Combined effects of brassinosteroid and kinetin mitigates salinity stress in tomato through the modulation of antioxidant and osmolyte metabolism

Effects of superoxide radical on photosynthesis and K+ and redox homeostasis in quinoa and spinach

Methyl viologen (MV), also known as paraquat, is a widely used herbicide but has also been reported as highly toxic to different life forms. The mode of its operation is related to superoxide radical (O2.-) production and consequent oxidative damage. However, besides the damage to key macromolecules, reactive oxygen species (ROS; to which O2.- belongs) are also known as regulators of numerous ion transport systems located at cellular membranes. In this study, we used MV as a tool to probe the role of O2.- in regulating membrane-transport activity and systemic acquired tolerance in halophytic Chenopodium quinoa and glycophytic spinach plants. Both plant species showed growth reduction in terms of reduced shoot length, lower shoot fresh and dry weight, photosynthesis rate, and chlorophyll contents; however, quinoa showed less reduction in growth compared with spinach. This whole plant response was further examined by measuring the ion concentration, gene expression of ion transporters, activation of antioxidants, and osmolyte accumulation. We observed that at the mechanistic level, the differences in growth in response to MV were conferred by at least four complementary physiological mechanisms: (1) higher K+ loss from spinach leaves resulted from higher expression of MV-induced plasma membrane-based depolarization-activated K+ efflux GORK channel, (2) higher activation of high-affinity K+ uptake transporter HAK5 in quinoa, (3) higher antioxidant production and osmolyte accumulation in quinoa as compared with spinach, and (4) maintaining a higher rate of photosynthesis due to higher chlorophyll contents, and efficiency of photosystem II and reduced ROS and MDA contents. Obtained results also showed that MV induced O2.- significantly reduced N contents in both species but with more pronounced effects in glycophytic spinach. Taken together this study has shown the role of O2.- in regulating membrane ion transport and N metabolism in the leaves of halophyte vs. glycophyte in the context of oxidative stress tolerance.

Salicylic Acid Priming Improves Cotton Seedling Heat Tolerance through Photosynthetic Pigment Preservation, Enhanced Antioxidant Activity, and Osmoprotectant Levels

The escalating global temperatures associated with climate change are detrimental to plant growth and development, leading to significant reductions in crop yields worldwide. Our research demonstrates that salicylic acid (SA), a phytohormone known for its growth-promoting properties, is crucial in enhancing heat tolerance in cotton (Gossypium hirsutum). This enhancement is achieved through modifications in various biochemical, physiological, and growth parameters. Under heat stress, cotton plants typically show significant growth disturbances, including leaf wilting, stunted growth, and reduced biomass. However, priming cotton plants with 1 mM SA significantly mitigated these adverse effects, evidenced by increases in shoot dry mass, leaf-water content, and chlorophyll concentrations in the heat-stressed plants. Heat stress also prompted an increase in hydrogen peroxide levels-a key reactive oxygen species-resulting in heightened electrolyte leakage and elevated malondialdehyde concentrations, which indicate severe impacts on cellular membrane integrity and oxidative stress. Remarkably, SA treatment significantly reduced these oxidative stresses by enhancing the activities of critical antioxidant enzymes, such as catalase, glutathione S-transferase, and ascorbate peroxidase. Additionally, the elevated levels of total soluble sugars in SA-treated plants enhanced osmotic regulation under heat stress. Overall, our findings reveal that SA-triggered protective mechanisms not only preserve photosynthetic pigments but also ameliorate oxidative stress and boost plant resilience in the face of elevated temperatures. In conclusion, the application of 1 mM SA is highly effective in enhancing heat tolerance in cotton and is recommended for field trials before being commercially used to improve crop resilience under increasing global temperatures.

Potential of melatonin and Trichoderma harzianum inoculation in ameliorating salt toxicity in watermelon: Insights into antioxidant system, leaf ultrastructure, and gene regulation

Melatonin (MT) is an extensively studied biomolecule with dual functions, serving as an antioxidant and a signaling molecule. Trichoderma Harzianum (TH) is widely recognized for its effectiveness as a biocontrol agent against many plant pathogens. However, the interplay between seed priming and MT (150 μm) in response to NaCl (100 mM) and its interaction with TH have rarely been investigated. This study aimed to evaluate the potential of MT and TH, alone and in combination, to mitigate salt stress (SS) in watermelon plants. The findings of this study revealed a significant decline in the morphological, physiological, and biochemical indices of watermelon seedlings exposed to SS. However, MT and TH treatments reduced the negative impact of salt stress. The combined application of MT and TH exerted a remarkable positive effect by increasing the growth, photosynthetic and gas exchange parameters, chlorophyll fluorescence indices, and ion balance (decreasing Na+ and enhancing K+). MT and TH effectively alleviated oxidative injury by inhibiting hydrogen peroxide formation in saline and non-saline environments, as established by reduced lipid peroxidation and electrolyte leakage. Moreover, oxidative injury induced by SS on the cells was significantly mitigated by regulation of the antioxidant system, AsA-GSH-related enzymes, the glyoxalase system, augmentation of osmolytes, and activation of several genes involved in the defense system. Additionally, the reduction in oxidative damage was examined by chloroplast integrity via transmission electron microscopy (TEM). Overall, the results of this study provide a promising contribution of MT and TH in safeguarding the watermelon crop from oxidative damage induced by salt stress.

Exogenous application of mycotoxin fusaric acid improve the morphological, cytogenetic, biochemical and anatomical parameters in salt (NaCl) stressed Allium cepa L

Salinity is one of the most important abiotic stress factors that negatively affect plant growth and development. In contrast, fusaric acid (FA), a mycotoxin produced by Fusarium and Giberella fungal genera, has biological and metabolic effects in various plants. In this study, it was aimed to investigate the protective effect of externally applied FA (0.1 nM) against the damage caused by salt (0.15 M NaCl) stress in onion (Allium cepa L.) plant. Salt stress resulted in an increase in the chromosomal aberrations (CAs) and micronucleus (MN) frequency, a decrease in the mitotic index (MI), fresh weight, root number, germination percentage, and root length. It promoted CAs such as irregular mitosis, bilobulated nuclei, chromosome loss, bridge, unequal seperation of chromosome, vagrant chromosome and polar slip in root meristem cells. In addition, salt stress caused a enhancement in free proline (PR), catalase (CAT), superoxide dismutase (SOD) and malondialdehyde (MDA) contents in the roots of onion plant. Moreover, it revealed damage and changes that include the accumulation of some chemical substances such as proline and sugars in epidermis and cortex layer cells, epidermal cell injury, flattening of the cell nucleus, wall thickening in cortex cells, necrotic areas and indistinct transmission tissue in the anatomical structure of onion roots. On the other hand, FA application promoted bulb germination and mitotic activity, strengthened the antioxidant defense system, and reduced chromosome and anatomical structure damages. In conclusion; it has been revealed that exogenous FA application may have a positive effect on increasing the resistance of onion plants to salt stress.

The Effects of Exogenous 2,4-Epibrassinolide on the Germination of Cucumber Seeds under NaHCO3 Stress

This investigation focused on the suppressive impact of varying NaHCO3 concentrations on cucumber seed germination and the ameliorative effects of 2,4-Epibrassinolide (EBR). The findings revealed a negative correlation between NaHCO3 concentration and cucumber seed germination, with increased NaHCO3 concentrations leading to a notable decline in germination. Crucially, the application of exogenous EBR significantly counteracted this inhibition, effectively enhancing germination rates and seed vigor. Exogenous EBR was observed to substantially elevate the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), thereby mitigating oxidative damage triggered under NaHCO3 stress conditions. Additionally, EBR improved enzyme activity under alkaline stress conditions and reduced starch content in the seeds. Pertinently, EBR upregulated genes that were associated with gibberellin (GA) synthesis (GA20ox and GA3ox), and downregulated genes that were linked to abscisic acid (ABA) synthesis (NCED1 and NCED2). This led to an elevation in GA3 concentration and a reduction in ABA concentration within the cucumber seeds. Therefore, this study elucidates that alleviating oxidative stress, promoting starch catabolism, and regulating the GA and ABA balance are key mechanisms through which exogenous EBR mitigates the suppression of cucumber seed germination resulting from alkaline stress.

Metabolic Adaptations in Rapeseed: Hemin-Induced Resilience to NaCl Stress by Enhancing Growth, Photosynthesis, and Cellular Defense Ability

This study aimed to investigate whether presoaking with hemin (5 μmol·L-1) could alleviate NaCl stress during rapeseed seedlings' growth and its role in the regulation of photosynthesis. In this experiment, 'HUAYOUZA 62 (HYZ 62)' and 'HUAYOUZA 158R (158R)' were used as materials for pot experiments to study the morphology, photosynthetic characteristics, antioxidant activity, and osmoregulatory factors of seedlings under different salt concentrations, as well as the regulatory effects of hemin-presoaked seeds. Our findings revealed that, compared the control, NaCl stress inhibited the growth of two rapeseed varieties, decreased the seedling emergence rate, and increased the content of malondialdehyde (MDA), the electrolyte leakage rate (EL) and antioxidant enzyme activity. Hemin soaking alleviated the adverse effects of salt stress and increased plant height, root elongation and dry matter accumulation. Compared with all NaCl treatments, hemin significantly enhanced photosynthetic indexes, including a percent increase of 12.99-24.36% and 5.39-16.52% in net photosynthetic rate (Pn), 17.86-48.08% and 8.6-23.44% in stomatal conductivity (Gs), and 15.42-37.94% and 11.09-19.08% in transpiration rate (Tr) for HYZ62 and 158R, respectively. Moreover, hemin soaking also increased antioxidant enzyme activities, including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX), reducing the malondialdehyde, and thus resulting in the alleviation of oxidative damage caused by NaCl stress. Furthermore, hemin stimulated the formation of soluble protein, which effectively regulated the osmo-protective qualities. The current findings strongly elucidate that hemin soaking could effectively alleviate the negative impacts of NaCl stress by regulating the morphological, photosynthetic, and antioxidant traits. This study provides a new idea regarding the effect of Hemin on the salt tolerance of rapeseed, and provides a basis for the practical application of Hemin in saline-alkali soil to improve the salt tolerance of cultivated rapeseed.

Effects of Exogenous Isosteviol on the Physiological Characteristics of Brassica napus Seedlings under Salt Stress

In this paper, the effect of isosteviol on the physiological metabolism of Brassica napus seedlings under salt stress is explored. Brassica napus seeds (Qinyou 2) were used as materials, and the seeds were soaked in different concentrations of isosteviol under salt stress. The fresh weight, dry weight, osmotic substance, absorption and distribution of Na+, K+, Cl-, and the content of reactive oxygen species (ROS) were measured, and these results were combined with the changes shown by Fourier transform infrared spectroscopy (FTIR). The results showed that isosteviol at an appropriate concentration could effectively increase the biomass and soluble protein content of Brassica napus seedlings and reduce the contents of proline, glycine betaine, and ROS in the seedlings. Isosteviol reduces the oxidative damage to Brassica napus seedlings caused by salt stress by regulating the production of osmotic substances and ROS. In addition, after seed soaking in isosteviol, the Na+ content in the shoots of the Brassica napus seedlings was always lower than that in the roots, while the opposite was true for the K+ content. This indicated that under salt stress the Na+ absorbed by the Brassica napus seedlings was mainly accumulated in the roots and that less Na+ was transported to the shoots, while more of the K+ absorbed by the Brassica napus seedlings was retained in the leaves. It is speculated that this may be an important mechanism for Brassica napus seedlings to relieve Na+ toxicity. The spectroscopy analysis showed that, compared with the control group (T1), salt stress increased the absorbance values of carbohydrates, proteins, lipids, nucleic acids, etc., indicating structural damage to the plasma membrane and cell wall. The spectra of the isosteviol seed soaking treatment group were nearly the same as those of the control group (T1). The correlation analysis shows that under salt stress the Brassica napus seedling tissues could absorb large amounts of Na+ and Cl- to induce oxidative stress and inhibit the growth of the plants. After the seed soaking treatment, isosteviol could significantly reduce the absorption of Na+ by the seedling tissues, increase the K+ content, and reduce the salt stress damage to the plant seedlings. Therefore, under salt stress, seed soaking with isosteviol at an appropriate concentration (10-9~10-8 M) can increase the salt resistance of Brassica napus seedlings by regulating their physiological and metabolic functions.

Plant hormones and secondary metabolites under environmental stresses: Enlightening defense molecules

The climatic changes have great threats to sustainable agriculture and require efforts to ensure global food and nutritional security. In this regard, the plant strategic responses, including the induction of plant hormones/plant growth regulators (PGRs), play a substantial role in boosting plant immunity against environmental stress-induced adversities. In addition, secondary metabolites (SMs) have emerged as potential 'stress alleviators' that help plants to adapt against environmental stressors imposing detrimental impacts on plant health and survival. The introduction of SMs in plant biology has shed light on their beneficial effects in mitigating environmental crises. This review explores SMs-mediated plant defense responses and highlights the crosstalk between PGRs and SMs under diverse environmental stressors. In addition, genetic engineering approaches are discussed as a potential revenue to enhance plant hormone-mediated SM production in response to environmental cues. Thus, the present review aims to emphasize the significance of SMs implications with PGRs association and genetic approachability, which could aid in shaping the future strategies that favor agro-ecosystem compatibility under unpredictable environmental conditions.

Tolerance and adaptation mechanism of Solanaceous crops under salinity stress

Solanaceous crops act as a source of food, nutrition and medicine for humans. Soil salinity is a damaging environmental stress, causing significant reductions in cultivated land area, crop productivity and quality, especially under climate change. Solanaceous crops are extremely vulnerable to salinity stress due to high water requirements during the reproductive stage and the succulent nature of fruits and tubers. Salinity stress impedes morphological and anatomical development, which ultimately affect the production and productivity of the economic part of these crops. The morpho-physiological parameters such as root-to-shoot ratio, leaf area, biomass production, photosynthesis, hormonal balance, leaf water content are disturbed under salinity stress in Solanaceous crops. Moreover, the synthesis and signalling of reactive oxygen species, reactive nitrogen species, accumulation of compatible solutes, and osmoprotectant are significant under salinity stress which might be responsible for providing tolerance in these crops. The regulation at the molecular level is mediated by different genes, transcription factors, and proteins, which are vital in the tolerance mechanism. The present review aims to redraw the attention of the researchers to explore the mechanistic understanding and potential mitigation strategies against salinity stress in Solanaceous crops, which is an often-neglected commodity.

Exogenous Brassinosteroid Enhances Zinc tolerance by activating the Phenylpropanoid Biosynthesis pathway in Citrullus lanatus L

Zinc (Zn) is an important element in plants, but over-accumulation of Zn is harmful. The phytohormone brassinosteroids (BRs) play a key role in regulating plant growth, development, and response to stress. However, the role of BRs in watermelon (Citrullus lanatus L.) under Zn stress, one of the most important horticultural crops, remains largely unknown. In this study, we revealed that 24-epibrassinolide (EBR), a bioactive BR enhanced Zn tolerance in watermelon plants, which was related to the EBR-induced increase in the fresh weight, chlorophyll content, and net photosynthetic rate (Pn) and decrease in the content of hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and Zn in watermelon leaves. Through RNA deep sequencing (RNA-seq), 350 different expressed genes (DEG) were found to be involved in the response to Zn stress after EBR treatment, including 175 up-regulated DEGs and 175 down-regulated DEGs. The up-regulated DEGs were significantly enriched in 'phenylpropanoid biosynthesis' pathway (map00940) using KEGG enrichment analysis. The gene expression levels of PAL, 4CL, CCR, and CCoAOMT, key genes involved in phenylpropanoid pathway, were significantly induced after EBR treatment. In addition, compared with Zn stress alone, EBR treatment significantly promoted the activities of PAL, 4CL, and POD by 30.90%, 20.69%, and 47.28%, respectively, and increased the content of total phenolic compounds, total flavonoids, and lignin by 23.02%, 40.37%, and 29.26%, respectively. The present research indicates that EBR plays an active role in strengthening Zn tolerance, thus providing new insights into the mechanism of BRs enhancing heavy metal tolerance.

Promotion of Ca2+ Accumulation in Roots by Exogenous Brassinosteroids as a Key Mechanism for Their Enhancement of Plant Salt Tolerance: A Meta-Analysis and Systematic Review

Brassinosteroids (BRs), the sixth major phytohormone, can regulate plant salt tolerance. Many studies have been conducted to investigate the effects of BRs on plant salt tolerance, generating a large amount of research data. However, a meta-analysis on regulating plant salt tolerance by BRs has not been reported. Therefore, this study conducted a meta-analysis of 132 studies to elucidate the most critical physiological mechanisms by which BRs regulate salt tolerance in plants from a higher dimension and analyze the best ways to apply BRs. The results showed that exogenous BRs significantly increased germination, plant height, root length, and biomass (total dry weight was the largest) of plants under salt stress. There was no significant difference between seed soaking and foliar spraying. However, the medium method (germination stage) and stem application (seedling stage) may be more effective in improving plant salt tolerance. BRs only inhibit germination in Solanaceae. BRs (2 μM), seed soaking for 12 h, and simultaneous treatment with salt stress had the highest germination rate. At the seedling stage, the activity of Brassinolide (C28H48O6) was higher than that of Homobrassinolide (C29H50O6), and post-treatment, BRs (0.02 μM) was the best solution. BRs are unsuitable for use in the germination stage when Sodium chloride is below 100 mM, and the effect is also weakest in the seedling stage. Exogenous BRs promoted photosynthesis, and antioxidant enzyme activity increased the accumulation of osmoregulatory and antioxidant substances and reduced the content of harmful substances and Na+, thus reducing cell damage and improving plant salt tolerance. BRs induced the most soluble protein, chlorophyll a, stomatal conductance, net photosynthetic rate, Glutathione peroxidase, and root-Ca2+, with BRs causing Ca2+ signals in roots probably constituting the most important reason for improving salt tolerance. BRs first promoted the accumulation of Ca2+ in roots, which increased the content of the above vital substances and enzyme activities through the Ca2+ signaling pathway, improving plant salt tolerance.

How Does Zinc Improve Salinity Tolerance? Mechanisms and Future Prospects

Salinity stress (SS) is a serious abiotic stress and a major constraint to agricultural productivity across the globe. High SS negatively affects plant growth and yield by altering soil physio-chemical properties and plant physiological, biochemical, and molecular processes. The application of micronutrients is considered an important practice to mitigate the adverse effects of SS. Zinc (Zn) is an important nutrient that plays an imperative role in plant growth, and it could also help alleviate the effects of salt stress. Zn application improves seed germination, seedling growth, water uptake, plant water relations, nutrient uptake, and nutrient homeostasis, therefore improving plant performance and saline conditions. Zn application also protects the photosynthetic apparatus from salinity-induced oxidative stress and improves stomata movement, chlorophyll synthesis, carbon fixation, and osmolytes and hormone accumulation. Moreover, Zn application also increases the synthesis of secondary metabolites and the expression of stress responsive genes and stimulates antioxidant activities to counter the toxic effects of salt stress. Therefore, to better understand the role of Zn in plants under SS, we have discussed the various mechanisms by which Zn induces salinity tolerance in plants. We have also identified diverse research gaps that must be filled in future research programs. The present review article will fill the knowledge gaps on the role of Zn in mitigating salinity stress. This review will also help readers to learn more about the role of Zn and will provide new suggestions on how this knowledge can be used to develop salt tolerance in plants by using Zn.

Coumarin regulated redox homeostasis to facilitate phytoremediation of saline and alkaline soils by bitter gourd (Momordica charantia L.)

The use of coumarin (COU) to alleviate the phytotoxic effects of salinity has great potential in improving the phytoremediation of saline and alkaline soils. 30-day bitter gourd plants were exposed to 15 dS m‒1 salinity of neutral (NaCl and Na2SO4) and alkaline (Na2CO3 and NaHCO3) salts. 60-day plants were harvested to record different growth, physiological and biochemical attributes. Salinity significantly subsided plant growth, chlorophyll, photosynthesis, and nutrient acquisition. Salinity induced notable oxidative damage in plants that displayed higher relative membrane permeability (RMP), accumulated elevated ROS (H2O2 and O2•‒) and MDA levels alongside intensified lipoxygenase (LOX) activity. The production of cytotoxic methylglyoxal was also significantly higher in plants under salinity. COU seed priming (50, 100 and 150 mg L‒1) promoted plant growth by circumventing oxidative injury and intensifying oxidative defense. Further, COU maintained the intricate balance between reduced (GSH) and oxidized (GSSG) glutathione to diminish ion excess toxicity, thereby facilitating the phytoremediation of saline soils. The lower doses of COU promoted methylglyoxal and ROS detoxification systems that, in turn, lessened the phytotoxic effects of salinity. COU restored ions homeostasis by augmenting osmotic adjustment in plants under salinity.

Improved production and quality of peppers irrigated with regenerated water by the application of 24-epibrassinolide

Water shortage for crop irrigation is reducing agricultural production worldwide and the use of sewage treatment plant (STP) water to irrigate horticultural fields is a solution to avoid the use of drinkable water in agriculture. In this study, two different genotypes of pepper (Red Cherry Small and Italian green) were irrigated with STP water, as an alternative to potable water. Moreover, the foliar application of a molecule with biostimulant properties (24-epibrassinolide; EBR) was tested as a strategy to ameliorate the production and quality of fruits. Both genotypes differed on their tolerance to the suffered oxidative stress due to their different salinity tolerance, but fruit commercial weight was reduced by 49% on the salt sensitive and by 37% on the salt tolerant. Moreover, ascorbic acid was also decreased by 37% after STP water irrigation in the Red Cherry Small peppers. However, EBR applications alleviated STP watering stress effects improving pepper plants fruit production and quality parameters, such as ascorbic acid and capsaicinoids. These results have important economic and environmental relevance to overcome present and future water deficiencies in the agricultural sector derived from climate change, guaranteeing the maintenance of production in peppers irrigated with STP water for a more sustainable agriculture following relevant circular economy actions.

Polyphosphate fertilizer impacts the enzymatic and non-enzymatic antioxidant capacity of wheat plants grown under salinity

By 2050, the predicted global population is set to reach 9.6 billion highlighting the urgent need to increase crop productivity to meet the growing demand for food. This is becoming increasingly challenging when soils are saline and/or deficient in phosphorus (P). The synergic effect of P deficiency and salinity causes a series of secondary stresses including oxidative stress. Reactive Oxygen Species (ROS) production and oxidative damage in plants caused either by P limitation or by salt stress may restrict the overall plant performances leading to a decline in crop yield. However, the P application in adequate forms and doses could positively impact the growth of plants and enhances their tolerance to salinity. In our investigation, we evaluated the effect of different P fertilizers forms (Ortho-A, Ortho-B and Poly-B) and increasing P rates (0, 30 and 45 ppm) on the plant's antioxidant system and P uptake of durum wheat (Karim cultivar) grown under salinity (EC = 3.003 dS/m). Our results demonstrated that salinity caused a series of variations in the antioxidant capacity of wheat plants, at both, enzymatic and non-enzymatic levels. Remarkably, a strong correlation was observed between P uptake, biomass, various antioxidant system parameters and P rates and sources. Soluble P fertilizers considerably enhanced the total plant performances under salt stress compared with control plants grown under salinity and P deficiency (C+). Indeed, salt-stressed and fertilized plants exhibited a robust antioxidant system revealed by the increase in enzymatic activities of Catalase (CAT) and Ascorbate peroxidase (APX) and a significant accumulation of Proline, total polyphenols content (TPC) and soluble sugars (SS) as well as increased biomass, Chlorophyll content (CCI), leaf protein content and P uptake compared to unfertilized plants. Compared to OrthoP fertilizers at 45 ppm P, Poly-B fertilizer showed significant positive responses at 30 ppm P where the increase reached + 18.2% in protein content, + 156.8% in shoot biomass, + 93% in CCI, + 84% in shoot P content, + 51% in CAT activity, + 79% in APX activity, + 93% in TPC and + 40% in SS compared to C+. This implies that PolyP fertilizers might be an alternative for the suitable management of phosphorus fertilization under salinity.

Investigation of the potential role of fusicoccin, a fungal phytotoxin, in mitigating salt stress in onion roots

Fusicoccin is a diterpene glycoside that plays an important role in the regulation of plant growth and development. Fusicoccin produced by Fusicoccum amydali fungus is known to affect plant growth positively with external applications due to its potential to stimulate the tolerance system of plants under stress conditions. In this study, it was aimed to reduce the negative effects of salt (0.15 M NaCl) stress on the germination and growth of onion (Allium cepa L.) bulbs by external fusicoccin (3 µM) application. For this purpose, the germination percentage, root length, root number, fresh weight, mitotic activity, micronucleus frequency, chromosomal abnormality, antioxidant enzyme activity, osmolyte accumulation, cell membrane damage and root anatomical structure were investigated in the current study. Salt stress caused a statistically significant difference (p < 0.05) in all examined parameters. External application of fusicoccin to onion bulbs germinated under salt stress conditions was found to be promising as a plant growth promoter and mitosis stimulator. In addition, fusicoccin application alleviated the harmful effects of salt stress on the chromosome structure and root anatomical structure and protected the cells from the cytotoxic and genotoxic effects of salt. Moreover, this application contributed to the fight against reactive oxygen species of onion plant and increased salt tolerance by regulating the accumulation of osmolyte substances such as proline and antioxidant enzymes such as superoxide dismutase and catalase, and by minimizing cell membrane damage in root cells. In conclusion, this study showed that exogenous application of 3 µM fusicoccin reduced the damage caused by oxidative stress in onion bulbs and served for healthy germination and growth.

Evaluation of Amino Acid Profiles of Rice Genotypes under Different Salt Stress Conditions

Amino acids are building blocks of proteins that are essential components of a wide range of metabolic pathways in plant species, including rice species. Previous studies only considered changes in the amino acid content of rice under NaCl stress. Here, we evaluated profiles of essential and non-essential amino acids in four rice genotype seedlings in the presence of three types of salts, namely NaCl, CaCl₂, and MgCl₂. Amino acid profiles in 14-day-old rice seedlings were determined. The total essential and non-essential amino acid contents in cultivar Cheongcheong were considerably increased upon NaCl and MgCl₂ application, whereas total amino acids were increased upon NaCl, CaCl₂, and MgCl₂ application in the cultivar Nagdong. The total amino acid content was significantly lower in the salt-sensitive cultivar IR28 and salt-tolerant Pokkali under different salt stress conditions. Glycine was not detected in any of the rice genotypes. We observed that cultivars with the same origin respond similarly to each other under salinity stress conditions: cultivars Cheongcheong and Nagdong were found to show increased total amino acid content, whereas the content in foreign cultivars IR28 and Pokkali was found to decrease. Thus, our findings showed that the amino acid profile of each rice cultivar might depend on the origin, immune level, and genetic makeup of the respective cultivar.

Transcriptional and metabolic responses of apple to different potassium environments

Potassium (K) is one of the most important macronutrients for plant development and growth. The influence mechanism of different potassium stresses on the molecular regulation and metabolites of apple remains largely unknown. In this research, physiological, transcriptome, and metabolite analyses were compared under different K conditions in apple seedlings. The results showed that K deficiency and excess conditions influenced apple phenotypic characteristics, soil plant analytical development (SPAD) values, and photosynthesis. Hydrogen peroxide (H₂O₂) content, peroxidase (POD) activity, catalase (CAT) activity, abscisic acid (ABA) content, and indoleacetic acid (IAA) content were regulated by different K stresses. Transcriptome analysis indicated that there were 2,409 and 778 differentially expressed genes (DEGs) in apple leaves and roots under K deficiency conditions in addition to 1,393 and 1,205 DEGs in apple leaves and roots under potassium excess conditions, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment showed that the DEGs were involved in flavonoid biosynthesis, photosynthesis, and plant hormone signal transduction metabolite biosynthetic processes in response to different K conditions. There were 527 and 166 differential metabolites (DMAs) in leaves and roots under low-K stress as well as 228 and 150 DMAs in apple leaves and roots under high-K stress, respectively. Apple plants regulate carbon metabolism and the flavonoid pathway to respond to low-K and high-K stresses. This study provides a basis for understanding the metabolic processes underlying different K responses and provides a foundation to improve the utilization efficiency of K in apples.

Ionic homeostasis and redox metabolism upregulated by 24-epibrassinolide are crucial for mitigating nickel excess in soybean plants, enhancing photosystem II efficiency and biomass

Nickel (Ni) excess often generates oxidative stress in chloroplasts, causing redox imbalance, membrane damage and negative impacts on biomass. 24-Epibrassinolide (EBR) is a plant growth regulator of great interest to the scientific community because it is a natural molecule extracted from plants, is biodegradable and environmentally friendly. This study aimed to determine whether EBR can improve ionic homeostasis, antioxidant enzymes, PSII efficiency and biomass by evaluating nutritional, physiological, biochemical and morphological responses of soybean plants subjected to Ni excess. The experiment used four randomized treatments, with two Ni concentrations (0 and 200 μm Ni, described as -Ni2+ and +Ni2+ , respectively) and two concentrations of EBR (0 and 100 nm EBR, described as -EBR and +EBR, respectively). In general, Ni had deleterious effects on chlorophyll fluorescence and gas exchange. In contrast, EBR enhanced the effective quantum yield of PSII photochemistry (15%) and electron transport rate (19%) due to upregulation of SOD, CAT, APX and POX. Exogenous EBR application promoted significant increases in biomass, and these results were explained by improved nutrient content and ionic homeostasis, as demonstrated by increased Ca2+ /Ni2+ , Mg2+ /Ni+2 and Mn2+ /Ni2+ ratios.

Regulation of Reactive Oxygen Species during Salt Stress in Plants and Their Crosstalk with Other Signaling Molecules-Current Perspectives and Future Directions

Salt stress is a severe type of environmental stress. It adversely affects agricultural production worldwide. The overproduction of reactive oxygen species (ROS) is the most frequent phenomenon during salt stress. ROS are extremely reactive and, in high amounts, noxious, leading to destructive processes and causing cellular damage. However, at lower concentrations, ROS function as secondary messengers, playing a critical role as signaling molecules, ensuring regulation of growth and adjustment to multifactorial stresses. Plants contain several enzymatic and non-enzymatic antioxidants that can detoxify ROS. The production of ROS and their scavenging are important aspects of the plant's normal response to adverse conditions. Recently, this field has attracted immense attention from plant scientists; however, ROS-induced signaling pathways during salt stress remain largely unknown. In this review, we will discuss the critical role of different antioxidants in salt stress tolerance. We also summarize the recent advances on the detrimental effects of ROS, on the antioxidant machinery scavenging ROS under salt stress, and on the crosstalk between ROS and other various signaling molecules, including nitric oxide, hydrogen sulfide, calcium, and phytohormones. Moreover, the utilization of "-omic" approaches to improve the ROS-regulating antioxidant system during the adaptation process to salt stress is also described.

Implementation of Biopolymeric Nanomaterials to Reduce the Negative Impacts of Salinity on Tomato Quantity and Quality

Sustainable waste reduction strategies and innovative waste reduction concepts, as well as their application in the creation of compounds and products with added value, can benefit the economy while reducing environmental pressures. This research aimed to use biopolymeric nanomaterials to reduce the negative effects of salinity on tomato yield and quality. Three types of biopolymers (cellulose, pectin, and starch) were synthesized and characterized using natural materials such as rice straw, orange peel, and potato peel. The polymer's ability to retain sodium ions was investigated. A greenhouse experiment was conducted to assess the potential of natural polymers (cellulose, starch, and pectin individually or in combination) to reduce the salinity side effects on tomato plants (Solanum Lycopersicon L.) cultivar (Super Strain B). Tomato seeds were germinated on soil bits for 20 days before planting five seedlings in each pot (20 cm diameter) with three replicates and filling each pot with sandy loam soil, with or without natural polymers at a rate of 2 g/Kg. The results revealed that all the polymers utilized had a superlative capability to hold sodium ions for both soluble and exchanged sodium. The use of various natural polymer hydrogels increased the number and fresh weight of tomato fruits. Data showed that using biopolymers hydrogels reduced salinity stress by rising the content of phenol, flavonoid, and antioxidant enzymes such as catalase and peroxidase. The use of natural biopolymers significantly improved total soluble solids, pH, and juice substance. Implementing biopolymeric materials could reduce environmental pressures while increasing farm income. Innovative waste reduction strategies, such as the creation of value-added products, will benefit the economy, and this work is a good start in that direction.

Modulation of NaCl-induced osmotic, cytogenetic, oxidative and anatomic damages by coronatine treatment in onion (Allium cepa L.)

Coronatine (COR), a bacterial phytotoxin produced by Pseudomonas syringae, plays important roles in many plant growth processes. Onion bulbs were divided four groups to investigate the effects of COR against sodium chloride (NaCl) stress exposure in Allium cepa L. root tips. While control group bulbs were soaked in tap water medium, treatment group bulbs were grown in 0.15 M NaCl, 0.01 µM COR and 0.01 µM COR + 0.15 M NaCl medium, respectively. NaCl stress seriously inhibited the germination, root lenght, root number and fresh weight of the bulbs. It significantly decreased the mitotic index (MI), whereas dramatically increased the micronucleus (MN) frequency and chromosomal aberrations (CAs). Moreover, in order to determine the level of lipid peroxidation occurring in the cell membrane, malondialdehyde (MDA) content was measured and it was determined that it was at the highest level in the group germinated in NaCl medium alone. Similarly, it was revealed that the superoxide dismutase (SOD), catalase (CAT) and free proline contents in the group germinated in NaCl medium alone were higher than the other groups. On the other hand, NaCl stress caused significant injuries such as epidermis/cortex cell damage, MN formation in epidermis/cortex cells, flattened cells nuclei, unclear vascular tissue, cortex cell wall thickening, accumulation of certain chemical compounds in cortex cells and necrotic areas in the anatomical structure of bulb roots. However, exogenous COR application significantly alleviated the negative effects of NaCl stress on bulb germination and growth, antioxidant defense system, cytogenetic and anatomical structure. Thus, it has been proven that COR can be used as a protective agent against the harmful effects of NaCl on onion.

Phytohormones regulate the abiotic stress: An overview of physiological, biochemical, and molecular responses in horticultural crops

Recent changing patterns of global climate have turned out to be a severe hazard to the horticulture crops production. A wide range of biotic and abiotic stresses often affect plants due to their sessile nature. Horticultural crop losses are mainly caused by abiotic factors such as drought, salt, heat, cold, floods, and ultraviolet radiation. For coping up with these adversities, well-developed mechanisms have been evolved in plants, which play a role in perceiving stress signals and enabling optimal growth responses. Interestingly, the use of phytohormones for suppressing the impact of abiotic stress has gained much attention in recent decades. For circumvention of stress at various levels, including physiological, molecular, as well as biochemical, a sophisticated mechanism is reported to be provided by the phytohormones, thus labeling these phytohormones a significant role in plant growth and development. Phytohormones can improves tolerance against abiotic stresses by increasing seed germination, seedling growth, leaf photosynthesis, root growth, and antioxidant enzymes and reducing the accumulation of reactive oxygen species, malonaldehyde, and electrolyte leakage. Recent discoveries highlight the significant role of a variety of phytohormones including melatonin (MEL), Gamma-aminobutyric acid (GABA), jasmonic acid (JA), salicylic acid (SA), brassinosteroids (BRs), and strigolactones (SLs) in abiotic stress tolerance enhancement of horticultural plants. Thus, current review is aimed to summarize the developmental concepts regarding role of phytohormones in abiotic-stress mitigation, mainly in horticultural crops, along with the description of recent studies which identified the role of different phytohormones in stressed environments. Hence, such a review will help in paving the path for sustainable agriculture growth via involvement of phytohormones in enhancement of abiotic stress tolerance of horticultural crops.

Different leafy vegetable cropping systems regulate growth, photosynthesis, and PSII functioning in mono-cropped eggplant by altering chemical properties and upregulating the antioxidant system

Continuous cropping of eggplant threatened regional ecological sustainability by facilitating replanting problems under mono-cropping conditions. Therefore, alternative agronomic and management practices are required to improve crop productivity at low environmental cost for the development of sustainable agricultural systems in different regions. This study examined changes in soil chemical properties, eggplant photosynthesis, and antioxidant functioning in five different vegetable cropping systems over a 2-year period., 2017 and 2018. The results showed that welsh onion-eggplant (WOE), celery-eggplant (CE), non-heading Chinese cabbage-eggplant (NCCE), and leafy lettuce-eggplant (LLE) rotation systems significantly impacted growth, biomass accumulation, and yield than fallow-eggplant (FE). In addition, various leafy vegetable cropping systems, WOE, CE, NCCE, and LLT induced significant increases in soil organic matter (SOM), available nutrients (N, P, and K), and eggplant growth by affecting the photosynthesis and related gas exchange parameters with much evident effect due to CE and NCCE. Moreover, eggplant raised with different leafy vegetable rotation systems showed higher activity of antioxidant enzymes, resulting in lower accumulation of hydrogen peroxide and hence reduced oxidative damage to membranes. In addition, fresh and dry plant biomass was significantly increased due to crop rotation with leafy vegetables. Therefore, we concluded that leafy vegetable crop rotation is a beneficial management practice to improve the growth and yield of eggplant.

Principal Component Analysis to Assess the Changes of Yield and Quality in Pinellia ternata at Different Stages after Brassinolide Treatments

Brassinolide (BR) is the "sixth class" plant hormone, which plays an important role in various physiological and biochemical processes of plants. The wide variety of functions of Pinellia ternata means that there is huge demand for it and thus it is in short supply. This paper mainly assessed the changes of yield and quality in P. ternata at different stages after BR treatments by principal component analysis, in order to improve the yield and quality of P. ternata and at the same time determine the best harvest time. The results showed that the tuber yield of P. ternata was significantly increased by BR treatments at different stages (except for the 15th day). After the 15th, 45th, 60th, 75th, 90th, and 105th day of treatments, the tuber yield of P. ternata reached peak values at 0.10 (0.65 g), 0.50 (1.97 g), 0.50 (1.98 g), 1.00 (2.37 g), 1.00 (2.84 g), and 2.00 mg/L (3.76 g) BR treatment, respectively. The optimal harvest time was the 75th day after 0.10, 0.50, and 1.00 mg/L BR treatments, which not only significantly improved the yield of P. ternata, but also retained high level of total alkaloids in the tubers (20.89, 5.37, and 13.44%) and bulbils (9.74, 20.42, and 13.62%), high total flavone content in the tubers (17.66, 16.26, and 12.74%) and bulbils (52.63, 12.79, and 38.69%), and high β-sitosterol content in the tubers (25.26, 16.65, and 0.62%) of P. ternata, compared with the control, respectively.

Differential activity of wheat antioxidant defense system and alterations in the accumulation of osmolytes at different developmental stages as influenced by marigold (Tagetes erecta L.) leachates

Experiments were conducted to evaluate the effectivity of Tagetes erecta L. leachates on various growth, physiological, and biochemical parameters of wheat at different stages of growth. Results suggested that Triticum aestivum L. seedlings/plants when exposed to higher concentrations of marigold leachates (10%, 20%, and 30% w/v of fresh parts and 5% and 10% w/v of dry parts) exhibited enhanced lipid peroxidation along with an increase in the activity of protease and phenylalanine ammonia lyase. Treatment with higher concentrations of leachates of fresh (30% w/v) and dry (10% w/v) T. erecta upregulated the activity of superoxide dismutase, catalase, ascorbate peroxidase, guaiacol peroxidase, glutathione S-transferase, and glutathione reductase and also increased the non-enzymatic components of antioxidant defense such as glutathione, ascorbic acid, and total phenols along with osmotic constituents comprising free proline, free sugars, and free amino acids in wheat. The growth and yield attributes of wheat exhibited a slight increase at treatments with lower concentrations (1% w/v) of dry leachates, whereas a decrease was recorded at higher concentrations (10% w/v). In general, treatments with flower leachates (higher concentrations) showed greater influence as compared with those with leaf leachates. Identification and understanding the mechanism of function of allelochemicals in these leachates may pave a way for further experimentation on Tagetes erecta L crop while it is cultivated and decomposed in the field.

Mitigation of Negative Effects of Chromium (VI) Toxicity in Faba Bean (Vicia faba) Plants through the Supplementation of Kinetin (KN) and Gibberellic Acid (GA3)

The present study was carried out to explore the possible role of kinetin and gibberellic acid (GA3) on faba bean under chromium (Cr) stress. Cr treatment negatively affected growth and biomass production, reduced photosynthetic pigments, and inhibited photosynthesis, gas exchange parameters, antioxidant enzymes, and the glyoxylase cycle. Moreover, Cr stress enhanced the production of malondialdehyde (MDA, 216.11%) and hydrogen peroxide (H₂O₂, 230.16%), electrolyte leakage (EL, 293.30%), and the accumulation of proline and glycine betaine. Exogenous application of kinetin and GA3 increased growth and biomass, improved pigment contents and photosynthesis, as well as up-regulated the antioxidant system by improving the antioxidant enzyme activities and the content of nonenzymatic components, and the glyoxylase cycle. Additionally, kinetin and GA3 application displayed a considerable enhancement in proline (602.61%) and glycine betaine (423.72), which help the plants to maintain water balance under stress. Furthermore, a decline in Cr uptake was also observed due to kinetin and GA3 application. Exogenous application of kinetin and GA3 ameliorated the toxic effects of Cr in faba bean plants, up-shooting the tolerance mechanisms, including osmolyte metabolism and the antioxidant system.

Abiotic Stress Tolerance in Plants: Brassinosteroids Navigate Competently

Brassinosteroid hormones (BRs) multitask to smoothly regulate a broad spectrum of vital physiological processes in plants, such as cell division, cell expansion, differentiation, seed germination, xylem differentiation, reproductive development and light responses (photomorphogenesis and skotomorphogenesis). Their importance is inferred when visible abnormalities arise in plant phenotypes due to suboptimal or supraoptimal hormone levels. This group of steroidal hormones are major growth regulators, having pleiotropic effects and conferring abiotic stress resistance to plants. Numerous abiotic stresses are the cause of significant loss in agricultural yield globally. However, plants are well equipped with efficient stress combat machinery. Scavenging reactive oxygen species (ROS) is a unique mechanism to combat the deleterious effects of abiotic stresses. In light of numerous reports in the past two decades, the complex BR signaling under different stress conditions (drought, salinity, extreme temperatures and heavy metals/metalloids) that drastically hinders the normal metabolism of plants is gradually being untangled and revealed. Thus, crop improvement has substantial potential by tailoring either the brassinosteroid signaling, biosynthesis pathway or perception. This review aims to explore and dissect the actual mission of BRs in signaling cascades and summarize their positive role with respect to abiotic stress tolerance.

Impact of OsBadh2 Mutations on Salt Stress Response in Rice

Mutations in the Betaine aldehyde dehydrogenase 2 (OsBadh2) gene resulted in aroma, which is a highly preferred grain quality attribute in rice. However, research on naturally occurring aromatic rice has revealed ambiguity and controversy regarding aroma emission, stress tolerance, and response to salinity. In this study, mutant lines of two non-aromatic varieties, Huaidao#5 (WT_HD) and Jiahua#1 (WT_JH), were generated by targeted mutagenesis of OsBadh2 using CRISPR/Cas9 technology. The mutant lines of both varieties became aromatic; however, WT_HD mutants exhibited an improved tolerance, while those of WT_JH showed a reduced tolerance to salt stress. To gain insight into the molecular mechanism leading to the opposite effects, comparative analyses of the physiological activities and expressions of aroma- and salinity-related genes were investigated. The WT_HD mutants had a lower mean increment rate of malondialdehyde, superoxide dismutase, glutamate, and proline content, with a higher mean increment rate of γ-aminobutyric acid, hydrogen peroxide, and catalase than the WT_JH mutants. Fluctuations were also detected in the salinity-related gene expression. Thus, the response mechanism of OsBadh2 mutants is complicated where the genetic makeup of the rice variety and interactions of several genes are involved, which requires more in-depth research to explore the possibility of producing highly tolerant aromatic rice genotypes.

Elucidating the genetic architecture controlling antioxidant status and ionic balance in barley under salt stress

Association genetic analysis empowered us to identify candidate genes underlying natural variation of morpho-physiological, antioxidants, and grain yield-related traits in barley. Novel intriguing genomic regions were identified and dissected. Salinity stress is one of the abiotic stresses that influence the morpho-physiological, antioxidants, and yield-related traits in crop plants. The plants of a core set of 138 diverse barley accessions were analyzed after exposure to salt stress under field conditions during the reproductive phase. A genome-wide association scan (GWAS) was then conducted using 19,276 single nucleotide polymorphisms (SNPs) to uncover the genetic basis of morpho-physiological and grain-related traits. A wide range of responses to salt stress by the accessions was explored in the current study. GWAS detected 263 significantly associated SNPs with the antioxidants, K⁺/Na⁺ content ratio, and agronomic traits. Five genomic regions harbored interesting putative candidate genes within LD ± 1.2 Mbp. Choromosome 2H harbored many candidate genes associated with the antioxidants ascorbic acid (AsA) and glutathione (GSH), such as superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR), under salt stress. Markedly, an A:C SNP at 153,773,211 bp on chromosome 7H is located inside the gene HORVU.MOREX.r3.7HG0676830 (153,772,300-153,774,057 bp) that was annotated as L-gulonolactone oxidase, regulating the natural variation of SOD_S and APX_S. The allelic variation at this SNP reveals a negative selection of accessions carrying the C allele, predominantly found in six-rowed spring landraces originating from Far-, Near-East, and central Asia carrying photoperiod sensitive alleles having lower activity of enzymatic antioxidants. The SNP-trait associations detected in the current study constitute a benchmark for developing molecular selection tools for antioxidant compound selection in barley.

Effect of Salinity and Plant Growth Promoters on Secondary Metabolism and Growth of Milk Thistle Ecotypes

Simple Summary

The present study shed light on the effect of salinity on the plant growth and secondary metabolites of medicinally important milk thistle plant ecotypes. At the same time, we also studied the effect of external supplementation with ascorbic acid, thiourea, and moringa leaf extract on improving growth-related attributes and secondary metabolites under salinity stress. Various parameters were studied related to stress alleviation. Ascorbic acid, followed by moringa leaf extract, was the most effective in improving growth under salt stress conditions. The present study demonstrated that milk thistle could withstand moderate doses of salt stress, while externally supplemented media improved all the growth parameters by increasing the accumulation of secondary metabolites.

Abstract

Milk thistle (Silybum marianum (L.)) is a wild medicinal herbal plant that is widely used in folk medicine due to its high content of secondary metabolites (SMs) and silymarin; however, the data regarding the response of milk thistle to salinity are still scarce and scanty. The present study evaluated the effect of salinity on a geographically diverse population of milk thistle and on the role of medium supplementation (MS) with ascorbic acid, thiourea, and moringa leaf extract in improving the SMs and growth-related attributes under salinity stress (SS). For germination, a 120 mM level of salinity was applied in the soil during the seedling stage. After salinity development, predetermined levels of the following compounds were used for MS: thiourea (250 µM), moringa leaf extract (3%), and ascorbic acid (500 µM). The data regarding growth attributes showed that SS impaired plant growth and development and increased SM production, including alkaloids, anthocyanin, and saponins. Moreover, ascorbic acid, followed by moringa leaf extract, was the most effective in improving growth by virtue of increased SMs, especially under salt stress conditions. The present study demonstrated that milk thistle could withstand moderate doses of SS, while MS improved all the growth parameters by increasing the accumulation of SMs.

Salt stress resilience in plants mediated through osmolyte accumulation and its crosstalk mechanism with phytohormones

Salinity stress is one of the significant abiotic stresses that influence critical metabolic processes in the plant. Salinity stress limits plant growth and development by adversely affecting various physiological and biochemical processes. Enhanced generation of reactive oxygen species (ROS) induced via salinity stress subsequently alters macromolecules such as lipids, proteins, and nucleic acids, and thus constrains crop productivity. Due to which, a decreasing trend in cultivable land and a rising world population raises a question of global food security. In response to salt stress signals, plants adapt defensive mechanisms by orchestrating the synthesis, signaling, and regulation of various osmolytes and phytohormones. Under salinity stress, osmolytes have been investigated to stabilize the osmotic differences between the surrounding of cells and cytosol. They also help in the regulation of protein folding to facilitate protein functioning and stress signaling. Phytohormones play critical roles in eliciting a salinity stress adaptation response in plants. These responses enable the plants to acclimatize to adverse soil conditions. Phytohormones and osmolytes are helpful in minimizing salinity stress-related detrimental effects on plants. These phytohormones modulate the level of osmolytes through alteration in the gene expression pattern of key biosynthetic enzymes and antioxidative enzymes along with their role as signaling molecules. Thus, it becomes vital to understand the roles of these phytohormones on osmolyte accumulation and regulation to conclude the adaptive roles played by plants to avoid salinity stress.

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.

Exogenous brassinolide improves the antioxidant capacity of Pinellia ternata by enhancing the enzymatic and nonenzymatic defense systems under non-stress conditions

Brassinolide (BR) improves the antioxidant capacity of plants under various abiotic stresses. However, it is not clear about the effect of BR on the antioxidant capacity in plants under non-stress conditions. In the present study, the antioxidant defense response of Pinellia ternata was to be assessed by applying BR and propiconazole (Pcz) under non-stress conditions. BR treatment enhanced the flavonoid content, peroxidase, and ascorbate peroxidase (APX) activity by 12.31, 30.62, and 25.08% and led to an increase in 2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity by 4.31% and a decrease in malondialdehyde content by 1.04%. Exogenous application of BR improved the expression levels of PAL, CHS, CHI, and DFR genes by 3. 18-, 3. 39-, 2. 21-, and 0.87-fold in flavonoid biosynthesis, PGI, PMI, and GME genes by 6. 60-, 1437. 79-, and 3.11-fold in ascorbic acid (ASA), biosynthesis, and γECs and GSHS genes by 6.08- and 2.61-fold in glutathione (GSH) biosynthesis pathway, and the expression of these genes were inhibited by Pcz treatment. In addition, BR treatment promoted the ASA-GSH cycle by enhancing the expression of APX, DHAR, and MDHAR genes, which were enhanced by 3. 33-, 157. 85-, and 154.91-fold, respectively. These results provided novel insights into the effect of BR on the antioxidant capacity in bulbil of P. ternata under non-stress conditions and useful knowledge of applying BR to enhance the antioxidant capacity of plants.

Physiological mechanisms of ABA-induced salinity tolerance in leaves and roots of rice

Abscisic acid (ABA) plays a crucial role in response to abiotic stress as important small molecules in regulating metabolism. This study aimed to evaluate the ability of foliar spraying ABA to regulate growth quality at rice seedling stage under salt stress. Results demonstrated that salt stress strongly reduced all the growth parameters of two rice seedlings (‘Chaoyouqianhao’ and ‘Huanghuazhan’), caused prominent decrease in the levels of photosynthetic pigments (mainly in Huanghuazhan), photosynthesis and fluorescence parameters. Salinity treatment increased the concentration of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) in roots, whereas significant decreased H₂O₂ was found in leaves of Huanghuazhan. Additionally, salinity triggered high Na⁺ content particularly in leaves and enhanced catalase (CAT) activities, ascorbate peroxidase (APX) and peroxidase (POD) activities of the two rice seedlings. Nevertheless, salinity-induced increased root ascorbic acid (AsA) and glutathione (GSH) levels while decreased in leaves, which depended on treatment time. Conversely, ABA application partially or completely mitigated salinity toxicity on the seedlings. ABA could reverse most of the changed physiological parameters triggered by salt stress. Specially, ABA treatment improved antioxidant enzyme levels and significantly reduced the Na⁺ content of two varieties as well as increased the K⁺, Mg²⁺ and Ca²⁺ content in leaves and roots. ABA treatment increased the hormone contents of 1-aminocclopropane carboxylic acid (ACC), trans-zeatin (TZ), N6-isopentyladenosine (IPA), Indole-3-acetic acid (IAA), and ABA in leaves of two rice varieties under salt stress. It is suggested that ABA was beneficial to protect membrane lipid peroxidation, the modulation of antioxidant defense systems and endogenous hormonal balance with imposition to salt stress.

ACC deaminase producing rhizobacterium Enterobacter cloacae ZNP-4 enhance abiotic stress tolerance in wheat plant

Plant growth promoting rhizobacterium (PGPR) designated as ZNP-4, isolated from the rhizosphere of Ziziphus nummularia, was identified as Enterobacter cloacae following 16S rRNA sequence analysis. The isolated strain exhibited various plant growth promoting (PGP) traits. The 1-aminocyclopropane-1-carboxylic acid deaminase (ACCD) activity was evaluated under diverse physiological conditions that could be useful for minimizing the abiotic stress-induced inhibitory effects on wheat plants. The strain showed resistance to salt (NaCl) and metal (ZnSO₄) stress. The effect of E. cloacae ZNP-4 on the augmentation of plant growth was studied under salinity stress of 150 mM (T1 treatment) & 200 mM (T2 treatment) NaCl. The inoculation of strain ZNP-4 significantly improved the various growth parameters of wheat plant such as shoot length (41%), root length (31%), fresh weight (28%), dry weight (29%), photosynthetic pigments chlorophyll a (62%) and chlorophyll b (34%). Additionally, the strain was found to be efficient for minimizing the imposed Zn stress in terms of improving plant growth, biomass and photosynthetic pigments in pots containing different levels of metal stress of 150 mg kg^-1 (treatment T1) and 250 mg kg^-1 (treatment T2). Isolate ZNP-4 also improved the proline content and decreased malondialdehyde (MDA) level under both salinity and metal stress, therefore maintaining the membrane integrity. Furthermore, bacterial inoculation increased the activities of antioxidative enzymes such as superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX). The positive effects of PGPR occurred concurrently with the decrease in abiotic stress-induced reactive oxygen species (ROS) molecules such as hydrogen peroxide (H₂O₂) and superoxide (O₂^-) contents. Overall, the observed results indicate that use of bacteria with such beneficial traits could be used as bio-fertilizers for many crops growing under stress conditions.

Salinity mediated cross-tolerance of arsenic toxicity in the halophyte Salvadora persica L. through metabolomic dynamics and regulation of stomatal movement and photosynthesis

Arsenic (As) is a highly toxic metalloid adversely affecting the environment, human health, and crop productivity. The present study assessed the synergistic effects of salinity and As on photosynthetic attributes, stomatal regulations, and metabolomics responses of the xero-halophyte Salvadora persica to decipher the As-salinity cross-tolerance mechanisms and to identify the potential metabolites/metabolic pathways involved in cross-tolerance of As with salinity. Salinity and As stress-induced significant stomatal closure in S. persica suggests an adaptive response to decrease water loss through transpiration. NaCl supplementation improved the net photosynthetic rate (by +39%), stomatal conductance (by +190%), water use efficiency (by +55%), photochemical quenching (by +37%), and electron transfer rate (54%) under As stress as compared to solitary As treatment. Our results imply that both stomatal and non-stomatal factors account for a reduction in photosynthesis under high salinity and As stress conditions. A total of 64 metabolites were identified in S. persica under salinity and/or As stress, and up-regulation of various metabolites support early As-salinity stress tolerance in S. persica by improving antioxidative defense and ROS detoxification. The primary metabolites such as polyphenols (caffeic acid, catechin, gallic acid, coumaric acid, rosmarinic acid, and cinnamic acid), amino acids (glutamic acid, cysteine, glycine, lysine, phenylalanine, and tyrosine), citrate cycle intermediates (malic acid, oxalic acid, and α-ketoglutaric acid), and most of the phytohormones accumulated at higher levels under combined treatment of As + NaCl compared to solitary treatment of As. Moreover, exogenous salinity increased glutamate, glycine, and cysteine, which may induce higher synthesis of GSH-PCs in S. persica. The metabolic pathways that were significantly affected in response to salinity and/or As include inositol phosphate metabolism, citrate cycle, glyoxylate and dicarboxylate metabolism, amino acid metabolism, and glutathione metabolism. Our findings indicate that inflections of various metabolites and metabolic pathways facilitate S. persica to withstand and grow optimally even under high salinity and As conditions. Moreover, the addition of salt enhanced the arsenic tolerance proficiency of this halophyte.

Regulation of photosynthesis under salt stress and associated tolerance mechanisms

Photosynthesis is crucial for the survival of all living biota, playing a key role in plant productivity by generating the carbon skeleton that is the primary component of all biomolecules. Salinity stress is a major threat to agricultural productivity and sustainability as it can cause irreversible damage to photosynthetic apparatus at any developmental stage. However, the capacity of plants to become photosynthetically active under adverse saline conditions remains largely untapped. This study addresses this discrepancy by exploring the current knowledge on the impact of salinity on chloroplast operation, metabolism, chloroplast ultrastructure, and leaf anatomy, and highlights the dire consequences for photosynthetic machinery and stomatal conductance. We also discuss enhancing photosynthetic capacity by modifying and redistributing electron transport between photosystems and improving photosystem stability using genetic approaches, beneficial microbial inoculations, and root architecture changes to improve salt stress tolerance under field conditions. Understanding chloroplast operations and molecular engineering of photosynthetic genes under salinity stress will pave the way for developing salt-tolerant germplasm to ensure future sustainability by rehabilitating saline areas.

Combined Treatment of Salinity Stress and Fruit Thinning Effect on Tomato

This was an experimental investigation of the combined treatments of salinity (SAL) stress and fruit thinning (FT) on the growth, yield, fruit quality, and water use efficiency (WUE) of tomatoes with non-soil cultivation. The experiment was carried out in a plastic tunnel, Japan. Tomato (Solanum lycopersicum) cv. Momotaro seedlings were transplanted in a randomized complete block (RCB) manner with six plants/treatment, and an overall 36 plants in 18 pots (2 plants/pot). The experiment involved varying SAL treatment (no-SAL, moderate SAL, and serious SAL, with electroconductivity of 0.8, 3.0, and 4.5 dS m⁻¹, separately) and FT treatment (NT: no thinning and 3FT: three-fruit treatment). The tomato growth, yield, and WUE were significantly suppressed with increasing SAL. In comparison, FT treatment had less effect on tomato growth and water consumption. Either SAL stress or FT treatment significantly improved fruit quality. The combined treatment proved better than single treatment of either SAL stress or FT, avoided the subsize fruit following SAL stress treatment, reduced fruit cracking found with FT treatment, and greatly improved fruit quality. The SAL thresholds of WUEs in relation to biomass, yield, and marketable yield were approximately 3.0 dS m⁻¹ under these soilless conditions. Path analysis showed that biomass and water consumption were important indexes affecting yield. Logistic equation fitting showed that SAL stress tended to inhibit and delay plant growth; however, FT tended to advance and shorten the period of plant growth.

Salt Stress Induced Changes in Photosynthesis and Metabolic Profiles of One Tolerant ('Bonica') and One Sensitive ('Black Beauty') Eggplant Cultivars (Solanum melongena L.)

The impact of salinity on the physiological and biochemical parameters of tolerant (‘Bonica’) and susceptible (‘Black Beauty’) eggplant varieties (Solanum melongena L.) was determined. The results revealed that the increase in salinity contributes to a significant decline in net photosynthesis (An) in both varieties; however, at the highest salt concentration (160 mM NaCl), the decrease in photorespiration (Rl) was less pronounced in the tolerant cultivar ‘Bonica’. Stomatal conductance (gs) was significantly reduced in ‘Black Beauty’ following exposure to 40 mM NaCl. However, gs of ‘Bonica’ was only substantially reduced at the highest level of NaCl (160 mM). In addition, a significant decrease in Chla, Chlb, total Chl, Chla/b and carotenoids (p > 0.05) was found in ‘Black Beauty’, and soluble carbohydrates accumulation and electrolyte leakage (EL) were more pronounced in ‘Black Beauty’ than in ‘Bonica’. The total phenols increase in ‘Bonica’ was 65% higher than in ‘Black Beauty’. In ‘Bonica’, the roots displayed the highest enzyme scavenging activity compared to the leaves. Salt stress contributes to a significant augmentation of root catalase and guaiacol peroxidase activities. In ‘Bonica’, the Na concentration was higher in roots than in leaves, whereas in ‘Black Beauty‘, the leaves accumulated more Na. Salt stress significantly boosted the Na/K ratio in ‘Black Beauty’, while no significant change occurred in ‘Bonica’. ACC deaminase activity was significantly higher in ‘Bonica’ than in ‘Black Beauty’.

Plant Stress Scenarios Differentially Affect Expression and IgE Reactivity of Grass Group-1 Allergen (β-Expansin) in Maize and Rice Pollen

Grass pollen is among the most common outdoor aeroallergens eliciting pollen allergies throughout the world. Grass group-1 allergen or β-expansin is recognized as a major pollen allergen, particularly in the grass family Poaceae. Expression of β-expansin has been shown to be dynamic and can be influenced by environmental stresses. This study evaluated the relative expression of β-expansin and IgE-binding ability of crude pollen extract protein of rice and maize under three different stress conditions: flood, salt, and drought. After 1 week of treatments, anthers containing pollen were collected followed by RNA extraction and cDNA synthesis. To evaluate relative expression, qRT-PCR was performed using specific primers for β-expansin and reference genes. Physiological characteristics of treated and untreated maize and rice: plant height; fresh weight of anthers; number of inflorescences, anthers, and pollen grains were also recorded. To assess IgE-binding ability of proteins in rice pollen extracts, soluble crude proteins were extracted and IgE immunoblot and ELISA were performed using serum samples from grass-allergic subjects and healthy control donors. Results showed that plant height, fresh weight of anthers, number of inflorescences, anthers, and pollen grains of both maize and rice decreased significantly under drought stress conditions, but not in other conditions. Expression of β-expansin in pollen of rice showed an apparent increase in all stress treatments relative to control samples. In contrast, a significant decrease of β-expansin expression was detected in maize pollen under all stress-treated conditions. IgE-reactive protein bands from rice pollen extract proteins were ~30 kDa, as expected of the grass-group 1 protein. The intensity of IgE-reactive protein bands and the level of IgE to rice pollen proteins showed significant differences among stress conditions. In conclusion, environmental stresses—flood, salt, and drought, can elicit a change of β-expansin expression and IgE reactivity to grass group-1 pollen allergens. Changes in expression level of this gene likely reflected its importance during stress. However, the response is highly dependent on different schemes employed by each plant species.

Potassium in plants: Growth regulation, signaling, and environmental stress tolerance

Potassium (K) is an essential element for the growth and development of plants; however, its scarcity or excessive level leads to distortion of numerous functions in plants. It takes part in the control of various significant functions in plant advancement. Because of the importance index, K is regarded second after nitrogen for whole plant growth. Approximately, higher than 60 enzymes are reliant on K for activation within the plant system, in which K plays a vital function as a regulator. Potassium provides assistance in plants against abiotic stress conditions in the environment. With this background, the present paper reviews the physiological functions of K in plants like stomatal regulation, photosynthesis and water uptake. The article also focuses upon the uptake and transport mechanisms of K along with its role in detoxification of reactive oxygen species and in conferring tolerance to plants against abiotic stresses. It also highlights the research progress made in the direction of K mediated signaling cascades.

Seed bulb size influences the effects of exogenous brassinolide on yield and quality of Pinellia ternata

In recent years, natural Pinellia ternata populations of have gradually been exhausted, while the cultivated yield has been limited due to lack of research and uncertain climate condition. Therefore, it is necessary to explore methods of improving yield and quality in P. ternata using brassinolide (BR) treatments and choice of a suitable seed bulb size. This article reports the effects of BR and two seed bulb sizes (diameter: 0.5-1.0 cm and 1.0-1.5 cm) on active and nutrient components and antioxidant activity in P. ternata. The experiment included six levels of BR (0, 0.05, 0.10, 0.50, 1.00 and 2.00 mg l^-1 ). The tuber yield of the two seed bulb sizes and bulbil yield of small seed bulbs increased 5.67%, 22.66% and 69.23% by day 105 after 0.50 mg l^-1 BR treatment, compared with the control. On day 105, only 0.05 mg l^-1 BR increased scores in principal components analysis (PCA) in tubers of small seed bulbs by 167.29%, and 0.05 and 0.50 mg l^-1 BR increased PCA score in bulbils of large seed bulbs by 145.66% and 252.97%, respectively, compared with the control. Significant BR × seed bulb size interactions were found on yield and quality of P. ternata. The results indicate that BR effects on yield and quality of tubers and bulbils of P. ternata are not only related to BR concentration but also to seed bulb size.

Gibberellic Acid and Jasmonic Acid Improve Salt Tolerance in Summer Squash by Modulating Some Physiological Parameters Symptomatic for Oxidative Stress and Mineral Nutrition

Gibberellic acid (GA) and jasmonic acid (JA) are considered to be endogenous regulators that play a vital role in regulating plant responses to stress conditions. This study investigated the ameliorative role of GA, JA, and the GA + JA mixture in mitigating the detrimental effect of salinity on the summer squash plant. In order to explore the physiological mechanisms of salt stress alleviation carried out by exogenous GA and JA, seed priming with 1.5 mM GA, 0.005 mM JA, and their mixture was performed; then the germinated summer squash seedlings were exposed to 50 mM NaCl. The results showed that a 50 mM NaCl treatment significantly reduced shoot and root fresh and dry weight, water content (%), the concentration of carotenoid (Car), nucleic acids, K+, and Mg++, the K+/Na+ ratio, and the activity of catalase (CAT) and ascorbate peroxidase (APX), while it increased the concentration of proline, thiobarbituric acid reactive substances (TBARS), Na+, and Cl- in summer squash plants, when compared with the control. However, seed priming with GA, JA and the GA + JA mixture significantly improved summer squash salt tolerance by reducing the concentration of Na+ and Cl-, TBARS, and the Chl a/b ratio and by increasing the activity of superoxide dismutase, CAT, and APX, the quantities of K+ and Mg++, the K+/Na+ ratio, and the quantities of RNA, DNA, chlorophyll b, and Car, which, in turn, ameliorated the growth of salinized plants. These findings suggest that GA and JA are able to efficiently defend summer squash plants from salinity destruction by adjusting nutrient uptake and increasing the activity of antioxidant enzymes in order to decrease reactive oxygen species accumulation due to salinity stress; these findings offer a practical intervention for summer squash cultivation in salt-affected soils. Synergistic effects of the GA and JA combination were not clearly observed, and JA alleviated most of the studied traits associated with salinity stress induced in summer squash more efficiently than GA or the GA + JA mixture.

Exogenous Myo-Inositol Alleviates Salt Stress by Enhancing Antioxidants and Membrane Stability via the Upregulation of Stress Responsive Genes in Chenopodium quinoa L

Myo-inositol has gained a central position in plants due to its vital role in physiology and biochemistry. This experimental work assessed the effects of salinity stress and foliar application of myo-inositol (MYO) on growth, chlorophyll content, photosynthesis, antioxidant system, osmolyte accumulation, and gene expression in quinoa (Chenopodium quinoa L. var. Giza1). Our results show that salinity stress significantly decreased growth parameters such as plant height, fresh and dry weights of shoot and root, leaf area, number of leaves, chlorophyll content, net photosynthesis, stomatal conductance, transpiration, and Fv/Fm, with a more pronounced effect at higher NaCl concentrations. However, the exogenous application of MYO increased the growth and photosynthesis traits and alleviated the stress to a considerable extent. Salinity also significantly reduced the water potential and water use efficiency in plants under saline regime; however, exogenous application of myo-inositol coped with this issue. MYO significantly reduced the accumulation of hydrogen peroxide, superoxide, reduced lipid peroxidation, and electrolyte leakage concomitant with an increase in the membrane stability index. Exogenous application of MYO up-regulated the antioxidant enzymes' activities and the contents of ascorbate and glutathione, contributing to membrane stability and reduced oxidative damage. The damaging effects of salinity stress on quinoa were further mitigated by increased accumulation of osmolytes such as proline, glycine betaine, free amino acids, and soluble sugars in MYO-treated seedlings. The expression pattern of OSM34, NHX1, SOS1A, SOS1B, BADH, TIP2, NSY, and SDR genes increased significantly due to the application of MYO under both stressed and non-stressed conditions. Our results support the conclusion that exogenous MYO alleviates salt stress by involving antioxidants, enhancing plant growth attributes and membrane stability, and reducing oxidative damage to plants.

Improvement of tomato salt tolerance by the regulation of photosynthetic performance and antioxidant enzyme capacity under a low red to far-red light ratio

The red light (R) to far-red light (FR) ratio (R:FR) regulates plant responses to salt stress, but the regulation mechanism is still unclear. In this study, tomato seedlings were grown under half-strength Hoagland solution with or without 150 mM NaCl at two different R:FR ratios (7.4 and 0.8). The photosynthetic capacity, antioxidant enzyme activities, and the phenotypes at chloroplast ultrastructure and whole plant levels were investigated. The results showed that low R:FR significantly alleviated the damage of tomato seedlings from salt stress. On day 4, 8, and 12 at low R:FR, the maximum photochemical quantum yields (F_v/F_m) of photosystem II (PSII) were increased by 4.53%, 3.89%, and 16.49%, respectively; the net photosynthetic rates (Pn) of leaves were increased by 16.21%, 90.81%, and 118.00%, respectively. Low R:FR enhanced the integrity and stability of the chloroplast structure of salinity-treated plants through maintaining the high activities of antioxidant enzymes and mitigated the degradation rate of photosynthetic pigments caused by reactive oxygen species (ROS) under salt stress. The photosynthesis, antioxidant enzyme-related gene expression, and transcriptome sequencing analysis of tomato seedlings under different treatments were also investigated. Low R:FR promoted the de novo synthesis of D1 protein via triggering psbA expression, and upregulated the transcripts of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) related genes. Meanwhile, the transcriptome analysis confirmed the positive function of low R:FR on enhancing tomato salinity stress tolerance from the regulation of photosynthesis and ROS scavenging systems.

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.

Leaf application of 24-epibrassinolide mitigates cadmium toxicity in young Eucalyptus urophylla plants by modulating leaf anatomy and gas exchange

Cadmium (Cd2+) soil pollution is a global environmental problem caused by the high toxicity of Cd. 24-Epibrassinolide (EBR) is a biodegradable plant steroid involved in response modulation to biotic and abiotic stresses. The aim of this study was to evaluate if the leaf-application of EBR improves the gas exchange and possible repercussions on leaf anatomy in young Eucalyptus urophylla plants exposed to Cd toxicity. The experiment involved six treatments, which included three Cd concentrations (0, 450, and 900 μM) and two EBR concentrations (0 and 100 nM, described as - EBR and + EBR, respectively). Plants exposed to Cd toxicity suffered decreases in leaf anatomical and gas exchange parameters. However, the plants treated with EBR + 900 μM Cd showed an increase of 46%, 40%, and 54% in the net photosynthetic rate, water-use efficiency, and instantaneous carboxylation efficiency, respectively. The EBR application-induced improvements in gas exchange parameters, causing beneficial effects on the photosynthetic apparatus, mainly the effective quantum yield of photosystem II (PSII) photochemistry and electron transport rate. Furthermore, this steroid mitigated the effect of Cd toxicity on leaf anatomical variables, more specifically palisade and spongy parenchyma, which are intrinsically related to stomatal density, and stimulated the net photosynthetic rate of plants.

Brassinosteroids as a multidimensional regulator of plant physiological and molecular responses under various environmental stresses

Biotic and abiotic stresses, especially heavy metal toxicity, are becoming a big problem in agriculture, which pose serious threats to crop production. Plant hormones have recently been used to develop stress tolerance in a variety of plants. Brassinosteroids (BRs) are the sixth class of plant steroid hormones, with pleiotropic effects on plants. Exogenous application of BRs to boost plant tolerance mechanisms to various stresses has been a major research focus. Numerous studies have revealed the role of these steroidal hormones in the up-regulation of stress-related resistance genes, as well as their interactions with other metabolic pathways. BRs interact with other phytohormones such as auxin, cytokinin, ethylene, gibberellin, jasmonic acid, abscisic acid, salicylic acid, and polyamines to regulate a variety of physiological and developmental processes in plants. BRs regulate expressions of many BR-inducible genes by activating the brassinazole-resistant 1 (BZR1)/BRI1-EMS suppressor 1 (BES1) complex. Moreover, to improve plant development under a variety of stresses, BRs regulate antioxidant enzyme activity, chlorophyll concentration, photosynthetic capability, and glucose metabolism. This review will provide insights into the mechanistic role and actions of brassinosteroids in plants in response to various stresses.