Salicylic acid alleviates decreases in photosynthesis under salt stress by enhancing nitrogen and sulfur assimilation and antioxidant metabolism differentially in two mungbean cultivars

Seed priming with potassium nitrate alleviates the high temperature stress by modulating growth and antioxidant potential in carrot seeds and seedlings

Early season carrot (Daucus carota) production is being practiced in Punjab, Pakistan to meet the market demand but high temperature hampers the seed germination and seedling establishment which cause marked yield reduction. Seed priming with potassium nitrate breaks the seed dormancy and improves the seed germination and seedling growth potential but effects vary among the species and ecological conditions. The mechanism of KNO3 priming in high temperature stress tolerance is poorly understood yet. Thus, present study aimed to evaluate high temperature stress tolerance potential of carrot seeds primed with potassium nitrate and impacts on growth, physiological, and antioxidant defense systems. Carrot seeds of a local cultivar (T-29) were primed with various concentration of KNO3 (T0: unprimed (negative control), T1: hydroprimed (positive control), T2: 50 mM, T3:100mM, T4: 150 mM, T5: 200 mM, T6: 250 mM and T7: 300 mM) for 12 h each in darkness at 20 ± 2℃. Seed priming with 50 mM of KNO3 significantly enhanced the seed germination (36%), seedling growth (28%) with maximum seedling vigor (55%) and also exhibited 16.75% more carrot root biomass under high temperature stress as compared to respective control. Moreover, enzymatic activities including peroxidase, catalase, superoxidase dismutase, total phenolic contents, total antioxidants contents and physiological responses of plants were also improved in response to seed priming under high temperature stress. By increasing the level of KNO3, seed germination, growth and root biomass were reduced. These findings suggest that seed priming with 50 mM of KNO3 can be an effective strategy to improve germination, growth and yield of carrot cultivar (T-29) under high temperature stress in early cropping. This study also proposes that KNO3 may induces the stress memory by heritable modulations in chromosomal structure and methylation and acetylation of histones that may upregulate the hormonal and antioxidant activities to enhance the stress tolerance in plants.

Ascorbic Acid Improves Tomato Salt Tolerance by Regulating Ion Homeostasis and Proline Synthesis

In this study, processing tomato (Solanum lycopersicum L.) 'Ligeer 87-5' was hydroponically cultivated under 100 mM NaCl to simulate salt stress. To investigate the impacts on ion homeostasis, osmotic regulation, and redox status in tomato seedlings, different endogenous levels of ascorbic acid (AsA) were established through the foliar application of 0.5 mM AsA (NA treatment), 0.25 mM lycorine (LYC, an inhibitor of AsA synthesis; NL treatment), and a combination of LYC and AsA (NLA treatment). The results demonstrated that exogenous AsA significantly increased the activities and gene expressions of key enzymes (L-galactono-1,4-lactone dehydrogenase (GalLDH) and L-galactose dehydrogenase (GalDH)) involved in AsA synthesis in tomato seedling leaves under NaCl stress and NL treatment, thereby increasing cellular AsA content to maintain its redox status in a reduced state. Additionally, exogenous AsA regulated multiple ion transporters via the SOS pathway and increased the selective absorption of K+, Ca2+, and Mg2+ in the aerial parts, reconstructing ion homeostasis in cells, thereby alleviating ion imbalance caused by salt stress. Exogenous AsA also increased proline dehydrogenase (ProDH) activity and gene expression, while inhibiting the activity and transcription levels of Δ1-pyrroline-5-carboxylate synthetase (P5CS) and ornithine-δ-aminotransferase (OAT), thereby reducing excessive proline content in the leaves and alleviating osmotic stress. LYC exacerbated ion imbalance and osmotic stress caused by salt stress, which could be significantly reversed by AsA application. Therefore, exogenous AsA application increased endogenous AsA levels, reestablished ion homeostasis, maintained osmotic balance, effectively alleviated the inhibitory effect of salt stress on tomato seedling growth, and enhanced their salt tolerance.

The genetic orchestra of salicylic acid in plant resilience to climate change induced abiotic stress: critical review

Climate change, driven by human activities and natural processes, has led to critical alterations in varying patterns during cropping seasons and is a vital threat to global food security. The climate change impose several abiotic stresses on crop production systems. These abiotic stresses include extreme temperatures, drought, and salinity, which expose agricultural fields to more vulnerable conditions and lead to substantial crop yield and quality losses. Plant hormones, especially salicylic acid (SA), has crucial roles for plant resiliency under unfavorable environments. This review explores the genetics and molecular mechanisms underlying SA's role in mitigating abiotic stress-induced damage in plants. It also explores the SA biosynthesis pathways, and highlights the regulation of their products under several abiotic stresses. Various roles and possible modes of action of SA in mitigating abiotic stresses are discussed, along with unraveling the genetic mechanisms and genes involved in responses under stress conditions. Additionally, this review investigates molecular pathways and mechanisms through which SA exerts its protective effects, such as redox signaling, cross-talks with other plant hormones, and mitogen-activated protein kinase pathways. Moreover, the review discusses potentials of using genetic engineering approaches, such as CRISPR technology, for deciphering the roles of SA in enhancing plant resilience to climate change related abiotic stresses. This comprehensive analysis bridges the gap between genetics of SA role in response to climate change related stressors. Overall goal is to highlight SA's significance in safeguarding plants and by offering insights of SA hormone for sustainable agriculture under challenging environmental conditions.

Multi-omics analyses of sid2 mutant reflect the need of isochorismate synthase ICS1 to cope with sulfur limitation in Arabidopsis thaliana

The SID2 (SA INDUCTION-DEFICIENT2) gene that encodes ICS1 (isochorismate synthase), plays a central role in salicylic acid biosynthesis in Arabidopsis. The sid2 and NahG (encoding a bacterial SA hydroxylase) overexpressing mutants (NahG-OE) have currently been shown to outperform wild type, presenting delayed leaf senescence, higher plant biomass and better seed yield. When grown under sulfate-limited conditions (low-S), sid2 mutants exhibited early leaf yellowing compared to the NahG-OE, the npr1 mutant affected in SA signaling pathway, and WT. This indicated that the hypersensitivity of sid2 to sulfate limitation was independent of the canonical npr1 SA-signaling pathway. Transcriptomic and proteomic analyses revealed that major changes occurred in sid2 when cultivated under low-S, changes that were in good accordance with early senescence phenotype and showed the exacerbation of stress responses. The sid2 mutants displayed a lower sulfate uptake capacity when cultivated under low-S and lower S concentrations in their rosettes. Higher glutathione concentrations in sid2 rosettes under low-S were in good accordance with the higher abundance of proteins involved in glutathione and ascorbate redox metabolism. Amino acid and lipid metabolisms were also strongly modified in sid2 under low-S. Depletion of total fatty acids in sid2 under low-S was consistent with the fact that S-metabolism plays a central role in lipid synthesis. Altogether, our results show that functional ICS1 is important for plants to cope with S limiting conditions.

The coexistence of arbuscular mycorrhizal fungi and dark septate endophytes synergistically enhanced the cadmium tolerance of maize

Introduction

Arbuscular mycorrhizal fungi (AMF) and dark septate endophytic fungi (DSEs) generally coexist in the roots of plants. However, our understanding of the effects of their coexistence on plant growth and stress resistance is limited.

Methods

In the present study, the effects of single and dual inoculation of AMF and DSE on the growth, photosynthetic physiology, glutathione (GSH) metabolism, endogenous hormones, and cadmium (Cd) content of maize under 25 mg•kg-1 Cd stress were investigated.

Results

Compared with that after the non-inoculation treatment, AMF+DSE co-inoculation significantly increased the photosynthetic rate (Pn) of maize leaves; promoted root GSH metabolism; increased the root GSH concentration and activity of γ-glutamyl cysteine synthase (γ-GCS), ATP sulfatase (ATPS) and sulfite reductase (SIR) by 215%, 117%, 50%, and 36%, respectively; and increased the concentration of endogenous hormones in roots, with increases in zeatin (ZR), indole-3 acetic acid (IAA), and abscisic acid (ABA) by 81%, 209%, and 72%, respectively. AMF inoculation, DSE inoculation and AMF+DSE co-inoculation significantly increased maize biomass, and single inoculation with AMF or DSE increased the Cd concentration in roots by 104% or 120%, respectively. Moreover, significant or highly significant positive correlations were observed between the contents of ZR, IAA, and ABA and the activities of γ-GCS, ATPS, and SIR and the glutathione (GSH) content. There were significant or highly significant positive interactions between AMF and DSE on the Pn of leaves, root GSH metabolism, and endogenous hormone contents according to two-way analysis of variance. Therefore, the coexistence of AMF and DSE synergistically enhanced the Cd tolerance of maize.

Azolla filiculoides extract improved salt tolerance in wheat (Triticum aestivum L.) is associated with prompting osmostasis, antioxidant potential and stress-interrelated genes

The growth and productivity of crop plants are negatively affected by salinity-induced ionic and oxidative stresses. This study aimed to provide insight into the interaction of NaCl-induced salinity with Azolla aqueous extract (AAE) regarding growth, antioxidant balance, and stress-responsive genes expression in wheat seedlings. In a pot experiment, wheat kernels were primed for 21 h with either deionized water or 0.1% AAE. Water-primed seedlings received either tap water, 250 mM NaCl, AAE spray, or AAE spray + NaCl. The AAE-primed seedlings received either tap water or 250 mM NaCl. Salinity lowered growth rate, chlorophyll level, and protein and amino acids pool. However, carotenoids, stress indicators (EL, MDA, and H2O2), osmomodulators (sugars, and proline), antioxidant enzymes (CAT, POD, APX, and PPO), and the expression of some stress-responsive genes (POD, PPO and PAL, PCS, and TLP) were significantly increased. However, administering AAE contributed to increased growth, balanced leaf pigments and assimilation efficacy, diminished stress indicators, rebalanced osmomodulators and antioxidant enzymes, and down-regulation of stress-induced genes in NaCl-stressed plants, with priming surpassing spray in most cases. In conclusion, AAE can be used as a green approach for sustaining regular growth and metabolism and remodelling the physio-chemical status of wheat seedlings thriving in salt-affected soils.

Chitosan and Chitosan Nanoparticles Differentially Alleviate Salinity Stress in Phaseolus vulgaris L. Plants

Salinity stress can significantly cause negative impacts on the physiological and biochemical traits of plants and, consequently, a reduction in the yield productivity of crops. Therefore, the current study aimed to investigate the effects of chitosan (Cs) and chitosan nanoparticles (CsNPs) to mitigate salinity stress (i.e., 25, 50, 100, and 200 mM NaCl) and improve pigment fractions, carbohydrates content, ions content, proline, hydrogen peroxide, lipid peroxidation, electrolyte leakage content, and the antioxidant system of Phaseolus vulgaris L. grown in clay-sandy soil. Methacrylic acid was used to synthesize CsNPs, with an average size of 40 ± 2 nm. Salinity stress negatively affected yield traits, pigment fractions, and carbohydrate content. However, in plants grown under salt stress, the application of either Cs or CsNPs significantly improved yield, pigment fractions, carbohydrate content, proline, and the antioxidant system, while these treatments reduced hydrogen peroxide, lipid peroxidation, and electrolyte leakage. The positive effects of CsNPs were shown to be more beneficial than Cs when applied exogenously to plants grown under salt stress. In this context, it could be concluded that CsNPs could be used to mitigate salt stress effects on Phaseolus vulgaris L. plants grown in saline soils.

Survival mechanisms of chickpea (Cicer arietinum) under saline conditions

Salinity is a significant abiotic stress that is steadily increasing in intensity globally. Salinity is caused by various factors such as use of poor-quality water for irrigation, poor drainage systems, and increasing spate of drought that concentrates salt solutions in the soil; salinity is responsible for substantial agricultural losses worldwide. Chickpea (Cicer arietinum) is one of the crops most sensitive to salinity stress. Salinity restricts chickpea growth and production by interfering with various physiological and metabolic processes, downregulating genes linked to growth, and upregulating genes encoding intermediates of the tolerance and avoidance mechanisms. Salinity, which also leads to osmotic stress, disturbs the ionic equilibrium of plants. Survival under salinity stress is a primary concern for the plant. Therefore, plants adopt tolerance strategies such as the SOS pathway, antioxidative defense mechanisms, and several other biochemical mechanisms. Simultaneously, affected plants exhibit mechanisms like ion compartmentalization and salt exclusion. In this review, we highlight the impact of salinity in chickpea, strategies employed by the plant to tolerate and avoid salinity, and agricultural strategies for dealing with salinity. With the increasing spate of salinity spurred by natural events and anthropogenic agricultural activities, it is pertinent to explore and exploit the underpinning mechanisms for salinity tolerance to develop mitigation and adaptation strategies in globally important food crops such as chickpea.

Hormesis management of Moringa oleifera with exogenous application of plant growth regulators under saline conditions

The study investigated the adaptability of Moringa oleifera to saline conditions, focusing on its hormesis behavior. It also examined how various plant growth regulators affected growth, physiological parameters, and bioactive compounds of moringa. In the first phase, different NaCl stress levels (0, 50, 100, 150, 200, and 250 mM) were applied. Notably, significant stimulation was observed at 100 mM stress for growth, total phenolics, total flavonoids and total chlorophyll content while 150 mM stress had a marked inhibitory effect, with survival decreasing at 200 and 250 mM NaCl levels. A 38% reduction in root attributes and shoot length, along with a 55% decrease in leaf score, was observed at 150 mM stress. Total phenolics showed a positive correlation with growth attributes. In the second phase, moringa plants grown under 50, 100, and 150 mM NaCl stress were treated with various plant growth regulators, including cytokinin (50 mg L-1), thiourea (5 mM), bezyl amino purine (BAP @50 mg L-1), salicylic acid (50 mg L-1), hydrogen peroxide (H2O2@120 μM), or ascorbic acid (50 mg L-1) to mitigate adverse effects of salinity. Cytokinin, BAP, and salicylic acid applications improved salinity tolerance, enhancing enzymatic, and non-enzymatic antioxidants, and the abundance of kaempferol, quercetin, hydroxybenzoic, and hydroxycinnamic acids. Pearson correlation and principal component analysis manifested relationships among growth parameters, antioxidant activities, flavonoids, and phenolic acids. This study provides new insights into hormesis management for moringa plants and the influence of plant growth regulators on flavonoids and phenolic acid levels in moringa leaves under saline conditions.

Differential response of phenylpropanoid pathway as linked to hormonal change in two Brassica napus cultivars contrasting drought tolerance

Oilseed rape (Brassica napus L.) is a significant agro-economic crop with a wide range of uses. Drought is the most frequent unfavourable environmental stressor restraining its growth and development worldwide. This study was conducted to characterize the drought-responsive phenylpropanoid pathway and its link to hormonal changes in two cultivars, drought-resistant "Saturnin" and drought-susceptible "Mosa." Drought susceptibility in cv. Mosa was confirmed by its lower water use efficiency and higher lipid peroxidation levels with reactive oxygen species (ROS) accumulation. In cv. Saturnin, higher salicylic acid (SA) levels and expression of dehydration-responsive element binding 2 (DREB2) and non-expressor of pathogenesis-related gene 1 (NPR1) led to an upregulation of production of anthocyanin pigment 1 (PAP1) and phenylpropanoid pathway-related gene (CHS, F5H and COMT1) expression, increasing hydroxycinnamic acid and flavonoid compound concentrations. However, in cv. Mosa, higher increases in the activity of lignifying enzymes (polyphenol oxidase, coniferyl alcohol peroxidase, syringaldazine peroxidase, guaiacol peroxidase) and expression of the lignin synthesis-related gene cinnamyl alcohol dehydrogenase 2 (CAD2) were found along with greater increases in abscisic acid (ABA) levels and upregulation of ABA-responsive element binding 2 (AREB2) and basic helix-loop-helix transcription factor MYC2. These results indicate that drought-induced SA-mediated activation of the hydroxycinnamic acid and flavonoid pathways contributes to drought resistance, whereas ABA-mediated lignification contributes to drought susceptibility.

Partial substitution of chemical fertilizer by Trichoderma biofertilizer improved nitrogen use efficiency in wolfberry (Lycium chinense) in coastal saline land

A two-year field trial was conducted to investigate the effects of partial substitution of chemical fertilizer (CF) by Trichoderma biofertilizer (TF) on nitrogen (N) use efficiency and associated mechanisms in wolfberry (Lycium chinense) in coastal saline land. As with plant biomass and fruit yield, apparent N use efficiency and plant N accumulation were also higher with TF plus 75% CF than 100% CF, indicating that TF substitution promoted plant growth and N uptake. As a reason, TF substitution stabilized soil N supply by mitigating steep deceases in soil NH4 +-N and NO3 -N concentrations in the second half of growing seasons. TF substitution also increased carbon (C) fixation according to higher photosynthetic rate (Pn) and stable 13C abundance with TF plus 75% CF than 100% CF. Importantly, leaf N accumulation significantly and positively related with Pn, biomass, and fruit yield, and structural equation modeling also confirmed the importance of the causal relation of N accumulation coupled with C fixation for biomass and yield formation. Consequently, physiological and agronomical N use efficiencies were significantly higher with TF plus 75% CF than 100% CF. Overall, partial substitution of CF by TF improved N use efficiency in wolfberry in coastal saline land by stabilizing soil N supply and coupling N accumulation with C fixation.

Seed Priming with Salicylic Acid Alleviates Salt Stress Toxicity in Barley by Suppressing ROS Accumulation and Improving Antioxidant Defense Systems, Compared to Halo- and Gibberellin Priming

Plants are highly sensitive to various environmental stresses, which can hinder their growth and reduce yields. In this study, we investigated the potential of seed priming with salicylic acid (SA), gibberellic acid (GA3), and sodium chloride (NaCl) to mitigate the adverse effects of salinity stress in Hordeum vulgare at the germination and early seedling stages. Exposing H. vulgare seeds to salt stress reduced the final germination percentage and seedling shoot and root growth. Interestingly, all seed treatments significantly improved salt-induced responses, with GA3 being more effective in terms of germination performance, plant growth, and photosynthesis. SA priming exhibited promising effects on antioxidant defense mechanisms, proline, sugar, and ascorbic acid production. Notably, SA priming also suppressed reactive oxygen species accumulation and prevented lipid peroxidation. These findings highlight the ability of SA to manage crosstalk within the seed, coordinating many regulatory processes to support plant adaptation to salinity stress.

Chlorophyll fluorescence-based high-throughput phenotyping facilitates the genetic dissection of photosynthetic heat tolerance in African (Oryza glaberrima) and Asian (Oryza sativa) rice

Rising temperatures and extreme heat events threaten rice production. Half of the global population relies on rice for basic nutrition, and therefore developing heat-tolerant rice is essential. During vegetative development, reduced photosynthetic rates can limit growth and the capacity to store soluble carbohydrates. The photosystem II (PSII) complex is a particularly heat-labile component of photosynthesis. We have developed a high-throughput chlorophyll fluorescence-based screen for photosynthetic heat tolerance capable of screening hundreds of plants daily. Through measuring the response of maximum PSII efficiency to increasing temperature, this platform generates data for modelling the PSII-temperature relationship in large populations in a small amount of time. Coefficients from these models (photosynthetic heat tolerance traits) demonstrated high heritabilities across African (Oryza glaberrima) and Asian (Oryza sativa, Bengal Assam Aus Panel) rice diversity sets, highlighting valuable genetic variation accessible for breeding. Genome-wide association studies were performed across both species for these traits, representing the first documented attempt to characterize the genetic basis of photosynthetic heat tolerance in any species to date. A total of 133 candidate genes were highlighted. These were significantly enriched with genes whose predicted roles suggested influence on PSII activity and the response to stress. We discuss the most promising candidates for improving photosynthetic heat tolerance in rice.

Uncovering the mechanisms of salicylic acid-mediated abiotic stress tolerance in horticultural crops

Salicylic acid (SA) has been recognized as a promising molecule for improving abiotic stress tolerance in plants due to its ability to enhance antioxidant defense system, and promote root architecture system. Recent research has focused on uncovering the mechanisms by which SA confers abiotic stress tolerance in horticultural crops. SA has been shown to act as a signaling molecule that triggers various physiological and morphological responses in plants. SA regulates the production of reactive oxygen species (ROS). Moreover, it can also act as signaling molecule that regulate the expression of stress-responsive genes. SA can directly interact with various hormones, proteins and enzymes involved in abiotic stress tolerance. SA regulates the antioxidant enzymes activities that scavenge toxic ROS, thereby reducing oxidative damage in plants. SA can also activate protein kinases that phosphorylate and activate transcription factors involved in stress responses. Understanding these mechanisms is essential for developing effective strategies to improve crop resilience in the face of changing environmental conditions. Current information provides valuable insights for farmers and plant researchers, offering new strategies to enhance crop resilience and productivity in the face of environmental challenges. By harnessing the power of SA and its signaling pathways, farmers can develop more effective stress management techniques and optimize crop performance. Plant researchers can also explore innovative approaches to breed or engineer crops with enhanced stress tolerance, thereby contributing to sustainable agriculture and food security.

The role of plant growth promoting rhizobacteria in plant drought stress responses

Climate change has exacerbated the effects of abiotic stresses on plant growth and productivity. Drought is one of the most important abiotic stress factors that interfere with plant growth and development. Plant selection and breeding as well as genetic engineering methods used to improve crop drought tolerance are expensive and time consuming. Plants use a myriad of adaptative mechanisms to cope with the adverse effects of drought stress including the association with beneficial microorganisms such as plant growth promoting rhizobacteria (PGPR). Inoculation of plant roots with different PGPR species has been shown to promote drought tolerance through a variety of interconnected physiological, biochemical, molecular, nutritional, metabolic, and cellular processes, which include enhanced plant growth, root elongation, phytohormone production or inhibition, and production of volatile organic compounds. Therefore, plant colonization by PGPR is an eco-friendly agricultural method to improve plant growth and productivity. Notably, the processes regulated and enhanced by PGPR can promote plant growth as well as enhance drought tolerance. This review addresses the current knowledge on how drought stress affects plant growth and development and describes how PGPR can trigger plant drought stress responses at the physiological, morphological, and molecular levels.

Salicylic acid-mitigates abiotic stress tolerance via altering defense mechanisms in Brassica napus (L.)

Under the changing climate due to global warming, various abiotic stresses including drought (D) and salinity (S) are expected to further trigger their devastating effects on the already vulnerable crop production systems. This experiment was designed to unravel and quantify the potential role of exogenous application of salicylic acid (SA) in mitigating both D and S stresses and their combination (D+S), with three replications using CRD (Completely Randomized Design). The obtained results of the current study demonstrated significant effects of all three types of stresses (D, S, and D+S) on various parameters in Brassica napus plants. Quantifying these parameters provides a more informative and precise understanding of the findings. Current results revealed that all three stress types (D, S, and D+S) resulted in a reduction in leaf area (13.65 to 21.87%), chlorophyll levels (30 to 50%), gaseous exchange rate (30 to 54%) and the concentration of mineral ions compared to non-stressed plants. However, application of SA helped in mitigating these stresses by ameliorating the negative effects of these stresses. Moreover, Malondialdehyde (MDA) contents, an indicator of lipid per-oxidation and oxidative stress, the levels of antioxidants, proline content, an osmolyte associated with stress tolerance, and sugar content in the leaves were elevated in response to all stress conditions. In addition, the ultra-structures within the leaves were negatively affected by the stresses, while an application of SA considerably minimized the deterioration of these structures thus providing protection to the brassica plants against the stresses. In a nutshell, the findings of this study suggest that SA application in S, D and S+ D stresses provides evasion to the plants by improving different physiological and growth indices. The application of Salicylic Acid (SA) mitigated the negative effects of the stresses on all the above parameters, reducing MDA contents (47%), antioxidants (11 to 20%), proline (28%), sugar contents (20.50%), and minimizing the deterioration of ultra-structures. The findings emphasize the potential mitigatory role of SA in mitigating D and S stresses and highlight the need for further research to understand the underlying mechanisms in detail and explore its practical application in farming practices.

Achieving abiotic stress tolerance in plants through antioxidative defense mechanisms

Climate change has increased the overall impact of abiotic stress conditions such as drought, salinity, and extreme temperatures on plants. Abiotic stress adversely affects the growth, development, crop yield, and productivity of plants. When plants are subjected to various environmental stress conditions, the balance between the production of reactive oxygen species and its detoxification through antioxidant mechanisms is disturbed. The extent of disturbance depends on the severity, intensity, and duration of abiotic stress. The equilibrium between the production and elimination of reactive oxygen species is maintained due to both enzymatic and non-enzymatic antioxidative defense mechanisms. Non-enzymatic antioxidants include both lipid-soluble (α-tocopherol and β-carotene) and water-soluble (glutathione, ascorbate, etc.) antioxidants. Ascorbate peroxidase (APX), superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR) are major enzymatic antioxidants that are essential for ROS homeostasis. In this review, we intend to discuss various antioxidative defense approaches used to improve abiotic stress tolerance in plants and the mechanism of action of the genes or enzymes involved.

CmCNIH1 improves salt tolerance by influencing the trafficking of CmHKT1;1 in pumpkin

Pumpkin is often used as a rootstock for other Cucurbitaceae crops due to its resistance to soil-borne diseases and abiotic stress. Pumpkin rootstocks use a sodium transporter (CmHKT1;1) to promote the transport of Na⁺ from the shoot to the root effectively and improve the salt tolerance of the scion. However, the molecular regulatory mechanisms that influence the activity of CmHKT1;1 during salt stress response remain unknown. In this study, CmCNIH1, a cornichon homolog, was identified as a potential cargo receptor for CmHKT1;1. Yeast two-hybrid, biomolecular fluorescence complementation and luciferase complementary assays demonstrated that CmCNIH1 and CmHKT1;1 could interact. CmCNIH1 was a key component of the cellular vesicle transport machinery located in the endoplasmic reticulum (ER), ER export site and Golgi apparatus. A CmCNIH1 knockout mutant was more sensitive to salt stress than the wild-type (WT). In addition, ion homeostasis was disrupted in cmcnih1 mutants, which had higher Na⁺ and lower K⁺ content in shoots and roots than the WT. Two-electrode voltage-clamp experiment displayed that CmCNIH1 could not influence the Na⁺ current that passed through the plasma membrane (PM) in CmHKT1;1-expressing Xenopus laevis oocytes. Data from co-localization assays indicated that intact CmCNIH1 protein could alter the subcellular localization of CmHKT1;1 in tobacco leaf, pumpkin root and yeast. In summary, CmCNIH1 may function as a cargo receptor that regulates the localization of CmHKT1;1 to the PM to improve salt tolerance in pumpkin.

Integrating Application Methods and Concentrations of Salicylic Acid as an Avenue to Enhance Growth, Production, and Water Use Efficiency of Wheat under Full and Deficit Irrigation in Arid Countries

As water deficit in arid countries has already become the norm rather than the exception, water conservation in crop production processes has become very critical. Therefore, it is urgent to develop feasible strategies to achieve this goal. Exogenous application of salicylic acid (SA) has been proposed as one of the effective and economical strategies for mitigating water deficit in plants. However, the recommendations concerning the proper application methods (AMs) and the optimal concentrations (Cons) of SA under field conditions seem contradictory. Here, a two-year field study was conducted to compare the effects of twelve combinations of AMs and Cons on the vegetative growth, physiological parameters, yield, and irrigation water use efficiency (IWUE) of wheat under full (FL) and limited (LM) irrigation regimes. These combinations included seed soaking in purified water (S₀), 0.5 mM SA (S₁), and 1.0 mM SA (S₂); foliar spray of SA at concentrations of 1.0 mM (F₁), 2.0 mM (F₂), and 3.0 mM (F₃); and combinations of S₁ and S₂ with F₁ (S₁F₁ and S₂F₁), F₂ (S₁F₂ and S₂F₂), and F₃ (S₁F₃ and S₂F₃). The results showed that the LM regime caused a significant reduction in all vegetative growth, physiological, and yield parameters, while it led to an increase in IWUE. The application of SA through seed soaking, foliar application, and a combination of both methods increased all of the studied parameters in all the evaluated times, resulting in higher values for all parameters than the treatment without SA (S₀). The multivariate analyses, including principal component analysis and heatmapping, identified the foliar application method with 1-3 mM SA alone or in combination with seed soaking with 0.5 mM SA as the best treatments for the optimal performance of wheat under both irrigation regimes. Overall, our results indicated that exogenous application of SA has the potential to greatly improve growth, yield, and IWUE under limited water application, while optimal coupling combinations of AMs and Cons were required for positive effects in field conditions.

Sustaining nitrogen dynamics: A critical aspect for improving salt tolerance in plants

In the current changing environment, salt stress has become a major concern for plant growth and food production worldwide. Understanding the mechanisms of how plants function in saline environments is critical for initiating efforts to mitigate the detrimental effects of salt stress. Agricultural productivity is linked to nutrient availability, and it is expected that the judicious metabolism of mineral nutrients has a positive impact on alleviating salt-induced losses in crop plants. Nitrogen (N) is a macronutrient that contributes significantly to sustainable agriculture by maintaining productivity and plant growth in both optimal and stressful environments. Significant progress has been made in comprehending the fundamental physiological and molecular mechanisms associated with N-mediated plant responses to salt stress. This review provided an (a) overview of N-sensing, transportation, and assimilation in plants; (b) assess the salt stress-mediated regulation of N dynamics and nitrogen use- efficiency; (c) critically appraise the role of N in plants exposed to salt stress. Furthermore, the existing but less explored crosstalk between N and phytohormones has been discussed that may be utilized to gain a better understanding of plant adaptive responses to salt stress. In addition, the shade of a small beam of light on the manipulation of N dynamics through genetic engineering with an aim of developing salt-tolerant plants is also highlighted.

Willow (Salix babylonica) Extracts Can Act as Biostimulants for Enhancing Salinity Tolerance of Maize Grown in Soilless Culture

Salinity negatively affects agricultural production by reducing crop growth and yield. Botanical biostimulants can be used as innovative and sustainable tools to cope with abiotic stress. In this study, salicylic acid (SA) (25 µM) and willow leaf (WL) (0.1 and 0.2%) and bark (WB) (0.1 and 0.2%) extracts were applied as plant-based biostimulants to hydroponically grown maize in the absence and presence of salinity stress (60 mM NaCl). The hormone-like activity and mineral composition of willow extracts were analyzed, and the effects of willow extracts on growth parameters, chlorophyll content, antioxidative enzyme activities, protein levels and mineral nutrient concentrations of maize plants were measured. Within the tested biostimulant applications, 0.2% WB, 0.1% WL and 0.2% WL gave the most promising results, considering the stress alleviating effects. The shoot biomass was increased up to 50% with 0.1% WL treatment and Na⁺ uptake was reduced with biostimulant applications under saline conditions. Under stress, the protein concentrations of maize leaves were enhanced by 50% and 80% with high doses of WB and WL applications, respectively. Results indicate that willow tree prunings can be valuable bio-economy resources, and aqueous extracts prepared from their leaves and barks can be used as effective and eco-friendly biostimulants.

Alleviation of the adverse effects of NaCl stress on tomato seedlings (Solanum lycopersicum L.) by Trichoderma viride through the antioxidative defense system

BACKGROUND

Trichoderma viride are well known for their biocontrol capabilities, but little is known about how they stimulate plant development and increase their resistance to salt stress. One of the main abiotic factors limiting crop development and yield is salt stress. Therefore, the purpose of this work was to ascertain how NaCl effects on T. viride growth as well as on the seedlings morphological and physio-biochemical parameters of tomato (Solanum lycopersicum L.) under plate culture conditions. Additionally, a pot experiment was conducted to determine how T. viride affected the development characteristics of tomato plants subjected to various salt concentrations (50 and 100 mM NaCl). T. viride's contribution to tomato seedling stress tolerance was also closely examined.

RESULTS

Results showed that 100 mM NaCl decreased the colony diameter of T. viride by 13.4% compared to the control. Under plate and greenhouse conditions, tomato seedlings exposed to salt exposure exhibited an overall decline in growth. Also, a reduction in relative water content (RWC) and protein contents occurred under salt stress. At the same time, increases were found in proline, total phenolics, flavonoids, H₂O₂ content, malondialdehyde, likewise the activities of peroxidase (POD), catalase (CAT), polyphenol oxidase (PPO), and ascorbate peroxidase (APX) enzymes. Even though, with T. viride application, the salt negative effects on both morphological and physio-biochemical parameters were mitigated to a greater extent. T. viride increased proline and total antioxidant capacity (TAC) in tomato seedlings at 100 mM NaCl by an average of 20.66 and 43.82% compared to their comparable control. T. viride increased the activities of CAT, PPO, and APX enzymes by 74.6, 58.48, and 61.61% at 50 mM NaCl compared to non-saline control seedlings. As well, T. viride decreased MDA and H₂O₂ contents by an average of 14 and 24.8% in tomato seedlings at 50 mM NaCl compared to their comparable control. Also, under 100 mM NaCl, the T. viride-treated tomato seedlings showed increased total phenolics (17.85%) and flavonoids (33.17%) compared to non- treated one.

CONCLUSION

Hence, our research sheds new insight on the pathways by which T. viride can boost tomato seedling tolerance to salt stress at morphological and physio-biochemical levels by activating both enzymatic and non-enzymatic antioxidant defense systems.

Instigating prevalent abiotic stress resilience in crop by exogenous application of phytohormones and nutrient

In recent times, the demand for food and feed for the ever-increasing population has achieved unparalleled importance, which cannot afford crop yield loss. Now-a-days, the unpleasant situation of abiotic stress triggers crop improvement by affecting the different metabolic pathways of yield and quality advances worldwide. Abiotic stress like drought, salinity, cold, heat, flood, etc. in plants diverts the energy required for growth to prevent the plant from shock and maintain regular homeostasis. Hence, the plant yield is drastically reduced as the energy is utilized for overcoming the stress in plants. The application of phytohormones like the classical auxins, cytokinins, ethylene, and gibberellins, as well as more recent members including brassinosteroids, jasmonic acids, etc., along with both macro and micronutrients, have enhanced significant attention in creating key benefits such as reduction of ionic toxicity, improving oxidative stress, maintaining water-related balance, and gaseous exchange modification during abiotic stress conditions. Majority of phytohormones maintain homeostasis inside the cell by detoxifying the ROS and enhancing the antioxidant enzyme activities which can enhance tolerance in plants. At the molecular level, phytohormones activate stress signaling pathways or genes regulated by abscisic acid (ABA), salicylic acid (SA), Jasmonic acid (JA), and ethylene. The various stresses primarily cause nutrient deficiency and reduce the nutrient uptake of plants. The application of plant nutrients like N, K, Ca, and Mg are also involved in ROS scavenging activities through elevating antioxidants properties and finally decreasing cell membrane leakage and increasing the photosynthetic ability by resynthesizing the chlorophyll pigment. This present review highlighted the alteration of metabolic activities caused by abiotic stress in various crops, the changes of vital functions through the application of exogenous phytohormones and nutrition, as well as their interaction.

Phytoremediation of dinitrophenol from wastewater by atriplex lentiformis: effect of salicylic acid

Quail bush [Atriplex lentiformis (Torr.) S. Wats] plants were used in removing 2, 4-dinitrophenol (DNP) from wastewater in a hydroponic experiment. The hydroponic system contained three doses of DNP, i.e., 0, 10, and 20 mg L-1. Quail bush plants were sprayed with 0.1 mM salicylic acid (SA) to study its role in resisting DNP toxicity. DNP significantly (p < 0.05) reduced plant growth. Exposure of A. lentiformis plants to 20 mg L-1 of DNP reduced the total chlorophyl and relative water content by 39 and 24%, respectively. SA improved the antioxidant defense in terms of ascorbate peroxidase (APX) and polyphenol oxidase (PPO) activities. SA alleviated DNP toxicity by enhancing the production of osmoprotectants, e.g.,proline, phenols, and carbohydrates. SA enhanced the removal efficiency of DNP and the highest removal efficiency (96%) was recorded in the plants sprayed with SA and grown on 10 mg L-1 of DNP. A. lentiformis is a halophytic plant that has good physiological characteristics to resist 2, 4-dinitrophenol toxicity in wastewaters and is qualified to purify water from these harmful compounds. Exogenous application of 0.1 mM SA increased the defense system in A. lentiformis against 2, 4-dinitrophenol toxicity and enhanced the removal efficiency.

Salicylic Acid's Impact on Growth, Photosynthesis, and Antioxidant Enzyme Activity of Triticum aestivum When Exposed to Salt

Recently, the application of salicylic acid (SA) for improving a plant's resistance to abiotic stresses has increased. A large part of the irrigated land (2.1% out of 19.5%) is severely affected by salinity stress worldwide. In 2020, total production of wheat (Triticum aestivum) was 761 million tons, representing the second most produced cereal after maize; therefore, research on its salinity tolerance is of world concern. Photosynthetic attributes such as net photosynthetic rate (P_N), stomatal conductance (gs), intercellular CO₂ concentration (Ci), and transpiration rate (E) were increased significantly by the application of SA. Salt stress increased antioxidant enzyme activity; however, SA further boosted their activity along with proline level. We conclude that SA interacts with meristematic cells, thereby triggering biochemical pathways conductive to the increment in morphological parameters. Further research is required to dissect the mechanisms of SA within the wheat plants under stress.

Combined application of asparagine and thiourea improves tolerance to lead stress in wheat by modulating AsA-GSH cycle, lead detoxification and nitrogen metabolism

Lead (Pb), like other heavy metals, is not essentially required for optimal plant growth; however, plants uptake it from the soil, which poses an adverse effect on growth and yield. Asparagine (Asp) and thiourea (Thi) are known to assuage the negative impacts of heavy metal pollution on plant growth; however, combined application of Asp and Thi has rarely been tested to discern if it could improve wheat yield under Pb stress. Thus, this experimentation tested the role of individual and combined applications of Asp (40 mM) and Thi (400 mg/L) in improving wheat growth under lead (Pb as PbCl₂, 0.1 mM) stress. Lead stress significantly reduced plant growth, chlorophyll contents and photosystem system II (PSII) efficiency, whereas it increased Pb accumulation in the leaves and roots, leaf proline contents, phytochelatins, and oxidative stress related attributes. The sole or combined application of Asp and Thi increased the vital antioxidant biomolecules/enzymes, including reduced glutathione (GSH), ascorbic acid (AsA), ascorbate peroxsidase (APX), catalase (CAT), superoxide dismutase (SOD), glutathione S-transferase (GST), dehydroascorbate reductase (DHAR), and glutathione reductase (GR). Furthermore, the sole or the combined application of Asp and Thi modulated nitrogen metabolism by stimulating the activities of nitrate and nitrite reductase, glutamate synthase (GOGAT) and glutamine synthetase (GS). Asp and Thi together led to improve plant growth and vital physiological processes, but lowered down Pb accumulation compared to those by their sole application. The results suggest that Asp and Thi synergistically can improve wheat growth under Pb-toxicity.

Involvement of ethylene in melatonin-modified photosynthetic-N use efficiency and antioxidant activity to improve photosynthesis of salt grown wheat

The involvement of melatonin in the regulation of salt stress acclimation has been shown in plants in this present work. We found that the GOAL cultivar of wheat (Triticum aestivum L.) was the most salt-tolerant among the investigated cultivars, GOAL, HD-2967, PBW-17, PBW-343, PBW-550, and WH-1105 when screened for tolerance to 100 mM NaCl. The application of 100 μM melatonin maximally reduced oxidative stress and improved photosynthesis in the cv. GOAL. Melatonin supplementation reduced salt stress-induced oxidative stress by upregulating the activity of antioxidant enzymes, such as superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR), and reduced the glutathione (GSH) production. This resulted in increased membrane stability, photosynthetic-N use efficiency and photosynthesis in plants. The application of 50 μM of the ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG) in the presence of melatonin and salt stress increased H₂ O₂ content but reduced GR activity and GSH, photosynthesis, and plant dry mass. This signifies that melatonin-mediated salt stress tolerance was related to ethylene synthesis as it improved antioxidant activity and photosynthesis of plants under salt stress. Thus, the interaction of melatonin and ethylene bears a prominent role in salt stress tolerance in wheat and can be used to develop salt tolerance in other crops.

Exogenously-Sourced Salicylic Acid Imparts Resilience towards Arsenic Stress by Modulating Photosynthesis, Antioxidant Potential and Arsenic Sequestration in Brassica napus Plants

In the current study, salicylic acid (SA) assesses the physiological and biochemical responses in overcoming the potential deleterious impacts of arsenic (As) on Brassica napus cultivar Neelam. The toxicity caused by As significantly reduced the observed growth and photosynthetic attributes and accelerated the reactive oxygen species (ROS). Plants subjected to As stress revealed a significant (p ≤ 0.05) reduction in the plant growth and photosynthetic parameters, which accounts for decreased carbon (C) and sulfur (S) assimilation. Foliar spray of SA lowered the oxidative burden in terms of hydrogen peroxide (H2O2), superoxide anion (O2•-), and lipid peroxidation in As-affected plants. Application of SA in two levels (250 and 500 mM) protected the Brassica napus cultivar from As stress by enhancing the antioxidant capacity of the plant by lowering oxidative stress. Among the two doses, 500 mM SA was most effective in mitigating the adverse effects of As on the Brassica napus cultivar. It was found that SA application to the Brassica napus cultivar alleviated the stress by lowering the accumulation of As in roots and leaves due to the participation of metal chelators like phytochelatins, enhancing the S-assimilatory pathway, carbohydrate metabolism, higher cell viability in roots, activity of ribulose 1, 5-bisphosphate carboxylase (Rubisco), and proline metabolism through the active participation of γ-glutamyl kinase (GK) and proline oxidase (PROX) enzyme. The current study shows that SA has the capability to enhance the growth and productivity of B. napus plants cultivated in agricultural soil polluted with As and perhaps other heavy metals.

Comparative transcriptome and metabolome analysis reveal key regulatory defense networks and genes involved in enhanced salt tolerance of Actinidia (kiwifruit)

The Actinidia (kiwifruit) is an emerging fruit plant that is severely affected by salt stress in northern China. Plants have evolved several signaling network mechanisms to cope with the detrimental effects of salt stress. To date, no reported work is available on metabolic and molecular mechanisms involved in kiwifruit salt tolerance. Therefore, the present study aims to decipher intricate adaptive responses of two contrasting salt tolerance kiwifruit species Actinidia valvata [ZMH (an important genotype), hereafter referred to as R] and Actinidia deliciosa ['Hayward' (an important green-fleshed cultivar), hereafter referred to as H] under 0.4% (w/w) salt stress for time courses of 0, 12, 24, and 72 hours (hereafter refered to as h) by combined transcriptome and metabolome analysis. Data revealed that kiwifruit displayed specific enrichment of differentially expressed genes (DEGs) under salt stress. Interestingly, roots of R plants showed a differential expression pattern for up-regulated genes. The KEGG pathway analysis revealed the enrichment of DEGs related to plant hormone signal transduction, glycine metabolism, serine and threonine metabolism, glutathione metabolism, and pyruvate metabolism in the roots of R under salt stress. The WGCNA resulted in the identification of five candidate genes related to glycine betaine (GB), pyruvate, total soluble sugars (TSS), and glutathione biosynthesis in kiwifruit. An integrated study of transcriptome and metabolome identified several genes encoding metabolites involved in pyruvate metabolism. Furthermore, several genes encoding transcription factors were mainly induced in R under salt stress. Functional validation results for overexpression of a candidate gene betaine aldehyde dehydrogenase (AvBADH, R_transcript_80484) from R showed significantly improved salt tolerance in Arabidopsis thaliana (hereafter referred to as At) and Actinidia chinensis ['Hongyang' (an important red-fleshed cultivar), hereafter referred to as Ac] transgenic plants than in WT plants. All in all, salt stress tolerance in kiwifruit roots is an intricate regulatory mechanism that consists of several genes encoding specific metabolites.

Multiple Facets of Nitrogen: From Atmospheric Gas to Indispensable Agricultural Input

Nitrogen (N) is a gas and the fifth most abundant element naturally found in the atmosphere. N's role in agriculture and plant metabolism has been widely investigated for decades, and extensive information regarding this subject is available. However, the advent of sequencing technology and the advances in plant biotechnology, coupled with the growing interest in functional genomics-related studies and the various environmental challenges, have paved novel paths to rediscovering the fundamentals of N and its dynamics in physiological and biological processes, as well as biochemical reactions under both normal and stress conditions. This work provides a comprehensive review on multiple facets of N and N-containing compounds in plants disseminated in the literature to better appreciate N in its multiple dimensions. Here, some of the ancient but fundamental aspects of N are revived and the advances in our understanding of N in the metabolism of plants is portrayed. It is established that N is indispensable for achieving high plant productivity and fitness. However, the use of N-rich fertilizers in relatively higher amounts negatively affects the environment. Therefore, a paradigm shift is important to shape to the future use of N-rich fertilizers in crop production and their contribution to the current global greenhouse gases (GHGs) budget would help tackle current global environmental challenges toward a sustainable agriculture.

Salicylic Acid Improves Growth and Physiological Attributes and Salt Tolerance Differentially in Two Bread Wheat Cultivars

Abiotic constraints such as salinity stress reduce cereal production. Salicylic acid is an elicitor of abiotic stress tolerance in plants. The aim of this study was to investigate the effects of salicylic acid on two bread wheat cultivars (SST806 and PAN3497) grown under salt stress (100 and 200 mM NaCl) in the presence and absence of 0.5 mM salicylic acid. The highest salt concentration (200 mM), in both PAN3497 and SST806, increased the days to germination and reduced the coleoptile and radicle dry weights. The shoot dry weight was reduced by 75 and 39%, root dry weight by 73 and 37%, spike number of both by 50%, spike weight by 73 and 54%, grain number by 62 and 15%, grain weight per spike by 80 and 45%, and 1000 grain weight by 9 and 29% for 200 and 100 mM NaCl, respectively. Salicylic acid in combination with 100 mM and 200 mM NaCl increased the shoot, root, and yield attributes. Salicylic acid increased the grain protein content, especially at 200 mM NaCl, and the increase was higher in SST806 than PAN3497. The macro-mineral concentration was markedly increased by an increase of NaCl. This was further increased by salicylic acid treatment for both SST806 and PAN3497. Regarding micro-minerals, Na was increased more than the other minerals in both cultivars. Mn, Zn, Fe, and Cu were increased under 100 mM and 200 Mm of salt, and salicylic acid application increased these elements further in both cultivars. These results suggested that salicylic acid application improved the salt tolerance of these two bread wheat cultivars.

Pivotal Role of Phytohormones and Their Responsive Genes in Plant Growth and Their Signaling and Transduction Pathway under Salt Stress in Cotton

The presence of phyto-hormones in plants at relatively low concentrations plays an indispensable role in regulating crop growth and yield. Salt stress is one of the major abiotic stresses limiting cotton production. It has been reported that exogenous phyto-hormones are involved in various plant defense systems against salt stress. Recently, different studies revealed the pivotal performance of hormones in regulating cotton growth and yield. However, a comprehensive understanding of these exogenous hormones, which regulate cotton growth and yield under salt stress, is lacking. In this review, we focused on new advances in elucidating the roles of exogenous hormones (gibberellin (GA) and salicylic acid (SA)) and their signaling and transduction pathways and the cross-talk between GA and SA in regulating crop growth and development under salt stress. In this review, we not only focused on the role of phyto-hormones but also identified the roles of GA and SA responsive genes to salt stress. Our aim is to provide a comprehensive review of the performance of GA and SA and their responsive genes under salt stress, assisting in the further elucidation of the mechanism that plant hormones use to regulate growth and yield under salt stress.

Ethylene and hydrogen sulphide are essential for mitigating hexavalent chromium stress in two pulse crops

Chromium toxicity to crops is a major scientific problem of the present time. Thus, scientific attempts have been made for reducing chromium toxicity to crop plants. In this study, we examined the potential of ethylene (ET, 25 µM) and hydrogen sulphide (H₂ S, 10 µM) to alleviate hexavalent chromium [Cr(VI), 50 µM] stress in two pulse crops, black bean and mung bean, by assessing physiological and biochemical attributes. Cr(VI) reduced shoot and root length in black bean and mung bean in comparison to the control. Plants had increased accumulation of oxidative stress markers, i.e. superoxide radicals (SOR), hydrogen peroxide (H₂ O₂ ) and lipid peroxidation (as malondialdehyde, MDA). The addition of AVG (an inhibitor of ET biosynthesis) and PAG (an inhibitor of H₂ S biosynthesis) to Cr(VI)-treated plants further increased Cr(VI) toxicity, suggesting their endogenous levels are important for tolerating Cr(VI) toxicity. However, supplementation with either ET or H₂ S alleviated Cr(VI) toxicity. Interestingly, ET did not rescue negative effects of PAG under Cr(VI) stress but NaHS rescued negative effect of AVG. Overall, results indicate that, although both ET and H₂ S alleviate Cr(VI) stress, endogenous H₂ S is better. Furthermore, H₂ S appears to be a downstream signal for ET in alleviating Cr(VI) stress in these two pulse crops.

Untargeted Metabolomic Approach to Determine the Regulatory Pathways on Salicylic Acid-Mediated Stress Response in Aphanamixis polystachya Seedlings

Plants thrive under abiotic and biotic stress conditions with the changes in phytohormones like salicylic acid (SA), resulting in the synthesis of secondary metabolites. The present study determines the response of plants in producing secondary metabolites towards different SA concentrations at varying time intervals. Liquid chromatography-mass spectrometry-based metabolomics studies in Aphanamixis polystachya (Wall.) Parker seedlings are grown at 10 mM, 50 mM, and 100 mM SA concentrations, showed the differential expression of metabolites towards the stress. Alkaloids like amaranthin showed a 15-fold increase on the second day, and analog of androvinblastin showed a 20-fold increase on the sixth day in 10 mM SA compared with other groups. Flavanoid cyanidin 3-3 glucosyl was found to be with a 22-fold increment along with terpenoids betavulgaroside (18-fold), asiaticoside (17-fold), mubenin B (20-fold), and deslanoside (22-fold) increment in 50 mM SA on the sixth day. The shock exerted by 100 mM was too harsh, and the lowered metabolite production level was insufficient for the seedlings to survive at this higher SA condition. Arrangement of stressed groups using Pearson correlation studies, principal component analysis, and partial least square analysis placed 10 mM SA and controlled group closer and 50 mM SA and 100 mM SA groups closer to each other. The study observed that SA regulates metabolites that mediate biotic stress responses at low concentrations, and higher concentrations regulate abiotic stress regulating metabolites.

Mitigation of Salinity Stress on Pomegranate (Punica granatum L. cv. Wonderful) Plant Using Salicylic Acid Foliar Spray

Salt stress significantly impacts plant morphological structure and physiological processes, resulting in decreased plant growth. Salicylic acid (SA) is a key signal molecule that protects plants from the negative impacts of salinity. Under natural conditions, the pomegranate plant generally exhibits salt-tolerant characteristics. The objective of this study was to elucidate the salt-tolerance level of pomegranate (Punica granatum L. cv. Wonderful) and the effect of the regulating strategy of SA foliar spray on growth, morphological structure, and physiological processes. SA levels were 0, 0.25, 0.50, and 1 mM in the presence of salinity levels of 10, 35, and 70 mM NaCl, respectively. Vegetative growth indices, including stem cross-sectional area, leaf area, and total dry weight, were lowered by salinity treatments. However, SA applications greatly improved morphological characteristics and plant growth under salt stress. The effects of salinity were effectively reversed by SA treatment at 1 mM compared to control and other treatments. Interestingly, SA applications enhanced the chlorophyll, total phenolic, carbohydrate, and proline contents of leaves while decreasing electrolyte leakage (EL), Na, and Cl levels. Moreover, the foliar SA treatments enhanced the nutrient content in the leaves and increased the activities of peroxidase (POD) and catalase (CAT), with a decrease in malondialdehyde (MDA) content. This study suggests that the alleviation of the salinity stress by SA may be due to the activation of the antioxidant enzymatic mechanism and decrease in the lipid peroxidation of the pomegranate plant.

Proline, a multifaceted signalling molecule in plant responses to abiotic stress: understanding the physiological mechanisms

Abiotic stresses have a detrimental impact on plant growth and productivity and are a major threat to sustainable crop production in rapidly changing environments. Proline, an important amino acid, plays an important role in maintaining the metabolism and growth of plants under abiotic stress conditions. Many insights indicate a positive relationship between proline accumulation and tolerance of plants to various abiotic stresses. Because of its metal chelator properties, it acts as a molecular chaperone, an antioxidative defence molecule that scavenges reactive oxygen species (ROS), as well as having signalling behaviour to activate specific gene functions that are crucial for plant recovery from stresses. It also acts as an osmoprotectant, a potential source to acquire nitrogen as well as carbon, and plays a significant role in the flowering and development of plants. Overproduction of proline in plant cells contributes to maintaining cellular homeostasis, water uptake, osmotic adjustment and redox balance to restore the cell structures and mitigate oxidative damage. Many reports reveal that transgenic plants, particularly those overexpressing genes tailored for proline accumulation, exhibit better adaptation to abiotic stresses. Therefore, this review aims to provide a comprehensive update on proline biosynthesis and accumulation in plants and its putative regulatory roles in mediating plant defence against abiotic stresses. Additionally, the current and future directions in research concerning manipulation of proline to induce gene functions that appear promising in genetics and genomics approaches to improve plant adaptive responses under changing climate conditions are also highlighted.

Foliar Application of Salicylic Acid Improves Salt Tolerance of Sorghum (Sorghum bicolor (L.) Moench)

It has been reported that around the world, approximately 19.5% of all irrigated land and 2.1% of dry land is affected by salt stress, and these percentages continue to increase. Sorghum is the fifth most important cereal in the world and therefore research on its salt tolerance is of global importance. In our research, we focused on foliar application of salicylic acid (SA) on salt-stressed sorghum. We performed a pot experiment with two salt levels (0 and 100 mM sodium chloride NaCl) and five SA concentrations (0, 50, 100, 150 and 200 mg/L). Our results suggest that in saline conditions foliar application of SA induced an adaptive response to salinity by inducing proline accumulation as well as antioxidant enzymes activities and enhanced the protection of the photosynthetic machinery, maintained photosynthesis activities, and improved the growth of sorghum plants. These alleviation effects were depended on applied SA concentration. Under saline condition 150 mg/L, SA was the most effective for relieving the adverse effect of salt stress. Under non-saline conditions 100 mg/L SA was the best for improving sorghum growth and dry matter production. Our results demonstrated that foliar SA application is effective in improving sorghum growth under salinity.

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

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

Climate change regulated abiotic stress mechanisms in plants: a comprehensive review

Global climate change is identified as a major threat to survival of natural ecosystems. Climate change is a dynamic, multifaceted system of alterations in environmental conditions that affect abiotic and biotic components of the world. It results in alteration in environmental conditions such as heat waves, intensity of rainfall, CO₂ concentration and temperature that lead to rise in new pests, weeds and pathogens. Climate change is one of the major constraints limiting plant growth and development worldwide. It impairs growth, disturbs photosynthesis, and reduces physiological responses in plants. The variations in global climate have gained the attention of researchers worldwide, as these changes negatively affect the agriculture by reducing crop productivity and food security. With this background, this review focuses on the effects of elevated atmospheric CO₂ concentration, temperature, drought and salinity on the morphology, physiology and biochemistry of plants. Furthermore, this paper outlines an overview on the reactive oxygen species (ROS) production and their impact on the biochemical and molecular status of plants with increased climatic variations. Also additionally, different tolerance strategies adopted by plants to combat environmental adversities have been discussed.

Improvement of the antioxidant activity, phytochemicals, and cannabinoid compounds of Cannabis sativa by salicylic acid elicitor

Recently, due to the valuable and high level of phytochemical compounds such as cannabinoids and other secondary metabolites, the cultivation of Cannabis sativa has increased in the world. The current study was conducted to evaluate the potential role of exogenous salicylic acid (control, 0.01, 0.1, and 1 M) on enhanced production of pharmaceutically important phytochemicals. The sprayed aerial parts were evaluated based on phenolic (TPC) and flavonoids (TFC) contents, antioxidant capacity (by FRAP and DPPH assay), photosynthetic pigments including chlorophyll a, b (Chl a and Chl b), total carotenoids (TCC), and cannabinoid compounds. Quantification of aerial parts metabolites was performed using gas chromatography. The results indicated that phytochemical compounds and antioxidant capacity in C. sativa were influenced by various concentrations of salicylic acid (SA). The highest TPC, TFC, TCC, Chl a, Chl b, and antioxidant capacity were obtained in 1 M treatment, whereas the lowest of them were found in control plants. The major cannabinoids in the analyzed extracts were CBD (19.91%-37.81%), followed by Δ9-THC (10.04%-22.84%), and CBL (nd-14.78%). The highest CBD (37.81%) and Δ9-THC (22.84%) were obtained in 1 M of SA. These results suggest that the elicitor SA (especially 1 M) was able to improve antioxidant capacity, phytochemicals, and cannabinoid compounds.

Effects of tea polyphenols on the activities of antioxidant enzymes and the expression of related gene in the leaves of wheat seedlings under salt stress

Longchun 30, a new wheat variety, was used to investigate seedling growth, element absorption, and antioxidant response under 150 mM NaCl and tea polyphenols (TP) (25 and 100 mg L^-1) treatments alone or in combination, thus revealing TP-alleviating mechanism on the salt damage to plants. 150 mM NaCl stress alone inhibited the seedling growth, increased sodium content and reactive oxygen species (ROS) accumulation, but reduced potassium (K) and calcium (Ca) levels at different culture times, thus resulting in the oxidative damage to the leaves. Even though 25 or 100 mg L^-1 TP treatment alone led to the significant increases of O₂^·- and H₂O₂ generation, TP-treated leaves exhibited the reduction of relative electrical conductivity and no change of malondialdehyde content. Moreover, high TP concentration alone stimulated the seedling growth. In addition, the activities and gene expression of superoxide dismutase, catalase, and peroxidase (POD) as well as diamine oxidase and polyamine oxidase were changed to different degrees due to NaCl or TP treatment alone. Further study showed that the presence of 25 or 100 mg L^-1 TP promoted the growth, increased K⁺ and Ca²⁺ contents, and reduced O₂^·- and H₂O₂ accumulation in salt-stressed wheat seedlings. Taken together, salinity-inhibitory effect on the growth of wheat seedlings might be associated with salt-induced imbalance of element content and the increase of oxidative damage resulting from ROS accumulation, while the application of TP effectively alleviated salinity-inhibitory effect on the seedling growth and improved the tolerance of wheat seedlings to salt environment, which might be associated with the increases of K⁺ and Ca²⁺ contents as well as the reduction of oxidative damage in the leaves of wheat seedlings under NaCl and TP treatment in combination.

Phytohormone profiles in non-transformed and AtCKX transgenic centaury (Centaurium erythraea Rafn) shoots and roots in response to salinity stress in vitro

Plant hormones regulate numerous developmental and physiological processes. Abiotic stresses considerably affect production and distribution of phytohormones as the stress signal triggers. The homeostasis of plant hormones is controlled by their de novo synthesis and catabolism. The aim of this work was to analyse the contents of total and individual groups of endogenous cytokinins (CKs) as well as indole-3-acetic acid (IAA) in AtCKX overexpressing centaury plants grown in vitro on graded NaCl concentrations (0, 50, 100, 150, 200 mM). The levels of endogenous stress hormones including abscisic acid (ABA), salicylic acid (SA) and jasmonic acid (JA) were also detected. The elevated contents of total CKs were found in all analysed centaury shoots. Furthermore, increased amounts of all five CK groups, as well as enhanced total CKs were revealed on graded NaCl concentrations in non-transformed and AtCKX roots. All analysed AtCKX centaury lines exhibited decreased amounts of endogenous IAA in shoots and roots. Consequently, the IAA/bioactive CK forms ratios showed a significant variation in the shoots and roots of all AtCKX lines. In shoots and roots of both non-transformed and AtCKX transgenic centaury plants, salinity was associated with an increase of ABA and JA and a decrease of SA content.

Plants Saline Environment in Perception with Rhizosphere Bacteria Containing 1-Aminocyclopropane-1-Carboxylate Deaminase

Soil salinity stress has become a serious roadblock for food production worldwide since it is one of the key factors affecting agricultural productivity. Salinity and drought are predicted to cause considerable loss of crops. To deal with this difficult situation, a variety of strategies have been developed, including plant breeding, plant genetic engineering, and a wide range of agricultural practices, including the use of plant growth-promoting rhizobacteria (PGPR) and seed biopriming techniques, to improve the plants' defenses against salinity stress, resulting in higher crop yields to meet future human food demand. In the present review, we updated and discussed the negative effects of salinity stress on plant morphological parameters and physio-biochemical attributes via various mechanisms and the beneficial roles of PGPR with 1-Aminocyclopropane-1-Carboxylate(ACC) deaminase activity as green bio-inoculants in reducing the impact of saline conditions. Furthermore, the applications of ACC deaminase-producing PGPR as a beneficial tool in seed biopriming techniques are updated and explored. This strategy shows promise in boosting quick seed germination, seedling vigor and plant growth uniformity. In addition, the contentious findings of the variation of antioxidants and osmolytes in ACC deaminase-producing PGPR treated plants are examined.

Nanobiotechnological Approaches to Enhance Potato Resistance against Potato Leafroll Virus (PLRV) Using Glycyrrhizic Acid Ammonium Salt and Salicylic Acid Nanoparticles

The present research was aiming to study In-Silico the effect of Glycyrrhizic Acid ammonium salt (GAS) and Salicylic acid (SA) on the coat protein of potato leafroll virus (PLRV). In addition, in-vitro studying the effect of (GAS NPs) and Salicylic acid (SA NPs) nanoparticles at concentrations 0.15, 0.30, 1.25 and 2.5 mM, respectively, to control, decline or reduce the presence of PLRV in potato plants Solanum tuberosum L. selena. (GAS NPs) and (SA NPs) were applied in the MS medium at concentrations 0.15, 0.30, 1.25 and 2.5 mM, respectively. Results revealed that, enhancement or decline the PLRV according to the initiation of specific pathways. The expression level of Kinase 3 gene increased significantly due to the two used concentrations of GAS NPs. While the expression of callose gene was upregulated significantly in response to treatment of PLRV infected plant with (GAS NPs) with concentration (0.30 mM). Treatment with (SA NPs) caused upregulation significance only of callose gene at (2.5 mM) concentration. The molecular modeling results of used compounds (glycyrrhizic acid ammonium salt and salicylic acid) showed highest score of binding and the best rms define value with a very good binding mode and perfect interactions with amino acids of the three subunits (A, B and C) forming the protein coat of leaf roll virus. Glycyrrhizic acid ammonium salt and salicylic acid nanoparticles could be perfect solution to produce potato plant free virus in-vitro. Further larger studies are needed to investigate the role of the studied compounds in vivo.

Control of Elevated Ion Accumulation, Oxidative Stress, and Lipid Peroxidation with Salicylic Acid-Induced Accumulation of Glycine Betaine in Salinity-Exposed Vigna radiata L

The identification of the sustainable approaches is required for the minimization of adverse impact of worldwide increasing soil salinity on plant growth, development, and productivity. This study investigated the protective role and major mechanism underlying salicylic acid (SA; 0.1, 0.5, or 1.0 mM)-induced glycine betaine (GB)-mediated tolerance to salinity (50 mM NaCl) in mungbean (Vigna radiata L. cultivar Punt Mung). The supply of 0.5 mM SA maximally increased the accumulation of GB (>40%) with respect to the control. This was further corroborated with the increase in water potential, antioxidant system (reduced glutathione (GSH), GSH/GSSG redox state, and glutathione reductase (GR) activity) and decreased Na+ and Cl- accumulation, Na+/K+ ratio, oxidative stress, and lipid peroxidation. This was also associated with the increased photosynthesis (14-18%) and growth (7-12%) parameters. Overall, SA-induced accumulation of GB protected photosynthesis and growth against 50 mM NaCl-accrued impacts in V. radiata through minimizing the accumulation of Na+ and Cl- ions, oxidative stress, and maintaining high GSH level that led to reduced cellular redox environment.

Coordinated Role of Nitric Oxide, Ethylene, Nitrogen, and Sulfur in Plant Salt Stress Tolerance

Salt stress significantly contributes to major losses in agricultural productivity worldwide. The sustainable approach for salinity-accrued toxicity has been explored. The use of plant growth regulators/phytohormones, mineral nutrients and other signaling molecules is one of the major approaches for reversing salt-induced toxicity in plants. Application of the signaling molecules such as nitric oxide (NO) and ethylene (ETH) and major mineral nutrient such as nitrogen (N) and sulfur (S) play significant roles in combatting the major consequences of salt stress impacts in plants. However, the literature available on gaseous signaling molecules (NO/ETH) or/and mineral nutrients (N/S) stands alone, and major insights into the role of NO or/and ETH along with N and S in plant-tolerance to salt remained unclear. Thus, this review aimed to (a) briefly overview salt stress and highlight salt-induced toxicity, (b) appraise the literature reporting potential mechanisms underlying the role of gaseous signaling molecules and mineral nutrient in salt stress tolerance, and (c) discuss NO and ETH along with N and S in relation to salt stress tolerance. In addition, significant issues that have still to be investigated in this context have been mentioned.

Abscisic Acid in Coordination with Nitrogen Alleviates Salinity-Inhibited Photosynthetic Potential in Mustard by Improving Proline Accumulation and Antioxidant Activity

This investigation was done to assess the role of abscisic acid (ABA; 25 µM) and/or nitrogen (N; 10 mM) in the alleviation of salinity (NaCl; 100 mM)-induced reduction in photosynthetic activity and growth, N and sulfur (S) assimilation of mustard (Brassica juncea L.) cv. RH0-749. Salinity treatment caused oxidative stress and significantly elevated the content of both H2O2 and thiobarbituric acid reactive substances (TBARS), and impaired photosynthetic activity and growth, but increased the content of nitrogenous osmolyte proline and the activity of antioxidant enzymes involved in the metabolism of reactive oxygen species. The application of 25 µM ABA under a controlled condition negatively affected photosynthesis and growth. However, ABA, when combined with N, minimized oxidative stress and mitigated the salinity-inhibited effects by increasing the activity of antioxidant enzymes (superoxide dismutase, SOD; glutathione reductase, GR; ascorbate peroxidase, APX) and proline content. Overall, the supplementation of 10 mM N combined with 25 µM ABA provides an important strategy for enhancing the photosynthetic potential of B. juncea under saline conditions.

Identification of a Biostimulating Potential of an Organic Biomaterial Based on the Botanical Extract from Arctium lappa L. Roots

The development of novel biomaterials based on plant extracts is expected to boost yields without adversely affecting environmental diversity. The potential biostimulating effects have so far been underreported. The assessment of the stimulating effect of botanical biomaterials is essential in the cultivation of economically-important crops. An attempt was undertaken in this study to develop a new biostimulating material in the form of granules, based on an extract from the roots of Arctium lappa L. The scope of the research included the characterization of the new material and the identification of its biostimulating potential. The designed and produced biogranulate is rich in bioactive compounds, including polyphenolic compounds, carbohydrates, and micro- and macro-elements. The analysis of the physicochemical properties of the biomaterial has shown that it had the features of intelligent biopreparations, i.e., slow-release preparations, at the pH appropriate for legume plants. Thus, knowledge about the design of new biomaterials is a milestone in the practical development of new perspectives for enhancing sustainability in agriculture.

Regulation of Reactive Oxygen Species and Antioxidant Defense in Plants under Salinity

The generation of oxygen radicals and their derivatives, known as reactive oxygen species, (ROS) is a part of the signaling process in higher plants at lower concentrations, but at higher concentrations, those ROS cause oxidative stress. Salinity-induced osmotic stress and ionic stress trigger the overproduction of ROS and, ultimately, result in oxidative damage to cell organelles and membrane components, and at severe levels, they cause cell and plant death. The antioxidant defense system protects the plant from salt-induced oxidative damage by detoxifying the ROS and also by maintaining the balance of ROS generation under salt stress. Different plant hormones and genes are also associated with the signaling and antioxidant defense system to protect plants when they are exposed to salt stress. Salt-induced ROS overgeneration is one of the major reasons for hampering the morpho-physiological and biochemical activities of plants which can be largely restored through enhancing the antioxidant defense system that detoxifies ROS. In this review, we discuss the salt-induced generation of ROS, oxidative stress and antioxidant defense of plants under salinity.