The role of salicylic acid in the prevention of oxidative stress elicited by cadmium in soybean plants

Multivariate characterization of salicylic acid and potassium induced physio-biochemical and phytoremediation responses in quinoa exposed to lead and cadmium contamination

The levels of soils pollutants such as lead (Pb) and cadmium (Cd) have significantly increased recently resulting in ecological disturbances and threatening crop production. Various amendments have been employed to enhance the tolerance of crops to withstand Cd and Pb stresses. However, the role of combined application of potassium (K) and of salicylic acid (SA) for Cd and Pb stress mitigation and phytoremediation by quinoa (Chenopodium quinoa Willd) has not been comprehended well. In the present study, the effect of 10 mM K and 0.1 mM SA was tested on the quinoa plants subjected to 250 μM Pb and/or 100 μM Cd. The Pb and Cd treatments were applied separately or together. Phytotoxicity induced by Pb and Cd resulted in drastic decrease (>60%) in chlorophyll contents, stomatal conductance, and plant biomass. The collective treatment of Pb and Cd induced an increase in the concentration of hydrogen peroxide (13-fold) and lipid peroxidation (16-fold) that resulted in a 61% reduction in membrane stability. The application of 10 mM K and/or 0.1 mM SA was remarkable in mitigating the adverse effect of Pb and Cd. The reduction in plant biomass was 17% when 10 mM K and 0.1 mM SA were applied together under the combined treatment of both the metals. The simultaneous application of K and SA effectively mitigated oxidative stress by enhancing the activities of superoxide dismutase, peroxidase, ascorbate peroxidase, and catalase by 12, 10, 7 and 10-folds respectively. The positive effect of K and SA on these attributes resulted in a remarkable reduction in metal accumulation and translocation and lipid peroxidation. The stressed plants supplemented with K and SA exhibited a significant improvement in the membrane stability index, chlorophyll content, and stomatal conductance. This study concluded that the combined application of K and SA could be a good approach for reducing Pb and Cd phytotoxicity in quinoa and enhancing their phytostabilization potential in the contaminated soils.

5-Aminolevulinic acid treatment mitigates pesticide stress in bean seedlings by regulating stress-related gene expression and retrotransposon movements

Overdoses of pesticides lead to a decrease in the yield and quality of plants, such as beans. The unconscious use of deltamethrin, one of the synthetic insecticides, increases the amount of reactive oxygen species (ROS) by causing oxidative stress in plants. In this case, plants tolerate stress by activating the antioxidant defense mechanism and many genes. 5-Aminolevulinic acid (ALA) improves tolerance to stress by acting exogenously in low doses. There are many gene families that are effective in the regulation of this mechanism. In addition, one of the response mechanisms at the molecular level against environmental stressors in plants is retrotransposon movement. In this study, the expression levels of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR), and stress-associated protein (SAP) genes were determined by Q-PCR in deltamethrin (0.5 ppm) and various doses (20, 40, and 80 mg/l) of ALA-treated bean seedlings. In addition, one of the response mechanisms at the molecular level against environmental stressors in plants is retrotransposon movement. It was determined that deltamethrin increased the expression of SOD (1.8-fold), GPX (1.4-fold), CAT (2.7-fold), and SAP (2.5-fold) genes, while 20 and 40 mg/l ALA gradually increased the expression of these genes at levels close to control, but 80 mg/l ALA increased the expression of these genes almost to the same level as deltamethrin (2.1-fold, 1.4-fold, 2.6-fold, and 2.6-fold in SOD, GPX, CAT, and SAP genes, respectively). In addition, retrotransposon-microsatellite amplified polymorphism (REMAP) was performed to determine the polymorphism caused by retrotransposon movements. While deltamethrin treatment has caused a decrease in genomic template stability (GTS) (27%), ALA treatments have prevented this decline. At doses of 20, 40, and 80 mg/L of ALA treatments, the GTS ratios were determined to be 96.8%, 74.6%, and 58.7%, respectively. Collectively, these findings demonstrated that ALA has the utility of alleviating pesticide stress effects on beans.

Eco-friendly approach to decrease the harmful effects of untreated wastewater on growth, yield, biochemical constituents, and heavy metal contents of carrot (Daucus carota L.)

Here, the impact of irrigation using untreated wastewater (WW) on carrots (Daucus carota L.) was examined. We hypothesized that the addition of ethylenediaminetetraacetic acid (EDTA), dry algal powder (Spirulina platensis or Chlorella vulgaris), and Salix alba leaves powder would function as chelators for harmful contaminants in wastewater. The findings showed that irrigation of carrot plants with the sampled untreated wastewater led to significant decreases in the shoot lengths, fresh, dry weights of shoots and roots at stage I, the diameter of roots, pigment content, carotenoids, total soluble carbohydrate content, and soluble protein content. Furthermore, a significantly increased level of proline, total phenols, and the activities of polyphenol oxidase (PPO), peroxidase (POX), superoxide dismutase (SOD), and catalase (CAT) was identified in stage I samples. In contrast to the stage I, the length of the roots, the number of leaves on each plant, wet and dry weights of the stage II roots were all greatly enhanced. In spite of the increased yield due to the wastewater irrigation, carrot roots irrigated with wastewater had significantly more cadmium (Cd), nickel (Ni), cobalt (Co), and lead (Pb) than is considered safe. Our data clearly show that the application of Spirulina platensis, Chlorella vulgaris, EDTA, and leaves powder of salix was able to alleviate the toxicity of wastewater on carrot plants. For example, we recorded a significant decrease in the accumulation of carrot's Cd, Ni, Co, and Pb contents. We conclude that the treatments with Spirulina platensis and Chlorella vulgaris can be utilized as eco-friendly tools to lessen the damaging effects of wastewater irrigation on carrot plants.

Salylic acid minimize cadmium accumulation in rice through regulating the fixation capacity of the cell wall to cadmium

Although salylic acid (SA) has been linked to how plants react to cadmium (Cd) stress, the exact mechanism is still unknown. The endogenous SA concentration in the rice (Oryza sativa L.) roots was enhanced by Cd stress in the current investigation, and exogenous SA reduced the hemicellulose content in root cell wall, which in turn inhibited its Cd binding capacity. What's more, exogenous SA also decreased the transcription level of genes such as Natural Resistance-Associated Macrophage Protein 5 (OsNRAMP5) and a major facilitator superfamily gene-OsCd1 that responsible for root Cd absorption. Finally, less Cd was accumulated in the rice as a result of the higher expression of Heavy Metal ATPase 3 (OsHMA3), Cation/Ca exchanger 2 (OsCCX2) and Pleiotropic Drug Resistance 9 (OsPDR9/OsABCG36) that were responsible for separating Cd into vacuole and getting Cd out of cells, respectively. In contrast, mutant with low SA level accumulated more Cd. Additionally, SA enhanced endogenous nitric oxide (NO) levels, and its alleviatory effects were mimicked by a NO donor, sodium nitroprusside (SNP). In conclusion, SA enhanced rice's Cd resistance through regulating the binding capacity of the cell wall to Cd, a pathway that might dependent on the NO accumulation.

Salicylic Acid- and Potassium-Enhanced Resilience of Quinoa (Chenopodium quinoa Willd.) against Salinity and Cadmium Stress through Mitigating Ionic and Oxidative Stress

Salinity and cadmium (Cd) contamination of soil are serious environmental issues threatening food security. This study investigated the role of salicylic acid (SA) and potassium (K) in enhancing the resilience of quinoa against the combined stress of salinity and Cd. Quinoa plants were grown under NaCl (0, 200 mM) and Cd (0, 100 µM) stress, with the addition of 0.1 mM SA and 10 mM K, separately or in combination. The joint stress of Cd and NaCl caused >50% decrease in plant growth, chlorophyll contents, and stomatal conductance compared to the control plants. The higher accumulation of Na and Cd reduced the uptake of K in quinoa tissues. The joint stress of salinity and Cd caused an 11-fold increase in hydrogen peroxide and 13-fold increase in thiobarbituric acid reactive substances contents, and caused a 61% decrease in membrane stability. An external supply of 0.1 mM SA and 10 mM K helped plants to better adapt to salinity and Cd stress with less of a reduction in plant biomass (shoot 19% and root 24%) and less accumulation of Na and Cd in plant tissues. The activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) were enhanced by 11-fold, 10-fold, 7.7-fold, and 7-fold, respectively, when SA and K were applied together to the plants subjected to the joint stress of Cd and salinity. Based on the values of the bioconcentration factor (>1), the translocation factor (<1), and the higher tolerance index, it was clear that Cd-contaminated, salty soils could be stabilized with quinoa under the combined supply of SA and K.

Exploring the Impact of Salicylic Acid and Farmyard Manure on Soil Rhizospheric Properties and Cadmium Stress Alleviation in Maize (Zea mays L.)

Cadmium (Cd) pollution is a growing environmental problem that negatively impacts plant growth and development, particularly in maize. In this research, the impact of farmyard manure (FYM) and salicylic acid (SA) on rhizospheric characteristics and the reduction of Cd stress in maize was examined at Government College (GC) University, Lahore, in 2022. The experiment was arranged with a randomized design, including three replications of 12 treatments (T1 = Control; T2 = Farmyard manure; T3 = Salicylic Acid; T4 = 100 mg/kg of soil Cd; T5 = 200 mg/kg of soil Cd; T6 = Farmyard manure + Salicylic acid; T7 = FYM + 100 mg/kg soil Cd; T8 = FYM + 200 mg/kg soil Cd; T9 = SA + 100 mg/kg soil Cd; T10 = SA + 200 mg/kg soil Cd; T11 = FYM + SA + 100 mg/kg soil Cd; T12 = FYM + SA + 200 mg/kg soil Cd). Results demonstrated that Cd stress negatively affected the maize plant and soil properties, but the application of SA and FYM was effective to mitigate the Cd stress up to a certain level. A reduction of 41.52%, 39.14%, and 39.94% in root length, length of the leaf, and crop growth rate was noticed, due to the Cd stress at 200 mg/kg soil, but this reduction was reduced to 18.83%, 10.35%, and 12.26%, respectively, when FYM and salicylic acid were applied as a combined application under the same stress level of Cd. The root biomass, leaf surface area, and length were all improved by SA and FYM, which enhanced the plant's capacity to absorb nutrients and improve growth under Cd stress. In conclusion, the use of salicylic acid together with farm manure can be an effective approach to mitigate Cd stress in maize crops.

Involvement of NO in V-ATPase Regulation in Cucumber Roots under Control and Cadmium Stress Conditions

Nitric oxide (NO) is a signaling molecule that participates in plant adaptation to adverse environmental factors. This study aimed to clarify the role of NO in the regulation of vacuolar H+-ATPase (V-ATPase) in the roots of cucumber seedlings grown under control and Cd stress conditions. In addition, the relationship between NO and salicylic acid (SA), as well as their interrelations with hydrogen sulfide (H2S) and hydrogen peroxide (H2O2), have been verified. The effect of NO on V-ATPase was studied by analyzing two enzyme activities, the expression level of selected VHA genes and the protein level of selected VHA subunits in plants treated with a NO donor (sodium nitroprusside, SNP) and NO biosynthesis inhibitors (tungstate, WO42- and N-nitro-L-arginine methyl ester, L-NAME). Our results indicate that NO functions as a positive regulator of V-ATPase and that this regulation depends on NO generated by nitrate reductase and NOS-like activity. It was found that the mechanism of NO action is not related to changes in the gene expression or protein level of the V-ATPase subunits. The results suggest that in cucumber roots, NO signaling interacts with the SA pathway and, to a lesser extent, with two other known V-ATPase regulators, H2O2 and H2S.

Mitigation of arsenic toxicity in rice by the co-inoculation of arsenate reducer yeast with multifunctional arsenite oxidizing bacteria

The study aimed to explicate the role of microbial co-inoculants for the mitigation of arsenic (As) toxicity in rice. Arsenate (AsV) reducer yeast Debaryomyces hansenii NBRI-Sh2.11 (Sh2.11) with bacterial strains of different biotransformation potential was attempted to develop microbial co-inoculants. An experiment to test their efficacy (yeast and bacterial strains) on plant growth and As uptake was conducted under a stressed condition of 20 mg kg-1 of arsenite (AsIII). A combination of Sh2.11 with an As(III)-oxidizer, Citrobacter sp. NBRI-B5.12 (B5.12), resulted in ∼90% decrease in grain As content as compared to Sh2.11 alone (∼40%). Reduced As accumulation in rice roots under co-treated condition was validated with SEM-EDS analysis. Enhanced As expulsion in the selected combination under in vitro conditions was found to be correlated with higher As content in the soil during their interaction with plants. Selected co-inoculant mediated enhanced nutrient uptake in association with better production of indole acetic acid (IAA) and gibberellic acid (GA) in shoot, support microbial co-inoculant mediated better biomass under stressful condition. Boosted defense response in association with enhanced glutathione-S-transferase (GST) and glutathione reductase (GR), activities under in vitro and in vivo conditions were observed. These results indicated that the As(III) oxidizer-B5.12 accelerated the As detoxification property of the As(V) reducer-Sh2.11. Henceforth, the results confer that the coupled reduction-oxidation process of the co-inoculant reduces the accumulation of As in rice grain. These co-inoculants can be further developed for field trials to achieve higher biomass with alleviated As toxicity in rice.

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

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

Salicylic Acid, a Multifaceted Hormone, Combats Abiotic Stresses in Plants

In recent decades, many new and exciting findings have paved the way to the better understanding of plant responses in various environmental changes. Some major areas are focused on role of phytohormone during abiotic stresses. Salicylic acid (SA) is one such plant hormone that has been implicated in processes not limited to plant growth, development, and responses to environmental stress. This review summarizes the various roles and functions of SA in mitigating abiotic stresses to plants, including heating, chilling, salinity, metal toxicity, drought, ultraviolet radiation, etc. Consistent with its critical roles in plant abiotic tolerance, this review identifies the gaps in the literature with regard to the complex signalling network between SA and reactive oxygen species, ABA, Ca²⁺, and nitric oxide. Furthermore, the molecular mechanisms underlying signalling networks that control development and stress responses in plants and underscore prospects for future research on SA concerning abiotic-stressed plants are also discussed.

Salicylic acid: A key regulator of redox signalling and plant immunity

In plants, the reactive oxygen species (ROS) formed during normal conditions are essential in regulating several processes, like stomatal physiology, pathogen immunity and developmental signaling. However, biotic and abiotic stresses can cause ROS over-accumulation leading to oxidative stress. Therefore, a suitable equilibrium is vital for redox homeostasis in plants, and there have been major advances in this research arena. Salicylic acid (SA) is known as a chief regulator of ROS; however, the underlying mechanisms remain largely unexplored. SA plays an important role in establishing the hypersensitive response (HR) and systemic acquired resistance (SAR). This is underpinned by a robust and complex network of SA with Non-Expressor of Pathogenesis Related protein-1 (NPR1), ROS, calcium ions (Ca²⁺), nitric oxide (NO) and mitogen-activated protein kinase (MAPK) cascades. In this review, we summarize the recent advances in the regulation of ROS and antioxidant defense system signalling by SA at the physiological and molecular levels. Understanding the molecular mechanisms of how SA controls redox homeostasis would provide a fundamental framework to develop approaches that will improve plant growth and fitness, in order to meet the increasing global demand for food and bioenergy.

Modulation of Cellular Redox Status and Antioxidant Defense System after Synergistic Application of Zinc Oxide Nanoparticles and Salicylic Acid in Rice (Oryza sativa) Plant under Arsenic Stress

The objective of this research was to determine the effect of zinc oxide nanoparticles (ZnONPs) and/or salicylic acid (SA) under arsenic (As) stress on rice (Oryza sativa). ZnONPs are analyzed for various techniques viz., X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). All of these tests established that ZnONPs are pure with no internal defects, and can be potentially used in plant applications. Hence, we further investigated for better understanding of the underlying mechanisms and the extent of ZnONPs and SA induced oxidative stress damages. More restricted plant growth, gas exchange indices, significant reduction in the SPAD index and maximum quantum yield (Fv/Fm) and brutal decline in protein content were noticed in As-applied plants. In contrast, foliar fertigation of ZnONPs and/or SA to As-stressed rice plants lessens the oxidative stress, as exposed by subordinate levels of reactive oxygen species (ROS) synthesis. Improved enzymatic activities of catalase (CAT), peroxidase (POX), and superoxide dismutase (SOD), proline and total soluble protein contents under ZnONPs and SA treatment plays an excellent role in the regulation of various transcriptional pathways participated in oxidative stress tolerance. Higher content of nitrogen (N; 13%), phosphorus (P; 10%), potassium (K; 13%), zinc (Zn; 68%), manganese (Mn; 14%), and iron (Fe; 19) in ZnONPs and SA treated plants under As-stress, thus hampered growth and photosynthetic efficiency of rice plants. Our findings suggest that toxicity of As was conquering by the application of ZnONPs and SA in rice plants.

Potential Use of Copper-Contaminated Soils for Hemp (Cannabis sativa L.) Cultivation

To mitigate climate change, reducing greenhouse gas emissions can be achieved by decreasing the use of fossil fuels and increasing that of alternative sources, such as energy crops. However, one of the most important problems in the use of biomass as a fuel is that of changing soil use and consumption, leading to competition with food crops. We addressed the topic by evaluating the possibility to exploit contaminated areas for energy crops cultivation. Indeed, soil contamination makes land inappropriate for cultivation, with damaging consequences for ecosystems, as well as posing serious health hazards to living beings. Specifically, this work aimed to evaluate the ability of hemp (Cannabis sativa L.) plants to grow on a copper (Cu)-contaminated medium. In addition, the effectiveness of an environment-friendly treatment with sulfate in improving plant ability to cope with Cu-induced oxidative stress was also explored. Results showed that plants were able to grow at high Cu concentrations. Therefore, hemp could represent an interesting energy crop in Cu-contaminated soils. Although the response of Cu-treated plants was evidenced by the increase in thiol content, following modulation of sulfur metabolism, it remains to be clarified whether the use of exogenous sulfate could be an agronomic practice to improve crop performance under these edaphic conditions.

Acclimation of cadmium-induced genotoxicity and oxidative stress in mung bean seedlings by priming effect of phytohormones and proline

In this research, eight local mung bean (Vigna radiata) varieties were analyzed for their performance against two levels of CdCl2 solution (0.3 and 0.5 mM) alone and priming with gibberellic acid (GA3) (100 μM), salicylic acid (SA) (50 μM) and proline (5 mM) solution prior to Cd exposure. Mung bean seedlings were analyzed for disturbance in cytological, morphological, biochemical and enzymatic parameters under cadmium stress. For cytological studies, 48 h grown mung bean seedlings root tips were used to prepare slides and studied for percent mitotic index (MI%) and to calculate percent C-mitosis, laggard, sticky and fragmented chromosomes, pictures were captured by a Nikon camera (DS-Fi 1 Japan) attached with a microscope. One-week grown mung seedlings were studied for growth traits, malondialdehyde (MDA), protein, proline and antioxidant enzymes. ANOVA and DMR test of this research revealed that all the tested mung bean varieties and treatments were significantly different regarding mitotic index and number of chromosomal aberrations. Both the Cd treatments exhibited increased total chromosomal aberrations with different types and a maximum decrease in MI%. In pretreated samples, GA3, SA and proline serve as mitigating agents that reduce mutagenic effects of Cd in mung bean by increasing MI% and decreasing chromosomal aberrations as compared to non-pretreated samples. Both the Cd treatments showed a decrease in all growth traits. Total proteins were also found to be significantly reduced in a dose-dependent manner in all genotypes. Cd treatment increased the activities of all antioxidant enzymes tested. Cd caused oxidative damage as indicated by elevated levels of MDA content in treated samples in comparison to control. Proline content levels were also high in Cd treated seedlings indicating stress. Results demonstrated that pretreatment with phytohormones and proline before Cd were found to improve all morphological parameters, by altering antioxidant enzymes activities along with a decrease in MDA and proline contents as well. It was further noticed that the performance of GA3 was better at 0.3 mM Cd treatment while SA was found to be a good mitigating agent at 0.5 mM Cd stress in all tested mung bean varieties. This research concluded less deleterious effects of Cd on AZRI-2006 while more sensitivity to NM-51 towards Cd. Priming with phytohormones and proline is a user-friendly, economical, and simple mitigation strategy to reduce Cd toxicity in plants and get better yield from contaminated lands.

SA-Mediated Regulation and Control of Abiotic Stress Tolerance in Rice

Environmental or abiotic stresses are a common threat that remains a constant and common challenge to all plants. These threats whether singular or in combination can have devastating effects on plants. As a semiaquatic plant, rice succumbs to the same threats. Here we systematically look into the involvement of salicylic acid (SA) in the regulation of abiotic stress in rice. Studies have shown that the level of endogenous salicylic acid (SA) is high in rice compared to any other plant species. The reason behind this elevated level and the contribution of this molecule towards abiotic stress management and other underlying mechanisms remains poorly understood in rice. In this review we will address various abiotic stresses that affect the biochemistry and physiology of rice and the role played by SA in its regulation. Further, this review will elucidate the potential mechanisms that control SA-mediated stress tolerance in rice, leading to future prospects and direction for investigation.

Salicylic acid application alleviates cadmium accumulation in brown rice by modulating its shoot to grain translocation in rice

Cadmium (Cd) contamination, which poses a serious threat to human health, has been recognized as a major threat to the agricultural system and crop production. Salicylic acid (SA) is a signaling molecule that plays an important role in against Cd toxicity. Previously, we found that spraying rice with SA could reduce the Cd accumulation in rice grains grown in Cd-contaminated soil. In this study, we studied the specific mechanism of SA spray on reducing Cd accumulation in rice grain. The results showed that treatment with SA could alleviate Cd toxicity in rice by increasing the activities of antioxidant enzymes that reduce hydrogen peroxide (H₂O₂) accumulation, but not by changing the pH, or total or available Cd of the soil. The key factor by which SA treatment reduced Cd accumulation in rice grains was by decreasing the Cd content in rice leaves at the flowering stage. This indicated that SA could modulate the Cd accumulation in shoots, reducing the Cd translocation to rice grains. Furthermore, SA could increase the H₂O₂ content, activating the SA-signaling pathway and modulating the expression levels of Cd transporters (OsLCT1 and OsLCD) in rice leaves to increase Cd tolerance and reduce Cd accumulation in the rice grain. Thus, spraying rice with SA may be effective measure to cope with Cd contamination in paddy soils.

Phytohormonal Roles in Plant Responses to Heavy Metal Stress: Implications for Using Macrophytes in Phytoremediation of Aquatic Ecosystems

Heavy metals can represent a threat to the health of aquatic ecosystems. Unlike organic chemicals, heavy metals cannot be eliminated by natural processes such as their degradation into less toxic compounds, and this creates unique challenges for their remediation from soil, water, and air. Phytoremediation, defined as the use of plants for the removal of environmental contaminants, has many benefits compared to other pollution-reducing methods. Phytoremediation is simple, efficient, cost-effective, and environmentally friendly because it can be carried out at the polluted site, which simplifies logistics and minimizes exposure to humans and wildlife. Macrophytes represent a unique tool to remediate diverse environmental media because they can accumulate heavy metals from contaminated sediment via roots, from water via submerged leaves, and from air via emergent shoots. In this review, a synopsis is presented about how plants, especially macrophytes, respond to heavy metal stress; and we propose potential roles that phytohormones can play in the alleviation of metal toxicity in the aquatic environment. We focus on the uptake, translocation, and accumulation mechanisms of heavy metals in organs of macrophytes and give examples of how phytohormones interact with plant defense systems under heavy metal exposure. We advocate for a more in-depth understanding of these processes to inform more effective metal remediation techniques from metal-polluted water bodies. Environ Toxicol Chem 2021;40:7-22. © 2020 SETAC.

Salicylic acid-induced nitric oxide enhances arsenic toxicity tolerance in maize plants by upregulating the ascorbate-glutathione cycle and glyoxalase system

The role of nitric oxide (NO) in salicylic acid (SA)-induced tolerance to arsenic (As) stress in maize plants is not reported in the literature. Before starting As stress (AsS) treatments, SA (0.5 mM) was sprayed to the foliage of maize plants. Thereafter, AsV (0.1 mM as sodium hydrogen arsenate heptahydrate) stress (AsS) was initiated and during the stress period, sodium nitroprusside (SNP 0.1 mM), a NO donor, was sprayed individually or in combination with SA. Furthermore, cPTIO (0.1 mM) was also applied as a NO scavenger during the stress period. Arsenic stress led to significant reductions in plant growth, photosynthesis, water relation parameters and endogenous NO content, but it increased hydrogen peroxide, malondialdehyde, electrolyte leakage, methylglyoxal, proline, the activities of major antioxidant enzymes, and leaf and root As content. The combined treatment of SA+SNP was more effective to reverse oxidative stress related parameters and reduce the As content in both leaves and roots, with a concomitant increase in antioxidant defense system, the ascorbate-glutathione (AsA-GSH) cycle-related enzymes, glyoxalase system enzymes, plant growth, and photosynthetic traits. The beneficial effects of SA were completely abolished with cPTIO supply by blocking the NO synthesis in AsS-maize plants, indicating that NO effectively participated in SA-improved tolerance to AsS in maize plants.

Reactivation of human cytomegalovirus inhibits expression of liver fibrosis related cytokines in patients chronically infected with hepatitis C virus genotype 4a

BACKGROUND

The impact of human cytomegalovirus (HCMV) reactivation on the expression pattern of matrix metalloproteinases, their inhibitors and related cytokines during HCV infection poorly understood.

METHODS

Reactivation of CMV in 95 subjects (75 chronically infected HCV patients and 20 healthy subjects) was examined. All studied subjects had detectable IgG antibodies for CMV, but only 35/75 of HCV patients (46.7%) had detectable CMV DNA. The expressions of 11 fibrosis related genes by quantitative real-time PCR were analyzed in subjects' PBMCs. The serum levels of TGFβ2 and PDGFα have been measured by ELISA.

RESULTS

Chronically infected HCV patients with reactivated CMV had less expression of TGF-β1, TGF-β2, PDGFα and STAT1 transcripts than HCV patients with latent CMV (p = 0.037, 0.006, 0.001 and 0.009; respectively) and normal controls (TGF-β2, p = 0.008). Moreover the expression of (TGFβ2 and PDGFα) genes decreased significantly in CMV-reactivated patients during the early stage of fibrosis relative to the comparable stage of HCV infection (p = 0.004 and 0.008; respectively). Besides, the mRNA abundance of STAT1 gene in CMV-reactivated patients decreased dramatically as compared to HCV infections during the late stage of fibrosis (p = 0.014). The TGFβ2 protein level has been declined dramatically in CMV-reactivated patients compared to HCV infected patients and control group (p = 0.001 and 0.033; respectively). Our results suggest that CMV reactivation disrupts the expression of several cytokines as compared to solitary infection with HCV. Noticeably, the expressions of matrix metalloproteinases genes and their inhibitors have not been significantly influenced by reactivation of CMV.

CONCLUSION

The current data reveal that reactivation of CMV partially blocks the upregulation of 2 important pro-inflammatory cytokines i.e. TGFβ 2 and PDGFα at early stages of fibrosis, moreover this CMV mediated blockage of the STAT1 shows statistical significance at late stage of fibrosis.

Influence of nitrogen availability on Cd accumulation and acclimation strategy of Populus leaves under Cd exposure

Nitrogen (N) plays crucial roles in chlorophyll concentration, photosynthesis, and stress tolerance of plant leaves. This study conducted a greenhouse experiment combined with Cd and N treatments to elucidate the mechanism underlying the influence of N on Cd accumulation and acclimation strategy in Populus leaves. Chlorophyll concentration and net photosynthetic rates (A) in leaves were unaltered by Cd exposure regardless of N condition. Nitrogen availability alter acclimation strategy of poplar leaves under cadmium exposure. Under sufficient N, Cd accumulation in leaves was elevated with increased intensity and duration of Cd exposure; Cd accumulation reached ca. 28 μg g^-1 dry weight and 260 μg plant^-1 after 60 days of exposure to high level of Cd (20 mg Cd kg^-1 soil), and this finding indicates a large potential for Cd phytoextraction. Poplar leaves exhibited high capacity for antioxidant defense and stress tolerance and avoided oxidative damage under high Cd exposure. The levels of phytohormones and antioxidants in leaves and the relative expressions of critical genes encoding antioxidant enzymes were up-regulated under sufficient N condition. Nitrogen deficiency decreased chlorophyll concentration and net photosynthetic rates (A) and interfered with the production of N metabolites, resulting in a low level of phytohormones and antioxidants that are responsible for stress tolerance. The low levels of Cd accumulation in leaves may be a self-protecting strategy to prevent severe oxidative damage due to the decreased capacities for stress tolerance under N deficiency.

Salicylic Acid Signals Plant Defence against Cadmium Toxicity

Salicylic acid (SA), as an enigmatic signalling molecule in plants, has been intensively studied to elucidate its role in defence against biotic and abiotic stresses. This review focuses on recent research on the role of the SA signalling pathway in regulating cadmium (Cd) tolerance in plants under various SA exposure methods, including pre-soaking, hydroponic exposure, and spraying. Pretreatment with appropriate levels of SA showed a mitigating effect on Cd damage, whereas an excessive dose of exogenous SA aggravated the toxic effects of Cd. SA signalling mechanisms are mainly associated with modification of reactive oxygen species (ROS) levels in plant tissues. Then, ROS, as second messengers, regulate a series of physiological and genetic adaptive responses, including remodelling cell wall construction, balancing the uptake of Cd and other ions, refining the antioxidant defence system, and regulating photosynthesis, glutathione synthesis and senescence. These findings together elucidate the expanding role of SA in phytotoxicology.

Root Proteomics Reveals the Effects of Wood Vinegar on Wheat Growth and Subsequent Tolerance to Drought Stress

Wood vinegar (WV) or pyroligneous acid (PA) is a reddish-brown liquid created during the dry distillation of biomass, a process called pyrolysis. WV contains important biologically active components, which can enhance plant growth and tolerance to drought stress. However, its mechanism of action remains unknown. Our results after presoaking wheat seeds with various concentrations of WV indicate that a 1:900 WV concentration can significantly enhance growth. To investigate the response of wheat roots to drought stress, we compared quantitative proteomic profiles in the roots of wheat plants grown from seeds either presoaked (treatment) or non-presoaked (control) with WV. Our results indicated that the abscisic acid (ABA) content of wheat roots in the WV treatment was significantly increased. Reactive oxygen species (ROS) and malonaldehyde (MDA) levels roots were significantly lower than in the control treatment under drought stress, while the activity of major antioxidant enzymes was significantly increased. Two-dimensional electrophoresis (2D-PAGE) identified 138 differentially accumulated protein (DAP) spots representing 103 unique protein species responding to drought stress in wheat roots of the control and WV-treated groups. These DAPs are mostly involved in the stress response, carbohydrate metabolism, protein metabolism, and secondary metabolism. Proteome profiles showed the DAPs involved in carbohydrate metabolism, stress response, and secondary metabolism had increased accumulation in roots of the WV-treated groups. These findings suggest that the roots from wheat seeds presoaked with WV can initiate an early defense mechanism to mitigate drought stress. These results provide an explanation of how WV enhances the tolerance of wheat plants to drought stress.

Coordinated effects of lead toxicity and nutrient deprivation on growth, oxidative status, and elemental composition of primed and non-primed rice seedlings

Rice crop is highly susceptible to the toxic levels of lead (Pb) during early growth stages. Moreover, a sufficient availability of mineral nutrients is critical for survival of plants particularly under stressful conditions. An experiment was carried out to unravel the coordinated effects of Pb stress (1-mM PbCl₂) and different nutrient treatments (sufficient nutrient supply, nitrogen (N) deprivation, phosphorus (P) deprivation, and potassium (K) deprivation) on morphological growth, reactive oxygen species (ROS), antioxidants, and nutrient status in primed and non-primed rice seedlings. Seeding were primed with distilled water, 60-μM selenium, or 100-mg L^-1 salicylic acid. Results indicated that Pb toxicity did not affect the root growth, but severely reduced the shoot growth (length and biomass) of rice in N- or P-deprived seedlings. Rice seedlings grown with sufficient supply of nutrients or K-deprivation showed no growth reduction under Pb toxicity. Exposure of Pb stress triggered the production of ROS (H₂O₂, O₂˙^-, OH^-) and lipid peroxidation rate particularly under N- or P-deprivation. Moreover, the shoot accumulations of macronutrients (P in particular) were also restricted under Pb toxicity. Seed priming treatments effectively alleviated the undesirable effects of Pb stress on rice growth. The primed rice seedlings showed minimal oxidative damage caused by excessive generation of ROS under Pb stress and/or nutrient deprivation. Seed priming strengthened the antioxidative defense system of rice seedlings by regulating the activities/levels of superoxide dismutase, catalase, peroxidase, and glutathione in rice leaves. Moreover, better accumulation of essential nutrients in primed rice seedlings prevented the excess uptake and translocation of Pb, as evident by the lowered shoot accumulation of Pb.

Relationship of Melatonin and Salicylic Acid in Biotic/Abiotic Plant Stress Responses

Melatonin (N-acetyl-5-methoxytryptamine) was discovered in plants in 1995, while salicylic acid was the name given to the active ingredient of willow in 1838. From a physiological point of view, these two molecules present in plants have never been compared, even though they have a great number of similarities, as we shall see in this work. Both molecules have biosynthesis pathways that share a common precursor and both play a relevant role in the physiology of plants, especially in aspects related to biotic and abiotic stress. They have also been described as biostimulants of photosynthetic processes and productivity enhancers in agricultural crops. We review the coincident aspects of both molecules, and propose an action model, by which the relationship between these molecules and other agents and plant hormones can be studied.

Identification and characterization of evolutionarily conserved alternative splicing events in a mangrove genus Sonneratia

Alternative splicing (AS), which produces multiple mRNA transcripts from a single gene, plays crucial roles in plant growth, development and environmental stress responses. Functional significances of conserved AS events among congeneric species have not been well characterized. In this study, we performed transcriptome sequencing to characterize AS events in four common species of Sonneratia, a mangrove genus excellently adaptive to intertidal zones. 7,248 to 12,623 AS events were identified in approximately 25% to 35% expressed genes in the roots of the four species. The frequency of AS events in Sonneratia was associated with genomic features, including gene expression level and intron/exon number and length. Among the four species, 1,355 evolutionarily conserved AS (ECAS) events were identified from 1,170 genes. Compared with non-ECAS events, ECAS events are of shorter length and less possibility to introduce premature stop codons (PTCs) and frameshifts. Functional annotations of the genes containing ECAS events showed that four of the 26 enriched Gene Ontology (GO) terms are involved in proton transport, signal transduction and carbon metabolism, and 60 genes from another three GO terms are implicated in responses to osmotic, oxidative and heat stresses, which may contribute to the adaptation of Sonneratia species to harsh intertidal environments.

Arsenic Uptake, Toxicity, Detoxification, and Speciation in Plants: Physiological, Biochemical, and Molecular Aspects

Environmental contamination with arsenic (As) is a global environmental, agricultural and health issue due to the highly toxic and carcinogenic nature of As. Exposure of plants to As, even at very low concentration, can cause many morphological, physiological, and biochemical changes. The recent research on As in the soil-plant system indicates that As toxicity to plants varies with its speciation in plants (e.g., arsenite, As(III); arsenate, As(V)), with the type of plant species, and with other soil factors controlling As accumulation in plants. Various plant species have different mechanisms of As(III) or As(V) uptake, toxicity, and detoxification. This review briefly describes the sources and global extent of As contamination and As speciation in soil. We discuss different mechanisms responsible for As(III) and As(V) uptake, toxicity, and detoxification in plants, at physiological, biochemical, and molecular levels. This review highlights the importance of the As-induced generation of reactive oxygen species (ROS), as well as their damaging impacts on plants at biochemical, genetic, and molecular levels. The role of different enzymatic (superoxide dismutase, catalase, glutathione reductase, and ascorbate peroxidase) and non-enzymatic (salicylic acid, proline, phytochelatins, glutathione, nitric oxide, and phosphorous) substances under As(III/V) stress have been delineated via conceptual models showing As translocation and toxicity pathways in plant species. Significantly, this review addresses the current, albeit partially understood, emerging aspects on (i) As-induced physiological, biochemical, and genotoxic mechanisms and responses in plants and (ii) the roles of different molecules in modulation of As-induced toxicities in plants. We also provide insight on some important research gaps that need to be filled to advance our scientific understanding in this area of research on As in soil-plant systems.

Exogenous salicylic acid-mediated modulation of arsenic stress tolerance with enhanced accumulation of secondary metabolites and improved size of glandular trichomes in Artemisia annua L

The present study was undertaken to find out individual and interactive effects of arsenic (As) and salicylic acid (SA) on an important medicinal plant, Artemisia annua. As uptake and its accumulation was detected and found to be maximum in roots at higher As concentration (150 μM). Under As treatments, H₂O₂ and MDA content were induced. Biomass and chlorophyll content were negatively affected under As treatments. Furthermore, enzymatic (SOD, CAT, APX, and GR) and non-enzymatic antioxidants were also enhanced under As treatments. Exogenous application of SA reduced the extent of H₂O₂ and O₂^- generation and lipid peroxidation, while reverted biomass and chlorophyll content to overcome oxidative stress. Simultaneous application of SA with As increased endogenous SA level, artemisinin, and dihydroartemisinic acid as compared with individual As treatment and pre-application of SA with As treatments. The expression of four key artemisinin biosynthetic pathway genes, i.e., ADS, CYP71AV1, DBR2, and ALDH1 were upregulated at a maximum in plants simultaneously treated with SA and As. Similar pattern of artemisinin accumulation and glandular trichome size was observed which attest that SA has a stimulatory impact on artemisinin biosynthesis under As stress. Our study suggests that exogenous application of SA and As together induced more tolerance in A. annua than a comparable dose of SA pre-treatment. The study may provide a platform with dual benefits by developing As-tolerant plants to be used for phytoremediation of arsenic from As-contaminated soil and obtaining high artemisinin-producing A. annua plants.

Protective effect exerted by soil phosphorus on soybean subjected to arsenic and fluoride

Objetive: Arsenic (As) and fluoride (F) are found in groundwater and soils around the world, causing different problems to crops. Because these elements compete against phosphorus (P) in soils and plants, their relationship is complex. The aim of this work was to study the oxidative stress of soybean plants subjected to different concentrations of As and F, and the effect of P.

METHODS

The following 10 treatments were carried out in each of two soils with different P content: three As levels (low 10 mg As kg-1, medium 50 mg As kg-1 and high 100 mg As kg-1), three F levels (low 160 mg F kg-1, medium 250 mg F kg-1 and high 500 mg F kg-1) and three As + F levels (same concentrations), and the control treatment (soil with the background As and F concentrations) Lipid peroxidation, chlorophyll, gluthatione contents and antioxidant enzymes activities were determination.

RESULTS

Increased lipid peroxidation and alterations in glutathione content, catalase, superoxide dismutase and peroxidase activities as well as in chlorophyll content revealed that As causes higher oxidative stress in plants grown in soils with low P content.

CONCLUSION

Stress parameters in F treatments were less affected. Plants grown in soils enriched with P revealed a decrease in the toxic effects caused by As and F.

A critical review on effects, tolerance mechanisms and management of cadmium in vegetables

Cadmium (Cd) accumulation in vegetables is an important environmental issue that threatens human health globally. Understanding the response of vegetables to Cd stress and applying management strategies may help to reduce the Cd uptake by vegetables. The aim of the present review is to summarize the knowledge concerning the uptake and toxic effects of Cd in vegetables and the different management strategies to combat Cd stress in vegetables. Leafy vegetables grown in Cd contaminated soils potentially accumulate higher concentrations of Cd, posing a threat to food commodities. The Cd toxicity decreases seed germination, growth, biomass and quality of vegetables. This reduces the photosynthesis, stomatal conductance and alteration in mineral nutrition. Toxicity of Cd toxicity also interferes with vegetable biochemistry causing oxidative stress and resulting in decreased antioxidant enzyme activities. Several management options have been employed for the reduction of Cd uptake and toxicity in vegetables. The exogenous application of plant growth regulators, proper mineral nutrition, and the use of organic and inorganic amendments might be useful for reducing Cd toxicity in vegetables. The use of low Cd accumulating vegetable cultivars in conjunction with insolubilizing amendments and proper agricultural practices might be a useful technique for reducing Cd exposure in the food chain.

Salicylic acid nanoparticles (SANPs) improve growth and phytoremediation efficiency of Isatis cappadocica Desv., under As stress

Arsenic (As) is a toxic metalloid dispersed in the environment and it cause serious toxicity to plants. Salicylic acid (SA) plays an important role in many plant growth processes involved in plant defence against heavy metal or metalloid stress. In the present study, for the first time, chitosan nanoparticles was synthesised, loaded by SA and the positive role of SA on growth and phytoremediation efficiency of Isatis cappadocica against As toxicity were evaluated. The highest arsenate treatment (1200 µM) caused a decrease in plant biomass that, however, its combined application with salicylic acid nanoparticles (SANPs) substantially increase in shoot height, root length and their biomass production compared with As stressed plants. The pretreatment of SANPs by increasing arsenate supply, simultaneously increased the As concentration in roots and shoots of I. cappadocica which reached a maximum of 705 and 1188 mg/kg, respectively. This results suggest that high levels of As stress induce stress status in I. cappadocica which SANPs pretreatment application limit these toxic effects of As. Therefore, SANPs has a significant beneficial effect on the growth and phytoremediation efficiency of I. cappadocica subjected to As stress.

Indications of Selenium Protection against Cadmium and Lead Toxicity in Oilseed Rape (Brassica napus L.)

The present study investigated the beneficial role of selenium (Se) in protecting oilseed rape (Brassica napus L.) plants from cadmium (Cd+2) and lead (Pb+2) toxicity. Exogenous Se markedly reduced Cd and Pb concentration in both roots and shoots. Supplementation of the medium with Se (5, 10, and 15 mg kg-1) alleviated the negative effect of Cd and Pb on growth and led to a decrease in oxidative damages caused by Cd and Pb. Furthermore, Se-enhanced superoxide free radicals ([Formula: see text]), hydrogen peroxide (H2O2), and lipid peroxidation, as indicated by malondialdehyde accumulation, but decreased superoxide dismutase and glutathione peroxidase activities. Meanwhile, the presence of Cd and Pb in the medium affected Se speciation in shoots. The results suggest that Se could alleviate Cd and Pb toxicity by preventing oxidative stress in oilseed rape plant.

Role of salicylic acid in resistance to cadmium stress in plants

We review and introduce the importance of salicylic acid in plants under cadmium stress, and provide insights into potential regulatory mechanisms for alleviating cadmium toxicity. Cadmium (Cd) is a widespread and potentially toxic environmental pollutant, originating mainly from rapid industrial processes, the application of fertilizers, manures and sewage sludge, and urban activities. It is easily taken up by plants, resulting in obvious toxicity symptoms, including growth retardation, leaf chlorosis, leaf and root necrosis, altered structures and ultrastructures, inhibition of photosynthesis, and cell death. Therefore, alleviating Cd toxicity in plants is a major aim of plant research. Salicylic acid (SA) is a ubiquitous plant phenolic compound that has been used in many plant species to alleviate Cd toxicity by regulating plant growth, reducing Cd uptake and distribution in plants, protecting membrane integrity and stability, scavenging reactive oxygen species and enhancing antioxidant defense system, improving photosynthetic capacity. Furthermore, SA functions as a signaling molecule involved in the expression of several important genes. Significant amounts of research have focused on understanding SA functions and signaling in plants under Cd stress, but several questions still remain unanswered. In this article, the influence of SA on Cd-induced stress in plants and the potential regulation mechanism for alleviating Cd toxicity are reviewed.

Role of Ethylene and Its Cross Talk with Other Signaling Molecules in Plant Responses to Heavy Metal Stress

Excessive heavy metals (HMs) in agricultural lands cause toxicities to plants, resulting in declines in crop productivity. Recent advances in ethylene biology research have established that ethylene is not only responsible for many important physiological activities in plants but also plays a pivotal role in HM stress tolerance. The manipulation of ethylene in plants to cope with HM stress through various approaches targeting either ethylene biosynthesis or the ethylene signaling pathway has brought promising outcomes. This review covers ethylene production and signal transduction in plant responses to HM stress, cross talk between ethylene and other signaling molecules under adverse HM stress conditions, and approaches to modify ethylene action to improve HM tolerance. From our current understanding about ethylene and its regulatory activities, it is believed that the optimization of endogenous ethylene levels in plants under HM stress would pave the way for developing transgenic crops with improved HM tolerance.

Salicylic acid-induced abiotic stress tolerance and underlying mechanisms in plants

Abiotic stresses (such as metals/metalloids, salinity, ozone, UV-B radiation, extreme temperatures, and drought) are among the most challenging threats to agricultural system and economic yield of crop plants. These stresses (in isolation and/or combination) induce numerous adverse effects in plants, impair biochemical/physiological and molecular processes, and eventually cause severe reductions in plant growth, development and overall productivity. Phytohormones have been recognized as a strong tool for sustainably alleviating adverse effects of abiotic stresses in crop plants. In particular, the significance of salicylic acid (SA) has been increasingly recognized in improved plant abiotic stress-tolerance via SA-mediated control of major plant-metabolic processes. However, the basic biochemical/physiological and molecular mechanisms that potentially underpin SA-induced plant-tolerance to major abiotic stresses remain least discussed. Based on recent reports, this paper: (a) overviews historical background and biosynthesis of SA under both optimal and stressful environments in plants; (b) critically appraises the role of SA in plants exposed to major abiotic stresses;

Minimising toxicity of cadmium in plants--role of plant growth regulators

A range of man-made activities promote the enrichment of world-wide agricultural soils with a myriad of chemical pollutants including cadmium (Cd). Owing to its significant toxic consequences in plants, Cd has been one of extensively studied metals. However, sustainable strategies for minimising Cd impacts in plants have been little explored. Plant growth regulators (PGRs) are known for their role in the regulation of numerous developmental processes. Among major PGRs, plant hormones (such as auxins, gibberellins, cytokinins, abscisic acid, jasmonic acid, ethylene and salicylic acid), nitric oxide (a gaseous signalling molecule), brassinosteroids (steroidal phytohormones) and polyamines (group of phytohormone-like aliphatic amine natural compounds with aliphatic nitrogen structure) have gained attention by agronomist and physiologist as a sustainable media to induce tolerance in abiotic-stressed plants. Considering recent literature, this paper: (a) overviews Cd status in soil and its toxicity in plants, (b) introduces major PGRs and overviews their signalling in Cd-exposed plants, (c) appraises mechanisms potentially involved in PGR-mediated enhanced plant tolerance to Cd and (d) highlights key aspects so far unexplored in the subject area.

Salicylic acid modulates arsenic toxicity by reducing its root to shoot translocation in rice (Oryza sativa L.)

Arsenic (As) is posing serious health concerns in South East Asia where rice, an efficient accumulator of As, is prominent crop. Salicylic acid (SA) is an important signaling molecule and plays a crucial role in resistance against biotic and abiotic stress in plants. In present study, ameliorative effect of SA against arsenate (As(V)) toxicity has been investigated in rice (Oryza sativa L.). Arsenate stress hampered the plant growth in terms of root, shoots length, and biomass as well as it enhanced the level of H2O2 and MDA in dose dependent manner in shoot. Exogenous application of SA, reverted the growth, and oxidative stress caused by As(V) and significantly decreased As translocation to the shoots. Level of As in shoot was positively correlated with the expression of OsLsi2, efflux transporter responsible for root to shoot translocation of As in the form of arsenite (As(III)). SA also overcame As(V) induced oxidative stress and modulated the activities of antioxidant enzymes in a differential manner in shoots. As treatment hampered the translocation of Fe in the shoot which was compensated by the SA treatment. The level of Fe in root and shoot was positively correlated with the transcript level of transporters responsible for the accumulation of Fe, OsNRAMP5, and OsFRDL1, in the root and shoot, respectively. Co-application of SA was more effective than pre-treatment for reducing As accumulation as well as imposed toxicity.

Exogenous abscisic acid alleviates zinc uptake and accumulation in Populus × canescens exposed to excess zinc

A greenhouse experiment was conducted to study whether exogenous abscisic acid (ABA) mediates the responses of poplars to excess zinc (Zn). Populus × canescens seedlings were treated with either basal or excess Zn levels and either 0 or 10 μm ABA. Excess Zn led to reduced photosynthetic rates, increased Zn accumulation, induced foliar ABA and salicylic acid (SA), decreased foliar gibberellin (GA3 ) and auxin (IAA), elevated root H2 O2 levels, and increased root ratios of glutathione (GSH) to GSSG and foliar ratios of ascorbate (ASC) to dehydroascorbate (DHA) in poplars. While exogenous ABA decreased foliar Zn concentrations with 7 d treatments, it increased levels of endogenous ABA, GA3 and SA in roots, and resulted in highly increased foliar ASC accumulation and ratios of ASC to DHA. The transcript levels of several genes involved in Zn uptake and detoxification, such as yellow stripe-like family protein 2 (YSL2) and plant cadmium resistance protein 2 (PCR2), were enhanced in poplar roots by excess Zn but repressed by exogenous ABA application. These results suggest that exogenous ABA can decrease Zn concentrations in P. × canescens under excess Zn for 7 d, likely by modulating the transcript levels of key genes involved in Zn uptake and detoxification.

H2O2 pretreated rice seedlings specifically reduces arsenate not arsenite: difference in nutrient uptake and antioxidant defense response in a contrasting pair of rice cultivars

The study investigated the reduction in metalloid uptake at equimolar concentrations (~53.3 μM) of As(III) and As(V) in contrasting pair of rice seedlings by pretreating with H2O2 (1.0 μM) and SA (1.0 mM). Results obtained from the contrasting pair (arsenic tolerant vs. sensitive) of rice seedlings (cv. Pant Dhan 11 and MTU 7029, respectively) shows that pretreatment of H2O2 and H2O2 + SA reduces As(V) uptake significantly in both the cultivars, while no reduction in the As(III) uptake. The higher growth inhibition, higher H2O2 and TBARS content in sensitive cultivar against As(III) and As(V) treatments along with higher As accumulation (~1.2 mg g(-1) dw) than in cv. P11, unravels the fundamental difference in the response between the sensitive and tolerant cultivar. In the H2O2 pretreated plants, the translocation of As increased in tolerant cultivar against AsIII, whereas, it decreased in sensitive cultivar both against AsIII and AsV. In both the cultivars translocation of Mn increased in the H2O2 pretreated plants against As(III), whereas, the translocation of Cu increased against As(V). In tolerant cultivar the translocation of Fe increased against As(V) with H2O2 pretreatment whereas, it decreased in the sensitive cultivar. In both the cultivars, Zn translocation increased against As(III) and decreased against As(V). The higher level of H2O2 and SOD (EC 1.15.1.1) activity in sensitive cultivar whereas, higher, APX (EC 1.11.1.11), GR (EC 1.6.4.2) and GST (EC 1.6.4.2) activity in tolerant cultivar, also demonstrated the differential anti-oxidative defence responses between the contrasting rice cultivars.

Higher sensitivity of pad2-1 and vtc2-1 mutants to cadmium is related to lower subcellular glutathione rather than ascorbate contents

Cadmium (Cd) interferes with ascorbate and glutathione metabolism as it induces the production of reactive oxygen species (ROS), binds to glutathione due to its high affinity to thiol groups, and induces the production of phytochelatins (PCs) which use glutathione as a precursor. In this study, changes in the compartment specific distribution of ascorbate and glutathione were monitored over a time period of 14 days in Cd-treated (50 and 100 μM) Arabidopsis Col-0 plants, and two mutant lines deficient in glutathione (pad2-1) and ascorbate (vtc2-1). Both mutants showed higher sensitivity to Cd than Col-0 plants. Strongly reduced compartment specific glutathione, rather than decreased ascorbate contents, could be correlated with the development of symptoms in these mutants suggesting that higher sensitivity to Cd is related to low glutathione contents rather than low ascorbate contents. On the subcellular level it became obvious that long-term treatment of wildtype plants with Cd induced the depletion of glutathione and ascorbate contents in all cell compartments except chloroplasts indicating an important protective role for antioxidants in chloroplasts against Cd. Additionally, we could observe an immediate decrease of glutathione and ascorbate in all cell compartments 12 h after Cd treatment indicating that glutathione and ascorbate are either withdrawn from or not redistributed into other organelles after their production in chloroplasts, cytosol (production centers for glutathione) and mitochondria (production center for ascorbate). The obtained data is discussed in respect to recently proposed stress models involving antioxidants in the protection of plants against environmental stress conditions.

Behind the scenes: the roles of reactive oxygen species in guard cells

Guard cells regulate stomatal pore size through integration of both endogenous and environmental signals; they are widely recognized as providing a key switching mechanism that maximizes both the efficient use of water and rates of CO₂ exchange for photosynthesis; this is essential for the adaptation of plants to water stress. Reactive oxygen species (ROS) are widely considered to be an important player in guard cell signalling. In this review, we focus on recent progress concerning the role of ROS as signal molecules in controlling stomatal movement, the interaction between ROS and intrinsic and environmental response pathways, the specificity of ROS signalling, and how ROS signals are sensed and relayed. However, the picture of ROS-mediated signalling is still fragmented and the issues of ROS sensing and the specificity of ROS signalling remain unclear. Here, we review some recent advances in our understanding of ROS signalling in guard cells, with an emphasis on the main players known to interact with abscisic acid signalling.