Salt Stress Induces Paramylon Accumulation and Fine-Tuning of the Macro-Organization of Thylakoid Membranes in Euglena gracilis Cells

The effects of salt stress condition on the growth, morphology, photosynthetic performance, and paramylon content were examined in the mixotrophic, unicellular, flagellate Euglena gracilis. We found that salt stress negatively influenced cell growth, accompanied by a decrease in chlorophyll (Chl) content. Circular dichroism (CD) spectroscopy revealed the changes in the macro-organization of pigment-protein complexes due to salt treatment, while the small-angle neutron scattering (SANS) investigations suggested a reduction in the thylakoid stacking, an effect confirmed by the transmission electron microscopy (TEM). At the same time, the analysis of the thylakoid membrane complexes using native-polyacrylamide gel electrophoresis (PAGE) revealed no significant change in the composition of supercomplexes of the photosynthetic apparatus. Salt stress did not substantially affect the photosynthetic activity, as reflected by the fact that Chl fluorescence yield, electron transport rate (ETR), and energy transfer between the photosystems did not change considerably in the salt-grown cells. We have observed notable increases in the carotenoid-to-Chl ratio and the accumulation of paramylon in the salt-treated cells. We propose that the accumulation of storage polysaccharides and changes in the pigment composition and thylakoid membrane organization help the adaptation of E. gracilis cells to salt stress and contribute to the maintenance of cellular processes under stress conditions.

Metabolomics and Physiological Insights into the Ability of Exogenously Applied Chlorogenic Acid and Hesperidin to Modulate Salt Stress in Lettuce Distinctively

Recent studies in the agronomic field indicate that the exogenous application of polyphenols can provide tolerance against various stresses in plants. However, the molecular processes underlying stress mitigation remain unclear, and little is known about the impact of exogenously applied phenolics, especially in combination with salinity. In this work, the impacts of exogenously applied chlorogenic acid (CA), hesperidin (HES), and their combination (HES + CA) have been investigated in lettuce (Lactuca sativa L.) through untargeted metabolomics to evaluate mitigation effects against salinity. Growth parameters, physiological measurements, leaf relative water content, and osmotic potential as well as gas exchange parameters were also measured. As expected, salinity produced a significant decline in the physiological and biochemical parameters of lettuce. However, the treatments with exogenous phenolics, particularly HES and HES + CA, allowed lettuce to cope with salt stress condition. Interestingly, the treatments triggered a broad metabolic reprogramming that involved secondary metabolism and small molecules such as electron carriers, enzyme cofactors, and vitamins. Under salinity conditions, CA and HES + CA distinctively elicited secondary metabolism, nitrogen-containing compounds, osmoprotectants, and polyamines.

Silicon Mediated Changes in Growth and Photosynthetic Pigment of Wheat Plant Under Salt Stress

Purpose Salinity is a most important environmental stress which adversely affects the crop production and yield. In recent years, Silicon (Si) is gaining an increased attention in the field of stress management. Wheat (Triticum aestivum L.) is one of the moderately prone crops to different abiotic stresses which instantly damage the crop yield under stress condition. This work demonstrates the positive impact of Si on growth and photosynthetic pigments in wheat under saline conditions.Methods In this research work, two genotypes of wheat i.e. KRL 210 and WH 1105, were grown-up in soil under different salt stress concentration. There were different treatments under which they grown included T0= Control without salt stress (0 dS m-1) , T1= Sodium silicate without salt stress (2 mM) , T2= Control with salt stress (4 dS m-1) T3= Control with salt stress (8 dS m-1) T4= Control with salt stress (12 dS m-1) T5= Sodium silicate with salt stress (4dS m -1 + 2mM Si) T6= Sodium silicate with salt stress (8dS m-1 +2 mM Si) T7= Sodium silicate with salt stress (12dS m-1 +2mM Si). At vegetative stage, both the wheat genotypes were compared with their growth parameters and photosynthetic pigments.Results Plant biomass, shoot-root length and photosynthetic pigments (chlorophyll- a, b, carotenoid & total chlorophyll) of wheat decreased under salt stress when increased up to 12 dS m-1 NaCl concentration. However, in salt stressed wheat plants, plant biomass increased by the Si application. Supplementation of Si improved the plant length as well as chlorophyll pigments which were decreased by the high salt concentration in plants. Silicon was found more effective in salt stressed condition than in alone with control.Conclusion So, it was determined that the Si application aided the wheat genotypes in alleviating salinity and enhancing their biomass and photosynthetic pigments which were declined in salt stress condition.

High-Throughput Sequencing-Based Identification of miRNAs and Their Target mRNAs in Wheat Variety Qing Mai 6 Under Salt Stress Condition

Soil salinization is one of the major abiotic stresses that adversely affect the yield and quality of crops such as wheat, a leading cereal crop worldwide. Excavating the salt-tolerant genes and exploring the salt tolerance mechanism can help breeding salt-tolerant wheat varieties. Thus, it is essential to identify salt-tolerant wheat germplasm resources. In this study, we carried out a salt stress experiment using Qing Mai 6 (QM6), a salt-tolerant wheat variety, and sequenced the miRNAs and mRNAs. The differentially expressed miRNAs and mRNAs in salt stress conditions were compared with the control. As results, a total of eight salt-tolerance-related miRNAs and their corresponding 11 target mRNAs were identified. Further analysis revealed that QM6 enhances salt tolerance through increasing the expression level of genes related to stress resistance, antioxidation, nutrient absorption, and lipid metabolism balance, and the expression of these genes was regulated by the identified miRNAs. The resulting data provides a theoretical basis for future research studies on miRNAs and novel genes related to salt tolerance in wheat in order to develop genetically improved salt-tolerant wheat varieties.

​Influence of Native Endophytes on Early Stages Growth of Vigna radiata (Moong) under Salt Stress Condition

Background: Green gram (Vigna radiata) also known as moong bean is an annually cultivated in East Asia, Southeast Asia and Indian subcontinent. V. radiata is very important source for the protein as in our regular diet and it proved essential amino acid such as phenylalanine, leucine, isoleucine, valine, lysine, arginine, methionine, threonine and tryptophan. Methods: Here, we studied the influence of seed endophytes on germination and development under salinity stress condition. Seeds were treated with sodium hypochlorite for 30 min under shaking condition at 100 rpm for surface sterilization and treated with 70% ethanol for 2 min and followed five times rinse with autoclaved water. Surface sterilised seeds were homogenised in autoclaved water with the help of mortal-pestle. Homogenised seed solution made serial dilution and spreaded over nutrient agar for endophytic bacterial growth. Seeds were treated with bacteriocide and fungicide to make endophytes free, followed by sown for germination at 0mM, 50mM, 100mM and 150mM NaCl concentration. Result: Endophyte free seedlings were more susceptible against salt stress over normal seedlings. Therefore endophyte free seedling shoot and root biomass was 23.5% and 65.7% lower than control seedling biomass at 0mM salt respectively, while root length was 70% lower than control seedling root at 0mM salt concentration. Proline content in shoot and root observed an increase with increase of salt concentration. At 0mM salt, proline content was 0.00782±0.00043 and 0.00648±0.00017 (µmol/mg) in root of normal and endophyte free seedling respectively, while in shoot, it was non-significant difference. Glycine betaine content found to be increasing upto 100mM, followed by decreasing at 150mM in both root and shoot tissue. Glycine betaine content in endophyte free and control seedling shoot was 74.2±2.5 and 96.0±2.73 (µg/200mg) respectively at 100mM salt concentration. This result suggests, not only heritable genomic DNA but also endophytes associated with seed are very much important for the seedling growth and development which is also finally helps to combat abiotic stress situation.

Multi-Omic Analyses Reveal Habitat Adaptation of Marine Cyanobacterium Synechocystis sp. PCC 7338

Cyanobacteria are considered as promising microbial cell factories producing a wide array of bio-products. Among them, Synechocystis sp. PCC 7338 has the advantage of growing in seawater, rather than requiring arable land or freshwater. Nonetheless, how this marine cyanobacterium grows under the high salt stress condition remains unknown. Here, we determined its complete genome sequence with the embedded regulatory elements and analyzed the transcriptional changes in response to a high-salt environment. Complete genome sequencing revealed a 3.70 mega base pair genome and three plasmids with a total of 3,589 genes annotated. Differential RNA-seq and Term-seq data aligned to the complete genome provided genome-wide information on genetic regulatory elements, including promoters, ribosome-binding sites, 5′- and 3′-untranslated regions, and terminators. Comparison with freshwater Synechocystis species revealed Synechocystis sp. PCC 7338 genome encodes additional genes, whose functions are related to ion channels to facilitate the adaptation to high salt and high osmotic pressure. Furthermore, a ferric uptake regulator binding motif was found in regulatory regions of various genes including SigF and the genes involved in energy metabolism, suggesting the iron-regulatory network is connected to not only the iron acquisition, but also response to high salt stress and photosynthesis. In addition, the transcriptomics analysis demonstrated a cyclic electron transport through photosystem I was actively used by the strain to satisfy the demand for ATP under high-salt environment. Our comprehensive analyses provide pivotal information to elucidate the genomic functions and regulations in Synechocystis sp. PCC 7338.

Salt Tolerant Rhizobacteria from Coastal Region of Bangladesh Portrayed the Potential for Plant Growth Promotion

Plant growth-promoting rhizobacteria can effectively reduce the severity of different abiotic stresses like water stress, temperature stress, salt stress, etc. on plant growth and development. The study aimed at isolating salt-tolerant rhizobacteria followed by their morphological, biochemical and plant growth promotion traits evaluation. Sixteen root samples of nine different plant species were collected from two locations of Patuakhali, a coastal southern district of Bangladesh. Thirty rhizobacteria were isolated, fifteen from each location, to assess their halotolerance and plant growth promoting potential. The isolated rhizobacteria were subjected to morphological (viz. shape, colour and elevation), biochemical (viz. Gram reaction, catalase test and HCN production) and growth-promoting traits [viz. phosphate solubilizing ability, salt tolerance, indole-3-acetic acid (IAA) production, and N2-fixation] characterization. Twenty-eight isolates were Gram positive, 27 were catalase positive, and nine showed varying degrees of phosphate solubilization on National Botanical Research Institute of Phosphate (NBRIP) medium. Isolate PWB5 showed the highest phosphate solubilizing index (PSI = 3.83±0.098) on the 6th day. To screen salt-tolerant rhizobacteria, the isolates were cultured in NBA media containing different (0%, 2.5%, 5%, 7.5%, 10%, 12%, 15%) NaCl concentrations. Isolate PWB12 and PWB13 grew at 15% NaCl concentration. Eleven isolates exhibited IAA producing ability on Winogradsky medium amended with L-tryptophan among which four (PMB13, PMB14, PMB15 and PWB6) were strong IAA producers. Twenty-seven isolates were potential N2-fixer and among them, 20 were highly efficient, but none of the isolates was HCN producer. The rhizobacteria isolated in the current research work showed some potential plant growth-promoting traits which seem applicable for crop production, especially, under salt stress condition.

Salt stress induced accumulation of biomolecules in groundnut genotypes

Salinity is one of the environmental limiting factors in agricultural production. The aim of this study was to find out one of more salt tolerant groundnut genotypes through monitoring the growth and changes in biomolecules under salt stress condition. Purposively four groundnut genotypes, including a Traditional variety, Zhingabadam, Binachinabadam-1 and Dacca-1 were grown under three salinity levels viz. 0, 3 and 5 dSm-1. The experiment was laid out in two factorial completely randomized design with three replications. This experiment was done in soil based pot culture up to 40 days. Increasing salt concentration drastically reduced all the growth parameters, and increase proline and sugar content of leaf. Among the varieties Traditional variety, Zhingabadam and Dacca-1 had statistically similar shoot and root dry weight. The leaves of the Traditional variety contain the highest amount of proline of 14.52 and 36.24 mg/100g fresh leaves in 3 and 5 dS/m salinity, respectively which was 236 and 737 % higher than that of respective control. At EC of 3 and 5 dS/m, the variety Binachinabadam-1 was appeared to be susceptible, having an increase of 6 and 113% proline content over the respective control. Based on the shoot dry weight, root dry weight, proline content, total sugar, reducing sugar and relative water content, the Traditional variety was strongly recommended to be grown in the coastal salt affected soils. The Zhingabadam and Dacca-1 variety also could be recommended as they had comparable performance of the Traditional variety.