Oxidative injury and antioxidant enzymes regulation in arsenic-exposed seedlings of four Brassica napus L. cultivars

Boron toxicity in plants: understanding mechanisms and developing coping strategies; a review

KEY MESSAGE

Boron is essential for plants, but excess can induce toxicity. Boron (B) is a vital micronutrient for plants, but excess B can induce toxicity symptoms and reduce crop yields. B bioavailability depends on soil properties, including clay type, pH, and organic matter content. Symptoms of B toxicity include reduced shoot and root growth, leaf chlorosis and necrosis, impaired photosynthesis, and disrupted pollen development. This review paper examines the current knowledge on B toxicity mechanisms, tolerance strategies, and management approaches in plants. This review covers (1) factors affecting B bioavailability; (2) toxicity symptoms in plants; (3) uptake, transport, and detoxification mechanisms; and (4) strategies. To mitigate toxicity, plants reduce B uptake, activate efflux transporters, compartmentalize B, and enhance antioxidant systems. On the basis of this review, future research should focus on identifying novel tolerance mechanisms, exploring genetic strategies for improved B management, and developing innovative agronomic interventions. These insights will facilitate the breeding and management of crops for enhanced productivity under B toxicity stress.

Untying arsenite tolerance mechanisms in contrasting maize genotypes attributed to NIPs-mediated controlled influx and root-to-shoot translocation, redox homeostasis and phytochelatin-mediated detoxification pathway

Contamination of ground water and soil with toxic metalloids like arsenic (As) poses a serious hazard to the global agricultural food production. One of the best ways to restrict entry of As into the food chain is selection of germplasms which accrue extremely low level of As in grains. Here, we screened diverse maize genotypes under high arsenite (100 μM AsIII) stress and identified PMI-PV-9 and PMI-PV-3 as AsIII-tolerant and -sensitive maize genotype respectively. Expression of genes associated with As uptake, vacuolar sequestration, biosynthesis of phytochelatins, root-to-shoot translocation, in vivo ROS generation, fine tuning of antioxidant defense system, DNA and membrane damage, H2O2 and superoxide anion (O2•-) levels were compared among the selected genotypes. PMI-PV-9 plants performed much better than PMI-PV-3 in terms of plant growth with no visible symptom of As toxicity. Susceptibility of PMI-PV-3 to AsIII stress may be attributed to comparatively low expression of genes involved in phytochelatins (PCs) biosynthesis. Concomitant decrease in ABCC1 expression might be another key factor for futile sequestration of AsIII into root vacuoles. Moreover, up-regulation of ZmNIP3;1 might contribute in high root-to-leaf As translocation. Substantial spike in H2O2, O2•- and MDA levels indicates that PMI-PV-3 plants have experienced more oxidative stress than PMI-PV-9 plants. Appearance of prominent deep brown and dark blue spots/stripes on leaves as revealed after DAB and NBT staining respectively suggest severe oxidative burst in PMI-PV-3 plants. Marked reduction in DHAR and MDAR activity rendered PMI-PV-3 cells to recycle ascorbate pool ineffectively, which might have exacerbated their susceptibility to AsIII stress. In a nutshell, incompetent PCs mediated detoxification system and disruption of cellular redox homeostasis owing to feeble antioxidant defence system resulting oxidative burst might be the prime reasons behind reduced performance of PMI-PV-3 plants under AsIII stress.

Silicon dioxide nanoparticles enhance plant growth, photosynthetic performance, and antioxidants defence machinery through suppressing chromium uptake in Brassica napus L

Chromium (Cr) is a highly toxic heavy metal that is extensively released into the soil and drastically reduces plant yield. Silicon nanoparticles (Si NPs) were chosen to mitigate Cr toxicity due to their ability to interact with heavy metals and reduce their uptake. This manuscript explores the mechanisms of Cr-induced toxicity and the potential of Si NPs to mitigate Cr toxicity by regulating photosynthesis, oxidative stress, and antioxidant defence, along with the role of transcription factors and heavy metal transporter genes in rapeseed (Brassica napus L.). Rapeseed plants were grown hydroponically and subjected to hexavalent Cr stress (50 and 100 μM) in the form of K2Cr2O7 solution. Si NPs were foliar sprayed at concentrations of 50, 100 and 150 μM. The findings showed that 100 μM Si NPs under 100 μM Cr stress significantly increased the leaf Si content by 169% while reducing Cr uptake by 92% and 76% in roots and leaves, respectively. The presence of Si NPs inside the plant leaf cells was confirmed by using energy-dispersive spectroscopy, inductively coupled plasma‒mass spectrometry, and confocal laser scanning microscopy. The study's findings showed that Cr had adverse effects on plant growth, photosynthetic gas exchange attributes, leaf mesophyll ultrastructure, PSII performance and the activity of enzymatic and nonenzymatic antioxidants. However, Si NPs minimized Cr-induced toxicity by reducing total Cr accumulation and decreasing oxidative damage, as evidenced by reduced ROS production (such as H2O2 and MDA) and increased enzymatic and nonenzymatic antioxidant activities in plants. Interestingly, Si NPs under Cr stress effectively increased the NPQ, ETR and QY of PSII, indicating a robust protective response of PSII against stress. Furthermore, the enhancement of Cr tolerance facilitated by Si NPs was linked to the upregulation of genes associated with antioxidant enzymes and transcription factors, alongside the concurrent reduction in metal transporter activity.

Co-application of copper nanoparticles and metal tolerant Bacillus sp. for improving growth of spinach plants in chromium contaminated soil

Chromium (Cr) is classified as a toxic metal as it exerts harmful effects on plants and human life. Bacterial-assisted nano-phytoremediation is an emerging and environment friendly technique that can be used for the detoxification of such pollutants. In current study, pot experiment was conducted in which spinach plants were grown in soil containing chromium (0, 5, 10, 20 mgkg-1) and treated with selected strain of Bacillus sp. and Cu-O nanoparticle (CuONPs). Data related to plant's growth, physiological parameters, and biochemical tests was collected and analyzed using an appropriate statistical test. It was observed that under chromium stress, all plant's growth parameters were significantly enhanced in response to co-application of CuONPs and Bacillus sp. Similarly, higher levels of catalase, superoxide dismutase, malondialdehyde, and hydrogen peroxide were also observed. However, contents of anthocyanin, carotenoid, total chlorophyll, chlorophyll a & b, were lowered under chromium stress, which were raised in response to the combined application of CuONPs and Bacillus sp. Moreover, this co-application has significant positive effect on total soluble protein, free amino acid, and total phenolics. From this study, it was evident that combined application of Bacillus sp. and CuONP alleviated metal-induced toxicity in spinach plants. The findings from current study may provide new insights for agronomic research for the utilization of bacterial-assisted nano-phytoremediation of contaminated sites.

Low-Arsenic Accumulating Cabbage Possesses Higher Root Activities against Oxidative Stress of Arsenic

Cabbage grown in contaminated soils can accumulate high levels of arsenic (As) in the edible parts, posing serious health risks. The efficiency of As uptake varies drastically among cabbage cultivars, but the underlying mechanisms are not clear. We screened out low (HY, Hangyun 49) and high As accumulating cultivars (GD, Guangdongyizhihua) to comparatively study whether the As accumulation is associated with variations in root physiological properties. Root biomass and length, reactive oxygen species (ROS), protein content, root activity, and ultrastructure of root cells of cabbage under different levels of As stress (0 (control), 1, 5, or 15 mg L^-1) were measured As results, at low concentration (1 mg L^-1), compared to GD, HY reduced As uptake and ROS content, and increased shoot biomass. At a high concentration (15 mg L^-1), the thickened root cell wall and higher protein content in HY reduced arsenic damage to root cell structure and increased shoot biomass compared to GD. In conclusion, our results highlight that higher protein content, higher root activity, and thickened root cell walls result in lower As accumulation properties of HY compared to GD.

Amelioration of the physio-biochemical responses to salinity stress and computing the primary germination index components in cauliflower on seed priming

The significant horticultural crop, cauliflower (Brassica oleracea L. var. botrytis) is vulnerable to the excessive salt concentration in the soil, which contributes to its scaled-down growth and productivity, among other indices. The current study examines the efficacy of hydropriming, halopriming, and osmopriming on the physio-biochemical attributes and tolerance to salinity (100 mM NaCl) in cauliflower under controlled conditions. The results showed that the salinity (100 mM NaCl) has significant deleterious impacts on cauliflower seed germination, seedling growth, and photosynthetic attributes, and provoked the production of reactive oxygen species. In contrast, different priming approaches proved beneficial in mitigating the negative effects of salinity and boosted the germination, vigor indices, seedling growth, and physio-biochemical attributes like photosynthetic pigments, protein, and proline content while suppressing oxidative damage and MDA content in cauliflower seedlings in treatment- and dose-dependent manner. PCA revealed 61% (PC1) and 15% (PC2) of the total variance with substantial positive relationships and high loading conditions on all germination attributes on PC1 with greater PC1 scores for PEG treatments showing the increased germination indices in PEG-treated seeds among all the priming treatments tested. All 13 distinct priming treatments tried clustered into three groups as per Ward's approach of systematic categorization, clustering the third group showing relatively poor germination performances. Most germination traits exhibited statistically significant associations at the p < 0.01 level. Overall, the results established the usefulness of the different priming approaches facilitating better germination, survival, and resistance against salinity in the cauliflower to be used further before sowing in the salt-affected agro-ecosystems.

Effects of plant age on antioxidant activity and endogenous hormones in Alpine Elymus sibiricus of the Tibetan Plateau

Elymus sibiricus L. is a perennial forage species that has potential to serve as a forage source in livestock grazing systems. However, E. sibiricus has been shown to have a rapid and substantial reduction of aboveground biomass and seed yield after 3 or 4 years and an accelerated aging process. To determine possible aging mechanisms, we planted E. sibiricus seeds in triplicate blocks in 2012, 2015, and 2016, respectively, and harvested samples of leaves and roots at the jointing and heading stages in 2018 and 2019 to determine oxidative indices and endogenous hormones. The fresh aboveground biomass of 4- and 5-year old plants declined by 34.2% and 52.4% respectively compared with 3-year old plants, and the seed yield declined by 12.7% and 34.1%, respectively. The water content in leaves was 51.7%, 43.3%, and 35.6%, and net photosynthesis was 7.73, 6.35, and 2.08 µmol/m²·s in 3-, 4-, and 5-year old plants, respectively. The superoxide anion radical generation rate in leaves and roots did not show any aging pattern. There was a non-significant increase in malondialdehyde concentration with plant age, particularly in leaves and roots at the heading stage in 2019. The superoxide dismutase activity showed a declining trend with age of plant roots at the jointing stage in both 2018 and 2019. The peroxidase activity declined with plant age in both leaves and roots, for example, and the catalase activity in roots 4- and 7-year old plants declined by 13.8% and 0.85%, respectively, compared to 3-year old plants at the heading stage in 2018. Therefore, the reduced capacity of the antioxidant system may lead to oxidative stress during plant aging process. Overall, the concentrations of plant hormones, auxin (IAA), gibberellin (GA), zeatin (ZT), and abscisic acid (ABA) were significantly lower in roots than in leaves. The IAA concentration in leaves and roots exhibited different patterns with plant age. The ZT concentrations in leaves of 3-year old plants was 2.39- and 2.62-fold of those in 4- and 7-year old plants, respectively at the jointing stage, and in roots, the concentration declined with plant age. The changes in the GA concentration with plant age varied between the physiological stages and between years. The ABA concentrations appeared to increase with plant age, particularly in leaves. In conclusion, the aging process of E. sibiricus was apparently associated with an increase in oxidative stress, a decrease of ZT and an increase of ABA, particularly in roots. These findings highlight the effects of plant age on the antioxidant and endogenous hormone activity of E. sibiricus. However, these plant age-related trends showed variations between plant physiological stages and between harvest years that needs to be researched in the future to develop strategies to manage this forage species.

Combined application of plant growth-promoting bacteria and iron oxide nanoparticles ameliorates the toxic effects of arsenic in Ajwain (Trachyspermum ammi L.)

Soil contamination with toxic heavy metals [such as arsenic (As)] is becoming a serious global problem because of the rapid development of the social economy. Although plant growth-promoting bacteria (PGPB) and nanoparticles (NPs) are the major protectants to alleviate metal toxicity, the study of these chemicals in combination to ameliorate the toxic effects of As is limited. Therefore, the present study was conducted to investigate the combined effects of different levels of Providencia vermicola (5 ppm and 10 ppm) and iron oxide nanoparticles (FeO-NPs) (50 mg/l^-1 and 100 mg/l^-1) on plant growth and biomass, photosynthetic pigments, gas exchange attributes, oxidative stress and response of antioxidant compounds (enzymatic and non-enzymatic), and their specific gene expression, sugars, nutritional status of the plant, organic acid exudation pattern As accumulation from the different parts of the plants, and electron microscopy under the soil, which was spiked with different levels of As [0 μM (i.e., no As), 50 μM, and 100 μM] in Ajwain (Trachyspermum ammi L.) seedlings. Results from the present study showed that the increasing levels of As in the soil significantly (p< 0.05) decreased plant growth and biomass, photosynthetic pigments, gas exchange attributes, sugars, and nutritional contents from the roots and shoots of the plants, and destroyed the ultra-structure of membrane-bound organelles. In contrast, increasing levels of As in the soil significantly (p< 0.05) increased oxidative stress indicators in term of malondialdehyde, hydrogen peroxide, and electrolyte leakage, and also increased organic acid exudation patter in the roots of T. ammi seedlings. The negative impact of As toxicity can overcome the application of PGPB (P. vermicola) and FeO-NPs, which ultimately increased plant growth and biomass by capturing the reactive oxygen species, and decreased oxidative stress in T. ammi seedlings by decreasing the As contents in the roots and shoots of the plants. Our results also showed that the FeO-NPs were more sever and showed better results when we compared with PGPB (P. vermicola) under the same treatment of As in the soil. Research findings, therefore, suggest that the combined application of P. vermicola and FeO-NPs can ameliorate As toxicity in T. ammi seedlings, resulting in improved plant growth and composition under metal stress, as depicted by balanced exudation of organic acids.

Effect of foliar and root exposure to polymethyl methacrylate microplastics on biochemistry, ultrastructure, and arsenic accumulation in Brassica campestris L

Despite the serious risk of microplastic pollution in the roots and leaves of crops, the phytotoxicity of microplastics (introduced via different exposure routes) in leafy vegetables remain insufficiently understood. Here, the effects of the root and foliar exposure of polymethyl methacrylate microplastic (PMMAMPs) on phytotoxicity, As accumulation, and subcellular distribution were investigated in rapeseed (Brassica campestris L). The relative chlorophyll content under PMMAMPs treatment decreased with time, and the 0.05 g L^-1 root exposure decreased it significantly (by 9.97-20.48%, P < 0.05). In addition, superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), and ascorbate peroxidase (APX) activities in rapeseed were more sensitive to PMMAMPs introduced through root exposure than through foliar exposure. There was dose-dependent ultrastructural damage, and root exposure had a greater impact than foliar exposure on root tip cells and chloroplasts. PMMAMPs entered the shoots and roots of rapeseed through root exposure. Under foliar exposure, PMMAMPs promoted As accumulation in rapeseed by up to 75.6% in shoots and 68.2% in roots compared to that under control (CK). As content in cell wall under PMMAMP treatments was 3.6-5.3 times higher than that of CK, as indicated by subcellular component results. In general, root exposure to PMMAMPs resulted in a stronger physiological impact and foliar exposure led to increased As accumulation in rapeseed.

Protective mechanisms of sulfur against arsenic phytotoxicity in Brassica napus by regulating thiol biosynthesis, sulfur-assimilation, photosynthesis, and antioxidant response

The contamination of agricultural soils with Arsenic (As) is a significant environmental stress that restricts plant growth, metabolism, and productivity worldwide. The present study examined the role of elemental sulfur (S⁰) in protecting Brassica napus plants from Arsenic (As) toxicity. Arsenic (100, and 200 mg As kg^-1 soil) in soil caused detrimental effects on five Brassica napus cultivars (Neelam, Teri-Uttam Jawahar, Him Sarson, GSC-101, and NUDB 26-11). The As toxicity inhibited the growth and photosynthesis indices in all cultivars with more deterioration effects in NUDB 26-11. Plant absorption and uptake of As caused the generation of oxidative injury by accumulating the reactive oxygen species (ROS), which simultaneously decreased the plant defence capability and ultimately the photosynthesis. Application of sulfur (S⁰, 100 or 200 mg S kg^-1 soil) alleviated the negative impacts and toxicity of As on the photosynthesis and growth matrices of plants, especially under high S level. S⁰ also boosted the antioxidant potential of plants and toned-down lipid peroxidation and ROS aggravation such as superoxide anion (O₂^•-) and H₂O₂, hydrogen peroxide, in As affected plants. In general, S⁰ at 200 mg kg^-1 soil more perceptibly increased the functionality of antioxidant enzymes, and non-enzymatic antioxidants, metal chelators and non-protein thiols. Further amendment of soil with S⁰ at fifteen days before seed sowing affected by As-induced toxic effects (added to soil at the time of sowing) considerably intensified the endogenous hydrogen sulfide (H₂S) content and its regenerating enzymes D-cysteine desulfhydrase (DCD) and L-cysteine desulfhydrase (LCD) that further strengthened the defense capability of plants to withstand As-stress. Our results suggest the role of H₂S in the S-induced defense operation of the B. napus plants in restraining As toxicity. The current study shows that S⁰ as a source of S might be used to promote the growth of B. napus plants in polluted agricultural soils.

Effect of uncontrolled fertilization and heavy metal toxicity associated with arsenic(As), lead(Pb) and cadmium (Cd), and possible remediation

In this growing age of population,agriculture plays a significant role by providing food and employment to millions of people. But to meet the growing need of food day by day the demand of fast and quality plant production becomes a must. Fertilization is one of such activities which are people accustomed to do for this purpose from a very long time. But the excessive uses of chemical fertilizers are showing negative influence on the environmental and public health. The paper mainly focuses on how the excessive use of chemical fertilizers are affecting the soil health as well as the water bodies by accumulating heavy metals (HMs) and other chemical elements present in them and the possible remediation measures.In adequate levels, all heavy metals are hazardous. However, some of them e.g., arsenic (As), lead (Pb) and Cadmium (Cd) are of particular relevance due to their environmental concentrations. The paper also provides a comprehensive discussion of the sources, uses, toxicity, and remediation of these particular HMs.

A review on bioremediation approach for heavy metal detoxification and accumulation in plants

Nowadays, the accumulation of toxic heavy metals in soil and water streams is considered a serious environmental problem that causes various harmful effects on plants and animals. Phytoremediation is an effective, green, and economical bioremediation approach by which the harmful heavy metals in the contaminated ecosystem can be detoxified and accumulated in the plant. Hyperaccumulators exude molecules called transporters that carry and translocate the heavy metals present in the soil to different plant parts. The hyperaccumulator plant genes can confine higher concentrations of toxic heavy metals in their tissues. The efficiency of phytoremediation relies on various parameters such as soil properties (pH and soil type), organic matters in soil, heavy metal type, nature of rhizosphere, characteristics of rhizosphere microflora, etc. The present review comprehensively discusses the toxicity effect of heavy metals on the environment and different phytoremediation mechanisms for the transport and accumulation of heavy metals from polluted soil. This review gave comprehensive insights into plants tolerance for the higher heavy metal concentration their responses for heavy metal accumulation and the different mechanisms involved for heavy metal tolerance. The current status and the characteristic features that need to be improved in the phytoremediation process are also reviewed in detail.

Arsenic-Induced Oxidative Stress and Antioxidant Defense in Plants

The non-essential metalloid arsenic (As) is widely distributed in soil and underground water of many countries. Arsenic contamination is a concern because it creates threat to food security in terms of crop productivity and food safety. Plants exposed to As show morpho-physiological, growth and developmental disorder which altogether result in loss of productivity. At physiological level, As-induced altered biochemistry in chloroplast, mitochondria, peroxisome, endoplasmic reticulum, cell wall, plasma membrane causes reactive oxygen species (ROS) overgeneration which damage cell through disintegrating the structure of lipids, proteins, and DNA. Therefore, plants tolerance to ROS-induced oxidative stress is a vital strategy for enhancing As tolerance in plants. Plants having enhanced antioxidant defense system show greater tolerance to As toxicity. Depending upon plant diversity (As hyperaccumulator/non-hyperaccumulator or As tolerant/susceptible) the mechanisms of As accumulation, absorption or toxicity response may differ. There can be various crop management practices such as exogenous application of nutrients, hormones, antioxidants, osmolytes, signaling molecules, different chelating agents, microbial inoculants, organic amendments etc. can be effective against As toxicity in plants. There is information gap in understanding the mechanism of As-induced response (damage or tolerance response) in plants. This review presents the mechanism of As uptake and accumulation in plants, physiological responses under As stress, As-induced ROS generation and antioxidant defense system response, various approaches for enhancing As tolerance in plants from the available literatures which will make understanding the to date knowledge, knowledge gap and future guideline to be worked out for the development of As tolerant plant cultivars.

Physiological and biochemical characterization of Kalongi (Nigella sativa) against arsenic stress: Implications for human health risk assessment

Arsenic (As) is a toxic metalloid that exhibits a varying degree of toxicity in plants depending upon the redox status of its species. Elemental arsenic [As(0)] is the least toxic of all the As species, however, under conducive environmental conditions, it can be readily oxidized into toxic forms. The present experiment was designed to evaluate the deleterious effects of As when applied in As(0) form on the morpho-physiological attributes of Kalongi (Nigella sativa). Seeds of N. sativa were sown in soil contaminated with various levels of As (0, 1.875, 3.75, 7.5, 15.0, and 30.0 mg nA(0) kg^-1 soil). The results indicated that plant biomass and grain yield of N. sativa were not much affected by various levels of As except at 30 mg nA(0) kg^-1 soil. Activities of antioxidant enzymes (SOD, APX, POX, and CAT), phenolic contents, and carotenoids were enhanced in response to the overproduction of H₂O₂, subsequently inhibiting lipid peroxidation. Arsenic accumulation in different plant organs increased with increasing soil As levels in the given trend root > shoot > leaf > seedpod > seed. Arsenic uptake affected the uptake of other elements (P, Fe, Zn, K, Na, Ca). Adaptive changes in total chlorophyll contents, MDA contents, and antioxidant enzymatic defense mechanism in response to As stress suggest that the N. sativa is tolerant to moderate As stress. Therefore, this crop can be cultivated on moderately As-contaminated soils without any significant risks of economic losses and food chain contamination.

Exploration of glutathione reductase for abiotic stress response in bread wheat (Triticum aestivum L.)

A total of seven glutathione reductase (GR) genes were identified in Triticum aestivum, which were used for comparative structural characterization, phylogenetic analysis and expression profiling with the GR genes of other cereal plants. The modulated gene expression and enzyme activity revealed the role of GRs in abiotic stress response in T. aestivum. Glutathione reductase (GR) is an enzymatic antioxidant that converts oxidized glutathione (GSSG) into reduced glutathione (GSH) through the ascorbate-glutathione cycle. In this study, a total of seven GR genes forming two homeologous groups were identified in the allohexaploid genome of bread wheat (Triticum aestivum). Besides, we identified three GR genes in each Aegilops tauschii, Brachypodium distachyon, Triticum urartu and Sorghum bicolor, which were used for comparative characterization. Phylogenetic analysis revealed the clustering of GR proteins into two groups; class I and class II, which were predicted to be localized in cytoplasm and chloroplast, respectively. The exon-intron and conserved motif patterns were almost conserved in each group, in which a maximum of 10 and 17 exons were present in chloroplastic and cytoplasmic GRs, respectively. The protein structure analysis confirmed the occurrence of conserved pyridine nucleotide disulfide oxidoreductase (Pyr_redox) and pyridine nucleotide disulfide oxidoreductase dimerization (Pyr_redox_dim) domains in each GR. The active site of GR proteins consisted of two conserved cysteine residues separated by four amino acid residues. Promoter analysis revealed the occurrence of growth and stress-related cis-active elements. Tissue-specific expression profiling suggested the involvement of GRs in both vegetative and reproductive tissue development in various plants. The differential expression of TaGR genes and enhanced GR enzyme activity suggested their roles under drought, heat, salt and arsenic stress. Interaction of GRs with other proteins and chemical compounds of the ascorbate-glutathione cycle revealed their coordinated functioning. The current study will provide a foundation for the validation of the precise role of each GR gene in future studies.

Mitigation effects of exogenous melatonin-selenium nanoparticles on arsenic-induced stress in Brassica napus

Melatonin (MT) and selenium (Se) application known to decrease heavy metal uptake and toxicity in plants. By mixing the Se in MT medium a new complex MT-Se nanoparticles (MT-Se NPs) was synthesized and we investigated the role of MT-Se NPs on B. napus growth and tolerance against As stress. The MT-Se particles significantly enhanced the plant growth and other associated physiological attributes under As stress. The As treatment at 80 μM was more phytotoxic, however MT-Se NPs application resulted in a substantial increase in leaf chlorophyll fluorescence, biomass accumulation, and decreased ROS relative to As stressed plants. The use of MT-Se NPs to As stressed plants reduced photosynthetic inhibition and oxidative stress and attenuated the increase in MDA and H₂O₂ contents. The application of MT-Se NPs also boosted the antioxidant enzymes activities such as SOD, POD and CAT as well as the APX, GR and GSH activates under As stress. The results also showed MT-Se NPs treatments alleviated the growth inhibition induced by As and reduced the accumulation of As in leaves and roots of B. napus seedlings. Moreover, treatment with MT-Se NPs improved the plant growth more successfully than treatment of MT and Se alone. This study explored the mechanism of melatonin and selenium efficiency in the composition can be jointly encouraged to exert synergistic effects and boost plant enzymatic activities.

Arsenic behavior in soil-plant system and its detoxification mechanisms in plants: A review

Arsenic (As) is one of the most toxic and cancer-causing metals which is generally entered the food chain via intake of As contaminated water or food and harmed the life of living things especially human beings. Therefore, the reduction of As content in the food could be of great importance for healthy life. To reduce As contamination in the soil and food, the evaluation of plant-based As uptake and transportation mechanisms is critically needed. Different soil factors such as physical and chemical properties of soil, soil pH, As speciation, microbial abundance, soil phosphates, mineral nutrients, iron plaques and roots exudates effectively regulate the uptake and accumulation of As in different parts of plants. The detoxification mechanisms of As in plants depend upon aquaporins, membrane channels and different transporters that actively control the influx and efflux of As inside and outside of plant cells, respectively. The xylem loading is responsible for long-distance translocation of As and phloem loading involves in the partitioning of As into the grains. However, As detoxification mechanism based on the clear understandings of how As uptake, accumulations and translocation occur inside the plants and which factors participate to regulate these processes. Thus, in this review we emphasized the different soil factors and plant cell transporters that are critically responsible for As uptake, accumulation, translocation to different organs of plants to clearly understand the toxicity reasons in plants. This study could be helpful for further research to develop such strategies that may restrict As entry into plant cells and lead to high crop yield and safe food production.

Arsenic uptake and toxicity in wheat (Triticum aestivum L.): A review of multi-omics approaches to identify tolerance mechanisms

Arsenic (As) due to its widespread has become a primary concern for sustainable food production, especially in Southeast Asian countries. In that context, the present review presented a comprehensive detail of the available literature marking an assortment of As-induced impacts on wheat. The conclusive findings of past research suggest that As tends to grossly affect the germination, elongation, biomass, grain yield, and induce oxidative stress. Several human studies are suggestive of higher cancer risks (>1 × 10^-6) due to the ingestion of wheat grains. However, the body of proof is limited and the scarcity of information limited understanding about tolerance mechanism in wheat against As. Therefore, the paper provided a reference from tolerance mechanism based studies in other crops like rice and maize. The generated knowledge of arsenomics would pave the way for plant breeders to develop resistant varieties for As to ensure sustainable food production.

Comprehensive proteomic analysis of arsenic induced toxicity reveals the mechanism of multilevel coordination of efficient defense and energy metabolism in two Brassica napus cultivars

Arsenic (As) a non-essential element is of particular concern with respect to harmful effects on plant metabolism. While extensive studies have been conducted on the physiological responses of plants to increase As concentrations, however, molecular differences elucidating species-specific changes remain largely unknown. In the present experiment, two oilseed Brassica napus (B. napus) cultivars, ZS758 and ZD622, were treated by elevated As concentration. Their responses to the As stress have been investigated through pulse amplitude modulated fluorometer and isobaric tags based proteomic (iTRAQ) analysis. The chlorophyll fluorescence attributes showed that As stress significantly decrease the photochemical efficiency of photosystem II (PSII) and photosystem I (PSI) as well as the comparatively closed stomata observed under scanning electron microscopy (SEM). In this study, 65 proteins displayed increased abundance and 52 down-regulated were found in the control vs As comparison in cultivar ZS758, while 44 up and 67 down-regulated proteins were found in the control vs As comparison in ZD622. Metabolic pathways, followed by ribosome and biosynthesis of secondary metabolites were the dominant functional annotation categories among the differentially expressed protein (DEPs). Many genes involved in primary metabolism, stress and defense were found to be As-responsive DEPs and/or DEPs between these two cultivars. Based on these results, a schematic description of key processes involved in As tolerance in ZS758 and ZD622 is proposed, which suggests that higher tolerance in ZS758 depends on a multilevel coordination of efficient defense and energy metabolism. Real-time quantitative PCR supported the expression patterns of several genes encoding a protein similar to their corresponding DEPs. In addition, these findings could shed light in unraveling the molecular mechanisms of B. napus exposed to As stress and provide or improve essential understandings in the development of advanced B. napus cultivars against As resistance.

Effects of arsenite on physiological, biochemical and grain yield attributes of quinoa (Chenopodium quinoa Willd.): implications for phytoremediation and health risk assessment

The objectives of this study were to investigate the effects of arsenic (As) on physiological and biochemical attributes of quinoa, and human health risks associated with the consumption of As contaminated grains of quinoa. Quinoa genotype, Puno was grown on soil contaminated with various levels of arsenite; 0, 10, 20, 30, and 40 mg As kg^-1 soil. Results revealed that plant growth, photosynthetic pigments, stomatal conductance, and grain yield of As treated plants were significantly less as compared to control plants. Plants exposed to elevated levels of 30 and 40 mg As kg^-1 of soil could not survive until maturity. Plant roots retained higher concentration of As than shoot indicating As phytostabilizing behavior of quinoa. Arsenic toxicity caused oxidative stress in quinoa plants, which elevated the H₂O₂ and TBARS contents and decreased membrane stability. This oxidative stress was partly mitigated by the induction of antioxidant enzymes (SOD, CAT, POD, APX). Perhaps, our results regarding As availability might be an overestimate of the typical natural conditions, As accumulation in quinoa grains posed both carcinogenic and non-carcinogenic health risks to humans. It was concluded that quinoa is sensitive to As and the consumption of quinoa grains from plants grown on As concentration ≥20 mg kg^-1 of soil was not safe for humans. Novelty statement: The tolerance potential of quinoa (Chenopodium quinoa Willd.) against the trivalent form of arsenic (arsenite), and the health risks due to the consumption of arsenic-contaminated grains has not been explored yet. This is the first study in which we have explored the effects of arsenite on physiological, biochemical and phytoremedial attributes of quinoa. Moreover, human health risks associated with the consumption of As contaminated grains of quinoa has have been investigated. The findings of the present study would be helpful for farmers who intend to grow quinoa on arsenic-contaminated soils.

Ilex Paraguariensis exposition to As and Cd in a closed soilless system

The exposition of mate (Ilex Paraguariensis A. St.-Hil.) to As and Cd was investigated in plants derived from young mini-cuttings. Mate plants were cultivated in a closed soilless system, composed of coarse sand as substrate and flood fertirrigation. Plantlets were fertirrigated with nutritive solution and As and Cd solutions were added to the nutritive solution in the final concentration of 8 and 17 mg L^-1 (As) and of 17 and 33 mg L^-1 (Cd) during 14 days. Results show that stem diameter and Dickson quality index (DQI) variables could not be used as a potential indicator of accumulation of As and Cd. The shoot height, number of leaves and chlorophyll index are variables easy and quick to measure and they can be used as parameters to evaluate the stress caused in mate plants cultivation in a closed soilless system. The highest concentration of As and Cd was in roots of plants. Beyond the roots, As and Cd also can be translocated to the leaves achieving high concentrations. In addition, leaves from the treated mate plants were submitted to a hot infusion extraction in order to simulate the traditional beverage and As and Cd were determined in the infusion. Regarding to the infusion procedure, considerable As and Cd amounts were extracted from the leaves leading to conclude that this way of consumption can be an important source of toxic elements for the human diet.

Multivariate Analysis Reveals Different Responses of Antioxidant Defense in Wheat Plants Exposed to Arsenic (As) and Cadmium (Cd)

Background:

Multivariate analysis is a chemometric tool that has been little explored to determine physiological status under heavy metal stress. Nevertheless, PCA has an unexplored potential to determine the plant physiologic status and its modification under stress factors like heavy metals.

Objectives:

This work aims to assess the physiological and biochemical effects and responses of wheat plants under the different exposition of As and Cd using multivariate models.

Materials and Methods:

Wheat plants growing in a greenhouse were exposed to 0, 10 and 50 mg kg-1 soil of As and 0, 10 and 33 50 mg kg-1 soil of Cd until growth stage 5. After 56 days, wheat leaves and roots were collected to determine dry weight, lipid peroxidation and the activity of three enzymes: catalase, ascorbate peroxidase and guaiacol peroxidase. These measures were considered as the variables of three performed multivariate models to determine physiological status.

Results:

Through the interpretation of score plot and loading plot in combination, it was possible to determine that both As and Cd affect chlorophyll content and antioxidant response. However, a chlorophyll decrease and a lipid peroxidation increase were observed together with an inhibition of antioxidant response more accentuated in wheat plants exposed to As than those exposed to Cd.

Conclusions:

Multivariate analysis allows us to determine the differences between the physiological behavior of both stressors, which turn this chemometric tools useful for the characterization of a physiological response.

Role of iron-lysine on morpho-physiological traits and combating chromium toxicity in rapeseed (Brassica napus L.) plants irrigated with different levels of tannery wastewater

Chromium (Cr) is among the most widespread toxic trace elements found in agricultural soils resulting from various anthropogenic activities. However, the role of micronutrient-amino acid chelates in reducing Cr toxicity in crop plants has recently been suggested. The present study was conducted to explore the effect of iron (Fe) chelated with lysine (lys) on plant growth, biomass, gaseous exchange attributes, oxidative stress indicators, antioxidant response, and Cr uptake in rapeseed (Brassica napus L.) plants irrigated with different levels of tannery wastewater in soil collected from District Kasur of Pakistan. B. napus seedlings (thirty-day-old) were shifted to pots irrigated with different levels of tannery wastewater. After two weeks, foliar application of Fe-lys (5 mM) was carried out for four successive weeks, and plants were harvested carefully post ten weeks of cultivation in tannery wastewater, under controlled conditions. Toxic levels of Cr in the soil significantly decreased plant height, fresh biomass of roots and leaves, dry biomass of roots and leaves, root length, number of leaves, leaf area, total chlorophyll contents, carotenoid contents, transpiration rate (E), stomatal conductance (g_s), net photosynthesis (P_N), and water use efficiency (WUE). Toxic Cr levels in the soil also increased oxidative stress in the roots and leaves of B. napus plants, which were overcome by the activities of various antioxidant enzymes, such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX). Moreover, increasing levels of Cr in the soil caused a significant increase in the Cr content of the roots and shoots of B. napus plants. The negative effects of Cr toxicity could be overturned by Fe-lys application, significantly increasing plant growth, biomass, chlorophyll content, and gaseous exchange attributes by reducing oxidative stress (H₂O₂, MDA, EL) and enhancing antioxidant enzyme activities. Furthermore, foliar application of Fe-lys reduced the Cr concentration and increased essential micronutrients (Fe contents) in the roots and shoots of B. napus plants. These results shed light on the effectiveness of Fe-lys in improving the growth and up-regulation of antioxidant enzyme activities of B. napus in response to Cr stress. However, further studies at field levels are required to explore the mechanisms of Fe-lys-mediated reduction of the toxicity of not only Cr, but possibly also other heavy metals in plants.

Reactive Oxygen Species (ROS) Metabolism and Nitric Oxide (NO) Content in Roots and Shoots of Rice (Oryza sativa L.) Plants under Arsenic-Induced Stress

Arsenic (As) is a highly toxic metalloid for all forms of life including plants. Rice is the main food source for different countries worldwide, although it can take up high amounts of As in comparison with other crops, showing toxic profiles such as decreases in plant growth and yield. The induction of oxidative stress is the main process underlying arsenic toxicity in plants, including rice, due to an alteration of the reactive oxygen species (ROS) metabolism. The aim of this work was to gain better knowledge on how the ROS metabolism and its interaction with nitric oxide (NO) operate under As stress conditions in rice plants. Thus, physiological and ROS-related biochemical parameters in roots and shoots from rice (Oryza sativa L.) were studied under 50 μM arsenate (AsV) stress, and the involvement of the main antioxidative systems and NO in the response of plants to those conditions was investigated. A decrease of 51% in root length and 27% in plant biomass was observed with 50 μM AsV treatment, as compared to control plants. The results of the activity of superoxide dismutase (SOD) isozymes, catalase, peroxidase (POD: total and isoenzymatic), and the enzymes of the ascorbate–glutathione cycle, besides the ascorbate and glutathione contents, showed that As accumulation provoked an overall significant increase of most of them, but with different profiles depending on the plant organ, either root or shoot. Among the seven identified POD isozymes, the induction of the POD-3 in shoots under As stress could help to maintain the hydrogen peroxide (H2O2) redox homeostasis and compensate the loss of the ascorbate peroxidase (APX) activity in both roots and shoots. Lipid peroxidation was slightly increased in roots and shoots from As-treated plants. The H2O2 and NO contents were enhanced in roots and shoots against arsenic stress. In spite of the increase of most antioxidative systems, a mild oxidative stress situation appears to be consolidated overall, since the growth parameters and those from the oxidative damage could not be totally counteracted. In these conditions, the higher levels of H2O2 and NO suggest that signaling events are simultaneously occurring in the whole plant.

Arsenic Distribution, Accumulation and Tolerance Mechanisms of Typha angustifolia in Different Phenological Growth Stages

Variations of phytoaccumulation and tolerance in different growth stages of plant are important factors for effective removal of pollutants in phytoremediation. The present work investigated arsenic (As) accumulation, As-tolerance and the physiological tolerance mechanisms of Typha angustifolia under different As-level during the seedling, fast-growing and breeding stages. The results showed that As mainly distributed in the underground part and total As accumulation increased with growth stages. Maximum growth rates under lower As occurred in seedling stage, whereas occurred in breeding stage under higher As. T. angustifolia exhibited the highest tolerance ability under 150 mg kg^-1 As and tolerance index (TI) varied from seedling to breeding stages. During seedling stage, TI was affected by plant height (H_shoot) and net photosynthesis, which control biomass production. During fast-growing stage, H_shoot and root glutathione (GSH) co-regulated plant As-tolerance. During breeding stage, physiological metabolic processes, especially GSH-mediated processes, played a critical role in improving plant As-tolerance.

Overview of biochar production from preservative-treated wood with detailed analysis of biochar characteristics, heavy metals behaviors, and their ecotoxicity

Concerns over the disposal of preservative-treated wood waste and its related environmental problems are the main driving forces of research into the recycling of preservative-treated wood. Preservative-treated wood waste composed of cellulose, hemicellulose, and lignin with several types of heavy metals can be recycled in various ways, such as wood-based composites, heavy metal extraction, energy recovery, etc. In particular, thermochemical conversion has attracted considerable attention recently because energy can be recovered from biomass as liquid fuel and bio-oil, as well as produce bio-char with a high carbon content, which can be applied to valuable products, such as soil amendment, adsorbents, solid fuels, and catalyst supports. On the other hand, environmental issues, such as heavy metal volatilization and heavy metal leaching, are still a challenge. This review reports the state-of-the-art knowledge of biochar production from preservative-treated wood with the main focus on the feedstock, process technology, biochar characteristics, application, and environmental issues. This review provides important information for future studies into the recycling of preservative-treated woods into biochar.

Evaluation of arsenic induced toxicity based on arsenic accumulation, translocation and its implications on physio-chemical changes and genomic instability in indica rice (Oryza sativa L.) cultivars

Arsenic (As) accumulation in rice is a principal route of As exposure for rice based population. We have tested physiochemical and molecular parameters together to identify low As accumulating rice cultivars with normal growth and vigor. The present study examined potential toxicity caused by arsenate (AsV) among four rice cultivars tested that varied with respect to accumulation of total arsenic, arsenite (AsIII) and their differential translocation rate which had deleterious impact on growth and metabolism. Intracellular homeostasis of rice cultivars viz., TN-1, IR-64, IR-20 and Tulaipanji was hampered by 21 days long As(V) treatment due to generation of reactive oxygen species (ROS) and inadequate activity of catalase (CAT; EC 1.11.1.6). Upregulation of oxidative stress markers viz., H₂O₂, proline and MDA along with alteration in enzymatic antioxidants profile were conspicuously pronounced in cv. Tulaipanji while cv. TN-1 was least affected under As(V) challenged environment. In addition to that genomic template stability and band sharing indices were qualitatively measured by DNA profiling of all tested cultivars treated with 25 μM, 50 μM, and 75 μM As(V). In rice cv. Tulaipanji genetic polymorphism was significantly detected with the application of random amplified polymorphic DNA (RAPD) tool and characterized as susceptible cultivar of As compared to cvs. TN-1, IR-64 and IR-20 that is in correlation with data obtained from cluster analysis. Hence, identified As tolerant cultivars viz., TN-1, IR64 and IR-20 especially TN-1 could be used in As contaminated agricultural field after appropriate field trial. This study could help to gather information regarding cultivar-specific tolerance strategy to avoid pollutant induced toxicity.

Assessing the Correlations between Different Traits in Copper-Sensitive and Copper-Resistant Varieties of Jute (Corchorus capsularis L.)

The current study was conducted to explore the potential for phytoremediation in different varieties of jute grown under toxic concentrations of copper (Cu). For this purpose, a Petri dish experiment was conducted under controlled conditions using four varieties of jute, i.e., HongTieGuXuan, C-3, GuBaChangaJia, and ShangHuoMa, grown in double filter paper under 50 µmol L-1 of artificially spiked copper (Cu) using CuSO4.H2O. The results of the present study revealed that jute varieties C-3 and HongTieGuXuan were able to survive under high concentrations of Cu without a significant decrease in plant height, plant fresh and dry weights, total chlorophyll content, or seed germination, while varieties GuBaChangaJia and ShangHuoMa exhibited a significant reduction in their growth and biomass. Furthermore, high concentrations of Cu in the medium resulted in lipid peroxidation. This could be due to the oxidative damage induced in the roots and leaves of the jute varieties, which might be a result of by hydrogen peroxide (H2O2) and electrolyte leakage. Reactive oxygen species (ROS) generated due to Cu toxicity can be overcome by the increasing activity of antioxidants, and it was also noted that GuBaChangaJia and ShangHuoMa exhibited high Cu stress, while C-3 and HongTieGuXuan showed some resistance to Cu toxicity. Contrastingly, Cu accumulation and uptake was higher in C-3 and HongTieGuXuan, while a little Cu was accumulated in the roots and leaves of GuBaChangaJia and ShangHuoMa. On the basis of these findings, it can be suggested that C-3 and HongTieGuXuan have the potential to cope with Cu stress and can be considered Cu-resistant varieties, while GuBaChangaJia and ShangHuoMa are considered Cu-sensitive varieties. Moreover, C-3 and HongTieGuXuan have the potential to revoke large amounts of Cu, and can be cultivated as phytoremediation tools in Cu-contaminated soil.

Effect of Endogenous Selenium on Arsenic Uptake and Antioxidative Enzymes in As-Exposed Rice Seedlings

Arsenic (As) and selenium (Se) are two metalloids found in the environment. As it poses a significant threat to human health and plant growth due to its prevalence and toxicity, however Se is a required micronutrient for human health. In this study hydroponic experiments were performed to investigate whether endogenous Se can mitigate As toxicity in rice (Oryza sativa L.). We found that As uptake by rice roots increased by pretreatment with selenateSe(VI) or selenite Se(IV). However, co-application of arsenate As(V) or arsenite As(III) with selenate markedly reduced the uptake of As by roots. Co- or pretreatment with Se with five µM of As(V) or one µM of As(III) significantly decreased shoot As content. Conversely, Se pretreatment before the addition of five µM of As(III) or one µM of As(V) resulted in As accumulation in the shoot compared to As and Se co-application. As translocation to the shoot was lower whereas the transfer factor was higher upon the simultaneous application of Se and As compared to Se pretreatment. Se supplementation with As(III) or pretreatment increased antioxidant enzymes: Superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) increased in the root and shoot, but decreased glutathione (GSH) and malondialdehyde (MDA) contents in the shoot. Plants under As(V) treatment showed the same trend except that CAT content decreased in the root and shoot, while MDA content increased in the shoot. These results suggest that cultivating rice in the presence of Se can reduce the accumulation of toxic As in seedlings, thus ensuring the safety of this important crop for human consumption.

Effect of pH and citric acid on the growth, arsenic accumulation, and phytochelatin synthesis in Eupatorium cannabinum L., a promising plant for phytostabilization

Heavy-metal contamination of soils has increased in the last decades due to anthropogenic and industrial activities. Arsenic is one of the pollutants that is commonly found in industrial soils and is toxic for both plants and humans. The pH of the soil or the culture medium is one of the most important factors that interferes with the bioavailability of this metalloid to the plant. The addition of chelating agents, such as citric acid (CA), can increase the absorption of As by plants. Therefore, the objective of this work is to study the effect of the pH and the exogenous addition of citric acid on the growth, As accumulation, and thiol compounds in Eupatorium cannabinum; this plant grows naturally in contaminated soils in Asturias, Spain, and has a potential use in phytoremediation. The results showed that E. cannabinum was able to tolerate As stress even at extreme pH values and accumulated a high amounts of As in its roots, which makes it a promising species for the phytostabilization of soils polluted with this metalloid. An addition of 20 mg CA L^-1 led to increased biomass and As accumulation at acidic pH. In order to determine if thiolic compounds, such as phytochelatins, are involved in As accumulation and detoxification in E. cannabinum, we analyzed the synthesis of these compounds in the presence and absence of As and/or citric acid. Our results suggest that these thiolic compounds play a major role in As detoxification, since the presence of CA as a chelating agent reduced the amount of thiols necessary to cope with the toxicity caused by As.

Physiological and iTRAQ-Based Quantitative Proteomics Analysis of Methyl Jasmonate-Induced Tolerance in Brassica napus Under Arsenic Stress

Brassica napus plants exposed to 200 μM arsenic (As) exhibited high-level of stress condition, which led to inhibited growth, enhanced lipid peroxidation, and disrupted cellular ultrastructures. Exogenous application of methyl jasmonate (MeJA) alleviated the As-induced oxidative stress and improved the plant growth and photosynthesis. In this study, changes in the B. napus leaf proteome are investigated in order to identify molecular mechanisms involved in MeJA-induced As tolerance. The study identifies 177 proteins that are differentially expressed in cultivar ZS 758; while 200 differentially expressed proteins are accumulated in Zheda 622, when exposed to As alone and MeJA+As treatments, respectively. The main objective was to identify the MeJA-regulated protein under As stress. Consistent with this, iTRAQ detected 61 proteins which are significantly accumulated in ZS 758 leaves treated with MeJA under As stress. While in Zheda 622, iTRAQ detected 49 MeJA-induced proteins under As stress. These significantly expressed proteins are further divided into five groups on the base of their function, that is, stress and defense, photosynthesis, carbohydrates and energy production, protein metabolism, and secondary metabolites. Taken together, this study sheds light on the molecular mechanisms involved in MeJA-induced As tolerance in B. napus leaves and suggests a more active involvement of MeJA in plant physiological processes.

Sodium arsenite effect on Vitis vinifera L. Physiology

Sodium arsenite (NaAsO₂) was especially used as a dormant spray to control grapevine trunk diseases (GTDs) in European vineyards until 2003 when it was banned. It was an efficient product but it was banned due to high risk for human health and the environment. Now, as one of the consequences with climatic changes, GTDs threaten the sustainability of vineyards since no similar and efficacious sprays are presently available to reduce the impact of GTDs. Research efforts were devoted to identify other active ingredients and biological control agents but they remained limited in term of efficacy. New solutions might follow from a better understanding of the modes of action of sodium arsenite which are currently lacking, specially its impact on grapevine physiology. For this study, grafted plants cv. Tempranillo were sprayed by sodium arsenite at the end of the winter. During the vegetative period, the impact on plant physiology was studied by measurement of the photosynthetic activity, the vine growth and development, and some defense responses. Our results showed that arsenic was translocated throughout the vine with an increasing gradient from the leaves to the root system, that photosynthesis was firstly reduced and then stimulated, and that plant tolerance responses were induced especially antioxidant system. The activation of grapevine defense responses by sodium arsenite could be a complementary action to fight fungal pathogens in addition to the fungicide effect.

Effects of kinetin on plant growth and chloroplast ultrastructure of two Pteris species under arsenate stress

Cytokinins (CTKs) are effective in alleviating abiotic stresses on plants, but little information is available regarding the effects of CTKs on arsenic (As) accumulation and changes of chloroplast ultrastructure in plants with different As-accumulating ability. Here a hydroponic experiment was designed to evaluate the effects of different concentration of kinetin (KT, 0-40 mg/L) on growth and chloroplast ultrastructure of As hyperaccumulator Pteris cretica var. nervosa and non-hyperaccumulator Pteris ensiformis treated by 5 mg/L arsenate for 14 days. The growth parameters, As accumulation, contents of photosynthetic pigments and chloroplast ultrastructure were examined. The results showed that KT promoted the growth of two plants, and significantly increased As accumulation and translocation in P. cretica var. nervosa and P. ensiformis at 5 and 20 mg/L, respectively. Additionally, the contents of chlorophyll a and carotenoid in two plants showed no significant difference at 20 mg/L KT compared to the control. Chloroplast ultrastructure of P. cretica var. nervosa was integral with KT application. Comparatively, the swollen chloroplasts were increased, plasmolysis appeared, and chloroplast grana slice layers and stroma lamellas were clearly separated or distorted at 5 mg/L KT in P. ensiformis. The length and width of chloroplasts in P. cretica var. nervosa were significantly increased with KT addition compared to the control. However, the length of chloroplasts in P. ensiformis was significantly decreased but their width showed no significant change. Furthermore, the deterioration of chloroplast ultrastructure in P. ensiformis was ameliorated by 40 mg/L KT. These results suggested that KT increased As accumulation and was beneficial to maintain the photosynthetic pigments for a good growth of plants. Therefore, KT could maintain and reorganize the ultrastructure integrality of As-stressed chloroplasts to some extent for the two plants, especially at high concentration.

Ecotoxicological and Interactive Effects of Copper and Chromium on Physiochemical, Ultrastructural, and Molecular Profiling in Brassica napus L

Heavy metal accumulation causes huge environmental problems, particularly in agricultural ecosystems which have deteriorative effects on the yield and quality of crops. Individual copper (Cu) and chromium (Cr) effects have been investigated extensively in plants; however, co-contamination of Cu and Cr induced stress on Brassica napus L. is still unclear. In the present experiment, the interactive effects of Cu and Cr were studied in two B. napus cultivars (Zheda 622 and ZS 758). Results showed that the application of Cr was more toxic than Cu, and their combined stress had shown a significant adverse effect on plant growth. Biomass and photosynthetic pigment were decreased remarkably under all metal treatments. Individual treatments of Cu and Cr and their combination cause the accumulation of ROS and lipid peroxidation. Moreover, the activities of antioxidant enzymes and their mRNA transcription levels, such as catalase (CAT), ascorbate peroxidase, glutathione reductase, superoxide dismutase, and peroxidase, were increased, especially when treated with Cr alone or under Cu+Cr combined treatment in both cultivars, except for the CAT activity which was decreased in both leaves and roots of sensitive cultivar Zheda 622 as compared with their respective controls. Additionally, nonenzymatic antioxidants like reduced and oxidized glutathione showed a differential activity pattern in roots and leaves of both cultivars. A more pronounced modification in chloroplast ultrastructure was observed in both cultivars under Cu+Cr treatment followed by Cr and Cu alone treatments. Furthermore, synergistic effects of Cu and Cr were prominent; this may be due to the enhanced metals uptake under combined treatment, which suggests that Cr and Cu interaction is not competitive but is rather additive and genotypic-dependent.

Arsenic-induced stress activates sulfur metabolism in different organs of garlic (Allium sativum L.) plants accompanied by a general decline of the NADPH-generating systems in roots

Arsenic (As) contamination is a major environmental problem which affects most living organisms from plants to animals. This metalloid poses a health risk for humans through its accumulation in crops and water. Using garlic (Allium sativum L.) plants as model crop exposed to 200μM arsenate, a comparative study among their main organs (roots and shoots) was made. The analysis of arsenic, glutathione (GSH), phytochelatins (PCs) and lipid peroxidation contents with the activities of antioxidant enzymes (catalase, superoxide dismutase, ascorbate-glutathione cycle), and the main components of the NADPH-generating system, including glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), NADP-malic enzyme (NADP-ME) and NADP-isocitrate dehydrogenase (NADP-ICDH) was carried out. Data showed a correlation among arsenic accumulation in the different organs, PCs content and the antioxidative response, with a general decline of the NADPH-generating systems in roots. Overall, our results demonstrate that there are clear connections between arsenic uptake, increase of their As-chelating capacity in roots and a decline of antioxidative enzyme activities (catalase and the ascorbate peroxidase) whose alteration provoked As-induced oxidative stress. Thus, the data suggest that roots act as barrier of arsenic mediated by a prominent sulfur metabolism which is characterized by the biosynthesis of high amount of PCs.

Arsenic-induced genotoxic responses and their amelioration by diphenylene iodonium, 24-epibrassinolide and proline in Glycine max L

Presence of the toxic metalloid, "arsenic (As)" is ubiquitous in the environment especially in the soil and water. Its excess availability in the soil retards growth and metabolism of plants via (a) slowing down the cell division/elongation, (b) overproduction of reactive oxygen species (ROS), (c) modulation of antioxidant enzymes, and (d) alteration of DNA profile/genomic template stability (GTS). In the current study, diphenylene iodonium (DPI), 24-epibrassinolide (EBL) and proline (Pro) were used to analyze their roles in eliminating the adverse effects of As. Glycine max L. (variety JS 335) seeds were subjected to As (75 μM, Sodium arsenite was used as source of As), and in combination with DPI (10 μM), EBL (0.5 μM) or Pro (10 mM), for five consecutive days, and effects of these treatment combinations were analyzed on germination percentage, biomass, membrane stability, GTS and expressions of defensive genes. In addition, the levels of As, ROS, malondialdehyde, DNA content, oxidation, fragmentation, polymorphism, DNase activity, endogenous Pro and pyrroline-5-carboxylate synthetase activity were evaluated. The results indicated that the treatments of DPI, EBL or Pro are capable to alleviate detrimental effects of As, gauged from above variables, but with different magnitudes. Apropos As-stress mitigation, Pro was found to be the most effective under the confines of the study protocol. This study certainly provides new ideas for intensifying studies to unravel elusive central mechanism of amelioration involving use of DPI, EBL or Pro in plants with confirmed As-toxicity.

Differential subcellular distribution and chemical forms of cadmium and copper in Brassica napus

Metal subcellular fractions and chemical profile highly reflect their level of toxicity to plants. Cadmium and Cu, two different but potentially toxic metals, were compared in the present study for their subcellular distribution and chemical forms in two Brassica napus cultivars (Zheda 622 and ZS 758). Five-week-old seedlings were hydroponically exposed to metal stress and analyzed after 15 days of treatment. In both cultivars, Cd was less retained at cell wall, thus major part of Cd accumulated in the soluble fraction. By contrast, handsome amount of Cu was sequestrated in both cell wall and vacuole containing fraction. Across sensitive organelles, Cu preferentially accumulated in chloroplasts, while Cd was equally distributed in chloroplasts and mitochondria; the two metals intruded nucleus at lesser degree. Further, Cd and Cu differentially interacted with various cellular ligands, and the extent of interaction was higher in the tolerant cultivar ZS 758. Copper was remarkably sequestrated by phosphates, and secondarily by peptide-ligands; inversely, the role of phosphates was secondary in Cd complexation, which was mainly achieved by peptide-ligands. Additional amount of Cu was aggregated with oxalates, but oxalate-bound Cd was scarcely detected. Current results have demonstrated varied toxicological and detoxification pathways of Cd and Cu in B. napus, suggesting that the efficiency of different alleviation strategies could vary against Cd and Cu toxicity to plants.

Role of exogenous salicylic acid in regulating physio-morphic and molecular changes under chromium toxicity in black- and yellow- seeded Brassica napus L

Salicylic acid (SA) mediates tolerance mechanisms in plants against a wide spectrum of biotic and abiotic stresses. Therefore, the present study was carried out to determine how SA regulates the plant protection mechanisms in two cultivars of oilseed rape (Brassica napus L.) under chromium (Cr) stress. Exogenously applied SA enhanced plant growth, increased dry biomasses, and strengthened the reactive oxygen scavenging system by improving cell organelles that were severely damaged via Cr toxicity. The contents of Cr were significantly enhanced in both root and leaf of cultivar Zheda 622 (yellow color) compared with cultivar ZS 758 (black color). Exogenous application of SA significantly reduced the Cr contents in both plant organs as well as enhanced the SA contents under Cr stress. A dose-dependent increase was observed in reactive oxygen species (ROS) generation under Cr stress. To ease the inimical effects of ROS, plants' defense systems were induced under Cr stress, and SA further enhanced protection. Further, TEM micrographs results showed that Cr stress alone significantly ruptured the plant cell organelles of both cultivars by increasing the size of starch grain and the number of plastoglobuli, damaging the chloroplast and mitochondrion structures. However, exogenously applied SA significantly recovered these damages in the plant cells of both cultivars. It was also observed that cultivar ZS 758 was proved to be more tolerant under Cr toxicity. Gene expression analysis revealed that combined treatments of Cr and SA increased antioxidant-related gene expression in both cultivars. Findings of the present study demonstrate that SA induces the enzymatic antioxidant activities and related gene expression, secondary metabolism, and improves the cell structural changes and the transcript level of specific stress-associated proteins in root and leaf of two oilseed rape cultivars under Cr toxicity.

Subcellular distribution, modulation of antioxidant and stress-related genes response to arsenic in Brassica napus L

Arsenic (As) is an environmental toxin pollutant that affects the numerous physiological processes of plants. In present study, two Brassica napus L. cultivars were subjected to various concentrations (0, 50, 100, and 200 µM) of As for 14 days, plants were examined for As subcellular distribution, photosynthesis parameters, oxidative stress, and ultrastructural changes under As-stress. Differential fraction analysis showed that significant amount of As was accumulated in the cell wall as compared to other organelles. Decline in photosynthetic efficiency under As stress was observed in term of reduced pigment contents and gas exchange parameters. Differential responses of antioxidants at both enzymatic and gene levels to higher As stress were more pronounced in cultivar ZS 758 as compared to Zheda 622. The qRT-PCR analysis showed that heat shock protein 90 (Hsp90) and metallothionein were over-expressed in As stressed B. napus plants. Disorganization of cell structure and the damages in different organelles were some of the obvious variations in cultivar Zheda 622 as compared to ZS 758.

Mechanisms of biochar-mediated alleviation of toxicity of trace elements in plants: a critical review

Trace elements (TEs) contamination is one of the main abiotic stresses which limit plant growth and deteriorate the food quality by their entry into food chain. In recent, biochar (BC) soil amendment has been widely reported for the reduction of TE(s) uptake and toxicity in plants. This review summarizes the role of BC in enhancing TE(s) tolerance in plants. Under TE(s) stress, BC application increased plant growth, biomass, photosynthetic pigments, grain yield, and quality. The key mechanisms evoked are immobilization of TE(s) in the soil, increase in soil pH, alteration of TE(s) redox state in the soil, and improvement in soil physical and biological properties under TE(s) stress. However, these mechanisms vary with plant species, genotypes, growth conditions, duration of stress imposed, BC type, and preparation methods. This review highlights the potential for improving plant resistance to TE(s) stress by BC application and provides a theoretical basis for application of BC in TE(s) contaminated soils worldwide.

Methyl Jasmonate Regulates Antioxidant Defense and Suppresses Arsenic Uptake in Brassica napus L

Methyl jasmonate (MJ) is an important plant growth regulator, involved in plant defense against abiotic stresses, however, its possible function in response to metal stress is poorly understood. In the present study, the effect of MJ on physiological and biochemical changes of the plants exposed to arsenic (As) stress were investigated in two Brassica napus L. cultivars (ZS 758 - a black seed type, and Zheda 622 - a yellow seed type). The As treatment at 200 μM was more phytotoxic, however, its combined application with MJ resulted in significant increase in leaf chlorophyll fluorescence, biomass production and reduced malondialdehyde content compared with As stressed plants. The application of MJ minimized the oxidative stress, as revealed via a lower level of reactive oxygen species (ROS) synthesis (H2O2 and OH(-)) in leaves and the maintenance of high redox states of glutathione and ascorbate. Enhanced enzymatic activities and gene expression of important antioxidants (SOD, APX, CAT, POD), secondary metabolites (PAL, PPO, CAD) and induction of lypoxygenase gene suggest that MJ plays an effective role in the regulation of multiple transcriptional pathways which were involved in oxidative stress responses. The content of As was higher in yellow seeded plants (cv. Zheda 622) as compared to black seeded plants (ZS 758). The application of MJ significantly reduced the As content in leaves and roots of both cultivars. Findings of the present study reveal that MJ improves ROS scavenging through enhanced antioxidant defense system, secondary metabolite and reduced As contents in both the cultivars.

Citric acid assisted phytoremediation of copper by Brassica napus L

Use of organic acids for promoting heavy metals phytoextraction is gaining worldwide attention. The present study investigated the influence of citric acid (CA) in enhancing copper (Cu) uptake by Brassica napus L. seedlings. 6 Weeks old B. napus seedlings were exposed to different levels of copper (Cu, 0, 50 and 100µM) alone or with CA (2.5mM) in a nutrient medium for 40 days. Exposure to elevated Cu levels (50 and 100µM) significantly reduced the growth, biomass production, chlorophyll content, gas exchange attributes and soluble proteins of B. napus seedlings. In addition, Cu toxicity increased the production of hydrogen peroxide (H2O2), malondialdehyde (MDA) and electrolyte leakage (EL) in leaf and root tissues of B. napus. Activities of antioxidant enzymes such as guaiacol peroxidase (POD), superoxide dismutase (SOD), catalases (CAT), ascorbate peroxidase (APX) in root and shoot tissues of B. napus were increased in response to lower Cu concentration (50µM) but increased under higher Cu concentration (100µM). Addition of CA into nutrient medium significantly alleviated Cu toxicity effects on B. napus seedlings by improving photosynthetic capacity and ultimately plant growth. Increased activities of antioxidant enzymes in CA-treated plants seems to play a role in capturing of stress-induced reactive oxygen species as was evident from lower level of H2O2, MDA and EL in CA-treated plants. Increasing Cu concentration in the nutrient medium significantly increased Cu concentration in in B. napus tissues. Cu uptake was further increased by CA application. These results suggested that CA might be a useful strategy for increasing phytoextraction of Cu from contaminated soils.