Salt Stress Treatment Research Articles

ALLEVIATION OF ADVERSE EFFECTS OF SALT STRESS ON LETTUCE (Lactuca sativa var. crispa) BY APPLICATION OF VERMICOMPOST

In arid and semiarid regions, soil salinity causes salt stress in plants and affects crop production negatively. In this respect, organic farming practices are becoming the foreground as applications that are sensitive to the environment and support sustainability in agriculture. This study aimed to explain the role of vermicompost (VC) for reducing the effect of salt stress on lettuce (Lactuca sativa var. crispa) plant. The experiments were performed with different concentrations of VC (0, 2.5 and 5% VC on a weight per weight basis of soil-w/w) and salt stress treatments (4 and 8 dS m–1 NaCl levels). Under salt stress, shoot heigth, relative,water content (RWC), stomatal conductance (gs), chlorophyll a (Chla) content decreased while electrolyte leakage (EL), malondialdehyde (MDA) contents and superoxide dismutase (SOD) and catalase (CAT) activitys significantly increased in parallel with the severity of stress. In this study, VC under salt stress significantly increased RWC, gs and Chla, Chlt and carotenoid contents in the leaf tissues; however, MDA and EL contents decreased and SOD and CAT activities increased compared to controls. In all levels of NaCl, the 5% ratio of VC significantly reduced the negative effects of salinity.

Enhancement of growth and salt tolerance of tomato seedlings by a natural halotolerant actinobacterium Glutamicibacter halophytocola KLBMP 5180 isolated from a coastal halophyte

Soil salinity stress affects the health and growth of crops. The use of plant growth-promoting rhizobacteria (PGPR) to improve the salt tolerance of plants is gaining acceptance worldwide. Here, a halotolerant, plant growth-promoting actinobacterium Glutamicibacter halophytocola KLBMP 5180, recently isolated from the root of a coastal halophyte Limonium sinense, was investigated for its capacity on the growth of tomato seedlings under the condition of saline stress. Tomato seedlings were inoculated with strain KLBMP 5180 and irrigated with 2% NaCl salt-stress treatment. Plant growth and physiological responses were determined after harvest. The genome of strain KLBMP 5180 was sequenced and analyzed. High salinity significantly reduced the growth and biomass of tomato seedlings. However, KLBMP 5180 inoculation significantly improved tomato growth in terms of seedling fresh weight and height, root length and fresh weight, and number of fibrous roots, along with increased osmolyte content (proline) and antioxidant defense enzymes and regulation of ion homeostasis under salt stress. From the genome, we identified a series of genes that may contribute to plant growth promotion, including genes for nitrogen fixation, biosynthesis of siderophores and exopolysaccharides. Additionally, several genes related to high salinity tolerance, such as Na+/H+ antiporter, K+ transporter, glycine-betaine synthesis and transport, and several heavy metal resistance and biodegradation genes were also identified in the genome of strain KLBMP 5180. Our results demonstrate that the halotolerant strain KLBMP 5180 can be used to improve tomato seedling growth in saline soil and act as a potential agricultural biofertilizer agent in future applications.

Effects of salt stress on growth, photosynthetic and fluorescence characteristics, and root architecture of Corylus heterophylla ×C. avellan seedlings

We examined the effects of different salt stress intensities (control, mild, moderate, severe) on the growth traits, photosynthetic and fluorescence characteristics, and root architecture of three Corylus heterophylla × C. avellan varieties (Xinzhen 1, Xinzhen 2, Xinzhen 3). The results showed that the new shoot length, basal diameter, leaf area, root biomass, shoot biomass, leaf biomass, and total biomass of the three varieties all decreased, but the root-shoot ratio increased with increasing salt stress. The net photosynthetic rate of the three varieties in the moderate and severe salt stress treatments significantly decreased by 20.5% and 43.2%, respectively. The transpiration rate and stomatal conductance in the mild, moderate, and severe salt stress treatments decreased by 2.0%, 16.3%, 32.0% and 10.2%, 35.7%, 60.1% than those of the control, respectively. With the increasing salt stress, the intercellular CO2 concentration gradually increased, while the water use efficiency increased first and then decreased and being the highest in the mild salt stress treatment. The initial fluorescence of the three varieties increased with the increasing salt stress. With the increasing salt stress, the maximum fluorescence, maximal photochemical efficiency, potential photochemical activity, actual photochemical efficiency, electron transfer rate and photochemical quenching coefficient decreased, while the non-photochemical quenching coefficient increased first and then decreased. Salt stress reduced root biomass, length, surface area and volume of the three varieties. In the same salt stress treatment, the reduction of root architecture parameters of Xinzhen 2 was lower than the other two varieties. The growth traits, photosynthetic and fluorescence characteristics, and root architecture parameters of Corylus heterophylla × C. avellan were affected by both varieties and salt stress. Xinzhen 2 displayed stronger growth and photosynthetic physiological adaptability to salt stress, showing stronger salt tolerance than the other two varieties.

Overexpression of the Cytokinin Oxidase/dehydrogenase (CKX) from Medicago sativa Enhanced Salt Stress Tolerance of Arabidopsis

Cytokinin oxidase/dehydrogenase (CKXs) are involved in various physiological processes, including cytokinins (CKs) catabolism, root system architecture and response to abiotic stresses in plants. Alfalfa (Medicago sativa) is a widely cultivated forage which is frequently threatened by high salinity, and the potential role of CKXs in alleviating the salt stress in alfalfa lacked attention. In this study, we isolated a CKX gene from alfalfa, MsCKX (MK177192), and identified its biological functions by overexpressing it in Arabidopsis. MsCKX shares high sequence identity with CKX from other legume plants, especially Medicago truncatula (98%). MsCKX was clearly tissue-specific, and it was mainly expressed in roots. In addition, the expression of MsCKX increased under salt stress and abscisic acid (ABA) treatment. Overexpression of MsCKX gene increased the activity of CKX, which led to an enlarged root system in transgenic Arabidopsis plants. Overexpression of MsCKX gene enhanced salt tolerance of transgenic plants by maintaining a higher K+/Na+ ratio, enhancing the activities of antioxidant enzymes to scavenge ROS and increasing the expression levels of stress-related genes (P5CS1, DREB2, ion transporters and H+ pumps). Taken together, these results shed light on the roles of MsCKX involved in salt tolerance and may have applications in salt-resistant breeding of alfalfa.

Dynamic Changes in Genome-Wide Histone3 Lysine27 Trimethylation and Gene Expression of Soybean Roots in Response to Salt Stress.

Soybean is an important economic crop for human diet, animal feeds and biodiesel due to high protein and oil content. Its productivity is significantly hampered by salt stress, which impairs plant growth and development by affecting gene expression, in part, through epigenetic modification of chromatin status. However, little is known about epigenetic regulation of stress response in soybean roots. Here, we used RNA-seq and ChIP-seq technologies to study the dynamics of genome-wide transcription and histone methylation patterns in soybean roots under salt stress. Eight thousand seven hundred ninety eight soybean genes changed their expression under salt stress treatment. Whole-genome ChIP-seq study of an epigenetic repressive mark, histone H3 lysine 27 trimethylation (H3K27me3), revealed the changes in H3K27me3 deposition during the response to salt stress. Unexpectedly, we found that most of the inactivation of genes under salt stress is strongly correlated with the de novo establishment of H3K27me3 in various parts of the promoter or coding regions where there is no H3K27me3 in control plants. In addition, the soybean histone modifiers were identified which may contribute to de novo histone methylation and gene silencing under salt stress. Thus, dynamic chromatin regulation, switch between active and inactive modes, occur at target loci in order to respond to salt stress in soybean. Our analysis demonstrates histone methylation modifications are correlated with the activation or inactivation of salt-inducible genes in soybean roots.

Involvement of abscisic acid-responsive element-binding factors in cassava (Manihot esculenta) dehydration stress response

Cassava (Manihot esculenta) is a major staple food, animal feed and energy crop in the tropics and subtropics. It is one of the most drought-tolerant crops, however, the mechanisms of cassava drought tolerance remain unclear. Abscisic acid (ABA)-responsive element (ABRE)-binding factors (ABFs) are transcription factors that regulate expression of target genes involved in plant tolerance to drought, high salinity, and osmotic stress by binding ABRE cis-elements in the promoter regions of these genes. However, there is little information about ABF genes in cassava. A comprehensive analysis of Manihot esculenta ABFs (MeABFs) described the phylogeny, genome location, cis-acting elements, expression profiles, and regulatory relationship between these factors and Manihot esculenta betaine aldehyde dehydrogenase genes (MeBADHs). Here we conducted genome-wide searches and subsequent molecular cloning to identify seven MeABFs that are distributed unevenly across six chromosomes in cassava. These MeABFs can be clustered into three groups according to their phylogenetic relationships to their Arabidopsis (Arabidopsis thaliana) counterparts. Analysis of the 5′-upstream region of MeABFs revealed putative cis-acting elements related to hormone signaling, stress, light, and circadian clock. MeABF expression profiles displayed clear differences among leaf, stem, root, and tuberous root tissues under non-stress and drought, osmotic, or salt stress conditions. Drought stress in cassava leaves and roots, osmotic stress in tuberous roots, and salt stress in stems induced expression of the highest number of MeABFs showing significantly elevated expression. The glycine betaine (GB) content of cassava leaves also was elevated after drought, osmotic, or salt stress treatments. BADH1 is involved in GB synthesis. We show that MeBADH1 promoter sequences contained ABREs and that MeBADH1 expression correlated with MeABF expression profiles in cassava leaves after the three stress treatments. Taken together, these results suggest that in response to various dehydration stresses, MeABFs in cassava may activate transcriptional expression of MeBADH1 by binding the MeBADH1 promoter that in turn promotes GB biosynthesis and accumulation via an increase in MeBADH1 gene expression levels and MeBADH1 enzymatic activity. These responses protect cells against dehydration stresses by preserving an osmotic balance that enhances cassava tolerance to dehydration stresses.

The RabGAP Gene Family in Tomato (Solanum lycopersicum) and Wild Relatives: Identification, Interaction Networks, and Transcriptional Analysis during Plant Development and in Response to Salt Stress

RabGTPase activating proteins (RabGAP) are responsible for directing the deactivation of vesicular trafficking master regulators associated to plant development, the RabGTPase proteins. Recently, RabGAPs were identified in Arabidopsis and rice, but studies were not yet reported in tomato. Herein, we identified 24 RabGAP-encoding genes in cultivated tomato (Solanum lycopersicum) and its wild relative genomes (Solanum pimpinellifolium and Solanum pennellii). We analyzed them based on their exon-intron structures, conserved protein motifs, putative subcellular localizations, phylogenetic and gene duplications analyses, interaction networks, and gene expression patterns in tomato. Phylogenetic relationship analysis also indicated that RabGAP family is classified into seven subclasses, of which subclasses I and II are plant-exclusive. Furthermore, segmental duplication events and positive evolutionary forces are associated with the maintenance of the number and function of their members. On the other hand, the protein–protein interaction networks on tomato suggested that members of subclasses I, II, and III could be associated to endocytic traffic routes. In addition, the qRT-PCR experiments in S. lycopersicum and Solanum chilense exposed to a salt stress treatment validated the differential expression patterns of 20 RabGAP genes in different tissues, development stages, and stress conditions obtained through extensive microarray-based analyses. This work suggests the critical role of RabGAP family in the context of intracellular vesicular trafficking in tomato, particularly under conditions of abiotic stress. It also contributes to the breeding programs associated with the development of crops tolerant to salt stress.

MdGRF11, an apple 14-3-3 protein, acts as a positive regulator of drought and salt tolerance

The 14-3-3 proteins are a family of highly conserved phosphoserine-binding proteins that participate in the regulation of diverse physiological and developmental processes. In this research, twenty 14-3-3 genes in apples, which contained a highly conserved 14-3-3 domain, were identified and divided into two subgroups. Among them, MdGRF11 was further cloned and investigated. qRT-PCR analyses and GUS staining show that MdGRF11 is expressed in various organs and tissues with the highest expression levels found in the fruit. MdGRF11 was upregulated by polyethylene glycol 6000 (PEG 6000), NaCl, abscisic acid (ABA) and low temperature (4 °C) treatments. MdGRF11-overexpressing transgenic Arabidopsis and apple calli exhibited reduced sensitivity to salt and PEG 6000 treatments. Moreover, the ectopic expression of MdGRF11 improved the tolerance of transgenic tobacco to salt and drought stresses, which grew longer roots, underwent more growth, and presented higher chlorophyll levels than the wild-type control under salt and drought stress conditions. Furthermore, MdGRF11 expression remarkably reduced electrolyte leakage, malondialdehyde content levels, H2O2 and O2- accumulation under salt and drought stress conditions, which relied on the regulation of ROS-scavenging signaling to reduce oxidative damage of cells after salt and drought stress treatment. MdGRF11 also enhanced tolerance to stress by upregulating expression levels of ROS-scavenging and stress-related genes, especially improving responses to drought stress by modifying the water loss rates and stomatal aperture. Moreover, MdGRF11 could interact with MdAREB/ABF transcription factors through yeast two hybrid analyses. In conclusion, our results indicate that MdGRF11 acts as a positive regulator of salt and drought stress responses through regulating ROS scavenging and other signaling systems.

Overexpression of Ks-type dehydrins gene OeSRC1 from Olea europaea increases salt and drought tolerance in tobacco plants.

Agricultural production is greatly affected by environmental stresses, such as cold, drought and high-salinity. It is possible to produce tolerant genotypes by transferring genes encoding protective proteins or enzymes from other organisms. In this regard, the current study was aimed to clone a novel OeSRC1 gene identified during the transcriptome profiling of olives (Olea europaea L.) and to investigate the function of this gene in tobacco plants. Functional evaluation of OeSRC1 gene in putative transgenic tobacco plants were carried out under drought, cold and salt stress conditions by using molecular and biochemical tools. It was observed that the transgenic tobacco plants exhibited higher seed germination and survival rates, better root and shoot growth under cold, salt and drought stress treatments compared to wild type plants. Our results also demonstrated that, under stress conditions, transgenic plants accumulated more free proline while no significant changes were observed regarding electrolyte leakage. Ascorbate peroxidase activity of OeSRC1-overexpressing plants was higher than those of the WT plants under different stress conditions. The overall results demonstrate the explicit role of OeSRC1 gene in conferring multiple abiotic stress tolerance at the whole-plant level. The multifunctional roleof olive OeSRC1 gene looks good to enhance environmental stress tolerance in diverse plants.

Systematic Analysis of MYB Family Genes in Potato and Their Multiple Roles in Development and Stress Responses

The MYB proteins represent a large family of transcription factors and play important roles in development, senescence, and stress responses in plants. In the current study, 233 MYB transcription factor-encoding genes were identified and analyzed in the potato genome, including 119 R1-MYB, 112 R2R3-MYB, and two R1R2R3-MYB members. R2R3-MYB is the most abundant MYB subclass and potato R2R3-MYB members together with their Arabidopsis homologs were divided into 35 well-supported subgroups as the result of phylogenetic analyses. Analyses on gene structure and protein motif revealed that members from the same subgroup shared similar exon/intron and motif organization, further supporting the results of phylogenetic analyses. Evolution of the potato MYB family was studied via syntenic analysis. Forty-one pairs of StMYB genes were predicted to have arisen from tandem or segmental duplication events, which played important roles in the expansion of the StMYB family. Expression profiling revealed that the StMYB genes were expressed in various tissues and several StMYB genes were identified to be induced by different stress conditions. Notably, StMYB030 was found to act as the homolog of AtMYB44 and was significantly up-regulated by salt and drought stress treatments. Furthermore, overexpression of StMYB030 in Arabidopsis enhanced salt stress tolerance of transgenic plants. The results from this study provided information for further functional analysis and for crop improvements through genetic manipulation of these StMYB genes.

Genome-wide identification and expression profile of HD-ZIP genes in physic nut and functional analysis of the JcHDZ16 gene in transgenic rice

BackgroundHomeodomain-leucine zipper (HD-ZIP) transcription factors play important roles in the growth, development and stress responses of plants, including (presumably) physic nut (Jatropha curcas), which has high drought and salinity tolerance. However, although physic nut’s genome has been released, there is little knowledge of the functions, expression profiles and evolutionary histories of the species’ HD-ZIP genes.ResultsIn this study, 32 HD-ZIP genes were identified in the physic nut genome (JcHDZs) and divided into four groups (I-IV) based on phylogenetic analysis with homologs from rice, maize and Arabidopsis. The analysis also showed that most of the JcHDZ genes were closer to members from Arabidopsis than to members from rice and maize. Of the 32 JcHDZ genes, most showed differential expression patterns among four tissues (root, stem cortex, leaf, and seed). Expression profile analysis based on RNA-seq data indicated that 15 of the JcHDZ genes respond to at least one abiotic stressor (drought and/or salinity) in leaves at least at one time point. Transient expression of a JcHDZ16-YFP fusion protein in Arabidopsis protoplasts cells showed that JcHDZ16 is localized in the nucleus. In addition, rice seedlings transgenically expressing JcHDZ16 had lower proline contents and activities of antioxidant enzymes (catalase and superoxide dismutase) together with higher relative electrolyte leakage and malondialdehyde contents under salt stress conditions (indicating higher sensitivity) than wild-type plants. The transgenic seedlings also showed increased sensitivity to exogenous ABA, and increases in the transcriptional abundance of several salt stress-responsive genes were impaired in their responses to salt stress. Further data on JcHDZ16-overexpressing plants subjected to salt stress treatment verified the putative role of JcHDZ genes in salt stress responses.ConclusionOur results may provide foundations for further investigation of functions of JcHDZ genes in responses to abiotic stress, and promote application of JcHDZ genes in physic nut breeding.

Salt Stress Triggered Changes in Osmoregulation and Antioxidants in Herbaceous Perennial Inula Plants (Asteraceae)

Global demand to cure ailments is a growing
 need. Inula genus extensively holds hundreds of species in warmer regions of
 Europe and Asia. It is being well-known for its phytochemical and
 pharmacological applications in industry thanks to its anti-inflammatory and
 antimicrobial interests. However, growth and production of Inula in the
 cutting-edge industry is commonly influenced by salt stress except for the
 halophyte species such as the Inula
 crithmoides. Salt tolerance level by means of changes in osmoregulation and
 antioxidant systems in an herbaceous perennial Inula plant has been
 biochemically evaluated here. Both salt stress treatments caused photosynthetic
 pigments’ degradation, increase in the leaf levels of osmolytes, and induction
 of oxidative stress indicated by the malondialdehyde (MDA). Higher hydrogen
 peroxide (H2O2) amount was recorded in high
 salt concentration than low salt. High salinity caused an increase in ascorbate
 (ASC) and glutathione (GSH) contents besides target enzymes of Inula leaves.
 NaCl tolerance of Inula also was found comprehensible through the higher
 concentrations of proline and to a lesser extent, total soluble sugar. Salt
 tolerance mechanisms of this rich bioresourse needs to be further studied in
 detail for herbal medicines in pharma sector.

The determination of gibberellic acid effects on seed germination of Echinacea purpurea (L.) Moench under salt stress

The research was conducted to determine the effect of gibberellic acid pre-treatments on germination of Echinacea purpurea seeds under salt stress. In the study, three different gibberellic acid concentrations (0, 100, 200 and 300 ppm) were pre-treated. Seeds planted in petri dishes were left to germinate after salt applications at 0, 50 and 100 mM (NaCl) concentrations. Responses of echinacea to priming and salt stress treatments were observed on the bases of some growth and viability (radicle and hypocotyl length, radicle fresh and dry weight, hypocotyl fresh and dry weight, germination power, germination speed, mean germination time, germination and sensitivity index) parameters. According to the result of the research; when the salt concentrations increase, the germination and growth parameters of echinacea seeds were inhibited. It was conducted determined that increasing doses of gibberellic acid pre-treatments had significant and positive effects on the germination and growth parameters of echinacea seeds under salt stress conditions. In physiological enhancement of echinacea seeds, the best results were obtained from the 300 ppm GA3+0 mM (control) salt combination.

The role analysis of APX gene family in the growth and developmental processes and in response to abiotic stresses in Arabidopsis thaliana

Oxidative stress caused by reactive oxygen species (ROS) is one of the major abiotic stresses in plants. Under adverse growth conditions, the incoordination of various metabolic processes in plant cells can result in increased hydrogen peroxide (H2O2), thus causing a variety of threats and injuries to plant cells. Ascorbate peroxidase (APX) is an important enzyme to remove H2O2 in plants. In Arabidopsis thaliana, there are eight APX gene family members, including APX1?APX6, sAPX and tAPX. In this study, we analyzed the expression patterns of the eight APX genes in the wild-type and apx mutant plants at different developmental stages and under different abiotic stress conditions. Meanwhile, the tolerance of each apx mutant to salt, drought and heat stresses was studied. qRT-PCR analysis showed that during development (from 4 to 8 weeks old), APX1 and APX2 exhibited the highest and lowest expression levels, respectively. In addition, the expression levels of APX4, sAPX and tAPX decreased during development, while the expression of APX6 increased with the maturity of the plants. Moreover, under different abiotic stress conditions, APX1, APX2 and APX6 were significantly induced by heat stress, sAPX actively responded to salt stress, and APX3 and APX5 exhibited obvious responses to salt, drought and heat stresses. Further tolerance analysis showed that the resistance of all apx mutants to salt and drought stresses was lower than that of the wild-type plant at both germination and maturity stages. At germination stage, all apx mutants were more sensitive to drought stress than to salt stress. At maturity stage, the apx1 and apx6 mutants were more sensitive to salt and drought stresses than the wild-type and other apx mutant plants. The physiological indexes indicated that the H2O2 content in all mutants, especially in the apx1, sapx and tapx, was significantly higher than that in the wild type 10 days after drought stress treatment, the malondialdehyde (MDA) content in all mutants was significantly higher than that in the wild type 5 days after salt stress treatment, while heat stress treatment for 2 h resulted in a significant increase in the contents of H2O2 and MDA in apx1, apx2 and apx6, especially in apx2. Taken together, our study revealed that all eight APX members of Arabidopsis participate in the growth and developmental processes and the abiotic stress responses, with some specific APXs playing a major role in a certain process.

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

Enhancement of growth and salt tolerance in Brassica napus L. seedlings by halotolerant Rhizobium strains containing ACC-deaminase activity

A greenhouse experiment was conducted with four (ACC) deaminase-producing halotolerant Rhizobium strains, R29 (Sinorhizobium mellilote), R103 (Sinorhizobium mellilote), R281 (Rhizobium legominozaroum bv. phaseoli) and R307 (Rhizobium legominozaroum bv. phaseoli) and evaluated for their efficiency in improving canola plant growth under salt stress (with (50 mM NaCl + MgCl2) and control treatments), as factorial in randomized complete block design with three replications. Results revealed that with increasing salinity in compared to the negative control (0 mM salt), the overall reduction of growth of canola seedlings was around 21.3%. However, Rhizobium strains inoculation significantly increase the shoot/root elongation, shoot/root dry weight, stem diameter, leaf numbers, RWC up to 15.3/27.5, 24.86/53.1, 18.4, 18.05 and 8.4% respectively, compared to positive control (50 mM salt). Salt stress also caused 1.12-fold reduction in the root/shoot dry weight ratio compared to the absence of salt, while the salt tolerance index (ratio of biomass of salt stressed to non-stressed plant) was significantly increased (up to 1.26-fold) in inoculated plants compared to positive control. Furthermore, nutrient uptakes (N, P, K up to 56.14, 38.2 and 36.5%) under salt stress by canola was significantly (P < 0.01) increased. In summary, this study indicates that the use of ACC-deaminase producing halotolerant Rhizobium bacteria mitigates the salt stress effects.

Effects of solid matrix priming (SMP) and salt stress on broccoli and cauliflower seed germination and early seedling growth

Salt stress affects seed germination and seedling growth. In this study, the effects of solid matrix priming (SMP) and salt stress on broccoli and cauliflower seed germination and early seedling growth were investigated. Physiological and biochemical changes in broccoli and cauliflower seeds and seedlings after the SMP and/or salt stress treatment were determined. Broccoli seeds were primed by mixing the seeds with vermiculite and H2O at a ratio of 1:1.5:2 (w/w/v) followed by two days incubation at 15 °C in the dark. Cauliflower seeds were primed by mixing the seeds with vermiculite and H2O at a ratio of 1:1.5:1 (w/w/v) followed by two days incubation at 20 °C in the dark. The primed and non-primed seeds were air-dried and then germinated on filter papers pre-wetted with H2O containing 0, 50, 100, 150 or 200 mM NaCl. The results showed that, without SMP treatment, the seed germination vigor (GV), germination index (GI) and vitality index (VI) were all inhibited and the mean germination time (MGT) was increased after the treatment with 100, 150 or 200 mM NaCl. The results also showed that the negative effects caused by the salt stress could be alleviated by the SMP treatment. The primed broccoli and cauliflower seeds showed an increase of GV, GI and VI compared with the non-primed seeds under the non-stressed or salt-stressed conditions. In addition, our result showed that the SMP treatment increased the activities of peroxidase and catalase, and the contents of proline, soluble sugar and soluble protein in both broccoli and cauliflower seedlings. We consider that the SMP treatment is useful approach for the improvement of broccoli and cauliflower seed germination and seedling establishment.

Pre-breeding: the role of antioxidant enzymes on maize in salt stress tolerance

Maize is a crop that is moderately sensitive to salt stress. Salinization of soil is a severe threat to maize production worldwide. Understanding the response and tolerance mechanism of maize to salt stress may be conducive to formulate strategies to improve maize performance under saline environments. In this study, salt-tolerant, salt-sensitive and moderate salt-tolerant maize plants were investigated, respectively, under salt stress conditions in three aspects: growth status, enzyme activity and gene expression level. After 30 days of planting and salt stress treatment, the plant height of USTB-297 (salt-tolerant maize) was 49.40% higher than that of USTB-265 (salt-sensitive maize) and 25.10% higher than that of USTB-109 (moderate salt-tolerant maize). Analysis of antioxidant enzymes superoxide dismutase (EC1.15.1.1), ascorbate peroxidase (EC1.11.1.11) and catalase (EC1.11.1.6) revealed that there are distinctions between these different breeds. Salt-tolerant breed with a higher plant height also had higher antioxidant enzyme activity and related genes expression compared to salt-sensitive or moderate salt-tolerant breed. The detection of gene expression in superoxide dismutase, catalase and ascorbate peroxidase using real-time PCR and the data of enzyme activity indicate that we can build a method of breeding for maize.

Application of Nano-Silicon Dioxide Improves Salt Stress Tolerance in Strawberry Plants

Silicon application can improve productivity outcomes for salt stressed plants. Here, we describe how strawberry plants respond to treatments including various combinations of salt stress and nano-silicon dioxide, and assess whether nano-silicon dioxide improves strawberry plant tolerance to salt stress. Strawberry plants were treated with salt (0, 25 or 50 mM NaCl), and the nano-silicon dioxide treatments were applied to the strawberry plants before (0, 50 and 100 mg L−1) or after (0 and 50 mg L−1) flowering. The salt stress treatments reduced plant biomass, chlorophyll content, and leaf relative water content (RWC) as expected. Relative to control (no NaCl) plants the salt treated plants had 10% lower membrane stability index (MSI), 81% greater proline content, and 54% greater cuticular transpiration; as well as increased canopy temperature and changes in the structure of the epicuticular wax layer. The plants treated with nano-silicon dioxide were better able to maintain epicuticular wax structure, chlorophyll content, and carotenoid content and accumulated less proline relative to plants treated only with salt and no nano-silicon dioxide. Analysis of scanning electron microscopic (SEM) images revealed that the salt treatments resulted in changes in epicuticular wax type and thickness, and that the application of nano-silicon dioxide suppressed the adverse effects of salinity on the epicuticular wax layer. Nano-silicon dioxide treated salt stressed plants had increased irregular (smoother) crystal wax deposits in their epicuticular layer. Together these observations indicate that application of nano-silicon dioxide can limit the adverse anatomical and biochemical changes related to salt stress impacts on strawberry plants and that this is, in part, associated with epicuticular wax deposition.

Genome-Wide Characterization and Expression Analysis of Soybean TGA Transcription Factors Identified a Novel TGA Gene Involved in Drought and Salt Tolerance.

The TGA transcription factors, a subfamily of bZIP group D, play crucial roles in various biological processes, including the regulation of growth and development as well as responses to pathogens and abiotic stress. In this study, 27 TGA genes were identified in the soybean genome. The expression patterns of GmTGA genes showed that several GmTGA genes are differentially expressed under drought and salt stress conditions. Among them, GmTGA17 was strongly induced by both stress, which were verificated by the promoter-GUS fusion assay. GmTGA17 encodes a nuclear-localized protein with transcriptional activation activity. Heterologous and homologous overexpression of GmTGA17 enhanced tolerance to drought and salt stress in both transgeinc Arabidopsis plants and soybean hairy roots. However, RNAi hairy roots silenced for GmTGA17 exhibited an increased sensitivity to drought and salt stress. In response to drought or salt stress, transgenic Arabidopsis plants had an increased chlorophyll and proline contents, a higher ABA content, a decreased MDA content, a reduced water loss rate, and an altered expression of ABA- responsive marker genes compared with WT plants. In addition, transgenic Arabidopsis plants were more sensitive to ABA in stomatal closure. Similarly, measurement of physiological parameters showed an increase in chlorophyll and proline contents, with a decrease in MDA content in soybean seedlings with overexpression hairy roots after drought and salt stress treatments. The opposite results for each measurement were observed in RNAi lines. This study provides new insights for functional analysis of soybean TGA transcription factors in abiotic stress.