Pb Stress Research Articles

The Silicon Effects on Antioxidant System of Wheat Cultivars under Pb Stress

Pb poses a major threat to plant growth and silicon can reduce its toxicity. This work was conducted hydroponically as a completely randomized factorial design to study the effect of Si (70 and 140 ppm) on Triticum aestivum cultivars Chamran and Shiroudi under Pb stress (150 ppm). Pb caused significant increases in the H2O2, free amino acids and proline contents of wheat cultivars and MDA content of cv. Chamran. Furthermore, Pb stimulated the activities of SOD and APX in cv. Chamran and POD in cv. Shiroudi. Si application significantly increased the free amino acid content of cultivars and proline content of cv. Chamran in absence of Pb. The protein content of wheat cultivars significantly increased at 70 ppm of Si in absence of Pb and at both levels in presence of Pb. In cv. Chamran, Si application significantly decreased the H2O2 content and the activities of SOD, POD and APX at both levels, free amino acids and proline contents at 70 ppm and MDA content at 140 ppm in presence of Pb. In cv. Shiroudi, Si application significantly decreased the proline content at both levels, H2O2 and free amino acids contents at 70 ppm and MDA content at 140 ppm.

Characterisation of early responses in lead accumulation and localization of Salix babylonica L. roots

BackgroundLead (Pb) is a harmful pollutant that disrupts normal functions from the cell to organ levels. Salix babylonica is characterized by high biomass productivity, high transpiration rates, and species specific Pb. Better understanding the accumulating and transporting Pb capability in shoots and roots of S. babylonica, the toxic effects of Pb and the subcellular distribution of Pb is very important.ResultsPb exerted inhibitory effects on the roots and shoots growth at all Pb concentrations. According to the results utilizing inductively coupled plasma atomic emission spectrometry (ICP-AES), S. babylonica can be considered as a plant with great phytoextraction potentials as translocation factor (TF) value > 1 is observed in all treatment groups throughout the experiment. The Leadmium™ Green AM dye test results indicated that Pb ions initially entered elongation zone cells and accumulated in this area. Then, ions were gradually accumulated in the meristem zone. After 24 h of Pb exposure, Pb accumulated in the meristem zone. The scanning electron microscopy (SEM) and energy-dispersive X-ray analyses (EDXA) results confirmed the fluorescent probe observations and indicated that Pb was localized to the cell wall and cytoplasm. In transverse sections of the mature zone, Pb levels in the cell wall and cytoplasm of epidermal cells was the lowest compared to cortical and vessel cells, and an increasing trend in Pb content was detected in cortical cells from the epidermis to vascular cylinder. Similar results were shown in the Pb content in the cell wall and cytoplasm of the transverse sections of the meristem. Cell damage in the roots exposed to Pb was detected by propidium iodide (PI) staining, which was in agreement with the findings of Pb absorption in different zones of S. babylonica roots under Pb stress.ConclusionS. babylonica L. is observed as a plant with great potential of Pb-accumulation and Pb-tolerance. The information obtained here of Pb accumulation and localization in S. babylonica roots can furthers our understanding of Pb-induced toxicity and its tolerance mechanisms, which will provide valuable and scientific information to phytoremediation investigations of other woody plants under Pb stress.

Auxins and Cytokinins Regulate Phytohormone Homeostasis and Thiol-Mediated Detoxification in the Green Alga Acutodesmus obliquus Exposed to Lead Stress

Phytohormones, such as auxins and cytokinins, take part in the integration of growth control and stress response, but their role in algal adaptation to heavy metal remains to be elucidated. The current research indicated that lead (Pb), one of the most toxic metals in nature, causes severe depletion of endogenous cytokinins, auxins, and gibberellin and an increase in abscisic acid content in the green alga Acutodesmus obliquus. Exogenous auxins and cytokinins alleviate Pb toxicity through the regulation of the endogenous phytohormones’ levels. Exogenously applied auxins provoked the coordinated activation metal tolerance mechanisms leading to the increase in phytochelatin synthase activity and accumulation of phytochelatins and their precursors, which are essential for Pb sequestration. On the other hand, phytochelatin synthesis decreased in algal cells treated with cytokinins. Significant changes in the levels of low molecular weight metabolites, mainly involved in metal chelation and glutathione synthesis pathway under the influence of phytohormones in algal cells growing in the presence of Pb stress, were observed. This is the first report showing that auxins and cytokinins are important regulatory factors in algal adaptation strategies to heavy metal stress based on thiol-mediated compounds and the maintenance of phytohormone homeostasis.

Lead Tolerance and Enrichment Characteristics of Several Ornamentals Under Hydroponic Culture.

The growth response, tolerance, and enrichment characteristics of six ornamental species, Chlorophytum comosum, Calendula officinalis, Iris lacteal, Belamcanda chinensis, Saponaria officinalis, and Polygonum lapathifolium were studied under hydroponic culture with lead (Pb) concentrations ranging from 0 to 1000mg/L. The results showed that the growth of the tested ornamental species under Pb stress was inhibited. Belamcanda chinensis presented the largest tolerance index (0.75), and Calendula officinalis had the highest toxicity threshold (500mg/L) under Pb stress. The highest Pb contents in the shoots were detected in Iris lacteal and Belamcanda chinensis. The enrichment coefficients in the shoots of Iris lacteal and Belamcanda chinensis were significantly higher than those in the other ornamental species. In conclusion, Iris lacteal and Belamcanda chinensis are the most tolerant and have the greatest Pb enrichment and translocation abilities under Pb stress, and thus, they have a strong potential to restore Pb-contaminated water bodies and soils.

Differential Growth and Metal Accumulation Response of Brachiaria Mutica and Leptochloa Fusca on Cadmium and Lead Contaminated Soil

ABSTRACT This work aims to assess growth, physiology, and metal uptake response of Brachiaria mutica and Leptochloa fusca under different contamination levels of Cd (10 and 50 mg kg−1) and Pb (50 and 250 mg kg−1) stress. Results of pot trial showed increasing metal concentration affected B. mutica more as compared to L. fusca. In B. mutica metal stress substantially reduced shoot dry biomass, root dry biomass, total chlorophylls, and carotenoids contents by 89%, 85%, 65%, and 61%, respectively, while enhanced the SOD activity up to 62 U min−1 g−1 FW. L. fusca showed better growth, chlorophylls and carotenoid contents, SOD activity (up to 79 U min−1 g−1 FW), shoot metal uptake potential (Cd 110 µg pot−1, Pb 91.57 µg pot−1), and root metal concentration (Cd 126 mg kg−1 dm, Pb 117 mg kg−1 dm) compared to B. mutica under Pb and Cd stress. While both grass species showed metal translocation factor less than unity under all levels of metal stress. Keeping in view the above results, it is concluded that L. fusca having better growth and physiology with TF < 1 could be used for phytostabilization of Pb and Cd to reclaim the soil having moderate to lower levels of contamination.

Lead induced changes in biomarkers and proteome map of Chicory (Cichorium intybus L.)

Lead (Pb) toxicity is a serious environmental problem as it affects the food production by interfering plant growth and development, thus declines the production yield. In the present research work, Cichorium intybus L. plants were subjected to different concentrations of Pb (0, 100, 200 and 300µM) upto 46days to determine the oxidative stress. The length of root and shoot, accumulation of biomass were estimated along with the changes in biomarkers (H2O2 and TBARS). Further proteomic analysis of chicory leaves (46days old) at 300µM Pb concentration was done to identify the proteins of interest. The root growth increased significantly in a concentration-dependent manner however; shoot growth, biomass accumulation declined significantly with Pb stress compared to control. Changes in biomarkers (H2O2 and TBARS) content elevated with the increment in the concentration of metal treatment but exhibited a gradual decline at 300µM Pb treatment.. Proteomics data of 46days old chicory plants under 300 µM Pb stress analyzed by PDQuest software detected approximately 168 protein spots on each gel and 81 spots were differentially expressed in which 16 were up-regulated and 13 were down-regulated. The present study suggested that chicory possess a strong antioxidative defense system to combat Pb stress and thus could be explored for cultivation in Pb contaminated soils.

Physiological responses and tolerance of flax (Linum usitatissimum L.) to lead stress

Flax (Linum usitatissimum L.) is a common commercial crop that is widely cultivated for fibre, oil and medicinal products globally. To select flax varieties with lead (Pb) tolerance and explore the associated tolerance mechanism under Pb stress, 19 flax varieties were grown using a hydroponic method with added Pb(NO3)2. Our results showed that L. usitatissimum ‘Milas’ displayed the highest tolerance to Pb stress, whereas L. usitatissimum ‘Yuan 2000’ was the most sensitive variety under 1 mM of Pb(NO3)2. ‘Milas’ accumulated lesser Pb than ‘Yuan 2000’. In addition, under Pb stress, the activities of peroxidase (POD) and superoxide dismutase (SOD) were higher in ‘Milas’ than in ‘Yuan 2000’, whereas the malondialdehyde (MDA) content of the aerial part and the root were lower in ‘Milas’ than in ‘Yuan 2000’. The expression levels of heavy metal stress-related genes were higher in ‘Milas’ than in ‘Yuan 2000’. Our results provide information about breeding flax varieties with Pb tolerance and the mechanisms underlying the response to Pb stress.

Genotoxic effects and proteomic analysis on Allium cepa var. agrogarum L. root cells under Pb stress.

Ionic lead (Pb) in the environment has accumulated due to anthropogenic activities, causing a potential threat to plants and plant consumers. We conducted this study to reveal the molecular mechanism of Pb stress response in plants. The effects of Pb (5.0 and 15.0 μM) on mitosis, DNA replication, gene expression and proteins in root-tip cells of Allium cepa var. agrogarum L. were addressed. The results indicated that root growth was inhibited dramatically in Pb treatment groups. Chromosomal aberrations were observed and the mitotic index decreased during Pb treatments at different concentrations. The accumulation of reactive oxygen species (ROS) in onion roots was induced by Pb stress. Pb increased DNA damage and suppressed cell cycle progression. The above toxic effects got more serious with increasing Pb concentration and prolonging exposure time. A total of 17 proteins were expressed differentially between control and Pb exposure groups. Under Pb treatment, the decreased expression of Anx D1 indicated decreased defensive response; the decreased expression of SHMT1 indicated decreased respiration; the decreased expression of COMT2 indicated decreased response of other funtions; the increased expression of NDPK indicated increased transcription and protein synthesis; the increased expression of PR1 and CHI1 indicated increased pathogen invasion; the increased expression of ORC5 and MPK5 indicated the reduced DNA replicating activity; the decreased expression of POLD1 indicated the reduced DNA repair activity. Our results provide new insights at the proteomic level into the Pb-induced responses, defensive responses and toxic effects, and provide new molecular markers of the early events of plant responses to Pb toxicity.

Growth responses and physiological and biochemical changes in five ornamental plants grown in urban lead-contaminated soils.

An increasing concentration of lead (Pb) in urban contaminated soil due to anthropogenic activities has been a global issue threatening human health. The use of urban ornamental plants as phytoremediation of Pb-contaminated soil is a new choice. In the present experiment, the physiological and biochemical response of five ornamental plants to increase in concentrations of C4H6O4Pb·H2O in the soil were measured to investigate these plans' Pb tolerance strategies and abilities. Our results showed that Pb stress significantly inhibited the growth and the biomass of all the plants. The root activity (RA), net photosynthetic rate (P n), and chlorophyll (Chl) content in Pb-stressed leaves were significantly decreased, whereas the leaf proline (Pro), soluble sugar (SS), and membrane stability index (MSI) were remarkable increased compared with those in the control group. By application of all-subsets regression and linear regression, the reduction in photosynthetic capacity in the five plants is mainly due to the decrease in the leaf Chl content caused by Pb stress. The bioconcentration factor (BCF) in Canna generalis was greater than 1, while in the other plants were lower than 1, suggesting that Canna generalis had the highest Pb accumulation ability. The translocation factor (TF) in all the plants were lower than 1, suggesting that Pb preferentially accumulated in the external part of roots. By calculating the comprehensive evaluation value (CEV), Iris germanica L. was found to be the most sensitive species, and Canna generalis was the most tolerant species, to Pb stress among the five ornamental plants.

How mycorrhiza symbiosis help coriander (Coriandrum sativum L.) plants grow better under contaminated soil?

Heavy metals (HMs) are environmental pollutants of great concern to plants because of their high potential toxicity, and plants that are not able to tolerate high concentrations of HMs in the soil can become tolerant or increase their performance when associated with arbuscular mycorrhizal (AFM) fungi. A greenhouse pot experiment was conducted to study the impact of arbuscular mycorrhiza on traits of Coriander plants under Pb stress. Experimental factors included soil contamination with Pb (0, 500, 1000, and 1500 ppm) and mycorrhizal fungus inoculation (Glomus mosseae). Biomass, photosynthetic pigments, enzymatic and non-enzymatic antioxidants, Malondialdehyde (MDA) content, Pb concentration in shoot and root, and root colonization were recorded. Pb stress affected coriander traits such as decreased biomass, photosynthetic pigments such as chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid almost 57, 13, 50, 23 and 10%, respectively. Also in contrast phenol, flavonoid in non-inoculated treatments, activities of superoxide dismutase (SOD), and peroxidase (POD) enzymes, and accumulation of malondialdehyde accumulation increased with increasing Pb concentrations, but catalase (CAT) activity increased just until 500 ppm Pb. Symbiosis with mycorrhizal fungi decreased the toxic effects of Pb stress on coriander plants via some mechanism such as adjusting enzymatic and non-enzymatic antioxidants and protecting photosynthetic pigments. The Pb accumulation decreased almost 9 and 15% in root and shoot by 1500 ppm Pb, respectively In general, these results suggest that mycorrhizal inoculation inhibits the detrimental effects of Pb stress on coriander plants.

Minimizing Adverse Effects of Pb on Maize Plants by Combined Treatment with Jasmonic, Salicylic Acids and Proline

Lead (Pb) is a toxic heavy metal (HM) that harms plant growth and productivity. Phytohormones, such as jasmonic acid (JA) and salicylic acid (SA), and osmoprotectants, such as proline (Pro), play an important role in the physiological and biochemical processes of plants. We investigated the effect of exogenous applications of JA, SA, Pro, and their combination on Pb-stress tolerance in maize as well as their effect on physiological, biochemical, and yield traits. Pb exposure severely affected maize plants, reducing growth, yield, photosynthetic pigments, and mineral (nitrogen, phosphorus, and potassium) nutrients, as well as enhancing electrolyte leakage (EL), malondialdehyde (MDA) accumulation, osmolytes, and non-enzymatic and enzymatic antioxidants. The application of JA, SA, Pro, and their combination enhanced plant growth and induced pigment biosynthesis, and decreased EL, MDA accumulation, and Pb concentration. All treatments enhanced Pro and total soluble sugar production, glutathione activity, ascorbic acid, phenol, superoxide dismutase, catalase, peroxidase, and mineral nutrients. JA, SA, and Pro application improved physiological processes directly or indirectly, thereby enhancing the ability of maize plants to overcome oxidative damage caused by Pb toxicity. The combination of JA, SA, and Pro was the most efficient treatment for maize plant growth and development, eliminating the negative consequences of Pb stress.

Changes in electricity production and microbial community evolution in constructed wetland-microbial fuel cell exposed to wastewater containing Pb(II)

Two constructed wetland microbial fuel cell (CW-MFC) devices, experimental group (EG, with 5 mg/L Pb(II) addition) and control group (CG) were built to explore the changes in power generation, wastewater purification and microbial community structure under Pb(II) stress. The voltage of EG (343.16 ± 12.14 mV) was significantly higher (p < 0.01) than that of CG (295.49 ± 13.91 mV), and the highest power density of the EG and CG were 7.432 mW·m−2 and 3.873 mW·m−2, respectively. There was no significant difference in the removal of common pollutants between these groups except for the NH4+-N removal efficiency, which was probably caused by the inhibition of the bioactivity of Comamonas (AOB) in the anode of the experimental group by Pb(II). Pb(II) was effectively removed by CW-MFC (84.86 ± 3%), and the abundant amount of fulvic acid-like matter in the extracellular polymeric substance (EPS) of the EG contributed to its removal. The presence of Pb(II) had a negative effect on both microbial community diversity and species richness. The abundance of a lead resistance gene, pbrT, decreased with long-term Pb(II) pressure. This is evidence of microbial adaptation to Pb(II).

Exogenous Melatonin Application Enhances Rhizophagus irregularis Symbiosis and Induces the Antioxidant Response of Medicago truncatula Under Lead Stress.

Melatonin is a new kind of plant growth regulator. The aim of this study was to figure out the effect of melatonin on arbuscular mycorrhizal (AM) symbiosis and heavy metal tolerance. A three-factor experiment was conducted to determine the effect of melatonin application on the growth, AM symbiosis, and stress tolerance of Medicago truncatula. A two-factor (AM inoculation and Pb stress) experiment was conducted to determine the effect of AM fungus on melatonin accumulation under Pb stress. AM plants under Pb stress had a higher melatonin accumulation than non-mycorrhizal (NM) plants under Pb stress. Acetylserotonin methyltransferase (ASMT) is the enzymatic reaction of the last step in melatonin synthesis. The accumulation of melatonin may be related to the expression of MtASMT. Melatonin application increased the relative expression of MtPT4 and AM colonization in AM plants. Melatonin application decreased Pb uptake with and without AM inoculation. Both melatonin application and AM inoculation improved M. truncatula growth and increased antioxidant response with Pb stress. These results indicated that melatonin application has positive effects on AM symbiosis and Pb stress tolerance under Pb stress. AM inoculation improve melatonin synthesis capacity under Pb stress. Melatonin application may improve AM plant growth by enhancing AM symbiosis, stimulating antioxidant response, and inhibiting Pb uptake.

Role of the proteome in providing phenotypic stability in control and ectomycorrhizal poplar plants exposed to chronic mild Pb stress

Lead is a dangerous pollutant that accumulates in plant tissues and causes serious damage to plant cell macromolecules. However, plants have evolved numerous tolerance mechanisms, including ectomycorrhizae, to maintain cellular Pb2+ at the lowest possible level. When those mechanisms are successful, Pb-exposed plants should exhibit no negative phenotypic changes. However, actual molecular-level plant adjustments at Pb concentrations below the toxicity threshold are largely unknown, similar to the molecular effects of protective ectomycorrhizal root colonization. In this study, we (1) determined the molecular adjustments in plants exposed to Pb but without visible Pb stress symptoms and (2) examined ectomycorrhizal root colonization (the role of fungal biofilters) with respect to molecular-level Pb perception by plant root cells. Biochemical, microscopic, proteomic and metabolomic studies were performed to determine the molecular status of Populus × canescens microcuttings grown in agar medium enriched with 0.75 mM Pb(NO3)2. Noninoculated and inoculated with Paxillus involutus poplars were analyzed in two independent comparisons of the corresponding control and Pb treatments. After six weeks of growth, Pb caused no negative phenotypic effects. No Pb-exposed poplar showed impaired growth or decreased leaf pigmentation. Proteomic signals of intensified Pb sequestration in the plant cell wall and vacuoles, cytoskeleton modifications, H+-ATPase-14-3-3 interactions, and stabilization of protein turnover in chronically Pb-exposed plants co-occurred with high metabolomic stability. There were no differentially abundant root primary metabolites; only a few differentially abundant root secondary metabolites and no Pb-triggered ROS burst were observed. Our results strongly suggest that proteome adjustments targeting Pb sequestration and ROS scavenging, which are considerably similar but less intensive in ectomycorrhizal poplars than in control poplars due to the P. involutus biofilter (as confirmed in a mineral study), were responsible for the metabolomic and phenotypic stability of poplars exposed to chronic mild Pb stress.

Cadmium and lead affect the status of mineral nutrients in alfalfa grown on a calcareous soil

ABSTRACT Cadmium (Cd) and lead (Pb) are toxic trace elements which are not essential for plants but can be easily taken up by roots and accumulated in various organs, and cause irreversible damages to plants. A pot experiment was carried out to investigate the individual and combined effects of Cd (0, 10, 20 mg kg−1) and Pb (0, 500, 1000 mg kg−1) level in a calcareous soil on the status of mineral nutrients, including K, P, Ca, Mg, S, Fe, Mn, Cu, and Zn, in alfalfa (Medicago sativa L.) plants. Soil Pb level considerably (P ≤ 0.05) affected the concentrations of more elements in plants than soil Cd level did, and there were combined effects of soil Cd level and Pb level on the concentrations of some nutrients (Ca, Mg, and Cu) in plants. The effects of soil Cd level and Pb level on plant nutrient concentrations varied among plant parts. Cd and Pb contamination did not considerably affect the exudation of carboxylates in the rhizosphere. An increase in rhizosphere pH and exudation of significant amounts of carboxylates (especially oxalate) in the rhizosphere might contribute to the exclusion and detoxification of Cd and Pb. Neither shoot dry mass nor root dry mass was significantly influenced by soil Cd level, but both of them were considerably reduced (by up to 25% and 45% on average for shoot dry mass and root dry mass, respectively) by increasing soil Pb level. The interaction between soil Cd level and Pb level was significant for root dry mass, but not significant for shoot dry mass. The results indicate that alfalfa is tolerant to Cd and Pb stress, and it is promising to grow alfalfa for phytostabilization of Cd and Pb on calcareous soils contaminated with Cd and Pb.

Toxic effects of heavy metals Pb and Cd on mulberry (Morus alba L.) seedling leaves: Photosynthetic function and reactive oxygen species (ROS) metabolism responses.

To explore the mechanism of how lead (Pb) and cadmium (Cd) stress affects photosynthesis of mulberry (Morus alba L.), we looked at the effects of different concentrations of Pb and Cd stress (at 100 and 200μmolL-1), which are two heavy metal elements, on leaf chlorophyll (Chl), photosynthesis gas exchange, Chl fluorescence, and reactive oxygen species (ROS) metabolism in mulberry leaves. The results showed that higher concentrations of Pb and Cd reduced leaf Chl content, especially in Chl a where content was more sensitive than in Chl b. Under Pb and Cd stress, the photosynthetic carbon assimilation capacity of mulberry leaves was reduced, which was a consequence of combined limitations of stomatal and non-stomatal factors. The main non-stomatal factors were decreased photosystem II (PSII) and photosystem I (PSI) activity and carboxylation efficiency (CE). Damage to the donor side of the PSII reaction center was greater than the acceptor side. After being treated with 100μmolL-1 of Pb and Cd, mulberry leaves continued to be able to dissipate excess excitation energy by starting non-photochemical quenching (NPQ), but when Pb and Cd concentrations were increased to 200μmolL-1, the protection mechanism that depends on NPQ was impaired. Excessive excitation energy from chloroplasts promoted a great increase of ROS, such as superoxide anion (O2•-) and H2O2. Moreover, under high Pb and Cd stress, superoxide dismutase (SOD) and ascorbate peroxidase (APX) were also inhibited to some extent, and excessive ROS also resulted in a significantly higher degree of oxidative damage. Compared with Cd, the effect of Pb stress at the same concentration level displayed a significantly lower impact on Chl content, photosynthetic carbon assimilation, and stomatal conductance. Meanwhile, Pb stress mainly damaged activity of the oxygen-evolving complex (OEC) located on PSII donor side, but it reduced the electronic pressure on the PSII acceptor side and PSI. Furthermore, under Pb stress, the NPQ, SOD, and APX activity were all significantly higher than those under Cd stress. Thus under Pb stress, the degree of photoinhibition and oxidative damage of PSII and PSI in mulberry leaves were significantly lower than under Cd stress.

The influence of root zone environment of Suaeda heteroptera on the existence and migration of Pb

ABSTRACT In this paper, the total metal content, exchangeable content, iron-manganese oxide-bound content, carbonate-bound content, organic sulphide-bound content, and residue-level content in the root soil of S. heteroptera under different concentrations of Pb stress were investigated. The changes of Pb in the root zone environment of S. heteroptera were studied, and its distribution characteristics, migration and transformation rules were studied, which provided a theoretical basis for the repair of heavy metal pollution by S. heteroptera. The results showed that planting S. heteroptera reduced the total amount of Pb in each soil layer in the root zone. Under Pb stress, the total heavy metal content, carbonate-bound state, organic sulphide-bound state, and residual Pb content in each layer of the root zone were directly proportional to the concentration. The organic matter sulphide-bound Pb in the surface layer, middle layer, and bottom layer of the root zone was transformed into exchangeable, carbonate-bound, Fe-Mn oxide-bound Pb, and the residual Pb content in the middle and bottom layers of the soil root zone decreased. The existence of S. heteroptera was confirmed, which increased the bioavailability of Pb, so that Pb can be easily absorbed and utilised by plants. Therefore, the cultivation of S. heteroptera has a positive impact on heavy metal pollution in the soil.

Transcriptome profiling of kenaf (Hibiscus cannabinus L.) under plumbic stress conditions implies the involvement of NAC transcription factors regulating reactive oxygen species-dependent programmed cell death.

Heavy metal contamination of soils has become a serious global issue, and bioremediation has been proposed as a potential solution. Kenaf (Hibiscus cannabinus L.) is a fast growing, non-woody multipurpose annual plant that is suitable for removing excess heavy metals from soils. However, there has been relatively little research on the kenaf molecular mechanisms induced in response to an exposure to heavy metal stress. Thus, whole kenaf seedlings grown under control (normal) and stress (plumbic treatment) conditions were sampled for transcriptome sequencing. Unigenes generated through the de novo assembly of clean reads were functionally annotated based on seven databases. Transcription factor (TF)-coding genes were predicted and the physiological traits of the seedlings were analyzed. A total of 44.57 Gb high-quality sequencing data were obtained, which were assembled into 136,854 unigenes. These unigenes included 1,697 that were regarded as differentially expressed genes (DEGs). A GO enrichment analysis of the DEGs indicated that many of them are related to catalytic activities. Moreover, the DEGs appeared to suggest that numerous KEGG pathways are suppressed (e.g., the photosynthesis-involving pathways) or enhanced (like the flavonoid metabolism pathways) in response to Pb stress. Of the 2,066 predicted TF-coding genes, only 55 were differentially expressed between the control and stressed samples. Further analyses suggested that the plumbic stress treatment induced reactive oxygen species-dependent programmed cell death in the kenaf plants via a process that may be regulated by the differentially expressed NAC TF genes.

Evaluating the ecotoxicological effects of Pb contamination on the resistance against Lymantria dispar in forest plant, Larix olgensis.

Heavy metal contamination in forest ecosystems has become increasingly severe, and there is an urgent need to better understand the ecotoxicological effects of heavy metals on the whole forest ecosystems, especially their effects on insect resistance of forest plant. In the present study, the resistance against gypsy moth (Lymantria dispar) larvae in Larix olgensis seedlings grown in non-amended or Pb-amended (at 500 and 1500 mg kg-1 ) soil was evaluated. Pb from the treated soil could be transferred and exerted bio-toxicological effects along the food chain consisting of L. olgensis seedlings and gypsy moth larvae, eventually causing significantly reduction in seedlings growth, as well as larval weight, survival rate and antioxidant capacity. With regard to phytochemical defense, the activities or contents of protease inhibitors (trypsin and chymotrypsin inhibitors) and secondary metabolites (condensed tannin and total phenolics) in Pb-treated larch needles presented a tendency of 'low-promotion, high-inhibition' with the increase of Pb exposure concentration. At the same time, Pearson's correlation coefficients showed that the trade-off hypothesis on energy allocation between phytochemical defense and plant growth was not supported by the data from the L. olgensis seedlings that were exposed to Pb stress, and elemental defense might replace the dominant role of phytochemical defense in L. olgensis seedlings under Pb stress against the gypsy moth larvae. These findings emphasize ecotoxicological effects of heavy metal contaminations along the food chains (forest plants and forest defoliators), and provide a new perspective for optimizing forest pest control strategies in the heavy metal polluted regions. © 2020 Society of Chemical Industry.

Exogenous brassinosteroids increase lead stress tolerance in seed germination and seedling growth of Brassica juncea L.

Lead (Pb) is a highly toxic heavy metal to plants, animals, and human beings. The use of growth regulators has reversed the effects of heavy metal stress on germination and early plant development. The aim of this study was to evaluate the effect of brassinosteroids on seed germination and seedling growth of Brassica juncea (L.) Czern. & Coss. under Pb stress conditions. Two forms of application of 24-epibrassinolide (EBL) were evaluated, application on seeds in pre-soaking and on germination paper, using EBL concentrations of 0, 10-10, 10-8, and 10-6M. Germination and seedling growth parameters were evaluated during the germination test. The activity of the enzymes superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase were determined, as well as the lead content in the seeds and seedlings. The EBL applied at the 10-8M concentration was the most effective in overcoming Pb stress in both forms of application. The antioxidant enzyme defense system was compromised by Pb exposure. However, 10-8M EBL increased the activity of antioxidant enzymes such as catalase and peroxidase to overcome the toxic effects caused by Pb. In addition, EBL at the concentration of 10-8M increased Pb content in seedlings without affecting seedling growth.