Enhanced drought tolerance of foxtail millet seedlings by sulfur dioxide fumigation

Rational design of a rapidly responsive and highly selective fluorescent probe for SO2 derivatives detection and imaging

Sulfur dioxide (SO2) is emerging as a double-edged molecule, while plays vital roles in food and biological system. However, the fast, highly sensitive, and versatile fluorescent probe still remains a tough challenge among current reports. Herein, we developed a novel aggregation-induced emission (AIE) fluorescent probe TPE-PN for specifically sensing SO2 derivatives with high sensitivity (150 nmol/L) and rapid response time (10 s) based on intramolecular charge transfer (ICT) mechanism. And the fluorescence at 575 nm decreased tremendously with 31-fold after the probe was treated with HSO3-. Employing the probe, the accurate analysis of HSO3- was successfully realized in food samples, cells, plant tissues, and zebrafishes. Furthermore, we successfully demonstrate the eruption of SO2 derivatives within plant during drought and salt stress processes. Therefore, probe TPE-PN illustrates significant potential for applications in food analysis and monitoring of SO2 derivatives levels in biological systems under stress conditions.

Hyperspectral Imaging and Machine Learning as a Nondestructive Method for Proso Millet Seed Detection and Classification

Millet is a small-seeded cereal crop with big potential. There are many different cultivars of proso millet (Panicum miliaceum L.) with different characteristics, bringing forth the issue of sorting which are important for growers, processors, and consumers. Current methods of grain cultivar detection and classification are subjective, destructive, and time-consuming. Therefore, there is a need to develop nondestructive methods for sorting the cultivars of proso millet. In this study, the feasibility of using near-infrared (NIR) hyperspectral imaging (900-1700 nm) to discriminate between different cultivars of proso millet seeds was evaluated. A total of 5000 proso millet seeds were randomly obtained and investigated from the ten most popular cultivars in the United States, namely Cerise, Cope, Earlybird, Huntsman, Minco, Plateau, Rise, Snowbird, Sunrise, and Sunup. To reduce the large dimensionality of the hyperspectral imaging, principal component analysis (PCA) was applied, and the first two principal components were used as spectral features for building the classification models because they had the largest variance. The classification performance showed prediction accuracy rates as high as 99% for classifying the different cultivars of proso millet using a Gradient tree boosting ensemble machine learning algorithm. Moreover, the classification was successfully performed using only 15 and 5 selected spectral features (wavelengths), with an accuracy of 98.14% and 97.6%, respectively. The overall results indicate that NIR hyperspectral imaging could be used as a rapid and nondestructive method for the classification of proso millet seeds.

Iron nanoparticle regulate succinate dehydrogenase activity in canola plants under drought stress

Application of nutrients as nanoparticle (NP) is an operative manner of nutrient supply for plants, especially under stress conditions. The present study was designed to highlight the role of iron NP on drought tolerance and elucidate the underlying mechanisms in drought-stressed canola plants. Drought stress was imposed by polyethylene glycol different concentrations (0, 10 and 15% (W/V)) with or without iron NP (1.5 and 3 mg/l). A comparative study of several physiological and biochemical parameters have been carried out in canola plants treated by drought and iron NP. Stressed-canola plants showed a reduction in growth parameters, whereas iron NP mostly stimulated growth of stressed plants, which was accompanied by reinforcement in defense mechanisms. Regarding impacts on compatible osmolytes, the data revealed that iron NP was able to regulate osmotic potential by increasing protein, proline and soluble sugar contents. The iron NP application was activated the enzymatic defense system (catalase and polyphenol oxidase) and promoted the non-enzymatic antioxidants (phenol, flavonol and flavonoid). Both of these adaptive responses declined free radicals as well as lipid peroxidation and enhanced the membrane stability and drought tolerance of the plants. Enhanced chlorophyll accumulation via induction of protoporphyrin, magnesium protoporphyrin and protochlorophyllide, by iron NP also contributed towards better stress tolerance. Enzymes of Krebs cycle, namely succinate dehydrogenase and aconitase, were induced by iron NP in canola plants grown under drought stress. These results propose a multifaceted involvement of iron NP, through regulation of activity of respiratory enzymes and antioxidant enzymes, production of reactive oxygen species, osmoregulation and secondary metabolites metabolism, in response to drought stress.

Sulfur dioxide improves the thermotolerance of maize seedlings by regulating salicylic acid biosynthesis

Heat stress (HS) has become a serious threat to crop growth and yield. Sulfur dioxide (SO₂) is being verified as a signal molecule in regulating the plant stress response. However, it is unknown whether SO₂ plays a significant role in the plant heat stress response (HSR). Herein, maize seedlings were pretreated with various concentrations of SO₂ and then kept at 45 °C for heat stress treatment, aiming to study the effect of SO₂ pretreatment on HSR in maize by phenotypic, physiological, and biochemical analyses. It was found that SO₂ pretreatment greatly improved the thermotolerance of maize seedlings. The SO₂-pretreated seedlings showed 30-40% lower ROS accumulation and membrane peroxidation, but 55-110% higher activities of antioxidant enzymes than the distilled water-pretreated seedlings under heat stress. Interestingly, endogenous salicylic acid (SA) levels were increased by ∼85% in SO₂-pretreated seedlings, as revealed by phytohormone analyses. Furthermore, the SA biosynthesis inhibitor paclobutrazol markedly reduced SA levels and attenuated SO₂-triggered thermotolerance of maize seedlings. Meanwhile, transcripts of several SA biosynthesis and signaling, and heat stress-responsive genes in SO₂-pretreated seedlings were significantly elevated under HS. These data have demonstrated that SO₂ pretreatment increased endogenous SA levels, which activated the antioxidant machinery and strengthened the stress defense system, thereby improving the thermotolerance of maize seedlings under HS. Our current study provides a new strategy for mitigating heat stress damage for safe crop production.

Multi-omics intervention in Setaria to dissect climate-resilient traits: Progress and prospects

Millets constitute a significant proportion of underutilized grasses and are well known for their climate resilience as well as excellent nutritional profiles. Among millets, foxtail millet (Setaria italica) and its wild relative green foxtail (S. viridis) are collectively regarded as models for studying broad-spectrum traits, including abiotic stress tolerance, C₄ photosynthesis, biofuel, and nutritional traits. Since the genome sequence release, the crop has seen an exponential increase in omics studies to dissect agronomic, nutritional, biofuel, and climate-resilience traits. These studies have provided first-hand information on the structure, organization, evolution, and expression of several genes; however, knowledge of the precise roles of such genes and their products remains elusive. Several open-access databases have also been instituted to enable advanced scientific research on these important crops. In this context, the current review enumerates the contemporary trend of research on understanding the climate resilience and other essential traits in Setaria, the knowledge gap, and how the information could be translated for the crop improvement of related millets, biofuel crops, and cereals. Also, the review provides a roadmap for studying other underutilized crop species using Setaria as a model.

Influence of water stress on engineering characteristics and oil content of sunflower seeds

Knowing some physical and mechanical characteristics and oil percentage of sunflower seeds could be useful for harvesting and processing equipment and activities such as transportation, storage, food production processes and establishing database of this seed. The main aim of this research was to study the effect of water stress during irrigation on seed's properties and quality. For this purpose, a field experiment was done under four deficit irrigation treatments [80%, 60%, 100-80 (100% irrigation requirement ETc to seed formation, and then reduced to 80% until harvesting) and 100-60% (100% ETc to seed formation, and then reduced to 60% until harvesting)] in comparable with full irrigation (100%). Geometrical, gravimetrical and mechanical characteristics as well as oil seed content and yield of sunflower seed were estimated. Result showed that there was no significant effect of low (100-80%) and medium (80%) irrigation deficit treatments on geometrical, gravimetrical and mechanical characteristics, while applying 60% of irrigation requirement (ETc) showed a significant effect on them. On the other hand, low and medium irrigation stress treatments improved the oil yield and seed oil content. The highest increase was 8.54% and 5.6% for oil yield and oil content respectively, considering T_100-80 followed by applying 80% ETc, but with high water stress (60% ETc) oil yield and seed oil content significantly decreased.

Sulfur dioxide improves drought tolerance through activating Ca2+ signaling pathways in wheat seedlings

Sulfur dioxide (SO₂) and drought are two important co-occurring abiotic stresses affecting the growth and productivity of plants. Here, we will investigate the role of Ca²⁺ in regulating antioxidant defense during drought or SO₂/drought stress, and the effect of SO₂ pretreatment on the physiological response of wheat seedlings to drought stress. The results showed that exogenous Ca²⁺ increased the activities of SOD, CAT and POD, and reduced the contents of H₂O₂ and MDA in drought-treated wheat seedlings, suggesting Ca²⁺ could improve drought tolerance by promoting antioxidant defense in plants. Moreover, exogenous Ca²⁺ up-regulated the expression of two stress-responsive transcription factor (TF) genes, ERF1 and MYB30, to cope with drought stress. Exposure of wheat seedlings to 10 mg m^-3 SO₂ significantly enhanced the activities of SOD, CAT and POD. The contents of H₂O₂ and MDA remained at control levels, showing that SO₂ at this concentration led to an activation of the antioxidant defense system and did not cause oxidative damage to the seedlings. Furthermore, 10 mg m^-3 SO₂ pretreatment increased the expression of CCaMK and CPK10, enhanced the activities of SOD and POD, and reduced the accumulation of H₂O₂ and MDA in drought-treated wheat seedlings, showing a role of SO₂ in protection of plants against drought stress. However, with removal of Ca²⁺ by spraying EGTA on the SO₂-pretreated wheat seedlings, the expression of transcription factor genes and activities of antioxidant enzymes were decreased, and the contents of H₂O₂ and MDA enhanced to the level of drought treatment alone, suggesting a role of Ca²⁺ in the SO₂-induced alleviation of drought stress. Together, these results indicated that exogenous Ca²⁺ increased defense-related gene expression and enzyme activity in response to drought stress, and that pre-exposure to appropriate levels of SO₂ could improve drought tolerance through activation of Ca²⁺ signaling pathways in plants. This study would provide new strategy for enhancing plant resistance to environmental stress.

Sulfur Dioxide: An Emerging Signaling Molecule in Plants

Sulfur dioxide (SO2) has long been viewed as toxic gas and air pollutant, but now is being verified as a signaling molecule in mammalian cells. SO2 can be endogenously produced and rapidly transformed into sulfur-containing compounds (e.g., hydrogen sulfide, cysteine, methionine, glutathione, glucosinolate, and phytochelatin) to maintain its homeostasis in plant cells. Exogenous application of SO2 in the form of gas or solution can trigger the expression of thousands of genes. The physiological functions of these genes are involved in the antioxidant defense, osmotic adjustment, and synthesis of stress proteins, secondary metabolites, and plant hormones, thus modulating numerous plant physiological processes. The modulated physiological processes by SO2 are implicated in seed germination, stomatal action, postharvest physiology, and plant response to environmental stresses. However, the review on the signaling role of SO2 in plants is little. In this review, the anabolism and catabolism of SO2 in plants were summarized. In addition, the signaling role of SO2 in seed germination, stomatal movement, fruit fresh-keeping, and plant response to environmental stresses (including drought, cold, heavy metal, and pathogen stresses) was discussed. Finally, the research direction of SO2 in plants is also proposed.

Enhancement of drought tolerance in Arabidopsis plants induced by sulfur dioxide

Sulfur dioxide (SO₂) is a common air pollutant that has multiple effects on plants. In the present study, the improvement of drought tolerance in Arabidopsis plants by SO₂ fumigation was investigated. The results showed that pre-exposure to 30 mg/m³ SO₂ for 72 h could reduce water loss, stomatal conductance (Gs) and the transpiration rate (Tr) but increased the net photosynthetic rate (Pn), water use efficiency (iWUE) and photosynthetic pigment contents under drought conditions. The activities of superoxide dismutase (SOD) and peroxidase (POD) were significantly increased, while the contents of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) were decreased in SO₂-pretreated Arabidopsis plants under drought stress. Additionally, the activity of o-acetylserine(thio)lyase (OASTL) and the content of cysteine (Cys), the rate-limiting enzyme and the first organic product of sulfur assimilation, were significantly increased in drought-stressed plants after SO₂ pretreatment, along with increases in other thiol-containing compounds, such as glutathione (GSH) and nonprotein thiol (NPT). Meanwhile, SO₂ pre-exposure induced a higher level of proline accumulation, with increased activity of proline synthase P5CS and decreased activity of proline dehydrogenase ProDH. Consistent with the changes in enzyme activity, their corresponding gene expression patterns were different after SO₂ treatment. Overall, the enhanced drought tolerance afforded by SO₂ might be related to the improvement of plant photosynthesis, antioxidant defense, sulfur assimilation and osmotic adjustment. These findings provide new insights into the role of SO₂ in plant adaptation to environmental stress.

Molecular Cloning and Characterization of MbMYB108, a Malus baccata MYB Transcription Factor Gene, with Functions in Tolerance to Cold and Drought Stress in Transgenic Arabidopsis thaliana

The MYB transcription factor (TF) family is one of the largest transcription families in plants, which is widely involved in the responses of plants to biotic and abiotic stresses, as well as plant growth, development, and metabolic regulation. In the present study, a new MYB TF gene, MbMYB108, from Malus baccata (L.) Borkh, was identified and characterized. The open reading frame (ORF) of MbMYB108 was found to be 903 bp, encoding 300 amino acids. Sequence alignment results and predictions of the protein structure indicated that the MbMYB108 protein contained the conserved MYB domain. Subcellular localization showed that MbMYB108 was localized to the nucleus. The expression of MbMYB108 was enriched in young and mature leaves, and was highly affected by cold and drought treatments in M. baccata seedlings. When MbMYB108 was introduced into Arabidopsis thaliana, it greatly increased the cold and drought tolerances in the transgenic plant. Increased expression of MbMYB108 in transgenic A. thaliana also resulted in higher activities of peroxidase (POD) and catalase (CAT), higher contents of proline and chlorophyll, while malondialdehyde (MDA) content and relative conductivity were lower, especially in response to cold and drought stresses. Therefore, these results suggest that MbMYB108 probably plays an important role in the response to cold and drought stresses in A. thaliana by enhancing the scavenging capability for reactive oxygen species (ROS).

H2S aids osmotic stress resistance by S-sulfhydration of melatonin production-related enzymes in Arabidopsis thaliana

Hydrogen sulfide closed Arabidopsis thaliana stomata by increasing the transcription of melatonin-producing enzymes and the post-translational modification levels to combat osmotic stress. Hydrogen sulfide (H₂S) and melatonin (MEL) reportedly have similar functions in many aspects of plant growth, development and stress response. They regulate stomatal movement and enhance drought resistance. However, their physiological relationship is not well understood. Here, their crosstalk involved in osmotic stress resistance in Arabidopsis thaliana was studied. Exogenous H₂S and MEL closed stomata under normal or osmotic stress conditions and increased the relative water contents of plants under osmotic stress conditions. At the same time, exogenous H₂S and MEL responded to osmotic stress by increasing the content of proline and soluble sugar, and reducing malondialdehyde (MDA) content and relative conductivity. Using mutants in the MEL-associated production of serotonin N-acetyltransferase (snat), caffeic acid O-methyltransferase (comt1) and N-acetylserotonin methyltransferase (asmt), we determined that H₂S was partially dependent on MEL to close stomata. Additionally, the overexpression of ASMT promoted stomatal closure. Exogenous H₂S increased the transcription levels of SNAT, ASMT and COMT1. Furthermore, exogenous H₂S treatments increased the endogenous MEL content significantly. At the post-translational level, H₂S sulfhydrated the SNAT and ASMT, but not COMT1, enzymes associated with MEL production. Thus, H₂S appeared to promote stomatal closure in response to osmotic stress by increasing the transcription levels of MEL synthesis-related genes and the sulfhydryl modification of the encoded enzymes. These results increased our understanding of H₂S and MEL functions and interactions under osmotic stress conditions.

Sulfur dioxide promotes seed germination by modulating reactive oxygen species production in maize

Sulfur dioxide (SO₂) is generally considered to be toxic to cells, but recent studies have shown that SO₂ has positive roles in stress defense responses in plants. However, whether SO₂ functions as a signaling molecule in the developmental process, especially in seed germination, is yet to be studied. Here, we present data supporting the role of SO₂ in seed germination and possible molecular mechanisms. SO₂ treatment significantly promoted the seed germination and seed vigor in maize. The germinating seeds treated with SO₂ treatment exhibited higher reactive oxygen species (ROS) levels and NADPH oxidase activities. Furthermore, the specific NADPH oxidase inhibitor diphenyleneiodinium (DPI) strongly inhibited ROS accumulations, and SO₂-promoted seed germination and vigor. Meanwhile, α-Amylase activity and transcripts in germinating seeds treated with SO₂ were significantly elevated. These data have demonstrated that NADPH oxidase-dependent ROS production contributes to the induction of α-Amylase activity, thereby promoting seed germination upon SO₂ exposure. SO₂ might function as a signaling molecule in plant growth and development, especially in seed germination. This study might provide a theoretical foundation for the potential exploitation of hydrated SO₂ in seed germination control in crop management.

Comparative analysis of alfalfa (Medicago sativa L.) seedling transcriptomes reveals genotype-specific drought tolerance mechanisms

Drought is one of the main abiotic factors that affect alfalfa yield. The identification of genes that control this complex trait can provide important insights for alfalfa breeding. However, little is known about how alfalfa responds and adapts to drought stress, particularly in cultivars of differing drought tolerance. In this study, the drought-tolerant cultivar Dryland 'DT' and the drought-sensitive cultivar WL343HQ 'DS' were used to characterize leaf and root physiological responses and transcriptional changes in response to water deficit. Under drought stress, Dryland roots (DTR) showed more differentially expressed genes than WL343HQ roots (DSR), whereas WL343HQ leaves (DSL) showed more differentially expressed genes than Dryland leaves (DTL). Many of these genes were involved in stress-related pathways, carbohydrate metabolism, and lignin and wax biosynthesis, which may have improved the drought tolerance of alfalfa. We also observed that several genes related to ABA metabolism, root elongation, peroxidase activity, cell membrane stability, ubiquitination, and genetic processing responded to drought stress in alfalfa. We highlighted several candidate genes, including sucrose synthase, xylan 1,4-beta-xylosidase, primary-amine oxidase, and alcohol-forming fatty acyl-CoA reductase, for future studies on drought stress resistance in alfalfa and other plant species. In summary, our results reveal the unique drought adaptation and resistance characteristics of two alfalfa genotypes. These findings, which may be valuable for drought resistance breeding, warrant further gene functional analysis to augment currently available information and to clarify the drought stress regulatory mechanisms of alfalfa and other plants.

Hydrogen peroxide potentiates defense system in presence of sulfur to protect chloroplast damage and photosynthesis of wheat under drought stress

The involvement of hydrogen peroxide (H₂ O₂ ) combined with sulfur (S) was studied in the protection of the photosynthetic performance of wheat (Triticum aestivum L.) under drought stress. The mechanisms of S-assimilation, the activity of antioxidants, glucose sensitivity, water and osmotic relations and abscisic acid (ABA) content were the focus. The combined application of 50 μM H₂ O₂ and 100 mg S kg^-1 soil (sulfur) resulted in a marked increase in S-assimilation and activity of antioxidant enzymes, with decreased glucose sensitivity and ABA content causing improvement in the structure and function of the photosynthetic apparatus under drought stress. The photosynthetic performance, pigment system (PS) II activity, and growth were improved conspicuously by H₂ O₂ in the presence of S, as H₂ O₂ induced S-assimilation capacity, the activity of antioxidant enzymes, and GSH synthesis under drought stress. Our study shows that H₂ O₂ is more effective in the reversal of drought stress in the presence of S through its influence on S-assimilation, glucose sensitivity, and antioxidant system. These results provide evidence for the effectiveness of H₂ O₂ in improving photosynthesis under drought stress in the presence of S.

Transcriptome profiling reveals the effects of drought tolerance in Giant Juncao

BACKGROUND

Giant Juncao is often used as feed for livestock because of its huge biomass. However, drought stress reduces forage production by affecting the normal growth and development of plants. Therefore, investigating the molecular mechanisms of drought tolerance will provide important information for the improvement of drought tolerance in this grass.

RESULTS

A total of 144.96 Gb of clean data was generated and assembled into 144,806 transcripts and 93,907 unigenes. After 7 and 14 days of drought stress, a total of 16,726 and 46,492 differentially expressed genes (DEGs) were observed, respectively. Compared with normal irrigation, 16,247, 23,503, and 11,598 DEGs were observed in 1, 5, and 9 days following rehydration, respectively. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses revealed abiotic stress-responsive genes and pathways related to catalytic activity, methyltransferase activity, transferase activity, and superoxide metabolic process. We also identified transcription factors belonging to several families, including basic helix-loop-helix (bHLH), WRKY, NAM (no apical meristem), ATAF1/2 and CUC2 (cup-shaped cotyledon) (NAC), fatty acyl-CoA reductase (FAR1), B3, myeloblastosis (MYB)-related, and basic leucine zipper (bZIP) families, which are important drought-rehydration-responsive proteins. Weighted gene co-expression network analysis was also used to analyze the RNA-seq data to predict the interrelationship between genes. Twenty modules were obtained, and four of these modules may be involved in photosynthesis and plant hormone signal transduction that respond to drought and rehydration conditions.

CONCLUSIONS

Our research is the first to provide a more comprehensive understanding of DEGs involved in drought stress at the transcriptome level in Giant Juncao with different drought and recovery conditions. These results may reveal insights into the molecular mechanisms of drought tolerance in Giant Juncao and provide diverse genetic resources involved in drought tolerance research.

Sulfur dioxide enhance drought tolerance of wheat seedlings through H2S signaling

Drought is one of the most common factors that limit plant growth and productivity. Sulfur dioxide (SO₂) has recently been found to play a benefical role in protection of plants against environmental stress. In this study, we investigated the effect of SO₂ on the physiological and molecular response of wheat seedlings to drought stress. Pretreatment with 10 mg/m³ SO₂ significantly increased the survival rate and relative water content (RWC) of wheat seedlings under drought stress, indicating that pre-exposure to appropriate level of SO₂ could enhance drought tolerance of plants. These responses were related to the enhanced proline accumulation in the drought-treated wheat seedlings that induced by SO₂ pretreatment. Meanwhile, SO₂ pretreatment increased the activities of superoxide dismutase (SOD) and peroxidase (POD), and effectively reduced the content of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) in drought-treated wheat seedlings, suggesting SO₂ could alleviate drought-induced oxidative damage by enhancing antioxidant defense system in plants. Expression analysis of transcription factor genes also showed that SO₂ pretreatment decreased the expression of TaNAC69, but the expression of TaERF1 and TaMYB30 changed slightly and maintained at higher levels in wheat seedlings in response to drought stress. Furthermore, SO₂ pretreatment triggered marked accumulation of hydrogen sulfide (H₂S) in wheat seedlings under drought stress. When scavenged H₂S by spraying Hypotaurine (HT), the activities of antioxidant enzymes and the expression of transcription factor genes were decreased, and the content of H₂O₂ and MDA increased to the level of drought treatment alone, suggesting a regulatory role of SO₂-induced H₂S in plant adaptation to drought stress. Together, this study indicated that SO₂ enhanced drought tolerance of wheat seedlings through H₂S signaling, and provided new strategy for enhancing plant tolerance to drought stress.

Phytoremediation of metal-contaminated rare-earth mining sites using Paspalumconjugatum

Over-exploitation of rare-earth elements causes cadmium (Cd)- and lead (Pb)-contamination of rare-earth mine tailings. Here, Paspalum conjugatum was used as a hyperaccumulating perennial herb to evaluate its phytoextraction potential for removing metals in a hydroponic experiment. Further, an in-situ experiment was conducted for two years (2016-2018) to investigate the potential of P. conjugatum for reducing soil metal concentrations and to assess microbiome recovery on abandoned rare-earth mining land. Pinus massoniana was used for control treatments. We found that P. conjugatum produced metal transfer coefficients of 0.85 and 0.89 for Cd and Pb, respectively. The concentrations of Cd and Pb accumulated in P. conjugatum were 98.33 mg kg^-1 and 137 mg kg^-1, respectively. Using P. conjugatum, soil Pb and Cd concentrations were significantly decreased, and Cd concentrations approached acceptable levels (0.209 mg kg^-1). The bacterial diversity in P. conjugatum-restored soil was higher than that in soil of P. massoniana. The bacterial genera Chloroflexi, Acidobacteria, and Actinobacteria were predominant in the restored soils. P. conjugatum was tolerant to drought and exhibited enhanced enzymatic activity. These results suggest that P. conjugatum can be used for efficient phytoremediation of Pb- and Cd-contaminated soils.

Sunflower (Helianthus annuus L.) biochemical properties and seed components affected by potassium fertilization under drought conditions

The seed yield and healthy oil in sunflower (Helianthus annuus L.), as an important industrial crop, decrease under stress. There is not much investigation, to our knowledge, on the use of potassium fertilization, a regulator of plant water potential, affecting the biochemical properties and seed components of sunflower under drought stress. Accordingly, such parameters were investigated in a split-split plot field experiment, conducted in two different field sites (Natanz (Nt) and Eghlid (Eg), Iran), using potassium fertilization (subplots, 0, 150 and 300 kg/ha) and six drought levels (main plots) in four replicates. Although stress significantly affected sunflower biochemical properties and seed components in the two fields, the effects of stress were more pronounced in the Eg site (significant interaction of field and drought). The plant alleviated the stress by increasing the proline, oleic and linoleic acid concentrations, however, potassium fertilization also increased plant tolerance further under stress by enhancing such components compared with control. Interestingly, the Eg site was more responsive to the potassium fertilization (significant interaction of field and fertilization), as the fertilizer resulted in a higher rate of plant biochemical properties and seed components. The use of potassium fertilization at 300 kg/ha (K3) was the most effective treatment in the alleviation of stress. Interestingly, under drought stress, potassium contributed to the enhanced quantity and quality of sunflower by increasing seed components, and enhancing the biochemical properties of the plant, which can also improve crop physiological mechanisms. The results can further increase our understanding related to the effects of potassium fertilization on the yield and physiology of sunflower under drought stress. Such results are of economic, environmental and health significance.

Overexpression of a Malus baccata NAC Transcription Factor Gene MbNAC25 Increases Cold and Salinity Tolerance in Arabidopsis

NAC (no apical meristem (NAM), Arabidopsis thaliana transcription activation factor (ATAF1/2) and cup shaped cotyledon (CUC2)) transcription factors play crucial roles in plant development and stress responses. Nevertheless, to date, only a few reports regarding stress-related NAC genes are available in Malus baccata (L.) Borkh. In this study, the transcription factor MbNAC25 in M. baccata was isolated as a member of the plant-specific NAC family that regulates stress responses. Expression of MbNAC25 was induced by abiotic stresses such as drought, cold, high salinity and heat. The ORF of MbNAC25 is 1122 bp, encodes 373 amino acids and subcellular localization showed that MbNAC25 protein was localized in the nucleus. In addition, MbNAC25 was highly expressed in new leaves and stems using real-time PCR. To analyze the function of MbNAC25 in plants, we generated transgenic Arabidopsis plants that overexpressed MbNAC25. Under low-temperature stress (4 °C) and high-salt stress (200 mM NaCl), plants overexpressing MbNAC25 enhanced tolerance against cold and drought salinity conferring a higher survival rate than that of wild-type (WT). Correspondingly, the chlorophyll content, proline content, the activities of antioxidant enzymes superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) were significantly increased, while malondialdehyde (MDA) content was lower. These results indicated that the overexpression of MbNAC25 in Arabidopsis plants improved the tolerance to cold and salinity stress via enhanced scavenging capability of reactive oxygen species (ROS).