Spermine application alleviates salinity induced growth and photosynthetic inhibition in Solanum lycopersicum by modulating osmolyte and secondary metabolite accumulation and differentially regulating antioxidant metabolism

Regulation of seed soaking with indole-3-butyric acid potassium salt (IBA-K) on rapeseed (Brassica napus L.) seedlings under NaCl stress

The growth and yield of rapeseed are significantly hampered by salt stress. Indole-3-butyric Acid Potassium Salt (IBA-K) has been found to alleviate the impact of salt stress on plant growth. However, the regulatory effect of IBA-K dipping on salt-stressed rapeseed remains unclear. To explore the implications of IBA-K on the growth and development of rapeseed during the seedling stage, we conducted potting experiments using the Huayouza 62 variety. Five different concentrations of IBA-K for seed soaking (0, 10, 20, 40, 80 mg·L- 1) were tested. The promotional impact of IBA-K on rapeseed demonstrated an initial increase followed by a decline, reaching a peak at 20 mg·L- 1. Therefore, 20 mg·L- 1 was determined as the optimal concentration for subsequent experiments. To further understand the mechanism of IBA-K's action on salt-stressed rapeseed seedlings, we utilized the moderately salt-resistant cabbage rapeseed variety Huayouza 158R and the highly salt-resistant Huayouza 62 as specimens. The investigation focused on their response and repair mechanisms under 150 mmol·L- 1 NaCl stress. The findings demonstrated that compared with the sole NaCl stress, the 20 mg·L- 1 IBA-K seed soaking treatment under salt stress significantly enhanced the plant height, stem diameter, and leaf area of both rapeseed varieties. It also led to greater biomass accumulation, increased chlorophyll content, and improved photosynthetic efficiency in rapeseed. Furthermore, this treatment bolstered the activity of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), while significantly reducing the levels of electrolyte leakage (EL) and malondialdehyde (MDA). Consequently, it alleviated the membrane lipid peroxidation damage induced by NaCl stress, enhanced the accumulation of soluble proteins, maintained cellular osmotic pressure, and effectively mitigated the adverse effects of NaCl stress on rapeseed.

SlWRKY81 regulates Spd synthesis and Na+/K+ homeostasis through interaction with SlJAZ1 mediated JA pathway to improve tomato saline-alkali resistance

Saline-alkali stress is an important abiotic stress factor affecting tomato (Solanum lycopersicum L.) plant growth. Although the involvement of the tomato SlWRKY gene family in responses to saline-alkali stress has been well established, the mechanism underlying resistance to saline-alkali stress remains unclear. In this study, we investigated the role of SlWRKY81 in conferring saline-alkali stress resistance by using overexpression and knockout tomato seedlings obtained via genetic modification. We demonstrated that SlWRKY81 improves the ability of tomato to withstand saline-alkali stress by enhancing antioxidant capacity, root activity, and proline content while reducing malondialdehyde levels. Saline-alkali stress induces an increase in jasmonic acid (JA) content in tomato seedlings, and the SlWRKY81 promoter responds to JA signaling, leading to an increase in SlWRKY81 expression. Furthermore, the interaction between SlJAZ1 and SlWRKY81 represses the expression of SlWRKY81. SlWRKY81 binds to W-box motifs in the promoter regions of SlSPDS2 and SlNHX4, thereby positively regulating their expression. This regulation results in increased spermidine (Spd) content and enhanced potassium (K+) absorption and sodium (Na+) efflux, which contribute to the resistance of tomato to saline-alkali stress. However, JA and SlJAZ1 exhibit antagonistic effects. Elevated JA content reduces the inhibitory effect of SlJAZ1 on SlWRKY81, leading to the release of additional SlWRKY81 protein and further augmenting the resistance of tomato to saline-alkali stress. In summary, the modulation of Spd synthesis and Na+/K+ homeostasis mediated by the interaction between SlWRKY81 and SlJAZ1 represents a novel pathway underlying tomato response to saline-alkali stress.

Supplementation of Jasmonic acid Mitigates the Damaging Effects of Arsenic Stress on Growth, Photosynthesis and Nitrogen Metabolism in Rice

Experiments were conducted to evaluate the role of exogenously applied jasmonic acid (JA; 0.1 and 0.5 µM) in alleviating the toxic effects of arsenic (As; 5 and 10 µM) stress in rice. Plants treated with As showed considerable decline in growth attributes like height, fresh and dry weight of plant. Arsenic stress reduced the content of δ-amino livulenic acid (δ-ALA), glutamate 1-semialdehyde (GSA), total chlorophylls and carotenoids, with more reduction evident at higher (10 µM) As concentrations, however exogenously supplied JA alleviated the decline to considerable extent. Arsenic stress mediated decline in photosynthetic gas exchange parameters, Fv/Fm (PSII activity) and Rubisco activity was alleviated by the exogenous treatment of JA. Arsenic stress caused oxidative damage which was evident as increased lipid peroxidation, lipoxygenase activity and hydrogen peroxide concentrations however, JA treatment declined these parameters. Treatment of JA improved the activity of nitrate reductase and glutamate synthase under unstressed conditions and also alleviated the decline triggered by As stress. Activity of antioxidant enzymes assayed increased due to As stress, and the supplementation of JA caused further increase in their activities. Moreover, the content of proline, free amino acids and total phenols increased significantly due to JA application under stressed and unstressed conditions. Treatment of JA increased the content of nitrogen and potassium while as reduced As accumulation significantly.

Synergistic influence of selenium and silicon supplementation prevents the oxidative effects of arsenic stress in wheat

Influence of supplementation of selenium (Se, 1 and 5 µM) and silicon (Si, 0.1 and 0.5 mM) was investigated in wheat under arsenic (30 µM As) stress. Plants grown under As stress exhibited a significant decline in growth parameters however, Se and Si supplementation mitigated the decline significantly. Treatment of Se and Si alleviated the reduction in the intermediate components of chlorophyll biosynthesis pathway and the content of photosynthetic pigments. Arsenic stressed plants exhibited increased reactive oxygen species accumulation and the NADPH oxidase activity which were lowered significantly due to Se and Si treatments. Moreover, Se and Si supplementation reduced lipid peroxidation and activity of lipoxygenase and protease under As stress. Supplementation of Se and Si significantly improved the antioxidant activities and the content of cysteine, tocopherol, reduced glutathione and ascorbic acid. Treatment of Se and Si alleviated the reduction in nitrate reductase activity. Exogenously applied Se and Si mitigated the reduction in mineral elements and reduced As accumulation. Hence, supplementation of Se and Si is beneficial in preventing the alterations in growth and metabolism of wheat under As stress.

Enhanced azadirachtin production in neem (Azadirachta indica) callus through NaCl elicitation: Insights into differential protein regulation via shotgun proteomics

With their remarkable bioactivity and evolving commercial importance, plant secondary metabolites (PSMs) have gained significant research interest in recent years. Plant tissue culture serves as a credible tool to examine how abiotic stresses modulate the production of PSMs, enabling clear insights into plant stress responses and the prospects for controlled synthesis of bioactive compounds. Azadirachta indica, or neem has been recognized as a repository of secondary metabolites for centuries, particularly for the compound named azadirachtin, due to its bio-pesticidal and high antioxidant properties. Introducing salt stress as an elicitor makes it possible to enhance the synthesis of secondary metabolites, specifically azadirachtin. Thus, in this research, in vitro callus cultures of neem were micro-propagated and induced with salinity stress to explore their effects on the production of azadirachtin and identify potential proteins associated with salinity stress through comparative shotgun proteomics (LCMS/MS). To induce salinity stress, 2-month-old calli were subjected to various concentrations of NaCl (0.05-1.5%) for 4 weeks. The results showed that the callus cultures were able to adapt and survive in the salinity treatments, but displayed a reduction in fresh weight as the NaCl concentration increased. Notably, azadirachtin production was significantly enhanced in the salinity treatment compared to control, where 1.5% NaCl-treated calli produced the highest azadirachtin amount (10.847 ± 0.037 mg/g DW). The proteomics analysis showed that key proteins related to primary metabolism, such as defence, energy, cell structure, redox, transcriptional and photosynthesis, were predominantly differentially regulated (36 upregulated and 93 downregulated). While a few proteins were identified as being regulated in secondary metabolism, they were not directly involved in the synthesis of azadirachtin. In conjunction with azadirachtin elicitation, salinity stress treatment could therefore be successfully applied in commercial settings for the controlled synthesis of azadirachtin and other plant-based compounds. Further complementary omics approaches can be employed to enhance molecular-level modifications, to facilitate large-scale production of bioactive compounds in the future.

Pure biochemicals and nanomaterials as next generation biostimulants for sustainable agriculture under abiotic stress - recent advances and future scope

Sustainable agriculture faces major challenges under abiotic stress conditions owing to extensive application of chemical fertilizers which pollute water, soil and atmosphere. Biostimulants (BSs), comprising of naturally derived complex mixtures of uncharacterized biomolecules, pure biochemicals and nanomaterials, enhance nutrient use efficiency (NUE) and trigger crop's natural defense mechanisms. While it is difficult to specify the metabolic effects of uncharacterized natural mixtures (seaweed extract, protein hydrolyzates, etc.), exogenous application of pure biochemicals and nanomaterials offers an edge as BSs since their physiological roles and mechanisms of action are decipherable. Foliar application or seed treatment of some amino acids, polyamines and biopolymers (chitosan, lipochitin oligosaccharides and thuricin 17) enable plants to overcome drought and salinity stress via activation of mechanisms for reactive oxygen species (ROS) scavenging, osmolyte regulation and chlorophyll accumulation. Interaction of nitric oxide (NO) with some vitamins and melatonin exhibits potential significance as BSs for mitigating stress by ROS scavenging and maintenance of intracellular ionic balance and membrane integrity. Near future is likely to see wide applications of nanoparticles (NPs) and nanomaterials (NMs) as BSs in view of their biphasic mode of action (bio-physical activation of membrane receptors followed by gradual release of BS into the plant cells).

Deciphering the mechanisms, hormonal signaling, and potential applications of endophytic microbes to mediate stress tolerance in medicinal plants

The global healthcare market in the post-pandemic era emphasizes a constant pursuit of therapeutic, adaptogenic, and immune booster drugs. Medicinal plants are the only natural resource to meet this by supplying an array of bioactive secondary metabolites in an economic, greener and sustainable manner. Driven by the thrust in demand for natural immunity imparting nutraceutical and life-saving plant-derived drugs, the acreage for commercial cultivation of medicinal plants has dramatically increased in recent years. Limited resources of land and water, low productivity, poor soil fertility coupled with climate change, and biotic (bacteria, fungi, insects, viruses, nematodes) and abiotic (temperature, drought, salinity, waterlogging, and metal toxicity) stress necessitate medicinal plant productivity enhancement through sustainable strategies. Plants evolved intricate physiological (membrane integrity, organelle structural changes, osmotic adjustments, cell and tissue survival, reclamation, increased root-shoot ratio, antibiosis, hypersensitivity, etc.), biochemical (phytohormones synthesis, proline, protein levels, antioxidant enzymes accumulation, ion exclusion, generation of heat-shock proteins, synthesis of allelochemicals. etc.), and cellular (sensing of stress signals, signaling pathways, modulating expression of stress-responsive genes and proteins, etc.) mechanisms to combat stresses. Endophytes, colonizing in different plant tissues, synthesize novel bioactive compounds that medicinal plants can harness to mitigate environmental cues, thus making the agroecosystems self-sufficient toward green and sustainable approaches. Medicinal plants with a host set of metabolites and endophytes with another set of secondary metabolites interact in a highly complex manner involving adaptive mechanisms, including appropriate cellular responses triggered by stimuli received from the sensors situated on the cytoplasm and transmitting signals to the transcriptional machinery in the nucleus to withstand a stressful environment effectively. Signaling pathways serve as a crucial nexus for sensing stress and establishing plants' proper molecular and cellular responses. However, the underlying mechanisms and critical signaling pathways triggered by endophytic microbes are meager. This review comprehends the diversity of endophytes in medicinal plants and endophyte-mediated plant-microbe interactions for biotic and abiotic stress tolerance in medicinal plants by understanding complex adaptive physiological mechanisms and signaling cascades involving defined molecular and cellular responses. Leveraging this knowledge, researchers can design specific microbial formulations that optimize plant health, increase nutrient uptake, boost crop yields, and support a resilient, sustainable agricultural system.

Exogenous Hydrogen Sulfide Supplementation Alleviates the Salinity-Stress-Mediated Growth Decline in Wheat (Triticum aestivum L.) by Modulating Tolerance Mechanisms

The impact of the exogenous supplementation of hydrogen sulfide (20 and 50 µM HS) on growth, enzyme activity, chlorophyll pigments, and tolerance mechanisms was studied in salinity-stressed (100 mM NaCl) wheat. Salinity significantly reduced height, fresh and dry weight, chlorophyll, and carotenoids. However, the supplementation of HS (at both concentrations) increased these attributes and also mitigated the decline to a considerable extent. The exogenous supplementation of HS reduced the accumulation of hydrogen peroxide (H2O2) and methylglyoxal (MG), thereby reducing lipid peroxidation and increasing the membrane stability index (MSI). Salinity stress increased H2O2, MG, and lipid peroxidation while reducing the MSI. The activity of nitrate reductase was reduced due to NaCl. However, the supplementation of HS alleviated the decline with obvious effects being seen due to 50 µM HS. The activity of antioxidant enzymes (superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase) was assayed and the content of reduced glutathione (GSH) increased due to salt stress and the supplementation of HS further enhanced their activity. A decline in ascorbic acid due to salinity stress was alleviated due to HS treatment. HS treatment increased the endogenous concentration of HS and nitric oxide (NO) under normal conditions. However, under salinity stress, HS supplementation resulted in a reduction in HS and NO as compared to NaCl-treated plants. In addition, proline and glycine betaine increased due to HS supplementation. HS treatment reduced sodium levels, while the increase in potassium justified the beneficial role of applied HS in improving salt tolerance in wheat.

Regulation of ethylene metabolism in tomato under salinity stress involving linkages with important physiological signaling pathways

The tomato is well-known for its anti-oxidative and anti-cancer properties, and with a wide range of health benefits is an important cash crop for human well-being. However, environmental stresses (especially abiotic) are having a deleterious effect on plant growth and productivity, including tomato. In this review, authors describe how salinity stress imposes risk consequences on growth and developmental processes of tomato through toxicity by ethylene (ET) and cyanide (HCN), and ionic, oxidative, and osmotic stresses. Recent research has clarified how salinity stress induced-ACS and - β-CAS expressions stimulate the accumulation of ET and HCN, wherein the action of salicylic acid (SA),compatible solutes (CSs), polyamines (PAs) and ET inhibitors (ETIs) regulate ET and HCN metabolism. Here we emphasize how ET, SA and PA cooperates with mitochondrial alternating oxidase (AOX), salt overly sensitive (SOS) pathways and the antioxidants (ANTOX) system to better understand the salinity stress resistance mechanism. The current literature evaluated in this paper provides an overview of salinity stress resistance mechanism involving synchronized routes of ET metabolism by SA and PAs, connecting regulated network of central physiological processes governing through the action of AOX, β-CAS, SOS and ANTOX pathways, which might be crucial for the development of tomato.

Alleviation of Adverse Effects of Drought Stress on Growth and Nitrogen Metabolism in Mungbean (Vigna radiata) by Sulphur and Nitric Oxide Involves Up-Regulation of Antioxidant and Osmolyte Metabolism and Gene Expression

The influence of drought induced by polyethylene glycol (PEG) and the alleviatory effect of nitric oxide (50 µM) and sulphur (S, 1 mM K2SO4) were studied in Vigna radiata. Drought stress reduced plant height, dry weight, total chlorophylls, carotenoids and the content of nitrogen, phosphorous, potassium and sulphur. The foliar applications of NO and sulphur each individually alleviated the decline, with a greater alleviation observed in seedlings treated with both NO and sulphur. The reduction in intermediates of chlorophyll synthesis pathways and photosynthesis were alleviated by NO and sulphur. Oxidative stress was evident through the increased hydrogen peroxide, superoxide and activity of lipoxygenase and protease which were significantly assuaged by NO, sulphur and NO + sulphur treatments. A reduction in the activity of nitrate reductase, glutamine synthetase and glutamate synthase was mitigated due to the application of NO and the supplementation of sulphur. The endogenous concentration of NO and hydrogen sulphide (HS) was increased due to PEG; however, the PEG-induced increase in NO and HS was lowered due to NO and sulphur. Furthermore, NO and sulphur treatments to PEG-stressed seedlings further enhanced the functioning of the antioxidant system, osmolytes and secondary metabolite accumulation. Activities of γ-glutamyl kinase and phenylalanine ammonia lyase were up-regulated due to NO and S treatments. The treatment of NO and S regulated the expression of the Cu/ZnSOD, POD, CAT, RLP, HSP70 and LEA genes significantly under normal and drought stress. The present study advocates for the beneficial use of NO and sulphur in the mitigation of drought-induced alterations in the metabolism of Vigna radiata.

Combined effect of trehalose and spermidine to alleviate zinc toxicity in Vigna radiata

Zinc toxicity is affecting the growth and yield of major crops plants throughout globe by reducing key metabolic processes. In this backdrop, experiments were conducted to evaluate the influence of exogenous supplementation of trehalose (500 µM Treh) and spermidine (500 µM Spd) in alleviating the damaging effects of zinc toxicity (100 µM ZnSO4) in Vigna radiata. Growth, chlorophyll and photosynthesis were reduced due to Zn toxicity; however, exogenous supplementation of trehalose and spermidine not only increased the parameters but also alleviated the decline to considerable levels. Toxicity of zinc increased H2O2, lipid peroxidation and electrolyte leakage by 100.43%, 84.53% and 134.64%, respectively, and application of trehalose and spermidine a reduction of 29.32%, 39.09% and 44.91%, respectively, over the zinc-treated plants. Application of trehalose and spermidine increased the activity of nitrate reductase and the content of nitrogen concomitant with alleviation of the decline caused due to zinc toxicity. The activity of antioxidant system enzymes superoxide dismutase, catalase and the enzymes of ascorbate-glutathione cycle was significantly enhanced due to trehalose and spermidine application. Proline, glycine betaine and activity of γ-glutamyl kinase increased maximally by 281.84%, 126.21% and 181.08%, respectively, in plants treated with zinc + trehalose + spermidine over control. Significant enhancement in the content of total phenols and flavonoids was observed due to the treatment of trehalose and spermidine individually as well as combinedly. Application of trehalose and spermidine reduced the content of methylglyoxal by up-regulating the activity of glyoxylase cycle enzymes. In addition under zinc toxicity conditions, the content of zinc declined in trehalose- and spermidine-treated plants.

Exogenous spermine alleviates the negative effects of combined salinity and paraquat in tomato plants by decreasing stress-induced oxidative damage

Plants are frequently exposed to different combinations of soil constraints including salinity and different herbicides. These abiotic conditions negatively affect photosynthesis, growth and plant development resulting in limitations in agriculture production. To respond to these conditions, plants accumulate different metabolites that restore cellular homeostasis and are key for stress acclimation processes. In this work, we analyzed the role of exogenous spermine (Spm), a polyamine involved in plant tolerance to abiotic stress, in tomato responses to the combination of salinity (S) and the herbicide paraquat (PQ). Our findings showed that application of Spm reduced leaf damage and enhanced survival, growth, photosystem II function and photosynthetic rate of tomato plants subjected to the combination of S and PQ. In addition, we revealed that exogenous Spm reduced H2O2 and malondialdehyde (MDA) accumulation in plants subjected to S+PQ, suggesting that the role of exogenous Spm in alleviating the negative effects of this stress combination could be attributed to a decrease in stress-induced oxidative damage in tomato plants. Taken together, our results identify a key role for Spm in improving plant tolerance to combined stress.

Spermine-Salicylic Acid Interplay Restrains Salt Toxicity in Wheat (Triticum aestivum L.)

Spermine (SPM) and salicylic acid (SA) are plant growth regulators, eliciting specific responses against salt toxicity. In this study, the potential role of 30 mgL^-1 SPM and/or 100 mgL^-1 SA in preventing salt damage was investigated. Wheat plants were grown under non-saline or saline conditions (6.0 and 12.0 dS m^-1) with and without SA and/or SPM foliar applications. Exogenously applied SA and/or SPM alleviated the inhibition of plant growth and productivity under saline conditions by increasing Calvin cycle enzyme activity. Foliage applications also improved ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase activities, which effectively scavenged hydrogen peroxide and superoxide radicals in stressed plants. Furthermore, foliar treatments increased antioxidants such as ascorbate and glutathione, which effectively detoxified reactive oxygen species (ROS). Exogenous applications also increased N, P, and K⁺ acquisition, roots' ATP content, and H⁺-pump activity, accompanied by significantly lower Na⁺ accumulation in stressed plants. Under saline environments, exogenous SA and/or SPM applications raised endogenous SA and SPM levels. Co-application of SA and SPM gave the best response. The newly discovered data suggest that the increased activities of Calvin cycle enzymes, root H⁺-pump, and antioxidant defense machinery in treated plants are a mechanism for salt tolerance. Therefore, combining the use of SA and SPM can be a superior method for reducing salt toxicity in sustainable agricultural systems.

Genome-wide transcriptomic analysis identifies candidate genes involved in jasmonic acid-mediated salt tolerance of alfalfa

Soil salinity imposes a major threat to plant growth and agricultural productivity. Despite being one of the most common fodder crops in saline locations, alfalfa is vulnerable to salt stress. Jasmonic acid (JA) is a phytohormone that influences plant response to abiotic stimuli such as salt stress. However, key genes and pathways by which JA-mediated salt tolerance of alfalfa are little known. A comprehensive transcriptome analysis was performed to elucidate the underlying molecular mechanisms of JA-mediated salt tolerance. The transcripts regulated by salt (S) compared to control (C) and JA+salt (JS) compared to C were investigated. Venn diagram and expression pattern of DEGs indicated that JS further altered a series of genes expression regulated by salt treatment, implying the roles of JA in priming salt tolerance. Enrichment analysis revealed that DEGs exclusively regulated by JS treatment belonged to primary or secondary metabolism, respiratory electron transport chain, and oxidative stress resistance. Alternatively, splicing (AS) was induced by salt alone or JA combined treatment, with skipped exon (SE) events predominately. DEGs undergo exon skipping involving some enriched items mentioned above and transcription factors. Finally, the gene expressions were validated using quantitative polymerase chain reaction (qPCR), which produced results that agreed with the sequencing results. Taken together, these findings suggest that JA modulates the expression of genes related to energy supply and antioxidant capacity at both the transcriptional and post-transcriptional levels, possibly through the involvement of transcription factors and AS events.

Unravelling the Morphological, Physiological, and Phytochemical Responses in Centella asiatica L. Urban to Incremental Salinity Stress

Centella asiatica L. as a traditional medicinal plant is popular in several Asian countries and characterized by the presence of phytochemicals, such as phenolics and flavonoids. Soil salinity can affect the growth and phytochemical composition in this plant species. In this study, the effects of incremental soil salinity (0, 25, 50, 75, and 100 mM NaCl) on growth, physiological characteristics, total phenolic and total flavonoid contents, including the antioxidant activity of Centella asiatica L., were evaluated under greenhouse conditions. Salinity stress reduced growth, biomass production, and total chlorophyll contents, while increasing electrolyte leakage, Na⁺ and Cl^- contents in the shoots and roots. With the increase of salt concentration, total phenolic, total flavonoid content and antioxidant activities were increased. The results showed that centella can tolerate saline conditions up to 100 mM NaCl. Na⁺ exclusion from the roots, and that increases of phytochemical content in the shoots were related to the salt tolerance of this species.

Plant Growth Stimulators Improve Two Wheat Cultivars Salt-Tolerance: Insights into Their Physiological and Nutritional Responses

Spermine (SPM) and salicylic acid (SA), plant growth stimulators, are involved in various biological processes and responses to environmental cues in plants. However, the function of their combined treatment on wheat salt tolerance is unclear. In this study, wheat (Triticum aestivum L. cvs. Shandawel 1 and Sids 14) plants were grown under non-saline and saline (6.0 and 12.0 dS m^-1) conditions and were foliar sprayed with 100 mgL^-1 SA and/or 30 mgL^-1 SPM. Exogenously applied SA and/or SPM relieved the adverse effects caused by salt stress and significantly improved wheat growth and production by inducing higher photosynthetic pigment (chlorophyll a, chlorophyll b, carotenoids) content, nutrient (N, P, K⁺, Ca²⁺, Mg²⁺, Fe, Zn, Cu) acquisition, ionic (K⁺/Na⁺, Ca²⁺/Na⁺, Mg²⁺/Na⁺) homeostatics, osmolyte (soluble sugars, free amino acids, proline, glycinebetaine) accumulation, protein content, along with significantly lower Na⁺ accumulation and chlorophyll a/b ratio. The best response was registered with SA and SPM combined treatment, especially in Shandawel 1. This study highlighted the recovery impact of SA and SPM combined treatment on salinity-damaged wheat plants. The newly discovered data demonstrate that this treatment significantly improved the photosynthetic pigment content, mineral homeostasis, and osmoprotector solutes buildup in salinity-damaged wheat plants. Therefore, it can be a better strategy for ameliorating salt toxicity in sustainable agricultural systems.

Effects of Salt Stress on the Antioxidant Activity and Malondialdehyde, Solution Protein, Proline, and Chlorophyll Contents of Three Malus Species

Understanding the different physiological responses of Malus species under salt stress in the seedling stages will be useful in breeding salt-tolerant dwarfing apple rootstocks. Seedlings of Malus Zumi (Mats.) Rehd. (M. zumi), Malus sieversii (Led.) Roem. (M. sieversii), and Malus baccata (L.) Borkh. (M. baccata) were treated with solution of 0, 0.20%, 0.40%, and 0.60% salinity. Physiological parameters of their leaves and roots were measured at 0 d, 4 d, 8 d and 12 d after salinity treatments. Superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), malondialdehyde (MDA), solution protein (SP), and proline (PRO) initially increased and then decreased. The activities and contents of these parameters were higher in the 0.40% and 0.60% NaCl treatments than in the 0.20% treatment and in the 0% control. M. zumi was the most resistant to salt stress, showing the lowest content of MDA in the leaves and roots, which increased slightly under salt stress. M. baccata had the highest increase in both the content and proportion of MDA. High enzyme activity was shown to play an important role in the salt resistance of M. zumi. Moreover, it can be speculated that there are other substances that also play a major role. We found that osmotic regulation played a key role in response to salt stress for M. baccata even though it was sensitive to salt stress. For M. sieversii, both the osmotic regulation and enzymatic antioxidants were observed to play a major role in mitigating salt stress.

Supplementation of nitric oxide and spermidine alleviates the nickel stress-induced damage to growth, chlorophyll metabolism, and photosynthesis by upregulating ascorbate-glutathione and glyoxalase cycle functioning in tomato

Experiments were conducted to evaluate the role of exogenously applied nitric oxide (NO; 50 µM) and spermidine (Spd; 100 µM) in alleviating the damaging effects of Ni (1 mM NiSO46H2O) toxicity on the growth, chlorophyll metabolism, photosynthesis, and mineral content in tomato. Ni treatment significantly reduced the plant height, dry mass, and the contents of glutamate 1-semialdehyde, δ-amino levulinic acid, prototoporphyrin IX, Mg-prototoporphyrin IX, total chlorophyll, and carotenoids; however, the application of NO and Spd alleviated the decline considerably. Supplementation of NO and Spd mitigated the Ni-induced decline in photosynthesis, gas exchange, and chlorophyll fluorescence parameters. Ni caused oxidative damage, while the application of NO, Spd, and NO+Spd significantly reduced the oxidative stress parameters under normal and Ni toxicity. The application of NO and Spd enhanced the function of the antioxidant system and upregulated the activity of glyoxalase enzymes, reflecting significant reduction of the oxidative effects and methylglyoxal accumulation. Tolerance against Ni was further strengthened by the accumulation of proline and glycine betaine due to NO and Spd application. The decrease in the uptake of essential mineral elements such as N, P, K, and Mg was alleviated by NO and Spd. Hence, individual and combined supplementation of NO and Spd effectively alleviates the damaging effects of Ni on tomato.

Metabolomics and lipidomics insight into the effect of different polyamines on tomato plants under non-stress and salinity conditions

Polyamines (PAs) are key signaling molecules involved in plant growth and stress acclimation processes. This work investigated the effect of spermidine, spermine, and putrescine (alone and in a mixture) in tomato plants using a combined metabolomics and lipidomics approach. The experiments were carried out under non-stress and 100 mM NaCl salinity conditions. Shoot and root biomass, as well as SPAD values, were increased by the application of exogenous PAs but with differences across treatments. Similarly, root length density (F: 34, p < 0.001), average root diameter (F: 14, p < 0.001), and very fine roots (0.0-0.5 mm) increased in PA-treated plants, compared to control. Metabolomics and lipidomics indicated that, despite being salinity the hierarchically prevalent factor, the different PA treatments imposed distinct remodeling at the molecular level. Plants treated with putrescine showed the broader modulation of metabolite profile, whereas spermidine and spermine induced a comparatively milder effect. The pathway analysis from differential metabolites indicated a broad and multi-level intricate modulation of several signaling molecules together with stress-related compounds like flavonoids and alkaloids. Concerning signaling processes, the complex crosstalk between phytohormones (mainly abscisic acid, cytokinins, the ethylene precursor, and jasmonates), and the membrane lipids signaling cascade (in particular, sphingolipids as well as ceramides and other glycerophospholipids), was involved in such complex response of tomato to PAs. Interestingly, PA-specific processes could be observed, with peculiar responses under either control or salinity conditions.

Phytotoxic effects of Acacia saligna dry leachates on germination, seedling growth, photosynthetic performance, and gene expression of economically important crops

The influence of dry leachates of Acasia saligna was tested on the seedling growth, photosynthesis, biochemical attributes, and gene expression of the economically important crops, including wheat (Triticum aestivum L.), radish (Raphanus sativus L.), barley (Hordeum vulgare L.) and arugula (Eruca sativa L.). Different concentrations (5%, 10%, 15%, 20%, and 25%) of stem extract (SE) and leaf extract (LE) of A. saligna were prepared, and seedlings were allowed to grow in Petri plates for 8 days. The results showed that all plant species exhibited reduced germination rate, plant height, and fresh and dry weight due to leachates extracts of A. saligna. Moreover, the activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX), exhibited differential regulation due to the extract treatment. The SOD was increased with increasing the concentration of extracts, while CAT and APX activities were decreased with increasing the extract concentrations. In addition, leachate extract treatment decrease chlorophyll content, photosynthesis, PSII activity, and water use efficiency, with evident effects at their higher concentrations. Furthermore, the content of proline, sugars, protein, total phenols, and flavonoids were reduced considerably due to leachates extract treatments. Furthermore, seedlings treated with high concentrations of LE increased the expression of genes. The present results lead to the conclusion that A. saligna contains significant allelochemicals that interfere with the growth and development of the tested crop species and reduced the crops biomass and negatively affected other related parameters. However, further studies are suggested to determine the isolation and purification of the active compounds present in A. saligna extracts.

Functional carbon nanodots improve soil quality and tomato tolerance in saline-alkali soils

High salinity and alkalinity of saline-alkali soil lead to soil deterioration, the subsequent osmotic stress and ion toxicity inhibited crops growth and productivity. In this research, 8 mg kg^-1 and 16 mg kg^-1 functional carbon nanodots (FCNs) can alleviate the adverse effects of saline-alkali on tomato plant at both seedling and harvest stages, thanks to their up-regulation effects on soil properties and plant physiological processes. On one hand, FCNs stimulate the plant potential of tolerance to saline-alkali and disease resistance through triggering the defense response of antioxidant system, enhancing the osmotic adjustment, promoting the nutrient uptake, transportation and utilization, and up-regulating the photosynthesis, thereby improve tomato growth and productivity in saline-alkali soils. On the other hand, FCNs application contributes to the improvement of soil physicochemical properties and fertilities, as well as decline soil salinity and alkalinity, which are related to plant growth and fruit quality. This research also focuses on the dose-dependent effects of FCNs on their regulation effects and toxicity to tomato growth under stress or non-stress. These findings recommend that FCNs could be applied as potential amendments to ameliorate the saline-alkali soil and improve the tomato tolerance and productivity in the Yellow River Delta.

Comparative Physiological and Transcriptomic Analyses Reveal Mechanisms of Exogenous Spermidine-Induced Tolerance to Low-Iron Stress in Solanum lycopersicum L

Iron (Fe) deficiency in plants is a major problem in agriculture. Therefore, we investigated both the physiological features and molecular mechanisms of plants’ response to low-Fe (LF) stress along with the mitigation of LF with exogenous spermidine (Spd) in tomato plants. The results showed that exogenous Spd foliar application relieved the suppressing effect of LF stress on tomato plants by regulating the photosynthetic efficiency, chlorophyll metabolism, antioxidant levels, organic acid secretion, polyamine metabolism and osmoregulatory systems. Analysis of transcriptomic sequencing results revealed that the differentially expressed genes of iron-deficiency stress were mainly enriched in the pathways of phytohormone signaling, starch and sucrose metabolism and phenyl propane biosynthesis in both leaves and roots. Moreover, Spd-induced promotion of growth under LF stress was associated with upregulation in the expression of some transcription factors that are related to growth hormone response in leaves (GH3, SAUR, ARF) and ethylene-related signaling factors in roots (ERF1, ERF2). We propose that traits associated with changes in low-iron-tolerance genes can potentially be used to improve tomato production. The study provides a theoretical basis for dealing with the iron deficiency issue to develop efficient nutrient management strategies in protected tomato cultivation.

The anthocyanin-rich tomato genotype LA-1996 displays superior efficiency of mechanisms of tolerance to salinity and drought

Tomato cultivation is affected by high soil salinity and drought stress, which cause major yield losses worldwide. In this work, we compare the efficiency of mechanisms of tolerance to salinity, and osmotic stress applied as mannitol or drought, in three tomato genotypes: LA-2838 (Ailsa Craig), LA-2662 (Saladette), and LA-1996 (Anthocyanin fruit - Aft), a genotype known for high anthocyanin content. Exposure to salinity or drought induced stress in all three genotypes, but the LA-1996 plants displayed superior tolerance to stress compared with the other two genotypes. They were more efficient in anthocyanin and proline accumulation, superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activity, and leaf Na⁺, K⁺, and Ca²⁺ homeostasis. In addition, they suffered lesser oxidative damage as measured by chlorophyll (Chl) loss and malondialdehyde (MDA) accumulation, and bioassays showed that they were less affected in terms of seed germination and root elongation. Exposure to stress induced the upregulation of stress-related genes SlNCED1, SlAREB1, SlABF4, SlWRKY8, and SlDREB2A more efficiently in LA-1996 than in the two susceptible genotypes. Conversely, the upregulation of the NADPH oxidase gene SlRBOH1 was more pronounced in LA-2838 and LA-2662. Principal component analysis showed obvious distinction between the tolerant genotype LA-1996 and the susceptible LA-2838 and LA-2662 in response to stress, and association of leaf and stem anthocyanin content with major stress tolerance traits. We suggest that anthocyanin accumulation can be considered as a marker of stress tolerance in tomato, and that LA-1996 can be considered for cultivation in salinity- or drought-affected areas.

Multidimensional Role of Silicon to Activate Resilient Plant Growth and to Mitigate Abiotic Stress

Sustainable agricultural production is critically antagonistic by fluctuating unfavorable environmental conditions. The introduction of mineral elements emerged as the most exciting and magical aspect, apart from the novel intervention of traditional and applied strategies to defend the abiotic stress conditions. The silicon (Si) has ameliorating impacts by regulating diverse functionalities on enhancing the growth and development of crop plants. Si is categorized as a non-essential element since crop plants accumulate less during normal environmental conditions. Studies on the application of Si in plants highlight the beneficial role of Si during extreme stressful conditions through modulation of several metabolites during abiotic stress conditions. Phytohormones are primary plant metabolites positively regulated by Si during abiotic stress conditions. Phytohormones play a pivotal role in crop plants' broad-spectrum biochemical and physiological aspects during normal and extreme environmental conditions. Frontline phytohormones include auxin, cytokinin, ethylene, gibberellin, salicylic acid, abscisic acid, brassinosteroids, and jasmonic acid. These phytohormones are internally correlated with Si in regulating abiotic stress tolerance mechanisms. This review explores insights into the role of Si in enhancing the phytohormone metabolism and its role in maintaining the physiological and biochemical well-being of crop plants during diverse abiotic stresses. Moreover, in-depth information about Si's pivotal role in inducing abiotic stress tolerance in crop plants through metabolic and molecular modulations is elaborated. Furthermore, the potential of various high throughput technologies has also been discussed in improving Si-induced multiple stress tolerance. In addition, a special emphasis is engrossed in the role of Si in achieving sustainable agricultural growth and global food security.

Root morphology ion absorption and antioxidative defense system of two Chinese cabbage cultivars (Brassica rapa L.) reveal the different adaptation mechanisms to salt and alkali stress

Salt stress and alkali stress are major factors that affect the growth and production of Chinese cabbage. To explore their tolerant mechanism to salt and alkali stress, three salinity levels (0, 50, 100 mmol/L NaCl) and three different pH levels (pH6.5, pH7.5, pH8.5) were interactively applied on Qinghua (salt-tolerant-alkali-sensitive) and Biyu (salt-sensitive-alkali-tolerant) cultivars; the root morphology, ion content and antioxidant enzymes were determined. The results showed that the root morphology and root water content of Qinghua under S₀pH_7.5 and S₀pH_8.5 were seriously affected, and the content of H₂O₂ and MDA increased by 143%, 190% and 234%, 294%, respectively, compared with S₀pH_6.5; when Biyu was under S₅₀pH_6.5 and S₁₀₀pH_6.5 stress, the content of H₂O₂ and MDA increase to 152%, 208% and to 240%, 263%, respectively, but the activities and genes expression of SOD, POD, CAT, AAO, APX, DHAR and MDHAR did not change. The root and the contents of H₂O₂ and MDA were not affected when Qinghua was treated with salt and Biyu was treated with alkali, but the activities of the antioxidant enzymes increased to 150-200%, and their relative expression was overexpressed and 2.5-3.5-fold of the S₀pH6.5. The increase of Na⁺ in Qinghua was limited under salt stress, Mg²⁺ in Biyu increased significantly under alkali stress. These all indicated that the adaptability of roots could reflect the degree of tolerance; Chinese cabbage with high salt and alkali tolerance enhanced the regulation of their absorption of ions and increased the relative expression and activities of related antioxidant enzymes.

Impact of Combined Heat and Salt Stresses on Tomato Plants-Insights into Nutrient Uptake and Redox Homeostasis

Currently, salinity and heat are two critical threats to crop production and food security which are being aggravated by the global climatic instability. In this scenario, it is imperative to understand plant responses to simultaneous exposure to different stressors and the cross-talk between underlying functional mechanisms. Thus, in this study, the physiological and biochemical responses of tomato plants (Solanum lycopersicum L.) to the combination of salinity (100 mM NaCl) and heat (42 °C; 4 h/day) stress were evaluated. After 21 days of co-exposure, the accumulation of Na+ in plant tissues was superior when salt-treated plants were also exposed to high temperatures compared to the individual saline treatment, leading to the depletion of other nutrients and a harsher negative effect on plant growth. Despite that, neither oxidative damage nor a major accumulation of reactive oxygen species took place under stress conditions, mostly due to the accumulation of antioxidant (AOX) metabolites alongside the activation of several AOX enzymes. Nonetheless, the plausible allocation of resources towards the defense pathways related to oxidative and osmotic stress, along with severe Na toxicity, heavily compromised the ability of plants to grow properly when the combination of salinity and heat was imposed.

Alleviation role of functional carbon nanodots for tomato growth and soil environment under drought stress

The biotoxicity and environmental applications of carbon nanomaterials have always been the focus of research. In this research, functional carbon nanodots (FCNs) show high promotion effects on regulating the growth, development and yield of tomato under drought stress, due to their up-regulation effects on the physiological processes of plants including photosynthesis, antioxidant system, osmotic adjustment, as well as soil amelioration in physicochemical properties and microbial environment during vegetative and reproductive growth stage. The reduction of tissue water content and water use efficiency are moderated by FCNs through improving root vigor and osmolytes (soluble sugar and proline) level, which contributes to maintain the enzyme function, photosynthesis and nutrient uptake in plant. FCNs regulate the enzymatic and non-enzymatic antioxidant system to scavenge reactive oxygen species (ROS) and inhibit the lipid peroxidation, thus protect the membrane structure and function of plant cells under stress. FCNs up-regulate soil microbial communities under drought stress by regulating the soil pH, enzyme activity, organic carbon and organic matters contents. Our results prove that FCNs are biological friendly to plant growth and soil environment under drought stress, thus exhibit potential as emendator to promote plant tolerance and improve agricultural productivity in water-deficient areas.

A Comprehensive Evaluation of Salt Tolerance in Tomato (Var. Ailsa Craig): Responses of Physiological and Transcriptional Changes in RBOH's and ABA Biosynthesis and Signalling Genes

Salinity is a ubiquitous stressor, depleting osmotic potential and affecting the tomato seedlings’ development and productivity. Considering this critical concern, we explored the salinity response in tomato seedlings by evaluating them under progressive salt stress duration (0, 3, 6, and 12 days). Intriguingly, besides the adverse effect of salt stress on tomato growth the findings exhibited a significant role of tomato antioxidative system, RBOH genes, ABA biosynthesis, and signaling transcription factor for establishing tolerance to salinity stress. For instance, the activities of enzymatic and non-enzymatic antioxidants continued to incline positively with the increased levels of reactive oxygen species (O₂^•−, H₂O₂), MDA, and cellular damage, suggesting the scavenging capacity of tomato seedlings against salt stress. Notably, the RBOH transcription factors activated the hydrogen peroxide-mediated signalling pathway that induced the detoxification mechanisms in tomato seedlings. Consequently, the increased gene expression of antioxidant enzymes and the corresponding ratio of non-enzymatic antioxidants AsA-GSH suggested the modulation of antioxidants to survive the salt-induced oxidative stress. In addition, the endogenous ABA level was enhanced under salinity stress, indicating higher ABA biosynthesis and signalling gene expression. Subsequently, the upregulated transcript abundance of ABA biosynthesis and signalling-related genes suggested the ABA-mediated capacity of tomato seedlings to regulate homeostasis under salt stress. The current findings have revealed fascinating responses of the tomato to survive the salt stress periods, in order to improve the abiotic stress tolerance in tomato.

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.

Exogenous Putrescine Alleviates Drought Stress by Altering Reactive Oxygen Species Scavenging and Biosynthesis of Polyamines in the Seedlings of Cabernet Sauvignon

Climate change imposes intensive dry conditions in most grape-growing regions. Drought stress is one of the most devastating abiotic factors threatening grape growth, yield, and fruit quality. In this study, the alleviation effect of exogenous putrescine (Put) was evaluated using the seedlings of Cabernet Sauvignon (Vitis vinifera L.) subjected to drought stress. The phenotype, photosynthesis index, membrane injury index (MII), and antioxidant system, as well as the dynamic changes of endogenous polyamines (PAs) of grape seedlings, were monitored. Results showed that drought stress increased the MII, lipid peroxidation, and the contents of reactive oxygen species (ROS) (H₂O₂ and O₂ ^-), while it decreased the antioxidant enzyme activity and the net photosynthesis rate (Pn). However, the application of Put alleviated the effects of drought stress by altering ROS scavenging, enhancing the antioxidant system, and increasing the net Pn. Put distinctly increased the activity of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), as well as the contents of ascorbic acid (AsA) and glutathione (GSH). Meanwhile, exogenous Put also promoted the metabolism of endogenous PAs by upregulating their synthetic genes. Our results confirmed that the exogenous application of Put can enhance the antioxidant capacity as well as alter the PA pool, which provides better drought tolerance for Cabernet Sauvignon seedlings.

Growth attributes, biochemical modulations, antioxidant enzymatic metabolism and yield in Brassica napus varieties for salinity tolerance

Improvement in salinity tolerance of plants is of immense significance as salt stress particularly threatens the productivity of agricultural crops. This study was designed to assess the tolerance level of six Brassica napus varieties (Super, Sandal, Faisal, CON-111, AC Excel and Punjab) under different levels of salinity (0, 50, 100, 150 & 200 mM) with three replications under CRD. Salt induced osmotic stress curtailed the plant growth attributes, photosynthetic pigments and disturbed ionic homeostasis (K⁺, Na⁺, Ca^2+, Cl^-) but least disturbance as compared to control was found in Super and Sandal cultivars. Punjab canola and AC Excel canola cultivars were least tolerant to salinity because these displayed greater decline in all growth and biochemical attributes. Plants subjected to NaCl induced stress exhibited considerable decline in all attributes under study with proline as exception. Antioxidants (CAT, SOD & POD) showed an obvious change in Canola plants under stress, but greatest decline was displayed at 200 mM NaCl level in all six cultivars. Over all these attributes presented a comparatively stable trend in super and sandal cultivars. This shows presence of physiological resilience and metabolic capacity in these two cultivars to tackle salinity. Similarly, all yield attributes displayed adverse behavior under 150 mM & 200 mM salinity stress. Our results demonstrated that Super and Sandal cultivars of Brassica napus exhibit good performance in salinity tolerance and can be good option for cultivation in salt affected areas.

Modulation of salinity impact on early seedling stage via nano-priming application of zinc oxide on rapeseed (Brassica napus L.)

Salinity stress negatively affects the plant's developmental stages through micronutrient imbalance. As an essential micronutrient, ZnO can substitute Na⁺ absorption under saline conditions. Therefore, nanoparticles as technological innovation, improve the plant growth efficiency under biotic and abiotic stresses. Nano-priming has become widely applicable in agricultural research during the last decade. The current study was conducted to highlight the impact of ZnONPs priming on seedling biological processes under 150 mM of NaCl using two rapeseed cultivars during the early seedling stage. All concentrations of ZnONPs increased the germination parameters i.e., FG%, GR, VI (I), and VI (II). Meanwhile, the high concentration (ZnO 100%) showed the highest increase in shoot length (9.60% and 25.63%), root length (41.64% and 48.17%) for Yang You 9 and Zhong Shuang 11 over hydro-priming, respectively, as well as biomass. Additionally, nano-priming improved the proline, soluble sugar, and soluble protein contents as a result of osmotic protection modulation. Moreover, nano-priming alleviated ROS and biosynthesis pigments through the reduction of accumulated (H₂O₂) and (O₂^-), and chlorophyll degradation, respectively, also enhanced antioxidant adjustment via improving the plant defense system. Nano-priming substituted the Na⁺ by Zn²⁺, K⁺, and Ca²⁺, and compensated the deficit of micronutrients, thus reduced the Na⁺ toxicity in the cell cytosol. To track the effects of priming during seed imbibition, it noticed that ZnO 100% and ZnO 100%+S increased the Linoleic and Linolenic acids among the studied fatty acids composition by 12.02%, 7.59%, 13.27%, and 10.38% (Yang You 9), 7.42%, 2.77%, 2.93%, and 1.49% (Zhong Shuang 11) over the hydro-priming, respectively. Moreover, the gene expression patterns of BnCAM and BnPER reflected the enhancement of germination levels, notably under the influence of ZnO 100% priming, which increased the level of BnCAM by 70.42% and 111.9% in Yang You 9 and Zhong Shuang 11, respectively. Consequently, ZnO nano-priming enhanced the seedling development through the biosynthesis of pigments, osmotic protection, reduction of ROS accumulation, adjustment of antioxidant enzymes, and improvement of the nutrient absorption, thus enhancing the economic yield under saline conditions.

Short term UV-B radiation mediated modulation of physiological traits and withanolides production in Withania coagulans (L.) Dunal under in-vitro condition

Accumulation of secondary metabolites is a key process in the growth and development of plants under different biotic/abiotic constraints. Many studies highlighted the regulatory potential of UV-B treatment towards the secondary metabolism of plants. In the present study, we examined the impact of UV-B on the physiology and secondary metabolism of Withania coagulans, which is an important ayurvedic plant with high anti-diabetic potential. Results showed that in-vitro UV-B exposure negatively influenced chlorophyll content and photosynthetic machinery. However, Fv/Fm ratio was found non-significantly altered up to 3 h UV-B exposure. The maximum lipid peroxidation level was recorded with 46.8% higher malondialdehyde content in the plants supplemented with 5 h UV-B radiation, that was indicated the oxidative stress in W. coagulans. Conversely, UV-B treatment significantly increased the plant's stress protective compounds like carotenoids, anthocyanin, phenol and proline, in W. coagulans. Free radical scavenging activity was also significantly increased ~ 18% than the control with 3 h UV-B treatment. The maximum antioxidative enzymes activities were observed with the short-term (up to 3 h) UV-B treatment. Specifically, UV-B radiation exposure significantly increased the content of withaferin A and withanolide A in W. coagulans with maximum 1.38 and 3.42-folds, respectively. Additionally, withanolides biosynthesis related genes transcript levels were found over-expressed under the response of UV-B elicitation. The acquired results suggested that short-term UV-B supplementation triggers secondary metabolism along with combating oxidative stress via improving the antioxidative defense system in W. coagulans. Also, UV-B can be used as an efficient abiotic elicitor to increase pharmaceutical compounds (withanolides) production.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01046-7.

RBOH1-dependent H2O2 mediates spermine-induced antioxidant enzyme system to enhance tomato seedling tolerance to salinity-alkalinity stress

Salinity-alkalinity stress is a limiting factor in tomato production in the world. Plants perceive salinity-alkalinity stress by activating signaling pathways to increase plant tolerance (Xu et al., 2020). Here, we investigated whether spermine (Spm) induces respiratory burst oxidase homolog 1 (RBOH1) and hydrogen peroxide (H₂O₂) signaling in response to salinity-alkalinity stress in tomato. The results showed that exogenous Spm induced the expression of RBOH1 and the accumulation of H₂O₂ under normal condition. Accordingly, we tested the function of H₂O₂ signal in tomato seedlings and found that exogenous H₂O₂ increased the expression levels of Cu/Zn-superoxide dismutase (Cu/Zn-SOD), catalase 1 (CAT1), cytosolic ascorbate peroxidase (cAPX), and glutathione reductase 1 (GR1) and the activities of SOD (EC 1.15.1.1), CAT (EC 1.11.1.6), ascorbate peroxidase (APX; EC 1.11.1.11), and GR (EC 1.6.4.2) in tomato seedlings under salinity-alkalinity stress. DMTU increased the malondialdehyde (MDA) content and relative electrical conductivity, and the relative water content (RWC), and accelerated leaf yellowing in tomato seedlings under salinity-alkalinity stress, even though we sprayed Spm on tomato leaves. We also found that RBOH1 silencing decreased the expression levels of Cu/Zn-SOD, CAT1, cAPX, and GR1 and the activities of SOD, CAT, APX, and GR when tomato seedlings were under salinity-alkalinity stress. Exogenous Spm did not increase RWC and decrease MDA content in RBOH1 silencing tomato seedlings under salinity-alkalinity stress.

Optimal water and fertilizer applications improve growth of Tamarix chinensis in a coal mine degraded area under arid conditions

Coal-mined areas are often associated with hostile environmental conditions where the scarcity of water and key nutrient resources negatively affect plant growth and development. In this study we specifically addressed how different combinations of water (W), nitrogen (N) and phosphorus (P) might affect morpho-physiological and biochemical attributes of a native shrub species, Tamarix chinensis, grown on coal mine spoils. Our results show that under greenhouse conditions the application of moderate-to-high doses of W, N and P considerably improved growth-associated parameters (i.e. plant height, stem diameter, dry weight), as well as gas-exchange parameters, photosynthetic pigment contents and leaf water status of T. chinensis. Under field conditions high W and low N, P doses led to significant increases in plant growth-associated traits, gas-exchange parameters and leaf water status. Plant growth was generally higher under greenhouse conditions mainly because seedlings faced multiple stress when growing under field conditions. Low W-regime, regardless of N-P additions, improved osmotic adjustments in leaf tissues and also boosted the activity of several antioxidant enzymes to reduce the oxidative stress associated with W scarcity under greenhouse conditions. Importantly, our study shows how maximum growth performance of T. chinensis under field conditions was achieved at W, N and P doses of 150 mm year^-1 , 80 kg ha^-1 and 40 kg ha^-1 , respectively. Our findings suggest that achieving optimal rates of W, N and P application is crucial for promoting the ecological restoration of coal-mined areas with T. chinensis under arid environmental conditions.

Exogenously applied spermidine confers protection against cinnamic acid-mediated oxidative stress in Pisum sativum

This study investigated the stress responses of cinnamic acid (CA) in pea plants and explored the protective role of spermidine (SPD) against CA-induced adverse effects. Pea seedlings exposed to CA had reduced length, biomass, moisture, chlorophyll, sugar, and protein contents and reduced nitrate reductase activity. These parameters increased when SPD was applied alone and in combination with CA. Electrolyte leakage and malondialdehyde content were high in seedlings treated with CA but decreased when the SPD + CA treatment was applied. Foliar exposure to SPD partially mitigated CA-induced stress effects by strengthening the antioxidant defense system, which helped preserve the integrity of biochemical processes. These results indicate that SPD (1 mM) could mitigate the adverse effects of CA and enhance plant defense system. Hence, SPD can be used as a growth regulator for the maintenance of physiological functions in pea plants in response to the pernicious consequences of CA stress.

The intricacy of silicon, plant growth regulators and other signaling molecules for abiotic stress tolerance: An entrancing crosstalk between stress alleviators

Unfavorable environmental conditions are the critical inimical to the sustainable agriculture. Among various novel strategies designed to protect plants from abiotic stress threats, use of mineral elements as 'stress mitigators' has emerged as the most crucial and interesting aspect. Silicon (Si) is a quasi-essential nutrient that mediates plant growth and development and interacts with plant growth regulators (PGRs) and signaling molecules to combat abiotic stress induced adversities in plants and increase stress tolerance. PGRs are one of the most important chemical messengers that mediate plant growth and development during stressful conditions. However, the individual roles of Si and PGRs have extensively defined but their exquisite crosstalk with each other to mediate plant stress responses is still indiscernible. The present review is an upfront effort to delineate an intricate crosstalk/interaction between Si and PGRs to reduce abiotic stress adversities. The combined effects of interaction of Si with other signaling molecules such as reactive oxygen species (ROS), nitric oxide (NO) and calcium (Ca²⁺) for the survival of plants under stress and optimal conditions are also discussed.

Nitric oxide donor, sodium nitroprusside, mitigates mercury toxicity in different cultivars of soybean

The present study reveals the effect of mercury (Hg) and sodium nitroprusside (SNP) on plant growth and metabolism in soybean cultivars (Pusa-24, Pusa-37and Pusa-40). Mercury stress decreased growth and biomass yield, and gas exchange attributes in all soybean cultivars. External supplementation of SNP mitigated Hg toxicity by improving growth and gas exchange parameters. Electrolyte leakage (EL) increased accompanied with elevated levels of malondialdehyde (MDA) and H2O2 under Hg stress, however, they were found to be reduced in all cultivars upon the exogenous application of SNP. The activities of anti-oxidative enzymes, superoxide dismutase and catalase (SOD and CAT) and those enzymes involved in the ascorbate-glutathione pathway were impaired by Hg stress, but they were regulated by the application of SNP. Accumulation of Hg and NO in the shoots and roots were also regulated by the application of NO. Although, all three cultivars were affected by Hg stress, Pusa-37 was relatively less affected. Mercury stress affected the growth and development of different soybean cultivars, but Pusa-37 being tolerant was less affected. Pusa-37 was found to be more responsive to SNP than Pusa-24, Pusa-40 under Hg toxicity. The external supplementation of SNP could be a sustainable approach to economically utilize Hg affected soils.

Improving growth and photosynthetic performance of drought stressed tomato by application of nano-organic fertilizer involves up-regulation of nitrogen, antioxidant and osmolyte metabolism

Organic fertilizer usage is been introduced into agricultural practices for preventing the damaging effects of chemical fertilizers. Present study investigated the beneficial role of organic fertilizer (nano-vermicompost) on the growth, oxidative stress parameters, antioxidant and nitrogen metabolism, osmolyte accumulation and mineral elements in tomato under drought stress. Drought stress resulted in reduced growth and biomass accumulation by triggering oxidative stress due to excess accumulation of reactive oxygen species (ROS) and reduced mineral uptake. Application of nano-vermicompost proved significantly beneficial in improving growth and mitigating the drought induced growth decline. Nano-vermicompost increased growth and dry matter content and ameliorated the decline in chlorophyll contents, photosynthesis and PSII activity more significantly at higher concentration (100 mg kg-1 soil). ROS accumulation was significantly reduced by nano-vermicompost application thereby enhancing the membrane stability under normal as well as drought conditions. Furthermore, lipid peroxidation and activities of protease and lypoxygenase were significantly reduced. Drought up-regulated antioxidant system and application of nano-vermicompost further enhanced the activities of antioxidant enzymes and the contents of non-enzymatic antioxidant components. Accumulation of osmolytes including proline, glycine betaine and sugars increased significantly due to nano-vermicompost application. Besides, decline in the activity of nitrate reductase and content of essential mineral elements like nitrogen, potassium and phosphorous was also ameliorated by nano-vermicompost application.

Salinity alleviates the arsenic toxicity in the facultative halophyte Salvadora persica L. by the modulations of physiological, biochemical, and ROS scavenging attributes

Heavy metal(loid)s contamination in soil is a major environmental concern that limits agricultural yield and threatens human health worldwide. Arsenic (As) is the most toxic non-essential metalloid found in soil which comes from various natural as well as human activities. S. persica is a facultative halophyte found abundantly in dry, semiarid and saline areas. In the present study, growth, mineral nutrient homeostasis, MDA content, phytochelatin levels, and ROS-scavenging attributes were examined in S. persica imposed to solitary treatments of salinity (250 mM and 750 mM NaCl), solitary treatments of arsenic (200 μM and 600 μM As), and combined treatments of As with 250 mM NaCl with an aim to elucidate salinity and As tolerance mechanisms. The results demonstrated that S. persica plants sustained under high levels of As (600 μM As) as well as NaCl (750 mM). The activity of superoxide dismutase, catalase, peroxidase, and glutathione reductase were either elevated or unaffected under salt or As stress. However, ascorbate peroxidase activity declined under both solitary and combination of As with NaCl. Furthermore, the cellular redox status measured in terms of reduced ascorbate/dehydroascorbate, and reduced glutathione/oxidized glutathione ratios also either increased or remained unaffected in seedlings treated with both solitary and combined treatments of As + NaCl. Significant accumulation of various oxidative stress indicators (H₂O₂ and O₂^-) were observed under high As stress condition. However, presence of salt with high As significantly reduced the levels of ROS. Furthermore, exogenous salt improved As tolerance index (Ti) under high As stress condition. The values of translocation factor (Tf) and As bioaccumulation factor (BF) were >1 in all the treatments. From this study, it can be concluded that the facultative halophyte S. persica is a potential As accumulator and may find application for phytoextraction of arsenic-contaminated saline soil.

Exogenous Spermidine Priming Mitigates the Osmotic Damage in Germinating Seeds of Leymus chinensis Under Salt-Alkali Stress

Spermidine (Spd) is known to protect macromolecules involved in physiological and biochemical processes in plants. However, it is possible that Spd also plays an osmotic regulatory role in promoting the seed germination of Leymus chinensis (L. chinensis) under salt-alkali stress. To investigate this further, seeds of L. chinensis were soaked in Spd solution or distilled water, and a culture experiment was performed by sowing the soaked seeds in saline-alkaline soils. The data showed that the Spd priming resulted in an increase of more than 50% in soluble sugar content and an increase of more than 30% in proline content in the germinating seeds. In addition, the Spd priming resulted in an increase of more than 30% in catalase activity and an increase of more than 25% in peroxidase activity in the germinating seeds and effectively mitigated the oxidative damage to the plasma membrane in the germinating seeds under salt-alkali stress. Moreover, the Spd priming of seeds affected the accumulation of polyamine (PA) and maintained the activities of macromolecules involved in physiological metabolism in germinating seeds exposed to salt-alkali stress. Furthermore, the Spd priming treatment increased the hydrogen peroxide (H₂O₂) level to more than 30% and the Ca²⁺ concentration to more than 20% in the germinating seeds, thus breaking the dormancy induction pathways in L. chinensis seeds through beneficial hormone enrichment. This study provides an insight into the Spd-mediated regulation pathway during exogenous Spd priming of L. chinensis seeds, which mitigates osmotic and oxidative damage and maintains the integrality of the cell lipid membrane. Thus, exogenous Spd priming increases PA oxidase activity and maintains the accumulation of H₂O₂. We found that the H₂O₂ beneficially affected the balance of Ca²⁺ and hormones, promoting the vigor and germination of L. chinensis in response to salt-alkali stress.

Pure Organic Active Compounds Against Abiotic Stress: A Biostimulant Overview

Biostimulants (BSs) are probably one of the most promising alternatives nowadays to cope with yield losses caused by plant stress, which are intensified by climate change. Biostimulants comprise many different compounds with positive effects on plants, excluding pesticides and chemical fertilisers. Usually mixtures such as lixiviates from proteins or algal extracts have been used, but currently companies are interested in more specific compounds that are capable of increasing tolerance against abiotic stress. Individual application of a pure active compound offers researchers the opportunity to better standarise formulations, learn more about the plant defence process itself and assist the agrochemical industry in the development of new products. This review attempts to summarise the state of the art regarding various families of organic compounds and their mode/mechanism of action as BSs, and how they can help maximise agricultural yields under stress conditions aggravated by climate change.

Melatonin improves K+ and Na+ homeostasis in rice under salt stress by mediated nitric oxide

Rice (Oryza sativa L.) productivity is greatly affected by soil salinity and melatonin (MLT) has long been recognized as a positive molecule that can alleviate the damage caused by salt. Here, the role of nitric oxide (NO) in the regulation of salt tolerance by MLT was investigated in rice. MLT pretreatment increased the fresh and dry weight of rice seedlings under salt stress. Its beneficial effects include less relative electrolyte leakage (REL) and better K⁺/Na⁺ homeostasis. MLT increased the activity of nitric oxide synthase (NOS). The polyamines (PAs) content and the utilization of arginine were also increased, thereby increasing NO content in salt-stressed rice seedlings. Pharmacological approach showed that NO, as a necessary downstream signaling molecule, was involved in the regulation of MLT on the K⁺/Na⁺ homeostasis of rice. Under salt stress, MLT improved the H⁺-pumps activities in plasma membrane (PM) and vacuole membrane (VM) in roots, MLT also increased the ATP content of rice roots by increasing the NO content of rice. Thus, the efflux of Na⁺ and the influx of K⁺ were promoted. When endogenous NO was scavenged, the regulation of K⁺/Na⁺ homeostasis by MLT was blocked. Therefore, MLT mediated K⁺/Na⁺ homeostasis of rice under salt stress by mediating NO.

Integration of silicon and secondary metabolites in plants: a significant association in stress tolerance

As sessile organisms, plants are unable to avoid being subjected to environmental stresses that negatively affect their growth and productivity. Instead, they utilize various mechanisms at the morphological, physiological, and biochemical levels to alleviate the deleterious effects of such stresses. Amongst these, secondary metabolites produced by plants represent an important component of the defense system. Secondary metabolites, namely phenolics, terpenes, and nitrogen-containing compounds, have been extensively demonstrated to protect plants against multiple stresses, both biotic (herbivores and pathogenic microorganisms) and abiotic (e.g. drought, salinity, and heavy metals). The regulation of secondary metabolism by beneficial elements such as silicon (Si) is an important topic. Silicon-mediated alleviation of both biotic and abiotic stresses has been well documented in numerous plant species. Recently, many studies have demonstrated the involvement of Si in strengthening stress tolerance through the modulation of secondary metabolism. In this review, we discuss Si-mediated regulation of the synthesis, metabolism, and modification of secondary metabolites that lead to enhanced stress tolerance, with a focus on physiological, biochemical, and molecular aspects. Whilst mechanisms involved in Si-mediated regulation of pathogen resistance via secondary metabolism have been established in plants, they are largely unknown in the case of abiotic stresses, thus leaving an important gap in our current knowledge.

Exogenous spermine-induced expression of SlSPMS gene improves salinity-alkalinity stress tolerance by regulating the antioxidant enzyme system and ion homeostasis in tomato

The study tested the function of exogenous spermine (Spm) in resisting salinity-alkalinity stress in tomato seedlings and found that tomato Spm synthase gene (SlSPMS) was involved in this regulation. The tomato seedlings cultivated in normal conditions or salinity-alkalinity conditions were irrigated with 100 ml one strength Hoagland nutrient solution 100 ml mixed solution (5 ml 300 mmol/L NaCl, 45 ml 300 mmol/L Na₂SO₄, 45 ml 300 mmol/L NaHCO₃, and 5 ml 300 mmol/L Na₂CO₃ (pH = 8.90)) every 2 days, respectively. The 0.5 mM Spm pretreatment improved superoxide dismutase (SOD; EC 1.15.1.1) activity, catalase (CAT; EC 1.11.1.6) activity, ascorbate peroxidase (APX; EC 1.11.1.11) activity, and glutathione reductase (GR; EC 1.6.4.2) activity and decreased endogenous hydrogen peroxide (H₂O₂) content, malondialdehyde (MDA) content, and relative electrical conductivity (REC) in tomato leaves. Na⁺ content declined and K⁺ concentration rose in tomato seedlings when pre-treated with Spm. However the results showed that under salinity-alkalinity stress, silencing of SlSPMS with virus-induced gene silencing had lower antioxidant enzyme activities and higher Na⁺ content and lower K⁺ content than normal tomato seedlings, meaning that they had low salinity-alkalinity tolerance. Exogenous Spm could not reconstruct the tolerance to salinity-alkalinity stress in SlSPMS gene-silencing tomato seedlings. Taken together, exogenous Spm could induce the expression level of SlSPMS, which regulated the antioxidant enzyme system and ion homeostasis in tomato seedlings living in salinity-alkalinity environment, thereby improving the ability of tomato seedlings to resist salinity-alkalinity stress.

Exogenous kinetin and putrescine synergistically mitigate salt stress in Luffa acutangula by modulating physiology and antioxidant defense

Salinity is one of the most vicious environmental constraints that hamper agricultural production. Experiments were done to explore the significant role of sole and synergistic supplementation of kinetin (100 µM KN) and putrescine (100 µM PUT) on Luffa acutangula in NaCl (100 mM) treatment. The harmful effects of salinity on growth were manifested by decreased seedling length, biomass, and pigment contents. We studied the effect of KN, and PUT in preventing salt (NaCl) induced physiological disorders and oxidative damages in 20-day-old Luffa acutangula seedlings. The individual application of KN and PUT increased growth and biochemical parameters, whereas combined KN + PUT treatment showed significant enhancement in growth, photosynthetic pigment content, and osmolyte accumulation in salt-affected plants. Application of KN and PUT also prevented hydrogen peroxide and superoxide production as confirmed by inhibition in electrolyte leakage and lipid peroxidation. Kinetin and PUT application upregulated the antioxidant defense system by enhancing antioxidant enzymes and non-enzymatic contents. Luffa seedlings treated with NaCl + KN + PUT showed 79, 26, 74, and 73% rise in superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase enzymes, respectively, in comparison to NaCl-stressed Luffa acutangula. Findings revealed that synergistic utilization of KN and PUT modulate growth and biochemical processes in seedlings efficaciously in comparison to the individual application under salt stress, and it may be due to a regulatory crosstalk mechanism.

Silicon confers cucumber resistance to salinity stress through regulation of proline and cytokinins

Salt stress is a continuous threat to global crop production. Here, we studied the alleviation role of exogenous silicon (Si) in NaCl-stressed cucumber, with special emphasis on plant growth, proline (Pro) and hormone metabolisms. The results showed that Si supplementation ameliorated the adverse effects of NaCl on plants growth, biomass, and oxidative stress. Salt stress greatly increased the content of Pro throughout the experiment, while Si regulated Pro content in two distinct ways. Si promoted the salt-induced Pro levels after 3 and 6 days of treatment, but decreased it after 9 and 12 days of treatment. Moreover, P5CS and ProDH activities and P5CS gene play important roles in Si and salt-regulated Pro levels in different stress phase. Under stress condition, Si addition tend to revert the content of ABA, IAA, cytokinin and SA to the control levels in most cases. Further correlation analysis revealed a negative correlation between the root cytokinin and Pro content after 3 days of treatment, suggesting the interaction between cytokinin and Pro metabolism. Exogenous application of Pro and ProDH competitive inhibitor D-Lactate confirmed the possible interplay between Pro and cytokinin metabolism. Further study identified several CKX (Csa4G647490 and Csa1G589070) and IPT (Csa7G392940 and Csa3G150100) genes that may be responsible for the regulation of cytokinin accumulation by Si and/or Pro after short-term of treatment. The results suggested that Pro is a key factor in Si-induced salt tolerance, and Si-increased Pro content may participate in the regulation of cytokinin metabolism under short-term of salt stress.

Exogenous allantoin improves the salt tolerance of sugar beet by increasing putrescine metabolism and antioxidant activities

Allantoin as a nitrogen metabolite can improve the salt tolerance in plants, but its mechanism of action remain elusive. Herein, the effects of pretreatment with exogenous allantoin in salt tolerance were investigated in sugar beet. The seedlings were subjected to salt stress (300 mM Na⁺) without or with different allantoin concentrations (0.01, 0.1, and 1 mM). The effects of allantoin on plant growth, homeostasis, oxidative damage, osmoregulation, and polyamine metabolism were studied. The results showed that salt stress inhibited the net photosynthetic rate and plant growth, and caused oxidative damage. However, these adverse effects were mitigated by exogenous allantoin in a dose-dependent manner, especially at 0.1 mM. Allantoin reduced the accumulation of ROS by increasing the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and AsA content. Under salt stress, allantoin reduced the root concentrations of free putrescine (Put) but increased the free spermine (Spm) in leaves and roots. Furthermore, allantoin decreased the Na⁺/K⁺ ratio and promoted the accumulation of betaine and soluble sugars in leaves and roots. Under salinity conditions, allantoin may enhance the antioxidant system and improve ion homeostasis by enhancing putrescine and/or spermine accumulation. In addition, Pearson's correlation and principal component analysis (PCA) established correlations between physiological parameters, and significant differences between different concentrations of allantoin were observed. In total, exogenous allantoin effectively reduced the oxidative damage and ion toxicity in sugar beet, caused by salinity, this finding would be helpful in improving salt tolerance in plant.