Individual or successiveseed priming with nitric oxide and calcium toward enhancing salt tolerance of wheat crop through early ROS detoxification and activation of antioxidant defense.

Despite the considerable efforts reported so far to enhance seed priming, novel ideas are still needed to be suggested to this sustainable sector of agri-seed industry. This could be the first study addressing the effect of nitric oxide (NO) under open field conditions. The impacts of seed redox-priming using sodium nitroprusside (SNP) and osmo-priming with calcium chloride (CaCl2), both applied individually or successively, were investigated under salinity stress conditions on wheat plants (Triticum aestivum L.). Various parameters, including water relations, growth, yield, photosynthetic pigments, and antioxidant activities (enzymatic and non-enzymatic), were recorded to assess the outcomes of these priming agents on mitigating the negative impacts of salinity stress on wheat plants. Water consumptive use (ETa) and irrigation water applied (IWA) decreased with seeds priming. Successive priming with SNP + CaCl2 induced the greatest values of crop water productivity (CWP), irrigation water productivity (IWP), seed index, grain yield and grain nitrogen content.Under salinity stress, the dry weight of plants was decreased. However, hydro-priming and successive chemical priming agents using combinations of calcium chloride and sodium nitroprusside (CaCl2 + SNP & SNP + CaCl2) preserved growth under salinity stress.Individual priming with sodium nitroprusside (SNP) and calcium chloride (CaCl2) resulted in the lowest recorded content of sodium in the shoot, with a value of 2 ppm. On the other hand, successive priming using CaCl2 + SNP or SNP + CaCl2 induced the contents of potassium in the shoot, with values of 40 ppm and 39 ppm, respectively. Malondialdehyde decreased in shoot significantly withapplicationof priming agents. Successive priming with CaCl2 + SNP induced the highest proline contents in shoot (6 µg/ g FW). The highest value of phenolics and total antioxidants contents in shoot were recorded under successive priming using CaCl2 + SNP and SNP + CaCl2.Priming agents improved the activities of ascorbate peroxidase and catalase enzymes. The successive priming improved water relations (ETa, IWA, CWP and IWP) and wheat growth and productivity under salinity stress more than individual priming treatments.

6-Benzylaminopurine mediated augmentation of cadmium phytostabilization potential in Strobilanthes alternata.

This study unveiled the cadmium phytoremediation potential and its augmentation using 6-Benzylaminopurine in Strobilanthes alternata. Cadmium stress was provided by applying 250 mg/kg cadmium chloride in soil and 25 ppm of 6-BAP (25 ml) was administered to the plants as foliar spray. The results revealed high bioconcentration factor (BCF) (18.82 ± 0.54) and low translocation factor (TF) values (0.055 ± 0.002) for the plant based on which we strongly recommend S. alternata as a promising candidate for Cd phytoremediation. The phytostabilization potential of the plant was further enhanced by applying 6-BAP, which augmented its BCF to 22.09 ± 0.64 and reduced the TF to 0.038 ± 0.001. Cd toxicity caused a reduction of plant growth parameters, root volume, adaxial-abaxial stomatal indices, relative water content, tolerance index, moisture content, membrane stability index, and xylem vessel diameter in S. alternata. However, Cd + 6-BAP treated plants exhibited an increase of the same compared to Cd-treated plants. FTIR analysis of Cd + 6-BAP treated plants revealed increased deposition of hemicellulose, causing enhanced retention of Cd in the root xylem walls, which is largely responsible for increased phytostabilization of Cd. Therefore, 6-BAP application in S. alternata can be exploited to restore Cd-contaminated areas effectively.

The research paper "6-Benzylaminopurine Mediated Augmentation of Cadmium Phytostabilization Potential in Strobilanthes alternata" has established the Cd phytostabilization potential of the plant Strobilanthes alternata and also identified the role of 6-BAP in augmenting the Cd phytoremediation potential of this plant for the very first time. The physiological and anatomical changes in relation to the applied stress signals were also studied for the first time in S. alternata.

Stress mitigation mechanism of rice leaf microbiota amid atmospheric deposition of heavy metals.

Leaf microbiota have been extensively applied in the biological control of plant diseases, but their crucial roles in mitigating atmospheric heavy metal (HM) deposition and promoting plant growth remain poorly understood. This study demonstrates that elevated atmospheric HM deposition on rice leaves significantly shapes distinct epiphytic and endophytic microbiota across all growth stages. HM stress consistently leads to the dominance of epiphytic Pantoea and endophytic Microbacterium in rice leaves, particularly during the booting and filling stages. Leaf-bound HMs stimulate the differentiation of specialized microbial communities in both endophytic and epiphytic compartments, thereby regulating leaf microbial interactions. Metagenomic binning retrieved high-quality genomes of keystone leaf microorganisms, indicating their potential for essential metabolic functions. Notably, Pantoea and Microbacterium show significant HM resistance, plant growth-promoting capabilities, and diverse element cycling functions. They possess genes associated with metal(loid) resistance, such as ars and czc, suggesting their ability to detoxify arsenic(As) and cadmium(Cd). They also support carbon, nitrogen, and sulfur cycling, with genes linked to carbon fixation, nitrogen fixation, and sulfur reduction. Additionally, these bacteria may enhance plant stress resistance and growth by producing antioxidants, phytohormones, and other beneficial compounds, potentially improving HM stress tolerance and nutrient availability in rice plants. This study shows that atmospheric HMs affect rice leaf microbial communities, prompting plants to seek microbial help to combat stress. The unique composition and metabolic potential of rice leaf microbiota offer a novel perspective for mitigating adverse stress induced by atmospheric HM deposition. This contributes to the utilization of leaf microbiota to alleviate the negative impact of heavy metal deposition on rice development and food security.

Enhanced wheat productivity in saline soil through the combined application of poultry manure and beneficial microbes.

BACKGROUND: Soil salinity is one of the major menaces to food security, particularly in dealing with the food demand of the ever-increasing global population. Production of cereal crops such as wheat is severely affected by soil salinity and improper fertilization. The present study aimed to examine the effect of selected microbes and poultry manure (PM) on seedling emergence, physiology, nutrient uptake, and growth of wheat in saline soil. A pot experiment was carried out in research area of Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad, Pakistan. Saline soil (12 dS m- 1 w/w) was developed by spiking using sodium chloride, and used in experiment along with two microbial strains (i.e., Alcaligenes faecalis MH-2 and Achromobacter denitrificans MH-6) and PM. Finally, wheat seeds (variety Akbar-2019) were sown in amended and unamended soil, and pots were placed following a completely randomized design. The wheat crop was harvested after 140 days of sowing. RESULTS: The results showed a 10-39% increase (compared to non-saline control) in agronomic, physiological, and nutritive attributes of wheat plants when augmented with PM and microbes. Microbes together with PM significantly enhanced seedling emergence (up to 38%), agronomic (up to 36%), and physiological (up to 33%) in saline soil as compared to their respective unamended control. Moreover, the co-use of microbes and PM also improved soil's physicochemical attributes and enhanced N (i.e., 21.7%-17.1%), P (i.e., 24.1-29.3%), and K (i.e., 28.7%-25.3%) availability to the plant (roots and shoots, respectively). Similarly, the co-use of amendments also lowered the Na+ contents in soil (i.e., up to 62%) as compared to unamended saline control. This is the first study reporting the effects of the co-addition of newly identified salt-tolerant bacterial strains and PM on seedling emergence, physiology, nutrient uptake, and growth of wheat in highly saline soil. CONCLUSION: Our findings suggest that co-using a multi-trait bacterial culture and PM could be an appropriate option for sustainable crop production in salt-affected soil.

Holistic Approaches to Plant Stress Alleviation: A Comprehensive Review of the Role of Organic Compounds and Beneficial Bacteria in Promoting Growth and Health.

Plants select microorganisms from the surrounding bulk soil, which act as a reservoir of microbial diversity and enrich a rhizosphere microbiome that helps in growth and stress alleviation. Plants use organic compounds that are released through root exudates to shape the rhizosphere microbiome. These organic compounds are of various spectrums and technically gear the interplay between plants and the microbial world. Although plants naturally produce organic compounds that influence the microbial world, numerous efforts have been made to boost the efficiency of the microbiome through the addition of organic compounds. Despite further crucial investigations, synergistic effects from organic compounds and beneficial bacteria combinations have been reported. In this review, we examine the relationship between organic compounds and beneficial bacteria in determining plant growth and biotic and abiotic stress alleviation. We investigate the molecular mechanism and biochemical responses of bacteria to organic compounds, and we discuss the plant growth modifications and stress alleviation done with the help of beneficial bacteria. We then exhibit the synergistic effects of both components to highlight future research directions to dwell on how microbial engineering and metagenomic approaches could be utilized to enhance the use of beneficial microbes and organic compounds.

Transcriptome Analyses in Adult Olive Trees Indicate Acetaldehyde Release and Cyanide-Mediated Respiration Traits as Critical for Tolerance against Xylella fastidiosa and Suggest AOX Gene Family as Marker for Multiple-Resilience.

Xylella fastidiosa (Xf) is a global bacterial threat for a diversity of plants, including olive trees. However, current understanding of host responses upon Xf-infection is limited to allow early disease prediction, diagnosis, and sustainable strategies for breeding on plant tolerance. Recently, we identified a major complex trait for early de novo programming, named CoV-MAC-TED, by comparing early transcriptome data during plant cell survival with SARS-CoV-2-infected human cells. This trait linked ROS/RNS balancing during first hours of stress perception with increased aerobic fermentation connected to alpha-tubulin-based cell restructuration and control of cell cycle progression. Furthermore, our group had advanced concepts and strategies for breeding on plant holobionts. Here, we studied tolerance against Xf-infection by applying a CoV-MAC-TED-related gene set to (1) progress proof-of-principles, (2) highlight the importance of individual host responses for knowledge gain, (3) benefit sustainable production of Xf-threatened olive, (4) stimulate new thinking on principle roles of secondary metabolite synthesis and microbiota for system equilibration and, (5) advance functional marker development for resilience prediction including tolerance to Xf-infections. We performed hypothesis-driven complex analyses in an open access transcriptome of primary target xylem tissues of naturally Xf-infected olive trees of the Xf-tolerant cv. Leccino and the Xf-susceptible cv. Ogliarola. The results indicated that cyanide-mediated equilibration of oxygen-dependent respiration and carbon-stress alleviation by the help of increased glycolysis-driven aerobic fermentation paths and phenolic metabolism associate to tolerance against Xf. Furthermore, enhanced alternative oxidase (AOX) transcript levels through transcription Gleichschaltung linked to quinic acid synthesis appeared as promising trait for functional marker development. Moreover, the results support the idea that fungal endophytes strengthen Xf-susceptible genotypes, which lack efficient AOX functionality. Overall, this proof-of-principles approach supports the idea that efficient regulation of the multi-functional AOX gene family can assist selection on multiple-resilience, which integrates Xf-tolerance, and stimulates future validation across diverse systems.

Characterization of a novel exopolysaccharide from Acinetobacter rhizosphaerae with ability to enhance the salt stress resistance of rice seedlings.

We here describe the isolation of a novel exopolysaccharide from Acinetobacter rhizosphaerae, named ArEPS. The structure of ArEPS was characterized by analysis of the monosaccharide composition, molecular weight, infrared spectrum, methylation, and nuclear magnetic resonance spectrum. ArEPS was found to be an acidic heteropolysaccharide composed of glucose, galactose, galacturonic acid, glucuronic acid, mannose, and glucosamine; the molecular weight was 1533 kDa. Structural analysis showed that the main-chain structure of ArEPS predominantly comprised 1,3,6-ß-Glcp, 1,3,4-α-Galp, 1,2-ß-Glcp, 1,4-ß-GlcpA, 1,4-ß-GalpA, and the side-chain structure comprised 1,6-ß-Glcp, 1,3-ß-Galp, 1-α-Glcp, 1-ß-Galp, 1-α-Manp, 1,4,6-α-Glcp, 1,2,4-ß-Glcp, 1,2,3-ß-Glcp, and 1,3-ß-GlcpN. ArEPS significantly enhanced the tolerance of rice seedlings to salt stress. Specifically, plant height, fresh weight, chlorophyll content, and the K+/Na+ ratio increased by 51 %, 63 %, 29 %, and 162 %, respectively, and the malondialdehyde content was reduced by 45 % after treatment with 100 mg/kg ArEPS compared to treatment with 100 mM NaCl. Finally, based on the quadratic regression between fresh weight and ArEPS addition, the optimal ArEPS addition level was estimated to be 135.12 mg/kg. These results indicate the prospects of ArEPS application in agriculture.

Seed Priming with Zinc Oxide Nanoparticles to Enhance Crop Tolerance to Environmental Stresses.

Drastic climate changes over the years have triggered environmental challenges for wild plants and crops due to fluctuating weather patterns worldwide. This has caused different types of stressors, responsible for a decrease in plant life and biological productivity, with consequent food shortages, especially in areas under threat of desertification. Nanotechnology-based approaches have great potential in mitigating environmental stressors, thus fostering a sustainable agriculture. Zinc oxide nanoparticles (ZnO NPs) have demonstrated to be biostimulants as well as remedies to both environmental and biotic stresses. Their administration in the early sowing stages, i.e., seed priming, proved to be effective in improving germination rate, seedling and plant growth and in ameliorating the indicators of plants' well-being. Seed nano-priming acts through several mechanisms such as enhanced nutrients uptake, improved antioxidant properties, ROS accumulation and lipid peroxidation. The target for seed priming by ZnO NPs is mostly crops of large consumption or staple food, in order to meet the increased needs of a growing population and the net drop of global crop frequency, due to climate changes and soil contaminations. The current review focuses on the most recent low-cost, low-sized ZnO NPs employed for seed nano-priming, to alleviate abiotic and biotic stresses, mitigate the negative effects of improper storage and biostimulate plants' growth and well-being. Taking into account that there is large variability among ZnO NPs and that their chemico-physical properties may play a role in determining the efficacy of nano-priming, for all examined cases, it is reported whether the ZnO NPs are commercial or lab prepared. In the latter cases, the preparation conditions are described, along with structural and morphological characterizations. Under these premises, future perspectives and challenges are discussed in relation to structural properties and the possibility of ZnO NPs engineering.

Promoting adult health: the neurophysiological benefits of watering plants and engaging in mental tasks within designed environments.

BACKGROUND: Indoor, sedentary lifestyles have disconnected individuals from nature, necessitating interventions to reestablish this bond. Performing horticultural activities, such as watering houseplants, offers a potential solution. This study sought to determine how participating in horticulture activities affected adults' cognitive and emotional moods. METHODS: We compared the benefits of watering houseplants (a gardening task) to those of standing while performing a computer task (a mental task). Chinese participants, aged 20 to 21 years, were recruited; their physiological and psychological reactions were measured using electroencephalograms, blood pressure assessments, and psychological assessments. RESULTS: Fifty participants were included. Watering indoor plants significantly reduced blood pressure, without affecting pulse rate. During the plant watering task as opposed to the mental activity, more dramatic different patterns of very high alpha and beta brainwave activity were identified. Participants reported increased happiness following gardening activities. CONCLUSIONS: The findings of this study highlight the substantial relaxation benefits, both mental and physical, associated with the simple act of watering indoor plants.

Rhizoactinobacteria Enhance Growth and Antioxidant Activity in Thai Jasmine Rice (Oryza sativa) KDML105 Seedlings under Salt Stress.

Salinity is one of the most devastating abiotic stresses hampering the growth and production of rice. Nine indole-3-acetic acid (IAA)-producing salt-tolerant plant-growth-promoting rhizobacteria (ST-PGPR) were inoculated into Thai jasmine rice (Oryza sativa L.) variety Khao Dawk Mali 105 (KDML105) seedlings grown under different concentrations of NaCl (0, 50, 100, and 150 mM). The ST-PGPR strains significantly promoted the growth parameters, chlorophyll content, nutrient uptake (N, P, K, Ca, and Mg), antioxidant activity, and proline accumulation in the seedlings under both normal and saline conditions compared to the respective controls. The K+/Na+ ratio of the inoculated seedlings was much higher than that of the controls, indicating greater salt tolerance. The most salt-tolerant and IAA-producing strain, Sinomonas sp. ORF15-23, yielded the highest values for all the parameters, particularly at 50 mM NaCl. The percentage increases in these parameters relative to the controls ranged from >90% to 306%. Therefore, Sinomonas sp. ORF15-23 was considered a promising ST-PGPR to be developed as a bioinoculant for enhancing the growth, salt tolerance, and aroma of KDML105 rice in salt-affected areas. Environmentally friendly technologies such as ST-PGPR bioinoculants could also support the sustainability of KDML105 geographical indication (GI) products. However, the efficiency of Sinomonas sp. ORF15-23 should be evaluated under field conditions for its effect on rice nutrient uptake and growth, including the 2AP level.

Comprehensive genome analysis of Pseudomonas sp. SWRIQ11, a new plant growth-promoting bacterium that alleviates salinity stress in olive.

The study presents the genome analysis of a new Pseudomonas sp. (SWRIQ11), which can alleviate salinity stress effects on growth of olive seedlings in greenhouse study. The strain SWRIQ11 can tolerate salinity up to 6%, produce siderophores, indole acetic acid (IAA), aminocyclopropane-1-carboxylate (ACC) deaminase, and has the phosphate-solubilizing capability. The SWRIQ11 genome contained an assembly size of 6,196,390 bp with a GC content of 60.1%. According to derived indices based on whole-genome sequences for species delineation, including tetra nucleotide usage patterns (TETRA), genome-to-genome distance (GGDC), and average nucleotide identity (ANI), Pseudomonas sp. SWRIQ11 can be considered a novel species candidate. The phylogenetic analysis revealed SWRIQ11 clusters with Pseudomonas tehranensis SWRI196 in the same clade. The SWRIQ11 genome was rich in genes related to stress sensing, signaling, and response, chaperones, motility, attachments, colonization, and enzymes for degrading plant-derived carbohydrates. Furthermore, the genes for production of exopolysaccharides, osmoprotectants, phytohormones, and ACC deaminase, ion homeostasis, nutrient acquisition, and antioxidant defenses were identified in the SWRIQ11 genome. The results of genome analysis (identification of more than 825 CDSs related to plant growth-promoting and stress-alleviating traits in the SWRIQ11 genome which is more than 15% of its total CDSs) are in accordance with laboratory and greenhouse experiments assigning the Pseudomonas sp. SWRIQ11 as a halotolerant plant growth-promoting bacterium (PGPB). This research highlights the potential safe application of this new PGPB species in agriculture as a potent biofertilizer.

Mechanisms underlying probiotic effects on neurotransmission and stress resilience in fish via transcriptomic profiling.

In recent years, studies have highlighted the significant impact of probiotic treatment on the central nervous system (brain) and stress regulation through the microbiota-gut-brain axis, yet there have been limited knowledge on this axis in fish. Therefore, this study aimed to enhance the current understanding of the mechanisms underlying probiotic effects on neurotransmission and stress alleviation in fish through transcriptomic profiling. In this study, olive flounders (Paralichthys olivaceus) were subjected to two trial setups: a 1-month lab-scale trial and a 6-month field-scale trial, with and without the probiotic strain Lactococcus lactis WFLU12. RNA-Seq analysis was performed using liver samples collected from fish at one-month post-feeding (mpf) in both trials. Additionally, fish growth was monitored monthly, and serological parameters were measured at one mpf in the field-scale experiment. The results of the lab-scale trial showed that probiotic administration significantly upregulated genes related to neurotransmission, such as htr3a, mao, ddc, ntsr1, and gfra2. These findings highlight the impact of probiotics on modulating neurotransmission via the microbiota-gut-brain axis. In the field-scale experiment, fish growth was significantly promoted and the sera levels of AST, LDH, and cortisol were significantly higher in the control group compared to the probiotics group. Furthermore, genes involved in stress responses (e.g. hsp70, hsp90B1, hspE1, prdx1, and gss) and transcriptional regulators (e.g. fos, dusp1, and dusp2) exhibited significant upregulation in the control group compared to the probiotics group, indicating that probiotic administration can alleviate stress levels in fish. Overall, this study provides valuable insights into the mechanisms underlying the beneficial effects of probiotics in fish, specifically regarding their impact on neurotransmission and stress alleviation.

Phyto-microbiome to mitigate abiotic stress in crop plants.

Plant-associated microbes include taxonomically diverse communities of bacteria, archaebacteria, fungi, and viruses, which establish integral ecological relationships with the host plant and constitute the phyto-microbiome. The phyto-microbiome not only contributes in normal growth and development of plants but also plays a vital role in the maintenance of plant homeostasis during abiotic stress conditions. Owing to its immense metabolic potential, the phyto-microbiome provides the host plant with the capability to mitigate the abiotic stress through various mechanisms like production of antioxidants, plant growth hormones, bioactive compounds, detoxification of harmful chemicals and toxins, sequestration of reactive oxygen species and other free radicals. A deeper understanding of the structure and functions of the phyto-microbiome and the complex mechanisms of phyto-microbiome mediated abiotic stress mitigation would enable its utilization for abiotic stress alleviation of crop plants and development of stress-resistant crops. This review aims at exploring the potential of phyto-microbiome to alleviate drought, heat, salinity and heavy metal stress in crop plants and finding sustainable solutions to enhance the agricultural productivity. The mechanistic insights into the role of phytomicrobiome in imparting abiotic stress tolerance to plants have been summarized, that would be helpful in the development of novel bioinoculants. The high-throughput modern approaches involving candidate gene identification and target gene modification such as genomics, metagenomics, transcriptomics, metabolomics, and phyto-microbiome based genetic engineering have been discussed in wake of the ever-increasing demand of climate resilient crop plants.

Acinetobacter oleivorans IRS14 alleviates cold stress in wheat by regulating physiological and biochemical factors.

AIMS: Climate change is responsible for extreme cold winters, causing a significant loss in crop yield and productivity due to chilling stress. This study aims to investigate the potential of psychrotrophic plant growth-promoting rhizobacteria (PGPR) strain to promote wheat growth under cold stress and explore the adaptive responses of wheat. METHODS AND RESULTS: Wheat seeds and seedlings were inoculated with the psychrotrophic strain IRS14 and the plants were cultivated for five weeks at 6°C ± 2°C. The genetic, biochemical, physiological, and molecular analysis of the bacterium and plant was done to evaluate the effect of the PGPR strain in alleviating chilling stress. IRS14 possesses antioxidant activity and produced multiple phytohormones, which enhanced seed germination (∼50%) and plant growth (∼50%) during chilling stress. CONCLUSIONS: Here, we reported that the application of IRS14 helps to regulate the biochemical and metabolic pathways in wheat plants. It alleviates chilling stress and increases plant growth rate and biomass. Strain IRS14 in wheat effectively increased chlorophyll content, antioxidants, carotenoid, proline, and endogenous phytohormones compared with untreated wheat.

Impact of dark septate endophytes on salt stress alleviation of tomato plants.

Fungal endophytes can improve plant tolerance to abiotic stress conditions. Dark septate endophytes (DSEs) belong to phylogenetically non-related groups of root colonizing fungi among the Ascomycota with high melanin-producing activities. They can be isolated from roots of more than 600 plant species in diverse ecosystems. Still the knowledge about their interaction with host plants and their contribution to stress alleviation is limited. The current work aimed to test the abilities of three DSEs (Periconia macrospinosa, Cadophora sp., Leptodontidium sp.) to alleviate moderate and high salt stress in tomato plants. By including an albino mutant, the role of melanin for the interaction with plants and salt stress alleviation could also be tested. P. macrospinosa and Cadophora sp. improved shoot and root growth 6 weeks after inoculation under moderate and high salt stress conditions. No matter how much salt stress was applied, macroelement (P, N, and C) contents were unaffected by DSE inoculation. The four tested DSE strains successfully colonized the roots of tomato, but the colonization level was clearly reduced in the albino mutant of Leptodontidium sp. Any difference in the effects on plant growth between the Leptodontidium sp. wild type strain and the albino mutant could, however, not be observed. These results show that particular DSEs are able to increase salt tolerance as they promote plant growth specifically under stress condition. Increased plant biomasses combined with stable nutrient contents resulted in higher P uptake in shoots of inoculated plants at moderate and high salt conditions and higher N uptake in the absence of salt stress in all inoculated plants, in P. macrospinosa-inoculated plants at moderate salt condition and in all inoculated plants except the albino mutants at high salt condition. In summary, melanin in DSEs seems to be important for the colonization process, but does not influence growth, nutrient uptake or salt tolerance of plants.

Salinity stress endurance of the plants with the aid of bacterial genes.

The application of plant growth-promoting bacteria (PGPB) is vital for sustainable agriculture with continuous world population growth and an increase in soil salinity. Salinity is one of the severe abiotic stresses which lessens the productivity of agricultural lands. Plant growth-promoting bacteria are key players in solving this problem and can mitigate salinity stress. The highest of reported halotolerant Plant growth-promoting bacteria belonged to Firmicutes (approximately 50%), Proteobacteria (40%), and Actinobacteria (10%), respectively. The most dominant genera of halotolerant plant growth-promoting bacteria are Bacillus and Pseudomonas. Currently, the identification of new plant growth-promoting bacteria with special beneficial properties is increasingly needed. Moreover, for the effective use of plant growth-promoting bacteria in agriculture, the unknown molecular aspects of their function and interaction with plants must be defined. Omics and meta-omics studies can unreveal these unknown genes and pathways. However, more accurate omics studies need a detailed understanding of so far known molecular mechanisms of plant stress protection by plant growth-promoting bacteria. In this review, the molecular basis of salinity stress mitigation by plant growth-promoting bacteria is presented, the identified genes in the genomes of 20 halotolerant plant growth-promoting bacteria are assessed, and the prevalence of their involved genes is highlighted. The genes related to the synthesis of indole acetic acid (IAA) (70%), siderophores (60%), osmoprotectants (80%), chaperons (40%), 1-aminocyclopropane-1-carboxylate (ACC) deaminase (50%), and antioxidants (50%), phosphate solubilization (60%), and ion homeostasis (80%) were the most common detected genes in the genomes of evaluated halotolerant plant growth-promoting and salinity stress-alleviating bacteria. The most prevalent genes can be applied as candidates for designing molecular markers for screening of new halotolerant plant growth-promoting bacteria.

Meta-Analysis of the Effect of Nitric Oxide Application on Heavy Metal Stress Tolerance in Plants.

Substantial single-species studies have reported the facility of nitric oxide (NO) in alleviating heavy metal-induced stress in plants. Understanding the mechanisms of NO-involved stress alleviation is progressing; however, a quantitative description of the alleviative capacity of NO against heavy metal stress is still lacking. We combined the results of 86 studies using meta-analysis to statistically assess the responses of heavy metal-stressed plants to NO supply across several metal stresses and plant families. The results showed that plant biomass was consistently improved following NO supply to metal-stressed plants. NO played an important role in mitigating oxidative damage caused by heavy metal stress by significantly stimulating the activities of antioxidant enzymes. Moreover, NO supply consistently increased the Ca, Fe, and Mg contents in both leaves and roots. Plant tissues accumulated less heavy metals when exposed to heavy metal stress after NO addition. Additionally, the best concentration of SNP (an NO donor) for hydroponic culture is in the range of 75-150 µM. We further confirmed that NO application can generally alleviate plant heavy metal stress and its action pathway. The results presented here can help guide future applications of NO as a plant growth regulator in agriculture and breeding plants for heavy metal stress tolerance.