Heavy metal (loid)s phytotoxicity in crops and its mitigation through seed priming technology.

Unexpected bioaccumulation and biomagnification of heavy metal(loid)s (HMs) in the environment have become a predicament for all living organisms, including plants. The presence of these HMs in the plant system raised the level of reactive oxygen species (ROS) and remodeled several vital cellular biomolecules. These lead to several morphological, physiological, metabolic, and molecular aberrations in plants ranging from chlorosis of leaves to the lipid peroxidation of membranes, and degradation of proteins and nucleic acid including the modulation of the enzymatic system, which ultimately affects the plant growth and productivity. Plants are equipped with several mechanisms to counteract the HMs toxicity. Among them, seed priming (SP) technology has been widely tested with the use of several inorganic chemicals, plant growth regulators (PGRs), gasotransmitters, nanoparticles, living organisms, and plant leaf extracts. The use of these compounds has the potential to alleviate the HMs toxicity through the strengthening of the antioxidant defense system, generation of low molecular weight metallothionein's (MTs), and phytochelatins (PCs), and improving seedling vigor during early growth stages. This review presents an account of the sources, uptake and transport, and phytotoxic effects of HMs with special attention to different mechanism/s, occurring to mitigate the HMs toxicity in plants employing SP technology.Novelty statement: To the best of our knowledge, this review has delineated the consequences of HMs on the crucial plant processes, which ultimately affect plant growth and development. This review also compiled the up to dated information on phytotoxicity of HMs through the use of SP technology, this review discussed how different types of SP approaches help in diminishing the concentration HMs in plant systems. Also, we depicted mechanisms, represent how HMs transport and their actions on cellular levels, and emphasized, how diverse SP technology effectiveness in the mitigation of plants' phytotoxicity in unique ways.

Correction to: Identification and validation of reference genes in vetiver (Chrysopogon zizanioides) root transcriptome.

[This corrects the article DOI: 10.1007/s12298-023-01315-7.].

Identification and validation of reference genes in vetiver (Chrysopogon zizanioides) root transcriptome.

Vetiver [Vetiveria zizanioides (L.) Roberty] is a perennial C-4 grass traditionally valued for its aromatic roots/root essential oil. Owing to its deep penetrating web-forming roots, the grass is now widely used across the globe for phytoremediation and the conservation of soil and water. This study has used the transcriptome data of vetiver roots in its two distinct geographic morphotypes (North Indian type A and South Indian type B) for reference gene(s) identification. Further, validation of reference genes using various abiotic stresses such as heat, cold, salt, and drought was carried out. The de novo assembly based on differential genes analysis gave 1,36,824 genes (PRJNA292937). Statistical tests like RefFinder, NormFinder, BestKeeper, geNorm, and Delta-Ct software were applied on 346 selected contigs. Eleven selected genes viz., GAPs, UBE2W, RP, OSCam2, MUB, RPS, Core histone 1, Core histone 2, SAMS, GRCWSP, PLDCP along with Actin were used for qRT-PCR analysis. Finally, the study identified the five best reference genes GAPs, OsCam2, MUB, Core histone 1, and SAMS along with Actin. The two optimal reference genes SAMS and Core histone 1 were identified with the help of qbase + software. The findings of the present analyses have value in the identification of suitable reference gene(s) in transcriptomic and molecular data analysis concerning various phenotypes related to abiotic stress and developmental aspects, as well as a quality control measure in gene expression experiments. Identifying reference genes in vetiver appears important as it allows for accurate normalization of gene expression data in qRT-PCR experiments. Supplementary Information: The online version contains supplementary material available at 10.1007/s12298-023-01315-7.

A rice glutaredoxin regulate the expression of aquaporin genes and modulate root responses to provide arsenic tolerance.

Rice is the most consumed food crop and essential determinant in global food security program. Currently, arsenic (As) accumulation in rice is a critical concern in terms of both crop productivity and grain quality; therefore, it is an urgent need to reduce As accumulation. Here, we selected a glutaredoxin (OsGrx_C7) gene that plays an essential role in AsIII tolerance in rice. To explore the mechanism, we raised OsGrx_C7 overexpression (OE) rice lines, which showed improved plant AsIII tolerance and lowered its accumulation in grains. Arsenic accumulation in husk, unpolished, and polished rice reduced by ca. 65%, 67%, and 85%, respectively, in OE lines, compared to wild-type (WT) plants. To know the rationale, expression of AsIII transporters (aquaporins) in root and shoot tissues were examined, and revealed that OsGrx_C7 regulates the expression of these genes, which ultimately reduces root to shoot AsIII translocation. Additionally, OsGrx_C7 improves root growth by regulating the expression of oxidative stress-induced root expansion related genes, promote root growth and plant health. Overall, current study suggested that AsIII induced OsGrx_C7 markedly enhanced tolerance to AsIII with reduced accumulation in grains by regulating root expansion and controlling root to shoot As transport by altered expression of AsIII aquaporins.

Self-cleansing properties of Ganga during mass ritualistic bathing on Maha-Kumbh.

The deterioration of water quality of river Ganga is a huge concern for Govt. of India. Apart from various pollution sources, the religious and ritualistic activities also have a good share in deteriorating Ganga water quality. Thus, the aim of the present study was to evaluate the changes in physico-chemical properties, microbial diversity and role of bacteriophages in controlling bacterial population of Ganga water during mass ritualistic bathing on the occasion of Maha-Kumbh in 2013. The BOD, COD, hardness, TDS and level of various ions significantly increased, while DO decreased in Ganga water during Maha-Kumbh. Ganga water was more affluent in trace elements than Yamuna and their levels further increased during Maha-Kumbh, which was correlated with decreased level of trace elements in the sediment. The bacterial diversity and evenness were increased and correlated with the number of devotees taking a dip at various events. Despite enormous increase in bacterial diversity during mass ritualistic bathing, the core bacterial species found in pre-Kumbh Ganga water were present in all the samples taken during Kumbh and post-Kumbh. In addition, the alteration in bacterial population during mass bathing was well under 2 log units which can be considered negligible. The study of bacteriophages at different bathing events revealed that Ganga was richer with the presence of bacteriophages in comparison with Yamuna against seven common bacteria found during the Maha-Kumbh. These bacteriophages have played a role in controlling bacterial growth and thus preventing putrefaction of Ganga water. Further, the abundance of trace elements in Ganga water might also be a reason for suppression of bacterial growth. Thus, the current study showed that Ganga has characteristic water quality in terms of physico-chemical property and microbial diversity that might have a role in the reported self-cleansing property of Ganga; however, the increased pollution load has surpassed its self-cleansing properties. Since water has been celebrated in all cultures, the outcome of the current study will not only be useful for the policy maker of cleaning and conservation of Ganga but also for restoration of other polluted rivers all over the world.

Selenite modulates the level of phenolics and nutrient element to alleviate the toxicity of arsenite in rice (Oryza sativa L.).

Arsenic (As) contamination of paddy rice is a serious threat all over the world particularly in South East Asia. Selenium (Se) plays important role in protection of plants against various abiotic stresses including heavy metals. Moreover, arsenite (AsIII) and selenite (SeIV) can be biologically antagonistic due to similar electronic configuration and sharing the common transporter for their uptake in plant. In the present study, the response of oxidative stress, phenolic compounds and nutrient elements was analyzed to investigate Se mediated As tolerance in rice seedlings during AsIII and SeIV exposure in hydroponics. Selenite (25µM) significantly decreased As accumulation in plant than As (25µM) alone treated plants. Level of oxidative stress related parameters viz., reactive oxygen species (ROS), lipid peroxidation, electrical conductivity, nitric oxide and pro-oxidant enzyme (NADPH oxidase), were in the order of As>As+Se>control>Se. Selenium ameliorated As phytotoxicity by increased level of phenolic compounds particularly gallic acid, protocatechuic acid, ferulic acid and rutin and thiol metabolism related enzymes viz., serine acetyl transferase (SAT) and cysteine synthase (CS). Selenium supplementation enhanced the uptake of nutrient elements viz., Fe, Mn, Co, Cu, Zn, Mo, and improved plant growth. The results concluded that Se addition in As contaminated environment might be an important strategy to reduce As uptake and associated phytotoxicity in rice plant by modulation of phenolic compounds and increased uptake of nutrient elements.

Selenate mitigates arsenite toxicity in rice (Oryza sativa L.) by reducing arsenic uptake and ameliorates amino acid content and thiol metabolism.

Arsenic (As) is a toxic element with the potential to cause health effects in humans. Besides rice is a source of both amino acids (AAs) and mineral nutrients, it is undesired source of As for billions of people consuming rice as the staple food. Selenium (Se) is an essential metalloid, which can regulate As toxicity by strengthening antioxidant potential. The present study was designed to investigate As(III) stress mitigating effect of Se(VI) in rice. The level of As, thiolic ligands and AAs was analyzed in rice seedlings after exposure to As(III)/Se(VI) alone and As(III)+Se(VI) treatments. Selenate supplementation (As(III) 25µM+Se(VI) 25µM) decreased total As accumulation in both root and shoot (179 & 144%) as compared to As(III) alone treatment. The As(III)+Se(VI) treatment also induced the levels of non-protein thiols (NPTs), glutathione (GSH) and phytochelatins (PCs) as compared to As(III) alone treatment and also modulated the activity of enzymes of thiol metabolism. The content of amino acids (AAs) was significantly altered with Se(VI) supplementation. Importantly, essential amino acids (EAAs) were enhanced in As(III)+Se(VI) treatment as compared to As(III) alone treatment. In contrast, stress related non-essential amino acids (NEAAs) like GABA, Glu, Gly, Pro and Cys showed enhanced levels in As(III) alone treatment. In conclusion, rice supplemented with Se(VI) tolerated As toxicity with reduced As accumulation and increased the nutrition quality by increasing EAAs.

Feasibility Study of Phragmites karka and Christella dentata Grown in West Bengal as Arsenic Accumulator.

A survey was undertaken, in arsenic (As) contaminated area of the Nadia district, West Bengal, India, to find native As accumulator plants. As was determined both in soil and plant parts. The results showed that the mean translocation factor of Pteris vittata L, Phragmites karka (Cav.) Trin. Ex. Steud and Christella dentata Forssk were higher than 1. It thus appeared that these plants can be efficient accumulators of As. Phytoremediation ability of C. dentata and P. karka was evaluated and compared with known As-hyperaccumulators -P. vittata and Adiantum capillus veneris L. Plants were grown in the As spiked soil (25, 50, 75 and 100 mg kg(-1)). As accumulation was found to be highest in P. vittata, 117.18 mg kg(-1) in leaf at 100 mg kg(-1) As treatment, followed by A. capillus veneris, P. karka and C. dentata being 74, 83.87 and 40.36 mg kg(-1), respectively. Lipid peroxidation increased after As exposure in all plants. However, the antioxidant enzyme activity and molecules concentration also increased which helped the plants to overcome As-induced oxidative stress. The study indicates that P. karka and C. dentata could be considered as As-accumulators and find application for As-phytoextraction in field conditions.

Mapping of arsenic pollution with reference to paddy cultivation in the middle Indo-Gangetic Plains.

A detailed field study was carried out to monitor (i) the arsenic contents in irrigation groundwater and paddy soil and (ii) the accumulation of arsenic in the roots and grains of different paddy varieties grown in the arsenic-contaminated middle Indo-Gangetic Plains of Northern India. Results showed the highest arsenic contamination in the irrigation groundwater (312 µg l(-1)) and in paddy soil (35 mg kg(-1)) values that were significantly exceeded the recommended threshold values of 100 µg l(-1) (EU) and 20 mg kg(-1) (FAO), respectively. The paddy soil arsenic content ranged from 3 to 35 mg kg(-1) with a mean value of 15 mg kg(-1). The soil arsenic content was found to be influenced by the soil texture, carbon, macronutrients, phosphorus, sulfur, hydrolases, and oxidoreductases properties of the paddy soils as revealed in the principal component analyses. Higher root accumulation (>10 mg kg(-1)) of arsenic was observed in 6 of the 17 paddy varieties grown in the study area. The range of arsenic content accumulated in the paddy roots was 4.1 to 16.2 mg kg(-1) dry weight (dw) and in the grains 0.179 to 0.932 mg kg(-1) dw. Out of 17 paddy varieties, eight had 0 > .55 mg kg(-1) grain arsenic content and were found unsafe for subsistence maximum daily tolerable dietary intake (MTDI) by human beings according to the regulatory standards.

Expression in Arabidopsis and cellular localization reveal involvement of rice NRAMP, OsNRAMP1, in arsenic transport and tolerance.

Irrigation of paddy fields to arsenic (As) containing groundwater leads to As accumulation in rice grains and causes serious health risk to the people worldwide. To reduce As intake via consumption of contaminated rice grain, identification of the mechanisms for As accumulation and detoxification in rice is a prerequisite. Herein, we report involvement of a member of rice NRAMP (Natural Resistance-Associated Macrophage Protein) transporter, OsNRAMP1, in As, in addition to cadmium (Cd), accumulation through expression in yeast and Arabidopsis. Expression of OsNRAMP1 in yeast mutant (fet3fet4) rescued iron (Fe) uptake and exhibited enhanced accumulation of As and Cd. Expression of OsNRAMP1 in Arabidopsis provided tolerance with enhanced As and Cd accumulation in root and shoot. Cellular localization revealed that OsNRAMP1 resides on plasma membrane of endodermis and pericycle cells and may assist in xylem loading for root to shoot mobilization. This is the first report demonstrating role of NRAMP in xylem mediated loading and enhanced accumulation of As and Cd in plants. We propose that genetic modification of OsNRAMP1 in rice might be helpful in developing rice with low As and Cd content in grain and minimize the risk of food chain contamination to these toxic metals.

Selenium ameliorates arsenic induced oxidative stress through modulation of antioxidant enzymes and thiols in rice (Oryza sativa L.).

Arsenic (As) contamination of rice is a major problem for South-East Asia. In the present study, the effect of selenium (Se) on rice (Oryza sativa L.) plants exposed to As was studied in hydroponic culture. Arsenic accumulation, plant growth, thiolic ligands and antioxidative enzyme activities were assayed after single (As and Se) and simultaneous supplementations (As + Se). The results indicated that the presence of Se (25 µM) decreased As accumulation by threefold in roots and twofold in shoots as compared to single As (25 µM) exposed plants. Arsenic induced oxidative stress in roots and shoots was significantly ameliorated by Se supplementation. The observed positive response was found associated with the increased activities of ascorbate peroxidase (APX; EC 1.11.1.11), catalase (CAT; EC 1.11.1.6) and glutathione peroxidase (GPx; EC 1.11.1.9) and induced levels of non-protein thiols (NPTs), glutathione (GSH) and phytochelatins (PCs) in As + Se exposed plants as compared to single As treatment. Selenium supplementation modulated the thiol metabolism enzymes viz., γ-glutamylcysteine synthetase (γ-ECS; EC 6.3.2.2), glutathione-S-transferase (GST; EC 2.5.1.18) and phytochelatin synthase (PCS; EC 2.3.2.15). Gene expression analysis of several metalloid responsive genes (LOX, SOD and MATE) showed upregulation during As stress, however, significant downregulation during As + Se exposure as compared to single As treatment. Gene expressions of enzymes of antioxidant and GSH and PC biosynthetic systems, such as APX, CAT, GPx, γ-ECS and PCS were found to be significantly positively correlated with their enzyme activities. The findings suggested that Se supplementation could be an effective strategy to reduce As accumulation and toxicity in rice plants.

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

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

Review on interactions between nanomaterials and phytohormones: Novel perspectives and opportunities for mitigating environmental challenges.

Nanotechnology offers the potential to provide innovative solutions for sustainable crop production as plants are exposed to a combination of climate change factors (CO2, temperature, UV radiation, ozone), abiotic (heavy metals, salinity, drought), and biotic (virus, bacteria, fungi, nematode, and insects) stresses. The application of particular sizes, shapes, and concentration of nanomaterials (NMs) potentially mitigate the negative impacts in plants by modulation of photosynthetic rate, redox homeostasis, hormonal balance, and nutrient assimilation through upregulation of anti-stress metabolites, antioxidant defense pathways, and genes and genes network. The present review inculcates recent advances in uptake, translocation, and accumulation mechanisms of NMs in plants. The critical theme of this review provides detailed insights into different physiological, biochemical, molecular, and stress tolerance mechanism(s) of NMs action and their cross-talk with different phytohormones. The role of NMs as a double-edged sword for climate change factors, abiotic, and biotic stresses for nutrients uptake, hormones synthesis, cytotoxic, and genotoxic effects including chromosomal aberration, and micronuclei synthesis have been extensively studied. Importantly, this review aims to provide an in-depth understanding of the hormesis effect at low and toxicity at higher doses of NMs under different stressors to develop innovative approaches and design smart NMs for sustainable crop production.

Investigation of biochemical responses of Bacopa monnieri L. upon exposure to arsenate.

Widespread contamination of arsenic (As) is recognized as a global problem due to its well-known accumulation by edible and medicinal plants and associated health risks for the humans. In this study, phytotoxicity imposed upon exposure to arsenate [As(V); 0-250 µM for 1-7 days] and ensuing biochemical responses were investigated in a medicinal herb Bacopa monnieri L. vis-à-vis As accumulation. Plants accumulated substantial amount of As (total 768 µg g(-1) dw at 250 µM As(V) after 7 days) with the maximum As retention being in roots (60%) followed by stem (23%) and leaves (17%). The level of cysteine and total nonprotein thiols (NP-SH) increased significantly at all exposure concentrations and durations. Besides, the level of metalloid binding ligands viz., glutathione (GSH) and phytochelatins (PCs) increased significantly at the studied concentrations [50 and 250 µM As(V)] in both roots and leaves. The activities of various enzymes viz., arsenate reductase (AR), glutathione reductase (GR), superoxide dismutase (SOD), guaiacol peroxidase (GPX), ascorbate peroxidase (APX), and catalase (CAT) showed differential but coordinated stimulation in leaves and roots to help plants combat As toxicity up to moderate exposure concentrations (50 µM). However, beyond 50 µM, biomass production was found to decrease along with photosynthetic pigments and total soluble proteins, whereas lipid peroxidation increased. In conclusion, As accumulation potential of Bacopa may warrant its use as a phytoremediator but if Bacopa growing in contaminated areas is consumed by humans, it may prove to be toxic for health.

Arsenite tolerance is related to proportional thiolic metabolite synthesis in rice (Oryza sativa L.).

Thiol metabolism is the primary detoxification strategy by which rice plants tolerate arsenic (As) stress. In light of this, it is important to understand the importance of harmonised thiol metabolism with As accumulation and tolerance in rice plant. For this aim, tolerant (T) and sensitive (S) genotypes were screened from 303 rice (Oryza sativa) genotypes on exposure to 10 and 25 µM arsenite (As(III)) in hydroponic culture. On further As accumulation estimation, contrasting (13-fold difference) T (IC-340072) and S (IC-115730) genotypes were selected. This difference was further evaluated using biochemical and molecular approaches to understand involvement of thiolic metabolism vis-a-vis As accumulation in these two genotypes. Various phytochelatin (PC) species (PC(2), PC(3) and PC(4)) were detected in both the genotypes with a dominance of PC(3). However, PC concentrations were greater in the S genotype, and it was noticed that the total PC (PC(2) + PC(3 )+ PC(4))-to-As(III) molar ratio (PC-SH:As(III)) was greater in T (2.35 and 1.36 in shoots and roots, respectively) than in the S genotype (0.90 and 0.15 in shoots and roots, respectively). Expression analysis of several metal(loid) stress-related genes showed significant upregulation of glutaredoxin, sulphate transporter, and ascorbate peroxidase in the S genotype. Furthermore, enzyme activity of phytochelatin synthase and cysteine synthase was greater on As accumulation in the S compared with the T genotype. It was concluded that the T genotype synthesizes adequate thiols to detoxify metalloid load, whereas the S genotype synthesizes greater but inadequate levels of thiols to tolerate an exceedingly greater load of metalloids, as evidenced by thiol-to-metalloid molar ratios, and therefore shows a phytotoxicity response.

Chromium toxicity and tolerance mechanisms in plants through cross-talk of secondary messengers: An overview of pathways and mechanisms.

Environmental sources of chromium (Cr) such as solid waste, battery chemicals, industrial /waste, automotive exhaust emissions, mineral mining, fertilizers, and pesticides, have detrimental effects on plants. An excessive amount of Cr exposure can lead to toxic accumulations in human, animal, and plant tissues. In plants, diverse signaling molecules like hydrogen sulfide (H2S) and nitric oxide (NO) play multiple roles during Cr stress. Consequently, the molecular mechanisms of Cr toxicity in plants, such as metal binding, modifying enzyme activity, and damaging cells are examined by several studies. The reactive oxygen species (ROS) that are formed when Cr reacts with lipids, membranes, DNA, proteins, and carbohydrates are all responsible for damage caused by Cr. ROS regulate plant growth, programmed cell death (PCD), cell cycle, pathogen defense, systemic communication, abiotic stress responses, and growth. Plants accumulate Cr mostly through the root system, with very little movement to the shoots. The characterization of stress-inducible proteins and metabolites involved in Cr tolerance and cross-talk messengers has been made possible due to recent advances in metabolomics, transcriptomics, and proteomics. This review discusses Cr absorption, translocation, subcellular distribution, and cross-talk between secondary messengers as mechanisms responsible for Cr toxicity and tolerance in plants. To mitigate this problem, soil-plant systems need to be monitored for the biogeochemical behavior of Cr and the identification of secondary messengers in plants.

Titanium dioxide nanoparticles potentially regulate the mechanism(s) for photosynthetic attributes, genotoxicity, antioxidants defense machinery, and phytochelatins synthesis in relation to hexavalent chromium toxicity in Helianthus annuus L.

Chromium (VI) is one of the hazardous heavy metal, heavily discharged into the soil and severely hampers the plants yield. The TiO2 NPs was selected due to its potential to alleviate the heavy metals toxicity. This manuscript unravels the mechanisms for Cr(VI) induced toxicity and how foliar application of TiO2 NPS potentially ameliorate the toxicity by regulating the photosynthetic attributes, DNA damage, antioxidants defense machinery, and phytochelatins synthesis in Helianthus annuus L. Plants were exposed to Cr(VI) concentrations [0, 15, 30, and 60 mg Cr(VI) kg-1 of soil], and TiO2 NPS (15 mg L-1, 25 nm size) were foliar sprayed thrice to the plants at three days interval. The maximum accumulation of total chromium was recorded in root (12.53 µg g-1 DW) followed by shoot (5.67 µg g-1 DW) at 60 mg Cr(VI) treatment. The presence and localization of TiO2 NPs inside the plant leaf cells were confirmed by TEM-EDS analysis. The results revealed that Cr(VI) exposure had a dose-dependent inhibitory effects on photosynthetic attributes, structure of guard and epidermal cells, photosynthetic pigments; inducing impacts on H2O2 and MDA productions, DNA damage, AsA-GSH cycle, and most importantly on PC2, and PC3 synthesis which is rarely reported. However, TiO2 NPs exposure minimized Cr(VI) induced toxicity through reduction of total chromium accumulation, H2O2 and MDA productions, thereby reducing DNA damage reported first time under combined treatment of Cr(VI)+ TiO2 NPs as evidenced through comet assay. It also positively regulate the photosynthetic pigments, AsA-GSH cycle, and modulates PC2 and PC3 synthesis which have crucial impacts on ROS quenching and Cr(VI) detoxification, respectively, and in turn, minimizes Cr(VI) toxicity in H. annuus L. Besides, this study strengthens the less acknowledged report that Cr(VI) is an inducer of PCs synthesis and also confirms that TiO2 NPs potentially counteract Cr(VI) toxicity.

Genome-wide identification of rice class I metallothionein gene: tissue expression patterns and induction in response to heavy metal stress.

Metallothioneins (MTs) are members of a family of cysteine-rich low molecular weight polypeptides which play an important role in heavy metal detoxification and homeostasis of intracellular metal ions in plant. Though MT genes from some selected plants have been characterized with respect to their protein sequences, kinetic properties and tissue-specific localization, no detailed study has been carried out in rice. Here, we present genome-wide identification, structural and expression analyses of rice MT gene family. Our analysis suggests presence of 11 class I MT genes in rice genome (Release 7 of the MSU Rice Genome Annotation Project) which are differentially expressed during growth and development, in various tissues and during biotic and abiotic stresses. Our analyses suggest that class I MT proteins in rice differ in tissue localization as well as in heavy metal coordination chemistry. We also suggest that some MTs have a predominant role in detoxification of As (V) in arsenic-tolerant rice cultivars. Our analysis suggests that apart from transcriptional regulation, post-transcriptional alternative splicing in some members of this family takes place during growth and development, in various tissues and during biotic and abiotic stresses.

Expression of phytochelatin synthase from aquatic macrophyte Ceratophyllum demersum L. enhances cadmium and arsenic accumulation in tobacco.

UNLABELLED: Phytochelatin synthase (PCS), the key enzyme involved in heavy metal detoxification and accumulation has been used from various sources to develop transgenic plants for the purpose of phytoremediation. However, some of the earlier studies provided contradictory results. Most of the PCS genes were isolated from plants that are not potential metal accumulators. In this study, we have isolated PCS gene from Ceratophyllum demersum cv. L. (CdPCS1), a submerged rootless aquatic macrophyte, which is considered as potential accumulator of heavy metals. The CdPCS1 cDNA of 1,757 bp encodes a polypeptide of 501 amino acid residues and differs from other known PCS with respect to the presence of a number of cysteine residues known for their interaction with heavy metals. Complementation of cad1-3 mutant of Arabidopsis deficient in PC (phytochelatin) biosynthesis by CdPCS1 suggests its role in the synthesis of PCs. Transgenic tobacco plants expressing CdPCS1 showed several-fold increased PC content and precursor non-protein thiols with enhanced accumulation of cadmium (Cd) and arsenic (As) without significant decrease in plant growth. We conclude that CdPCS1 encodes functional PCS and may be part of metal detoxification mechanism of the heavy metal accumulating plant C. demersum. KEY MESSAGE: Heterologous expression of PCS gene from C. demersum complements Arabidopsis cad1-3 mutant and leads to enhanced accumulation of Cd and As in transgenic tobacco.

Differential response of oxidative stress and thiol metabolism in contrasting rice genotypes for arsenic tolerance.

The mechanism of arsenic (As) tolerance was investigated on two contrasting rice (Oryza sativa L.) genotypes, selected for As tolerance and accumulation. One tolerant (Triguna) and one sensitive (IET-4786) variety were exposed to various arsenate (0-50 µM) levels for 7 d for biochemical analyses. Arsenic induced oxidative stress was more pronounced in IET-4786 than Triguna especially in terms of reactive oxygen species, lipid peroxidation, EC and pro-oxidant enzymes (NADPH oxidase and ascorbate oxidase). However, Triguna tolerated As stress through the enhanced enzymes activities particularly pertaining to thiol metabolism such as serine acetyl transferase (SAT), cysteine synthase (CS), γ-glutamyl cysteine synthase (γ-ECS), γ-glutamyl transpeptidase (γ-GT), and glutathione-S-transferase (GST) as well as arsenate reductase (AR). Besides maintaining the ratio of redox couples GSH/GSSG and ASC/DHA, the level of phytochelatins (PCs) and phytochelatin synthase (PCS) activity were more pronounced in Triguna, in which harmonized responses of thiol metabolism was responsible for As tolerance in contrast to IET-4786 showing its susceptible nature towards As exposure.