Exogenous calcium induces tolerance to atrazine stress in Pennisetum seedlings and promotes photosynthetic activity, antioxidant enzymes and psbA gene transcripts

Deciphering the alleviation potential of nitric oxide, for low temperature and chromium stress via maintaining photosynthetic capacity, antioxidant defence, and redox homeostasis in rice (Oryza sativa)

Sodium nitroprusside (SNP) is a potent nitric oxide (NO) donor that enhances plant tolerance to various abiotic stresses. This research aims to assess the effect of SNP application on rice seedlings subjected to individual and combined exposure to two abiotic stresses viz., low-temperature (LT) and chromium (Cr). Exposure to LT, Cr, and LT+Cr caused severe oxidative damage by stimulating greater production and accumulation of reactive oxygen species (ROS) leading to lipid peroxidation and cell membrane instability. The combined LT+CR stress more intensly increased the cellular oxidative stress and excessive Cr uptake that in turn deteriorated the chlorophyll pigments and photosynthesis, as well as effected the level of tetrapyrrole biosynthesis in rice plants. The reduction in rice seedling growth was more obvious under LT+Cr treatment than their individual effects. The exogenous application of SNP diminished the toxic impact of LT and Cr stress. This was attributed to the positive role of SNP in regulating the endogenous NO levels, free amino acids (FAAs) contents, tetrapyrrole biosynthesis and antioxidants. Consequently, SNP-induced NO decreased photorespiration, ROS generation, lipid peroxidation, and electrolyte leakage. Moreover, exogenous SNP diminished the Cr uptake and accumulation by modulating the ionic homeostasis and strengthening the heavy metals detoxification mechanism, thus improving plant height, biomass and photosynthetic indexes. Essentially, SNP boosts plant tolerance to LT and Cr stress by regulating antioxidants, detoxification mechanism, and the plant's physio-biochemical. Hence, applying SNP is an effective method for boosting rice plant resilience and productivity in the face of escalating environmental stresses and pollutants.

The role of reactive oxygen species in regulation of the plasma membrane H+-ATPase activity in Masson pine (Pinus massoniana Lamb.) roots responding to acid stress

To understand the role of reactive oxygen species (ROS) in regulation of the plasma membrane (PM) H+-ATPase in acid-stressed Masson pine roots, different acidity (pH 6.6 as the control, pH 5.6 and pH 4.6) of simulated acid rain (SAR) added with and without external chemicals (H2O2, enzyme inhibitors and ROS scavenger) was prepared. After 30 days of SAR exposure, the plant morphological phenotype attributes, levels of cellular ROS and lipid peroxidation, enzymatic activities of antioxidants, PM nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity and PM H+-ATPase activity in pine seedlings were measured. Compared with the control, the growth of pine seedlings exposed to SAR in the presence or absence of H2O2 was well-maintained, but the application of Na3VO4, 1,3-dimethyl-2-thiourea, N, N-dimethylthiourea (DMTU) and diphenyleneiodonium chloride (DPI) caused a substantial growth inhibition. In addition, SAR exposure, SAR with H2O2 treatment, and SAR with Na3VO4 treatment increased the cellular H2O2 content, O2- content and malondialdehyde (MDA) content, while the use of DMTU and DPI lead to relatively low levels. Similarly, the enzymatic activities of antioxidants, PM NADPH oxidase and PM H+-ATPase in acid stressed pine seedlings elevated with the increasing acidity. A significant stimulation of these enzymatic activities obtained from SAR with H2O2 treatment was observed, whereas which decreased obviously with the addition of Na3VO4, DMTU and DPI (P < 0.05). Moreover, a positive correlation was found between plant morphological attributes and the PM H+-ATPase activity (P < 0.05). Besides, the PM H+-ATPase activity positively correlated with the cellular ROS contents and the enzymatic activities of antioxidants and PM NADPH oxidase (P < 0.05). Therefore, the PM H+-ATPase is instrumental in the growth of pine seedlings resisting to acid stress by enhancing its activity. The process involves the signaling transduction of cellular ROS and coordination with PM NADPH oxidase.

Emerging technologies for the removal of pesticides from contaminated soils and their reuse in agriculture

Pesticides are becoming more prevalent in agriculture to protect crops and increase crop yields. However, nearly all pesticides used for this purpose reach non-target crops and remain as residues for extended periods. Contamination of soil by widespread pesticide use, as well as its toxicity to humans and other living organisms, is a global concern. This has prompted us to find solutions and develop alternative remediation technologies for sustainable management. This article reviews recent technological developments for remediating pesticides from contaminated soil, focusing on the following major points: (1) The application of various pesticide types and their properties, the sources of pesticides related to soil pollution, their transport and distribution, their fate, the impact on soil and human health, and the extrinsic and intrinsic factors that affect the remediation process are the main points of focus. (2) Sustainable pesticide degradation mechanisms and various emerging nano- and bioelectrochemical soil remediation technologies. (3) The feasible and long-term sustainable research and development approaches that are required for on-site pesticide removal from soils, as well as prospects for applying them directly in agricultural fields. In this critical analysis, we found that bioremediation technology has the potential for up to 90% pesticide removal from the soil. The complete removal of pesticides through a single biological treatment approach is still a challenging task; however, the combination of electrochemical oxidation and bioelectrochemical system approaches can achieve the complete removal of pesticides from soil. Further research is required to remove pesticides directly from soils in agricultural fields on a large-scale.

Therapeutic potential of salvigenin to combat atrazine induced liver toxicity in rats via regulating Nrf-2/Keap-1 and NF-κB pathway

Atrazine (ATR) is the second most extensively used herbicide which adversely affects the body organs including liver. Salvigenin (SGN) is a flavonoid which demonstrates a wide range of biological and pharmacological abilities. This study was planned to assess the protective ability of SGN to avert ATR induced liver damage in rats. Thirty-two rats (Rattus norvegicus) were divided into four groups including control, ATR (5 mg/kg), ATR (5 mg/kg) + SGN (10 mg/kg) and SGN (10 mg/kg) alone supplemented group. ATR exposure reduced the expression of Nrf-2 while instigating an upregulation in Keap-1 expression. Furthermore, the activities of catalase (CAT), glutathione peroxidase (GPx), superoxide dismutase (SOD), heme‑oxygenase-1 (HO-1) and glutathione reductase (GSR) contents were decreased while increasing reactive oxygen species (ROS) and malondialdehyde (MDA) levels after ATR treatment. Moreover, ATR poisoning increased the levels of ALT, AST, and ALP while reducing the levels of total proteins, and albumin in hepatic tissues of rats. Besides, ATR administration escalated the expressions of Bax and Caspase-3 while inducing a downregulation in the expressions of Bcl-2. Similarly, ATR intoxication increased the levels of Interleukin-6 (IL-6), Nuclear factor kappa-B (NF-κB), Interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and the activity of cyclooxygenase-2 (COX-2). Furthermore, ATR disrupted the normal histology of hepatic tissues. However, SGN treatment remarkably protected the liver tissues via regulating antioxidant, anti, inflammatory, anti-apoptotic as well as histology parameters. Therefore, it is concluded that SGN can be used as therapeutic agent to combat ATR-induced hepatotoxicity.

Physiological and molecular mechanisms of the inhibitory effects of artemisinin on Microcystis aeruginosa and Chlorella pyrenoidosa

Artemisinin, a novel plant allelochemical, has attracted attention for its potential selective inhibitory effects on algae, yet to be fully explored. This study compares the sensitivity and action targets of Microcystis aeruginosa (M. aeruginosa) and Chlorella pyrenoidosa (C. pyrenoidosa) to artemisinin algaecide (AMA), highlighting their differences. Results indicate that at high concentrations, AMA displaces the natural PQ at the QB binding site within M. aeruginosa photosynthetic system, impairing the D1 protein repair function. Furthermore, AMA disrupts electron transfer from reduced ferredoxin (Fd) to NADP+ by interfering with the iron-sulfur clusters in the ferredoxin-NADP+ reductases (FNR) domain of Fd. Moreover, significant reactive oxygen species (ROS) accumulation triggers oxidative stress and interrupts the tricarboxylic acid cycle, hindering energy acquisition. Notably, AMA suppresses arginine synthesis in M. aeruginosa, leading to reduced microcystins (MCs) release. Conversely, C. pyrenoidosa counters ROS accumulation via photosynthesis protection, antioxidant defenses, and by regulating intracellular osmotic pressure, accelerating damaged protein degradation, and effectively repairing DNA for cellular detoxification. Additionally, AMA stimulates the expression of DNA replication-related genes, facilitating cell proliferation. Our finding offer a unique approach for selectively eradicating cyanobacteria while preserving beneficial algae, and shed new light on employing eco-friendly algicides with high specificity.

Zinc Oxide Nanoparticles and Vitamin C Ameliorate Atrazine-Induced Hepatic Apoptosis in Rat via CYP450s/ROS Pathway and Immunomodulation

Atrazine, as an herbicide, is used widely worldwide. Because of its prolonged persistence in the environment and accumulation in the body, atrazine exposure is a potential threat to human health. The present study evaluated the possible protective effects of zinc oxide nanoparticles and vitamin C against atrazine-induced hepatotoxicity in rats. Atrazine administered to rats orally at a dose of 300 mg/kg for 21 days caused liver oxidative stress as it increased malondialdehyde (MDA) formation and decreased reduced glutathione (GSH) contents. Atrazine induced inflammation accompanied by apoptosis via upregulation of hepatic gene expression levels of NF-κB, TNF-α, BAX, and caspase-3 and downregulation of Bcl-2 gene expression levels. Additionally, it disturbed the metabolic activities of cytochrome P450 as it downregulated hepatic gene expression levels of CYP1A1, CYP1B1, CYP2E1. The liver function biomarkers were greatly affected upon atrazine administration, and the serum levels of AST and ALT were significantly increased, while BWG%, albumin, globulins, and total proteins levels were markedly decreased. As a result of the above-mentioned influences of atrazine, histopathological changes in liver tissue were recorded in our findings. The administration of zinc oxide nanoparticles or vitamin C orally at a dose of 10 mg/kg and 200 mg/kg, respectively, for 30 days prior and along with atrazine, could significantly ameliorate the oxidative stress, inflammation, and apoptosis induced by atrazine and regulated the hepatic cytochrome P450 activities. Furthermore, they improved liver function biomarkers and histopathology. In conclusion, our results revealed that zinc oxide nanoparticles and vitamin C supplementations could effectively protect against atrazine-induced hepatotoxicity.

Assessing phytotoxicity and cyto-genotoxicity of two insecticides using a battery of in-vitro biological assays

Intensive use of chemical pesticides in agriculture poses environmental risks and may have negative impacts on agricultural productivity. The potential phytotoxicity of two chemical pesticides, chlorpyrifos (CPS) and fensulfothion (FSN), were evaluated using Cicer arietinum and Allium cepa as model crops. Different concentrations (0-100 μgmL-1) of both CPS and FSN decreased germination and biological attributes of C. arietinum. High pesticide doses significantly (p ≤ 0.05) caused membrane damage by producing thiobarbituric acid reactive substances (TBARS) and increasing proline (Pro) content. Pesticides elevated ROS levels and substantially increased the superoxide anions and H2O2 concentrations, thus aggravating cell injury. Plants exposed to high pesticide dosages displayed significantly higher antioxidant levels to combat pesticide-induced oxidative stress. Ascorbate peroxidase (APX), guaiacol peroxidase (GPX), catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) increased by 48%, 93%, 71%, 52% and 94%, respectively, in C. arietinum roots exposed to 100 µgFSNmL-1. Under CLSM, pesticide-exposed C. arietinum and 2',7'-dichlorodihydrofluorescein diacetate (2'7'-DCF) and 3,3'-diaminobenzidine stained roots exhibited increased ROS production in a concentration-dependent manner. Additionally, enhanced Rhodamine 123 (Rhd 123) and Evan's blue fluorescence in roots, as well as changes in mitochondrial membrane potential (ΔΨm) and cellular apoptosis, were both associated with high pesticide dose. Allium cepa chromosomal aberration (CAs) assay showed a clear reduction in mitotic index (MI) and numerous chromosomal anomalies in root meristematic cells. Additionally, a-dose-dependent increase in DNA damage in root meristematic cells of A. cepa and conversion of the super-coiled form of DNA to open circular in pBR322 plasmid revealed the genotoxic potential of pesticides. The application of CPS and FSN suggests phytotoxic and cyto-genotoxic effects that emphasize the importance of careful monitoring of current pesticide level in soil before application and addition at optimal levels to soil-plant system. It is appropriate to prepare both target-specific and slow-release agrochemical formulations for crop protection with concurrent safeguarding of agroecosystems.

Exogenously applied sodium nitroprusside alleviates nickel toxicity in maize by regulating antioxidant activities and defense-related gene expression

Nickel (Ni) stress adversely affects plant growth and biomass accumulation, posturing severe menace to crop production and food security. The current study aimed to determine the putative role of sodium nitroprusside (SNP) in mitigating Ni-induced phytotoxicity and identify the underlying defense mechanisms in maize, which are poorly understood. Our findings showed that SNP significantly augmented plant growth, biomass, and photosynthesis-related attributes (Fv/Fm, Fm, qP ETR, and ΦPSII) through diminishing Ni uptake and translocation in root and shoot tissues of maize under Ni stress conditions. In parallel, exogenous SNP substantially relieved maize seedlings from Ni-induced stress by enhancing enzymatic (SOD, CAT, and GPX) and non-enzymatic (phenol and flavonoids) antioxidant defenses and reducing oxidative stress indicators (MDA and H2 O2 ). The results revealed that SNP treatment increased the content of organic osmolyte glycine betaine and the activity of GST, concomitantly with ATP and ionic exchange capacity (including Ca2+ -ATPase and Mg2+ -ATPase), advocating its sufficiency to promote plant growth and avert Ni-induced stress in maize plants. The only exception was the production of organic acids (citric, oxalic, malic, and formic acids), which was reduced as SNP treatment relieved maize seedlings from Ni-induced oxidative damage. The application of SNP also displayed higher expression of defense- and detoxifying-related genes than in control treatments. Together, our data highlighted the mechanism involved in the amelioration of Ni toxicity by SNP; thus, suggesting a potential role of SNP in mitigating the adverse effects of Ni-contaminated soils to boost growth and yield of crop plants, that is, maize.

Amended compost alleviated the stress of heavy metals to pakchoi plants and affected the distribution of heavy metals in soil-plant system

With the development of the social economy, soil heavy metal pollution has become a common worldwide issue. Therefore, the remediation of soil heavy metal pollution is imminent. This study aimed to investigate the effect of amended compost on reducing heavy metal bioavailability in soil and relieving heavy metals stress on plants under Cu and Zn stress in a pot experiment. To model the restoration of heavy metal-polluted farming soil, conventional compost (CKw), activated carbon compost (ACw), modified biochar compost (BCw) and rhamnolipid compost (RLw) were utilized. The results showed that the application of amended compost could promote the growth and quality of pakchoi and enhance the stress ability of malondialdehyde and antioxidant enzymes to heavy metals. The distribution of Cu and Zn in different subcellular parts of pakchoi was also affected. The application of amended compost significantly reduced the heavy metals content in the shoot of pakchoi, among which the content of Cu and Zn in the shoot of pakchoi in RLw was significantly decreased by 57.29% and 60.07%, respectively. Our results can provide a new understanding for efficient remediation of contaminated farmland soil by multiple heavy metals.

Exogenous application of Bradyrhizobium japonicum AC20 enhances soybean tolerance to atrazine via regulating rhizosphere soil microbial community and amino acid, carbohydrate metabolism related genes expression

Atrazine is used to control broad-leaved weeds in farmland and has negative impacts on soybean growth. Legume-rhizobium symbiosis plays an important role in regulating abiotic stress tolerance of plants, however, the mechanisms of rhizobia regulate the tolerance of soybean to atrazine based on the biochemical responses of the plant-soil system are limited. In this experiment, Glycine max (L.) Merr. Dongnong 252, planted in 20 mg kg^-1 of atrazine-contaminated soil, was inoculated with Bradyrhizobium japonicum AC20, and the plant growth, rhizosphere soil microbial diversity and the expression of the genes related to soybean carbon and nitrogen metabolism were assessed. The results indicated that strain AC20 inoculation alleviated atrazine-induced growth inhibition via increasing the contents of leghemoglobin and total nitrogen in soybean seedlings. The psbA gene expression level of the soybean seedlings that inoculated strain AC20 was 1.4 times than that of no rhizobium inoculating treatments. Moreover, the inoculated AC20 increased the abundance of Acidobacteria and Actinobacteria in soybean rhizosphere. Transcriptome analysis demonstrated that strain AC20 regulated the genes expression of amino acid metabolism and carbohydrate metabolism of soybean seedlings. Correlation analysis between 16S rRNA and transcriptome showed that strain AC20 reduced Planctomycetes abundance so as to down-regulated the expression of genes Glyma. 13G087800, Glyma. 12G005100 and Glyma.12G098900 involved in starch synthesis pathway of soybean leaves. These results provide available information for the rhizobia application to enhance the atrazine tolerate in soybean seedlings.

Roles of Calcium Signaling in Gene Expression and Photosynthetic Acclimatization of Solanum lycopersicum Micro-Tom (MT) after Mechanical Damage

A momentary increase in cytoplasmic Ca²⁺ generates an oscillation responsible for the activation of proteins, such as calmodulin and kinases, which interact with reactive oxygen species (ROS) for the transmission of a stress signal. This study investigated the influence of variations in calcium concentrations on plant defense signaling and photosynthetic acclimatization after mechanical damage. Solanum lycopersicum Micro-Tom was grown with 0, 2 and 4 mM Ca²⁺, with and without mechanical damage. The expression of stress genes was evaluated, along with levels of antioxidant enzymes, hydrogen peroxide, lipid peroxidation, histochemistry, photosynthesis and dry mass of organs. The ROS production generated by mechanical damage was further enhanced by calcium-free conditions due to the inactivation of the oxygen evolution complex, contributing to an increase in reactive species. The results indicated that ROS affected mechanical damage signaling because calcium-free plants exhibited high levels of H₂O₂ and enhanced expression of kinase and RBOH1 genes, necessary conditions for an efficient response to stress. We conclude that the plants without calcium supply recognized mechanical damage but did not survive. The highest expression of the RBOH1 gene and the accumulation of H₂O₂ in these plants signaled cell death. Plants grown in the presence of calcium showed higher expression of SlCaM2 and control of H₂O₂ concentration, thus overcoming the stress caused by mechanical damage, with photosynthetic acclimatization and without damage to dry mass production.

Review of the Mechanisms by Which Transcription Factors and Exogenous Substances Regulate ROS Metabolism under Abiotic Stress

Reactive oxygen species (ROS) are signaling molecules that regulate many biological processes in plants. However, excess ROS induced by biotic and abiotic stresses can destroy biological macromolecules and cause oxidative damage to plants. As the global environment continues to deteriorate, plants inevitably experience abiotic stress. Therefore, in-depth exploration of ROS metabolism and an improved understanding of its regulatory mechanisms are of great importance for regulating cultivated plant growth and developing cultivars that are resilient to abiotic stresses. This review presents current research on the generation and scavenging of ROS in plants and summarizes recent progress in elucidating transcription factor-mediated regulation of ROS metabolism. Most importantly, the effects of applying exogenous substances on ROS metabolism and the potential regulatory mechanisms at play under abiotic stress are summarized. Given the important role of ROS in plants and other organisms, our findings provide insights for optimizing cultivation patterns and for improving plant stress tolerance and growth regulation.

Insights into the recent advances in nano-bioremediation of pesticides from the contaminated soil

In the present scenario, the uncontrolled and irrational use of pesticides is affecting the environment, agriculture and livelihood worldwide. The excessive application of pesticides for better production of crops and to maintain sufficient food production is leading to cause many serious environmental issues such as soil pollution, water pollution and also affecting the food chain. The efficient management of pesticide use and remediation of pesticide-contaminated soil is one of the most significant challenges to overcome. The efficiency of the current methods of biodegradation of pesticides using different microbes and enzymes depends on the various physical and chemical conditions of the soil and they have certain limitations. Hence, a novel strategy is the need of the hour to safeguard the ecosystem from the serious environmental hazard. In recent years, the application of nanomaterials has drawn attention in many areas due to their unique properties of small size and increased surface area. Nanotechnology is considered to be a promising and effective technology in various bioremediation processes and provides many significant benefits for improving the environmental technologies using nanomaterials with efficient performance. The present article focuses on and discusses the role, application and importance of nano-bioremediation of pesticides and toxic pollutants to explore the potential of nanomaterials in the bioremediation of hazardous compounds from the environment.

Asymmetric interaction and concurrent remediation of copper and atrazine by Acorus tatarinowii in an aquatic system

To clarify the influence of organic pesticides on phytoremediation of potentially toxic metal elements, hydroponically-grown Acorus tatarinowii was used to repair copper pollution at six concentration levels with and without atrazine. Removal outcomes and processes exhibited asymmetry in an aquatic system. In plants, the addition of atrazine brought as much as 20.5% copper than control. Total amounts, percentage of protein or pectin combined copper and leaf: root ratio of copper were enhanced correspondingly. In solutions, cupric ions (Cu²⁺) were eliminated as much as 95.6% in plant remediation system. Though atrazine resulted in a quarter more absorption equilibrium concentration, the absorption reaction rate half declined. Copper removal in the system was contributed by both bound copper in solution and plant accumulation, and atrazine magnified contribution weight of the later one. Concurrent copper decreased absolute and relative amounts of atrazine in A. tatarinowii, indicating the influence of copper was mainly to reduce atrazine uptake by A. tatarinowii rather than to change the transformation of atrazine in plants. Copper exhibited antagonistic effects with atrazine in term of plant biomass, photosynthesis and oxidative-related responses (malondialdehyde, Ca, Fe and Mn), which might give support to asymmetry interaction between copper and atrazine accumulation in A. tatarinowii.

Physiological and oxidative stress responses of Solanum lycopersicum (L.) (tomato) when exposed to different chemical pesticides

Pesticide overuse can have negative effects on developmental processes of non-target host plants. By increasing reactive oxygen species (ROS) levels, pesticides negatively affect cellular metabolism, biochemistry and physiological machinery of plants. Considering these problems, the current study was planned to assess the effect of three different groups of pesticides, namely diazinon (DIZN), imidacloprid (IMID) and mancozeb (MNZB) on Solanum lycopersicum L. (tomato). In general, pesticides resulted in a progressive decrease in physiological and biometric parameters of S. lycopersicum (L.), which varies significantly among concentrations and species of pesticides. Among them, 200 μgMNZB mL-1 had the most severe negative impact and reduced germination rate, root biomass, chl a, chl b, total chlorophyll and carotenoids by 62, 87, 90, 88, 92 and 90%, respectively. In addition, higher doses of pesticides greatly reduced the flowering, fruit attributes and lycopene content. Furthermore, plants exposed to 200 μgDIZN mL-1 showed a progressive drop in root cell viability (54% decrease), total soluble sugar (TSS) (64% decrease) and total soluble protein (TSP) (67% decrease) content. Data analysis indicated that greater doses of pesticides dramatically raised ROS levels and induced membrane damage through production of thiobarbituric acid reactive substances (TBARS), as well as increased cell injury. To deal with pesticide-induced oxidative stress, plants subjected to greater pesticide dosages, showed a substantial increase in antioxidant levels. For instance, ascorbate peroxidase (APX), catalase (CAT), superoxide dismutase (SOD), peroxidase (POD) and guaiacol peroxidase (GPX) were maximally increased by 48, 93, 71, 52 and 94%, respectively following 200 μgMNZB mL-1 soil exposures. Additionally, under a confocal laser scanning microscope (CLSM), pesticide exposed S. lycopersicum (L.) roots stained with 2',7'-dichlorodihydrofluorescein diacetate (2'7'-DCF) and 3,3'-diaminobenzidine, exhibited an increased ROS production in a concentration-dependent manner. Further, elevated pesticide concentrations resulted in alterations in mitochondrial membrane potential (ΔΨ m) and cellular death in roots, as evidenced by increased Rhodamine 123 (Rhd 123) and Evan's blue fluorescence, respectively. These findings clearly showed that applying pesticides in excess of permissible amounts might induce oxidative stress and cause oxidative damage in non-target host plants. Overall, the current study indicates that a thorough and secure method be used before selecting pesticides for increasing production of agronomically important vegetable crops in various agro-climatic zones.

Life Table and Preference Choice of Frankliniella occidentalis (Thysanoptera: Thripidae) for Kidney Bean Plants Treated by Exogenous Calcium

Simple Summary

Western flower thrips, Frankliniella occidentalis, is an invasive key pest that damages vegetables and ornamentals worldwide. The activation of induced resistance by chemicals may provide a simple and feasible way of achieving improvement of resistance to stress in crop plants, which is an important technology for the development of sustainable agriculture. Calcium (Ca) is an essential element for plants; numerous studies have shown that Ca can confer crop plants with resistance to abiotic and biotic stresses. For the first time, we report the negative effects of exogenous Ca on kidney bean plants in relation to the performance of F. occidentalis, including a reduced preference of thrips. Therefore, Ca could potentially be used to control F. occidentalis.

Abstract

Exogenous calcium (Ca) has been used to induce host plant resistance in response to abiotic and biotic stresses, including from thrips attack. The aim of this study was to determine whether exogenously applied Ca affects the performance of Frankliniella occidentalis. We assessed the development time, total longevity, reproduction, and population parameters of F. occidentalis, and its preference choice on Ca-treated or untreated control kidney bean plants under laboratory conditions. The results showed that F. occidentalis fed on Ca-treated leaves had a longer developmental time but lower longevity (female and male) and fecundity than F. occidentalis fed on control leaves. Population parameters, including the intrinsic rate of increase (r), finite rate of increase (λ), and net reproductive rate (R₀), were all found higher in control leaves than in Ca-treated leaves, and the mean generation time (T) was shorter. In preference choices, the number of thrips on control plants was higher than the number of thrips on Ca-treated kidney bean plants. Overall, our results indicated that exogenous Ca pretreatment on kidney bean plants affected the life history and preference choice of F. occidentalis, suggesting Ca might be used as a promising elicitor of inducible plant defense against thrips.

Inoculation with Bacillus amyloliquefaciens and mycorrhiza confers tolerance to drought stress and improve seed yield and quality of soybean plant

The present study aimed to evaluate the effect of Bacillus amyloliquefaciens and/or Arbuscular Mycorrhizal Fungi (AMF) as natural biofertilizers on biomass, yield, and seed nutritive quality of soybean (Giza 111). The conditions investigated include a well-watered (WW) control and irrigation withholding at the seed development stage (R5, after 90 days from sowing) (DS). Co-inoculation with B. amyloliquefaciens and AMF, resulted in the highest plant biomass and yield under WW and DS conditions. The nuclear DNA content analysis suggested that co-inoculation with B. amyloliquefaciens and AMF decreased the inhibition of drought stress on both the size and granularity of seed cells, which were comparable to the normal level. The single or co-inoculation with B. amyloliquefaciens and AMF increased the primary metabolites content and alleviated the drought-induced reduction in soluble sugars, lipids, protein and oil contents. Plant inoculation induced the expression of genes involved in lipid and protein biosynthesis, whereas an opposite trend was observed for genes involved in lipid and protein degradation, supporting the observed increase in lipid and protein content. Plant inoculated with B. amyloliquefaciens showed the highest α-amylase and β-amylase activities, indicating improved osmolyte (soluble sugar) synthesis, particularly under drought. Interestingly, single or co-inoculation further strengthen the positive effect of drought on the antioxidant and osmoprotectant levels, i.e. phenol, flavonoid, glycine betaine contents, and glutathione-S-transferase (GST) activity. As a result of stress release, there was a decrease in the level of stress hormones (abscisic acid, ABA) and an increase in gibberellin (GA), trans-zeatin-riboside (ZR), and indole acetic acid (IAA) in the seeds of inoculated plants. Additionally, the ATP content, hydrolytic activities of plasma membrane H+ -ATPase, Ca2+ -ATPase, and Mg2+ -ATPase were also increased by the inoculation.

Water contamination with atrazine: is nitric oxide able to improve Pistia stratiotes phytoremediation capacity?

Atrazine is an herbicide commonly used in several countries. Due to its long half-life, associated with its use in large scales, atrazine residues remain as environmental pollutants in water bodies. Phytoremediation is often pointed out as an interesting approach to remove atrazine from the aquatic environment, but its practical application is limited by the high toxicity of this herbicide. Here, we characterize the damages triggered by atrazine in Pistia stratiotes, evaluating the role of nitric oxide (NO), a cell-signaling molecule, in increasing the tolerance to the pollutant and the phytoremediation potential of this species. Pistia stratiotes plants were exposed to four treatments: Control; Sodium nitroprusside (SNP) (0.05 mg L^-1); Atrazine (ATZ) (150 μg L^-1) and ATZ + SNP. The plants remained under those conditions for 24 h for biochemical and physiological analysis and 3 days for the evaluation of relative growth rate. The presence of atrazine in plant cells triggered a series of biochemical and physiological damages, such as the increase in the generation of reactive oxygen species, damages to cell membranes, photosynthesis impairment, and negative carbon balance. Despite this, the plants maintained greater growth rates than other aquatic macrophytes exposed to atrazine and showed high bioconcentration and translocation factors. The addition of SNP, a NO donor, decreased the herbicide toxicity, with an increase of over 60% in the IC₅₀ value (Inhibitor Concentration). Indeed, the NO signaling action was able to increase the tolerance of plants to atrazine, which resulted in increments in pollutant uptake and translocation, with the maintenance of overall cell (e.g. membranes) and organs (root system) structure, and the functioning of central physiological processes (e.g. photosynthesis). These factors allowed for more quickly and efficient removal of the pollutant from the environment, reducing costs, and increasing the viability of the phytoremediation process.

CAX3 (cation/proton exchanger) mediates a Cd tolerance by decreasing ROS through Ca elevation in Arabidopsis

KEY MESSAGE

Over-expression of CAX3 encoding a cation/proton exchanger enhances Cd tolerance by decreasing ROS (Reactive Oxygen Species) through activating anti-oxidative enzymes via elevation of Ca level in Arabidopsis CAXs (cation/proton exchangers) are involved in the sequestration of cations such as Mn, Li, and Cd, as well as Ca, from cytosol into the vacuole using proton gradients. In addition, it has been reported that CAX1, 2 and 4 are involved in Cd tolerance. Interestingly, it has been reported that CAX3 expressions were enhanced by Cd in Cd-tolerant transgenic plants expressing Hb1 (hemoglobin 1) or UBC1 (Ub-conjugating enzyme 1). Therefore, to investigate whether CAX3 plays a role in increasing Cd tolerance, CAX3 of Arabidopsis and tobacco were over-expressed in Arabidopsis thaliana. Compared to control plants, both transgenic plants displayed an increase in Cd tolerance, no change in Cd accumulation, and enhanced Ca levels. In support of these, AtCAX3-Arabidopsis showed no change in expressions of Cd transporters, but reduced expressions of Ca exporters and lower rate of Ca efflux. By contrast, atcax3 knockout Arabidopsis exhibited a reduced Cd tolerance, while the Cd level was not altered. The expression of Δ90-AtCAX3 (deletion of autoinhibitory domain) increased Cd and Ca tolerance in yeast, while AtCAX3 expression did not. Interestingly, less accumulation of ROS (H2O2 and O2-) was observed in CAX3-expressing transgenic plants and was accompanied with higher antioxidant enzyme activities (SOD, CAT, GR). Taken together, CAX3 over-expression may enhance Cd tolerance by decreasing Cd-induced ROS production by activating antioxidant enzymes and by intervening the positive feedback circuit between ROS generation and Cd-induced spikes of cytoplasmic Ca.

Enhancing the atrazine tolerance of Pennisetum americanum (L.) K. Schum by inoculating with indole-3-acetic acid producing strain Pseudomonas chlororaphis PAS18

Atrazine as a kind of herbicide could cause damage to the sensitive plants. Though plant growth promoting rhizobacteria (PGPR) have been proven with the potential to enhance the resistance of plants against various abiotic stresses, whether it could alleviate phytotoxicity caused by atrazine is sill unclear. In present study, the effects of strain Pseudomonas chlororaphis PAS18, a kind of PGPR enable to produce indole-3-acetic acid (IAA), on the growth and physiological responses of Pennisetum americanum (L.) K.Schum seedlings were investigated under three different levels (0, 20 and 100 mg kg^-1) of atrazine in pot experiment. The results suggest that strain PAS18 could alleviate the growth and physiological interference caused by 20 mg kg^-1 of atrazine. Physiological analysis showed strain PAS18 could further decrease the damaged extent of photosystem II, superoxide radical level and malondialdehyde content of test plant via up-regulating psbA expression, enhancing superoxide dismutase activity and reducing atrazine accumulation in the test plant. Moreover, ion flux measurements suggest that IAA could alleviate the Ca²⁺ exflux state of the test plant which caused by atrazine stress. Hence, it is plausible that strain PAS18 could alleviate atrazine-induced stress to P. americanum by enhancing the photosystem II repair and antioxidant defense ability as well as balancing the Ca²⁺ flux.

Effect of exogenous calcium on growth, nutrients uptake and plasma membrane H+-ATPase and Ca2+-ATPase activities in soybean (Glycine max) seedlings under simulated acid rain stress

Calcium (Ca) is one of essential elements for plant growth and development, and also plays a role in regulating plant cell physiology and cellular response to the environment. Here, we studied whether calcium played a role in enhancing tolerance of plants to acid rain stress by hydroponics and simulating acid rain stress. Our results show that acid rain (pH 4.5/pH 3.0) caused decreases in dry weight biomass, chlorophyll content and uptake of nutrients elements (NO3-, P, K, Mg, Zn and Mo) and an increase in membrane permeability of root. However, all parameters in soybean treated with exogenous calcium (5 mM) and acid rain at pH 4.5 were closed to the control levels. In addition, exogenous calcium (5 mM) alleviated the inhibition induced by pH 3.0 acid rain on the activity of plasma membranes H+-ATPase and the expression of GmPHA1 at transcriptional level, being benefiting to maintaining uptake of nutrients (NO3-, P, K, Mg, and Zn), and then lower the decrease in dry weight biomass and chlorophyll content. After a 5-day recovery (without acid rain stress), all parameters in soybean treated with acid rain at pH 3.0 and exogenous calcium were still worse than those of the control, but obviously better than those treated with acid rain at pH 3.0. Higher activity of plasma membrane H+-ATPase in soybean treated with acid rain at pH 3.0 and exogenous calcium was good to uptake of nutrients and promoted the recovery of soybean growth, compared with soybean treated with acid rain at pH 3.0. In conclusion, exogenous calcium could alleviate the inhibition caused by acid rain on soybean growth by increasing the activity of plasma membrane H+-ATPase for providing driving force to nutrient absorption, and its regulating effect was limited by intensity of acid rain. Furthermore, the application of exogenous calcium can be one of ways to alleviate the damage caused by acid rain to plants.

Ecophysiological Responses of Calcicole Cyclobalanopsis glauca (Thunb.) Oerst. to Drought Stress and Calcium Supply

Water deficit and high calcium (Ca2+) content and are two typical soil characteristics in the Karst region. However, the problem of whether high Ca2+ in Karst calcareous soil could increase drought tolerance in calcicole plants has not been solved. We investigated the ecophysiological responses of Cyclobalanopsis glauca (Thunb.) Oerst. cuttings to short-term drought stress and Ca2+ application. Drought stress (10% PEG-6000) markedly reduced relative water content (RWC) and water potential (WP), and enhanced the levels of reactive oxygen species (ROS) production (H2O2 and O2•−) and malondialdehyde (MDA) content in C. glauca leaves. Under drought treatment, exogenous Ca2+ application (20 mM CaCl2) markedly increased the RWC and WP, and reduced the H2O2, O2•−, and MDA content. Furthermore, water deficit induced a significant increase in the activities of antioxidant enzymes such as peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), and glutathione peroxidase (GPX), and increased the accumulation of osmoregulation substances. External Ca2+ alleviated drought-induced oxidative stress and osmotic stress with further increased activities of antioxidant enzymes, and enhanced the accumulation of osmoregulation substances. In addition, exogenous Ca2+ treatment alleviated the reduction of the photosynthesis rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and chlorophyll content (SPAD), and further increased water use efficiency (WUE) under drought stress. This study confirms that exogenouos Ca2+ application induces improvements in the water status, osmotic adjustment, antioxidant defense, and photosynthesis efficiency of C. glauca under drought stress.

Low doses of triazine xenobiotics mobilize ABA and cytokinin regulations in a stress- and low-energy-dependent manner

The extent of residual contaminations of pesticides through drift, run-off and leaching is a potential threat to non-target plant communities. Arabidopsis thaliana responds to low doses of the herbicide atrazine, and of its degradation products, desethylatrazine and hydroxyatrazine, not only in the long term, but also under conditions of short-term exposure. In order to investigate underlying molecular mechanisms of low-dose responses and to decipher commonalities and specificities between different chemical treatments, parallel transcriptomic studies of the early effects of the atrazine-desethylatrazine-hydroxyatrazine chemical series were undertaken using whole-genome microarrays. All of the triazines under study produced coordinated and specific changes in gene expression. Hydroxyatrazine-responsive genes were mainly linked to root development, whereas atrazine and desethylatrazine mostly affected molecular signaling networks implicated in stress and hormone responses. Analysis of signaling-related genes, promoter sites and shared-function interaction networks highlighted the involvement of energy-, stress-, abscisic acid- and cytokinin-regulated processes, and emphasized the importance of cold-, heat- and drought-related signaling in the perception of low doses of triazines. These links between low-dose xenobiotic impacts and stress-hormone crosstalk pathways give novel insights into plant-pesticide interactions and plant-pollution interactions that are essential for toxicity evaluation in the context of environmental risk assessment.

Physiological and molecular responses of pearl millet seedling to atrazine stress

Pearl millet has been recommended beneficial for several therapeutic purposes. However, little is known of the physiological responses to abiotic stressors, especially of atrazine. In order to elucidate the physiological and molecular responses of pearl millet to atrazine stress, we studied the response of various biomarkers under increasing herbicide concentrations (0, 5, 10, and 50 mg/kg). We also quantified the levels of malondialdehyde (MDA) and reactive oxygen species (ROS) (H₂O₂ and O₂•^-) produced in the leaves to evaluate the extent of oxidative damage. Increasing atrazine concentrations significantly increased ROS and MDA production in the plant leaves. Ascorbate peroxidase (APX) and peroxidase (POD) activities increased, while catalase (CAT) and superoxide dismutase activities reduced with increasing atrazine concentrations. Generally, atrazine applied at 50 mg/kg suppressed chlorophyll contents, whereas, chlorophyll (a/b) ratio was increased. Atrazine applied at 50 mg/kg significantly suppressed antioxidant gene expressions to the lowest. The APX gene showed overall low response to the atrazine treatments. The chloroplastic psbA gene showed highest expression with 10 mg/kg atrazine, whereas atrazine at 50 mg/kg significantly suppressed the gene expression to its lowest. Pearl millet was able to suppress oxidative stress under low atrazine levels, but high atrazine concentration could induce more oxidative damage.

Expression and functional analysis of the Propamocarb-related gene CsDIR16 in cucumbers

BACKGROUND

Cucumber downy mildew is among the most important diseases that can disrupt cucumber production. Propamocarb, also known as propyl-[3-(dimethylamino)propyl]carbamate (PM), is a systemic carbamate fungicide pesticide that is widely applied in agricultural production because of its high efficiency of pathogens control, especially cucumber downy mildew. However, residual PM can remain in cucumbers after the disease has been controlled. To explore the molecular mechanisms of PM retention, cucumber cultivars 'D9320' (with the highest residual PM content) and 'D0351' (lowest residual PM content) were studied. High-throughput tag-sequencing (Tag-Seq) results showed that the CsDIR16 gene was related to PM residue, which was verified using transgenic technology.

RESULTS

We investigated the activity of a dirigent cucumber protein encoded by the CsDIR16 in gene response to stress induced by PM treatment. Gene-expression levels of CsDIR16 were up-regulated in the fruits, leaves, and stems of 'D0351' plants in response to PM treatment. However, in cultivar 'D9320', CsDIR16 levels were down-regulated in the leaves and stems after PM treatment, with no statistically significant differences observed in the fruits. Induction by jasmonic acid, abscisic acid, polyethylene glycol 4000, NaCl, and Corynespora cassiicola Wei (Cor) resulted in CsDIR16 up-regulation in 'D0351' and 'D9320'. Expression after salicylic acid treatment was up-regulated in 'D0351', but was down-regulated in 'D9320'. CsDIR16 overexpression lowered PM residues, and these were more rapidly reduced in CsDIR16(+) transgenic 'D9320' plants than in wild-type 'D9320' and CsDIR16(-) transgenic plants.

CONCLUSIONS

Analyses of the CsDIR16-expression patterns in the cucumber cultivars with the highest and lowest levels of PM residue, and transgenic validation indicated that CsDIR16 plays a positive role in reducing PM residues. The findings of this study help understand the regulatory mechanisms occurring in response to PM stress in cucumbers and in establishing the genetic basis for developing low-pesticide residue cucumber cultivars.

Atrazine triggers hepatic oxidative stress and apoptosis in quails (Coturnix C. coturnix) via blocking Nrf2-mediated defense response

The bioaccumulation and environmental persistence of atrazine (ATZ) poses a severe hazard to animal ecosystem. Quail has strong sensitivity to environmental pollutant, thus it is one of the most important ecological pollution indicator. However, true proof for the effects of ATZ exposure on the liver of quails is lacking. To evaluate the liver injury and the role of Nrf2-mediated defense responses during ATZ exposure, male quails were treated with ATZ (0, 50, 250 and 500mg/kg) by oral gavage for 45 days. Histopathological and ultrastructural changes, oxidative stress indices, apoptosis-related factors and Nrf2 pathway were detected. ATZ caused irreparable mitochondrial damage and destroyed morphophysiological integrity of the quail liver. Lower level ATZ (<250mg/kg) activated Nrf2 signaling pathway to protect liver against oxidative stress and apoptosis via enhancing antioxidative activity. Higher level ATZ (>500mg/kg) induced oxidative stress and apoptosis through decrease of non-enzymatic antioxidant, antioxidant enzymes and anti-apoptosis factors and increase of apoptosis factors expressions. Taken together, our results suggested that ATZ-induced hepatotoxicity in quails was associated with blocking Nrf2-mediated defense response.