Up-regulation of lipid metabolism and glycine betaine synthesis are associated with choline-induced salt tolerance in halophytic seashore paspalum

Integrative analysis of transcriptome and metabolome reveal the differential tolerance mechanisms to low and high salinity in the roots of facultative halophyte Avicennia marina

Mangroves perform a crucial ecological role along the tropical and subtropical coastal intertidal zone where salinity fluctuation occurs frequently. However, the differential responses of mangrove plant at the combined transcriptome and metabolome level to variable salinity are not well documented. In this study, we used Avicennia marina (Forssk.) Vierh., a pioneer species of mangrove wetlands and one of the most salt-tolerant mangroves, to investigate the differential salt tolerance mechanisms under low and high salinity using inductively coupled plasma-mass spectrometry, transcriptomic and metabolomic analysis. The results showed that HAK8 was up-regulated and transported K+ into the roots under low salinity. However, under high salinity, AKT1 and NHX2 were strongly induced, which indicated the transport of K+ and Na+ compartmentalization to maintain ion homeostasis. In addition, A. marina tolerates low salinity by up-regulating ABA signaling pathway and accumulating more mannitol, unsaturated fatty acids, amino acids' and L-ascorbic acid in the roots. Under high salinity, A. marina undergoes a more drastic metabolic network rearrangement in the roots, such as more L-ascorbic acid and oxiglutatione were up-regulated, while carbohydrates, lipids and amino acids were down-regulated in the roots, and, finally, glycolysis and TCA cycle were promoted to provide more energy to improve salt tolerance. Our findings suggest that the major salt tolerance traits in A. marina can be attributed to complex regulatory and signaling mechanisms, and show significant differences between low and high salinity.

Lipid remodelling and the conversion of lipids into sugars associated with tolerance to cadmium toxicity during white clover seed germination

Cadmium (Cd) is a leading environmental issue worldwide. The current study was conducted to investigate Cd tolerance of 10 commercial white clover (Trifolium repens) cultivars during seed germination and to further explore differences in lipid remodelling, glycometabolism, and the conversion of lipids into sugars contributing to Cd tolerance in the early phase of seedling establishment as well as the accumulation of Cd in seedlings and mature plants. The results show that Cd stress significantly reduced seed germination of 10 cultivars. Compared to Cd-sensitive Sulky, Cd-tolerant Pixie accelerated amylolysis to produce more glucose, fructose, and sucrose by maintaining higher amylase and sucrase activities under Cd stress. Pixie maintained higher contents of various lipids, higher DGDG/MGDG ratio, and lower unsaturation levels of lipids, which could be beneficial to membrane stability and integrity as well as signal transduction in cells after being subjected to Cd stress. In addition, Pixie upregulated expression levels of key genes (TrACX1, TrACX4, TrSDP6, and TrPCK1) involved in the conversion of lipids into sugars for early seedling establishment under Cd stress. These findings indicate that lipid remodelling, enhanced glycometabolism, and accelerated conversion of lipids into sugars are important adaptive strategies for white clover seed germination and subsequent seedling establishment under Cd stress. In addition, Pixie not only accumulated more Cd in seedlings and mature plants than Sulky but also had significantly better growth and phytoremediation efficiency under Cd stress. Pixie could be used as a suitable and critical germplasm for the rehabilitation and re-establishment of Cd-contaminated areas.

Low-cost and reliable substrate-based phenotyping platform for screening salt tolerance of cutting propagation-dependent grass, paspalum vaginatum

BACKGROUND

Salt tolerance in plants is defined as their ability to grow and complete their life cycle under saline conditions. Staple crops have limited salt tolerance, but forage grass can survive in large unexploited saline areas of costal or desert land. However, due to the restriction of self-incompatible fertilization in many grass species, vegetative propagation via stem cuttings is the dominant practice; this is incompatible with current methodologies of salt-tolerance phenotyping, which have been developed for germination-based seedling growth. Therefore, the performance of seedlings from cuttings under salt stress is still fuzzy. Moreover, the morphological traits involved in salt tolerance are still mostly unknown, especially under experimental conditions with varying levels of stress.

RESULTS

To estimate the salt tolerance of cutting propagation-dependent grasses, a reliable and low-cost workflow was established with multiple saline treatments, using Paspalum vaginatum as the material and substrate as medium, where cold stratification and selection of stem segments were the two variables used to control for experimental errors. Average leaf number (ALN) was designated as the best criterion for evaluating ion-accumulated salt tolerance. The reliability of ALN was revealed by the consistent results among four P. vaginatum genotypes, and three warm-season (pearl millet, sweet sorghum, and wild maize) and four cold-season (barley, oat, rye, and ryegrass) forage cultivars. Dynamic curves simulated by sigmoidal mathematical models were well-depicted for the calculation of the key parameter, Salt50. The reliability of the integrated platform was further validated by screening 48 additional recombinants, which were previously generated from a self-fertile mutant of P. vaginatum. The genotypes displaying extreme ALN-based Salt50 also exhibited variations in biomass and ion content, which not only confirmed the reliability of our phenotyping platform but also the representativeness of the aerial ALN trait for salt tolerance.

CONCLUSIONS

Our phenotyping platform is proved to be compatible with estimations in both germination-based and cutting propagation-dependent seedling tolerance under salt stresses. ALN and its derived parameters are prone to overcome the species barriers when comparing salt tolerance of different species together. The accuracy and reliability of the developed phenotyping platform is expected to benefit breeding programs in saline agriculture.

Metabolomics reveals the phytotoxicity mechanisms of foliar spinach exposed to bulk and nano sizes of PbCO3

PbCO3 is an ancient raw material for Pb minerals and continues to pose potential risks to the environment and human health through mining and industrial processes. However, the specific effects of unintentional PbCO3 discharge on edible plants remain poorly understood. This study unravels how foliar application of PbCO3 induces phytotoxicity by potentially influencing leaf morphology, photosynthetic pigments, oxidative stress, and metabolic pathways related to energy regulation, cell damage, and antioxidant defense in Spinacia oleracea L. Additionally, it quantifies the resultant human health risks. Plants were foliarly exposed to PbCO3 nanoparticles (NPs) and bulk products (BPs), as well as Pb2+ at 0, 5, 10, 25, 50, and 100 mg·L-1 concentrations once a day for three weeks. The presence and localization of PbCO3 NPs inside the plant cells were confirmed by TEM-EDS analysis. The maximum accumulation of total Pb was recorded in the root (2947.77 mg·kg-1 DW for ion exposure), followed by the shoot (942.50 mg·kg-1 DW for NPs exposure). The results revealed that PbCO3 and Pb2+ exposure had size- and dose-dependent inhibitory effects on spinach length, biomass, and photosynthesis attributes, inducing impacts on the antioxidase activity of CAT, membrane permeability, and nutrient elements absorption and translocation. Pb2+ exhibited pronounced toxicity in morphology and chlorophyll; PbCO3 BP exposure accumulated the most lipid peroxidation products of MDA and H2O2; and PbCO3 NPs triggered the largest cell membrane damage. Furthermore, PbCO3 NPs at 10 and 100 mg·L-1 induced dose-dependent metabolic reprogramming in spinach leaves, disturbing the metabolic mechanisms related to amino acids, antioxidant defense, oxidative phosphorylation, fatty acid cycle, and the respiratory chain. The spinach showed a non-carcinogenic health risk hierarchy: Pb2+ > PbCO3 NPs > PbCO3 BPs, with children more vulnerable than adults. These findings enhance our understanding of PbCO3 particle effects on food security, emphasizing the need for further research to minimize their impact on human dietary health.

Metabolomics-mediated elucidation of rice responses to salt stress

MAIN CONCLUSION

Role of salinity responsive metabolites of rice and its wild species has been discussed. Salinity stress is one of the important environmental stresses that severely affects rice productivity. Although, several vital physio-biochemical and molecular responses have been activated in rice under salinity stress which were well described in literatures, the mechanistic role of salt stress and microbes-induced metabolites to overcome salt stress in rice are less studied. Nevertheless, over the years, metabolomic studies have allowed a comprehensive analyses of rice salt stress responses. Hence, we review the salt stress-triggered alterations of various metabolites in rice and discuss their significant roles toward salinity tolerance. Some of the metabolites such as serotonin, salicylic acid, ferulic acid and gentisic acid may act as signaling molecules to activate different downstream salt-tolerance mechanisms; whereas, the other compounds such as amino acids, sugars and organic acids directly act as protective agents to maintain osmotic balance and scavenger of reactive oxygen species during the salinity stress. The quantity, type, tissues specificity and time of accumulation of metabolites induced by salinity stress vary between salt-sensitive and tolerant rice genotypes and thus, contribute to their different degrees of salt tolerance. Moreover, few tolerance metabolites such as allantoin, serotonin and melatonin induce unique pathways for activation of defence mechanisms in salt-tolerant varieties of rice, suggesting their potential roles as the universal biomarkers for salt tolerance. Therefore, these metabolites can be applied exogenously to the sensitive genotypes of rice to enhance their performance under salt stress. Furthermore, the microbes of rhizosphere also participated in rice salt tolerance either directly or indirectly by regulating their metabolic pathways. Thus, this review for the first time offers valuable and comprehensive insights into salt-induced spatio-temporal and genotype-specific metabolites in different genotypes of rice which provide a reference point to analyze stress-gene-metabolite relationships for the biomarker designing in rice. Further, it can also help to decipher several metabolic systems associated with salt tolerance in rice which will be useful in developing salt-tolerance cultivars by conventional breeding/genetic engineering/exogenous application of metabolites.

Strategies of NaCl Tolerance in Saline-Alkali-Tolerant Green Microalga Monoraphidium dybowskii LB50

Studying how freshwater cells modify metabolism and membrane lipids in response to salt stress is important for understanding how freshwater organisms adapt to salt stress and investigating new osmoregulatory ways. Physiological, biochemical, metabolic, and proteomic analyses were applied in a novel saline-alkali-tolerant microalga Monoraphidium dybowskii LB50 under different NaCl concentrations. Cells adopt a variety of strategies to adapt to salt stress, including increasing ion transport and osmolytes, regulating cell cycle and life history, and accumulating triacylglycerol (TAG). A large number of metabolic activities point to TAG accumulation. With increasing NaCl concentration, the C resource for TAG accumulation went from photosynthetically fixed C and a small amount of lipid remodeling to macromolecule degradation and a mass of lipid remodeling, respectively. The energy for TAG accumulation went from linear electron transfer and oxidative phosphate pentose pathway to cyclic electron flow, substrate phosphorylation, oxidation phosphorylation, and FA oxidation. Additionally, digalacturonic acid and amino acids of the N-acetyl group, which usually were the osmotica for marine organisms, were important for M. dybowskii LB50. Freshwater organisms evolved many biological ways to adapt to salt stress. This insight enriches our understanding of the adaptation mechanisms underlying abiotic stress.

Combined transcriptomic and metabolomic analysis of alginate oligosaccharides alleviating salt stress in rice seedlings

BACKGROUND

Salt stress is one of the key factors limiting rice production. Alginate oligosaccharides (AOS) enhance plant stress resistance. However, the molecular mechanism underlying salt tolerance in rice induced by AOS remains unclear. FL478, which is a salt-tolerant indica recombinant inbred line and IR29, a salt-sensitive rice cultivar, were used to comprehensively analyze the effects of AOS sprayed on leaves in terms of transcriptomic and metabolite profiles of rice seedlings under salt stress.

RESULTS

In this experiment, exogenous application of AOS increased SOD, CAT and APX activities, as well as GSH and ASA levels to reduce the damage to leaf membrane, increased rice stem diameter, the number of root tips, aboveground and subterranean biomass, and improved rice salt tolerance. Comparative transcriptomic analyses showed that the regulation of AOS combined with salt treatment induced the differential expression of 305 and 1030 genes in FL478 and IR29. The expressed genes enriched in KEGG pathway analysis were associated with antioxidant levels, photosynthesis, cell wall synthesis, and signal transduction. The genes associated with light-trapping proteins and RLCK receptor cytoplasmic kinases, including CBA, LHCB, and Lhcp genes, were fregulated in response to salt stress. Treatment with AOS combined with salt induced the differential expression of 22 and 50 metabolites in FL478 and IR29. These metabolites were mainly related to the metabolism of amino and nucleotide sugars, tryptophan, histidine, and β -alanine. The abundance of metabolites associated with antioxidant activity, such as 6-hydroxymelatonin, wedelolactone and L-histidine increased significantly. Combined transcriptomic and metabolomic analyses revealed that dehydroascorbic acid in the glutathione and ascorbic acid cycles plays a vital role in salt tolerance mediated by AOS.

CONCLUSION

AOS activate signal transduction, regulate photosynthesis, cell wall formation, and multiple antioxidant pathways in response to salt stress. This study provides a molecular basis for the alleviation of salt stress-induced damage by AOS in rice.

Physiological and lipidomic response of exogenous choline chloride alleviating salt stress injury in Kentucky bluegrass (Poa pratensis)

Introduction

Choline participates in plant stress tolerance through glycine betaine (GB) and phospholipid metabolism. As a salt-sensitive turfgrass species, Kentucky bluegrass (Poa pratensis) is the main turfgrass species in cool-season areas.

Methods

To improve salinity tolerance and investigate the effects of choline on the physiological and lipidomic responses of turfgrass plants under salinity stress conditions, exogenous choline chloride was applied to Kentucky bluegrass exposed to salt stress.

Results

From physiological indicators, exogenous choline chloride could alleviate salt stress injury in Kentucky bluegrass. Lipid analysis showed that exogenous choline chloride under salt-stress conditions remodeled the content of phospholipids, glycolipids, and lysophospholipids. Monogalactosyl diacylglycerol, digalactosyl diacylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and lysophosphatidylcholine content were increased and phosphatidic acid content were decreased in plants after exogenous choline chloride under salt treatment. Plant leaf choline content increased, but GB was not detected in exogenous choline chloride treatment plants under nonstress or salt-stress conditions.

Discussion

GB synthesis pathway related genes showed no clear change to choline chloride treatment, whereas cytidyldiphosphate-choline (CDP-choline) pathway genes were upregulated by choline chloride treatment. These results reveal that lipid remodeling through choline metabolism plays an important role in the salt tolerance mechanism of Kentucky bluegrass. Furthermore, the lipids selected in this study could serve as biomarkers for further improvement of salt-sensitive grass species.

Lipid metabolism and antioxidant system contribute to salinity tolerance in halophytic grass seashore paspalum in a tissue-specific manner

Soil salinization is a growing issue that limits agriculture globally. Understanding the mechanism underlying salt tolerance in halophytic grasses can provide new insights into engineering plant salinity tolerance in glycophytic plants. Seashore paspalum (Paspalum vaginatum Sw.) is a halophytic turfgrass and genomic model system for salt tolerance research in cereals and other grasses. However, the salt tolerance mechanism of this grass largely unknown. To explore the correlation between Na⁺ accumulation and salt tolerance in different tissues, we utilized two P. vaginatum accessions that exhibit contrasting tolerance to salinity. To accomplish this, we employed various analytical techniques including ICP-MS-based ion analysis, lipidomic profiling analysis, enzyme assays, and integrated transcriptomic and metabolomic analysis. Under high salinity, salt-tolerant P. vaginatum plants exhibited better growth and Na⁺ uptake compared to salt-sensitive plants. Salt-tolerant plants accumulated heightened Na⁺ accumulation in their roots, leading to increased production of root-sourced H₂O₂, which in turn activated the antioxidant systems. In salt-tolerant plants, metabolome profiling revealed tissue-specific metabolic changes, with increased amino acids, phenolic acids, and polyols in roots, and increased amino acids, flavonoids, and alkaloids in leaves. High salinity induced lipidome adaptation in roots, enhancing lipid metabolism in salt-tolerant plants. Moreover, through integrated analysis, the importance of amino acid metabolism in conferring salt tolerance was highlighted. This study significantly enhances our current understanding of salt-tolerant mechanisms in halophyte grass, thereby offering valuable insights for breeding and genetically engineering salt tolerance in glycophytic plants.

A Culturomics-Based Bacterial Synthetic Community for Improving Resilience towards Arsenic and Heavy Metals in the Nutraceutical Plant Mesembryanthemum crystallinum

Plant-growth-promoting bacteria (PGPB) help plants thrive in polluted environments and increase crops yield using fewer inputs. Therefore, the design of tailored biofertilizers is of the utmost importance. The purpose of this work was to test two different bacterial synthetic communities (SynComs) from the microbiome of Mesembryanthemum crystallinum, a moderate halophyte with cosmetic, pharmaceutical, and nutraceutical applications. The SynComs were composed of specific metal-resistant plant-growth-promoting rhizobacteria and endophytes. In addition, the possibility of modulating the accumulation of nutraceutical substances by the synergetic effect of metal stress and inoculation with selected bacteria was tested. One of the SynComs was isolated on standard tryptone soy agar (TSA), whereas the other was isolated following a culturomics approach. For that, a culture medium based on M. crystallinum biomass, called Mesem Agar (MA), was elaborated. Bacteria of three compartments (rhizosphere soil, root endophytes, and shoot endophytes) were isolated on standard TSA and MA media, stablishing two independent collections. All bacteria were tested for PGP properties, secreted enzymatic activities, and resistance towards As, Cd, Cu, and Zn. The three best bacteria from each collection were selected in order to produce two different consortiums (denominated TSA- and MA-SynComs, respectively), whose effect on plant growth and physiology, metal accumulation, and metabolomics was evaluated. Both SynComs, particularly MA, improved plant growth and physiological parameters under stress by a mixture of As, Cd, Cu, and Zn. Regarding metal accumulation, the concentrations of all metals/metalloids in plant tissues were below the threshold for plant metal toxicity, indicating that this plant is able to thrive in polluted soils when assisted by metal/metalloid-resistant SynComs and could be safely used for pharmaceutical purposes. Initial metabolomics analyses depict changes in plant metabolome upon exposure to metal stress and inoculation, suggesting the possibility of modulating the concentration of high-value metabolites. In addition, the usefulness of both SynComs was tested in a crop plant, namely Medicago sativa (alfalfa). The results demonstrate the effectiveness of these biofertilizers in alfalfa, improving plant growth, physiology, and metal accumulation.

A Trifolium repens flavodoxin-like quinone reductase 1 (TrFQR1) improves plant adaptability to high temperature associated with oxidative homeostasis and lipids remodeling

Maintenance of stable mitochondrial respiratory chains could enhance adaptability to high temperature, but the potential mechanism was not elucidated clearly in plants. In this study, we identified and isolated a TrFQR1 gene encoding the flavodoxin-like quinone reductase 1 (TrFQR1) located in mitochondria of leguminous white clover (Trifolium repens). Phylogenetic analysis indicated that amino acid sequences of FQR1 in various plant species showed a high degree of similarities. Ectopic expression of TrFQR1 protected yeast (Saccharomyces cerevisiae) from heat damage and toxic levels of benzoquinone, phenanthraquinone and hydroquinone. Transgenic Arabidopsis thaliana and white clover overexpressing TrFQR1 exhibited significantly lower oxidative damage and better photosynthetic capacity and growth than wild-type in response to high-temperature stress, whereas AtFQR1-RNAi A. thaliana showed more severe oxidative damage and growth retardation under heat stress. TrFQR1-transgenic white clover also maintained better respiratory electron transport chain than wild-type plants, as manifested by significantly higher mitochondrial complex II and III activities, alternative oxidase activity, NAD(P)H content, and coenzyme Q10 content in response to heat stress. In addition, overexpression of TrFQR1 enhanced the accumulation of lipids including phosphatidylglycerol, monogalactosyl diacylglycerol, sulfoquinovosyl diacylglycerol and cardiolipin as important compositions of bilayers involved in dynamic membrane assembly in mitochondria or chloroplasts positively associated with heat tolerance. TrFQR1-transgenic white clover also exhibited higher lipids saturation level and phosphatidylcholine:phosphatidylethanolamine ratio, which could be beneficial to membrane stability and integrity during a prolonged period of heat stress. The current study proves that TrFQR1 is essential for heat tolerance associated with mitochondrial respiratory chain, cellular reactive oxygen species homeostasis, and lipids remodeling in plants. TrFQR1 could be selected as a key candidate marker gene to screen heat-tolerant genotypes or develop heat-tolerant crops via molecular-based breeding.

Microbiome-metabolome analysis directed isolation of rhizobacteria capable of enhancing salt tolerance of Sea Rice 86

Soil salinization has been recognized as one of the main factors causing the decrease of cultivated land area and global plant productivity. Application of salt tolerant plants and improvement of plant salt tolerance are recognized as the major routes for saline soil restoration and utilization. Sea rice 86 (SR86) is known as a rice cultivar capable of growing in saline soil. Genome sequencing and transcriptome analysis of SR86 have been conducted to explore its salt tolerance mechanisms while the contribution of rhizobacteria is underexplored. In the present study, we examined the rhizosphere bacterial diversity and soil metabolome of SR86 seedlings under different salinity to understand their contribution to plant salt tolerance. We found that salt stress could significantly change rhizobacterial diversity and rhizosphere metabolites. Keystone taxa were identified via co-occurrence analysis and the correlation analysis between keystone taxa and rhizosphere metabolites indicated lipids and their derivatives might play an important role in plant salt tolerance. Further, four plant growth promoting rhizobacteria (PGPR), capable of promoting the salt tolerance of SR86, were isolated and characterized. These findings might provide novel insights into the mechanisms of plant salt tolerance mediated by plant-microbe interaction, and promote the isolation and application of PGPR in the restoration and utilization of saline soil.

Plant hormones and neurotransmitter interactions mediate antioxidant defenses under induced oxidative stress in plants

Due to global climate change, abiotic stresses are affecting plant growth, productivity, and the quality of cultivated crops. Stressful conditions disrupt physiological activities and suppress defensive mechanisms, resulting in stress-sensitive plants. Consequently, plants implement various endogenous strategies, including plant hormone biosynthesis (e.g., abscisic acid, jasmonic acid, salicylic acid, brassinosteroids, indole-3-acetic acid, cytokinins, ethylene, gibberellic acid, and strigolactones) to withstand stress conditions. Combined or single abiotic stress disrupts the normal transportation of solutes, causes electron leakage, and triggers reactive oxygen species (ROS) production, creating oxidative stress in plants. Several enzymatic and non-enzymatic defense systems marshal a plant's antioxidant defenses. While stress responses and the protective role of the antioxidant defense system have been well-documented in recent investigations, the interrelationships among plant hormones, plant neurotransmitters (NTs, such as serotonin, melatonin, dopamine, acetylcholine, and γ-aminobutyric acid), and antioxidant defenses are not well explained. Thus, this review discusses recent advances in plant hormones, transgenic and metabolic developments, and the potential interaction of plant hormones with NTs in plant stress response and tolerance mechanisms. Furthermore, we discuss current challenges and future directions (transgenic breeding and genome editing) for metabolic improvement in plants using modern molecular tools. The interaction of plant hormones and NTs involved in regulating antioxidant defense systems, molecular hormone networks, and abiotic-induced oxidative stress tolerance in plants are also discussed.

Enhanced Adaptability to Limited Water Supply Regulated by Diethyl Aminoethyl Hexanoate (DA-6) Associated With Lipidomic Reprogramming in Two White Clover Genotypes

Membrane lipid reprogramming is one of the most important adaptive strategies in plant species under unfavorable environmental circumstances. Therefore, the present experiment was conducted to elucidate the effect of diethyl aminoethyl hexanoate (DA-6), a novel synthetic plant growth regulator, on oxidative damage, photosynthetic performance, changes in lipidomic profile, and unsaturation index of lipids in two white clover (Trifolium repens) cultivars (drought-sensitive "Ladino" and drought-resistant "Riverdel") under PEG-6000-induced water-deficit stress. Results revealed that water-deficit stress significantly enhanced oxidative damage and decreased photosynthetic functions in both cultivars. However, the damage was less in Riverdel. In addition, water-deficit stress significantly decreased the relative content of monogalactocyl-diacylglycerols (MGDG), sulfoquinovosyl-diacylglycerols (SQDG), phosphatidic acisd (PA), phosphatidyl-ethanolamines (PE), phosphatidyl-glycerols (PG), phosphatidyl-serines (PS), ceramides (Cer), hexosylmonoceramides (Hex1Cer), sphingomyelins (SM), and sphingosines (Sph) in both cultivars, but a more pronounced decline was observed in Ladino. Exogenous application of DA-6 significantly increased the relative content of digalactocyl-diacylglycerols (DGDG), monogalactocyl-diacylglycerolsabstra (MGDG), sulfoquinovosyl-diacylglycerols (SQDG), phosphatidic acids (PA), phosphatidyl-ethanolamines (PE), phosphatidyl-glycerols (PG), phosphatidyl-inositols (PI), phosphatidyl-serines (PS), ceramides (Cer), hexosylmonoceramides (Hex1Cer), neutral glycosphingolipids (CerG2GNAc1), and sphingosines (Sph) in the two cultivars under water-deficit stress. DA-6-treated Riverdel exhibited a significantly higher DGDG:MGDG ratio and relative content of sphingomyelins (SM) than untreated plants in response to water deficiency. Furthermore, the DA-6-pretreated plants increased the unsaturation index of phosphatidic acids (PA) and phosphatidylinositols (PI) in Ladino, ceramides (Cer) and hexosylmonoceramides (Hex1Cer) in Riverdel, and sulfoquinovosyl-diacylglycerols (SQDG) in both cultivars under water stress. These results suggested that DA-6 regulated drought resistance in white clover could be associated with increased lipid content and reprogramming, higher DGDG:MGDG ratio, and improved unsaturation index of lipids, contributing to enhanced membrane stability, integrity, fluidity, and downstream signaling transduction.

Comprehensive Transcriptome Analysis Uncovers Distinct Expression Patterns Associated with Early Salinity Stress in Annual Ryegrass (Lolium Multiflorum L.)

Soil salination is likely to reduce crop production worldwide. Annual ryegrass (Lolium multiflorum L.) is one of the most important forages cultivated in temperate and subtropical regions. We performed a time-course comparative transcriptome for salinity-sensitive (SS) and salinity-insensitive (SI) genotypes of the annual ryegrass at six intervals post-stress to describe the transcriptional changes and identify the core genes involved in the early responses to salt stress. Our study generated 215.18 Gb of clean data and identified 7642 DEGs in six pairwise comparisons between the SS and SI genotypes of annual ryegrass. Function enrichment of the DEGs indicated that the differences in lipid, vitamins, and carbohydrate metabolism are responsible for variation in salt tolerance of the SS and SI genotypes. Stage-specific profiles revealed novel regulation mechanisms in salinity stress sensing, phytohormones signaling transduction, and transcriptional regulation of the early salinity responses. High-affinity K+ (HAKs) and high-affinity K1 transporter (HKT1) play different roles in the ionic homeostasis of the two genotypes. Moreover, our results also revealed that transcription factors (TFs), such as WRKYs, ERFs, and MYBs, may have different functions during the early signaling sensing of salt stress, such as WRKYs, ERFs, and MYBs. Generally, our study provides insights into the mechanisms of the early salinity response in the annual ryegrass and accelerates the breeding of salt-tolerant forage.

Effects of Organic Biostimulants Added with Zeolite on Zucchini Squash Plants Infected by Tomato Leaf Curl New Delhi Virus

The use of organic substances in integrated pest management can contribute to human- and environment-safe crop production. In the present work, a combination of organic biostimulants (Fullcrhum Alert and BioVeg 500) and an inorganic corroborant (Clinogold, zeolite) was tested for the effects on the plant response to the quarantine pest tomato leaf curl New Delhi virus (ToLCNDV). Biostimulants were applied to healthy and infected greenhouse-grown zucchini plants, and the vegetative parameters and viral titer were evaluated. Although no antiviral effects were observed in terms of both virus replication and symptom expression, these biostimulants were shown to influence plant fitness. A significant increase in biomass and in leaf, flower, and fruit production was induced in both healthy and infected plants. Biostimulants also enhanced the production of metabolites commonly involved in plant response to virus infection, such as carbohydrates, phenylpropanoids and free amino acids. These results encourage new field trials to evaluate the actual productivity of infected plants after treatments and the possible application of organic biostimulants in agriculture.

Defining key metabolic roles in osmotic adjustment and ROS homeostasis in the recretohalophyte Karelinia caspia under salt stress

The recretohalophyte Karelinia caspia is of forage and medical value and can remediate saline soils. We here assess the contribution of primary/secondary metabolism to osmotic adjustment and ROS homeostasis in Karelinia caspia under salt stress using multi-omic approaches. Computerized phenomic assessments, tests for cellular osmotic changes and lipid peroxidation indicated that salt treatment had no detectable physical effect on K. caspia. Metabolomic analysis indicated that amino acids, saccharides, organic acids, polyamine, phenolic acids, and vitamins accumulated significantly with salt treatment. Transcriptomic assessment identified differentially expressed genes closely linked to the changes in above primary/secondary metabolites under salt stress. In particular, shifts in carbohydrate metabolism (TCA cycle, starch and sucrose metabolism, glycolysis) as well as arginine and proline metabolism were observed to maintain a low osmotic potential. Chlorogenic acid/vitamin E biosynthesis was also enhanced, which would aid in ROS scavenging in the response of K. caspia to salt. Overall, our findings define key changes in primary/secondary metabolism that are coordinated to modulate the osmotic balance and ROS homeostasis to contribute to the salt tolerance of K. caspia.

Phospholipids in Salt Stress Response

High salinity threatens crop production by harming plants and interfering with their development. Plant cells respond to salt stress in various ways, all of which involve multiple components such as proteins, peptides, lipids, sugars, and phytohormones. Phospholipids, important components of bio-membranes, are small amphoteric molecular compounds. These have attracted significant attention in recent years due to the regulatory effect they have on cellular activity. Over the past few decades, genetic and biochemical analyses have partly revealed that phospholipids regulate salt stress response by participating in salt stress signal transduction. In this review, we summarize the generation and metabolism of phospholipid phosphatidic acid (PA), phosphoinositides (PIs), phosphatidylserine (PS), phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylglycerol (PG), as well as the regulatory role each phospholipid plays in the salt stress response. We also discuss the possible regulatory role based on how they act during other cellular activities.

Integration of environmental metabolomics and physiological approach for evaluation of saline pollution to rice plant

Salinisation of soil is associated with urban pollution, industrial development and rising sea level. Understanding how high salinity is managed at the plant cellular level is vital to increase sustainable farming output. Previous studies focus on plant stress responses under salinity tolerance. Yet, there is limited knowledge about the mechanisms involved from stress state until the recovery state; our research aims to close this gap. By using the most tolerance genotype (SS1-14) and the most susceptible genotype (SS2-18), comparative physiological, metabolome and post-harvest assessments were performed to identify the underlying mechanisms for salinity stress recovery in plant cells. The up-regulation of glutamine, asparagine and malonic acid were found in recovered-tolerant genotype, suggesting a role in the regulation of panicle branching and spikelet formation for survival. Rice could survive up to 150 mM NaCl (∼15 ds/m) with declined of production rate 5-20% ranged from tolerance to susceptible genotype. This show that rice farming may still be viable on the high saline affected area with the right selection of salt-tolerant species, including glycophytes. The salt recovery biomarkers identified in this study and the adaption underlined could be empowered to address salinity problem in rice field.

Lipidomic metabolism associated with acetic acid priming-induced salt tolerance in Carex rigescens

Acetic acid priming may mitigate salt stress to plants by modulating lipid metabolism. Carex rigescens is a stress-tolerant turfgrass species with a widespread distribution in north China. The objective of this study was to figure out whether modification of lipid profiles, including the contents, compositions and saturation levels of leaf lipids, may contribute to acetic acid modulated salt tolerance in C. rigescens. Plants of C. rigescens were primed with or without acetic acid (30 mM) and subsequently exposed to salt stress (300 mM NaCl) for 15 days. Salt stress affected the physiological performance of C. rigescens, while acetic acid-primed plants showed significantly lower malondialdehyde content, proline content, and electrolyte leakage than non-primed plants under salt stress. Acetic acid priming enhanced the contents of phospholipids and glycolipids involved in membrane stabilization and stress signaling (phosphatidic acid, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, digalactosyl diacylglycerol, monogalactosyl diacylglycerol, and sulfoquinovosyldiacylglycerol), reduced the content of toxic lipid intermediates (free fatty acids) during subsequent exposure to salt stress. Furthermore, expression levels of genes involved in lipid metabolism such as CK and PLDα changed due to acetic acid priming. These results demonstrated that acetic acid priming could enhance salt tolerance of C. rigescens by regulating lipid metabolism. The lipids could be used as biomarkers to select for salt-tolerant grass germplasm.

A Review on Plant Responses to Salt Stress and Their Mechanisms of Salt Resistance

Nowadays, crop insufficiency resulting from soil salinization is threatening the world. On the basis that soil salinization has become a worldwide problem, studying the mechanisms of plant salt tolerance is of great theoretical and practical significance to improve crop yield, to cultivate new salt-tolerant varieties, and to make full use of saline land. Based on previous studies, this paper reviews the damage of salt stress to plants, including suppression of photosynthesis, disturbance of ion homeostasis, and membrane peroxidation. We have also summarized the physiological mechanisms of salt tolerance, including reactive oxygen species (ROS) scavenging and osmotic adjustment. Four main stress-related signaling pathways, salt overly sensitive (SOS) pathway, calcium-dependent protein kinase (CDPK) pathway, mitogen-activated protein kinase (MAPKs) pathway, and abscisic acid (ABA) pathway, are included. We have also enumerated some salt stress-responsive genes that correspond to physiological mechanisms. In the end, we have outlined the present approaches and techniques to improve salt tolerance of plants. All in all, we reviewed those aspects above, in the hope of providing valuable background knowledge for the future cultivation of agricultural and forestry plants.

Choline-Mediated Lipid Reprogramming as a Dominant Salt Tolerance Mechanism in Grass Species Lacking Glycine Betaine

Choline, as a precursor of glycine betaine (GB) and phospholipids, is known to play roles in plant tolerance to salt stress, but the downstream metabolic pathways regulated by choline conferring salt tolerance are still unclear for non-GB-accumulating species. The objectives were to examine how choline affects salt tolerance in a non-GB-accumulating grass species and to determine major metabolic pathways of choline regulating salt tolerance involving GB or lipid metabolism. Kentucky bluegrass (Poa pratensis) plants were subjected to salt stress (100 mM NaCl) with or without foliar application of choline chloride (1 mM) in a growth chamber. Choline or GB alone and the combined application increased leaf photochemical efficiency, relative water content and osmotic adjustment and reduced leaf electrolyte leakage. Choline application had no effects on the endogenous GB content and GB synthesis genes did not show responses to choline under nonstress and salt stress conditions. GB was not detected in Kentucky bluegrass leaves. Lipidomic analysis revealed an increase in the content of monogalactosyl diacylglycerol, phosphatidylcholine and phosphatidylethanolamine and a decrease in the phosphatidic acid content by choline application in plants exposed to salt stress. Choline-mediated lipid reprogramming could function as a dominant salt tolerance mechanism in non-GB-accumulating grass species.

QTL controlling fiber quality traits under salt stress in upland cotton (Gossypium hirsutum L.)

QTL for fiber quality traits under salt stress discerned candidate genes controlling fatty acid metabolism. Salinity stress seriously affects plant growth and limits agricultural productivity of crop plants. To dissect the genetic basis of response to salinity stress, a recombinant inbred line population was developed to compare fiber quality in upland cotton (Gossypium hirsutum L.) under salt stress and normal conditions. Based on three datasets of (1) salt stress, (2) normal growth, and (3) the difference value between salt stress and normal conditions, 51, 70, and 53 QTL were mapped, respectively. Three QTL for fiber length (FL) (qFL-Chr1-1, qFL-Chr5-5, and qFL-Chr24-4) were detected under both salt and normal conditions and explained 4.26%, 9.38%, and 3.87% of average phenotypic variation, respectively. Seven genes within intervals of two stable QTL (qFL-Chr1-1 and qFL-Chr5-5) were highly expressed in lines with extreme long fiber. A total of 35 QTL clusters comprised of 107 QTL were located on 18 chromosomes and exhibited pleiotropic effects. Thereinto, two clusters were responsible for improving five fiber quality traits, and 6 influenced FL and fiber strength (FS). The QTL with positive effect for fiber length exhibited active effects on fatty acid synthesis and elongation, but the ones with negative effect played passive roles on fatty acid degradation under salt stress.