Impact of salt-induced toxicity on growth and yield-potential of local wheat cultivars: oxidative stress and ion toxicity are among the major determinants of salt-tolerant capacity

The potential and prospects of modified biochar for comprehensive management of salt-affected soils and plants: A critical review

Soil salinization has become a global problem that threatens farmland health and restricts crop production. Salt-affected soils seriously restrict the development of agricultural, mainly because of sodium ion (Na+) toxicity, nutrient deficiency, and structural changes in the soil. Biochar is a carbon (C)-based substance produced by heating typical biomass waste at high temperatures in anaerobic circumstances. It has high cation exchange capacity (CEC), adsorption capacity, and C content, which is often used as a soil amendment. Biochar generally reduces the concentration of Na+ in soil colloids through its strong adsorption, or uses the calcium (Ca) or magnesium (Mg) rich on its surface to exchange sodium ions (Ex-Na) from soil colloids through cation exchange to accelerate salt leaching during irrigation. Nowadays, biochar is widely used for acidic soils improvement due to its alkaline properties. Although the fact that biochar has gained increasing attention for its significant role in saline alkali soil remediation, there is currently a lack of systematic research on biochar improvers and their potential mechanisms for identifying physical, chemical, and biological indicators of soil eco-environment assessment and plant growth conditions affected by salt stress. This paper reviews the preparation, modification, and activation of biochar, the effects of biochar and its combination with beneficial salt-tolerant strains on salt-affected soils and plant growth. Finally, the limitations, benefits, and future needs of biochar-based soil health assessment technology in salt-affected soils and plant were discussed. This article elaborates on the future opportunities and challenges of biochar in the treatment of saline land, and a green method was provided for the integrate control to salt-affected soils.

Photosynthetic pigments and quantum yield of West Indian cherry under salt stress and NPK combinations

West Indian cherry cultivation has proved to be an important economic activity in northeastern Brazil. However, irrigation with brackish waters limits cultivation, requiring new strategies to minimize the effect of salt stress. In this context, the present study aimed to evaluate the effect of nitrogen (N), phosphorus (P), and potassium (K) combinations on the photosynthetic pigments and quantum yield of West Indian cherry cultivated under salt stress, in the second year of production. The assay was conducted in a protected environment by adopting an experimental design in randomized blocks, with treatments distributed in a 2×10 factorial arrangement referring to two electrical conductivity levels of irrigation water - ECw (0.6 and 4.0 dS m-1) and 10 NPK fertilization combinations - FC (80-100-100; 100-100-100; 120-100-100; 140-100-100; 100-80-100; 100-120-100; 100-140-100; 100-100-80; 100-100-120, and 100-100-140% of the recommendation, in the second year of production), with three replications, each consisting of one plant. Irrigation with the electrical conductivity of 4.0 dS m-1 negatively affected the synthesis of photosynthetic pigments and the photochemical efficiency of the West Indian cherry cv. Flor Branca. The NPK combinations did not attenuate the effects of salt stress on the analyzed variables. However, the combinations referring to 120-100-100%, 140-100-100%, and 100-120-100% of NPK recommendation improved the quantum yield of photosystem II by reducing the initial fluorescence and increasing the maximum fluorescence of the West Indian cherry cv. Flor Branca.

Organic amendments improve salinity-induced osmotic and oxidative stress tolerance in Okra (Abelmoschus esculentus (L.)Moench)

AIMS

Salinity adversely affects okra [Abelmoschus esculentus (L.) Moench] plants by inducing osmotic and oxidative stresses. This study was designed to enhance salinity-induced osmotic and oxidative stress tolerance in okra plants by applying organic amendments.

METHODS

The effects of different organic amendments (municipal solid waste compost, farmyard manure (FYM) and press mud) on osmotic potential, water use efficiency, activities of antioxidant enzymes, total soluble sugar, total soluble proline, total soluble protein and malondialdehyde (MDA) contents of okra plants grown under saline conditions (50 mM sodium chloride) were evaluated in a pot experiment. The organic amendments were applied each at the rate of 5% and 10% per pot or in various combinations (compost + FYM, FYM + press mud and compost + press mud each at the rate of 2.5% and 5% per pot).

RESULTS

As compared to control, high total soluble sugar (60.41), total soluble proline (33.88%) and MDA (51%) contents and increased activities of antioxidant enzymes [superoxide dismutase (83.54%), catalase (78.61%), peroxidase (53.57%] in salinity-stressed okra plants, were indicative of oxidative stress. Salinity significantly reduced the osmotic potential (41.78%) and water use efficiency (4.75%) of okra plants compared to control. Under saline conditions, 5% (farmyard manure + press mud) was the most effective treatment, which significantly improved osmotic potential (27.05%), total soluble sugar (4.20%), total soluble protein (73.62%) and total soluble proline (23.20%) contents and superoxide dismutase activity (32.41%), compared to saline soil. Application of 2.5% (FYM + press mud), 5% press mud, and 10% compost significantly reduced MDA content (27%) and improved activities of catalase (38.64%) and peroxidase (48.29%), respectively, compared to saline soil, thus facilitated to alleviate oxidative stress in okra plants.

CONCLUSIONS

Using organic amendments (municipal solid waste compost, farmyard manure and press mud) was a cost-effective approach to improve salinity-induced osmotic and oxidative stress tolerance in okra plants.

Synergistic Effects of Rhizobacteria and Salicylic Acid on Maize Salt-Stress Tolerance

Maize (Zea mays L.) is a salt-sensitive plant that experiences stunted growth and development during early seedling stages under salt stress. Salicylic acid (SA) is a major growth hormone that has been observed to induce resistance in plants against different abiotic stresses. Furthermore, plant growth-promoting rhizobacteria (PGPR) have shown considerable potential in conferring salinity tolerance to crops via facilitating growth promotion, yield improvement, and regulation of various physiological processes. In this regard, combined application of PGPR and SA can have wide applicability in supporting plant growth under salt stress. We investigated the impact of salinity on the growth and yield attributes of maize and explored the combined role of PGPR and SA in mitigating the effect of salt stress. Three different levels of salinity were developed (original, 4 and 8 dS m^-1) in pots using NaCl. Maize seeds were inoculated with salt-tolerant Pseudomonas aeruginosa strain, whereas foliar application of SA was given at the three-leaf stage. We observed that salinity stress adversely affected maize growth, yield, and physiological attributes compared to the control. However, both individual and combined applications of PGPR and SA alleviated the negative effects of salinity and improved all the measured plant attributes. The response of PGPR + SA was significant in enhancing the shoot and root dry weights (41 and 56%), relative water contents (32%), chlorophyll a and b contents (25 and 27%), and grain yield (41%) of maize under higher salinity level (i.e., 8 dS m^-1) as compared to untreated unstressed control. Moreover, significant alterations in ascorbate peroxidase (53%), catalase (47%), superoxide dismutase (21%), MDA contents (40%), Na⁺ (25%), and K⁺ (30%) concentration of leaves were pragmatic under combined application of PGPR and SA. We concluded that integration of PGPR and SA can efficiently induce salinity tolerance and improve plant growth under stressed conditions.

Salt Stress Inhibits Photosynthesis and Destroys Chloroplast Structure by Downregulating Chloroplast Development-Related Genes in Robinia pseudoacacia Seedlings

Soil salinization is an important factor limiting food security and ecological stability. As a commonly used greening tree species, Robinia pseudoacacia often suffers from salt stress that can manifest as leaf yellowing, decreased photosynthesis, disintegrated chloroplasts, growth stagnation, and even death. To elucidate how salt stress decreases photosynthesis and damages photosynthetic structures, we treated R. pseudoacacia seedlings with different concentrations of NaCl (0, 50, 100, 150, and 200 mM) for 2 weeks and then measured their biomass, ion content, organic soluble substance content, reactive oxygen species (ROS) content, antioxidant enzyme activity, photosynthetic parameters, chloroplast ultrastructure, and chloroplast development-related gene expression. NaCl treatment significantly decreased biomass and photosynthetic parameters, but increased ion content, organic soluble substances, and ROS content. High NaCl concentrations (100-200 mM) also led to distorted chloroplasts, scattered and deformed grana lamellae, disintegrated thylakoid structures, irregularly swollen starch granules, and larger, more numerous lipid spheres. Compared to control (0 mM NaCl), the 50 mM NaCl treatment significantly increased antioxidant enzyme activity while upregulating the expression of the ion transport-related genes Na⁺/H⁺ exchanger 1(NHX 1) and salt overly sensitive 1 (SOS 1) and the chloroplast development-related genes psaA, psbA, psaB, psbD, psaC, psbC, ndhH, ndhE, rps7, and ropA. Additionally, high concentrations of NaCl (100-200 mM) decreased antioxidant enzyme activity and downregulated the expression of ion transport- and chloroplast development-related genes. These results showed that although R. pseudoacacia can tolerate low concentrations of NaCl, high concentrations (100-200 mM) can damage chloroplast structure and disturb metabolic processes by downregulating gene expression.

CRISPR/Cas genome editing system and its application in potato

Potato is the largest non-cereal food crop worldwide and a vital substitute for cereal crops, considering its high yield and great nutritive value. It plays an important role in food security. The CRISPR/Cas (clustered regularly interspaced short palindromic repeats/CRISPR-associated) system has the advantages of easy operation, high efficiency, and low cost, which shows a potential in potato breeding. In this paper, the action mechanism and derivative types of the CRISPR/Cas system and the application of the CRISPR/Cas system in improving the quality and resistance of potatoes, as well as overcoming the self-incompatibility of potatoes, are reviewed in detail. At the same time, the application of the CRISPR/Cas system in the future development of the potato industry was analyzed and prospected.

Physiological and transcriptome analyses demonstrate the silver nanoparticles mediated alleviation of salt stress in pearl millet (Pennisetum glaucum L)

Pearl millet (Pennisetum glaucum L.) is a highly nutritive-value summer-annual forage crop used for hay, silage, grazing, and green chop. However, abiotic stresses including salinity negatively affect its growth and productivity. Furthermore, the nanotechnology is attaining greater consideration to reduce the impact of environmental stresses in plants. In the present study, transcriptome responses of silver nanoparticles (AgNPs) in pearl millet under salinity were investigated. The treatments were given as Control, NaCl (250 mM), AgNPs (20 mg/L), and NaCl + AgNPs to pearl millet seedlings after thirteen days of seed sowing. After 1 h of given treatments, leaf samples were collected and subjected to physio-chemical examination and transcriptome analyses. Salt stress increased the hydrogen peroxide (H₂O₂), malondialdehyde (MDA) content, and proline as compared to other treatments. In addition, the combined applications of NaCl + AgNPs ameliorated the oxidative damage by increasing antioxidant enzymes activities including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). Furthermore, RNA sequencing data showed 6016 commonly annotated Differentially Expressed Transcripts (DETs) among various treated combinations. Among them, 427 transcripts were upregulated, and 136 transcripts were downregulated at nanoparticles vs control, 1469 upregulated and 1182 downregulated at salt vs control, 494 upregulated and 231 downregulated at salt + nanoparticles vs control, 783 upregulated and 523 downregulated at nanoparticles vs salt. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that Mitogen-activated protein kinase (MAPK) signaling pathway, biosynthesis of secondary metabolites, and plant hormonal signal transduction pathway were the enriched among all identified pathways. In addition, Reverse transcription quantitative real-time polymerase chain reaction (qRT-PCR) showed that salinity up regulated the relative expression of DETs in pearl millet while, AgNPs optimized their expression that are associated with various molecular and metabolic functions. Overall, AgNPs treatments effectively improved the morphology, physiology, biochemistry, and gene expression pattern under salinity which could be attributed to positive impacts of AgNPs on pearl millet.

Transcriptome-Wide Identification and Functional Characterization of CIPK Gene Family Members in Actinidia valvata under Salt Stress

Fruit plants are severely constrained by salt stress in the soil due to their sessile nature. Ca²⁺ sensors, which are known as CBL-interacting protein kinases (CIPKs), transmit abiotic stress signals to plants. Therefore, it is imperative to investigate the molecular regulatory role of CIPKs underlying salt stress tolerance in kiwifruit. In the current study, we have identified 42 CIPK genes from Actinidia. valvata (A.valvata). All the AvCIPKs were divided into four different phylogenetic groups. Moreover, these genes showed different conserved motifs. The expression pattern analysis showed that AvCIPK11 was specifically highly expressed under salt stress. The overexpression of AvCIPK11 in 'Hongyang' (a salt sensitive commercial cultivar from Actinidia chinensis) enhanced salt tolerance by maintaining K⁺/Na⁺ homeostasis in the leaf and positively improving the activity of POD. In addition, the salt-related genes AcCBL1 and AcNHX1 had higher expression in overexpression lines. Collectively, our study suggested that AvCIPK11 is involved in the positive regulation of salt tolerance in kiwifruit.

Validation of a QTL on Chromosome 1DS Showing a Major Effect on Salt Tolerance in Winter Wheat

Salt stress is one the most destructive abiotic stressors, causing yield losses in wheat worldwide. A prerequisite for improving salt tolerance is the identification of traits for screening genotypes and uncovering causative genes. Two populations of F₃ lines developed from crosses between sensitive and tolerant parents were tested for salt tolerance at the seedling stage. Based on their response, the offspring were classified as salt sensitive and tolerant. Under saline conditions, tolerant genotypes showed lower Na⁺ and proline content but higher K⁺, higher chlorophyll content, higher K⁺/Na⁺ ratio, higher PSII activity levels, and higher photochemical efficiency, and were selected for further molecular analysis. Five stress responsive QTL identified in a previous study were validated in the populations. A QTL on the short arm of chromosome 1D showed large allelic effects in several salt tolerant related traits. An expression analysis of associated candidate genes showed that TraesCS1D02G052200 and TraesCS5B02G368800 had the highest expression in most tissues. Furthermore, qRT-PCR expression analysis revealed that ZIP-7 had higher differential expressions under saline conditions compared to KefC, AtABC8 and 6-SFT. This study provides information on the genetic and molecular basis of salt tolerance that could be useful in development of salt-tolerant wheat varieties.

CRISPR/Cas genome editing improves abiotic and biotic stress tolerance of crops

Abiotic stress such as cold, drought, saline-alkali stress and biotic stress including disease and insect pest are the main factors that affect plant growth and limit agricultural productivity. In recent years, with the rapid development of molecular biology, genome editing techniques have been widely used in botany and agronomy due to their characteristics of high efficiency, controllable and directional editing. Genome editing techniques have great application potential in breeding resistant varieties. These techniques have achieved remarkable results in resistance breeding of important cereal crops (such as maize, rice, wheat, etc.), vegetable and fruit crops. Among them, CRISPR/Cas (clustered regularly interspaced short palindromic repeats/CRISPR-associated) provides a guarantee for the stability of crop yield worldwide. In this paper, the development of CRISRR/Cas and its application in different resistance breeding of important crops are reviewed, the advantages and importance of CRISRR/Cas technology in breeding are emphasized, and the possible problems are pointed out.

Effect of Trichoderma asperellum on Wheat Plants' Biochemical and Molecular Responses, and Yield under Different Water Stress Conditions

Eight Trichoderma strains were evaluated for their potential to protect wheat seedlings against severe (no irrigation within two weeks) water stress (WS). Considering the plant fresh weight and phenotype, T. asperellum T140, which displays 1-aminocyclopropane-1-carboxylic acid deaminase activity and which is able to produce several phytohormones, was selected. The molecular and biochemical results obtained from 4-week-old wheat seedlings linked T140 application with a downregulation in the WS-response genes, a decrease in antioxidant activities, and a drop in the proline content, as well as low levels of hydrogen peroxide and malondialdehyde in response to severe WS. All of these responses are indicative of T140-primed seedlings having a higher tolerance to drought than those that are left untreated. A greenhouse assay performed under high nitrogen fertilization served to explore the long-term effects of T140 on wheat plants subjected to moderate (halved irrigation) WS. Even though all of the plants showed acclimation to moderate WS regardless of T140 application, there was a positive effect exerted by T. asperellum on the level of tolerance of the wheat plants to this stress. Strain T140 modulated the expression of a plant ABA-dependent WS marker and produced increased plant superoxide dismutase activity, which would explain the positive effect of Trichoderma on increasing crop yields under moderate WS conditions. The results demonstrate the effectiveness of T. asperellum T140 as a biostimulant for wheat plants under WS conditions, making them more tolerant to drought.

Contribution of Exogenous Proline to Abiotic Stresses Tolerance in Plants: A Review

Abiotic stresses are the major environmental factors that play a significant role in decreasing plant yield and production potential by influencing physiological, biochemical, and molecular processes. Abiotic stresses and global population growth have prompted scientists to use beneficial strategies to ensure food security. The use of organic compounds to improve tolerance to abiotic stresses has been considered for many years. For example, the application of potential external osmotic protective compounds such as proline is one of the approaches to counteract the adverse effects of abiotic stresses on plants. Proline level increases in plants in response to environmental stress. Proline accumulation is not just a signal of tension. Rather, according to research discussed in this article, this biomolecule improves plant resistance to abiotic stress by rising photosynthesis, enzymatic and non-enzymatic antioxidant activity, regulating osmolyte concentration, and sodium and potassium homeostasis. In this review, we discuss the biosynthesis, sensing, signaling, and transport of proline and its role in the development of various plant tissues, including seeds, floral components, and vegetative tissues. Further, the impacts of exogenous proline utilization under various non-living stresses such as drought, salinity, high and low temperatures, and heavy metals have been extensively studied. Numerous various studies have shown that exogenous proline can improve plant growth, yield, and stress tolerance under adverse environmental factors.

Recent Advances in Bacterial Amelioration of Plant Drought and Salt Stress

Simple Summary

Salt and drought stress cause enormous crop losses worldwide. Several different approaches may be taken to address this problem, including increased use of irrigation, use of both traditional breeding and genetic engineering to develop salt-tolerant and drought-resistant crop plants, and the directed use of naturally occurring plant growth-promoting bacteria. Here, the mechanisms used by these plant growth-promoting bacteria are summarized and discussed. Moreover, recently reported studies of the effects that these organisms have on the growth of plants in the laboratory, the greenhouse, and the field under high salt and/or drought conditions is discussed in some detail. It is hoped that by understanding the mechanisms that these naturally occurring plant growth-promoting bacteria utilize to overcome damaging environmental stresses, it may be possible to employ these organisms to increase future agricultural productivity.

Abstract

The recent literature indicates that plant growth-promoting bacteria (PGPB) employ a range of mechanisms to augment a plant’s ability to ameliorate salt and drought stress. These mechanisms include synthesis of auxins, especially indoleacetic acid, which directly promotes plant growth; synthesis of antioxidant enzymes such as catalase, superoxide dismutase and peroxidase, which prevents the deleterious effects of reactive oxygen species; synthesis of small molecule osmolytes, e.g., trehalose and proline, which structures the water content within plant and bacterial cells and reduces plant turgor pressure; nitrogen fixation, which directly improves plant growth; synthesis of exopolysaccharides, which protects plant cells from water loss and stabilizes soil aggregates; synthesis of antibiotics, which protects stress-debilitated plants from soil pathogens; and synthesis of the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase, which lowers the level of ACC and ethylene in plants, thereby decreasing stress-induced plant senescence. Many of the reports of overcoming these plant stresses indicate that the most successful PGPB possess several of these mechanisms; however, the involvement of any particular mechanism in plant protection is nearly always inferred and not proven.

Phytogenic Selenium Nanoparticles Elicited the Physiological, Biochemical, and Antioxidant Defense System Amelioration of Huanglongbing-Infected ‘Kinnow’ Mandarin Plants

Citrus greening or huanglongbing (HLB) is commonly known as yellow dragon disease and affects citrus production worldwide. Therefore, it has a significant impact on and deleterious effects in the agro-industrial sector. Significant efforts have been made to combat this disease and mitigate its destructive impact on citrus production, but still, there is no effective biocompatible treatment available to control HLB disorder. This study is considered the first biocompatible approach to evaluate the potential of phytogenic selenium nanoparticles (SeNPs) to improve the health of HLB-infected ‘Kinnow’ mandarin plants. Polymerase chain reactions (PCRs) with specific primers were used to detect HLB disease in ‘Kinnow’ mandarin plants, and PCR products were sequenced to identify Candidatus Liberibacter asiaticus (CLas), and accession numbers for CLas1 and CLas2, MZ851933 and MZ851934, respectively, were obtained. SeNPs were synthesized by using Allium sativum L. clove extract as a reducing, capping, and stabilizing agent and various techniques such as UV-visible spectrophotometry, energy dispersive X-rays, scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR), and X-ray diffraction analysis (XRD) were used to confirm the biogenesis of SeNPs. Different concentrations of SeNPs (25, 50, 75, and 100 mg L⁻¹) were exogenously applied to HLB-infected ‘Kinnow’ mandarin plants and obtained spectacular results. The obtained results from the current study proved that 75 mg L⁻¹ of SeNPs was most effective to improve the chlorophyll, carotenoids, relative water content (RWC), membrane stability index (MSI), total soluble sugar (TSS), superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), total flavonoid content (TFC), and total phenolic content (TPC) and significant decrease was observed in hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and proline (PRO) contents of HLB-infected ‘Kinnow’ mandarin plants as compared to untreated diseased citrus plants. In conclusion, these results allow us to synthesize the SeNPs formulation as a promising management strategy to treat the HLB disease in citrus plants.

Salicylic acid mitigates salt induced toxicity through the modifications of biochemical attributes and some key antioxidants in capsicum annuum

Abiotic stress causes extensive loss to agricultural yield production worldwide. Salt stress is one of them crucial factor which leads to decreased the agricultural production through detrimental effect on growth and development of crops. In our study, we examined the effect of a defense growth substance, salicylic acid (SA 1 mM) on mature vegetative (60 Days after sowing) and flowering (80 DAS) stage of Pusa Sadabahar (PS) variety of Capsicum annuum L. plants gown under different concentrations of NaCl (25, 50, 75, 100 and 150 mM) and maintained in identical sets in pots during the whole experiment. Physiological studies indicated that increase in root & shoot length, fresh & dry weight, number of branches per plant, and yield (number of fruits per plant) under salt + SA treatment. Biochemical studies, enzymatic antioxidants like CAT, POX, and non-enzymatic antioxidant such as ascorbic acid (AsA content), carotenoids, phenolics, besides other defense compounds like proline, protein, chlorophyll contents were studied at 10 days after treatment at the mature vegetative and flowering stage. The addition of SA led to lowering of in general, all studied parameters in the mature vegetative stage but increased the same during the flowering stage, especially in the presence of NaCl; although the control I (without SA and NaCl) remained lower in value than control II (with SA, without NaCl). Interestingly, total phenolics were higher in control I (without SA or NaCl) whereas chlorophylls were higher in treatments with SA and NaCl. Thus, physiological concentration of SA (1 mM) appears to be significantly effective against salt stress during the flowering stage. In addition, during the mature vegetative stage, however, proline accumulates in SA treated sets, to help in developing NaCl-induced drought stress tolerance.

Positive Salt Tolerance Modulation via Vermicompost Regulation of SOS1 Gene Expression and Antioxidant Homeostasis in Viciafaba Plant

Strategic implementation of vermicompost as safe biofertilizer besides defensing saline soils offer dual function solving problems in developing countries. The current study aims to utilize vermicompost (VC) for amelioration of 200mM NaCl in Vicia faba Aspani cultivar and investigate the molecular role of salt overly sensitive pathway (SOS1). The experiment was conducted following a completely randomized design with three replicates. Treatments include 0; 2.5; 5; 10; 15% dried VC intermingled with soil mixture (clay: sand; 1:2) and/or 200 mM NaCl. The results show that salinity stress decreased broad bean fresh and dry weight; and K⁺/Na⁺. However, malonedialdehyde and H₂O₂ contents; increased. Application of 10% VC and salinity stress increases Ca²⁺ (41% and 50%), K⁺/Na⁺ (125% and 89%), Mg²⁺ (25% and 36%), N (8% and 11%), indole acetic acid (70% and 152%) and proteins (9% and 13%) for root and shoot, respectively, in comparison to salt treated pots. Moreover, all examined enzymatic antioxidants and their substrates increased, except glutathione reductase. A parallel decrease in abscisic acid (75% and 29%) and proline (59% and 58%) was also recorded for roots and leaves, respectively. Interestingly, the highly significant increase in gene expression of SOS1 (45-fold) could drive defense machinery of broad bean to counteract 200 mM NaCl.

Proso millet (Panicum miliaceum L.): A potential crop to meet demand scenario for sustainable saline agriculture

Proso millet (Panicum miliaceum L.) is resilient to abiotic stress, especially to land degradation caused by soil salinization. However, the mechanisms by which its roots adapt and tolerate salt stress are obscure. In this study, plants of a salt-sensitive cultivar (SS 212) and a salt-tolerant cultivar (ST 47) of proso millet were exposed to severe salt stress and subsequent re-watering. ST 47 exhibited greater salt tolerance than SS 212, as evidenced by higher increases in total root length (TRL), root surface area (RSA), root tip number (RTN). Moreover, microstructural analysis showed that relative to SS 212, the roots of ST 47 could maintain more intact internal structures and thicker cell walls under salt stress. Digital RNA sequence analysis revealed that ST 47 maintained better Na⁺/K⁺ balance to resist Na⁺ toxicity via a higher capability to restrict Na⁺ uptake, vacuolar Na⁺ sequestration, and Na⁺ exclusion. The mechanism for Na⁺ toxicity resistance in ST 47 involved promoting cell wall composition changes via efficient regulation of galactose metabolism and biosynthesis of cellulose and phenylpropanoids. Overall, this study provides valuable salt-tolerant cultivar resources and mechanisms for regulating salt tolerance, which could be applied for the rehabilitation of saline lands.

Chitosan-Selenium Nanoparticle (Cs-Se NP) Foliar Spray Alleviates Salt Stress in Bitter Melon

Salt stress severely reduces growth and yield of plants. Considering the positive effects of selenium (Se) and chitosan (Cs) separately against abiotic stress, in these experiments, we synthesized chitosan-selenium nanoparticles (Cs-Se NPs) and investigated their ability to reduce the negative effects of salt stress on growth and some biochemical parameters of bitter melon (Momordica charantia). Bitter melon plants were grown at three NaCl salinity levels (0, 50, and 100 mM) and a foliar spray of Cs-Se NPs (0, 10, and 20 mg L-1) was applied. Some key morphological, biochemical, and physiological parameters in leaf samples and essential oil from fruit were measured at harvest. Salinity decreased growth and yield while foliar application of Cs-Se NPs increased these critical parameters. Furthermore, Cs-Se NPs enhanced bitter melon tolerance to salinity by increasing antioxidant enzyme activity, proline concentration, relative water content, and K+, and decreasing MDA and H2O2 oxidants and Na aggregation in plant tissues. Yield was also improved, as the highest amount of essential oils was produced by plants treated with Cs-Se NPs. Generally, the greatest improvement in measured parameters under saline conditions was obtained by treating plants with 20 mg L-1 Cs-Se NPs, which significantly increased salinity tolerance in bitter melon plants.

Silver nanoparticles improved the plant growth and reduced the sodium and chlorine accumulation in pearl millet: a life cycle study

Salt stress in agricultural soils is a global issue and little information is available about the efficiency of silver nanoparticles (AgNPs) in plants under salt stress. The aim of current study was to assess the efficacy of AgNPs in improving plant growth and reducing the salt-induced damages in pearl millet. The exposure of pearl millet plants grown in pots containing soil to different doses of salinity (0, 120, 150 mM) and AgNPs (0, 10, 20 and 30 mM) significantly influenced the morphology, physiology and yield-related attributes. Salt stress remarkably increased the concentration of sodium (Na) and chloride (Cl) in different organs of pearl millet plants. This led to increase the enhancement of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) content and caused severe oxidative damage by augmenting the activities of antioxidant enzymes. The obvious decrease in plant growth, height, dry biomass of root and shoot, chlorophylls and carotenoid contents was observed in salt-stressed plants which ultimately reduced the yield of plants. The AgNPs remarkably improved the plant growth by reducing oxidative stress and Na and Cl uptake by salt-stressed plants. The AgNPs were also found to maintain the ionic balance of cell (Na⁺, K⁺ and Na⁺/K⁺ ratio). The AgNPs improved the superoxide dismutase, catalase activities and decreased the peroxidase activity while reduced the H₂O₂ and MDA contents in plants under salt stress. Overall, AgNPs increased the plant height, yield, and photosynthesis of salt-stressed plants in a dose-additive manner.

Impact of Foliar Application of Chitosan Dissolved in Different Organic Acids on Isozymes, Protein Patterns and Physio-Biochemical Characteristics of Tomato Grown under Salinity Stress

In this study, the anti-stress capabilities of the foliar application of chitosan, dissolved in four different organic acids (acetic acid, ascorbic acid, citric acid and malic acid) have been investigated on tomato (Solanum lycopersicum L.) plants under salinity stress (100 mM NaCl). Morphological traits, photosynthetic pigments, osmolytes, secondary metabolites, oxidative stress, minerals, antioxidant enzymes activity, isozymes and protein patterns were tested for potential tolerance of tomato plants growing under salinity stress. Salinity stress was caused a reduction in growth parameters, photosynthetic pigments, soluble sugars, soluble proteins and potassium (K⁺) content. However, the contents of proline, ascorbic acid, total phenol, malondialdehyde (MDA), hydrogen peroxide (H₂O₂), sodium (Na⁺) and antioxidant enzyme activity were increased in tomato plants grown under saline conditions. Chitosan treatments in any of the non-stressed plants showed improvements in morphological traits, photosynthetic pigments, osmolytes, total phenol and antioxidant enzymes activity. Besides, the harmful impacts of salinity on tomato plants have also been reduced by lowering MDA, H₂O₂ and Na⁺ levels. Chitosan treatments in either non-stressed or stressed plants showed different responses in number and density of peroxidase (POD), polyphenol oxidase (PPO) and superoxide dismutase (SOD) isozymes. NaCl stress led to the diminishing of protein bands with different molecular weights, while they were produced again in response to chitosan foliar application. These responses were varied according to the type of solvent acid. It could be suggested that foliar application of chitosan, especially that dissolved in ascorbic or citric acid, could be commercially used for the stimulation of tomato plants grown under salinity stress.

Mitigation of NaCl Stress in Wheat by Rhizosphere Engineering Using Salt Habitat Adapted PGPR Halotolerant Bacteria

There is a great interest in mitigating soil salinity that limits plant growth and productivity. In this study, eighty-nine strains were isolated from the rhizosphere and endosphere of two halophyte species (Suaeda mollis and Salsola tetrandra) collected from three chotts in Algeria. They were screened for diverse plant growth-promoting traits, antifungal activity and tolerance to different physico-chemical conditions (pH, PEG, and NaCl) to evaluate their efficiency in mitigating salt stress and enhancing the growth of Arabidopsis thaliana and durum wheat under NaCl–stress conditions. Three bacterial strains BR5, OR15, and RB13 were finally selected and identified as Bacillus atropheus. The Bacterial strains (separately and combined) were then used for inoculating Arabidopsis thaliana and durum wheat during the seed germination stage under NaCl stress conditions. Results indicated that inoculation of both plant spp. with the bacterial strains separately or combined considerably improved the growth parameters. Three soils with different salinity levels (S1 = 0.48, S2 = 3.81, and S3 = 2.80 mS/cm) were used to investigate the effects of selected strains (BR5, OR15, and RB13; separately and combined) on several growth parameters of wheat plants. The inoculation (notably the multi-strain consortium) proved a better approach to increase the chlorophyll and carotenoid contents as compared to control plants. However, proline content, lipid peroxidation, and activities of antioxidant enzymes decreased after inoculation with the plant growth-promoting rhizobacteria (PGPR) that can attenuate the adverse effects of salt stress by reducing the reactive oxygen species (ROS) production. These results indicated that under saline soil conditions, halotolerant PGPR strains are promising candidates as biofertilizers under salt stress conditions.

Glutathione improves rice tolerance to submergence: insights into its physiological and biochemical mechanisms

Complete submergence (Sub) imposes detrimental effects on growth and survival of crop plants, including rice. Here, we investigated the beneficial effects of reduced glutathione (GSH) in mitigating Sub-induced adverse effects in two high-yielding rice cultivars BRRI dhan29 and dhan52. Both cultivars experienced growth defects, severe yellowing, necrosis and chlorosis, when they were completely immersed in water for 14 days. The poor growth performance of these cultivars was linked to biomass reduction, decreased levels of photosynthetic pigments and proline, increased levels of H₂O₂ and malondialdehyde, and declined activities of enzymatic antioxidants like superoxide dismutase, ascorbate peroxidase, peroxidase, catalase, glutathione peroxidase and glutathione S-transferase. Pretreatment with exogenous GSH led to significant growth restoration in both cultivars exposed to Sub. The elevated Sub-tolerance promoted by GSH could partly be attributed to increased levels of chlorophylls, carotenoids, soluble proteins and proline. Exogenous GSH also mitigated Sub-induced oxidative damage, as evidenced from reduced levels of H₂O₂ and malondialdehyde in accordance with the increased activities of antioxidant enzymes. Results revealed that dhan52 was more tolerant to Sub-stress than dhan29, and GSH successfully rescued both cultivars from the damage of Sub-stress. Collectively, our findings provided an insight into the GSH-mediated active recovery of rice from Sub-stress, thereby suggesting that external supply of GSH may be an effective strategy to mitigate the adverse effects of Sub in rice.

Regulation of ROS Metabolism in Plants under Environmental Stress: A Review of Recent Experimental Evidence

Various environmental stresses singly or in combination generate excess amounts of reactive oxygen species (ROS), leading to oxidative stress and impaired redox homeostasis. Generation of ROS is the obvious outcome of abiotic stresses and is gaining importance not only for their ubiquitous generation and subsequent damaging effects in plants but also for their diversified roles in signaling cascade, affecting other biomolecules, hormones concerning growth, development, or regulation of stress tolerance. Therefore, a good balance between ROS generation and the antioxidant defense system protects photosynthetic machinery, maintains membrane integrity, and prevents damage to nucleic acids and proteins. Notably, the antioxidant defense system not only scavenges ROS but also regulates the ROS titer for signaling. A glut of studies have been executed over the last few decades to discover the pattern of ROS generation and ROS scavenging. Reports suggested a sharp threshold level of ROS for being beneficial or toxic, depending on the plant species, their growth stages, types of abiotic stresses, stress intensity, and duration. Approaches towards enhancing the antioxidant defense in plants is one of the vital areas of research for plant biologists. Therefore, in this review, we accumulated and discussed the physicochemical basis of ROS production, cellular compartment-specific ROS generation pathways, and their possible distressing effects. Moreover, the function of the antioxidant defense system for detoxification and homeostasis of ROS for maximizing defense is also discussed in light of the latest research endeavors and experimental evidence.

Evaluating the Contribution of Growth, Physiological, and Ionic Components Towards Salinity and Drought Stress Tolerance in Jatropha curcas

Salinity and drought stress, singly or in combination, are major environmental menaces. Jatropha curcas L. is a biodiesel plant that can tolerate long periods of drought. However, the growth performance and stress tolerance based on physical, chemical, and physiological attributes of this plant have not yet been studied. To address this question, J. curcas seedlings were grown in a completely randomized design in plastic pots filled with soil to evaluate the effects of salinity and drought stresses on growth, ionic composition, and physiological attributes. The experiment consisted of six treatments: control (without salinity and drought stress), salinity alone (7.5 dS m⁻¹, 15 dS m⁻¹), drought, and a combination of salinity and drought (7.5 dS m⁻¹+ Drought, 15 dS m⁻¹+Drought). Our results revealed that, compared with the control, both plant height (PH) and stem diameter (SD) were reduced by (83%, 80%, and 77%) and (69%, 56%, and 55%) under salinity and drought combination (15 dS m⁻¹+Drought) after three, six, and nine months, respectively. There was 93% more leaf Na⁺ found in plants treated with 15 dS m⁻¹+Drought compared with the control. The highest significant average membrane stability index (MSI) and relative water content (RWC) values (81% and 85%, respectively) were found in the control. The MSI and RWC were not influenced by 7.5 dS m⁻¹ and drought treatments and mostly contributed towards stress tolerance. Our findings imply that J. curcas is moderately tolerant to salinity and drought. The Na⁺ toxicity and disturbance in K⁺: Na⁺ ratio were the main contributing factors for limited growth and physiological attributes in this plant.

Physiological and quantitative proteomic analysis of NtPRX63-overexpressing tobacco plants revealed that NtPRX63 functions in plant salt resistance

High salinity is harmful to crop yield and productivity. Peroxidases (PRXs) play crucial roles in H2O2 scavenging. In our previous study, PRX63 significantly upregulated in tobacco plants under salt stress. Thus, in order to understand the function of PRX63 in tobacco salt response, we overexpressed this gene in tobacco (Nicotiana tabacum L.), investigated the morphological, physiological and proteomic profiles of NtPRX63-overexpressing tobacco transgenic lines and wild type. The results showed that, compared with the wild type, the transgenic tobacco plants presented enhanced salt tolerance and displayed lower ROS (reactive oxygen species), malondialdehyde (MDA) and Na+ contents; higher biomass, potassium content, soluble sugar content, and peroxidase activity; and higher expression levels of NtSOD, NtPOD and NtCAT. Protein abundance analysis revealed 123 differentially expressed proteins between the transgenic and wild-type plants. These proteins were functionally classified into 18 categories and are involved in 41 metabolic pathways. Furthermore, among the 123 proteins, eight proteins involved in the ROS-scavenging system, 12 involved in photosynthesis and energy metabolism processes, two stress response proteins, one signal transduction protein and one disulfide isomerase were significantly upregulated. Furthermore, three novel proteins that may be involved in the plant salt response were also identified. The results of our study indicate that an enhanced ROS-scavenging ability, together with the expression of proteins related to energy mobilization and the stress response, functions in the confirmed salt resistance of transgenic tobacco plants. Our data provide valuable information for research on the function of NtPRX63 in tobacco in response to abiotic stress.

Comparing transcriptome expression profiles to reveal the mechanisms of salt tolerance and exogenous glycine betaine mitigation in maize seedlings

Salt stress is a common abiotic stress that limits the growth, development and yield of maize (Zea mays L.). To better understand the response of maize to salt stress and the mechanism by which exogenous glycine betaine (GB) alleviates the damaging effects of salt stress, the morphology, physiological and biochemical indexes, and root transcriptome expression profiles of seedlings of salt-sensitive inbred line P138 and salt-tolerant inbred line 8723 were compared under salt stress and GB-alleviated salt stress conditions. The results showed that under salt stress the growth of P138 was significantly inhibited and the vivo ion balance was disrupted, whereas 8723 could prevent salt injury by maintaining a high ratio of K+ to Na+. The addition of a suitable concentration of GB could effectively alleviate the damage caused by salt stress, and the mitigating effect on salt-sensitive inbred line P138 was more obvious than that on 8723. Transcriptome analysis revealed that 219 differentially expressed genes (DEGs) were up-regulated and 153 DEGs were down-regulated in both P138 and 8723 under NaCl treatment, and that 487 DEGs were up-regulated and 942 DEGs were down-regulated in both P138 and 8723 under salt plus exogenous GB treatment. In 8723 the response to salt stress is mainly achieved through stabilizing ion homeostasis, strong signal transduction activation, increasing reactive oxygen scavenging. GB alleviates salt stress in maize mainly by inducing gene expression changes to enhance the ion balance, secondary metabolic level, reactive oxygen scavenging mechanism, signal transduction activation. In addition, the transcription factors involved in the regulation of salt stress response and exogenous GB mitigation mainly belong to the MYB, MYB-related, AP2-EREBP, bHLH, and NAC families. We verified 10 selected up-regulated DEGs by quantitative real-time polymerase chain reaction (qRT-PCR), and the expression results were basically consistent with the transcriptome expression profiles. Our results from this study may provide the theoretical basis for determining maize salt tolerance mechanisms and the mechanism by which GB regulates salt tolerance.

Melatonin foliar sprays elicit salinity stress tolerance and enhance fruit yield and quality in strawberry (Fragaria × ananassa Duch.)

The increasing salinity in soils and irrigation water is a major concern for growers of strawberry, a salt-sensitive horticultural crop. The hormone melatonin (N-acetyl-5-methoxytryptamine) is involved in many biological processes and affects plant responses to environmental stresses. The effects of weekly 100 and 200 μM melatonin sprays on leaf composition parameters (photosynthetic pigment and macronutrient concentrations, oxidative stress markers, antioxidant defense systems and abscisic acid concentrations), fruit yield and quality parameters (soluble solids, total acidity, ascorbic acid, total antioxidants and phenolics and sugars), and leaf and fruit melatonin have been studied in strawberry grown under non-saline, moderate and intense salinity conditions (0, 40 and 80 mM NaCl, respectively). Salinity led to decreases in yield, fruit quality parameters and leaf photosynthetic pigments and macronutrient concentrations, as well as to increases in oxidative stress, with melatonin foliar application alleviating all these changes. On the other hand, salinity led to increases in the leaf levels of antioxidant enzymes, abscisic acid and melatonin, with foliar applications of melatonin boosting those increases. In the absence of salinity stress, melatonin led to smaller changes in all parameters in the same direction to that observed in the presence of salinity. Furthermore, melatonin resulted in increases in strawberry fruit yield and quality, especially in plants grown under salinity. Results indicate that the effects of melatonin application are associated with a boost in leaf antioxidant enzymes and abscisic acid, and support that the application of melatonin is a promising tool for mitigating salt stress in strawberry.

Plant growth promoting Streptomyces strains are selectively interacting with the wheat cultivars especially in saline conditions

Plant growth promoting (PGP) effect of Streptomyces on wheat growth in different conditions has been mostly reported although mechanisms which caused wheat cultivars differently response to a PGP Streptomyces has been less studied. In this study, the effect of two Streptomyces strains, previously reported as PGPR, on the growth of four salt-sensitive commercial wheat cultivars under normal and saline conditions was investigated. Strain C-2012 differently affected the growth of the cultivars in the normal and stress conditions. Cultivars Gonbad with the highest (63%) and Zarin without increased dry biomass upon C-2012 treatments were selected for further study. Salinity significantly decreased seedling fresh and dry weight, K⁺ and chlorophyll content and glutathione S-transferase activity. Moreover, the stress increased proline and Na⁺ content and peroxidase (POX) and ascorbate peroxidase (APX) activity in both cultivars. Strain C-2012, generally, ameliorated the negative effect of the stress with increased chlorophyll and carotenoid and reduced Na⁺ content and APX and SOD activity in both cultivars, however, its effect on biomass was different. Increase in SOD, APX and POX activities in bacterial inoculated-Zarin, but not Gonbad, under normal conditions suggested that this cultivar may recognize strain C-2012 as a gentle stressor and not as a PGPR. These results showed that the responses of the wheat cultivars to a defined PGPR is different in the physiological, phenotypic and molecular level. Based on the results, the evaluation of the effect of a bio-fertilizer on each wheat cultivar is necessary prior to use in a commercial field.

Genome-wide identification and transcriptional expression analysis of superoxide dismutase (SOD) family in wheat (Triticum aestivum)

Superoxide dismutases (SODs) are a family of key antioxidant enzymes that play a crucial role in plant growth and development. Previously, this gene family has been investigated in Arabidopsis and rice. In the present study, a genome-wide analysis of the SOD gene family in wheat were performed. Twenty-six SOD genes were identified from the whole genome of wheat, including 17 Cu/Zn-SODs, six Fe-SODs, and three Mn-SODs. The chromosomal location mapping analysis indicated that these three types of SOD genes were only distributed on 2, 4, and 7 chromosomes, respectively. Phylogenetic analyses of wheat SODs and several other species revealed that these SOD proteins can be assigned to two major categories. SOD1 mainly comprises of Cu/Zn-SODs, and SOD2 mainly comprises of Fe-SODs and Mn-SODs. Gene structure and motif analyses indicated that most of the SOD genes showed a relatively conserved exon/intron arrangement and motif composition. Analyses of transcriptional data indicated that most of the wheat SOD genes were expressed in almost all of the examined tissues and had important functions in abiotic stress resistance. Finally, quantitative real-time polymerase chain reaction (qRT-PCR) analysis was used to reveal the regulating roles of wheat SOD gene family in response to NaCl, mannitol, and polyethylene glycol stresses. qRT-PCR showed that eight randomly selected genes with relatively high expression levels responded to all three stresses based on released transcriptome data. However, their degree of response and response patterns were different. Interestingly, among these genes, TaSOD1.7, TaSOD1.9, TaSOD2.1, and TaSOD2.3 feature research value owing to their remarkable expression-fold change in leaves or roots under different stresses. Overall, our results provide a basis of further functional research on the SOD gene family in wheat and facilitate their potential use for applications in the genetic improvement on wheat in drought and salt stress environments.

Microbiological Insights into the Stress-Alleviating Property of an Endophytic Bacillus altitudinis WR10 in Wheat under Low-Phosphorus and High-Salinity Stresses

An indole-3-acetic acid producing Bacillus altitudinis WR10 was previously isolated from the root of wheat (Triticum aestivum L.). In this study, the strain WR10 was used for relieving abiotic stresses in wheat under low phosphorus and high saline in hydroponic co-culture models. Significantly, strain WR10 improved wheat seed relative germination rate under salinity stress (200/400 mM NaCl) and the root dry weight in wheat seedlings under phosphorus stress (10 μM KH2PO3) when insoluble phosphates are available. To provide insights into its abiotic stress-alleviating properties, the strain was characterized further. WR10 grows well under different culture conditions. Particularly, WR10 resists salt (12% NaCl) and hydrolyzes both inorganic and organic insoluble phosphates. WR10 uses many plant-derived substrates as sole carbon and energy sources. It produces catalase, amylase, phosphatase, phytase, reductase, and 1-aminocyclopropane-1-carboxylate (ACC) deaminase. In addition, WR10 possesses long peritrichous flagella, and its biofilm formation, as well as phytase production, is induced by abiotic stresses. Overall, the salinity-alleviating property of WR10 in wheat can be attributed to its inherent tolerance to NaCl, formation of biofilm, and production of enzymes, like catalase, amylase, and ACC deaminase. Meanwhile, B. altitudinis WR10 reduces low-phosphorus stress in wheat by production of phosphatases and phytases in the presence of insoluble phosphates.

Alleviation of the effect of salinity on growth and yield of strawberry by foliar spray of selenium-nanoparticles

The present study investigated the beneficial role of selenium-nanoparticles (Se-NPs) in mitigating the adverse effects of soil-salinity on growth and yield of strawberry (Fragaria × ananassa Duch.) plants by maneuvering physiological and biochemical mechanisms. The foliar spray of Se-NPs (10 and 20 mg L^-1) improved the growth and yield parameters of strawberry plants grown on non-saline and different saline soils (0, 25, 50 and 75 mM NaCl), which was attributed to their ability to protect photosynthetic pigments. Se-NPs-treated strawberry plants exhibited higher levels of key osmolytes, including total soluble carbohydrates and free proline, compared with untreated plants under saline conditions. Foliar application of Se-NPs improved salinity tolerance in strawberry by reducing stress-induced lipid peroxidation and H₂O₂ content through enhancing activities of antioxidant enzymes like superoxide dismutase and peroxidase. Additionally, Se-NPs-treated strawberry plants showed accumulation of indole-3-acetic acid and abscisic acid, the vital stress signaling molecules, which are involved in regulating different morphological, physiological and molecular responses of plants to salinity. Moreover, the enhanced levels of organic acids (e.g., malic, citric and succinic acids) and sugars (e.g., glucose, fructose and sucrose) in the fruits of Se-NPs-treated strawberry plants under saline conditions indicated the positive impacts of Se-NPs on the improvement of fruit quality and nutritional values. Our results collectively demonstrate the definite roles of Se-NPs in management of soil salinity-induced adverse effects on not only strawberry plants but also other crops.

The Roles of Environmental Factors in Regulation of Oxidative Stress in Plant

Exposure to a variety of environmental factors such as salinity, drought, metal toxicity, extreme temperature, air pollutants, ultraviolet-B (UV-B) radiation, pesticides, and pathogen infection leads to subject oxidative stress in plants, which in turn affects multiple biological processes via reactive oxygen species (ROS) generation. ROS include hydroxyl radicals, singlet oxygen, and hydrogen peroxide in the plant cells and activates signaling pathways leading to some changes of physiological, biochemical, and molecular mechanisms in cellular metabolism. Excessive ROS, however, cause oxidative stress, a state of imbalance between the production of ROS and the neutralization of free radicals by antioxidants, resulting in damage of cellular components including lipids, nucleic acids, metabolites, and proteins, which finally leads to the death of cells in plants. Thus, maintaining a physiological level of ROS is crucial for aerobic organisms, which relies on the combined operation of enzymatic and nonenzymatic antioxidants. In order to improve plants' tolerance towards the harsh environment, it is vital to reinforce the comprehension of oxidative stress and antioxidant systems. In this review, recent findings on the metabolism of ROS as well as the antioxidative defense machinery are briefly updated. The latest findings on differential regulation of antioxidants at multiple levels under adverse environment are also discussed here.

Potential for Heightened Sulfur-Metabolic Capacity in Coastal Subtropical Microalgae

The activities of microalgae support nutrient cycling that helps to sustain aquatic and terrestrial ecosystems. Most microalgal species, especially those from the subtropics, are genomically uncharacterized. Here we report the isolation and genomic characterization of 22 microalgal species from subtropical coastal regions belonging to multiple clades and three from temperate areas. Halotolerant strains including Halamphora, Dunaliella, Nannochloris, and Chloroidium comprised the majority of these isolates. The subtropical-based microalgae contained arrays of methyltransferase, pyridine nucleotide-disulfide oxidoreductase, abhydrolase, cystathionine synthase, and small-molecule transporter domains present at high relative abundance. We found that genes for sulfate transport, sulfotransferase, and glutathione S-transferase activities were especially abundant in subtropical, coastal microalgal species and halophytic species in general. Our metabolomics analyses indicate lineage- and habitat-specific sets of biomolecules implicated in niche-specific biological processes. This work effectively expands the collection of available microalgal genomes by ∼50%, and the generated resources provide perspectives for studying halophyte adaptive traits.

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We have sequenced 20+ microallgal genomes from the subtropics

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This new collection increases the available microalgal genomes by ∼50%

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Metabolomics indicates lineage- and habitat-specificity of biomolecules

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Coastal, subtropical species of microalgae show expansion of sulfur-metabolic genes

Insight into salt tolerance mechanisms of the halophyte Achras sapota: an important fruit tree for agriculture in coastal areas

Sapota (Achras sapota), a fruit tree with nutritional and medicinal properties, is known to thrive in salt-affected areas. However, the underlying mechanisms that allow sapota to adapt to saline environment are yet to be explored. Here, we examined various morphological, physiological, and biochemical features of sapota under a gradient of seawater (0, 4, 8, and 12 dS m^-1) to study its adaptive responses against salinity. Our results showed that seawater-induced salinity negatively impacted on growth-related attributes, such as plant height, root length, leaf area, and dry biomass in a dose-dependent manner. This growth reduction was positively correlated with reductions in relative water content, stomatal conductance, xylem exudation rate, and chlorophyll, carbohydrate, and protein contents. However, the salt tolerance index did not decline in proportional to the increasing doses of seawater, indicating a salt tolerance capacity of sapota. Under salt stress, ion analysis revealed that Na⁺ mainly retained in roots, whereas K⁺ and Ca²⁺ were more highly accumulated in leaves than in roots, suggesting a potential mechanism in restricting transport of excessive Na⁺ to leaves to facilitate the uptake of other essential minerals. Sapota plants also maintained an improved leaf succulence with increasing levels of seawater. Furthermore, increased accumulations of proline, total amino acids, soluble sugars, and reducing sugars suggested an enhanced osmoprotective capacity of sapota to overcome salinity-induced osmotic stress. Our results demonstrate that the salt adaptation strategy of sapota is attributed to increased leaf succulence, selective transport of minerals, efficient Na⁺ retention in roots, and accumulation of compatible solutes.

Anthocyanins of Coloured Wheat Genotypes in Specific Response to SalStress

The present study investigated the effect of salt stress on the development of adaptive responses and growth parameters of different coloured wheat genotypes. The different coloured wheat genotypes have revealed variation in the anthocyanin content, which may affect the development of adaptive responses under increasing salinity stress. In the early stage of treatment with salt at a lower NaCl concentration (100 mM), anthocyanins and proline accumulate, which shows rapid development of the stress reaction. A dose-dependent increase in flavonol content was observed for wheat genotypes with more intense purple-blue pigmentation after treatment with 150 mM and 200 mM NaCl. The content of Na⁺ and K⁺ obtained at different levels of salinity based on dry weight (DW) was more than 3 times greater than the control, with a significant increase of both ions under salt stress. Overall, our results demonstrated that coloured wheat genotypes with high anthocyanin content are able to maintain significantly higher dry matter production after salt stress treatment.

Exogenous nanosilica improves germination and growth of cucumber by maintaining K+/Na+ ratio under elevated Na+ stress

The current work was aimed to elucidate the role of engineered nanosilica (SiNPs) particles to mitigate the damaging impacts of Na⁺-derived salinity on cucumber (Cucumis sativus) Beit Alpha variety by conducting in vitro experiments applying various Na⁺ concentrations i.e. 0, 1000, 2000, 3000, 4000 and 5000 mg L^-1. By treating seeds and seedlings, respectively, of cucumber with SiNPs (0, 100, 200 and 300 ppm) and subsequent determination some germination and vegetative parameters as well as chemical analysis of seedlings, we verified that SiNPs succeeded to alleviate the detrimental effects of high Na⁺ salinity by increasing germination parameters and vegetative growth of cucumber seedlings. Even as little as 100 ppm of N-Si results in considerable improvement of seed germination and seedlings growth of cucumber compared to the control, while 200 ppm was optimal among the doses tested. At 5000 mg Na⁺ L^-1, applying SiNPs with 200 ppm increased final germination percentage by 101% over control, vigor index by 101%, germination rate index by 116%, germination index by 110%, fresh mass by 13%, K⁺/Na⁺ ratio by 77%, shoot dry mass by 384%, root dry mass by 304% and plant height by 70%. The results mentioned in this paper obviously outline the large practical relevance of SiNPs and imply that applying of SiNPs for cucumber seeds and seedlings under high Na⁺-derived salinity enhances germination and growth as a result for decreasing Na⁺ uptake and sequentially improves high K⁺/Na⁺ ratio.

Sargassum muticum and Jania rubens regulate amino acid metabolism to improve growth and alleviate salinity in chickpea

The present study evaluates the potential of Sar gassum muticum (Sar) and Jan ia rubens (Jan) seaweeds for enhancing growth and mitigating soil-salinity in chickpea (Cicer arietinum L.). Under control conditions, Sar and Jan extracts improved chickpea growth which was attributed to their potential for increasing photosynthetic pigments, K⁺ and amino acids, particularly proline, in comparison with water-sprayed control. Upon stress imposition, chickpea growth was reduced in NaCl concentration-dependent manner, and principal component analysis (PCA) revealed Na⁺ accumulation and oxidative damage as major determinants of sensitivity at high salinity. Furthermore, amino acid quantification indicated activation/deactivation of overall metabolism in roots/shoots, as an adaptive strategy, for maintaining plant growth under salt stress. Sar and Jan extract supplementations provided stress amelioration, and PCA confirmed that improved growth parameters at high salinity were associated with enhanced activities of superoxide dismutase and peroxidase. Besides, four key amino acids, including serine, threonine, proline and aspartic acids, were identified from roots which maximally contribute to Sar- and Jan-mediated stress amelioration. Sar showed higher effectiveness than Jan under both control and salt stress conditions. Our findings highlight "bio-stimulant" properties of two seaweeds and provide mechanistic insight into their salt-ameliorating action which is relevant for both basic and applied research.

PtrA/NINV, an alkaline/neutral invertase gene of Poncirus trifoliata, confers enhanced tolerance to multiple abiotic stresses by modulating ROS levels and maintaining photosynthetic efficiency

BACKGROUND

Alkaline/neutral invertase (A/N-INV), an enzyme that hydrolyzes sucrose irreversibly into glucose and fructose, is essential for normal plant growth,development, and stress tolerance. However, the physiological and/or molecular mechanism underpinning the role of A/N-INV in abiotic stress tolerance is poorly understood.

RESULTS

In this report, an A/N-INV gene (PtrA/NINV) was isolated from Poncirus trifoliata, a cold-hardy relative of citrus, and functionally characterized. PtrA/NINV expression levels were induced by cold, salt, dehydration, sucrose, and ABA, but decreased by glucose. PtrA/NINV was found to localize in both chloroplasts and mitochondria. Overexpression of PtrA/NINV conferred enhanced tolerance to multiple stresses, including cold, high salinity, and drought, as supported by lower levels of reactive oxygen species (ROS), reduced oxidative damages, decreased water loss rate, and increased photosynthesis efficiency, relative to wild-type (WT). The transgenic plants exhibited higher A/N-INV activity and greater reducing sugar content under normal and stress conditions.

CONCLUSIONS

PtrA/NINV is an important gene implicated in sucrose decomposition, and plays a positive role in abiotic stress tolerance by promoting osmotic adjustment, ROS detoxification and photosynthesis efficiency. Thus, PtrA/NINV has great potential to be used in transgenic breeding for improvement of stress tolerance.