Plants' Physio-Biochemical and Phyto-Hormonal Responses to Alleviate the Adverse Effects of Drought Stress: A Comprehensive Review

Response of seed yield and biochemical traits of Eruca sativa Mill. to drought stress in a collection study

Drought tolerance is a complex trait in plants that involves different biochemical mechanisms. During two years of study (2019-2020), the responses of 64 arugula genotypes to drought stress were evaluated in a randomized complete block design with three replications under field conditions. Several metabolic traits were evaluated, i.e. relative water content, photosynthetic pigments (chlorophyll and carotenoids), proline, malondialdehyde, enzymatic antioxidants (catalase, ascorbate peroxidase, and peroxidase), total phenolic and flavonoid contents and seed yield. On average, the drought stress significantly increased the proline content (24%), catalase (42%), peroxidase (60%) and malondialdehyde activities (116%) over the two years of study. As a result of the drought stress, the seed yield (18%), relative water content (19.5%) and amount of photosynthetic pigments (chlorophyll and carotenoids) dropped significantly. However, the total phenolic and flavonoid contents showed no significant changes. Under drought stress, the highest seed yields were seen in the G50, G57, G54, G55 and G60 genotypes, while the lowest value was observed in the G16 genotype (94 g plant-1). According to the findings, when compared to the drought-sensitive genotypes, the drought-tolerant arugula genotypes were marked with higher levels of proline accumulation and antioxidant enzyme activity. Correlation analysis indicated the positive effects of peroxidase, catalase and proline on seed yield under drought conditions. These traits can be considered for the selection of drought-tolerant genotypes in breeding programs.

Melatonin Enhances the Photosynthesis and Antioxidant Enzyme Activities of Mung Bean under Drought and High-Temperature Stress Conditions

Mung bean, a legume, is sensitive to abiotic stresses at different growth stages, and its yield potential is affected by drought and high-temperature stress at the sensitive stage. Melatonin is a multifunctional hormone that plays a vital role in plant stress defense mechanisms. This study aimed to evaluate the efficiency of melatonin under individual and combined drought and high-temperature stress in mung bean. An experiment was laid out with five treatments, including an exogenous application of 100 µM melatonin as a seed treatment, foliar spray, and a combination of both seed treatment and foliar spray, as well as absolute control (ambient condition) and control (stress without melatonin treatment). Stresses were imposed during the mung bean's reproductive stage (31-40 DAS) for ten days. Results revealed that drought and high-temperature stress significantly decreased chlorophyll index, Fv/Fm ratio, photosynthetic rate, stomatal conductance, and transpiration rate through increased reactive oxygen species (ROS) production. Foliar application of melatonin at 100 µM concentration enhanced the activity of antioxidant enzymes such as superoxide dismutase, catalase, and ascorbate peroxidase and the concentration of metabolites involved in osmoregulation and ion homeostasis; thereby, it improves physiological and yield-related traits in mung bean under individual and combined stress at the reproductive stage.

Seed Priming Modulates Physiological and Agronomic Attributes of Maize (Zea mays L.) under Induced Polyethylene Glycol Osmotic Stress

Drought and osmotic stresses are major threats to agricultural crops as they affect plants during their life cycle. The seeds are more susceptible to these stresses during germination and establishment of seedlings. To cope with these abiotic stresses, various seed priming techniques have broadly been used. The present study aimed to assess seed priming techniques under osmotic stress. Osmo-priming with chitosan (1 and 2%), hydro-priming with distilled water, and thermo-priming at 4 °C were used on the physiology and agronomy of Zea mays L. under polyethylene glycol (PEG-4000)-induced osmotic stress (-0.2 and -0.4 MPa). The vegetative response, osmolyte content, and antioxidant enzymes of two varieties (Pearl and Sargodha 2002 White) were studied under induced osmotic stress. The results showed that seed germination and seedling growth were inhibited under osmotic stress and germination percentage, and the seed vigor index was enhanced in both varieties of Z. mays L. with chitosan osmo-priming. Osmo-priming with chitosan and hydro-priming with distilled water modulated the level of photosynthetic pigments and proline, which were reduced under induced osmotic stress; moreover, the activities of antioxidant enzymes were improved significantly. In conclusion, osmotic stress adversely affects the growth and physiological attributes; on the contrary, seed priming ameliorated the stress tolerance resistance of Z. mays L. cultivars to PEG-induced osmotic stress by activating the natural antioxidation enzymatic system and accumulating osmolytes.

Trichoderma longibrachiatum Inoculation Improves Drought Resistance and Growth of Pinus massoniana Seedlings through Regulating Physiological Responses and Soil Microbial Community

Drought stress poses a serious threat to Pinus massoniana seedling growth in southern China. Trichoderma species, as beneficial microorganisms, have been widely used in agriculture to enhance plant growth and drought tolerance, but the interaction mechanisms remain unclear. To investigate the effect of drought-resistant Trichoderma longibrachiatum inoculation on P. massoniana growth under drought stress, the plant physiological indicators and rhizosphere microbiome diversity were measured to identify Trichoderma-activated mechanisms. Trichoderma longibrachiatum inoculation significantly promoted P. massoniana growth under drought treatment, and enhanced nitrogen, phosphorus, and potassium absorption compared with those of non-inoculated seedlings. Trichoderma longibrachiatum treatment alleviated the damage to cell membranes and needle tissue structure, and significantly increased antioxidant enzyme activities, osmotic substance contents, and photosynthesis in P. massoniana in response to drought stress. Soil nutrient contents, activities of sucrase, phosphatase, and urease as well as the relative abundances of the dominant genera Burkholderia, Rhodanobacter, and Trichoderma were elevated in the rhizosphere soil of P. massoniana inoculated with T. longibrachiatum under drought stress. A network analysis showed that certain crucial dominant taxa driven by T. longibrachiatum inoculation, including Penicillium, Trichoderma, Simplicillium, Saitozyma, Burkholderia, Bradyrhizobium, Sinomonas, and Mycobacterium, had more correlations with other microorganisms in the soil. Trichoderma longibrachiatum enhanced P. massoniana seedling growth under drought stress by regulating physiological responses and soil microbial community.

Bacterial-Mediated Salinity Stress Tolerance in Maize (Zea mays L.): A Fortunate Way toward Sustainable Agriculture

Sustainable agriculture is threatened by salinity stress because of the low yield quality and low crop production. Rhizobacteria that promote plant growth modify physiological and molecular pathways to support plant development and reduce abiotic stresses. The recent study aimed to assess the tolerance capacity and impacts of Bacillus sp. PM31 on the growth, physiological, and molecular responses of maize to salinity stress. In comparison to uninoculated plants, the inoculation of Bacillus sp. PM31 improved the agro-morphological traits [shoot length (6%), root length (22%), plant height (16%), fresh weight (39%), dry weight (29%), leaf area (11%)], chlorophyll [Chl a (17%), Chl b (37%), total chl (22%)], carotenoids (15%), proteins (40%), sugars (43%), relative water (11%), flavonoids (22%), phenols (23%), radical scavenging capacity (13%), and antioxidants. The Bacillus sp. PM31-inoculated plants showed a reduction in the oxidative stress indicators [electrolyte leakage (12%), H2O2 (9%), and MDA (32%)] as compared to uninoculated plants under salinity and increased the level of osmolytes [free amino acids (36%), glycine betaine (17%), proline (11%)]. The enhancement of plant growth under salinity was further validated by the molecular profiling of Bacillus sp. PM31. Moreover, these physiological and molecular mechanisms were accompanied by the upregulation of stress-related genes (APX and SOD). Our study found that Bacillus sp. PM31 has a crucial and substantial role in reducing salinity stress through physiological and molecular processes, which may be used as an alternative approach to boost crop production and yield.

Silicic and Ascorbic Acid Induced Modulations in Photosynthetic, Mineral Uptake, and Yield Attributes of Mung Bean (Vigna radiata L. Wilczek) under Ozone Stress

Most of the world's crop production and plant growth are anticipated to be seriously threatened by the increasing tropospheric ozone (O₃) levels. The current study demonstrates how different mung bean genotypes reacted to the elevated level of O₃ in the presence of exogenous ascorbic and silicic acid treatments. It is the first report to outline the potential protective effects of ascorbic and silicic acid applications against O₃ toxicity in 12 mung bean {Vigna radiata (L.) Wilken} varieties. Under controlled circumstances, the present investigation was conducted in a glass house. There were four different treatments used: control (ambient O₃ concentration of 40-45 ppb), elevated O₃ (120 ppb), elevated O₃ with silicic acid (0.1 mM), and elevated O₃ with ascorbic acid (10 mM). Three varieties, viz. NM 20-21, NM 2006, and NM 2016, showcased tolerance to O₃ toxicity. Our findings showed that ascorbic and silicic acid applications gradually increased yield characteristics such as seed yield, harvest index, days to maturity, and characteristics related to gas exchange such as transpiration rate, stomatal conductance, net photosynthetic activity, and water-use efficiency. Compared to the control, applying both growth regulators enhanced the mineral uptake across all treatments. Based on the findings of the current study, it is concluded that the subject mung bean genotypes responded to silicic acid treatment more efficiently than ascorbic acid to mitigate the harmful effects of O₃ stress.

Shattering and yield expression of sesame (Sesamum indicum L) genotypes influenced by paclobutrazol concentration under rainfed conditions of Pothwar

Seed shattering is a critical challenge that significantly reduces sesame production by 50%. These shattering losses can be reduced by selecting shattering resistant genotypes or by incorporating modern agronomic management such as paclobutrazol, which can boost productivity and prevent seed shattering in sesame. Two-years of field trials were conducted to examine the effect of sesame genotypes, environment, and paclobutrazol (PBZ) concentrations. Twelve sesame genotypes were used in a four-way factorial RCBD with three replications and five PBZ concentrations (T₀ = Control; T₁ = 150; T₂ = 300; T₃ = 450; and T₄ = 600 mg L^- 1) under rainfed conditions of Pothwar. The findings revealed significant variations in the major effects of all examined variables (genotypes, locations, years, and PBZ levels). Sesame genotypes PI-154304 and PI-175907 had the highest plant height, number of capsule plant^- 1, seed capsule^- 1, 1000 seed weight, biological yield, and seed yield, while also having the lowest seed losses and shattering percentage. Regarding environments, NARC-Islamabad generated the highest plant height, number of capsule plant^- 1, shattering percentage, and biological yield; however, the URF-Koont produced the highest seed yield with the lowest shattering percentage. Additionally, plant height, capsules plant^- 1, and biological yield were higher in 2021, while seed capsule^- 1, 1000 seed weight, seed losses, shattering percentage, and seed yield were higher in 2020. PBZ concentration affected all measured parameters; plant height and number of seed capsule^- 1 decreased with increasing PBZ concentrations. 450 mg L^- 1 PBZ concentration generated the highest biomass, number of capsules plant^- 1, and seed yield. At the same time, PBZ concentration 600 mg L^- 1 generated the smallest plant, the lowest seed capsules^- 1, the greatest thousand seed weight, and the lowest shattering percentage. The study concluded that paclobutrazol could dramatically reduce shattering percentage and shattering losses while increasing economic returns through better productivity. Based on the findings, the genotypes PI-154304 and PI-175907 with paclobutrazol level 450 mgL^- 1 may be suggested for cultivation in Pothwar farming community under rainfed conditions, as they showed promising shattering resistance as well as enhanced growth and yield.

Conferring of Drought and Heat Stress Tolerance in Wheat (Triticum aestivum L.) Genotypes and Their Response to Selenium Nanoparticles Application

In this study, the role of selenium nanoparticles (SeNPs, 10 mg·L^-1) has been investigated in modulating the negative effects of drought and heat stresses on eight bread wheat (Triticum aestivum L.) genotype seedlings. Those genotypes included Giza-168, Giza-171, Misr-1, Misr-3, Shandweel-1, Sids-1, Sids-12, and Sids-14. The study included six treatments as follows: regular irrigation with 100% Field Capacity (FC) at a temperature of 23 ± 3 °C (T1), drought stress with 60% FC (T2), heat stress of 38 °C for 5 h·day^-1 (T3), foliar spray of 10 mg·L^-1 of SeNPs only (T4), a combination of drought stress with foliar spray of 10 mg·L^-1 of SeNPs (T5), and heat stress with foliar spray of 10 mg·L^-1 of SeNPs (T6). The experiment continued for 31 days. Foliar application of SeNPs improved the plant growth, morpho-physiological and biochemical responses, and expression of stress-responsive genes in wheat (T. aestivum L.) seedlings. Overall, morpho-physiological traits such as plant height (PH), shoot fresh weight (SFW), shoot dry weight (SDW), root fresh weight (RFW), and root dry weight (RDW) of wheat genotypes grown under different conditions ranged from 25.37-51.51 cm, 3.29-5.15 g, 0.50-1.97 g, 0.72-4.21 g, and 0.11-1.23 g, respectively. From the morpho-physiological perspective, drought stress had a greater detrimental impact on wheat plants than heat stress, whereas heat stress significantly impacted the expression of stress-responsive genes. Stress responses to drought and heat varied between wheat genotypes, suggesting that different genotypes are more resilient to stress. Exogenous spraying of 10 mg·L^-1 of SeNPs improved the photosynthetic pigments, photosynthetic rate, gas exchange, and transpiration rate of wheat plants and enhanced drought and heat tolerance by increasing the activity of antioxidant enzymes including catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD) and the expression level of stress-responsive genes. Our results showed that spraying wheat seedlings with 10 mg·L^-1 of SeNPs enhanced SOD activity for all genotypes as compared to the control, with the Sids-12 genotype having the highest value (196.43 U·mg^-1 FW·min^-1) and the Giza-168 genotype having the lowest (152.30 U·mg^-1 FW·min^-1). The expression of PIP1, LEA-1, HSP70, and HSP90 stress-responsive genes was more significant in tolerant genotypes (Giza-171 and Giza-168) than in sensitive ones (Misr-1 and Misr-3) in response to drought and heat stresses. Under stress conditions, the shoot and root fresh weights, photosynthetic pigment content, stomatal conductance (SC), and transpiration rate (TR) were positively correlated with plant height (PH), while root and shoot dry weights, malondialdehyde (MDA), proline, hydrogen peroxide (H₂O₂), and APX were negatively correlated. Multivariate analysis and biplot results revealed that genotypes Giza-168, Giza-171, Sids-12, and Sids-14 performed well in both stress situations and were classified as stress-tolerant genotypes. These best genotypes may be employed in future breeding projects as tools to face climate change. This study concluded that various physio-biochemicals and gene expression attributes under drought and heat stress could be modulated by foliar application of SeNPs in wheat genotypes, potentially alleviating the adverse effects of drought and heat stress.

Interactions of Polyamines and Phytohormones in Plant Response to Abiotic Stress

Numerous environmental conditions negatively affect plant production. Abiotic stresses, such as salinity, drought, temperature, and heavy metals, cause damage at the physiological, biochemical, and molecular level, and limit plant growth, development, and survival. Studies have indicated that small amine compounds, polyamines (PAs), play a key role in plant tolerance to various abiotic stresses. Pharmacological and molecular studies, as well as research using genetic and transgenic approaches, have revealed the favorable effects of PAs on growth, ion homeostasis, water maintenance, photosynthesis, reactive oxygen species (ROS) accumulation, and antioxidant systems in many plant species under abiotic stress. PAs display a multitrack action: regulating the expression of stress response genes and the activity of ion channels; improving the stability of membranes, DNA, and other biomolecules; and interacting with signaling molecules and plant hormones. In recent years the number of reports indicating crosstalk between PAs and phytohormones in plant response to abiotic stresses has increased. Interestingly, some plant hormones, previously known as plant growth regulators, can also participate in plant response to abiotic stresses. Therefore, the main goal of this review is to summarize the most significant results that represent the interactions between PAs and plant hormones, such as abscisic acid, brassinosteroids, ethylene, jasmonates, and gibberellins, in plants under abiotic stress. The future perspectives for research focusing on the crosstalk between PAs and plant hormones were also discussed.

What Makes the Life of Stressed Plants a Little Easier? Defense Mechanisms against Adverse Conditions

Plants experience a wide array of external factors, some of which negatively affect their metabolism, growth, and development [...].

Salinity stress improves antioxidant potential by modulating physio-biochemical responses in Moringa oleifera Lam

Moringa oleifera Lam. is a common edible plant, famous for several nutritional and therapeutic benefits. This study investigates the salt -induced modulations in plant growth, physio-biochemical responses, and antioxidant performance of M. oleifera grown under 0, 50, and 100 mM NaCl concentrations. Results showed that the plant effectively managed moderate salinity (50 mM NaCl) by maintaining succulence, weight ratios, and biomass allocation patterns of both shoot and root with minimal reduction in dry biomass. However, high salinity (100 mM NaCl) remarkably declined all growth parameters. The plant accumulated more Na⁺ and Cl^-, while less K⁺ under salinity as compared to the control. Consequently, osmotic potentials of both root and leaf decreased under salinity, which was corroborated by the high amount of proline and soluble sugars. Increased level of H₂O₂ with significantly unchanged membrane fluidity indicating its role in perceiving and managing stress at moderate salinity. In addition, increased activities of superoxide dismutase, and catalase, with increased glutathione and flavonoid contents suggest an integrated participation of both enzymatic and non-enzymatic antioxidant components in regulating ROS. On the other hand, high salinity caused an outburst of ROS indicated by high H₂O₂, MDA, and electrolyte leakage. As a response, moringa drastically increased the activities of all antioxidant enzymes and contents of antioxidant molecules including ascorbic acid, glutathione, total phenols, and flavonoids with high radical scavenging and reducing power capacities. However, a considerable amount of energy was used in such management resulting in a significant growth reduction at 100 mM NaCl. This study suggests that moringa effectively resisted moderate salinity by modulating physio-biochemical attributes and effectively managing ion toxicity and oxidative stress. Salt stress also enhanced the medicinal potentials of moringa by increasing the contents of antioxidant compounds including ascorbic acid, glutathione, total phenols, and flavonoids and their resulting activities. It can be grown on degraded/ saline lands and biomass of this plant can be used for edible and medicinal purposes, besides providing other benefits in a global climate change scenario.

Mechanisms and Applications of Bacterial Inoculants in Plant Drought Stress Tolerance

Agricultural systems are highly affected by climatic factors such as temperature, rain, humidity, wind, and solar radiation, so the climate and its changes are major risk factors for agricultural activities. A small portion of the agricultural areas of Brazil is irrigated, while the vast majority directly depends on the natural variations of the rains. The increase in temperatures due to climate change will lead to increased water consumption by farmers and a reduction in water availability, putting production capacity at risk. Drought is a limiting environmental factor for plant growth and one of the natural phenomena that most affects agricultural productivity. The response of plants to water stress is complex and involves coordination between gene expression and its integration with hormones. Studies suggest that bacteria have mechanisms to mitigate the effects of water stress and promote more significant growth in these plant species. The underlined mechanism involves root-to-shoot phenotypic changes in growth rate, architecture, hydraulic conductivity, water conservation, plant cell protection, and damage restoration through integrating phytohormones modulation, stress-induced enzymatic apparatus, and metabolites. Thus, this review aims to demonstrate how plant growth-promoting bacteria could mitigate negative responses in plants exposed to water stress and provide examples of technological conversion applied to agroecosystems.

Fungi That Promote Plant Growth in the Rhizosphere Boost Crop Growth

The fungi species dwelling in the rhizosphere of crop plants, revealing functions that endeavor sustainability of the plants, are commonly referred to as 'plant-growth-promoting fungi' (PGPF). They are biotic inducers that provide benefits and carry out important functions in agricultural sustainability. The problem encountered in the agricultural system nowadays is how to meet population demand based on crop yield and protection without putting the environment and human and animal health at risk based on crop production. PGPF including Trichoderma spp., Gliocladium virens, Penicillium digitatum, Aspergillus flavus, Actinomucor elegans, Podospora bulbillosa, Arbuscular mycorrhizal fungi, etc., have proven their ecofriendly nature to ameliorate the production of crops by improving the growth of the shoots and roots of crop plants, the germination of seeds, the production of chlorophyll for photosynthesis, and the abundant production of crops. PGPF's potential mode of action is as follows: the mineralization of the major and minor elements required to support plants' growth and productivity. In addition, PGPF produce phytohormones, induced resistance, and defense-related enzymes to inhibit or eradicate the invasion of pathogenic microbes, in other words, to help the plants while encountering stress. This review portrays the potential of PGPF as an effective bioagent to facilitate and promote crop production, plant growth, resistance to disease invasion, and various abiotic stresses.

Metabolomic Analysis Reveals the Metabolic Diversity of Wild and Cultivated Stellaria Radix (Stellaria dichotoma L. var. lanceolata Bge.)

Stellaria Radix, called Yinchaihu in Chinese, is a traditional Chinese medicine, which is obtained from the dried roots of Stellaria dichotoma L. var. lanceolata Bge. Cultivated yinchaihu (YCH) has become a main source of production to alleviate the shortage of wild plant resources, but it is not clear whether the metabolites of YCH change with the mode of production. In this study, the contents of methanol extracts, total sterols and total flavonoids in wild and cultivated YCH are compared. The metabolites were analyzed by ultra-high performance liquid chromatography-tandem time-of-flight mass spectrometry. The content of methanol extracts of the wild and cultivated YCH all exceeded the standard content of the Chinese Pharmacopoeia. However, the contents of total sterols and total flavonoids in the wild YCH were significantly higher than those in the cultivated YCH. In total, 1586 metabolites were identified by mass spectrometry, and 97 were significantly different between the wild and cultivated sources, including β-sitosterol, quercetin derivatives as well as many newly discovered potential active components, such as trigonelline, arctiin and loganic acid. The results confirm that there is a rich diversity of metabolites in the wild and cultivated YCH, and provide a useful theoretical guidance for the evaluation of quality in the production of YCH.

Tomato Yellow Leaf Curl Sardinia Virus Increases Drought Tolerance of Tomato

Drought stress is one of the major physiological stress factors that adversely affect agricultural production, altering critical features of plant growth and metabolism. Plants can be subjected simultaneously to abiotic and biotic stresses, such as drought and viral infections. Rewarding effects provided by viruses on the ability of host plants to endure abiotic stresses have been reported. Recently, begomoviruses causing the tomato yellow leaf curl disease in tomatoes were shown to increase heat and drought tolerance. However, biological bases underlying the induced drought tolerance need further elucidation, particularly in the case of tomato plants. In this work, tomato plants infected by the tomato yellow leaf curl Sardinia virus (TYLCSV) were subjected to severe drought stress, followed by recovery. Morphological traits, water potential, and hormone contents were measured in leaves together with molecular analysis of stress-responsive and hormone metabolism-related genes. Wilting symptoms appeared three days later in TYLCSV-infected plants compared to healthy controls and post-rehydration recovery was faster (2 vs. 4 days, respectively). Our study contributes new insights into the impact of viruses on the plant's adaptability to environmental stresses. On a broader perspective, such information could have important practical implications for managing the effects of climate change on agroecosystems.

Biostimulants alleviate water deficit stress and enhance essential oil productivity: a case study with savory

Water deficit stress exposure frequently constrains plant and agri-food production globally. Biostimulants (BSs) can be considered a new tool in mitigating water deficit stress. This study aimed to understand how BSs influence water deficit stress perceived by savory plants (Satureja hortensis L.), an important herb used for nutritional and herbal purposes in the Middle East. Three BS treatments, including bio-fertilizers, humic acid and foliar application of amino acid (AA), were implemented. Each treatment was applied to savory plants using three irrigation regimes (low, moderate and severe water deficit stress FC100, FC75 and FC50, respectively). Foliar application of AA increased dry matter yield, essential oil (EO) content and EO yield by 22%, 31% and 57%, respectively. The greatest EO yields resulted from the moderate (FC75) and severe water deficit stress (FC50) treatments treated with AA. Primary EO constituents included carvacrol (39-43%), gamma-terpinene (27-37%), alpha-terpinene (4-7%) and p-cymene (2-5%). Foliar application of AA enhanced carvacrol, gamma-terpinene, alpha-terpinene and p-cymene content by 6%, 19%, 46% and 18%, respectively. Physiological characteristics were increased with increasing water shortage and application of AA. Moreover, the maximum activities of superoxide dismutase (3.17 unit mg^-1 min^-1), peroxidase (2.60 unit mg^-1 min^-1) and catalase (3.08 unit mg^-1 min^-1) were obtained from plants subjected to severe water deficit stress (FC50) and treated with AA. We conclude that foliar application of AA under water deficit stress conditions would improve EO quantity and quality in savory.

Drought-induced recruitment of specific root-associated bacteria enhances adaptation of alfalfa to drought stress

Drought is a major abiotic stress that threatens crop production. Soil microbiomes are thought to play a role in enhancing plant adaptation to various stresses. However, it remains unclear whether soil microbiomes play a key role when plants are challenged by drought and whether different varieties are enriched with specific bacteria at the rhizosphere. In this study, we measured changes in growth phenotypes, physiological and biochemical characteristics of drought-tolerant alfalfa (AH) and drought-sensitive (QS) under sterilized and unsterilized soil conditions with adequate watering and with drought stress, and analyzed the rhizosphere bacterial community composition and changes using 16S rRNA high-throughput sequencing. We observed that the unsterilized treatment significantly improved the growth, and physiological and biochemical characteristics of alfalfa seedlings under drought stress compared to the sterilized treatment. Under drought stress, the fresh and dry weight of seedlings increased by 35.24, 29.04, and 11.64%, 2.74% for unsterilized AH and QS, respectively, compared to sterilized treatments. The improvement was greater for AH than for QS. AH and QS recruited different rhizosphere bacteria when challenged by drought. Interestingly, under well-watered conditions, the AH rhizosphere was already rich in drought-tolerant bacterial communities, mainly Proteobacteria and Bacteroidetes, whereas these bacteria started to increase only when QS was subjected to drought. When drought stress was applied, AH was enriched with more drought-tolerant bacteria, mainly Acidobacteria, while the enrichment was weaker in QS rhizosphere. Therefore, the increase in drought tolerance of the drought-tolerant variety AH was greater than that of the drought-sensitive variety QS. Overall, this study confirmed the key role of drought-induced rhizosphere bacteria in improving the adaptation of alfalfa to drought stress, and clarified that this process is significantly related to the variety (genotype). The results of this study provide a basis for improving drought tolerance in alfalfa by regulating the rhizosphere microbiome.

Seed Bio-priming of wheat with a novel bacterial strain to modulate drought stress in Daegu, South Korea

Wheat is one of the major cereal crop grown food worldwide and, therefore, plays has a key role in alleviating the global hunger crisis. The effects of drought stress can reduces crop yields by up to 50% globally. The use of drought-tolerant bacteria for biopriming can improve crop yields by countering the negative effects of drought stress on crop plants. Seed biopriming can reinforce the cellular defense responses to stresses via the stress memory mechanism, that its activates the antioxidant system and induces phytohormone production. In the present study, bacterial strains were isolated from rhizospheric soil taken from around the Artemisia plant at Pohang Beach, located near Daegu, in the South Korea Republic of Korea. Seventy-three isolates were screened for their growth-promoting attributes and biochemical characteristics. Among them, the bacterial strain SH-8 was selected preferred based on its plant growth-promoting bacterial traits, which are as follows: abscisic acid (ABA) concentration = 1.08 ± 0.05 ng/mL, phosphate-solubilizing index = 4.14 ± 0.30, and sucrose production = 0.61 ± 0.13 mg/mL. The novel strain SH-8 demonstrated high tolerance oxidative stress. The antioxidant analysis also showed that SH-8 contained significantly higher levels of catalase (CAT), superoxide dismutase (SOD), and ascorbic peroxidase (APX). The present study also quantified and determined the effects of biopriming wheat (Triticum aestivum) seeds with the novel strain SH-8. SH-8 was highly effective in enhancing the drought tolerance of bioprimed seeds; their drought tolerance and germination potential (GP) were increased by up to 20% and 60%, respectively, compared with those in the control group. The lowest level of impact caused by drought stress and the highest germination potential, seed vigor index (SVI), and germination energy (GE) (90%, 2160, and 80%, respectively), were recorded for seeds bioprimed with with SH-8. These results show that SH-8 enhances drought stress tolerance by up to 20%. Our study suggests that the novel rhizospheric bacterium SH-8 (gene accession number OM535901) is a valuable biostimulant that improves drought stress tolerance in wheat plants and has the potential to be used as a biofertilizer under drought conditions.

Combined application of plant growth-promoting bacteria and iron oxide nanoparticles ameliorates the toxic effects of arsenic in Ajwain (Trachyspermum ammi L.)

Soil contamination with toxic heavy metals [such as arsenic (As)] is becoming a serious global problem because of the rapid development of the social economy. Although plant growth-promoting bacteria (PGPB) and nanoparticles (NPs) are the major protectants to alleviate metal toxicity, the study of these chemicals in combination to ameliorate the toxic effects of As is limited. Therefore, the present study was conducted to investigate the combined effects of different levels of Providencia vermicola (5 ppm and 10 ppm) and iron oxide nanoparticles (FeO-NPs) (50 mg/l^-1 and 100 mg/l^-1) on plant growth and biomass, photosynthetic pigments, gas exchange attributes, oxidative stress and response of antioxidant compounds (enzymatic and non-enzymatic), and their specific gene expression, sugars, nutritional status of the plant, organic acid exudation pattern As accumulation from the different parts of the plants, and electron microscopy under the soil, which was spiked with different levels of As [0 μM (i.e., no As), 50 μM, and 100 μM] in Ajwain (Trachyspermum ammi L.) seedlings. Results from the present study showed that the increasing levels of As in the soil significantly (p< 0.05) decreased plant growth and biomass, photosynthetic pigments, gas exchange attributes, sugars, and nutritional contents from the roots and shoots of the plants, and destroyed the ultra-structure of membrane-bound organelles. In contrast, increasing levels of As in the soil significantly (p< 0.05) increased oxidative stress indicators in term of malondialdehyde, hydrogen peroxide, and electrolyte leakage, and also increased organic acid exudation patter in the roots of T. ammi seedlings. The negative impact of As toxicity can overcome the application of PGPB (P. vermicola) and FeO-NPs, which ultimately increased plant growth and biomass by capturing the reactive oxygen species, and decreased oxidative stress in T. ammi seedlings by decreasing the As contents in the roots and shoots of the plants. Our results also showed that the FeO-NPs were more sever and showed better results when we compared with PGPB (P. vermicola) under the same treatment of As in the soil. Research findings, therefore, suggest that the combined application of P. vermicola and FeO-NPs can ameliorate As toxicity in T. ammi seedlings, resulting in improved plant growth and composition under metal stress, as depicted by balanced exudation of organic acids.

Screening Bambara Groundnut (Vigna subterranea L. Verdc) Genotypes for Drought Tolerance at the Germination Stage under Simulated Drought Conditions

Bambara groundnut (Vigna subterranea L. Verdc) is grown by smallholders and subsistence farmers in the marginal parts of sub-Saharan Africa. This legume is native to Africa and is cultivated throughout semi-arid sub-Saharan Africa. It is hardy and has been recognized as a nutritious food source in times of scarcity. Drought can negatively affect the germination or establishment of seedlings in the early stages of crop growth. Drought can limit the growing season of certain crops and create conditions that encourage the invasion of insects and diseases. Drought can also lead to a lack of crop yield, leading to rising food prices, shortages, and possibly malnutrition in vulnerable populations. A drought-tolerant genotype can be identified at the germination stage of Bambara groundnut by screening for drought-tolerance traits, and this knowledge can be applied to Bambara crop improvement programs to identify drought-tolerant traits during early growth phases. As an osmolyte, polyethylene glycol (PEG 6000) reduced water potential and simulated drought stress in Bambara groundnut seeds of different genotypes. Osmolytes are low-molecular-weight organic compounds that influence biological fluid properties. In this study, 24 Bambara groundnut genotypes were used. Data were collected on seed germination percentage (G%), germination velocity index (GVI), mean germination time (MGT), root dry mass (RDM), root fresh mass (RFM), and seven drought tolerance indices: mean productivity (MP), tolerance index (TOL), geometric mean productivity (GMP), stress susceptibility index (SSI), yield index (YI), yield stability index (YSI), stress tolerance index (STI) as well as seed coat color measurements. The data were applied to the mean observation of genotypes under simulated drought conditions (Ys) and the mean observation of genotypes under controlled conditions (Yp). Germination%, germination velocity index (GVI), mass germination time (MGT), and root fresh mass (RFM) differed significantly (p < 0.001) between the two stress conditions. Bambara genotypes Acc 82 and Acc 96 were found to be the most drought-tolerant.

Roles of Glutamate Receptor-Like Channels (GLRs) in Plant Growth and Response to Environmental Stimuli

Plant glutamate receptor-like channels (GLRs) are the homologues of ionotropic glutamate receptors (iGluRs) that mediate neurotransmission in mammals, and they play important roles in various plant-specific physiological processes, such as pollen tube growth, sexual reproduction, root meristem proliferation, internode cell elongation, stomata aperture regulation, and innate immune and wound responses. Notably, these biological functions of GLRs have been mostly linked to the Ca²⁺-permeable channel activity as GLRs can directly channel the transmembrane flux of Ca²⁺, which acts as a key second messenger in plant cell responses to both endogenous and exogenous stimuli. Thus, it was hypothesized that GLRs are mainly involved in Ca²⁺ signaling processes in plant cells. Recently, great progress has been made in GLRs for their roles in long-distance signal transduction pathways mediated by electrical activity and Ca²⁺ signaling. Here, we review the recent progress on plant GLRs, and special attention is paid to recent insights into the roles of GLRs in response to environmental stimuli via Ca²⁺ signaling, electrical activity, ROS, as well as hormone signaling networks. Understanding the roles of GLRs in integrating internal and external signaling for plant developmental adaptations to a changing environment will definitely help to enhance abiotic stress tolerance.

Plant Microbiome Engineering: Hopes or Hypes

Rhizosphere microbiome is a dynamic and complex zone of microbial communities. This complex plant-associated microbial community, usually regarded as the plant's second genome, plays a crucial role in plant health. It is unquestioned that plant microbiome collectively contributes to plant growth and fitness. It also provides a safeguard from plant pathogens, and induces tolerance in the host against abiotic stressors. The revolution in omics, gene-editing and sequencing tools have somehow led to unravel the compositions and latent interactions between plants and microbes. Similarly, besides standard practices, many biotechnological, (bio)chemical and ecological methods have also been proposed. Such platforms have been solely dedicated to engineer the complex microbiome by untangling the potential barriers, and to achieve better agriculture output. Yet, several limitations, for example, the biological obstacles, abiotic constraints and molecular tools that capably impact plant microbiome engineering and functionality, remained unaddressed problems. In this review, we provide a holistic overview of plant microbiome composition, complexities, and major challenges in plant microbiome engineering. Then, we unearthed all inevitable abiotic factors that serve as bottlenecks by discouraging plant microbiome engineering and functionality. Lastly, by exploring the inherent role of micro/macrofauna, we propose economic and eco-friendly strategies that could be harnessed sustainably and biotechnologically for resilient plant microbiome engineering.

PGP-Bacterium Pseudomonas protegens Improves Bread Wheat Growth and Mitigates Herbicide and Drought Stress

The reaction of plants to simultaneous stress action and treatment with biological stimulants still remains poorly studied. Laboratory and field experiments have been conducted to study the growth and yield of bread wheat (Triticum aestivum L.) of the variety Ekada 113; stress markers and quantitative ratios of phytohormones in plants under insufficient soil moisture; the effects of spraying with herbicide containing 2,4-D and dicamba and growth-stimulating bacterium Pseudomonas protegens DA1.2; and combinations of these factors. Under water shortage conditions, spraying plants with Chistalan reduced their growth compared to non-sprayed plants, which was associated with inhibition of root growth and a decrease in the content of endogenous auxins in the plants. Under conditions of combined stress, the treatment of plants with the strain P. protegens DA1.2 increased the IAA/ABA ratio and prevented inhibition of root growth by auxin-like herbicide, ensuring water absorption by the roots as well as increased transpiration. As a result, the content of malondialdehyde oxidative stress marker was reduced. Bacterization improved the water balance of wheat plants under arid field conditions. The addition of bacterium P. protegens DA1.2 to the herbicide Chistalan increased relative water content in wheat leaves by 11% compared to plants treated with herbicide alone. Application of the bacterial strain P. protegens DA1.2 increased the amount of harvested grain from 2.0-2.2 t/ha to 3.2-3.6 t/ha. Thus, auxin-like herbicide Chistalan and auxin-producing bacterium P. protegens DA1.2 may affect the balance of phytohormones in different ways. This could be the potential reason for the improvement in wheat plants' growth during dry periods when the bacterium P. protegens DA1.2 is included in mixtures for weed control.

Short-term responses of Spinach (Spinacia oleracea L.) to the individual and combinatorial effects of Nitrogen, Phosphorus and Potassium and silicon in the soil contaminated by boron

While of lesser prevalence than boron (B) deficient soils, B-rich soils are important to study as they can cause B toxicity in the field and subsequently decrease crop yields in different regions of the world. We have conducted the present study to examine the role of the individual or combined application of silicon (Si) and NPK fertilizer in B-stressed spinach plants (Spinacia oleracea L.). S. oleracea seedlings were subjected to different NPK fertilizers, namely, low NPK (30 kg ha-2) and normal NPK (60 kg ha-2)], which were also supplemented by Si (3 mmol L-1), for varying levels of B in the soil i.e., 0, 250, and 500 mg kg-1. Our results illustrated that the increasing levels of B in the soil caused a substantial decrease in the plant height, number of leaves, number of stems, leaf area, plant fresh weight, plant dry weight, chlorophyll a, chlorophyll b, total chlorophyll, carotenoid content, net photosynthesis, stomatal conductance, transpiration rate, magnesium content in the roots, magnesium contents in the shoots, phosphorus content in the roots, phosphorus content in the leaves in the shoots, iron content in the roots, iron content in the shoots, calcium content in the roots, and calcium content in the shoots. However, B toxicity in the soil increased the concentration of malondialdehyde, hydrogen peroxide, and electrolyte leakage which were also manifested by the increasing activities of enzymatic [superoxidase dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX)], and non-enzymatic antioxidants (phenolic, flavonoid, ascorbic acid, and anthocyanin content). B toxicity in the soil further increased the concentration of organic acids in the roots such as oxalic acid, malic acid, formic acid, citric acid, acetic acid, and fumaric acid. The addition of Si and fertilizer levels in the soil significantly alleviated B toxicity effects on S. oleracea by improving photosynthetic capacity and ultimately plant growth. The increased activity of antioxidant enzymes in Si and NPK-treated plants seems to play a role in capturing stress-induced reactive oxygen species, as was evident from the lower levels of oxidative stress indicators, organic acid exudation, and B concentration in the roots and shoots of Si and NPK-treated plants. Research findings, therefore, suggested that the Si and NPK application can ameliorate B toxicity in S. oleracea seedlings and result in improved plant growth and composition under metal stress as depicted by the balanced exudation of organic acids.

Impact of Plantago ovata Forsk leaf extract on morpho-physio-biochemical attributes, ions uptake and drought resistance of wheat (Triticum aestivum L.) seedlings

The present study was conducted to examine the potential role of Plantago ovata Forsk leaf extract (POLE) which was applied at various concentration levels (control, hydropriming, 10, 20, 30, and 40% POLE) to the wheat (Triticum aestivum L.) seedlings. Drought stressed was applied at 60% osmotic potential (OM) to the T. aestivum seedlings to study various parameters such as growth and biomass, photosynthetic pigments and gas exchange characteristics, oxidative stress and response of various antioxidants and nutritional status of the plants. Various growth parameters such as gaseous exchange attributes, antioxidants and nutritional status of T. aestivum were investigated in this study. It was evident that drought-stressed condition had induced a negative impact on plant growth, photosynthetic pigment, gaseous exchange attributes, stomatal properties, and ion uptake by different organs (roots and shoots) of T. aestivum. The decrease in plant growth resulted from oxidative stress and overcome by the antioxidant (enzymatic and non-enzymatic) compounds, since their concentration increased in response to dehydration. Seed priming with POLE positively increased plant growth and photosynthesis, by decreasing oxidative stress indicators and increasing activities of antioxidant (enzymatic and non-enzymatic) compounds, compared to the plants which were grown without the application of POLE. Our results also depicted that optimum concentration of POLE for T. aestivum seedlings under drought condition was 20%, while further increase in POLE (30 and 40%) induced a non-significant (P < 0.05) effect on growth (shoot and root length) and biomass (fresh and dry weight) of T. aestivum seedling. Here we concluded that the understanding of the role of seed priming with POLE in the increment of growth profile, photosynthetic measurements and nutritional status introduces new possibilities for their effective use in drought-stressed condition and provides a promising strategy for T. aestivum tolerance against drought-stressed condition.

New opportunities in plant microbiome engineering for increasing agricultural sustainability under stressful conditions

Plant microbiome (or phytomicrobiome) engineering (PME) is an anticipated untapped alternative strategy that could be exploited for plant growth, health and productivity under different environmental conditions. It has been proven that the phytomicrobiome has crucial contributions to plant health, pathogen control and tolerance under drastic environmental (a)biotic constraints. Consistent with plant health and safety, in this article we address the fundamental role of plant microbiome and its insights in plant health and productivity. We also explore the potential of plant microbiome under environmental restrictions and the proposition of improving microbial functions that can be supportive for better plant growth and production. Understanding the crucial role of plant associated microbial communities, we propose how the associated microbial actions could be enhanced to improve plant growth-promoting mechanisms, with a particular emphasis on plant beneficial fungi. Additionally, we suggest the possible plant strategies to adapt to a harsh environment by manipulating plant microbiomes. However, our current understanding of the microbiome is still in its infancy, and the major perturbations, such as anthropocentric actions, are not fully understood. Therefore, this work highlights the importance of manipulating the beneficial plant microbiome to create more sustainable agriculture, particularly under different environmental stressors.

Thiourea-Capped Nanoapatites Amplify Osmotic Stress Tolerance in Zea mays L. by Conserving Photosynthetic Pigments, Osmolytes Biosynthesis and Antioxidant Biosystems

Salinity is one of the most prevalent abiotic stresses which not only limits plant growth and yield, but also limits the quality of food products. This study was conducted on the surface functionalization of phosphorus-rich mineral apatite nanoparticles (ANPs), with thiourea as a source of nitrogen (TU-ANPs) and through a co-precipitation technique for inducing osmotic stress tolerance in Zea mays. The resulting thiourea-capped apatite nanostructure (TU-ANP) was characterized using complementary analytical techniques, such as EDX, SEM, XRD and IR spectroscopy. The pre-sowing of soaked seeds of Zea mays in 1.00 µg/mL, 5.00 µg/mL and 10 µg/mL of TU-ANPs yielded growth under 0 mM, 60 mM and 100 mM osmotic stress of NaCl. The results show that Ca and P salt acted as precursors for the synthesis of ANPs at an alkaline pH of 10-11. Thiourea as a source of nitrogen stabilized the ANPs' suspension medium, leading to the synthesis of TU-ANPs. XRD diffraction analysis validated the crystalline nature of TU-ANPs with lattice dimensions of 29 nm, calculated from FWHM using the Sherrer equation. SEM revealed spherical morphology with polydispersion in size distribution. EDS confirmed the presence of Ca and P at a characteristic KeV, whereas IR spectroscopy showed certain stretches of binding functional groups associated with TU-ANPs. Seed priming with TU-ANPs standardized germination indices (T50, MGT, GI and GP) which were significantly declined by NaCl-based osmotic stress. Maximum values for biochemical parameters, such as sugar (39.8 mg/g at 10 µg/mL), protein (139.8 mg/g at 10 µg/mL) and proline (74.1 mg/g at 10 µg/mL) were recorded at different applied doses of TU-ANP. Antioxidant biosystems in the form of EC 1.11.1.6 catalase (11.34 IU/g FW at 10 µg/mL), EC 1.11.1.11 APX (0.95 IU/G FW at 10 µg/mL), EC 1.15.1.1 SOD (1.42 IU/g FW at 5 µg/mL), EC 1.11.1.7 POD (0.43 IU/g FW at 5 µg/mL) were significantly restored under osmotic stress. Moreover, photosynthetic pigments, such as chlorophyll A (2.33 mg/g at 5 µg/mL), chlorophyll B (1.99 mg/g at 5 µg/mL) and carotenoids (2.52 mg/g at 10 µg/mL), were significantly amplified under osmotic stress via the application of TU-ANPs. Hence, the application of TU-ANPs restores the growth performance of plants subjected to induced osmotic stress.

Mitigation of salinity stress in barley genotypes with variable salt tolerance by application of zinc oxide nanoparticles

Salinity has become a major environmental concern of agricultural lands, impairing crop production. The current study aimed to examine the role of zinc oxide nanoparticles (ZnO NPs) in reducing the oxidative stress induced by salinity and the overall improvement in phytochemical properties in barley. A total of nine different barley genotypes were first subjected to salt (NaCl) stress in hydroponic conditions to determine the tolerance among the genotypes. The genotype Annora was found as most sensitive, and the most tolerant genotype was Awaran 02 under salinity stress. In another study, the most sensitive (Annora) and tolerant (Awaran 02) barley genotypes were grown in pots under salinity stress (100 mM). At the same time, half of the pots were provided with the soil application of ZnO NPs (100 mg kg-1), and the other half pots were foliar sprayed with ZnO NPs (100 mg L-1). Salinity stress reduced barley growth in both genotypes compared to control plants. However, greater reduction in barley growth was found in Annora (sensitive genotype) than in Awaran 02 (tolerant genotype). The exogenous application of ZnO NPs ameliorated salt stress and improved barley biomass, photosynthesis, and antioxidant enzyme activities by reducing oxidative damage caused by salt stress. However, this positive effect by ZnO NPs was observed more in Awaran 02 than in Annora genotype. Furthermore, the foliar application of ZnO NPs was more effective than the soil application of ZnO NPs. Findings of the present study revealed that exogenous application of ZnO NPs could be a promising approach to alleviate salt stress in barley genotypes with different levels of salinity tolerance.

Bacillus thuringiensis PM25 ameliorates oxidative damage of salinity stress in maize via regulating growth, leaf pigments, antioxidant defense system, and stress responsive gene expression

Soil salinity is the major abiotic stress that disrupts nutrient uptake, hinders plant growth, and threatens agricultural production. Plant growth-promoting rhizobacteria (PGPR) are the most promising eco-friendly beneficial microorganisms that can be used to improve plant responses against biotic and abiotic stresses. In this study, a previously identified B. thuringiensis PM25 showed tolerance to salinity stress up to 3 M NaCl. The Halo-tolerant Bacillus thuringiensis PM25 demonstrated distinct salinity tolerance and enhance plant growth-promoting activities under salinity stress. Antibiotic-resistant Iturin C (ItuC) and bio-surfactant-producing (sfp and srfAA) genes that confer biotic and abiotic stresses were also amplified in B. thuringiensis PM25. Under salinity stress, the physiological and molecular processes were followed by the over-expression of stress-related genes (APX and SOD) in B. thuringiensis PM25. The results detected that B. thuringiensis PM25 inoculation substantially improved phenotypic traits, chlorophyll content, radical scavenging capability, and relative water content under salinity stress. Under salinity stress, the inoculation of B. thuringiensis PM25 significantly increased antioxidant enzyme levels in inoculated maize as compared to uninoculated plants. In addition, B. thuringiensis PM25-inoculation dramatically increased soluble sugars, proteins, total phenols, and flavonoids in maize as compared to uninoculated plants. The inoculation of B. thuringiensis PM25 significantly reduced oxidative burst in inoculated maize under salinity stress, compared to uninoculated plants. Furthermore, B. thuringiensis PM25-inoculated plants had higher levels of compatible solutes than uninoculated controls. The current results demonstrated that B. thuringiensis PM25 plays an important role in reducing salinity stress by influencing antioxidant defense systems and abiotic stress-related genes. These findings also suggest that multi-stress tolerant B. thuringiensis PM25 could enhance plant growth by mitigating salt stress, which might be used as an innovative tool for enhancing plant yield and productivity.

Impact of foliar application of syringic acid on tomato (Solanum lycopersicum L.) under heavy metal stress-insights into nutrient uptake, redox homeostasis, oxidative stress, and antioxidant defense

Soil contamination with toxic heavy metals [such as lead (Pb)] is becoming a serious global problem due to the rapid development of the social economy. However, accumulation of Pb in plant parts is very toxic for plant growth and decreases crop yield and productivity. In the present study, we have investigated the different concentrations of Pb in the soil i.e., [0 (no Pb), 50, and 100 mg kg^-1] to study plant growth and biomass, photosynthetic pigments and gas exchange characteristics, oxidative stress indicators and the response of various antioxidants (enzymatic and non-enzymatic), nutritional status of the plant, organic acid exudation pattern and also Pb accumulation in the roots and shoots of the plants of two varieties of tomato (Solanum lycopersicum L.) i.e., Roma and Cchuas, grown under different levels of synergic acid [no spray (NS), water spray (WS), 0.3-0.5°μM]. Results from the present study showed that the increasing levels of Pb in the soil decreased non-significantly (P < 0.05) shoot length, root length, shoot fresh weight, root fresh weight, shoot dry weight, root dry weight, chlorophyll-a, chlorophyll-b, total chlorophyll, carotenoid content, net photosynthesis, stomatal conductance, transpiration rate, soluble sugar, reducing sugar, non-reducing sugar contents, calcium (Ca²⁺), magnesium (Mg²⁺), iron (Fe²⁺), and phosphorus (P) contents in the roots and shoots of the plants. However, Pb toxicity also induced oxidative stress in the roots and shoots of the plants by increasing malondialdehyde (MDA), hydrogen peroxide (H₂O₂), and electrolyte leakage (EL) which also induced increased the compounds of various enzymatic and non-enzymatic antioxidants and also organic acids exudation pattern in the roots such as fumaric acid, acetic acid, citric acid, formic acid, malic acid, oxalic acid contents and increased the concentration of Pb in different parts of the plants. Results also show that the Cchuas showed better growth and development compared to Roma, under the same levels of Pb in the soil. The alleviation of Pb toxicity was induced by the application of synergic acid, and results showed that the application of synergic acid increased plant growth and biomass and also increased the gas exchange characteristics and antioxidant capacity in the roots and shoots of the plants. Research findings, therefore, suggested that synergic acid application can ameliorate Pb toxicity in S. lycopersicum varieties and result in improved plant growth and composition under metal stress as depicted by balanced exudation of organic acids.