) grown under salt stress. Application of 30 µmol L−1 melatonin alleviated salt-induced growth inhibition, and the shoot fresh weight, the shoot dry weight, the root fresh weight, and the root dry weight of seedlings treated with exogenous melatonin increased by 128.2, 142.9, 122.2, and 124.2%, respectively, compared to those under salt stress. In addition, several physiological parameters were evaluated. The activities of antioxidant enzymes including peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) were enhanced by 16.5, 19.3, and 14.2% compared to their activities in plants without exogenous melatonin application under salt stress, while the H2O2 content was decreased by 11.2% by exogenous melatonin. Furthermore, melatonin treatment promoted solute accumulation by increasing the contents of proline (26.8%), soluble sugars (15.1%) and proteins (58.8%). The results also suggested that higher concentrations (>50 µmol L−1) of melatonin could attenuate or even prevent the beneficial effects on seedling development. In conclusion, application of a low concentration of exogenous melatonin to rapeseed plants under salt stress can improve the H2O2-scavenging capacity by enhancing the activities of antioxidant enzymes such as POD, CAT and APX, and can also alleviate osmotic stress by promoting the accumulation of osmoregulatory substances such as soluble proteins, proline, and water soluble glucan. Ultimately, exogenous melatonin facilitates root development and improves the biomass of rapeseed seedlings grown under salt stress, thereby effectively alleviating the damage of salt stress in rapeseed seedlings.

Proteomic Analysis of Differentially Accumulated Proteins in Cucumber (Cucumis sativus) Fruit Peel in Response to Pre-storage Cold Acclimation.

Harvested fruits are still living organs and respond to environmental stimuli. Low temperature storage is effective in extending life of harvested fruit, but it may also cause chilling injury. Cold acclimation has been shown to induce chilling tolerance in plants, but what proteomic changes caused by cold acclimation are related to defense against chilling stress remains largely unclear. Here, 3 d of pre-storage cold acclimation (PsCA) at 10°C reduced chilling injury and secondary disease severity in cucumber stored at 5°C by 51 and 94%, respectively, compared with the control which was directly stored at 5°C. Proteomic analysis of cucumber peel identified 21 significant differentially-accumulated proteins (SDAPs) right after PsCA treatment and 23 after the following cold storage (PsCA+CS). These proteins are mainly related to stress response and defense (SRD), energy metabolism, protein metabolism, signal transduction, primary metabolism, and transcription. The SRD proteins, which made up 37% of the 21 and 47% of the 23, respectively, represented the largest class of SDAPs, and all but one protein were up-regulated, suggesting accumulation of proteins involved in defense response is central feature of proteomic profile changes brought about by PsCA. In fruit just after PsCA treatment, the identified SDAPs are related to responses to various stresses, including chilling, salt stress, dehydration, fungi, bacteria, insects, and DNA damage. However, after prolonged cold storage, the targeted proteins in acclimated fruit were narrowed down in scope to those involved in defense against chilling and pathogens. The change patterns at the transcription level of the majority of the up-regulated differentially-accumulated proteins were highly consistent with those at protein level. Taken all, the results suggest that the short-time cold acclimation initiated comprehensive defense responses in cucumber fruit at first, while the long term storage thereafter altered the responses more specifically to chilling. These findings add to the understanding of plants' molecular responses to cold acclimation.

Enhancing antioxidant systems by exogenous spermine and spermidine in wheat (Triticum aestivum) seedlings exposed to salt stress.

Plants have evolved complex mechanisms to mitigate osmotic and ionic stress caused by high salinity. The effect of exogenous spermine (Spm) and spermidine (Spd) on defence responses of wheat seedlings under NaCl stress was investigated by measuring antioxidant enzyme activities and the transcript expression of corresponding genes. Exogenous Spm and Spd decreased the level of malondialdehyde, increased chlorophyll and proline contents, and modulated PSII activity in wheat seedlings under salt stress. Spermidine alleviated negative effects on CO2 assimilation induced by salt stress in addition to significantly increasing the activity and content of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco). It appears Spd conferred salinity tolerance in wheat seedlings by enhancing photosynthetic capacity through regulation of gene expression and the activity of key CO2 assimilation enzymes. Exogenous Spm regulated activities of different antioxidant enzymes (catalase, glutathione reductase, dehydroascorbate reductase, ascorbate peroxidase, and superoxide dismutase) and efficiently modulate their transcription levels in wheat seedlings under salt stress. It is likely that Spm plays a key role in alleviating oxidative damage of salt stress by adjusting antioxidant enzyme activities in plants. In addition, exogenous Spd increased transcript level of spermine synthase under salt stress. Salinity stress also caused an increase in transcript levels of diamine oxidase (DAO) and polyamine oxidase (PAO). Exogenous Spd application resulted in a marked increase in free Spd and Spm contents under saline conditions. These results show that exogenous Spd and Spm effectively upregulated transcriptional levels of antioxidant enzyme genes and improved the defence response of plants under salt stress.

Salt stress resilience potential of a fungal inoculant isolated from tea cultivation area in maize

AbstractAgriculture needs to be sustained by organic processes in current era as population explosion energy and the number of individuals undernourished are raising public concerns. Global warming poses additional threat by lifting the damage of salt stress especially in agro-economically vital crops like maize whose cultivation dates back to Mayans. To that end, cost-effective and organic fungal agents may be great candidates in stress resilience. We isolated the fungal strain from the soil of tea plants and characterized that via 5.8 S rDNA gene with internal transcribed spacer ITS-1 and ITS-2 regions, then named the target strain as TA. Reduced maximum quantum efficiency of PS II (Fv/Fm), the effective quantum yield of PS2 (ΦPS2), electron transport rate (ETR), photochemical quenching (qP) and increased non-photochemical quenching (NPQ) were detected in maize plants stressed with dose dependent salt. Enhanced Fv/Fm, ΦPS2, ETR, qP and decreased NPQ was observed in TA primed plus NaCl treated plants. TA biopriming significantly increased the lengths, fresh and dry weights of root/shoots and decreased the lipid peroxidation. Maize seedlings bioprimed with TA had less MDA and higher soluble protein, proline, total chlorophyll, carotenoid and RWC under NaCl. Furthermore, SOD, GPX and GR activities were much more increased in root and leaves of TA primed seedlings, however CAT activity did not significantly change. This is the first report to our knowledge that TA reverses the damage of NaCl stress on maize growth through improving water status, antioxidant machinery and especially photosynthetic capacity.

Exogenous salicylic acid alleviates salt-stress damage in cucumber under moderate nitrogen conditions by controlling endogenous salicylic acid levels

Salicylic acid (SA) is a signaling compound that plays an important role in plant responses to biotic and abiotic stress. Exogenous application of SA can improve abiotic stress tolerance in various plants, a response that varies depending on the nutrient status of the plant. Based on the hypothesis that the nutrient status of a plant affects SA-induced stress tolerance, we investigated SA-induced stress tolerance in cucumber grown under moderate nitrogen (MN, 120 ppm) and low nitrogen (LN, 40 ppm) conditions. Cucumbers grown under MN conditions showed SA-induced tolerance to salt stress, along with mild increases in endogenous SA levels. In cucumbers without SA pretreatment, the increase in endogenous SA levels after salt stress treatment was approximately 2-fold higher than that of SA-pretreated plants. On the other hand, exogenous SA did not increase salt-stress tolerance in plants grown in LN exhibiting leaf chlorosis, although SA levels increased in the leaves of these plants. These results indicate that exogenous SA-induced salt stress tolerance is well established in cucumber grown in MN. In addition, SA pretreatment can improve the ability of plants to regulate endogenous SA levels after salt stress when grown under suitable nutrient conditions.

Overexpression of Cucumber Phospholipase D alpha Gene (CsPLDα) in Tobacco Enhanced Salinity Stress Tolerance by Regulating Na+-K+ Balance and Lipid Peroxidation.

Plant phospholipase D (PLD), which can hydrolyze membrane phospholipids to produce phosphatidic acid (PA), a secondary signaling molecule, has been proposed to function in diverse plant stress responses. In this research, we characterized the roles of the cucumber phospholipase D alpha gene (PLDα, GenBank accession number EF363796) in growth and tolerance to short- and long-term salt stress in transgenic tobacco (Nicotiana tabacum). Fresh and dry weights of roots, PLD activity and content, mitogen activated protein kinase (MAPK) gene expression, Na+–K+ homeostasis, expression of genes encoding ion exchange, reactive oxygen species (ROS) metabolism and osmotic adjustment substances were investigated in wild type (WT) and CsPLDα-overexpression tobacco lines grown under short- and long-term high salt (250 mM) stress. Under short-term stress (5 h), in both overexpression lines, the PA content, and the expression levels of MAPK and several genes related to ion exchange (NtNHX1, NtNKT1, NtHAK1, NtNHA1, NtVAG1), were promoted by high PLD activity. Meanwhile, the Na+/K+ ratio decreased. Under long-term stress (16 days), ROS scavenging systems (superoxide dismutase, peroxidase, catalase, ascorbate peroxidase activities) in leaves of transgenic lines were more active than those in WT plants. Meanwhile, the contents of proline, soluble sugar, and soluble protein significantly increased. In contrast, the contents of O2•− and H2O2, the electrolytic leakage and the accumulation of malondialdehyde in leaves significantly decreased. The root fresh and dry weights of the overexpression lines increased significantly. Na+–K+ homeostasis had the same trend as under the short-term treatment. These findings suggested that CsPLDα-produced PA can activate the downstream signals’ adaptive response to alleviate the damage of salt stress, and the main strategies for adaptation to salt stress are the accumulation of osmoprotective compounds, maintaining Na+–K+ homeostasis and the scavenging of ROS, which function in the osmotic balancing and structural stabilization of membranes.

Foliar-application of α-tocopherol enhanced salt tolerance of Carex leucochlora

Several different concentrations of α-tocopherol were applied to Carex leucochlora after plants had been treated with high salinity (0.8 % NaCl) in a greenhouse for one month. The results revealed that 0.8 mM α-tocopherol treatment showed the greatest alleviation of growth inhibition and cell membrane damage induced by salt stress. In comparison with NaCl alone, the 0.8 mM α-tocopherol application significantly decreased the content of hydrogen peroxide and the rate of superoxide radical generation, and increased the content of chlorophyll b, carotenoids, free proline, and soluble protein, but had no effect on the content of chlorophyll a and soluble sugar. These results suggest that α-tocopherol could effectively protect C. leucochlora plants from salt stress damage presumably by quenching the excessive reactive oxygen species to protect the photosynthetic pigments and by enhancing the osmotic adjustment.

Effect of Sulfated Chitooligosaccharides on Wheat Seedlings (Triticum aestivum L.) under Salt Stress.

In this study, sulfated chitooligosaccharide (SCOS) was applied to wheat seedlings to investigate its effect on the plants' defense response under salt stress. The antioxidant enzyme activities, chlorophyll contents, and fluorescence characters of wheat seedlings were determined at a certain time. The results showed that treatment with exogenous SCOS could decrease the content of malondialdehyde, increase the chlorophyll contents, and modulate fluorescence characters in wheat seedlings under salt stress. In addition, SCOS was able to regulate the activities of antioxidant enzymes containing superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, glutathione reductase, and dehydroascorbate reductase. Similarly, the mRNA expression levels of several antioxidant enzymes were efficiently modulated by SCOS. The results indicated that SCOS could alleviate the damage of salt stress by adjusting the antioxidant enzyme activities of plant. The effect of SCOS on the photochemical efficiency of wheat seedlings was associated with its enhanced capacity for antioxidant enzymes, which prevented structure degradation of the photosynthetic apparatus under NaCl stress. Furthermore, the effective activities of alleviating salt stress indicated the activities of SCOS were closely related with the sulfate group.

Overexpression of a Triticum aestivum Calreticulin gene (TaCRT1) Improves Salinity Tolerance in Tobacco.

Calreticulin (CRT) is a highly conserved and abundant multifunctional protein that is encoded by a small gene family and is often associated with abiotic/biotic stress responses in plants. However, the roles played by this protein in salt stress responses in wheat (Triticum aestivum) remain obscure. In this study, three TaCRT genes were identified in wheat and named TaCRT1, TaCRT2 and TaCRT3-1 based on their sequence characteristics and their high homology to other known CRT genes. Quantitative real-time PCR expression data revealed that these three genes exhibit different expression patterns in different tissues and are strongly induced under salt stress in wheat. The calcium-binding properties of the purified recombinant TaCRT1 protein were determined using a PIPES/Arsenazo III analysis. TaCRT1 gene overexpression in Nicotiana tabacum decreased salt stress damage in transgenic tobacco plants. Physiological measurements indicated that transgenic tobacco plants showed higher activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) than non-transgenic tobacco under normal growth conditions. Interestingly, overexpression of the entire TaCRT1 gene or of partial TaCRT1 segments resulted in significantly higher tolerance to salt stress in transgenic plants compared with their WT counterparts, thus revealing the essential role of the C-domain of TaCRT1 in countering salt stress in plants.

Phytohormone Responses and Cell Viability during Salinity Stress in Two Creeping Bentgrass Cultivars Differing in Salt Tolerance

Salinity stress is becoming more prevalent in turfgrass management with the increasing use of recycled water for irrigation. Creeping bentgrass (Agrostis stolonifera) is a cool-season turfgrass species that contains significant cultivar variation in salt stress tolerance, but the mechanism related to this cultivar variation is not well understood. Our objectives were to determine whether differential hormone content could play a role in cultivar variation of salt responses and to evaluate whether cell viability assays using dye techniques could differentiate salt stress damage levels in turfgrass species. Therefore, a growth chamber study with potted plants was conducted to evaluate salt ion concentrations, physiological responses, and hormone analysis [abscisic acid (ABA), indole-3-acetic acid (IAA), jasmonic acid (JA), salicylic acid (SA), zeatin riboside (ZR), and ethylene] at 4, 8, and 12 dS·m−1 in relatively salt-tolerant ‘Mariner’ compared with salt-sensitive ‘Penncross’ creeping bentgrass. A hydroponics-based growth chamber study was performed for evaluation of whether dead-cell stains coupled with image analysis could be a quick method for indicating cell viability variation between cultivars. Greater salt tolerance was evident in ‘Mariner’ at 12 dS·m−1, which showed significantly lower electrolyte leakage, higher leaf relative water content (RWC), osmotic potential, photochemical efficiency, and photochemical yield compared with ‘Penncross’. A higher K+ and lower Na+ content was maintained in leaves of ‘Mariner’ compared with ‘Penncross’ while roots of ‘Mariner’ maintained higher Ca2+ content under stressed and nonstressed conditions. Phytohormone levels showed a decline in salt-stressed roots compared with nonstressed plants but ‘Mariner’ roots were able to maintain levels higher than ‘Penncross’. ‘Mariner’ leaves showed an increased accumulation of ABA, JA, SA, and ZR while roots maintained higher IAA and SA compared with ‘Penncross’. The results suggest that ‘Mariner’ was able to mitigate salt stress by better ion regulation and differential regulation of hormones compared with ‘Penncross’. ‘Mariner’ leaves and roots showed significantly lower dead cells compared with ‘Penncross’ under salt stress. The results suggest that staining for cell viability could be a useful technique for studying turfgrass stress or other cellular responses.

Effect of chitooligosaccharides with different degrees of acetylation on wheat seedlings under salt stress

In this study, chitooligosaccharides (COSs) with varying degrees of acetylation (DAs) were applied to wheat seedlings in order to investigate their effect on the plants’ defence response under salt stress. The results showed that treatment with exogenous COSs that had different DAs could promote the growth of plants, decrease the concentration of malondialdehyde (MDA), improve the photosynthetic efficiency and enhance the activities of antioxidant enzymes. The mRNA expression level examination of several salt stress response genes suggested that COS could protect plants from the damage of salt stress by adjusting intracellular ion concentration and enhancing the activities of antioxidant enzymes. Furthermore, COS with DA 50% was the most effective in alleviating salt stress to wheat seedlings, which indicated that the activity of COS was closely related with its DAs.

Function of glutathione peroxidases in legume root nodules.

Glutathione peroxidases (Gpxs) are antioxidant enzymes not studied so far in legume nodules, despite the fact that reactive oxygen species are produced at different steps of the symbiosis. The function of two Gpxs that are highly expressed in nodules of the model legume Lotus japonicus was examined. Gene expression analysis, enzymatic and nitrosylation assays, yeast cell complementation, in situ mRNA hybridization, immunoelectron microscopy, and LjGpx-green fluorescent protein (GFP) fusions were used to characterize the enzymes and to localize each transcript and isoform in nodules. The LjGpx1 and LjGpx3 genes encode thioredoxin-dependent phospholipid hydroperoxidases and are differentially regulated in response to nitric oxide (NO) and hormones. LjGpx1 and LjGpx3 are nitrosylated in vitro or in plants treated with S-nitrosoglutathione (GSNO). Consistent with the modification of the peroxidatic cysteine of LjGpx3, in vitro assays demonstrated that this modification results in enzyme inhibition. The enzymes are highly expressed in the infected zone, but the LjGpx3 mRNA is also detected in the cortex and vascular bundles. LjGpx1 is localized to the plastids and nuclei, and LjGpx3 to the cytosol and endoplasmic reticulum. Based on yeast complementation experiments, both enzymes protect against oxidative stress, salt stress, and membrane damage. It is concluded that both LjGpxs perform major antioxidative functions in nodules, preventing lipid peroxidation and other oxidative processes at different subcellular sites of vascular and infected cells. The enzymes are probably involved in hormone and NO signalling, and may be regulated through nitrosylation of the peroxidatic cysteine essential for catalytic function.

Effects of seed priming on physiology of seed germination and seeding growth of Marsdenia tenacissima under NaCl stress

To offer the reference and method for salt damage in the cultivation of Marsdenia tenacissima, the seeds of M. tenacissima collected from Maguan city ( Yunnan province) were taken as the test materials to study the effects of different priming materials on improving germination and growth under high-level salt stress condition. Four different treatments, which were GA3, KNO3-KH2PO4, PEG-6000, NaCl, combined with ANOVA were applied to test the performance of germination energy, germination percentage, germination index, MDA, SOD, and CAT. The results showed that the seed germination was obviously inhibited under salt stress and the soaked seeds with different priming materials could alleviate the damage of salt stress. Under these treatments, the activities of SOD, CAT the content of soluble protein significantly increased. While the content of MDA significantly decreased. The maximum index was obtained when treated with 1.20% KNO3-KH2PO4, the germination percentage increased from 52.67% to 87.33% and the activity of SOD increased from 138.01 to 219.44 respectively. Comparing with the treatment of 1.20% KNO3-KH2PO4, the germination percentage of treating with 300 mg x L(-1) GA3 increased from 52.67% to 80.67%, while the activity of SOD increased from 138.01 to 444.61.

High vapor pressure deficit drives salt-stress-induced rice yield losses in India.

Flooded rice is grown across wide geographic boundaries from as far north as Manchuria and as far south as Uruguay and New South Wales, primarily because of its adaptability across diverse agronomic and climatic conditions. Salt-stress damage, a common occurrence in delta and coastal rice production zones, could be heightened by the interactions between high temperature and relative humidity (vapor pressure deficit--VPD). Using temporal and spatial observations spanning 107 seasons and 19 rice-growing locations throughout India with varying electrical conductivity (EC), including coastal saline, inland saline, and alkaline soils, we quantified the proportion of VPD inducing salinity damage in rice. While controlling for time-invariant factors such as trial locations, rice cultivars, and soil types, our regression analysis indicates that EC has a nonlinear detrimental effect on paddy rice yield. Our estimates suggest these yield reductions become larger at higher VPD. A one standard deviation (SD) increase in EC from its mean value is associated with 1.68% and 4.13% yield reductions at median and maximum observed VPD levels, respectively. Yield reductions increase roughly sixfold when the one SD increase is taken from the 75th percentile of EC. In combination, high EC and VPD generate near catastrophic crop loss as predicted yield approaches zero. If higher VPD levels driven by global warming materialize in conjunction with rising sea levels or salinity incursion in groundwater, this interaction becomes an important and necessary predictor of expected yield losses and global food security.

Application of Exogenous Spermidine (Spd) Improved Salt Tolerance of Rice at the Seedling and Reproductive Stages

Rice productivity in many areas is affected by salinity stress. Application of plant growth regulators may reduce the damage caused by salinity. This study aimed to alleviate salt stress damage using spermidine (Spd) as priming agents and spraying. Two cultivars of rice (Oryza sativa L.) including, Niewdam Gs.no.00621 (salt-tolerant) and KKU-LLR-039 (salt-sensitive) were used in this study. At seedling stage, the seeds of the two cultivars were primed separately with distilled water and 1mM Spd. Primed seeds were germinated and the resultant seedlings were hydroponically grown for 21 days before being exposed to salinity stress (150mM NaCl) for 10 days. Seed priming with Spd improved salt-induced reductions in growth. Salt stress induced pronounced increases in Na+/K+ ratios which were significantly reduced in the seedlings grown from Spd-primed seeds. Priming rice seeds with Spd also resulted in seedlings which possessed higher anthocyanin, phenolic contents and greater antioxidant capacity (based on DPPH, ABTS and FRAP assay) than the control seedlings. For reproductive stage, the plants were grown in pots until early booting stage. Thereafter, the plants were sprayed with 1mM Spd for 7 days before being stressed by adding 25mM NaCl until harvest. Pretreatment by foliar spraying of Spd to rice plants during the early booting stage significantly improved yields particularly of the salt-sensitive KKU-LLR-039. Spd pretreatment resulted in a reduction in Na+/K+ ratio in rice grains. Moreover, pretreatment with Spd further increased anthocyanin, phenolic content and antioxidant capacities (DPPH, ABTS and FRAP) in mature grains both rice cultivars.

Exogenous jasmonic acid can enhance tolerance of wheat seedlings to salt stress

Jasmonic acid (JA) is regarded as endogenous regulator that plays an important role in regulating stress responses, plant growth and development. To investigate the physiological mechanisms of salt stress mitigated by exogenous JA, foliar application of 2mM JA was done to wheat seedlings for 3days and then they were subjected to 150mM NaCl. Our results showed that 150mM NaCl treatment significantly decreased plant height, root length, shoot dry weight, root dry weight, the concentration of glutathione (GSH), chlorophyll b (Chl b) and carotenoid (Car), the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), enhanced the concentration of malondialdehyde (MDA), hydrogen peroxide (H2O2) and the rate of superoxide radical (O2−) generation in the wheat seedlings when compared with the control. However, treatments with exogenous JA for 3days significantly enhanced salt stress tolerance in wheat seedlings by decreasing the concentration of MDA and H2O2, the production rate of O2− and increasing the transcript levels and activities of SOD, POD, CAT and APX and the contents of GSH, Chl b and Car, which, in turn, enhanced the growth of salt stressed seedlings. These results suggested that JA could effectively protect wheat seedlings from salt stress damage by enhancing activities of antioxidant enzymes and the concentration of antioxidative compounds to quench the excessive reactive oxygen species caused by salt stress and presented a practical implication for wheat cultivation in salt-affected soils.

Exogenous Sorbitol and Trehalose Mitigated Salt Stress Damage in Salt-sensitive but not Salt-tolerant Rice Seedlings

Exogenous Sorbitol and Trehalose Mitigated Salt Stress Damage in Salt-sensitive but not Salt-tolerant Rice Seedlings

Effect of exogenous Ca2+, ALA, SA and Spd on seed germination and physiological characteristics of Perilla frutescens seedlings under NaCl stress

To find a method for improving the salt resistance of seeds and seedlings for Perilla Frutescens under NaCl stress, seed germination and physiological characteristics of P. frutescens seedlings were studied. Several physiological indexes of P. frutescens seeds treated with different concentrations of Ca2+, 5-aminolevulinic acid (ALA), salicylic acid (SA) and spermidine (Spd) under NaCl stress like the germination vigor, germination rate, germination index and vigor index were measured. And other indexes like the biomass of the seedlings, the content of malondialdehyde (MDA) in leaves, the activities of superoxide (SOD), peroxidase (POD) and catalase (CAT) were also measured. The germination of P. frutescens seeds under NaCl stress (100 mmol x L(-1)) was inhibited obviously. But after the treatment with Ca2+, ALA , SA and Spd, all germination indexes were increased. Ca2+ (10 mmol x L(-1)), ALA (100 mg x L(-1)), SA (50 mg x L(-1)) and Spd (0.25 mmol x L(-1)) could obviously alleviate the damage of salt stress to the seeds of P. frutescens. ALA (100 mg x L(-1)) significantly increased all indexes. The germination vigor was 65.3%, the germination rate was 89.7%, the germination index and vigor index were 15.2 and 0.1238, respectively. All treatments decreased the content of MDA in leaves. The activities of three enzymes including SOD, POD and CAT were all increased. ALA (100 mg x L(-1)) had the enzymes activity reach the maximum with 0.72, 6, 82 and 5.64 U x mg(-1), respectively. Ca2+ ALA , SA and Spd with appropriate concentration could significantly alleviate the damages to the seeds and seedlings of P. frutescens under NaCl stress and promote the salt resistance of the seeds and seedlings.