Soil salinity is a severe abiotic stress that damages plant growth and development. As an antioxidant and free radical scavenger, melatonin is well known for helping plants survive abiotic conditions, including salinity stress. Here, we report that the salt-related gene MsSNAT1, encoding a rate-limiting melatonin biosynthesis enzyme, is located in the chloroplast and contributes to salinity stress tolerance in alfalfa. We found that the MsSNAT1 overexpressing alfalfa lines exhibited higher endogenous melatonin levels and increased tolerance to salt stress by promoting antioxidant systems and improving ion homeostasis. Furthermore, through a combination of transcriptome sequencing, dual-luciferase assays and transgenic analysis, we identified that the basic leucine zipper (bZIP) transcription factor, MsbZIP55, is associated with salt response and MsSNAT1 expression. EMSA analysis and ChIP-qPCR uncovered that MsbZIP55 can recognize and directly bind to the MsSNAT1 promoter in vitro and in vivo. MsbZIP55 acts as a negative regulator of MsSNAT1 expression, thereby reducing melatonin biosynthesis. Morphological analysis revealed that overexpressing MsbZIP55 conferred salt sensitivity to transgenic alfalfa through a higher Na+/K+ ratio and lower antioxidant activities, which could be alleviated by applying exogenous melatonin. Silencing of MsbZIP55 by RNA interference in alfalfa resulted in higher expression of MsSNAT1 and promoted salt tolerance by enhancing the antioxidant system enzyme activities and ion homeostasis. Our findings indicate that the MsbZIP55-MsSNAT1 module plays a crucial role in regulating melatonin biosynthesis in alfalfa while facilitating protection against salinity stress. These results shed light on the regulatory mechanism of melatonin biosynthesis related to the salinity stress response in alfalfa.

Exploring the saline-adapted species and the mechanisms by which they have evolved in saline conditions would be a feasible way to utilize saline soils. Based on this approach, this study aimed to evaluate the seed germination and seedling responses of the five abundant Asteraceae species to salinity stress and determine the antioxidant and non-antioxidant defense strategies by which these species demonstrated variations in salinity tolerance. Milk thistle (Silybum marianum), blessed thistle (Cnicus benedictus), pot marigold (Calendula officinalis), safflower (Carthamus tinctorius), and cardoon (Cynara cardunculus) were subjected to 0 (control), 50, 100, 150, 200 and 250 Mm NaCl concentrations. Calendula officinalis (CO) showed the highest, Silybum marianum (SM) and Cnicus benedictus (CB) moderate, and Carthamus tinctorius (CT) followed by Cynara cardunculus (CC) the least inhibition of seed germination and seedling growth at all given salinity levels. Each species utilized different antioxidant mechanisms in response to salinity. Peroxidase (POX) was the major antioxidative enzyme in resistance species, CT and CC, while catalase and superoxide dismutase were more pronounced in moderate, SM and CB, and susceptible, CO, species, respectively. Besides, all species accumulate a considerable amount of proline in response to salinity, which was more evident in the 150 and 200 Mm NaCl concentrations. From the results, it can be concluded that CT and CC had superior saline-tolerance capacity compared to other species due to their longer seedling roots, higher POX activity, and proline accumulation associated with reduced cellular damage.

Plants activate physiological responses against salinity stress through hormone signaling pathways such as melatonin (M) and methyl jasmonate (MeJ). These hormones trigger defense responses, but comparing their individual and combined effects under salt stress has not been studied. This research investigates defense responses in tomato plants induced by 100 mu M of M and MeJ, along with their combined application (MeJ+M, 100+100 mu M) under non-stress, threshold (0.9 g NaCl kg-1 soil) and severe (1.8 g NaCl kg-1 soil) salinity conditions. Compared to melatonin, MeJ application caused adverse effects, including chlorophyll degradation (34.2 %), root inhibition (17.2 %), and elevated H2O2 (28.9 %), O2-center dot (33.7 %), and malondialdehyde (14.3 %) in the plant under non-stress conditions. Evaluation of the MeJ+M treatment in non-stress conditions indicated that M prevented MeJ-induced damage. Besides, the optimal potassium uptake and plant growth were obtained in the MeJ+M treatment under non-stress and threshold salinity levels. Phytohormones application increased enzymatic antioxidant activity (superoxide dismutase, catalase, ascorbate peroxidase, and peroxidase), modified the activity of phenylalanine ammonia-lyase and polyphenol oxidase, and consequently boosted non-enzymatic antioxidants (phenolic, flavonoid, and anthocyanin content), resulting in a significant reduction of damage from severe salinity stress. However, due to their almost similar physiological changes induced by MeJ, M, and MeJ+M, these treatments were not superior compared to each other in severe stress. Thus, owing to the disruption of the normal morpho-physiological processes in non-stress conditions by MeJ, M can be considered a safer treatment for practical usage. Additionally, the MeJ+M application can not only optimize antioxidant protection under stress conditions but also stimulate plant growth under non-stress conditions.

Soil salinity results in reduced productivity in field peas, making soil salinity tolerance a critical breeding objective. In this study, four pot experiments were carried out in semi-controlled environments over four consecutive years to assess the contribution of seedling vigour to salinity tolerance at the seedling stage. Split-plot designs were used to assess the effect of salt stress (sodium chloride solution at 16 dSm(-1)) and control conditions. Extensive sets of advanced breeding lines were used in 2018-2020 to assess growth differences in relation to the treatment, with elemental analysis used on a subset of 15 lines in 2021. A salt tolerance index (STI) was defined as a proportion of shoot biomass under salt stress (DWstress) relative to the shoot dry weight under control (DWctrl). Visual scores of salt stress were recorded on a 1-10 scale (1 = tolerant, 10 = susceptible) from salt stress treatments. The consistent positive and significant correlations (p < 0.01) between shoot DWctrl and DWstress indicated that vigorous genotypes maintained higher shoot DWstress. Both the shoot DWctrl and shoot DWstress had negative and significant (p < 0.01) correlations with visual scores of salt stress. Shoot DWstress showed strong positive correlations with STI (p < 0.01). Both the shoot DWctrl and Shoot DWstress had negative correlations (p < 0.01) with shoot Na+ whereas shoot DWstress had a positive correlation (p < 0.05) with root Na+ concentration. The results indicated that seedling vigour (measured as shoot DWctrl) contributed to salinity tolerance by maintaining improved shoot DWstress, limiting Na+ deposition in shoot and enduring less tissue damage in field pea seedlings. Additional field evaluations are required to establish the correlations of tolerance at seedling stage with yield under saline conditions. The insights obtained from this study may assist field pea breeders in identifying salt-tolerant parent plants, offspring, and breeding lines during the initial growth phases.

Hydrangea macrophylla is a shrub endemic to Japan, and inhabits the limited coastal zones in the Izu, Miura and Boso peninsulas, and the Izu and Bonin islands. Even though H. macrophylla is demanded as an important genetic resource for ecological conservation and utilities of landscaping and gardening in salinity-stressed lands, there is still a lack of information regarding its ecology and adaptative response to salinity-stressed coastal environments. This study aimed to understand the ecology and adaptation to salinity stress of H. macrophylla. Thus, we examined distribution, geography, vegetation, morphology, soil characteristics, and cation concentrations of the leaves in the native habitats. Most of the populations were mainly distributed in coastal zones that have sea-salt aerosols triggered by high wind speed and high soil salinity, causing severe damage to other plant species. The cation analysis suggested H. macrophylla adapted to coastal zones by regulating Na+ allocation of leaves and tolerating to high Na+ concentration. Otherwise, we found many populations inhabited inland or semi-coastal areas with mountainous vegetation in Izu islands. They had thinner leaves with weaker glossy, and some individuals developed trichomes which are not originally present in H. macrophylla, suggesting in initial stage of the process of adaptative radiation to mountainous environment. The other individuals grew in oligotrophic environments such as rocky surfaces and volcanic ash scoria, and epiphyte-like individuals inhabited stem surfaces of Cyathea spinulosa, implying these individuals had adaptability to oligotrophic environments. The comprehensive information should help facilitate further studies on ecological conservation and horticultural utilities.

Global climate change and the decreasing availability of high-quality water lead to an increase in the salinization of agricultural lands. This rising salinity represents a significant abiotic stressor that detrimentally influences plant physiology and gene expression. Consequently, critical processes such as seed germination, growth, development, and yield are adversely affected. Salinity severely impacts crop yields, given that many crop plants are sensitive to salt stress. Plant growth-promoting microorganisms (PGPMs) in the rhizosphere or the rhizoplane of plants are considered the second genome of plants as they contribute significantly to improving the plant growth and fitness of plants under normal conditions and when plants are under stress such as salinity. PGPMs are crucial in assisting plants to navigate the harsh conditions imposed by salt stress. By enhancing water and nutrient absorption, which is often hampered by high salinity, these microorganisms significantly improve plant resilience. They bolster the plant's defenses by increasing the production of osmoprotectants and antioxidants, mitigating salt-induced damage. Furthermore, PGPMs supply growth-promoting hormones like auxins and gibberellins and reduce levels of the stress hormone ethylene, fostering healthier plant growth. Importantly, they activate genes responsible for maintaining ion balance, a vital aspect of plant survival in saline environments. This review underscores the multifaceted roles of PGPMs in supporting plant life under salt stress, highlighting their value for agriculture in salt-affected areas and their potential impact on global food security.

Plants play a crucial role in soil fixation and enhancement of slope stability, and saline-alkaline stress is one of the main restrictions inhibiting plant growth and development. At present, there is a lack of research on the effects of saline-alkaline composite stress on the mechanical properties of the root system and the erosion resistance of the root-soil complex. In this study, three gradients of saline-alkaline composite stress treatments and a control of saline-free treatment was set up for Oenothera biennis, Perilla frutescens, Echinops sphaerocephalus, and Lychnis fulgens. The plant salt damage rate, osmotic index, antioxidant enzyme activity and plant root morphological indicators were measured. The biomechanical characteristics were determined by stretching tests, the resistance of the plant was measured by a whole-plant vertical uprooting test, and the anti-erosion capacity of the root soil composite was measured by scrubbing test. The results showed that, at 200 mM, the salt damage index and salt damage rate of the four plants, in descending order, were as follows: E. sphaerocephalus < L. fulgens < O. biennis < P. frutescens. Among them, SOD of Perilla frutescens did not play an obvious protective role, and the substantial changes in CAT and POD, as well as the content of soluble sugars, soluble proteins, and proline, showed its sensitivity to saline and alkaline stresses. Root growth was also significantly suppressed in all four plants, the 100- and 200-mM concentrations of saline solution significantly reduced the average tensile strength of O. biennis and P. frutescens, while the saline-alkali solution of 200 mM significantly reduced the elongation of E. sphaerocephalus and L. fulgens, and significantly elevated the soil detachment rate of the root-soil composite for E. sphaerocephalus. Additionally, all three concentrations of saline treatments significantly reduced the pullout resistance of all 4 plants. There was a negative power rate relationship between tensile resistance and root diameter in four plant species, while the relationship between tensile strength and root diameter showed a negative power law only for L. fulgens treated with 0-50 mM saline solution. There was no significant correlation between elongation and root diameter in the four plants. P. frutescens had the greatest tensile resistance and strength, as well as the lowest rate of elongation, while L. fulgens possessed the greatest pullout resistance, and both had comparable resistance to erosion of the root-soil complex. Therefore, compared to the other three plants, L. fulgens is more suitable for soil reinforcement applications on saline slopes.

High soil salinity has an unfavorable consequence on the growth and productivity of rice crop. However, some salt-tolerant plant growth-promoting bacteria (ST-PGPB) regulate specific physiological, biochemical, and molecular properties to promote crop growth while minimizing the detrimental effects of salt stress. In this regard, we isolated ST-PGPB from rhizospheric soil and examined it to mitigate the salinity stress in rice seedlings. The growth of the bacterium at 3 M NaCl demonstrated its halotolerance, and 16S rRNA sequencing identified it as Bacillus siamensis, and the isolated strain was named BW. Further study indicated that biopriming with BW strain helps plant growth promotion-related phenotype and significantly mitigates salinity stress in rice seedlings. Treatment of rice seeds with BW resulted in significantly improved germination of seedlings at 75 mM to 150 mM NaCl, along with better physiology and biochemical parameters than the untreated ones. Furthermore, Bacillus sp. BW efficiently colonizes rice roots and produces auxin and siderophore, via forming biofilm under different salt concentrations. Under 100-200 mM NaCl treatment conditions, the extracellular metabolite profile from BW showed a substantial abundance in specific metabolites, such as osmoprotective chemicals, suggesting the likely protective mechanism against salinity stress damage. This study demonstrates the role and potential of a halotolerant- BW strain in supporting the growth of rice plants under salinity conditions.

Introduction: Soil salinity poses a severe threat to rice production, resulting in stunted growth, leaf damage, and substantial yield losses. This study focuses on developing an early maturing seedling stage salinity tolerant rice variety by integrating conventional breeding methods with marker assisted breeding (MAB) approaches.Methods: Seedling-stage salinity tolerance Quantitative Trait Locus (QTL) Saltol from the salt-tolerant parent FL478 was introduced into the high-yielding but salt-sensitive rice variety ADT 45. This was achieved through a combination of conventional breeding and MAB. The breeding process involved rigorous selection, screening, and physiological parameter assessments.Results: KKL(R) 3 (KR 15066) identified as the top performing Recombinant Inbred Line (RIL), consistently demonstrating maximum mean grain yields under both salinity (3435.6 kg/ha) and normal (6421.8 kg/ha) conditions. In comparison to the early maturing, salt-tolerant national check variety CSR 10, KKL(R) 3 exhibited a substantial yield increase over 50%.Discussion: The notable improvement observed in KKL(R) 3 positions it as a promising variety for release, offering a reliable solution to maximize yields, ensure food security, and promote agricultural sustainability in both saline and non-saline environments. The study highlights the effectiveness of MAB in developing salt-tolerant rice varieties and emphasizes the significance of the Saltol QTL in enhancing seedling stage salinity tolerance. The potential release of KKL(R) 3 has the capacity to revolutionize rice production in salt affected regions, providing farmers with a reliable solution to maximize yields and contribute to food security while ensuring agricultural sustainability.

Oat (Avena nuda L.) is a globally important cereal crop grown for its nutritious grains and is considered as moderately salt-tolerant. Studying salinity tolerant mechanisms of oats could assist breeders in increasing oat production and their economic income in salt-affected areas, as the total amount of saline land in the world is still increasing. The present study was carried out to better understand the salt tolerance mechanism of the naked oat line Bayou1. A soil experiment was conducted on 17 days-old Bayou1 seedlings treated with varying concentrations of NaCl for a period of 12 days. Bayou1 plants grew optimally when treated with 50 mM NaCl, demonstrating their salinity tolerance. Reduced water uptake, decreased Ca2+, Mg2+, K+, and guaiacol peroxidase activity, as well as increased Na+ concentration in leaves, all contributed to a reduction in shoot growth. However, the damage to ionic homeostasis caused by increased Na+ concentrations and decreased K+ concentrations in the roots of Bayou1 did not inhibit its root growth, indicating that the main salt-tolerant mechanism in Bayou1 existed in its roots. Further, a hydroponic experiment found that increasing Na+ concentration in root cell sap enhanced root growth, while maintaining the integrity of root cell membranes. The accumulated Na+ may have facilitated the root growth of Bayou1 exposed to NaCl by effectively adjusting cellular osmotic potential, thereby ensuring root cell turgor and expansion.