Salicylic acid confers salt tolerance in potato plants by improving water relations, gaseous exchange, antioxidant activities and osmoregulation

The Combination of Salicylic Acid, Nicotinamide, and Proline Mitigates the Damage Caused by Salt Stress in Nasturtium (Tropaeolum majus)

Salinity represents a significant challenge for agriculture, especially in semi-arid regions, affecting the growth and productivity of plants such as nasturtium (Tropaeolum majus), which is valued for its ornamental, medicinal, and food uses. Salt stress disrupts biochemical, physiological, and anatomical processes, limiting plant development. This study investigated the application of attenuators, including salicylic acid, nicotinamide, and proline, to mitigate the effects of salt stress on nasturtium cultivated in a hydroponic system. The treatments involved different combinations of these compounds under saline conditions (40 mM NaCl). The attenuators reduced the negative impacts of salt stress, promoting improvements in gas exchange, such as increased net photosynthesis, water-use efficiency, and stomatal conductance. Additionally, the treatments enhanced vegetative and reproductive growth, increasing the dry biomass of leaves, stems, and flowers, as well as the number of flowers and flower buds. The combination of salicylic acid, nicotinamide, and proline stood out by providing greater efficiency in carbon assimilation, stability of photosynthetic pigments, and higher tolerance to salt stress. These findings reinforce the potential of using attenuators to optimize the cultivation of nasturtium in saline environments, promoting higher productivity and plant quality.

Salicylic Acid Cooperates With Lignin and Sucrose Signals to Alleviate Waxy Maize Leaf Senescence Under Heat Stress

Leaf senescence induced by high temperature (HT) has become a primary factor limiting maize yield, particularly during the filling stage. Exogenous salicylic acid (SA) has emerged as an effective strategy to mitigate leaf senescence and HT-induced damage, though its underlying mechanisms remain unclear. This study investigated the regulatory mechanism of SA application on waxy maize subjected to HT during the early filling stage. Compared to HT alone, exogenous SA alleviated the inhibition of photosynthesis and oxidative damage by enhancing the activities of enzymes involved in photosynthesis and antioxidant system and modulating phytohormone metabolism and signal transduction pathways, thereby reducing leaf senescence and mitigating yield loss under HT. Transcriptomic and metabolomic analyses showed that HT downregulated most genes involved in the starch and sucrose metabolism pathway in leaves but promoted soluble sugar accumulation, which represents a plant strategy to cope with HT. Conversely, exogenous SA reversed this change and further enhanced soluble sugar accumulation in leaves. SA also regulated sugar metabolism by inhibiting trehalose-6-phosphate synthesis and activating SnRK1 to resist HT. Furthermore, SA stimulated lignin biosynthesis through the phenylpropanoid pathway, ensuring cell membrane integrity under HT. The relationship between SA signalling and plant heat tolerance was validated using a maize SA synthesis-synthetic mutant.

Assessment of salicylic acid and potassium nitrate to mitigate frost stress in autumn-sown potato crop cv. Sutlej

Potato is cultivated all the year round in Pakistan. However, the major crop is the autumn crop which is planted in mid-October and contributes 80-85% of the total production. The abrupt climate change has affected the weather patterns all over the world, resulting in the reduction of the mean air temperature in autumn by almost 1.6 °C in Pakistan, which in turn, has adversely affected the crop performance and tuber yield. This trial, therefore, was conducted to optimize and evaluate the concentration of salicylic acid (SA) and potassium nitrate (KNO3) for inducing frost stress tolerance in an autumn-sown potato crop cv. Sutlej. The findings revealed that the foliar application of 0.5 mM SA significantly enhanced the growth, yield, fluorescent, and biochemical indices of potato plants outperforming 100 mM KNO₃ application in comparison with the control. This included increased plant height by 14% and 17.6%, leaf area index by 6.3% and 26.3%, shoot biomass by 15.4% and 46.2%, crop growth rate by 16.7% and 43.3%, average tuber weight by 8.2% and 23%, tuber diameter by 6.8% and 12.2%, tuber yield by 26.1% and 46.3%, leaf angle by 16.2% and 21.6%, quantum yield of photosystem II by 20.6% and 28.2%, photosynthetically active radiations by 20.5% and 32.4%, chlorophyll content by 6.3% and 14.6%, leaf thickness by 14% and 29%, linear electron flow by 20% and 32.7%, O-2 by 6% and 14.4%, H2O2 by 11.7% and 27.6%, enzyme activities of catalase by 20.7% and 28.5%, superoxide dismutase by 28.6% and 28.5%, peroxidase by 8.3% and 13.5%, ascorbate peroxidase by 17.2% and 37.8%, total protein by 21% and 37%, proline by 36.2% and 114%, and phenolic content by 33% and 63.3% with a reduction in non-photochemical quenching by 12.7% and 29.6%, non-regulatory energy dissipation by 169.5% and 268.5%, and leaf electrolyte leakage by 57.5% and 180%, compared to KNO3 and the control, respectively. Based on the above findings, it can be concluded and recommended that 0.5 mM foliar spray of SA can be utilized on potato crop cv. Sutlej in frost-sensitive regions. However, the application rate of KNO3 needs to be optimized in order to use its maximal frost stress tolerance potential.

Foliar application of salicylic acid improved morpho-anatomical features of potato by irrigating with wastewater

BACKGROUND

This study aimed to evaluate the suitability of using drain water as a source of irrigation and its effects along with salicylic acid on morphological, anatomical, physico-chemical as well as yield attributes of potato. For this study, potato tubers were grown in pots and irrigated with different concentrations of drain water. Salicylic acid treatments vis. 0, 0.5 and 1.0 mM were applied foliarly. Pre- and post-harvest analysis was carried out to determine different attributes of soil, water and plants after 60 days.

RESULTS

The growth of potato plant was increased as the concentration of SA increased through increasing shoot length, fresh/dry weight and tuber number/plant. In this research work, plant respond to overcome metal stresses by up regulating antioxidant defense system such as, peroxidase, catalase and superoxide dismutase) by application of highest treatment of SA when irrigated with 6% drain water. Plants accumulated the highest concentrations of Cd, Cr, and Pb in the leaves when treated with 1 mM of SA, compared to other plant parts. It was observed that photosynthetic pigment enhanced in 6% drain water treated plants when applied with 1mM SA as compared to control. An increase in epidermis and cortical cell thickness, as well as stomatal closure, was observed, helping to maintain water loss under stress conditions.

CONCLUSIONS

According to these results, it can be suggested that SA is potent signaling molecule can play an essential role in maintaining potato growth when irrigated with drain water containing heavy metals through stimulating metal up take and up regulation of antioxidant enzymes.

Co-Expression Network Analysis of the Transcriptome Identified Hub Genes and Pathways Responding to Saline-Alkaline Stress in Sorghum bicolor L

Soil salinization, an intractable problem, is becoming increasingly serious and threatening fragile natural ecosystems and even the security of human food supplies. Sorghum (Sorghum bicolor L.) is one of the main crops growing in salinized soil. However, the tolerance mechanisms of sorghum to saline-alkaline soil are still ambiguous. In this study, RNA sequencing was carried out to explore the gene expression profiles of sorghum treated with sodium bicarbonate (150 mM, pH = 8.0, treated for 0, 6, 12 and 24 h). The results show that 6045, 5122, 6804, 7978, 8080 and 12,899 differentially expressed genes (DEGs) were detected in shoots and roots after 6, 12 and 24 h treatments, respectively. GO, KEGG and weighted gene co-expression analyses indicate that the DEGs generated by saline-alkaline stress were primarily enriched in plant hormone signal transduction, the MAPK signaling pathway, starch and sucrose metabolism, glutathione metabolism and phenylpropanoid biosynthesis. Key pathway and hub genes (TPP1, WRKY61, YSL1 and NHX7) are mainly related to intracellular ion transport and lignin synthesis. The molecular and physiological regulation processes of saline-alkali-tolerant sorghum are shown by these results, which also provide useful knowledge for improving sorghum yield and quality under saline-alkaline conditions.

Salicylic acid alleviates Zn-induced inhibition of growth via enhancing antioxidant system and glutathione metabolism in alfalfa

Zinc (Zn) is considered as one of the heavy metal pollutants in soil affecting agriculture. Salicylic acid (SA) is an important phytohormone that can mitigate effects against various abiotic stresses in plants, however, its exploration to improve Zn stress tolerance in alfalfa plants is still elusive. Thus, in the present study, exogenous SA treatment was conducted on alfalfa plants under Zn stress. The effects of exogenous SA on the physiological effects of alfalfa plants and the expression levels related genes were studied. This study tested the biomass, relative water content, chlorophyll levels, photosynthetic capacity, proline and soluble sugar contents, detected the activity of antioxidant enzymes (such as peroxidase and superoxide dismutase), glutathione biosynthesis, and endogenous SA levels, and quantified the genes associated with the antioxidant system and glutathione metabolism-mediated Zn stress. The results showed that exogenous SA could elevate the physiological adaptability of alfalfa plants through enhancing photosynthesis, proline and soluble sugar levels, stimulating antioxidant system and glutathione metabolism, and inducing the transcription level of related genes, thereby diminishing oxidative stress, inhibiting excessive Zn accumulation of alfalfa plants, increasing tolerance to Zn stress, and reducing the toxicity of Zn. Collectively, the application of SA alleviates Zn toxicity in alfalfa plants. The findings gave first insights into the regulatory mechanism of the Zn stress tolerance of alfalfa by exogenous SA and this might have positive implications for managing other plants which are suffering Zn stress.

A Review of Potato Salt Tolerance

Potato is the world's fourth largest food crop. Due to limited arable land and an ever-increasing demand for food from a growing population, it is critical to increase crop yields on existing acreage. Soil salinization is an increasing problem that dramatically impacts crop yields and restricts the growing area of potato. One possible solution to this problem is the development of salt-tolerant transgenic potato cultivars. In this work, we review the current potato planting distribution and the ways in which it overlaps with salinized land, in addition to covering the development and utilization of potato salt-tolerant cultivars. We also provide an overview of the current progress toward identifying potato salt tolerance genes and how they may be deployed to overcome the current challenges facing potato growers.

Dual Inoculation with Rhizophagus irregularis and Bacillus megaterium Improves Maize Tolerance to Combined Drought and High Temperature Stress by Enhancing Root Hydraulics, Photosynthesis and Hormonal Responses

Climate change is leading to combined drought and high temperature stress in many areas, drastically reducing crop production, especially for high-water-consuming crops such as maize. This study aimed to determine how the co-inoculation of an arbuscular mycorrhizal (AM) fungus (Rhizophagus irregularis) and the PGPR Bacillus megaterium (Bm) alters the radial water movement and physiology in maize plants in order to cope with combined drought and high temperature stress. Thus, maize plants were kept uninoculated or inoculated with R. irregularis (AM), with B. megaterium (Bm) or with both microorganisms (AM + Bm) and subjected or not to combined drought and high temperature stress (D + T). We measured plant physiological responses, root hydraulic parameters, aquaporin gene expression and protein abundances and sap hormonal content. The results showed that dual AM + Bm inoculation was more effective against combined D + T stress than single inoculation. This was related to a synergistic enhancement of efficiency of the phytosystem II, stomatal conductance and photosynthetic activity. Moreover, dually inoculated plants maintained higher root hydraulic conductivity, which was related to regulation of the aquaporins ZmPIP1;3, ZmTIP1.1, ZmPIP2;2 and GintAQPF1 and levels of plant sap hormones. This study demonstrates the usefulness of combining beneficial soil microorganisms to improve crop productivity under the current climate-change scenario.

Harnessing the role of mitogen-activated protein kinases against abiotic stresses in plants

Crop plants are vulnerable to various biotic and abiotic stresses, whereas plants tend to retain their physiological mechanisms by evolving cellular regulation. To mitigate the adverse effects of abiotic stresses, many defense mechanisms are induced in plants. One of these mechanisms is the mitogen-activated protein kinase (MAPK) cascade, a signaling pathway used in the transduction of extracellular stimuli into intercellular responses. This stress signaling pathway is activated by a series of responses involving MAPKKKs→MAPKKs→MAPKs, consisting of interacting proteins, and their functions depend on the collaboration and activation of one another by phosphorylation. These proteins are key regulators of MAPK in various crop plants under abiotic stress conditions and also related to hormonal responses. It is revealed that in response to stress signaling, MAPKs are characterized as multigenic families and elaborate the specific stimuli transformation as well as the antioxidant regulation system. This pathway is directed by the framework of proteins and stopping domains confer the related associates with unique structure and functions. Early studies of plant MAPKs focused on their functions in model plants. Based on the results of whole-genome sequencing, many MAPKs have been identified in plants, such as Arbodiposis, tomato, potato, alfalfa, poplar, rice, wheat, maize, and apple. In this review, we summarized the recent work on MAPK response to abiotic stress and the classification of MAPK cascade in crop plants. Moreover, we highlighted the modern research methodologies such as transcriptomics, proteomics, CRISPR/Cas technology, and epigenetic studies, which proposed, identified, and characterized the novel genes associated with MAPKs and their role in plants under abiotic stress conditions. In-silico-based identification of novel MAPK genes also facilitates future research on MAPK cascade identification and function in crop plants under various stress conditions.

Salicylic Acid Enhances Cadmium Tolerance and Reduces Its Shoot Accumulation in Fagopyrum tataricum Seedlings by Promoting Root Cadmium Retention and Mitigating Oxidative Stress

Soil cadmium (Cd) contamination seriously reduces the production and product quality of Tartary buckwheat (Fagopyrum tataricum), and strategies are urgently needed to mitigate these adverse influences. Herein, we investigated the effect of salicylic acid (SA) on Tartary buckwheat seedlings grown in Cd-contaminated soil in terms of Cd tolerance and accumulation. The results showed that 75-100 µmol L^-1 SA treatment enhanced the Cd tolerance of Tartary buckwheat, as reflected by the significant increase in plant height and root and shoot biomass, as well as largely mitigated oxidative stress. Moreover, 100 µmol L^-1 SA considerably reduced the stem and leaf Cd concentration by 60% and 47%, respectively, which is a consequence of increased root biomass and root Cd retention with promoted Cd partitioning into cell wall and immobile chemical forms. Transcriptome analysis also revealed the upregulation of the genes responsible for cell wall biosynthesis and antioxidative activities in roots, especially secondary cell wall synthesis. The present study determines that 100 µmol L^-1 is the best SA concentration for reducing Cd accumulation and toxicity in Tartary buckwheat and indicates the important role of root in Cd stress in this species.

Using the Maize Nested Association Mapping (NAM) Population to Partition Arbuscular Mycorrhizal Effects on Drought Stress Tolerance into Hormonal and Hydraulic Components

In this study, a first experiment was conducted with the objective of determining how drought stress alters the radial water flow and physiology in the whole maize nested association mapping (NAM) population and to find out which contrasting maize lines should be tested in a second experiment for their responses to drought in combination with an arbuscular mycorrhizal (AM) fungus. Emphasis was placed on determining the role of plant aquaporins and phytohormones in the responses of these contrasting maize lines to cope with drought stress. Results showed that both plant aquaporins and hormones are altered by the AM symbiosis and are highly involved in the physiological responses of maize plants to drought stress. The regulation by the AM symbiosis of aquaporins involved in water transport across cell membranes alters radial water transport in host plants. Hormones such as IAA, SA, ABA and jasmonates must be involved in this process either by regulating the own plant-AM fungus interaction and the activity of aquaporins, or by inducing posttranscriptional changes in these aquaporins, which in turns alter their water transport capacity. An intricate relationship between root hydraulic conductivity, aquaporins and phytohormones has been observed, revealing a complex network controlling water transport in maize roots.

Foliar Application of Salicylic Acid to Mitigate Water Stress in Tomato

Salicylic acid (SA) is an important plant regulator reported as a mitigator of water deficit in plants, however without a recommendation for use in field conditions. Thus, this research aims to validate the use of SA under field conditions in regions with low water availability. For that, we evaluated CO₂ assimilation (A), stomatal conductance (g_s), transpiration (E), water use efficiency (WUE), and carboxylation efficiency (A/Ci) at 15, 30, and 45 days of continuous stress water deficit, as well as the application of salicylic acid (0.0; 0.5; 1.0; 1.5; 2.0 mM) in tomato plants subjected to continuous water deficit (45 days), in two years (2019 and 2020). The water deficit reduced the A, g_s, E and A/Ci, while the foliar application of SA increased these parameters in all evaluated times, resulting in similar or even higher values than in plants without water deficit. Water deficit caused floral abortion in tomato plants, without the application of SA, reducing the number of fruit production. In contrast, plants that received about 1.3 mM of SA increased A and A/Ci and translocated the photo-assimilates, mainly to flowers and fruits, reducing floral abortion and increasing fruit production. Thus, foliar application of SA was efficient in mitigating the deleterious effects of water deficit in tomato plants regarding the gas exchange and fruit production.

Plant Salinity Stress Response and Nano-Enabled Plant Salt Tolerance

The area of salinized land is gradually expanding cross the globe. Salt stress seriously reduces the yield and quality of crops and endangers food supply to meet the demand of the increased population. The mechanisms underlying nano-enabled plant tolerance were discussed, including (1) maintaining ROS homeostasis, (2) improving plant's ability to exclude Na+ and to retain K+, (3) improving the production of nitric oxide, (4) increasing α-amylase activities to increase soluble sugar content, and (5) decreasing lipoxygenase activities to reduce membrane oxidative damage. The possible commonly employed mechanisms such as alleviating oxidative stress damage and maintaining ion homeostasis were highlighted. Further, the possible role of phytohormones and the molecular mechanisms in nano-enabled plant salt tolerance were discussed. Overall, this review paper aims to help the researchers from different field such as plant science and nanoscience to better understand possible new approaches to address salinity issues in agriculture.

Exogenous SA Affects Rice Seed Germination under Salt Stress by Regulating Na+/K+ Balance and Endogenous GAs and ABA Homeostasis

Salinity reduces agricultural productivity majorly by inhibiting seed germination. Exogenous salicylic acid (SA) can prevent the harm caused to rice by salinity, but the mechanisms by which it promotes rice seed germination under salt stress are unclear. In this study, the inhibition of germination in salt-sensitive Nipponbare under salt stress was greater than that in salt-tolerant Huaidao 5. Treatment with exogenous SA significantly improved germination of Nipponbare, but had little effect on Huaidao 5. The effects of exogenous SA on ion balance, metabolism of reactive oxygen species (ROS), hormone homeostasis, starch hydrolysis, and other physiological processes involved in seed germination of rice under salt stress were investigated. Under salt stress, Na⁺ content and the Na⁺/K⁺ ratio in rice seeds increased sharply. Seeds were subjected to ion pressure, which led to massive accumulation of H₂O₂, O₂⁻, and malonaldehyde (MDA); imbalanced endogenous hormone homeostasis; decreased gibberellic acid (GA1 and GA4) content; increased abscisic acid (ABA) content; inhibition of α-amylase (EC 3.2.1.1) activity; and slowed starch hydrolysis rate, all which eventually led to the inhibition of the germination of rice seeds. Exogenous SA could effectively enhance the expression of OsHKT1;1, OsHKT1;5, OsHKT2;1 and OsSOS1 to reduce the absorption of Na+ by seeds; reduce the Na⁺/K⁺ ratio; improve the activities of SOD, POD, and CAT; reduce the accumulation of H₂O₂, O₂⁻, and MDA; enhance the expression of the GA biosynthetic genes OsGA20ox1 and OsGA3ox2; inhibit the expression of the ABA biosynthetic gene OsNCED5; increase GA1 and GA4 content; reduce ABA content; improve α-amylase activity, and increase the content of soluble sugars. In summary, exogenous SA can alleviate ion toxicity by reducing Na⁺ content, thereby helping to maintain ROS and hormone homeostasis, promote starch hydrolysis, and provide sufficient energy for seed germination, all of which ultimately improves rice seed germination under salt stress. This study presents a feasible means for improving the germination of direct-seeded rice in saline soil.

Salicylic acid alleviates selenium stress and promotes selenium uptake of grapevine

To determine suitable cultivation measures to enrich selenium (Se) and alleviate the Se stress in fruit trees, the effects of different exogenous salicylic acid (SA) concentrations (0, 50, 100, 150 and 200 mg/L) on the growth and Se uptake of grapevine under Se stress were studied. Under Se stress, SA increased the biomass of grapevine to some extent and had a linear relationship with both root and shoot biomass. The chlorophyll content, net photosynthetic rate, transpiration rate, stomatal conductance, and intercellular CO₂ concentration of grapevine tended to increase when the concentration of SA was < 150 mg/L and decrease when the concentration of SA was > 150 mg/L. Different concentrations of SA enhanced the activity of superoxide dismutase, while reducing that of peroxidase. It had no significant effect on the catalase activity of grapevine. SA decreased the content of osmotically active substances in grapevine to some extent. SA also increased the contents of total Se, inorganic Se and organic Se in grapevine to some extent, and had a linear or quadratic polynomial relationship with the total Se contents in both roots and shoots. When the SA concentration was 250 mg/L, the total Se contents in the roots and shoots were the highest and increased by 10.41% and 58.46%, respectively, compared with the control. Therefore, exogenous SA could promote the growth and Se uptake of grapevine under Se stress, with 250 mg/L serving as the most effective concentration.

Exogenous salicylic acid alleviates the negative impacts on production components, biomass and gas exchange in tomato plants under water deficit improving redox status and anatomical responses

Salicylic acid (SA) is an interesting messenger in plant metabolism that modulates multiple pathways, including the antioxidant defence pathway, and stimulates anatomical structures essential to carbon dioxide fixation during the photosynthetic process. The aim of this research was to determine whether pre-treatment with exogenous SA can alleviate the deleterious effects induced by water deficit on production components, biomass and gas exchange, measuring reactive oxygen species, antioxidant enzymes, variables connected to photosynthetic machinery, anatomical responses, and agro-morphological traits in tomato plants under water deficit. The experiment used a factorial design with four treatments, including two water conditions (control and water deficit) and two salicylic acid concentrations (0 and 0.1 mM salicylic acid). Water deficit negatively impacted the biomass and fruit number of tomato plants. Pre-treatment using 0.1 mM SA in plants submitted to water restriction induced increments in fruit number, weight, and biomass. These results were related to the protective role triggered by this substance, stimulating superoxide dismutase (27.07%), catalase (17.81%), ascorbate peroxidase (50.52%), and peroxidase (10.81%) as well as reducing the cell damage (malondialdehyde and electrolyte leakage) caused by superoxide and hydrogen peroxide. Simultaneously, application of SA improved the net photosynthetic rate (84.55%) and water-use efficiency (65.00%) of stressed plants in which these factors are connected to anatomical benefits, as verified by stomatal density, palisade and spongy parenchyma, combined with improved performance linked to photosystem II.

Exogenous Application of Foliar Salicylic Acid and Propolis Enhances Antioxidant Defenses and Growth Parameters in Tomato Plants

Salicylic acid (SA) and propolis (PR) are known to regulate the physiological process and to have a relevant role in bioactive compounds content. Our experiment was designed to evaluate the effect of SA and PR application on the growth, yield, and quality parameters of tomato grown for the fresh market in field conditions in Egypt. We studied the effect of twelve treatments where SA (0.50, 1.00, 1.50, 2.00, and 2.50 mM) and PR (1, 2, 10, 20, and 100 mg propolis mL^-1) were applied at increasing doses as a sole agent or combined each other (1.50 mM + 10 mg mL^-1 for SA and PR, respectively). An untreated control was also considered. Tomato plants treated with SA (0.50, 1.00, and 1.50 mM) showed a significant effect in all traits especially SA1 (0.50 mM) in growth parameters and SA2 (1.00 mM) in pigment and antioxidant content. Propolis foliar application was more effective than SA as it revealed that raising the concentration of aqueous extract enhanced the growth parameters and pigment in tomato. The best result was obtained by the 10 mg mL^-1 treatment. The effect of propolis on antioxidant enzymes varied as the 10 mg mL^-1 treatment was effective on peroxidases and superoxide dismutase, while 100 mg mL^-1 was more effective on catalase. Salicylic acid and propolis have a positive effect on both preserving tomato plants and on nutrient supply, so the mixed intermediate concentration (1.50 mM + 10 mg mL^-1) is considered very effective and results in an improvement of all plant traits.

StMAPK3 controls oxidase activity, photosynthesis and stomatal aperture under salinity and osmosis stress in potato

Mitogen-activated protein kinase 3 (MAPK3) is involved in plant growth and development, as well as response to adverse stress. Here we aimed to explore the role of StMAPK3 in response to salt and osmosis stress. Polyethylene glycol (PEG) (5% and 10%) and mannitol (40 mM and 80 mM) were used to induce osmosis stress. To induce salinity stress, potato plant was cultured with NaCl (40 mM and 80 mM). StMAPK3 overexpression and RNA interference-mediated StMAPK3 knockdown were constructed to explore the role of StMAPK3 in potato growth, stomatal aperture size, activity of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD), and contents of H₂O₂, proline and malonaldehyde (MDA). Meanwhile, we detected transpiration, net photosynthesis, stomatal conductance, and water use efficiency. Subcellular location of StMAPK3 protein was also detected. PEG, mannitol and NaCl treatments induced the accumulation of StMAPK3 mRNA in potato plants. StMAPK3 protein was located on the membrane and nucleus. Abnormal expression of StMAPK3 changed potato phenotypes, enzyme activity of SOD, CAT and POD, as well as H₂O₂, proline and MDA contents under osmosis and salinity stress. Photosynthesis and stomatal aperture were regulated by StMAPK3 in potato treated by PEG, mannitol and NaCl. Modulation of potato phenotypes and physiological activity indicates StMAPK3 as a regulator of osmosis and salinity tolerance.

Class III peroxidase: an indispensable enzyme for biotic/abiotic stress tolerance and a potent candidate for crop improvement

Class III peroxidases are secretory enzymes which belong to a ubiquitous multigene family in higher plants and have been identified to play role in a broad range of physiological and developmental processes. Potentially, it is involved in generation and detoxification of hydrogen peroxide (H2O2), and their subcellular localization reflects through three different cycles, namely peroxidative cycle, oxidative and hydroxylic cycles to maintain the ROS level inside the cell. Being an antioxidant, class III peroxidases are an important initial defence adapted by plants to cope with biotic and abiotic stresses. Both these stresses have become a major concern in the field of agriculture due to their devastating effect on plant growth and development. Despite numerous studies on plant defence against both the stresses, only a handful role of class III peroxidases have been uncovered by its functional characterization. This review will cover our current understanding on class III peroxidases and the signalling involved in their regulation under both types of stresses. The review will give a view of class III peroxidases and highlights their indispensable role under stress conditions. Its future application will be discussed to showcase their importance in crop improvement by genetic manipulation and by transcriptome analysis.

Sphingobacterium sp. BHU-AV3 Induces Salt Tolerance in Tomato by Enhancing Antioxidant Activities and Energy Metabolism

Salt tolerant bacteria can be helpful in improving a plant's tolerance to salinity. Although plant-bacteria interactions in response to salt stress have been characterized, the precise molecular mechanisms by which bacterial inoculation alleviates salt stress in plants are still poorly explored. In the present study, we aimed to determine the role of a salt-tolerant plant growth-promoting rhizobacteria (PGPR) Sphingobacterium BHU-AV3 for improving salt tolerance in tomato through investigating the physiological responses of tomato roots and leaves under salinity stress. Tomato plants inoculated with BHU-AV3 and challenged with 200 mM NaCl exhibited less senescence, positively correlated with the maintenance of ion balance, lowered reactive oxygen species (ROS), and increased proline content compared to the non-inoculated plants. BHU-AV3-inoculated plant leaves were less affected by oxidative stress, as evident from a reduction in superoxide contents, cell death, and lipid peroxidation. The reduction in ROS level was associated with the increased antioxidant enzyme activities along with multiple-isoform expression [peroxidase (POD), polyphenol oxidase (PPO), and superoxide dismutase (SOD)] in plant roots. Additionally, BHU-AV3 inoculation induced the expression of proteins involved in (i) energy production [ATP synthase], (ii) carbohydrate metabolism (enolase), (iii) thiamine biosynthesis protein, (iv) translation protein (elongation factor 1 alpha), and the antioxidant defense system (catalase) in tomato roots. These findings have provided insight into the molecular mechanisms of bacteria-mediated alleviation of salt stress in plants. From the study, we can conclude that BHU-AV3 inoculation effectively induces antioxidant systems and energy metabolism in tomato roots, which leads to whole plant protection during salt stress through induced systemic tolerance.

Enhancement of endogenous SA accumulation improves poor-nutrition stress tolerance in transgenic tobacco plants overexpressing a SA-binding protein gene

Salicylic acid (SA) plays an important role in the response of plants to abiotic stresses. Starvation stress affects plant cell metabolic activities, which further limits the normal growth and development of plants. It was reported that SA might play a regulatory role in the process of plant against starvation stress, but the mechanism involved in this process is still unclear. Thus, in this study, the transgenic plants overexpressing a SA binding protein 2 (SABP2) gene were exposed to starvation stress and the transgenic lines showed starvation-tolerant phenotype. Compared with wild-type (WT) plants, transgenic plants showed better growth status under poor-nutrition stress. Transgenic plants also showed more vigorous roots than WT plants. Physiological tests indicated that the transgenic plants showed higher relative water content (RWC), chlorophyll content, photosynthetic capacity, endogenous SA content, and lower ROS level compared to WT plants. Transcriptome analysis of tobacco plants identified 3, 748 differentially expressed genes (DEGs) between transgenic and WT plants under starvation stress. These DEGs are mainly involved in glycolysis/gluconeogenesis pathway group, MAPK signaling pathway group and plant hormone signal transduction pathway group. As determined by qPCR, up-regulated expression of fifteen genes such as abscisic acid receptor PYR1-like gene (NtPYR1-like), bidirectional sugar transporter N3-like gene (NtSWEETN3-like) and superoxide dismutase [Fe] chloroplastic-like gene (NtFeSOD-like), etc., was observed in transgenic plants under poor-nutrition stress which was in accordance with RNA-sequencing results. The modified pathways involved in plant hormone signaling are thought to be at least one of the main causes of the increased starvation tolerance of transgenic tobacco plants with altered SA homeostasis.

Radial water transport in arbuscular mycorrhizal maize plants under drought stress conditions is affected by indole-acetic acid (IAA) application

Drought stress is one of the most devastating abiotic stresses, compromising crop growth, reproductive success and yield. The arbuscular mycorrhizal (AM) symbiosis has been demonstrated to be beneficial in helping the plant to bear with water deficit. In plants, development and stress responses are largely regulated by a complex hormonal crosstalk. Auxins play significant roles in plant growth and development, in responses to different abiotic stresses or in the establishment and functioning of the AM symbiosis. Despite these important functions, the role of indole-3acetic acid (IAA) as a regulator of root water transport and stress response is not well understood. In this study, the effect of exogenous application of IAA on the regulation of root radial water transport in AM plants was analyzed under well-watered and drought stress conditions. Exogenous IAA application affected root hydraulic parameters, mainly osmotic root hydraulic conductivity (Lo), which was decreased in both AM and non-AM plants under water deficit conditions. Under drought, the relative apoplastic water flow was differentially regulated by IAA application in non-AM and AM plants. The effect of IAA on the internal cell component of root water conductivity suggests that aquaporins are involved in the IAA-dependent inhibition of this water pathway.

Salicylic Acid Protects Photosystem II by Alleviating Photoinhibition in Arabidopsis thaliana under High Light

Salicylic acid (SA) is considered to play an important role in plant responses to environmental stresses. However, the detailed protective mechanisms in photosynthesis are still unclear. We therefore explored the protective roles of SA in photosystem II (PSII) in Arabidopsis thaliana under high light. The results demonstrated that 3 h of high light exposure resulted in a decline in photochemical efficiency and the dissipation of excess excitation energy. However, SA application significantly improved the photosynthetic capacity and the dissipation of excitation energy under high light. Western blot analysis revealed that SA application alleviated the decrease in the levels of D1 and D2 protein and increased the amount of Lhcb5 and PsbS protein under high light. Results from photoinhibition highlighted that SA application could accelerate the repair of D1 protein. Furthermore, the phosphorylated levels of D1 and D2 proteins were significantly increased under high light in the presence of SA. In addition, we found that SA application significantly alleviated the disassembly of PSII-LHCII super complexes and LHCII under high light for 3 h. Overall, our findings demonstrated that SA may efficiently alleviate photoinhibition and improve photoprotection by dissipating excess excitation energy, enhancing the phosphorylation of PSII reaction center proteins, and preventing the disassembly of PSII super complexes.

Foliar application of salicylic acid alleviate the cadmium toxicity by modulation the reactive oxygen species in potato

Heavy metal toxicity is one of the main factors that limit crop growth and yield in the world. Salicylic acid (SA) is thought to be a plant hormone that plays an important role in plant growth, development, and resistance to abiotic stresses. To uncover the toxic alleviation effects of SA on potato plants to cadmium (Cd) stress, the morphological, physiological, and biochemical indexes including antioxidant defense system were assayed in potato plants under 200 μM Cd stress in 1/2 Hoagland solution with foliar application of 600 μM SA concentration (10 ml/plant). Interestingly, exogenous SA treatment mitigated Cd toxicity by increasing the relative water content (RWC), chlorophyll, proline, and endogenous SA contents along with decline in malondialdehyde (MDA), hydrogen peroxide (H₂O₂), and superoxide anion radicals (O₂^-). Correspondingly, our study also proved that SA may stimulate the antioxidant enzymatic mechanism pathway including superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11), and glutathione reductase (GR, EC 1.6.4.2) in potato plants subjected to Cd stress. Moreover, the expression level of selected genes relate to SA and reactive oxygen species (ROS) metabolism (StSABP2, StSOD and StAPX) were enhanced in SA-treated potato plants under Cd stress, indicating that SA treatment regulated the expression of these genes, which in turn enhanced potato tolerance to Cd stress. Taken together, our results indicated that exogenous SA can play a positive regulatory role in alleviating Cd toxicity in potato plants.

The high-affinity transporter BnPHT1;4 is involved in phosphorus acquisition and mobilization for facilitating seed germination and early seedling growth of Brassica napus

BACKGROUND

Seed germination and seedling establishment are two of the most critical phases in plant development. However, the molecular mechanisms underlying the effect of phosphorus on seed germination and post-germinated growth of oilseed rape are unclear so far. Here, we report the role of BnPHT1;4 in seed germination and early seedling development of Brassica napus.

RESULTS

Our results show that BnPHT1;4 is preferentially expressed in cotyledons of early developing seedlings. Overexpression of BnPHT1;4 in oilseed rape promoted seed germination and seedling growth. Expression levels of the genes related to ABA and GA biosynthesis and signaling were significantly altered in BnPHT1;4 transgenic seedlings. Consequently, active GA level was up-regulated, whereas ABA content was down-regulated in BnPHT1;4 transgenic seedlings. Furthermore, exogenous GA could promote seed germination of wild type, while exogenous ABA could partially recover the advanced-germination phenotype of BnPHT1;4 transgenic seeds. Total phosphorus content in cotyledons of the transgenic seedlings was decreased more rapidly than that in wild type when Pi was supplied or deficient, and Pi contents in shoots and roots of the BnPHT1;4 transgenic plants were higher than those in wild type under high and low Pi conditions.

CONCLUSIONS

Our data suggest that the high-affinity transporter BnPHT1;4 is involved in phosphorus acquisition and mobilization for facilitating seed germination and seedling growth of Brassica napus by modulating ABA and GA biosynthesis.

Effects of Two Doses of Organic Extract-Based Biostimulant on Greenhouse Lettuce Grown Under Increasing NaCl Concentrations

The enhancement of plant tolerance toward abiotic stresses is increasingly being supported by the application of biostimulants. Salinity represents a serious problem in the Mediterranean region. To verify the effects deriving from the application of biostimulants, trials on Romaine lettuce plants under salt exposure were performed, in greenhouse. Plants were subjected to three NaCl solutions with 0.8, 1.3, and 1.8 dS/m of electrical conductivity. The volume of the solution was 200 mL/plant and delivered every 3 days. Biostimulant treatments started after crop establishment and were: control (water) and two doses (0.1 or 0.2 mL/plant) of the commercial biostimulant Retrosal® (Valagro S.p.A), containing calcium, zinc, and specific active ingredients. Four Retrosal® treatments were applied, every 7 days, directly to the substrate. Non-destructive analyses were conducted to assess the effects on leaf photosynthetic efficiency. At harvest, plants fresh weight (FW) and dry weight were determined, as well as the concentration of chlorophylls, carotenoids, total sugars, nitrate, proline, and abscisic acid (ABA). The biostimulant tested increased significantly the FW of lettuce (+65% in the highest dose) compared to controls. Results indicate that treatments positively affected the chlorophyll content measured in vivo (+45% in the highest dose) and that a general positive effect was observable on net photosynthesis rate. Retrosal® seems to improve the gas exchanges under our experimental conditions. The total sugars levels were not affected by treatments. Biostimulant allowed maintaining nitrate concentration similar to the untreated and unstressed controls. The increasing levels of water salinity caused a raise in proline concentration in control plants (+85%); biostimulant treatments at 0.2 mL/plant dose kept lower the proline levels. All plants treated with the biostimulant showed lower value of ABA (-34%) compared to controls. Results revealed that Retrosal® is able to stimulate plant growth independently from the salinity exposure. However, treated plants reached faster the commercial maturity stage. The fresh biomass of control at the end of experiment, after 30 days, ranged from 15 to 42 g/head, while in biostimulant treated plants ranged from 45 to 94 g/head. The product applied at maximum dose seems to be the most effective in our experimental conditions.