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Special Issue "Heavy Metals Accumulation, Toxicity and Detoxification in Plants"

A special issue of International Journal of Molecular Sciences (ISSN 1422-0067). This special issue belongs to the section "Molecular Plant Sciences".

Deadline for manuscript submissions: closed (31 December 2019).

Special Issue Editors

Prof. Dr. Luigi De Bellis
Website
Guest Editor
Department of Biological and Environmental Sciences and Technologies - DBEST; Università del Salento; Centro Ecotekne via Provinciale Lecce Monteroni; 73100 Lecce, Italy
Interests: plant physiology; genomics; biotechnology; pathology; fruit quality
Special Issues and Collections in MDPI journals
Dr. Alessio Aprile
Website
Guest Editor
Department of Biological and Environmental Sciences and Technologies (DiSTeBA), University of Salento, 73100 Lecce, Italy
Interests: crop physiology; plant physiology; heavy metal assimilation; abiotic stresses; drought; antioxidant compounds; biotic stress; Xylella fastidiosa

Special Issue Information

Dear Colleagues,

In recent years, heavy metals have been widely used in agricultural, chemical, domestic, and technological applications causing environmental and soil contaminations. Heavy metals enter the plant system through soil or via the atmosphere and can accumulate, affecting physiological processes; plant growth; yield; and human health if heavy metals are stored in edible tissues. Understanding the regulation mechanisms of plant heavy metals accumulation and partitioning is important to improve the safety of the food chain.

This Special Issue aims to explore three main issues:

(1) The accumulation and partitioning of heavy metals in crops and wild plants;

(2) The toxicity and molecular behaviours of cells, tissues, and their effects on physiology and plant growth;

(3) Detoxification strategies, plant tolerance, and phytoremediation.

Prof. Dr. Luigi De Bellis
Dr. Alessio Aprile
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. International Journal of Molecular Sciences is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. There is an Article Processing Charge (APC) for publication in this open access journal. For details about the APC please see here. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Heavy metals
  • Plant physiological responses to heavy metals
  • Phytoremediation
  • Heavy metal accumulation in plants
  • Toxicity
  • Tolerance
  • Detoxification

Published Papers (20 papers)

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Editorial

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Open AccessEditorial
Editorial for Special Issue “Heavy Metals Accumulation, Toxicity, and Detoxification in Plants”
Int. J. Mol. Sci. 2020, 21(11), 4103; https://doi.org/10.3390/ijms21114103 - 09 Jun 2020
Abstract
“Heavy metals” is a collective term widely applied for the group of metals and metalloids with an atomic density above 4 g/cm3 [...] Full article
(This article belongs to the Special Issue Heavy Metals Accumulation, Toxicity and Detoxification in Plants)
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Research

Jump to: Editorial, Review

Open AccessArticle
Hormesis in Plants: The Role of Oxidative Stress, Auxins and Photosynthesis in Corn Treated with Cd or Pb
Int. J. Mol. Sci. 2020, 21(6), 2099; https://doi.org/10.3390/ijms21062099 - 19 Mar 2020
Cited by 3
Abstract
Hormesis, which describes the stimulatory effect of low doses of toxic substances on growth, is a well-known phenomenon in the plant and animal kingdoms. However, the mechanisms that are involved in this phenomenon are still poorly understood. We performed preliminary studies on corn [...] Read more.
Hormesis, which describes the stimulatory effect of low doses of toxic substances on growth, is a well-known phenomenon in the plant and animal kingdoms. However, the mechanisms that are involved in this phenomenon are still poorly understood. We performed preliminary studies on corn coleoptile sections, which showed a positive correlation between the stimulation of growth by Cd or Pb and an increase in the auxin and H2O2 content in the coleoptile sections. Subsequently, we grew corn seedlings in hydroponic culture and tested a wide range of Cd or Pb concentrations in order to determine hormetic growth stimulation. In these seedlings the gas exchange and the chlorophyll a fluorescence, as well as the content of chlorophyll, flavonol, auxin and hydrogen peroxide, were measured. We found that during the hormetic stimulation of growth, the response of the photosynthetic apparatus to Cd and Pb differed significantly. While the application of Cd mostly caused a decrease in various photosynthetic parameters, the application of Pb stimulated some of them. Nevertheless, we discovered that the common features of the hormetic stimulation of shoot growth by heavy metals are an increase in the auxin and flavonol content and the maintenance of hydrogen peroxide at the same level as the control plants. Full article
(This article belongs to the Special Issue Heavy Metals Accumulation, Toxicity and Detoxification in Plants)
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Open AccessArticle
Full-Length Transcriptome Assembly of Italian Ryegrass Root Integrated with RNA-Seq to Identify Genes in Response to Plant Cadmium Stress
Int. J. Mol. Sci. 2020, 21(3), 1067; https://doi.org/10.3390/ijms21031067 - 06 Feb 2020
Cited by 2
Abstract
Cadmium (Cd) is a toxic heavy metal element. It is relatively easily absorbed by plants and enters the food chain, resulting in human exposure to Cd. Italian ryegrass (Lolium multiflorum Lam.), an important forage cultivated widely in temperate regions worldwide, has the [...] Read more.
Cadmium (Cd) is a toxic heavy metal element. It is relatively easily absorbed by plants and enters the food chain, resulting in human exposure to Cd. Italian ryegrass (Lolium multiflorum Lam.), an important forage cultivated widely in temperate regions worldwide, has the potential to be used in phytoremediation. However, genes regulating Cd translocation and accumulation in this species are not fully understood. Here, we optimized PacBio ISO-seq and integrated it with RNA-seq to construct a de novo full-length transcriptomic database for an un-sequenced autotetraploid species. With the database, we identified 2367 differentially expressed genes (DEGs) and profiled the molecular regulatory pathways of Italian ryegrass with Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis in response to Cd stress. Overexpression of a DEG LmAUX1 in Arabidopsis thaliana significantly enhanced plant Cd concentration. We also unveiled the complexity of alternative splicing (AS) with a genome-free strategy. We reconstructed full-length UniTransModels using the reference transcriptome, and 29.76% of full-length models had more than one isoform. Taken together, the results enhanced our understanding of the genetic diversity and complexity of Italian ryegrass under Cd stress and provided valuable genetic resources for its gene identification and molecular breeding. Full article
(This article belongs to the Special Issue Heavy Metals Accumulation, Toxicity and Detoxification in Plants)
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Open AccessArticle
Comparative Transcriptome Analysis of the Molecular Mechanism of the Hairy Roots of Brassica campestris L. in Response to Cadmium Stress
Int. J. Mol. Sci. 2020, 21(1), 180; https://doi.org/10.3390/ijms21010180 - 26 Dec 2019
Cited by 1
Abstract
Brassica campestris L., a hyperaccumulator of cadmium (Cd), is considered a candidate plant for efficient phytoremediation. The hairy roots of Brassica campestris L are chosen here as a model plant system to investigate the response mechanism of Brassica campestris L. to Cd stress. [...] Read more.
Brassica campestris L., a hyperaccumulator of cadmium (Cd), is considered a candidate plant for efficient phytoremediation. The hairy roots of Brassica campestris L are chosen here as a model plant system to investigate the response mechanism of Brassica campestris L. to Cd stress. High-throughput sequencing technology is used to identify genes related to Cd tolerance. A total of 2394 differentially expressed genes (DEGs) are identified by RNA-Seq analysis, among which 1564 genes are up-regulated, and 830 genes are down-regulated. Data from the gene ontology (GO) analysis indicate that DEGs are mainly involved in metabolic processes. Glutathione metabolism, in which glutathione synthetase and glutathione S-transferase are closely related to Cd stress, is identified in the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. A Western blot shows that glutathione synthetase and glutathione S-transferase are involved in Cd tolerance. These results provide a preliminary understanding of the Cd tolerance mechanism of Brassica campestris L. and are, hence, of particular importance to the future development of an efficient phytoremediation process based on hairy root cultures, genetic modification, and the subsequent regeneration of the whole plant. Full article
(This article belongs to the Special Issue Heavy Metals Accumulation, Toxicity and Detoxification in Plants)
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Open AccessArticle
Isolation and Characterization of Copper- and Zinc- Binding Metallothioneins from the Marine Alga Ulva compressa (Chlorophyta)
Int. J. Mol. Sci. 2020, 21(1), 153; https://doi.org/10.3390/ijms21010153 - 25 Dec 2019
Cited by 4
Abstract
In this work, transcripts encoding three metallothioneins from Ulva compressa (UcMTs) were amplified: The 5′and 3′ UTRs by RACE-PCR, and the open reading frames (ORFs) by PCR. Transcripts encoding UcMT1.1 (Crassostrea-like), UcMT2 (Mytilus-like), and UcMT3 (Dreissena-like) showed [...] Read more.
In this work, transcripts encoding three metallothioneins from Ulva compressa (UcMTs) were amplified: The 5′and 3′ UTRs by RACE-PCR, and the open reading frames (ORFs) by PCR. Transcripts encoding UcMT1.1 (Crassostrea-like), UcMT2 (Mytilus-like), and UcMT3 (Dreissena-like) showed a 5′UTR of 61, 71, and 65 nucleotides and a 3′UTR of 418, 235, and 193 nucleotides, respectively. UcMT1.1 ORF encodes a protein of 81 amino acids (MW 8.2 KDa) with 25 cysteines (29.4%), arranged as three motifs CC and nine motifs CXC; UcMT2 ORF encode a protein of 90 amino acids (9.05 kDa) with 27 cysteines (30%), arranged as three motifs CC, nine motifs CXC, and one motif CXXC; UcMT3 encode a protein of 139 amino acids (13.4 kDa) with 34 cysteines (24%), arranged as seven motifs CC and seven motifs CXC. UcMT1 and UcMT2 were more similar among each other, showing 60% similarity in amino acids; UcMT3 showed only 31% similarity with UcMT1 and UcMT2. In addition, UcMTs displayed structural similarity with MTs of marine invertebrates MTs and the terrestrial invertebrate Caenorhabtidis elegans MTs, but not with MTs from red or brown macroalgae. The ORFs fused with GST were expressed in bacteria allowing copper accumulation, mainly in MT1 and MT2, and zinc, in the case of the three MTs. Thus, the three MTs allowed copper and zinc accumulation in vivo. UcMTs may play a role in copper and zinc accumulation in U. compressa. Full article
(This article belongs to the Special Issue Heavy Metals Accumulation, Toxicity and Detoxification in Plants)
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Open AccessArticle
OsMSR3, a Small Heat Shock Protein, Confers Enhanced Tolerance to Copper Stress in Arabidopsis thaliana
Int. J. Mol. Sci. 2019, 20(23), 6096; https://doi.org/10.3390/ijms20236096 - 03 Dec 2019
Cited by 2
Abstract
Copper is a mineral element essential for the normal growth and development of plants; however, excessive levels can severely affect plant growth and development. Oryza sativa L. multiple stress-responsive gene 3 (OsMSR3) is a small, low-molecular-weight heat shock protein (HSP) gene. A previous [...] Read more.
Copper is a mineral element essential for the normal growth and development of plants; however, excessive levels can severely affect plant growth and development. Oryza sativa L. multiple stress-responsive gene 3 (OsMSR3) is a small, low-molecular-weight heat shock protein (HSP) gene. A previous study has shown that OsMSR3 expression improves the tolerance of Arabidopsis to cadmium stress. However, the role of OsMSR3 in the Cu stress response of plants remains unclear, and, thus, this study aimed to elucidate this phenomenon in Arabidopsis thaliana, to further understand the role of small HSPs (sHSPs) in heavy metal resistance in plants. Under Cu stress, transgenic A. thaliana expressing OsMSR3 showed higher tolerance to Cu, longer roots, higher survival rates, biomass, and relative water content, and accumulated more Cu, abscisic acid (ABA), hydrogen peroxide, chlorophyll, carotenoid, superoxide dismutase, and peroxidase than wild-type plants did. Moreover, OsMSR3 expression in A. thaliana increased the expression of antioxidant-related and ABA-responsive genes. Collectively, our findings suggest that OsMSR3 played an important role in regulating Cu tolerance in plants and improved their tolerance to Cu stress through enhanced activation of antioxidative defense mechanisms and positive regulation of ABA-responsive gene expression. Full article
(This article belongs to the Special Issue Heavy Metals Accumulation, Toxicity and Detoxification in Plants)
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Open AccessArticle
Combined Effect of Cadmium and Lead on Durum Wheat
Int. J. Mol. Sci. 2019, 20(23), 5891; https://doi.org/10.3390/ijms20235891 - 24 Nov 2019
Cited by 3
Abstract
Cadmium (Cd) and lead (Pb) are two toxic heavy metals (HMs) whose presence in soil is generally low. However, industrial and agricultural activities in recent years have significantly raised their levels, causing progressive accumulations in plant edible tissues, and stimulating research in this [...] Read more.
Cadmium (Cd) and lead (Pb) are two toxic heavy metals (HMs) whose presence in soil is generally low. However, industrial and agricultural activities in recent years have significantly raised their levels, causing progressive accumulations in plant edible tissues, and stimulating research in this field. Studies on toxic metals are commonly focused on a single metal, but toxic metals occur simultaneously. The understanding of the mechanisms of interaction between HMs during uptake is important to design agronomic or genetic strategies to limit contamination of crops. To study the single and combined effect of Cd and Pb on durum wheat, a hydroponic experiment was established to examine the accumulation of the two HMs. Moreover, the molecular mechanisms activated in the roots were investigated paying attention to transcription factors (bHLH family), heavy metal transporters and genes involved in the biosynthesis of metal chelators (nicotianamine and mugineic acid). Cd and Pb are accumulated following different molecular strategies by durum wheat plants, even if the two metals interact with each other influencing their respective uptake and translocation. Finally, we demonstrated that some genes (bHLH 29, YSL2, ZIF1, ZIFL1, ZIFL2, NAS2 and NAAT) were induced in the durum wheat roots only in response to Cd. Full article
(This article belongs to the Special Issue Heavy Metals Accumulation, Toxicity and Detoxification in Plants)
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Open AccessArticle
Lead, Cadmium and Zinc Phytotoxicity Alter DNA Methylation Levels to Confer Heavy Metal Tolerance in Wheat
Int. J. Mol. Sci. 2019, 20(19), 4676; https://doi.org/10.3390/ijms20194676 - 20 Sep 2019
Cited by 9
Abstract
Being a staple food, wheat (Triticum aestivum) nutritionally fulfills all requirements of human health and also serves as a significant link in the food chain for the ingestion of pollutants by humans and animals. Therefore, the presence of the heavy metals [...] Read more.
Being a staple food, wheat (Triticum aestivum) nutritionally fulfills all requirements of human health and also serves as a significant link in the food chain for the ingestion of pollutants by humans and animals. Therefore, the presence of the heavy metals such as lead (Pb) and cadmium (Cd) in soil is not only responsible for the reduction of wheat crop yield but also the potential threat for human and animal health. However, the link between DNA methylation and heavy metal stress tolerance in wheat has not been investigated yet. In this study, eight high yielding wheat varieties were screened based on their phenotype in response to Pb stress. Out of these, Pirsabak 2004 and Fakhar-e-sarhad were identified as Pb resistant and sensitive varieties, respectively. In addition, Pirsabak 2004 and Fakhar-e-sarhad varieties were also found resistant and sensitive to Cd and Zinc (Zn) stress, respectively. Antioxidant activity was decreased in Fakhar-e-sarhad compared with control in response to Pb/Cd/Zn stresses, but Fakhar-e-sarhad and Pirsabak 2004 accumulated similar levels of Pb, Cd and Zn in their roots. The expression of Heavy Metal ATPase 2 (TaHMA2) and ATP-Binding Cassette (TaABCC2/3/4) metal detoxification transporters are significantly upregulated in Pirsabak 2004 compared with Fakhar-e-sarhad and non-treated controls in response to Pb, Cd and Zn metal stresses. Consistent with upregulation of metal detoxification transporters, CG DNA hypomethylation was also found at the promoter region of these transporters in Pirsabak 2004 compared with Fakhar-e-sarhad and non-treated control, which indicates that DNA methylation regulates the expression of metal detoxification transporters to confer resistance against metal toxicity in wheat. This study recommends the farmers to cultivate Pirsabak 2004 variety in metal contaminated soils and also highlights that DNA methylation is associated with metal stress tolerance in wheat. Full article
(This article belongs to the Special Issue Heavy Metals Accumulation, Toxicity and Detoxification in Plants)
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Open AccessArticle
MAPK Pathway under Chronic Copper Excess in Green Macroalgae (Chlorophyta): Influence on Metal Exclusion/Extrusion Mechanisms and Photosynthesis
Int. J. Mol. Sci. 2019, 20(18), 4547; https://doi.org/10.3390/ijms20184547 - 13 Sep 2019
Cited by 7
Abstract
There is currently no information regarding the role that whole mitogen activated protein kinase (MAPK) pathways play in counteracting environmental stress in photosynthetic organisms. To address this gap, we exposed Ulva compressa to chronic levels of copper (10 µM) specific inhibitors of Extracellular [...] Read more.
There is currently no information regarding the role that whole mitogen activated protein kinase (MAPK) pathways play in counteracting environmental stress in photosynthetic organisms. To address this gap, we exposed Ulva compressa to chronic levels of copper (10 µM) specific inhibitors of Extracellular Signal Regulated Kinases (ERK), c-Jun N-terminal Kinases (JNK), and Cytokinin Specific Binding Protein (p38) MAPKs alone or in combination. Intracellular copper accumulation and photosynthetic activity (in vivo chlorophyll a fluorescence) were measured after 6 h, 24 h, 48 h, and 6 days of exposure. By day 6, when one (except JNK) or more of the MAPK pathways were inhibited under copper stress, there was a decrease in copper accumulation compared with algae exposed to copper alone. When at least two MAPKs were blocked, there was a decrease in photosynthetic activity expressed in lower productivity (ETRmax), efficiency (αETR), and saturation of irradiance (EkETR), accompanied by higher non-photochemical quenching (NPQmax), compared to both the control and copper-only treatments. In terms of accumulation, once the MAPK pathways were partially or completely blocked under copper, there was crosstalk between these and other signaling mechanisms to enhance metal extrusion/exclusion from cells. Crosstalk occurred among MAPK pathways to maintain photosynthesis homeostasis, demonstrating the importance of the signaling pathways for physiological performance. This study is complemented by a parallel/complementary article Rodríguez-Rojas et al. on the role of MAPKs in copper-detoxification. Full article
(This article belongs to the Special Issue Heavy Metals Accumulation, Toxicity and Detoxification in Plants)
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Open AccessArticle
MAPK Pathway under Chronic Copper Excess in Green Macroalgae (Chlorophyta): Involvement in the Regulation of Detoxification Mechanisms
Int. J. Mol. Sci. 2019, 20(18), 4546; https://doi.org/10.3390/ijms20184546 - 13 Sep 2019
Cited by 8
Abstract
Following the physiological complementary/parallel Celis-Plá et al., by inhibiting extracellular signal regulated kinases (ERK), c-Jun N-terminal kinases (JNK), and cytokinin specific binding protein (p38), we assessed the role of the mitogen-activated protein kinases (MAPK) pathway in detoxification responses mediated by chronic copper (10 [...] Read more.
Following the physiological complementary/parallel Celis-Plá et al., by inhibiting extracellular signal regulated kinases (ERK), c-Jun N-terminal kinases (JNK), and cytokinin specific binding protein (p38), we assessed the role of the mitogen-activated protein kinases (MAPK) pathway in detoxification responses mediated by chronic copper (10 µM) in U. compressa. Parameters were taken at 6, 24, and 48 h, and 6 days (d). H2O2 and lipid peroxidation under copper and inhibition of ERK, JNK, or p38 alone increased but recovered by the sixth day. By blocking two or more MAPKs under copper, H2O2 and lipid peroxidation decayed even below controls. Inhibition of more than one MAPK (at 6 d) caused a decrease in total glutathione (reduced glutathione (GSH) + oxidised glutathione (GSSG)) and ascorbate (reduced ascorbate (ASC) + dehydroascorbate (DHA)), although in the latter it did not occur when the whole MAPK was blocked. Catalase (CAT), superoxide dismutase (SOD), thioredoxin (TRX) ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), and glutathione synthase (GS), were downregulated when blocking more than one MAPK pathway. When one MAPK pathway was blocked under copper, a recovery and even enhancement of detoxification mechanisms was observed, likely due to crosstalk within the MAPKs and/or other signalling processes. In contrast, when more than one MAPK pathway were blocked under copper, impairment of detoxification defences occurred, demonstrating that MAPKs were key signalling mechanisms for detoxification in macroalgae. Full article
(This article belongs to the Special Issue Heavy Metals Accumulation, Toxicity and Detoxification in Plants)
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Open AccessArticle
Insight into the Phytoremediation Capability of Brassica juncea (v. Malopolska): Metal Accumulation and Antioxidant Enzyme Activity
Int. J. Mol. Sci. 2019, 20(18), 4355; https://doi.org/10.3390/ijms20184355 - 05 Sep 2019
Cited by 3
Abstract
Metal hyperaccumulating plants should have extremely efficient defense mechanisms, enabling growth and development in a polluted environment. Brassica species are known to display hyperaccumulation capability. Brassica juncea (Indiana mustard) v. Malopolska plants were exposed to trace elements, i.e., cadmium (Cd), copper (Cu), lead [...] Read more.
Metal hyperaccumulating plants should have extremely efficient defense mechanisms, enabling growth and development in a polluted environment. Brassica species are known to display hyperaccumulation capability. Brassica juncea (Indiana mustard) v. Malopolska plants were exposed to trace elements, i.e., cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn), at a concentration of 50 μM and were then harvested after 96 h for analysis. We observed a high index of tolerance (IT), higher than 90%, for all B. juncea plants treated with the four metals, and we showed that Cd, Cu, Pb, and Zn accumulation was higher in the above-ground parts than in the roots. We estimated the metal effects on the generation of reactive oxygen species (ROS) and the levels of protein oxidation, as well as on the activity and gene expression of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX). The obtained results indicate that organo-specific ROS generation was higher in plants exposed to essential metal elements (i.e., Cu and Zn), compared with non-essential ones (i.e., Cd and Pb), in conjunction with SOD, CAT, and APX activity and expression at the level of encoding mRNAs and existing proteins. In addition to the potential usefulness of B. juncea in the phytoremediation process, the data provide important information concerning plant response to the presence of trace metals. Full article
(This article belongs to the Special Issue Heavy Metals Accumulation, Toxicity and Detoxification in Plants)
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Open AccessArticle
Selenium Modulates the Level of Auxin to Alleviate the Toxicity of Cadmium in Tobacco
Int. J. Mol. Sci. 2019, 20(15), 3772; https://doi.org/10.3390/ijms20153772 - 01 Aug 2019
Cited by 7
Abstract
Cadmium (Cd) is an environmental pollutant that potentially threatens human health worldwide. Developing approaches for efficiently treating environmental Cd is a priority. Selenium (Se) plays important role in the protection of plants against various abiotic stresses, including heavy metals. Previous research has shown [...] Read more.
Cadmium (Cd) is an environmental pollutant that potentially threatens human health worldwide. Developing approaches for efficiently treating environmental Cd is a priority. Selenium (Se) plays important role in the protection of plants against various abiotic stresses, including heavy metals. Previous research has shown that Se can alleviate Cd toxicity, but the molecular mechanism is still not clear. In this study, we explore the function of auxin and phosphate (P) in tobacco (Nicotiana tabacum), with particular focus on their interaction with Se and Cd. Under Cd stress conditions, low Se (10 μM) significantly increased the biomass and antioxidant capacity of tobacco plants and reduced uptake of Cd. We also measured the auxin concentration and expression of auxin-relative genes in tobacco and found that plants treated with low Se (10 μM) had higher auxin concentrations at different Cd supply levels (0 μM, 20 μM, 50 μM) compared with no Se treatment, probably due to increased expression of auxin synthesis genes and auxin efflux carriers. Overexpression of a high affinity phosphate transporter NtPT2 enhanced the tolerance of tobacco to Cd stress, possibly by increasing the total P and Se content and decreasing Cd accumulation compared to that in the wild type (WT). Our results show that there is an interactive mechanism among P, Se, Cd, and auxin that affects plant growth and may provide a new approach for relieving Cd toxicity in plants. Full article
(This article belongs to the Special Issue Heavy Metals Accumulation, Toxicity and Detoxification in Plants)
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Open AccessArticle
Ectopic Expression of Poplar ABC Transporter PtoABCG36 Confers Cd Tolerance in Arabidopsis thaliana
Int. J. Mol. Sci. 2019, 20(13), 3293; https://doi.org/10.3390/ijms20133293 - 04 Jul 2019
Cited by 5
Abstract
Cadmium (Cd) is one of the most toxic heavy metals for plant growth in soil. ATP-binding cassette (ABC) transporters play important roles in biotic and abiotic stresses. However, few ABC transporters have been characterized in poplar. In this study, we isolated an ABC [...] Read more.
Cadmium (Cd) is one of the most toxic heavy metals for plant growth in soil. ATP-binding cassette (ABC) transporters play important roles in biotic and abiotic stresses. However, few ABC transporters have been characterized in poplar. In this study, we isolated an ABC transporter gene PtoABCG36 from Populus tomentosa. The PtoABCG36 transcript can be detected in leaves, stems and roots, and the expression in the root was 3.8 and 2 times that in stems and leaves, respectively. The PtoABCG36 expression was induced and peaked at 12 h after exposure to Cd stress. Transient expression of PtoABCG36 in tobacco showed that PtoABCG36 is localized at the plasma membrane. When overexpressed in yeast and Arabidopsis, PtoABCG36 could decrease Cd accumulation and confer higher Cd tolerance in transgenic lines than in wild-type (WT) lines. Net Cd2+ efflux measurements showed a decreasing Cd uptake in transgenic Arabidopsis roots than WT. These results demonstrated that PtoABCG36 functions as a cadmium extrusion pump participating in enhancing tolerance to Cd through decreasing Cd content in plants, which provides a promising way for making heavy metal tolerant poplar by manipulating ABC transporters in cadmium polluted areas. Full article
(This article belongs to the Special Issue Heavy Metals Accumulation, Toxicity and Detoxification in Plants)
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Open AccessArticle
Comparative Transcriptomic Studies on a Cadmium Hyperaccumulator Viola baoshanensis and Its Non-Tolerant Counterpart V. inconspicua
Int. J. Mol. Sci. 2019, 20(8), 1906; https://doi.org/10.3390/ijms20081906 - 17 Apr 2019
Cited by 3
Abstract
Many Viola plants growing in mining areas exhibit high levels of cadmium (Cd) tolerance and accumulation, and thus are ideal organisms for comparative studies on molecular mechanisms of Cd hyperaccumulation. However, transcriptomic studies of hyperaccumulative plants in Violaceae are rare. Viola baoshanensis is [...] Read more.
Many Viola plants growing in mining areas exhibit high levels of cadmium (Cd) tolerance and accumulation, and thus are ideal organisms for comparative studies on molecular mechanisms of Cd hyperaccumulation. However, transcriptomic studies of hyperaccumulative plants in Violaceae are rare. Viola baoshanensis is an amazing Cd hyperaccumulator in metalliferous areas of China, whereas its relative V. inconspicua is a non-tolerant accumulator that resides at non-metalliferous sites. Here, comparative studies by transcriptome sequencing were performed to investigate the key pathways that are potentially responsible for the differential levels of Cd tolerance between these two Viola species. A cascade of genes involved in the ubiquitin proteosome system (UPS) pathway were observed to have constitutively higher transcription levels and more activation in response to Cd exposure in V. baoshanensis, implying that the enhanced degradation of misfolded proteins may lead to high resistance against Cd in this hyperaccumulator. Many genes related to sucrose metabolism, especially those involved in callose and trehalose biosynthesis, are among the most differentially expressed genes between the two Viola species, suggesting a crucial role of sucrose metabolism not only in cell wall modification through carbon supply but also in the antioxidant system as signaling molecules or antioxidants. A comparison among transcriptional patterns of some known transporters revealed that several tonoplast transporters are up-regulated in V. baoshanensis under Cd stress, suggesting more efficient compartmentalization of Cd in the vacuoles. Taken together, our findings provide valuable insight into Cd hypertolerance in V. baoshanensis, and the corresponding molecular mechanisms will be useful for future genetic engineering in phytoremediation. Full article
(This article belongs to the Special Issue Heavy Metals Accumulation, Toxicity and Detoxification in Plants)
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Open AccessArticle
Exogenous Glycinebetaine Reduces Cadmium Uptake and Mitigates Cadmium Toxicity in Two Tobacco Genotypes Differing in Cadmium Tolerance
Int. J. Mol. Sci. 2019, 20(7), 1612; https://doi.org/10.3390/ijms20071612 - 31 Mar 2019
Cited by 5
Abstract
Greenhouse hydroponic experiments were conducted using Cd-sensitive (cv. Guiyan1) and Cd-tolerant (cv. Yunyan2) tobacco cultivars to study the ameliorative effects of exogenous glycinebetaine (GB) upon 5 μM Cd stress. The foliar spray of GB markedly reduced Cd concentrations in plants and [...] Read more.
Greenhouse hydroponic experiments were conducted using Cd-sensitive (cv. Guiyan1) and Cd-tolerant (cv. Yunyan2) tobacco cultivars to study the ameliorative effects of exogenous glycinebetaine (GB) upon 5 μM Cd stress. The foliar spray of GB markedly reduced Cd concentrations in plants and alleviated Cd-induced soil plant analysis development (SPAD) value, plant height and root length inhibition, with the mitigation effect being more obvious in Yunyan2. External GB markedly reduced Cd-induced malondialdehyde (MDA) accumulation, induced stomatal closure, ameliorated Cd-induced damages on leaf/root ultrastructure, and increased the chlorophyll content and fluorescence parameters of Fo, Fm, and Fv/Fm in both cultivars and Pn in Yunyan2. Exogenous GB counteracted Cd-induced alterations of certain antioxidant enzymes and nutrients uptake, e.g., the depressed Cd-induced increase of superoxide dismutase (SOD) and peroxidase (POD) activities, but significantly elevated the depressed catalase (CAT) and ascorbate peroxidase (APX) activities. The results indicate that alleviated Cd toxicity by GB application is related to the reduced Cd uptake and MDA accumulation, balanced nutrients and antioxidant enzyme activities, improved PSII, and integrated ultrastructure in tobacco plants. Full article
(This article belongs to the Special Issue Heavy Metals Accumulation, Toxicity and Detoxification in Plants)
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Open AccessArticle
Transcriptome Analysis Reveals Cotton (Gossypium hirsutum) Genes That Are Differentially Expressed in Cadmium Stress Tolerance
Int. J. Mol. Sci. 2019, 20(6), 1479; https://doi.org/10.3390/ijms20061479 - 24 Mar 2019
Cited by 2
Abstract
High concentrations of heavy metals in the soil should be removed for environmental safety. Cadmium (Cd) is a heavy metal that pollutes the soil when its concentration exceeds 3.4 mg/kg. Although the potential use of cotton to remediate heavy Cd-polluted soils is known, [...] Read more.
High concentrations of heavy metals in the soil should be removed for environmental safety. Cadmium (Cd) is a heavy metal that pollutes the soil when its concentration exceeds 3.4 mg/kg. Although the potential use of cotton to remediate heavy Cd-polluted soils is known, little is understood about the molecular mechanisms of Cd tolerance. In this study, transcriptome analysis was used to identify Cd tolerance genes and their potential mechanisms in cotton. We exposed cotton plants to excess Cd and identified 4627 differentially expressed genes (DEGs) in the root, 3022 DEGs in the stem and 3854 DEGs in the leaves through RNA-Seq analysis. Among these genes were heavy metal transporter coding genes (ABC, CDF, HMA, etc.), annexin genes and heat shock genes (HSP), amongst others. Gene ontology (GO) analysis showed that the DEGs were mainly involved in the oxidation–reduction process and metal ion binding. The DEGs were mainly enriched in two pathways, the influenza A and pyruvate pathway. GhHMAD5, a protein containing a heavy-metal binding domain, was identified in the pathway to transport or to detoxify heavy metal ions. We constructed a GhHMAD5 overexpression system in Arabidopsis thaliana that showed longer roots compared to control plants. GhHMAD5-silenced cotton plants showed more sensitivity to Cd stress. The results indicate that GhHMAD5 is involved in Cd tolerance, which gives a preliminary understanding of the Cd tolerance mechanism in upland cotton. Overall, this study provides valuable information for the use of cotton to remediate soils polluted with Cd and potentially other heavy metals. Full article
(This article belongs to the Special Issue Heavy Metals Accumulation, Toxicity and Detoxification in Plants)
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Open AccessReview
Advances in the Mechanisms of Plant Tolerance to Manganese Toxicity
Int. J. Mol. Sci. 2019, 20(20), 5096; https://doi.org/10.3390/ijms20205096 - 14 Oct 2019
Cited by 7
Abstract
Manganese (Mn) is an essential element for plant growth due to its participation in a series of physiological and metabolic processes. Mn is also considered a heavy metal that causes phytotoxicity when present in excess, disrupting photosynthesis and enzyme activity in plants. Thus, [...] Read more.
Manganese (Mn) is an essential element for plant growth due to its participation in a series of physiological and metabolic processes. Mn is also considered a heavy metal that causes phytotoxicity when present in excess, disrupting photosynthesis and enzyme activity in plants. Thus, Mn toxicity is a major constraint limiting plant growth and production, especially in acid soils. To cope with Mn toxicity, plants have evolved a wide range of adaptive strategies to improve their growth under this stress. Mn tolerance mechanisms include activation of the antioxidant system, regulation of Mn uptake and homeostasis, and compartmentalization of Mn into subcellular compartments (e.g., vacuoles, endoplasmic reticulum, Golgi apparatus, and cell walls). In this regard, numerous genes are involved in specific pathways controlling Mn detoxification. Here, we summarize the recent advances in the mechanisms of Mn toxicity tolerance in plants and highlight the roles of genes responsible for Mn uptake, translocation, and distribution, contributing to Mn detoxification. We hope this review will provide a comprehensive understanding of the adaptive strategies of plants to Mn toxicity through gene regulation, which will aid in breeding crop varieties with Mn tolerance via genetic improvement approaches, enhancing the yield and quality of crops. Full article
(This article belongs to the Special Issue Heavy Metals Accumulation, Toxicity and Detoxification in Plants)
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Open AccessReview
Cadmium and Plant Development: An Agony from Seed to Seed
Int. J. Mol. Sci. 2019, 20(16), 3971; https://doi.org/10.3390/ijms20163971 - 15 Aug 2019
Cited by 10
Abstract
Anthropogenic pollution of agricultural soils with cadmium (Cd) should receive adequate attention as Cd accumulation in crops endangers human health. When Cd is present in the soil, plants are exposed to it throughout their entire life cycle. As it is a non-essential element, [...] Read more.
Anthropogenic pollution of agricultural soils with cadmium (Cd) should receive adequate attention as Cd accumulation in crops endangers human health. When Cd is present in the soil, plants are exposed to it throughout their entire life cycle. As it is a non-essential element, no specific Cd uptake mechanisms are present. Therefore, Cd enters the plant through transporters for essential elements and consequently disturbs plant growth and development. In this review, we will focus on the effects of Cd on the most important events of a plant’s life cycle covering seed germination, the vegetative phase and the reproduction phase. Within the vegetative phase, the disturbance of the cell cycle by Cd is highlighted with special emphasis on endoreduplication, DNA damage and its relation to cell death. Furthermore, we will discuss the cell wall as an important structure in retaining Cd and the ability of plants to actively modify the cell wall to increase Cd tolerance. As Cd is known to affect concentrations of reactive oxygen species (ROS) and phytohormones, special emphasis is put on the involvement of these compounds in plant developmental processes. Lastly, possible future research areas are put forward and a general conclusion is drawn, revealing that Cd is agonizing for all stages of plant development. Full article
(This article belongs to the Special Issue Heavy Metals Accumulation, Toxicity and Detoxification in Plants)
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Open AccessReview
Advances in the Uptake and Transport Mechanisms and QTLs Mapping of Cadmium in Rice
Int. J. Mol. Sci. 2019, 20(14), 3417; https://doi.org/10.3390/ijms20143417 - 11 Jul 2019
Cited by 4
Abstract
Cadmium (Cd), as a heavy metal, presents substantial biological toxicity and has harmful effects on human health. To lower the ingress levels of human Cd, it is necessary for Cd content in food crops to be reduced, which is of considerable significance for [...] Read more.
Cadmium (Cd), as a heavy metal, presents substantial biological toxicity and has harmful effects on human health. To lower the ingress levels of human Cd, it is necessary for Cd content in food crops to be reduced, which is of considerable significance for ensuring food safety. This review will summarize the genetic traits of Cd accumulation in rice and examine the mechanism of Cd uptake and translocation in rice. The status of genes related to Cd stress and Cd accumulation in rice in recent years will be summarized, and the genes related to Cd accumulation in rice will be classified according to their functions. In addition, an overview of quantitative trait loci (QTLs) mapping populations in rice will be introduced, aiming to provide a theoretical reference for the breeding of rice varieties with low Cd accumulation. Finally, existing problems and prospects will be put forward. Full article
(This article belongs to the Special Issue Heavy Metals Accumulation, Toxicity and Detoxification in Plants)
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Open AccessReview
Heavy Metal Pollutions: State of the Art and Innovation in Phytoremediation
Int. J. Mol. Sci. 2019, 20(14), 3412; https://doi.org/10.3390/ijms20143412 - 11 Jul 2019
Cited by 19
Abstract
Mineral nutrition of plants greatly depends on both environmental conditions, particularly of soils, and the genetic background of the plant itself. Being sessile, plants adopted a range of strategies for sensing and responding to nutrient availability to optimize development and growth, as well [...] Read more.
Mineral nutrition of plants greatly depends on both environmental conditions, particularly of soils, and the genetic background of the plant itself. Being sessile, plants adopted a range of strategies for sensing and responding to nutrient availability to optimize development and growth, as well as to protect their metabolisms from heavy metal toxicity. Such mechanisms, together with the soil environment, meaning the soil microorganisms and their interaction with plant roots, have been extensively studied with the goal of exploiting them to reclaim polluted lands; this approach, defined phytoremediation, will be the subject of this review. The main aspects and innovations in this field are considered, in particular with respect to the selection of efficient plant genotypes, the application of improved cultural strategies, and the symbiotic interaction with soil microorganisms, to manage heavy metal polluted soils. Full article
(This article belongs to the Special Issue Heavy Metals Accumulation, Toxicity and Detoxification in Plants)
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