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An arsenic-accumulating, hypertolerant brassica, Isatis capadocica: Rapid report
Abstract
Isatis capadocica, a brassica collected from Iranian arsenic-contaminated mine spoils and control populations, was examined to determine arsenate tolerance, metabolism and accumulation. I. cappadocica exhibited arsenate hypertolerance in both mine and nonmine populations, actively growing at concentrations of > 1 mm arsenate in hydroponic solution. I. cappadocica had an ability to accumulate high concentrations of arsenic in its shoots, in excess of 100 mg kg(-1) DW, with a shoot : root transfer ratio of > 1. The ability to accumulate arsenic was exhibited in both hydroponics and contaminated soils. Tolerance in this species was not achieved through suppression of high-affinity phosphate/arsenate root transport, in contrast to other monocotyledons and dicotyledons. A high percentage (> 50%) of arsenic in the tissues was phytochelatin complexed; however, it is argued that this is a constitutive, rather than an adaptive, mechanism of tolerance.
... The sterilized seeds were germinated in moist perlite for 5 days. After reaching the four-leaf stage, uniform seedlings were transplanted (4 seedlings per pot) in one-liter pots under hydroponic condition containing Hoagland solution (Karimi et al. 2009). The experiment was conducted in a completely randomized design in a factorial arrangement with three replications (one pot in each replication). ...
... For example, the As stress (625 μM) imposed through As(V) caused a 37% reduction in shoot fresh weight whereas plants ceased to grow leading to death in the case of As(III) stress. This suggests Isatis plants can better tolerate As(V) toxicity than As(III) (Tables 1, 2) as has been noticed from its growth in As(V) polluted areas (Karimi et al. 2009;Souri et al. 2018). This hyper-tolerance of Isatis to As(V) is achieved through phytochelatin complexation (> 50%), which is involved in constitutive plant responses (Karimi et al. 2009). ...
... This suggests Isatis plants can better tolerate As(V) toxicity than As(III) (Tables 1, 2) as has been noticed from its growth in As(V) polluted areas (Karimi et al. 2009;Souri et al. 2018). This hyper-tolerance of Isatis to As(V) is achieved through phytochelatin complexation (> 50%), which is involved in constitutive plant responses (Karimi et al. 2009). The toxicity of As(III) to plant growth can be associated with its binding ability to key proteins resulting in cellular metabolism inhibition and reduction in cell growth and proliferation (Ahmad et al. 2020). ...
Arsenic (As) toxicity hinders plant growth and productivity and poses human health concerns. However, silicon (Si) nutrition
can help improve plant tolerance to abiotic stresses. This study evaluated the influence of Si application on plant growth and
As accumulation in an As hyperaccumulator plant, Isatis (Isatis cappadocica Desv.) under As stress. Isatis seedlings were
exposed to 0, 5, 25, 125, and 625 μM Na2HAsO4.7H2O (AsV) and NaAsO2 (AsIII) and then Si was applied as Na2SiO3 (1
and 2 mM). Plant exposure to As(V: 650 μM) and As(III: 125 µM) caused significant reduction in plant fresh weight by 31
and 42%, and photosynthetic pigments by 47 and 62%, respectively. The same treatments caused 37- and 4.2-fold increase in levels of reactive oxygen species. However, exogenous application of Si effectively mitigated As stress and caused a
decrease in shoot As concentration up to 15% and 21% in As(V) and As(III) treated plants, respectively. In this regard, Si
application at the 1 mM level was more effective. The Si-induced tolerance against As in Isatis was attributed to the activation
of the antioxidant defense system (increase in the activities of glutathione-S-transferase and guaiacol peroxidase, carotenoids,
proline and anthocyanin contents). In conclusion, Si application improved the As tolerance in Isatis plants by modulating
plant growth, decreasing As accumulation and activating the antioxidant defense system.
... Glutathione reductase (GR) is an NADPH-dependent enzyme responsible for reducing GSSG to GSH thus maintaining the required level of GSH pool for the proper functioning of cells. Role of GR in mitigating the toxic effect of As in Isatis cappadocica has been demonstrated by increased activity of GR (Karimi et al., 2009). Along with Isatis cappadocica, the importance of GR in the other plants during As stress has been documented (Begum et al., 2016;Degola et al., 2015). ...
... In presence of As the levels of GSH are reduced as GSH is utilized as a substrate for the biosynthesis of PCs. The higher demand of GSH is fulfilled by the increased activity of GR in plants during As stress (Karimi et al., 2009). Studies indicated that enhancement in As supply increased the activities of antioxidant enzymes in various plant species, such as Glycine max L., Helianthus annuus, Triticum aestivum, and Oryza sativa Chandrakar et al., 2017;Saidi et al., 2017;Sharma et al., 2017). ...
... In some As-hyperaccumulator plants such as H. Lanatus, Silene paradoxa, Pteris vittata, and Pteris cretica, PCs have not been responsible for a significant role in providing As-tolerance (Raab et al., 2007;Arnetoli et al., 2008). However, in some other, As hyperaccumulator plants such as in Isatis cappadocica, hyperaccumulation and tolerance are achieved by PCs complexation (>50%) which is observed to be a constitutive tolerance mechanism (Karimi et al., 2009). Sequestration of the AsIII-PCs complexes in vacuoles is an essential step in As detoxification metabolism. ...
The present book not only discusses the traditional biomonitoring concepts but also highlights the newly developed biomonitoring techniques.
... Apart from this, hyperaccumulator plants can be utilized for cleaning up As-contaminated areas (Chen et al. 2002;Karimi et al. 2010). As hyperaccumulator plants have potential to uptake, translocate and tolerate As with very less adverse effects to the plants (Karimi et al. 2009;Zhao et al. 2009;Souri et al. 2017a, b). Previous reports have indicated that Isatis cappadocica is a brassica As hyperaccumulator (Karimi et al. 2009(Karimi et al. , 2010Souri 2015, 2016;Souri and Karimi 2017;Souri et al. 2020Souri et al. , 2021a, which can be used as a phytoremediator for As-contaminated soil (Karimi et al. 2010). ...
... As hyperaccumulator plants have potential to uptake, translocate and tolerate As with very less adverse effects to the plants (Karimi et al. 2009;Zhao et al. 2009;Souri et al. 2017a, b). Previous reports have indicated that Isatis cappadocica is a brassica As hyperaccumulator (Karimi et al. 2009(Karimi et al. , 2010Souri 2015, 2016;Souri and Karimi 2017;Souri et al. 2020Souri et al. , 2021a, which can be used as a phytoremediator for As-contaminated soil (Karimi et al. 2010). Besides, this plant can easily be cultivated and has capacity to produce high biomass and strongly branched inflorescence (Karimi et al. 2010). ...
... Besides, this plant can easily be cultivated and has capacity to produce high biomass and strongly branched inflorescence (Karimi et al. 2010). These characteristics potentially make it a sole angiosperm candidate for reclamation of As-contaminated soil and are also suggested from previous reports (Karimi et al. 2009(Karimi et al. , 2010Karimi and Souri 2015;Souri et al. 2017aSouri et al. , 2018Souri et al. , 2020Souri et al. , 2021a. ...
The current study was conducted to investigate the role of sulfur (S) and reduced glutathione (GSH) in mitigating arsenic (As) toxicity in Isatis cappadocica and Erysimum allionii. These plants were exposed for 3 weeks to different concentrations (0, 400 and 800 μM) of As to measure fresh weight, total chlorophyll, proline and hydrogen peroxide (H2O2) content, As and S accumulation, and guaiacol peroxidase (POD) and glutathione S-transferase (GST) along with the supplementation of 20 mg L-1 of S and 500 μM of GSH. Results revealed the significant reduction of fresh weight (especially in E. allionii), activities of POD and GST enzymes and proline content as compare to control. However, the application of S and GSH enhanced the fresh weight. Inhibition in H2O2 accumulation and improvement in antioxidant responses were measured with the application of S and GSH. Hence, the supplementation of S and GSH enhanced fresh weight and total chlorophyll in both I. cappadocica and E. allionii by alleviating the adverse effects of As stress via decreased H2O2 content and restricted As uptake.
... Rice is of concern for grain As and one studied crop for the mechanisms of As uptake, distribution, and detoxification (Zhao 2020). As tolerance in As excluders is likely partly based on the suppression of high affinity phosphate/arsenate co-transport systems (Karimi et al. 2009, Karimi andSouri 2016). ...
... Isatis cappadocica metallicolous (M) and non-metallicolous (NM) populations (Iran, temperate Asia) are claimed As accumulators, with potentially constitutive As chelation by thiols and PCs, and tolerance not based through deletion of high-affinity P/As co-transport (Karimi et al. 2009). Both NM and M populations are more resistant than other commercial Brassicaceae (e.g. ...
... Indian mustard (Brassica juncea, Gupta et al. 2009) and Ethiopian mustard (B. carinata, Irtelli and Nacari-Izzo 2008) can display high shoot As concentration, but their phenotype is not well established (Karimi et al. 2009). In Indian mustard cultivars with shoot As concentration ranging from 16 to 1138 mg kg −1 DW, 10,870 genes are differentially expressed mainly in reaction to stress, metabolic processes, transporter activity, and signal transduction (Thakur et al. 2019). ...
Owing to their roles in the arsenic (As) biogeochemical cycle, microorganisms and plants offer significant potential for developing innovative biotechnological applications able to remediate As pollutions. This possible use in bioremediation processes and phytomanagement is based on their ability to catalyse various biotransformation reactions leading to, e.g. the precipitation, dissolution, and sequestration of As, stabilisation in the root zone and shoot As removal. On the one hand, genomic studies of microorganisms and their communities are useful in understanding their metabolic activities and their interaction with As. On the other hand, our knowledge of molecular mechanisms and fate of As in plants has been improved by laboratory and field experiments. Such studies pave new avenues for developing environmentally friendly bioprocessing options targeting As, which worldwide represents a major risk to many ecosystems and human health.
... To combat oxidative stress, plants employ a complex antioxidative defense system that comprises enzymatic antioxidants such as ascorbate peroxidase (APX), catalase (CAT), glutathione S-transferase (GST), guaiacol peroxidase (GPX), glutathione reductase (GR), superoxide dismutase (SOD), and several nonenzymatic antioxidants such as glutathione (GSH) and ascorbate (ASA), which help scavenge free radicals and maintain the balance of cellular ROS levels (Mittler et al. 2004, Liu et al. 2011, Wang et al. 2016, Soares et al. 2019). Among them, GSH acts as a substrate for phytochelatins (PCs), which chelate both metalloids and metals and therefore decrease their physiological availability inside cells (Karimi et al. 2009, Singh et al. 2015. Together, ROS and the plant antioxidant defense system serve as molecular bioindicators for contaminant-induced oxidative damage, reflecting the magnitude of responses in various plants exposed to toxic metals (Liu et al. 2011, Štork et al. 2013, Liu et al. 2018. ...
... Nevertheless, there are few studies available on the role of endogenous NO on plant response to heavy metal stress. Some plant species are able to detoxify and bioaccumulate high concentrations of heavy metals (Karimi et al. 2009, Karimi and Souri 2016, Souri et al. 2018. These species are hyperaccumulators, and they offer a promising, costeffective strategy to decrease the concentration of heavy metal contaminants in the soil (Ensley 2000, Lasat 2002. ...
... Isatis cappadocica is a brassica known as an arsenic-hyperaccumulating plant species (Karimi et al. 2009, Karimi and Souri 2015, 2020, but little is known about its capability to accumulate Cd and tolerate its toxicity. In general, Brassica species are tolerant to Cd due to their high biomass production and ability to uptake greater amount of Cd (Meng et al. 2009, Ali et al. 2014. ...
Isatis cappadocica is a well‐known arsenic‐hyperaccumulator, but there are no reports of its responses to cadmium (Cd). Nitric oxide (NO) is a signaling molecule, which induces cross‐stress tolerance and mediates several physio‐biochemical processes related to heavy metal toxicity. In this study, the effects of Cd and sodium nitroprusside (SNP as NO donor) on the growth, defense responses and Cd accumulation in I. cappadocica were investigated. When I. cappadocica was treated with 100 and 200 μM Cd, there was an insignificant inhibition of shoot growth. However, Cd stress at Cd400 treatment decreased significantly the dry weight of root and shoot by 73 and 38%, respectively, as compared to control. The application of SNP significantly improved the growth parameters and mitigated Cd toxicity. In addition, SNP decreased reactive oxygen species (ROS) production induced by Cd. The increased total thiol and glutathione (GSH) concentrations after SNP application may play a decisive role in maintaining cellular redox homeostasis, thereby protecting plants against oxidative damage under Cd stress. Bovine hemoglobin (Hb as NO scavenger) reduced the protective role of SNP, suggesting a major role of NO in the defensive effect of SNP. Furthermore, the reduction in shoot growth and the increase of oxidative damage were more severe after the addition of Hb, which confirms the protective role of NO against Cd‐induced oxidative stress. The protective role of SNP in decreasing Cd‐induced oxidative stress may be related to NO production, which can lead to stimulation of the thiols synthesis and improve defense system.
... Applying hyperaccumulating plants to take up metals and metalloids from contaminated soils and groundwater and concentrate them in aboveground tissues is an appealing approach to enhance As removal (Pilon-Smits, 2005;Lampis et al., 2015). Many As hyperaccumulating plants have been identified so far, with the Chinese fern as the first reported natural As hyperaccumulator (Ma et al., 2001;Karimi et al., 2009;Souri and Karimi, 2017). Since then, many other As hyperaccumulating plants from the same or different families have been reported. ...
... Among these hyperaccumulators, Isatis cappadocica from the family Brassicaceae, has displayed high efficiency for As accumulation in heavily contaminated sites (Karimi et al., 2009(Karimi et al., , 2010Karimi and Souri, 2015;Souri and Karimi, 2017), indicating its high tolerance to As (Souri et al., 2020). However, I. cappadocica can still suffer from oxidative stress induced by high concentrations of As at the physiological and biochemical level, leading to lower plant biomass and slower plant growth Souri, 2015, 2016;Souri et al., 2017aSouri et al., , 2018Souri et al., , 2020. ...
... Seeds of Isatis cappadocica were collected from an old gold-As mine in the Zarshuran area, Iran, where the As concentration ranges from 145 to 6525 mg kg − 1 (Karimi et al., 2009(Karimi et al., , 2010. Seed disinfection and germination were performed as previously described (Souri et al., 2020). ...
Widespread arsenic (As) contamination is a severe environmental and public health concern. Isatis cappadocica, an arsenic hyperaccumulator, holds great potential to clean up As-contaminated soil and groundwater. Iron oxide is one of the most common metal oxides in the natural environment and its nanoparticulate form has been previously utilized for the removal of heavy metals/metalloids from wastewater. However, there is a paucity of information on the impact of iron oxide nanoparticles on the growth and physiological properties of I. cappadocica and its effectiveness on As removal. Current study reports for the first time the impact of superparamagnetic iron oxide nanoparticles and glutathione (GSH) modified superparamagnetic iron oxide nanoparticles (nFe3O4 and nFe3O4@GSH) on the physiological characteristic of I. cappadocica and its accumulation of As under hydroponic condition. nFe3O4@GSH alleviated the harmful impact of As and significantly increased the shoot biomass of I. cappadocica by enhancing the plant defense mechanisms. The application of GSH, nFe3O4 and nFe3O4@GSH all lowered the As concentration in plant shoots as a protective mechanism. However, the substantial shoot biomass increase due to nFe3O4@GSH resulted in a 56% higher As accumulation in plant shoots than in plants exposed to As alone, indicating the strong effectiveness of nFe3O4@GSH as a novel enhancer of the As phytoremediation by I. cappadocica. Our data further showed that the beneficial effect of nFe3O4@GSH on As phytoremediation is due to the enhancement of activities of several enzymatic and nonenzymatic antioxidants.
... capitata, showed higher As concentrations in shoot, than in the roots (De Freitas-Silva et al. 2016). A hyperaccumulator plant Isatis cappadocica showed higher accumulation in the shoots as compared to the roots (Karimi et al. 2009). Upon entry into the shoot, As may again be complexed and sequestered into the vacuoles similar to the phenomenon observed in the roots. ...
... (d) Se hyperaccumulators -Brassicaceae, Scrophulariaceae, Fabaceae, Asteraceae (Reeves and Baker 2000). (e) As hyperaccumulators -Brassicaceae, Isatis cappadocica and Hesperis persica, ferns belonging to the genus Pteris (Karimi et al. 2009). (f) Strict metallophytes -Endemic to metalliferous soils. ...
... Varieties of Isatis cappadocica isolated from mines and non-mine sites both showed incredible ability to accumulate As, in excess of 100 mg kg −1 of dry weight of the plant. The plant shows transfer rates for rootto-shoot transport of As exceeding 1, with a greater accumulation in shoots than roots (Karimi et al. 2009). This species has immense potential for phytoremediation of As, even from extremely contaminated soils. ...
Arsenic (As) is a predominant contaminant in soil and water in many regions of the world, including China, India and Bangladesh. The metalloid is capable of accumulating to toxic levels in many plants, including crops, and can severely reduce the yield and quality of the same. Arsenic is a potent carcinogen, and causes severe and chronic toxicity in humans (arsenicosis), making the contamination of soil and plants with As an additional source of concern. Certain plants are able to tolerate high levels of metalloid without showing symptoms of toxicity. A further specialized variety of heavy metal–tolerant plants are the hyperaccumulators, which can accumulate high levels of the toxicant endogenously, without compromising its own growth. Brassica is an important genus of oil crops belonging to the family Brassicaceae that is cultivated worldwide. Several members of this family show significant potential in accumulating As from contaminated soil. Various mechanisms of As transport, metabolism and tolerance in plants are presented; and the potential of utilization of Brassica in phytoremediation of As-contaminated soil has been discussed. A brief outline of the different tolerance pathways exhibited by Brassica at the molecular level deciphered to date is also highlighted in detail. Further studies into the molecular mechanisms of tolerance and accumulation in Brassica may offer an economically productive mode of phytoremediation of As-contaminated soil utilizing different species of Brassica.
... capitata, showed higher As concentrations in shoot, than in the roots (De Freitas-Silva et al. 2016). A hyperaccumulator plant Isatis cappadocica showed higher accumulation in the shoots as compared to the roots (Karimi et al. 2009). Upon entry into the shoot, As may again be complexed and sequestered into the vacuoles similar to the phenomenon observed in the roots. ...
... (d) Se hyperaccumulators -Brassicaceae, Scrophulariaceae, Fabaceae, Asteraceae (Reeves and Baker 2000). (e) As hyperaccumulators -Brassicaceae, Isatis cappadocica and Hesperis persica, ferns belonging to the genus Pteris (Karimi et al. 2009). (f) Strict metallophytes -Endemic to metalliferous soils. ...
... Varieties of Isatis cappadocica isolated from mines and non-mine sites both showed incredible ability to accumulate As, in excess of 100 mg kg −1 of dry weight of the plant. The plant shows transfer rates for rootto-shoot transport of As exceeding 1, with a greater accumulation in shoots than roots (Karimi et al. 2009). This species has immense potential for phytoremediation of As, even from extremely contaminated soils. ...
Oilseed Brassica crops play an important role in the vegetable oil economy of India and the world. There is an urgently felt need to increase their yield levels across varying growing conditions to meet the ever-growing demand for edible oil. The production level fluctuates widely over time and space mainly due to the challenges posed by various biotic and abiotic stresses. To combat these stresses that are very complex in nature, we need to have multi-pronged strategy by combining agronomical and breeding approaches. A major shift in yield level of any crop plant with increased tolerance to biotic and abiotic stresses is possible only with extensive genetic manipulation through breeding, and the breeding efforts in turn will require the continued collection, conservation, evaluation, and deployment of diverse crop genetic resources in a targeted way. Various activities enshrined in the management of rapeseed-mustard genetic resources are systematically explained in this chapter with an aim firstly to sensitize the readers about the importance of PGR and then to explain the principles and methodologies underlying the various activities involved in PGR management with special emphasis on rapeseed-mustard group of crops. Status of rapeseed-mustard germplasm in India and the world in terms of their number, characterization, evaluation, utilization so far, and future thrust area required are also discussed in this chapter.
... The contamination of soil and groundwater due to As is a serious problem in certain contaminated areas in Iran such as the Zarshuran gold mine, where high levels of As cause health problems, including chronic As poisoning (arsenicosis), as well as skin and bladder cancer (Karimi et al., 2010). Interestingly, the hyperaccumulator plant Isatis cappadocica has grown well in this contaminated area (Karimi et al., 2009(Karimi et al., , 2010. ...
... In this study, we investigated the effect of NO on As uptake, growth and antioxidant defense responses in I. cappadocica, which has been reported to be an As-hyperaccumulating plant (Karimi et al., 2009(Karimi et al., , 2013Karimi and Souri, 2015). Although the mechanisms involved in both As tolerance and hyperaccumulation are not fully understood, the GSH complex and phytochelatin (PC) production have been reported to be potential mechanisms induced in plants to remove As and to prevent toxicity (Karimi et al., 2013;Karimi and Souri, 2015). ...
... Isatis cappadocica seeds, collected from a seed population at the Zarshuran mine (gold and As deposits) at 36 43 0 04 00 N 47 08 0 02 00 E, 40 km north of the town of Takab in the western province of Azerbaijan in northwestern Iran, were germinated for 7 d. The uniform seedlings were then transferred to hydroponic pots filled with 100 mL of a modified Hoagland nutrient solution (1/5 Hoagland solution; Karimi et al., 2009), containing 0.5 mM KNO 3 , 0.75 mM Ca (NO 3 ) 2 , 0.5 mM KH 2 PO 4 , 0.2 mM MgSO 4 , 15 mM H 3 BO 3 , 2 mM MnCl 2 , 1 mM ZnSO 4 , 1 mM CuSO 4 , 1 mM Na 2 MoO 4 . 2H 2 O and 50 mM Fe-EDTA, and kept in a controlled growth chamber with a light intensity of 150 mmol photons m À2 s À1 , a 14/10 h light/dark regime, a 25/20 C day/night temperature and 60% relative humidity (Karimi et al., 2009). ...
Arsenic (As) is a toxic metalloid that severely hampers plant growth and also poses health risks for humans through the food chain. Although nitric oxide (NO) is known to improve plant resistance to multiple stresses including metal toxicity, little is known about its role in the As tolerance of hyperaccumulator plants. This study investigates the role of the exogenously applied NO donor, sodium nitroprusside (SNP), in improving the As tolerance of Isatis cappadocica, which has been reported to hyperaccumulate As. Exposure to toxic As concentrations significantly increases NO production and damages the cell membrane, as indicated by increased hydrogen peroxide (H2O2) and malondialdehyde (MDA) concentrations, thereby reducing plant growth. However, the addition of SNP improves growth and alleviates As-induced oxidative stress by enhancing the activity of superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), glutathione S-transferase (GST), glutathione (GSH), as well as proline and thiol concentrations, thereby confirming the beneficial role played by NO in increasing As stress tolerance. Furthermore, the As-induced decrease in growth and the increase in oxidative stress were more marked in the presence of bovine hemoglobin (Hb; a NO scavenger) and N(G)-nitro-l-arginine methyl ester (l-NAME; a NO synthase inhibitor), thus demonstrating the protective role of NO against As toxicity. The reduction in NO concentrations by l-NAME suggests that NOS-like activity is involved in the generation of NO in response to As in I. cappadocica.
... The resulting solution was then added to a mixture containing 10% (v/v) HCl, 10% KI (w/v), and 5% ascorbic acid (w/v). In the final step, a Shimadzu AA-6200 atomic absorption spectrometer (HG-AAS), was utilized to determine the accumulation of Mn and Cr using an external standard [105]. The accumulation of nitric oxide was detected by converting ...
... The resulting solution was then added to a mixture containing 10% (v/v) HCl, 10% KI (w/v), and 5% ascorbic acid (w/v). In the final step, a Shimadzu AA-6200 atomic absorption spectrometer (HG-AAS), was utilized to determine the accumulation of Mn and Cr using an external standard [105]. The accumulation of nitric oxide was detected by converting the oxygen-hemoglobin content to methemoglobin. ...
Sodium nitroprusside (SNP), as a single minuscule signaling molecule, has been employed to alleviate plant stress in recent years. This approach has a beneficial effect on the biological and physiological processes of plants. As a result, an in vitro tissue culture experiment was carried out to investigate the effect of high and low levels of SNP on the amelioration of manganese (Mn) and chromium (Cr) toxicity in a one-year-old bamboo plant, namely Pleioblastus pygmaea L. Five different concentrations of SNP were utilized as a nitric oxide (NO) donor (0, 50, 80, 150, 250, and 400 µM) in four replications of 150 µM Mn and 150 µM Cr. The results revealed that while 150 µM Mn and 150 µM Cr induced an over-generation of reactive oxygen species (ROS) compounds, enhancing plant membrane injury, electrolyte leakage (EL), and oxidation in bamboo species, the varying levels of SNP significantly increased antioxidant and non-antioxidant activities, proline (Pro), glutathione (GSH), and glycine betaine (GB) content, photosynthesis, and plant growth parameters, while also reducing heavy metal accumulation and translocation in the shoot and stem. This resulted in an increase in the plant’s tolerance to Mn and Cr toxicity. Hence, it is inferred that NO-induced mechanisms boosted plant resistance to toxicity by increasing antioxidant capacity, inhibiting heavy metal accumulation in the aerial part of the plant, restricting heavy metal translocation from root to leaves, and enhancing the relative water content of leaves.
... Research on the use of marigold plants as potentially useful for As phytoextraction has also produced quite good results (Chintakovid et al. 2008). Another hyperaccumulating species are broadleaf cattail (Typha latifolia), which accumulates As mostly in roots (Lyubenova et al. 2013), and Isatis cappadocica (Karimi et al. 2009). The latter is an As hyperaccumulator due to its capacity to tolerate and accumulate As, exceeding the content of 300 mg kg À1 of arsenic in shoots, which is at least one order of magnitude higher than in other species at the same As contaminated area, and without showing any As toxicity symptoms (Karimi et al. 2009). ...
... Another hyperaccumulating species are broadleaf cattail (Typha latifolia), which accumulates As mostly in roots (Lyubenova et al. 2013), and Isatis cappadocica (Karimi et al. 2009). The latter is an As hyperaccumulator due to its capacity to tolerate and accumulate As, exceeding the content of 300 mg kg À1 of arsenic in shoots, which is at least one order of magnitude higher than in other species at the same As contaminated area, and without showing any As toxicity symptoms (Karimi et al. 2009). Hyperaccumulators of As, such as I. cappadocica and P. vittata, accumulate approximately 60-80% of As in shoots, with a shoot to root ratio higher than 1 (Karimi et al. 2013;Chen et al. 2016), while only 5-10% of total As is found in the shoots of nonaccumulating species such as the fern Pteris. ...
Pollution of the soils with toxic elements is a serious problem all over the world. One of environmentally friendly techniques of their removal is phytoremediation. This paper is a summary of literature data and the results of own studies about the potential of Sinapis alba for bioaccumulation of Tl, As and PGEs, and its usefulness in remediation of polluted environment. S. alba is characterized with low living requirements, BFs ≫ 1 and high TFs, especially for Tl (up to 3). The influence of different forms of studied elements on plants was discussed based on biomass production, morphological changes and the impact on photosynthesis activity. The plants were cultivated in hydroponics and solid media of various composition, for example, in soil supplemented with MnO2, which resulted in BFs lower 6–7 times for leaves, and about 3–4 times for stems, as well as twice lower leaf development. Application of advanced analytical techniques was presented in studies of the detoxification mechanisms, identification of particular chemical forms of the elements and the presence of phytochelatins and their complexes with the investigated elements.
Novelty Statement
The paper summarizes both literature and original data on Sinapis alba exposed to such elements as thallium, arsenic and platinum group metals. The influence of different forms of studied elements on white mustard was discussed based on biomass production and morphological changes, as well as the impact on photosynthesis activity. The study covers such aspects as bioaccumulation, phytotoxicity as well as the usefulness of white mustard in remediation of polluted environment.
... Hyperaccumulation of As has been observed mostly in fern plants of the Pteris genus like P. vittata [40], P. longifolia [41], P. quadriaurita, P. cretica, P. ryiunkensis [42], etc. and Pityrogramma calomelanos [43]. One of the plants from the Brassicaceae family, Isatis cappadocica, shows As hyperaccumulation [44]. P. vittata has worldwide distribution from North America to Europe and Asia and can grow in a wide range of environmental conditions ranging from temperate to tropical [45]. ...
... Favas et al. [60] found Callitriche lusitanica to be a potential As accumulator with As concentrations reaching up to 2346 mg/kg DW. Other potential accumulators in higher plants have been identified in lab and field studies, e.g., Isatis cappadocica [44], Sesuvium portulacastrum [61], and Eclipta alba [62]. Sesuvium is a halophytic plant with a high tolerance not only to salt but also to a number of metals and showed As accumulation 155 µg/g dw upon exposure to 1000 µM As(V) in 30 d [61]. ...
Arsenic contamination of the environment is a serious problem threatening the health of millions of people exposed to arsenic (As) via drinking water and crops grown in contaminated areas. The remediation of As-contaminated soil and water bodies needs to be sustainable, low-cost and feasible to apply in the most affected low-to-middle income countries, like India and Bangladesh. Phytoremediation is an aesthetically appreciable and successful approach that can be used for As decontamination with use of the best approach(es) and the most promising plant(s). However, phytoremediation lacks the required speed and sometimes the stress caused by As could diminish plants’ potential for remediation. To tackle these demerits, we need augment plants’ potential with appropriate technological methods including microbial and nanoparticles applications and genetic modification of plants to alleviate the As stress and enhance As accumulation in phytoremediator plants. The present review discusses the As phytoremediation prospects of soil and water bodies and the usefulness of various plant systems in terms of high biomass, high As accumulation, bioenergy potential, and economic utility. The potential and prospects of assisted phytoremediation approaches are also presented.
... Certain plants can be very efficient in accumulation and tolerance of heavy metals e.g. Pteris vittata species and Isatis cappadocica species (belonging to the Brassicaceae family) are examples for As (Karimi et al. 2009;Karimi and Souri 2015;Souri et al. 2017). The main tolerance strategy of I. cappadocica species to As is achieved by increasing thiol e.g. ...
... The main tolerance strategy of I. cappadocica species to As is achieved by increasing thiol e.g. either synthesis of cysteine (Cys), glutathione (GSH), or phytochelatins (PCs) or chelation of GSH and PCs (Karimi et al. 2009;Souri et al. 2017). It has also been suggested that As-hyperaccumulator plants such as I. cappadocica species and P. vittata species, employ different tolerance mechanisms that prevent the negative effects of As e.g. the generation of reactive oxygen species (ROS), as by-products of photosynthesis, and thus prevent the negative effects of ROS on photosynthesis apparatus. ...
Heavy metals are among the main pollutants affecting plant photosynthesis. A broad literature screening reveals that heavy metals impair, in a type‐ and dose‐dependent manner, many aspects related to the photosynthetic apparatus. This chapter explores how stomatal and mesophyll conductances, chloroplasts, photosynthetic pigments, photosystems I and II, photosynthetic enzymes, and the antioxidant defense mechanism are negatively affected by heavy metals. It also describes how hyperaccumulator plants cope with potential disturbances in photosynthesis upon heavy metal stress.
... According to literature data, up to date, there were identified around 500 taxa as hyperaccumulators of one or more metals, from which more than 75% are Ni hyperaccumulators (around 25% belonging to the family of Brassicaceae) (Li et al., 2003;Muszyńska and Hanus-Fajerska, 2015;Parmar and Singh, 2015). Other hyperaccumulating plants were reported for accumulating Pb, Co, Cu, As, or Zn, while fewer plants are available for Cd and Mn (Liang et al., 2009;Parmar and Singh, 2015 It was observed that Thlaspi caerulescens was mainly reported to accumulate Zn and Cd in high levels in shoots without suffering growth effects (Karimi et al., 2009;Miransari, 2011). ...
Environmental damage is caused by a large variety of pollutants: of these, heavy metals are often a major problem. Metals exist in the environment naturally, but since anthropogenic activities generate large quantities, different concentrations reach the environmental compartments. This chapter highlights that, when exceeding natural concentrations, pollution of the environment with heavy metals is inevitable. The presence of heavy metals in water, soil, and air can cause considerable concerns for both environmental quality and human health. Although living organisms require certain types of heavy metals in certain amounts, excessive levels are considerably carcinogenic or toxic. This chapter argues that the accumulation of heavy metals above the tolerance level can induce adverse effects in the plant. Some plants tolerate metal toxicity up to a certain threshold. Phytoremediation is discussed as a considerably promising method for removing heavy metals from the environment by hyper‐accumulating plants. The mechanisms by which plants significantly concentrate elements and compounds in the environment and therefore induce molecular metabolism in tissues are described, as well as the association of plants with the microbial rhizosphere, causing sequestration or mobilization of metals in soil and water matrices. Heavy metals cannot be degraded but can be transformed from a state of oxidation to another in inorganic complexes through microbial remediation. This process uses microorganisms, often in synergism with some plants to decontaminate or remove heavy metals from the environment. Bioremediation, seen as phytoremediation and microbial remediation, is reflected as an environmentally friendly technological solution to overcome heavy metal contamination.
... Hyperaccumulative plants also have strong antioxidative defence ability which could constitute an important As detoxification strategy. Nitrogen dioxide plays a significant role in enhancing As stress tolerance in plants by activating antioxidant enzyme and phytochelatin (Shah and Nongkynrih, 2007;Bhattacharya et al., 2007;Karimi et al., 2009). ...
Metal contaminated waters and soils are a main ecological crisis and the majority of conventional methods do not present adequate exposition. The contamination of the environment by toxic metals poses a threat for 'Man and biosphere'. It is also known that some metal contaminated soils are usually excavated and land filled. Considering these constraints, phytoremediation is one innovative approach that offers more natural advantages and a cost-effective alternative. Oxidoreductase metalloenzymes play an important role in the defence mechanism under metallic stress conditions. The proposed phytoremediation techniques are based on the highly successful and optimization of reaction called oxidative coupling mediated by metalloperoxidases. Oxidative stress is a leading one of the most provocation that leads to damage in plants mostly due to exposure to incompatible types of environmental stress which includes heavy metals. Phytochelatins alongwith antioxidative enzymes can form a synergistic defensive regime in plants under metallic stress which, in turn, can strengthen plants resistance against metal intoxication. Approach for plants with high oxidoreductase action bioengineered with expanded substantial metal resistance and take-up of heavy metals with the end goal of phytoremediation is examined.It has been shown that genes can act as a candidate for the future devise in plants for utilization in phytoremediation. We recommend that metalloenzymes activities add to heavy metal resistance and remediation.
... The ambient metal/metalloid concentration in water was the major factor influencing the metal/metalloid uptake efficiency. In general, when the metal/metalloid concentration in (Wang and Lewis, 1997;Karimi et al., 2009). In the present study, the effects of bio-concentration factor values of arsenic (III) and chromium (VI) at different concentration and exposure times were presented in Fig. 5.3 and Fig. 5.4, respectively. ...
... Then, the obtained solution was added to 10% KI, 10% HCl, and 5% ascorbic acid. To analyze Pb and Cd accumulation, the solution was transferred to an atomic absorption spectrometer (HG-AAS) (Shimadzu AA-6200) using optimal standards [33]. Nitric oxide concentrations Antioxidants 2021, 10, 1981 4 of 21 were obtained by analyzing the conversion of oxygen-hemoglobin to methemoglobin. ...
Recently, nitric oxide (NO) has been reported to increase plant resistance to heavy metal stress. In this regard, an in vitro tissue culture experiment was conducted to evaluate the role of the NO donor sodium nitroprusside (SNP) in the alleviation of heavy metal toxicity in a bamboo species (Arundinaria pygmaea) under lead (Pb) and cadmium (Cd) toxicity. The treatment included 200 µmol of heavy metals (Pb and Cd) alone and in combination with 200 mM SNP: NO donor, 0.1% Hb, bovine hemoglobin (NO scavenger), and 50 mM L-NAME, N(G)-nitro-L-arginine methyl ester (NO synthase inhibitor) in four replications in comparison to controls. The results demonstrated that the addition of L-NAME, and Hb as an NO synthase inhibitor and NO scavenger significantly increased oxidative stress and injured the cell membrane of the bamboo species. The addition of sodium nitroprusside (SNP) for NO synthesis increased antioxidant activity, protein content, photosynthetic properties, plant biomass, and plant growth under heavy metal (Pb and Cd) toxicity. It was concluded that NO can increase plant tolerance for metal toxicity with some key mechanisms, such as increasing antioxidant activities, limiting metal translocation from roots to shoots, and diminishing metal accumulation in the roots, shoots, and stems of bamboo species under heavy metal toxicity (Pb and Cd).
... Chromium phytoextraction depends on the specific hyperaccumulator-contaminant interaction [24][25][26][27][28][29]. ...
This work presents the results of experimental tests to evaluate the effects of prolonged contamination by Cr on Moso Bamboo (MB) (Phyllostachys pubescens) and the adaptability of the MB to the Mediterranean climate. A preliminary test on the MB was developed in the laboratory, simulating irrigation under Mediterranean conditions (600 mm per year) and tropical conditions (1800 mm per year), to evaluate the rate of growth and the MB’s capability for Cr phytoextraction from contaminated soil. The tolerance of MB to Cr was also performed showing a good response of the plant to 100 mg Cr/L solution, utilized for irrigation of the pots. The results show that the rate of MB’s removal of Cr from soil ranged from 49.2% to 61.7% as a function of the soil degree of contamination, which varied from approx. 100 mg/kg to 300 mg/kg. The distribution of Cr in the various sections of the bamboo revealed that the greater percentage was present in rhizomes: 42%, equal to 114 mg Cr for 600 mm per year, and 50%, equal to 412 mg Cr for 1800 mm per year. A noteworthy diffusion of the metal towards the outermost parts of the plant was shown. The values of Cr retained in the stems and leaves of MB tissues were quite high and varied from 1100 mg/kg to 1700 mg/kg dry weight.
... BCF is, therefore, a useful parameter for evaluating the potential of the plants to accumulate heavy metals, i.e. the phytoremediation potential of the plant [23][24][25]. Generally, when the heavy metal concentration in wastewater increases, the amount of metal accumulation in plants tissue increases [26,27]. BCF is calculated as follows [28][29][30]. ...
The use of three macrophytes namely Azolla pinnata, Eichhornia crassipes and Lemna minor for the phytore-mediation of emulsion paint wastewater was investigated. Samples of the paint wastewater and test plants were collected and analyzed for physicochemical characteristics and heavy metal concentrations before and after phy-toremediation for six weeks. The TDS of the treated wastewater was reduced by over 80.0% by each of the test plants while the TSS increased as a result of debris from withered test plants. Dissolved oxygen reduction ranged from 12.5% to 50.0%, COD from 49.5% to 57.1%, BOD from 46.7% to 54.7, heavy metals from 11.0 to 92.5%. A. pinnata appears to have performed significantly better (P < 0.05) than the other plants followed by E. crassipies and L. minor. It can be concluded that the test plants (especially A. pinnata) can be effectively used for the preliminary treatment of paint wastewater.
... A few plant species which belong to the family of Pteridaceae, were known as As hyperaccumulators (Delil et al., 2020). Isatis cappadocica is a plant present in Iran which, as a resistant mechanism includes an increase in the synthesis of thiol and chelation with PCs and glutathione (Karimi et al., 2009). In the list of top hazardous pollutants, arsenic is the most toxic metalloids, which cause mutagenic and carcinogenic effects in the living organisms (Sodhi et al., 2019). ...
Environmental contamination of heavy metals is now becoming increasingly a concern and a significant problem due to its harmful effects worldwide. The plant-meditated approach is encouraging to eliminate toxins avoiding side effects from polluted wastewater. For the development of appropriate plant species for the mechanisms of heavy metal absorption, transport, detoxification, identification, and signaling pathways would be important facts. Transporter genes like ATP-phosphoribosyl transferase (ATP-PRT), Yellow Stripe-like (YSL), NAS (nicotinamide synthase), SAMS (S-adenosyl-methionine synthetase), FER (ferritin Fe (III) binding), HMA (heavy metal ATPase), IREG (iron-regulated transporter), and proteins like cation diffusion facilitators (CDF), ZRT, IRT-like protein (ZIP), and natural resistance-associated macrophage protein (NRAMP) are active in heavy metal accumulation, translocalisation, sequestration, and resistance. Besides, chelating agents and metabolites can be used either to increase heavy metal bioavailability, which facilitates heavy metal accumulation in plants and further promote plant growth and fitness. This review paper addresses key roles and potential transporter genes and proteins for the remediation of heavy metals from hyperaccumulator plants. This review specifically focuses on the efficacy of transporter genes and proteins in hyperaccumulator plants in metal restoration, discussing the use of these plants for wastewater treatment processes.
... Isatis cappadocica, a plant found in Iran is considered as As hyperaccumulator. Under As stress, this plant produces excess thiol and chelate As with GSH and PCs (Karimi et al. 2009). However, Pteris vittata, a fern is also well equipped with proficient systems for uptake, translocation, and sequestration of As V / As III (Xie et al. 2009;Danh et al. 2014). ...
Since the onset of the industrial revolution, metalloids are an exceptional class of toxicants that adversely affects plant growth and productivity when present in high concentrations in the agricultural soil. Various transporters are accountable for the entry and distribution of different elements inside the plant. Due to similar structural properties, many toxic metalloid ions share the similar transport network like phosphate transporters, aquaglyceroporins, hexose transporters, sulfate transporters, etc. Incidence of surplus quantity of toxic metalloid ions inside the plant tissues causes severe damages to cellular biomolecules, affects key metabolic processes, and hampers plant growth, ultimately leading to reduced crop productivity. Therefore, detoxification strategies of metalloids at the physiological and molecular level are crucial in order to curtail their toxic consequences. Implementing genetic engineering techniques, efforts have been made by various scientists to impede the uptake of toxic metalloids by plants by reducing the transporters activities and to upregulate metalloid binding peptides and proteins such as metallothioneins and phytochelatins, for sequestration of toxic metalloids in the tissues. Reduced transport of metalloids in the tissues together with their augmented sequestration inside the cells would result in production of metalloid-tolerant plants. The present chapter summarizes current status of knowledge related to transport mechanisms and detoxification strategies of metalloids in plants in relation to plant-metalloid tolerance.
... Species accumulating selenium are distributed in generas of different families like Fabaceae, Asteraceae, Brassicaceae, Scrophulariaceae and Chenopodiaceae (Reeves and Baker 2000). Isatis cappadocica and Herperis persica belonging to Brassicaceae, along with ferns belonging to Pteris, are recognized as potential accumulators of As (Karimi et al. 2009). ...
... Although As III is more toxic than As V , both forms distinctly perturb plant metabolism (Finnegan and Chen, 2012). Many plant species, such as most of the Pteridaceae and Brassicaceae family plants, including Pteris vittata (fern) and Isatis cappadocica, respectively, can grow in soils containing higher concentrations of As because they have evolved mechanisms to cope with or tolerate As toxicity (Souri et al., 2017;Indriolo et al., 2010;Karimi et al., 2009;Xie et al., 2009). Nonetheless, when exposed to low As concentrations, many plant species can still show devastating effects (Jedynak et al., 2009). ...
Arsenic (As), a non-biodegradable contaminant, is extremely toxic to plants and animals in its inorganic form. As negatively affects plant growth and development, primarily by inducing oxidative stress through redox imbalance. Here we characterized the Arabidopsis F-box protein gene AT2G16220 (Arsenic Stress-Related F-box (ASRF)) that we identified in the genome-wide association study. The asrf mutant seedlings showed high sensitivity to arsenate (As V) stress. As V significantly affected asrf seedling growth when germinated on or exposed to As V-supplemented growth regimes. As V stress significantly induced production of reactive oxygen species and proline accumulation in asrf, so the asrf maintained high proline content, possibly for cellular protection and redox homeostasis. Heterozygous seedlings (Col-0 x asrf, F1 progeny) were relatively less affected by As V stress than asrf mutant but showed slightly reduced growth compared with the Col-0 wild type, which suggests that the homozygous ASRF locus is important for As V stress resistance. Transcriptome analysis involving the mutant and wild type revealed altered phosphate homeostasis in asrf seedlings, which implies that ASRF is required for maintaining phosphate and cellular-homeostasis under excess As V. Our findings confirm the roles of ASRF in As stress tolerance in plants, for a novel way to mitigate arsenic stress.
... Phytoremediation can be applied both in the presence of inorganic contaminants, such as heavy metals, through extraction or stabilization processes, and in the presence of organic contaminants, through degradation or extraction processes (Gardea-Torresdey et al. 2004;Anderson et al. 2005;Karimi et al. 2009;Ranieri et al. 2013;Petrella et al. 2016;Ranieri et al. 2020). Phytoextraction, which can be defined as the use of plants to remove non-degradable contaminants from the soil, is considered a green technology that can be applied to some heavy metals (McGrath et al. 2006;Reeves and Baker 2009;Tangahu et al. ...
An experimentation has been carried out in simulated Mediterranean and tropical laboratory conditions aimed to show the Moso bamboo capability of phytoextraction chromium from contaminated soil. Electronic microscopy supported the analyses performed on soil and on the different plant tissues. A preliminary test on the bamboo has been carried out in laboratory evaluating his growth with irrigation in Mediterranean conditions (600 mm/year) and tropical conditions (1.800 mm/year). A test of the bamboo tolerance of was also carried out by measuring his growth with irrigation with a solution of 100 mg Cr/l, reporting not significant damages to the plant tissues. Subsequently chromium phytoextraction was tested highlighting that bamboo removes Cr from soil with a percentage ranging from 43% (600 mm/year) to 47.4% (1.800 mm/year) of the total content in soil. Lastly, the distribution of chromium in the different fragments of the bamboo plants has been performed. It has been shown that approx. 69% of chromium, in Mediterranean conditions, was in the rhizomes and approx. 68% in tropical conditions. A slightly higher tendency to chromium translocation to leaves has been shown in tropical conditions than in Mediterranean conditions.
... The Brassicaceae family contains a large number of hyperaccumulating species with widest range of metals, these include 87 species from 11 genera (Baker and Brooks,1989). However, new reports of this kind of plants continue to accrue (Robinson, et al.,2006;Karimi et al., 2009), so that it is conceivable that many yet unidentified hyperaccumulators may occur in nature. Europe (Baker and Brooks,1989). ...
... The other objective in selecting metallophytes might be their nutritional or medicinal quality which can be included in our daily cuisines or can be used as animal fodder. Considering these points, the scientists are continuously working on identifying metallophyte species, this number is increasing (Sun et al. 2006;Karimi et al. 2009). ...
Moringa oleifera L. was grown under cadmium and lead stress conditions and the variations in its mineral content, polyphenolics, and antioxidant activities were studied and how these heavy metals affect plant growth and development. In this study, the metal translocation factor was found <1 which indicates more metal accumulation in moringa roots than stem. A significant increase in enzymatic and non-enzymatic antioxidant activities was observed in leaves, stem, and roots under metal stress which shows moringa can withstand under metalliferous conditions by regulating its antioxidant system. Various parts of moringa plants exhibited good nutritional quality; even significant variation was recorded in nutritional attributes. A significant variation was also noted in the expression of polyphenolics in moringa stem, roots, and leaves which are indicators of plant defense system under abiotic stress conditions. The results of the present study clearly manifest that the nutritional quality and concentration of polyphenolics in moringa plants are least affected by cadmium and lead uptake. These findings suggested the cultivation of moringa plants on cadmium and lead affected soils which cannot only remediate soil metalliferous conditions but can also provide nutritious fodder for livestock. For better understanding of the involved mechansisms, there is need to study the genes which are associated with moringa tolerance under metalliferous conditions.
... The most studied As hyperaccumulator plant is Pteris vittata, identified in Central Florida soils contaminated with chromated copper arsenate (Ma et al., 2001). Apart from ferns, the only angiosperms displaying As hyperaccumulation are two Brassicaceae species, Isatis cappadocica and Hesperis persica (Karimi, Ghaderian, Maroofi, & Schat, 2009;Karimi, Ghaderian, Raab, Feldmann, & Meharg, 2009). ...
To succeed in life, living organisms have to adapt to the environmental issues to which they are subjected. Some plants, defined hyperaccumulators , have adapted to metalliferous environments acquiring the ability to tolerate and accommodate high amounts of toxic metal into their shoot, without showing symptoms of toxicity.
The determinants for these traits and their mode of action have long been the subject of research, whose attention lately moved to the evolution of the hypertolerance and hyperaccumulation traits. Genetic evidence indicates that the evolution of both traits includes significant evolutionary events that result in species–wide tolerant and accumulating backgrounds. Different edaphic environments are responsible for subsequent refinement, by local adaptive processes, leading to specific strategies and various degrees of hypertolerance and hyperaccumulation which characterize metallicolous from non‐metallicolous ecotypes belonging to the same genetic unit.
In this review, we overview the most updated concepts regarding the evolution of hyperaccumulation and hypertolerance, highlighting also the ecological context concerning the plant populations displaying this fascinating phenomenon.
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... It has been outlined that plants upon exposure to As, reduce the available As 5+ to As 3+ through complexation by phytochelatins (Rosas-Castor et al. 2014). The formed As complexes are sequestrated and stored in the vacuoles, thereby reducing As toxicity (Karimi et al. 2009;Mallick, Sinam, and Sinha 2011). Roots being the first channel of As exposure, contained higher As than shoots, which has also been confirmed in other studies (Abedin, Cotter-Howells, and Meharg 2002). ...
Ninety-four barley genotypes were used to investigate the genotypic differences in arsenic (As) uptake and translocation and their relationships with As tolerance index (TI) and translocation factor (TF). Two As treatments (300 µM and 500 µM) were applied in the initial screening and the confirmatory experiments, respectively. The results showed significant (p < 0.05) differences in tissue biomass, shoot height, root length, As TI and TF among genotypes. Based on As TI, 11 barley genotypes were selected and divided into 3 groups, i.e. tolerant, mildly tolerant and sensitive. There was more As uptake in the roots of the As tolerant genotypes, while the As sensitive genotypes contained more As in shoots, which was further proved by the greater TF. Significantly negative correlation was observed between shoot and root As concentration. The results showed that As tolerant genotypes are able to restrict the upward movement of As, thus developing their tolerance.
... It has been outlined that plants upon exposure to As, reduce the available As 5+ to As 3+ through complexation by phytochelatins (Rosas-Castor et al. 2014). The formed As complexes are sequestrated and stored in the vacuoles, thereby reducing As toxicity (Karimi et al. 2009;Mallick, Sinam, and Sinha 2011). Roots being the first channel of As exposure, contained higher As than shoots, which has also been confirmed in other studies (Abedin, Cotter-Howells, and Meharg 2002). ...
Ninety-four barley genotypes were used to investigate the genotypic differences in arsenic (As) uptake and translocation and their relationships with As tolerance index (TI) and translocation factor (TF). Two As treatments (300 µM and 500 µM) were applied in the initial screening and the confirmatory experiments, respectively. The results showed significant (p < 0.05) differences in tissue biomass, shoot height, root length, As TI and TF among genotypes. Based on As TI, 11 barley genotypes were selected and divided into 3 groups, i.e. tolerant, mildly tolerant and sensitive. There was more As uptake in the roots of the As tolerant genotypes, while the As sensitive genotypes contained more As in shoots, which was further proved by the greater TF. Significantly negative correlation was observed between shoot and root As concentration. The results showed that As tolerant genotypes are able to restrict the upward movement of As, thus developing their tolerance.
... As(V) is a phosphate analogue and shares the phosphate transporters (e.g. OsPHT1) with phosphate [36]. We quantified the total concentration of phosphorous in both roots and shoots and it was unaffected by either Zn treatment, Fig. S1, suggesting that the function of phosphate/arsenate transporters was unaffected by Zn addition. ...
Accumulation of arsenic (As) and cadmium (Cd) in rice grains is a serious food safety concern for populations consuming rice as a staple food worldwide. Some agricultural practices such as water and nutrient management strategies can exhibit significant impact on their fate and bioavailability in rice paddies due to the profound impact of these activities on paddy soil properties. However, due to the unique biogeochemistry of As and Cd in rice paddies, their bioavailability often goes opposite directions and thus simultaneous control of both As and Cd in rice grains has not been achieved. Several previous studies have showed that some engineered nanoparticles (ENPs) can substantially lower the accumulation of either As or Cd in rice grains. The primary goal of this study was to evaluate whether zinc oxide nanoparticles, a popular nanofertilizer, can simultaneous lower both As and Cd in rice tissues using a greenhouse setup. The results suggested that both zinc oxide nanoparticles (ZnONPs) and zinc ions (Zn²⁺) significantly reduced the total As in rice roots (−39.5% and −83.3%) and shoots (−60.2% and −80.0%) and the reduction was primarily due to the lowered inorganic As(III) and organic As species. However, only ZnONPs reduced the Cd accumulation in rice shoots. Zn²⁺ significantly increased Cd content in rice shoot by 26.8%, suggesting the differential impact of ZnONPs and Zn²⁺ on As and Cd accumulation in rice tissues. Only ZnONPs holds the potential to simultaneously reduce both As and Cd in rice grains in As and Cd co-contaminated rice paddies. The results provide new insights into the sustainable applications of nanotechnology in agriculture.
... porosity and aeration were solely dependent on genetic makeup of a species that play vital role in differential As accumulation. Previous reports explained that in As hyper-tolerant plants potential reduction of As(V) into As(III) was followed by efflux of As(III) from cortex to the external medium through xylem sap (Karimi et al. 2009;Indriolo et al. 2010). This findings are in line with our study where cvs. ...
Arsenic (As) accumulation in rice is a principal route of As exposure for rice based population. We have tested physiochemical and molecular parameters together to identify low As accumulating rice cultivars with normal growth and vigor. The present study examined potential toxicity caused by arsenate (AsV) among four rice cultivars tested that varied with respect to accumulation of total arsenic, arsenite (AsIII) and their differential translocation rate which had deleterious impact on growth and metabolism. Intracellular homeostasis of rice cultivars viz., TN-1, IR-64, IR-20 and Tulaipanji was hampered by 21 days long As(V) treatment due to generation of reactive oxygen species (ROS) and inadequate activity of catalase (CAT; EC 1.11.1.6). Upregulation of oxidative stress markers viz., H2O2, proline and MDA along with alteration in enzymatic antioxidants profile were conspicuously pronounced in cv. Tulaipanji while cv. TN-1 was least affected under As(V) challenged environment. In addition to that genomic template stability and band sharing indices were qualitatively measured by DNA profiling of all tested cultivars treated with 25 μM, 50 μM, and 75 μM As(V). In rice cv. Tulaipanji genetic polymorphism was significantly detected with the application of random amplified polymorphic DNA (RAPD) tool and characterized as susceptible cultivar of As compared to cvs. TN-1, IR-64 and IR-20 that is in correlation with data obtained from cluster analysis. Hence, identified As tolerant cultivars viz., TN-1, IR64 and IR-20 especially TN-1 could be used in As contaminated agricultural field after appropriate field trial. This study could help to gather information regarding cultivar-specific tolerance strategy to avoid pollutant induced toxicity.
... Concerning inorganic forms such as As 3+ and As 5+ , these are structurally similar to silicic acid and phosphate, respectively. Phosphate is indispensable for plant growth and production since it is linked to several processes, such as energy storage and transfer, cell division, and photosynthesis (Karimi et al. 2009;Korndörfer 2015). Once absorbed by the roots, As 5+ is reduced to As 3+ by arsenate reductase (AR). ...
Arsenic (As) is a toxic and ubiquitously present element. It is present in some places of the world in excessively high concentrations in water and soil that threaten public health. North America constitutes one of the hotspots of As contamination. In Canada and the USA, a number of reports show the contamination of As in a number of food items including rice, rice-based products, fruits, beverages, animal food items, etc. Further, As contamination of water sources is also known to occur in different states of both Canada and the USA. Thus, the problem of As contamination is widespread and needs attention. This chapter provides an overview of As contamination of water and food sources of North America.
... Concerning inorganic forms such as As 3+ and As 5+ , these are structurally similar to silicic acid and phosphate, respectively. Phosphate is indispensable for plant growth and production since it is linked to several processes, such as energy storage and transfer, cell division, and photosynthesis (Karimi et al. 2009;Meharg and Zhao 2012;Korndörfer 2015). Once absorbed by the roots, As 5+ is reduced to As 3+ by arsenate reductase (AR). ...
Currently, there is a range of rice-based foods such as baby foods, crackers, porridge, and milk, among others. Children and celiac population highly consume these foods. Rice and rice-based food are essential for society due to their health benefits and historical cultivation. However, nowadays, rice is the focus of several studies not only for the benefits but also because it is a plant able to absorb about tenfold more arsenic (As) than other cereals. Arsenic is known by its genotoxic and carcinogenic capacity, mainly concerning inorganic As (i-As), about 100-fold more toxic than organic As. Several rice-based foods were above 200 μg kg⁻¹, the maximum limit recommended by Codex for i-As, such as husked rice flour with a concentration of 528 μg kg⁻¹. Other rice-based foods with lower concentrations of i-As, such as milk with 4.3 μg kg⁻¹, are also relevant to mention since there is no safe daily intake for As. In this regard, values for confidence limit lower than the reference dose (BMDL 0.1) of 0.3 to 8 μg kg⁻¹ body weight per day are used for assessment and characterization of the related health risks, such as bladder cancer. Thus, the determination of As concentrations in these foods is fundamental for a better risk assessment, especially concerning children, due to their physical and physiological condition, in which they may be more exposed to the damages caused by As when compared to adults in general.
... 41,42 The majority of phytoremediators are reported to accumulate metals in belowground biomass, reducing the potential for contaminant recovery; however, Karimi et al. reported an arsenic-accumulating species of brassica (Isatis capadocica), which favours accumulation in the aboveground biomass. 43 Isatis capadocica populations grown on mining-contaminated land (sourced from the gold-arsenic Zarshuran deposit) and non-contaminated land were studied. The metal tolerance of the two plant populations was compared through exposure to either a hydroponic metal solution, or metal-contaminated soils. ...
Intense anthropogenic activity continues to expose the natural environment to heavy metal contamination. Whilst a number of physical and chemical solutions for remediation exist, the use of higher plants and algae for clean‐up of contaminated landscapes, termed “phytoremediation” and “phycoremediation”, respectively, offer an attractive and sustainable alternative. However, these remediation processes will always lead to a high‐moisture, heavy metal‐contaminated biomass, which must be further processed to partition, or render inert, the metal contaminants. Conversion of this metal‐rich biomass into second‐generation biofuels offers a useful route to subsidise the economics of remediation activities. Here we briefly review the various methods for bioremediation of heavy metals, and discuss the potential to produce bioenergy from these biomass sources. Ultimately, coupling the bioremediation activity to bioenergy production gives far‐reaching social and economic benefits; however, established processes such as direct combustion and anaerobic digestion risk releasing heavy metals back into the environment. Alternatively, thermochemical conversions such as pyrolysis or hydrothermal liquefaction (HTL) offer significant advantages in terms of the segregation of metals into a relatively inert and compact solid phase while producing a biocrude oil for bioenergy production. In addition, preliminary work suggests that the HTL process can also be used to partition essential macronutrients, such as N, P and K, into an aqueous medium, allowing additional nutrient recycling. This article is protected by copyright. All rights reserved.
Arsenic (As) poisoning in agroecosystem is a major concern globally because rice is a main food source for a vital community in As-polluted areas. This effort is notable for its thorough examination of an extensive series of topics, including the health concerns allied with As disclosure; As sources in soil-rice systems; As toxicity symptoms at various stages of rice growth; As uptake, metabolism, and detoxification; and strategies to reduce As bioaccumulation. Moreover, significant efforts are being made to reduce As accumulation. The effectiveness of mitigation strategies has been thoroughly investigated, with a focus on soil amendments, irrigation management, electrokinetic remediation, exogenous application of chemicals and hormones, phytoremediation, bioremediation, transgenic variety development, and other agronomic techniques. Furthermore, among the various methods currently in use, biotechnology may be a good strategy for reducing As accretion in rice grains. Molecular engineering could be a feasible method for identifying the genes involved in the As metabolic route in plants. Despite this, the majority of these novel approaches are still being researched. As a result, this study explores into As accessibility in paddy soil, the mechanism of plant As uptake, the effects on humans and plants, and remediation approaches for mitigating As accretion.
Heavy metals and metalloids (cumulatively referred to as metal(loid)s) are ubiquitous in the environment. They originate from Earth’s crust, and their traces are present in all the environmental compartments. However, the concentration of many toxic heavy metal(loid)s has reached to a level causing serious health effects on humans. The sources and level of contamination of arsenic (As), cadmium (Cd), lead (Pb), and mercury (Hg) in water, soil, and food commodities have been discussed in details in the previous chapter. In the current chapter, the common and specific mode of toxicity through chronic dietary exposure of these priority heavy metal(loid)s to humans and target organs/systems has been discussed. The conventional and recent developments in mitigation techniques of these metal(loid)s from water and soil have also been included.
Heavy metals and metalloids (cumulatively referred to as metal(loid)s) are
ubiquitous in the environment. They originate from Earth’s crust, and their
traces are present in all the environmental compartments. However, the
concentration of many toxic heavy metal(loid)s has reached to a level
causing serious health effects on humans. The sources and level of
contamination of arsenic (As), cadmium (Cd), lead (Pb), and mercury (Hg) in water, soil, and food commodities have been discussed in details in
the previous chapter. In the current chapter, the common and specific mode
of toxicity through chronic dietary exposure of these priority heavy metal
(loid)s to humans and target organs/systems has been discussed. The
conventional and recent developments in mitigation techniques of these
metal(loid)s from water and soil have also been included.
Potentially toxic elements (PTEs) in soils accumulate in plants, obstruct their growth, and pose hazards to the consumer via the food chain. Many kinds of grass, grass-like plants, and other higher plant species have evolved a tolerance to PTEs. Holcus lanatus L., a wild grass, is also tolerant (an excluder) of PTEs, such as arsenic (As), cadmium (Cd), lead (Pb), and zinc (Zn). However, the extent of tolerance varies among ecotypes and genotypes. The PTE tolerance mechanism of H. lanatus curtails the typical uptake process and causes a reduced translocation of PTEs from the roots to the shoots, while such a characteristic is useful for contaminated land management. The ecology and response patterns of Holcus lanatus L. to PTEs, along with the associated mechanisms, are reviewed in the current work.
Arsenate (AsV) is one of the most common forms of arsenic (As) in environment and plant high-affinity phosphate transporters (PHT1s) are the primary plant AsV transporters. However, few PHT1s involved in AsV absorption have been identified in crops. In our previous study, TaPHT1;3, TaPHT1;6 and TaPHT1;9 were identified to function in phosphate absorption. Here, their AsV absorption capacities were evaluated using several experiments. Ectopic expression in yeast mutants indicated that TaPHT1;9 had the highest AsV absorption rates, followed by TaPHT1;6, while not for TaPHT1;3. Under AsV stress, further, BSMV-VIGS-mediated TaPHT1;9-silencing wheat plants exhibited higher AsV tolerance and lower As concentrations than TaPHT1;6-silenced plants, whereas TaPHT1;3-silencing plants had similar phenotype and AsV concentrations to control. These suggested that TaPHT1;9 and TaPHT1;6 possessed AsV absorption capacity with the former showing higher activities. Under hydroponic condition, furthermore, CRISPR-edited TaPHT1;9 wheat mutants showed the enhanced tolerance to AsV with decreased As distributions and concentrations, whereas TaPHT1;9 ectopic expression transgenic rice plants had the opposite results. Also, under AsV-contaminated soil condition, TaPHT1;9 transgenic rice plants exhibited depressed AsV tolerance with increased As concentrations in roots, straws and grains. Moreover, Pi addition alleviated the AsV toxicity. These suggested that TaPHT1;9 should be a candidate target gene for AsV phytoremediation.
Arsenic (As) is an environmental contaminant food chain toxin and negatively affects both plants and animals. Plants modulate the genomic, proteomic, and metabolomic responses to alleviate the As stress. There could be species-dependent variation in the key components of omic responses to As stress, or it may be common to other metal(loid) stresses, including As stress. The omic factor, including antioxidant machinery, transporter, enzymes, and molecules of As detoxification pathways, can be considered as biomarkers to As stress. The mechanisms of As uptake, transport, and detoxification may vary according to plant species belonging to As-hyperaccumulator or nonhyperaccumulator categories, including crop plants. The variation in metabolites, activities of certain antioxidant enzymes such as MDA, SOD, APX, CAT, and GR validate the appearance of oxidative stress during the As stress in plants. Due to the complexity between specific metabolic pathways in response to particular stresses, the specific biomarkers are rare. However, some genomic or proteomic agents are specific for As transport and detoxification, for instance, ACR3-mediated As detoxification mechanism in fern, which is nonfunctional in flowering plants. The complexation of AsIII with thiolic ligands, vacuolar sequestration of AsIII–PCs complex via ABCC1 and ABCC2 transporter are crucial methods for As metabolism in crops and other plants. Albeit the role of PCs in detoxification of As in hyperaccumulator plants is extremely limited, it seems to be a ubiquitous metal(loid) detoxification mechanism in nonhyperaccumulator plants including crop plants. Whereas phytochelatin constitutes the qualitative biomarkers of metal(loid) stress, the two rice MTs such as OsMT1-1b and OsMT1-1d appear to be unambiguous biomarkers for As stress. In this chapter, we discussed the molecules that play a role in As metabolism and can be used as biomarker for As stress in plants.
Heavy metals (HMs) are environmental and food chain contaminants having chronic and epidemic effects on human health. Introduction of HMs in the food chain takes place by their excessive uptake from soil through the crop plants, making it a global issue of concern to take necessary steps to counteract the problem. The HMs also cause toxicities to plants by affecting their growth and productivity. With the continuously changing global climatic conditions, the HM contamination in the soil is exaggerating, thereby resulting in the considerable yield reduction of major crop species. Furthermore, HM-induced soil pollution associated with the improper fertilization practices appears as a serious threat to the sustainable agriculture. It is therefore, a serious worldwide concern to minimize the HM toxicity in crop plants. Phytoremediation is a promising plant-based, cost-effective, and eco-friendly approach for the effective removal of the HMs from the environment. Several plants known as metallophytes accumulate higher level of HMs without having any toxic effects and, therefore, can be used to remove large amounts of HMs from the soil. The present chapter summarizes the mechanisms of HM uptake, translocation, and detoxification in plants. The mechanism adopted by the metallophytes in HM hyperaccumulation and their role in ameliorating the HM toxicity has also been discussed.KeywordsHeavy metal (HM)DetoxificationMetallophytesPhytoremediationDetoxification
Arsenic (As) and cadmium (Cd) belong to the group of major pollutants extremely toxic to plants. Metal hyperaccumulating plants play an important role in phytoextraction of heavy metals. Silicon (Si) plays an important role in the amelioration of heavy metal stress through physio-biochemical mechanisms, which remain poorly understood in hyperaccumulators. The main purpose of this study was to determine the impact of Si on growth and performance of As hyperaccumulator Isatis cappadocica Desv., exposed to As and Cd. Results showed that Si (especially at 1 mM level) alleviated the harmful impact of As/Cd and significantly increased the root and shoot biomass, root and shoot length and chlorophyll contents of I. cappadocica by enhancing the plant defense mechanisms. Between the two investigated harmful elements, As was accumulated in plant parts significantly more than Cd, however with considerably lower toxic growth effects. The As/Cd concentration, bioaccumulation and translocation factor and total As content both in roots and shoots of Si-supplied plant were significantly reduced as a protective mechanism, especially in Cd exposed plant. In comparison with single As/Cd treatment, Si supply reduced H2O2 content, increased total soluble protein content and enhanced glutathione S-transferase activity in shoots. The results of this study clearly showed that Si minimized As/Cd uptake and root to shoot translocation, and therefore Si cannot enhance the phytoextraction potential of this plant species. Additionally, Si-improved growth and reduced oxidative damages caused by excess of As and Cd suggested that the similar mechanisms of metal(loid) alleviation are adopted in hyperaccumulators as well as non-hyperaccumulating plants.
Increasing levels of freshwater contaminants, mainly due to anthropogenic activities, have resulted in a great deal of interest in finding new eco-friendly, cost-effective and efficient methods for remediating polluted waters. The aim of this work was to assess the feasibility of using a green microalga Desmodesmus sp., a cyanobacterium Nostoc sp. and a hemicryptophyte Ampelodesmos mauritanicus to bioremediate a water polluted with an excess of nutrients (nitrogen and phosphorus) and heavy metals (copper and nickel). We immediately determined that Nostoc sp. was sensitive to metal toxicity, and thus Desmodesmus sp. was chosen for sequential tests with A. mauritanicus. First, A. mauritanicus plants were grown in the ‘polluted’ culture medium for seven days and were, then, substituted by Desmodesmus sp. for a further seven days (14 days in total). Heavy metals were shown to negatively affect both the growth rates and nutrient removal capacity. The sequential approach resulted in high metal removal rates in the single metal solutions up to 74% for Cu and 85% for Ni, while, in the bi-metal solutions, the removal rates were lower and showed a bias for Cu uptake. Single species controls showed better outcomes; however, further studies are necessary to investigate the behavior of new species.
Metalloids are the group of special elements that possess both the physical and chemical qualities of metals and nonmetals. The amount of metalloids in the soil depends upon natural weathering of metalloid-bearing rocks, along with anthropogenic activities. On the basis of ascending atomic number, boron, silicon, germanium, arsenic, antimony, tellurium, and polonium are well-known metalloids. An extreme amount of metalloids in the soil, water, or air consequently lead to their entrance in the food chain. The metalloids are usually absorbed from the soil by plant roots with the help of transporters/channels and subsequently moved to various parts of the plants. The metalloid transport proteins include protein families like phosphate transporters, sulfate transporters, aquaglyceroporins, nodulin 26-like intrinsic proteins, silicon influx transporter, hexose transporters, etc. The metalloids exhibit toxic properties due to their resemblance to biological components involved in a variety of metabolic processes. In the present chapter, we focus on understanding the metalloid transporters/channels, the mechanisms of transport, sequestration, and the tolerance mechanisms in plants.
The present work was conducted to assess the effects of arsenic (As, 1000 µM), diphenyleneiodonium (DPI, 10 µM) and reduced glutathione (GSH, 500 µM) on Isatis cappadocica. As treatment decreased plant growth and fresh and dry weight of shoot and root and also enhanced the accumulation of As. As stress also enhanced the oxidative stress biomarkers, hydrogen peroxide (H2O2) and malondialdehyde (MDA) content. However, the application of GSH decreased the content of H2O2 and MDA by 43% and 55%, respectively, as compared to As treatment. The antioxidants like superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), glutathione reductase (GR) and glutathione S-transferase (GST) also enhanced with As stress. NADPH oxidase inhibitor, the DPI, enhances the effect of As toxicity by increasing the accumulation of As, H2O2, MDA. DPI also enhances the activity of antioxidant enzymes except GR and GST, However, the application GSH increased the plant growth and biomass yield, decreases accumulation of As, H2O2 and MDA content in As as well as As + DPI treated plants. The thiols content [total thiol (TT), non-protein thiol (NPT) protein thiols (PT), and glutathione (GSH)] were decreased in the As + DPI treatment but supplementation of GSH enhanced them.
Novelty statement: The study reveals the beneficial role of GSH in mitigating the deleterious effects of Arsenic toxicity through its active involvement in the antioxidant metabolism, thiol synthesis and osmolyte accumulation. Apart from As, We provided the plants NADPH oxidase inhibitor, the diphenyleneiodonium (DPI), which boosts the As toxicity. At present, there is dearth of information pertaining to the effects of DPI on plants growth and their responses under heavy metal stress.
GSH application reversed the effect of diphenyleneiodonium (DPI) under As stress preventing the oxidative damage to biomolecules through the modulation of different antioxidant enzymes. The application of GSH for As stressed soil could be a sustainable approach for crop production.
This chapter includes the sources of cadmium and chromium contamination of soil and various detrimental effects on plants and animals. Ecofriendly approach of soil clean up by phytoremediation is the main focus of the author. Heavy metal-induced oxidative stress of plants and their detoxification potentiality has been discussed here to create a wholesome idea about the basic and acute need of phytoremediation. Both enzymatic and non-enzymatic antioxidative defense mechanisms and various other biochemical parameters of metal hyperaccumulator plants are mentioned.
Arsenic (As), a non-biodegradable contaminant, is extremely toxic to plants and animals in its inorganic form. As negatively affects plant growth and development, primarily by inducing oxidative stress through redox imbalance. Here we characterized the Arabidopsis F-box protein gene AT2G16220 (Arsenic Stress-Related F-box (ASRF)) that we identified in the genome-wide association study. The asrf mutant seedlings showed high sensitivity to arsenate (AsV) stress. AsV significantly affected asrf seedling growth when germinated on or exposed to AsV-supplemented growth regimes. AsV stress significantly induced production of reactive oxygen species and proline accumulation in asrf, so the asrf maintained high proline content, possibly for cellular protection and redox homeostasis. Heterozygous seedlings (Col-0 x asrf, F1 progeny) were relatively less affected by AsV stress than asrf mutant but showed slightly reduced growth compared with the Col-0 wild type, which suggests that the homozygous ASRF locus is important for AsV stress resistance. Transcriptome analysis involving the mutant and wild type revealed altered phosphate homeostasis in asrf seedlings, which implies that ASRF is required for maintaining phosphate and cellular-homeostasis under excess AsV. Our findings confirm the roles of ASRF in As stress tolerance in plants, for a novel way to mitigate arsenic stress.
Most of the heavy metals (HMs), and metals/metalloids are released into the nature either by natural phenomenon or anthropogenic activities. Being sessile organisms,
plants are constantly exposed to HMs in the environment. The metal nonhyperaccumulating plants are susceptible to excess metal concentrations. They tend
to sequester metals in their root vacuoles by forming complexes with metal ligands,
as a detoxification strategy. In contrast, the metal-hyperaccumulating plants have
adaptive intrinsic regulatory mechanisms to hyperaccumulate or sequester excess
amounts of HMs into their above-ground tissues rather than accumulating them in
roots. They have unique abilities to successfully carry out normal physiological functions without showing any visible stress symptoms unlike metal non-hyperaccumulators. The unique abilities of accumulating excess metals in
hyperaccumulators partly owes to constitutive overexpression of metal transporters
and ability to quickly translocate HMs from root to shoot. Various metal ligands also
play key roles in metal hyperaccumulating plants. These metal hyperaccumulating
plants can be used in metal contaminated sites to clean-up soils. Exploiting the
knowledge of natural populations of metal hyperaccumulators complemented with
cutting-edge biotechnological tools can be useful in the future. The present review
highlights the recent developments in physiological and molecular mechanisms of
metal accumulation of hyperaccumulator plants in the lights of metal ligands and
transporters. The contrasting mechanisms of metal accumulation between hyperaccumulators and non-hyperaccumulators are thoroughly compared. Moreover, uses
of different metal hyperaccumulators for phytoremediation purposes are also discussed in detail.
Arsenic (As) which is a heavy metal is ubiquitously present in soil as well as in water. As has been ranked as a potent carcinogen and is found to be very harmful to all the living beings ranging from bacteria to plant to animals as well as humans. All the organisms possess various defense mechanisms to combat such types of stresses. However, if it remains detoxified in plants, it may lead to oxidative stress, misfolded proteins thus disrupting the functioning of the proteins, mutations in the genetic material which ultimately results in the inhibition of the growth, disruption of photosynthesis, and loss in crop yield. Plants are sessile creatures of nature so they are more vulnerable to any type of stress. However, they possess a very strong defense system that fights against these stresses. There are various mechanisms responsible for defense against As stress such as phytochelatin (PC)-dependent defense in which As forms complex with PCs and these complexes are sequestered inside the vacuole. The antioxidant defense system is a very basic and strong player in this defense system. One of the interesting parts of this system is the hyperaccumulation of As. However, hyperaccumulation is not common to all the plants. This is a trait of some specific plant species which had gained a very high capacity of accumulation of As in the aboveground part without suffering phytotoxic effects during evolution. Hyperaccumulator plants differ from normal or non-accumulator plants in various ways. Among them, very fast translocation of As from root to aboveground part, much higher detoxification ability, and higher sequestration capacity of As in aboveground part are the main mechanism which differentiates hyperaccumulator plants to non-accumulator plants. In particular, a determinant role in driving the uptake, translocation to leaves, and, finally, sequestration in vacuoles is played in hyperaccumulators by constitutive overexpression of genes encoding transmembrane transporters, such as members of arsenical compound resistance 3 (ACR3). In this chapter, we will discuss mainly the As toxicity in the plants along with the mechanisms that are involved in hyperaccumulator plants, detoxification of As in plants, as well as the tolerance of As in plants.
Arsenic (As) in rice grains is a serious food safety concern. Some coexisting engineered nanoparticles (ENPs) were shown to alter the accumulation and speciation of As in rice grains. However, investigation on the effects of copper oxide nanoparticles (CuO NPs), a popular ingredient in pesticides, on the uptake and accumulation of As is rare. We explored the potentially different impact of CuO NPs and corresponding Cu(II) ions on the accumulation of two As species in rice seedlings in a hydroponic system. Rice seedlings were treated with a combinations of 1 mg/L of arsenite (As(III)) or arsenate (As(V)) and 100 mg/L of CuO NPs or Cu(II) for 6 days. Both forms of Cu significantly reduced the accumulation of total As in rice tissues, with Cu(II) exhibiting significantly greater effect than CuO NPs. As speciation in rice roots was markedly affected by both forms of Cu, and the impacts were Cu-form dependent. For example, the co-existence of As(V) with CuO NPs led to a 45% decrease of As(V) in rice roots, while the co-existence of As(V) with Cu(II) caused a 47% increase in As(V) in rice roots. As speciation in rice shoots was less affected by co-present Cu than in rice roots. Co-occurring As(III) or As(V) lowered Cu concentration in rice roots by 40% and 50% in treatments with CuO NPs, but did not affect Cu content in rice roots co-exposed to Cu(II). The study confirmed the reciprocal effect of co-occurring CuO NPs or Cu(II) and As in rice paddies and highlighted the unique "nano-effect" of CuO NPs. The results alsos showed that the initial oxidation state of As plays an important role in the interactions between As and Cu. The results shed light on the current debate on the safe applications of nano-enabled agrichemicals vs. conventional metal salts in agriculture.
The genetics of arsenate tolerance in Holcus lanatus is investigated. Three tolerant plants from an abandoned arsenic mine, and three non-tolerant plants and one less tolerant plant (C9) from an uncontaminated site were crossed. Five polycrosses between plants from F1 crosses between mine and non-tolerants were set up. Four polycrosses between tolerant F2 progeny, and four polycrosses between non-tolerant F2 progeny, were established. A polycross involving the progeny of a single tolerant plant allowed to cross at random with a normal population was also established. The results are broadly compatible with a single-gene model for tolerance, with tolerance being dominant. The majority of F2 crosses segregated in to 3:1 ratios, and backcrosses gave 1:1 ratios. The crosses between C9 and non-tolerants gave 1:1 ratios, which suggests that the less tolerant C9 was heterozygous for tolerance. All crosses between non-tolerants gave all non-tolerant offspring. In one cross a major gene for albinism also segregated, and linkage of the tolerance gene to this gene (r.f. = 35%
) was demonstrated. A number of families produced progeny ratios incompatible with the simple major gene model. Possible causes of these anomalous crosses are discussed and it is suggested that the tolerance gene may show variable penetrance depending on the genetic background.Keywords: arsenate tolerance, genetics, modifiers, penetrance
Zarshuran deposit is the most famous and important As-Au mine in Iran. However, there is no information on the impact of mining activity on the surrounding environment, especially on water systems. This paper attempts to document the concentration of arsenic and associated elements in waters and sediments resulting from the mining history of Zarshuran, a period covering hundreds of years. Water and sediment samples collected from Zarshuran Stream indicate high content of some potentially toxic elements, especially of As which ranges from 0.028 to 40ng/l in water and 182 to 36,000mg/kg in sediment samples. Mining activity, exposure of a large volume of mining wastes to weathering, and the anomalously high background of trace metals in the mining area are considered to be the main sources of heavy metal pollution.
A hardy, versatile, fast-growing plant helps to remove arsenic from contaminated soils.
To elucidate the mechanisms of arsenic resistance in the arsenic hyperaccumulator fern Pteris vittata L., a cDNA for a glutaredoxin (Grx) Pv5–6 was isolated from a frond expression cDNA library based on the ability of the cDNA
to increase arsenic resistance in Escherichia coli. The deduced amino acid sequence of Pv5–6 showed high homology with an Arabidopsis chloroplastic Grx and contained two CXXS putative catalytic motifs. Purified recombinant Pv5–6 exhibited glutaredoxin activity that was increased 1.6-fold by 10
mm arsenate. Site-specific mutation of Cys67 to Ala67 resulted in the loss of both GRX activity and arsenic resistance. PvGrx5 was expressed in E. coli mutants in which the arsenic resistance genes of the ars operon were deleted (strain AW3110), a deletion of the gene for the ArsC arsenate reductase (strain WC3110), and a strain
in which the ars operon was deleted and the gene for the GlpF aquaglyceroporin was disrupted (strain OSBR1). Expression of PvGrx5 increased
arsenic tolerance in strains AW3110 and WC3110, but not in OSBR1, suggesting that PvGrx5 had a role in cellular arsenic resistance
independent of the ars operon genes but dependent on GlpF. AW3110 cells expressing PvGrx5 had significantly lower levels of arsenite when compared
with vector controls when cultured in medium containing 2.5 mm arsenate. Our results are consistent with PvGrx5 having a role in regulating intracellular arsenite levels, by either directly
or indirectly modulating the aquaglyceroporin. To our knowledge, PvGrx5 is the first plant Grx implicated in arsenic metabolism.
Arsenic (As) bioaccumulation by plants can be used as a strategy to detoxify arsenic polluted sites. Genetic engineering may provide a means of optimizing this natural process to increase its efficiency. However, this approach requires a thorough understanding of As metabolism and detoxification in plants. Identifying As-containing metabolites in plants is an important first step in elucidating As metabolism. Brassica juncea
(Indian mustard) is studied here as a model for As accumulation in terms of total metalloid accumulation and its elemental speciation. A study on extraction conditions using 25 mM ammonium acetate buffer at increasing pH of 4.4, 5.6 and 7.8 has been performed. Those extracting solutions were also employed as mobile phases for the separation of the As species formed by size exclusion chromatography with inductively coupled plasma mass spectrometry (ICP-MS) as a selective As detector. Two main As containing species have been found in Brassica tissues (one of them at about 2 kDa and the other below 1.2 kDa). The first As species was found to be associated to thiol groups (monitoring 32S with double focusing ICP-MS). This can be ascribed to the presence of As-phytochelatin complexes. Electrospray-quadrupole-time of flight (ESI-Q-TOF) results indicated the presence of phytochelatins (apo-forms), the main metal bioligands in plants, which have also been shown to be induced by As. Oligomers of two, three and four sub-units, respectively (PC2, PC3 and PC4), with internal oxidation of the SH groups, have been extracted from Brassica leaves as well as a potential As–PC4 complex. These species have been further identified by collisional induced dissociation (CID).
The uptake and translocation into shoots of arsenate, methylarsonate (MA), and dimethylarsinate (DMA) by 46 different plant species were studied. The plants (n = 3 per As species) were exposed for 24 h to 1 mg of As per litre under identical conditions. Total arsenic was measured in the roots and the shoots by acid digestion and inductively coupled plasma mass spectrometry from which, besides total As values, root absorption factors and shoot-to-root transfer factors were calculated. As uptake into the root for the different plant species ranged from 1.2 to 95 (µ go f As per go f dry weight) for AsV, from 0.9 to 44 for MAV and from 0.8 to 13 for DMAV, whereas in shoots the As concentration ranged from 0.10 to 17 for AsV, 0.1 to 13 for MAV, and 0.2 to 17 for DMAV. The mean root absorption factor for AsV (1.2 to 95%) was five times higher than for DMAV (0.8 to 13%) and 2.5 times higher than for MAV (0.9 to 44%). Although the uptake of arsenic in the form of AsV was significantly higher than that of MAV and DMAV, the translocation of the methylated species was more efficient in most plant species studied. Thus, an exposure of plants to DMAV or MAV can result in higher arsenic concentrations in the shoots than when exposed to AsV. Shoot-to-root transfer factors (TFs) for all plants varied with plant and arsenic species. While AsV had a median TF of 0.09, the TF of DMAV was nearly a factor of 10 higher (0.81). The median TF for MAV was in between (0.30). Although the TF for MAV correlates well with the TF for DMAV, the plants can be separated into two groups according to their TF of DMAV in relation to their TF of AsV. One group can immobilise DMAV in the roots, while the other group translocates DMAV very efficiently into the shoot.
Summary • Pteris vittata is the first plant reported to be a hyperaccumulator of arsenic (As), and little is known about the mechanisms of As hyperaccumulation in this plant. • Arsenic distribution at the whole plant (fronds) and cellular level was investigated using chemical analyses and energy dispersive X-ray microanalyses (EDXA). Specia- tion of As in the fronds was determined using X-ray absorption near edge spectro- scopy (XANES) analyses. • The majority of As was found in the pinnae (96% of total As). The concentration of As in pinnae decreased from the base to the apex of the fronds. Arsenic concen- trations in spores and midribs were much lower than in the pinnae. EDXA analyses revealed that As was compartmentalized mainly in the upper and lower epidermal cells, probably in the vacuoles. The distribution pattern of potassium was similar to As, whereas other elements (Ca, Cl, K, Mg, P and S) were distributed differently. • XANES analyses showed that approximately 75% of the As in fronds was present in the As(III) oxidation state and the remaining as As(V).
Elevation of arsenic levels in soils causes considerable concern with respect to plant uptake and subsequent entry into wildlife and human food chains. Arsenic speciation in the environment is complex, existing in both inorganic and organic forms, with interconversion between species regulated by biotic and abiotic processes. To understand and manage the risks posed by soil arsenic it is essential to know how arsenic is taken up by the roots and metabolized within plants. Some plant species exhibit phenotypic variation in response to arsenic species, which helps us to understand the toxicity of arsenic and the way in which plants have evolved arsenic resistances. This knowledge, for example, could be used produce plant cultivars that are more arsenic resistant or that have reduced arsenic uptake. This review synthesizes current knowledge on arsenic uptake, metabolism and toxicity for arsenic resistant and nonresistant plants, including the recently discovered phenomenon of arsenic hyperaccumulation in certain fern species. The reasons why plants accumulate and metabolize arsenic are considered in an evolutionary context.
The influx of arsenate, arsenite and dimethyl arsinic acid (DMA) were studied in 7-day-old excised maize roots (Zea mays L.), and then related to arsenate, arsenite and DMA toxicity. Arsenate, arsenite and DMA influx was all found concentration dependent with significant genotypic differences for arsenite and DMA. Arsenate influx in phosphate starved plants best fitted the four-parameter Michaelis–Menten model corresponding to an additive high and low affinity uptake system, while the uptake of phosphate replete plants followed the two parameter model of Michaelis–Menten kinetics. Arsenite influx was well described
by the two parameter model of ‘Michaelis–Menten’ kinetics. DMA influx was comprised of linear phase and a hyperbolic phase. DMA influx was much lower than that for arsenite and arsenate. Arsenate and DMA influx decreased when phosphate was given as a pre-treatment as opposed to phosphate starved plants. The +P treatment tended to decrease influx by 50% for arsenate while this figure was 90% for DMA. Arsenite influx increasing slightly at higher arsenite concentrations in P starved plants but at lower arsenite concentrations, there was little or no difference in arsenite uptake. Low toxicity was found for DMA on maize compared with arsenate and arsenite and the relative toxicity of arsenic species was As(V) > As(III) >> DMA.
The time- and concentration-dependent uptake kinetics for arsenate and arsenite were determined in 15-day-old excised roots.
In both cases, arsenite showed a mono-phasic influx with the isotherm data fitting a linear model better than a non-linear
one. The time- and the concentration-dependent uptake of arsenate displayed a hyperbolic kinetic. Greater uptake of arsenate,
compared with arsenite, was found especially at lower external substrate concentrations. Competitive inhibition of uptake
with phosphate showed that arsenite and arsenate were taken up by different uptake systems because arsenate uptake was strongly
inhibited in the presence of phosphate, whereas arsenite uptake was not affected.
Phytochelatins (PCs) are post-translationally synthesized thiol reactive peptides that play important roles in detoxification of heavy metal and metalloids in plants and other living organisms. The overall goal of this study is to develop transgenic plants with increased tolerance for and accumulation of heavy metals and metalloids from soil by expressing an Arabidopsis
thaliana
AtPCS1 gene, encoding phytochelatin synthase (PCS), in Indian mustard (Brassica juncea L.). A FLAG-tagged AtPCS1 gDNA, under its native promoter, is expressed in Indian mustard, and transgenic pcs lines have been compared with wild-type plants for tolerance to and accumulation of cadmium (Cd) and arsenic (As). Compared to wild type plants, transgenic plants exhibit significantly higher tolerance to Cd and As. Shoots of Cd-treated pcs plants have significantly higher concentrations of PCs and thiols than those of wild-type plants. Shoots of wild-type plants accumulated significantly more Cd than those of transgenic plants, while accumulation of As in transgenic plants was similar to that in wild type plants. Although phytochelatin synthase improves the ability of Indian mustard to tolerate higher levels of the heavy metal Cd and the metalloid As, it does not increase the accumulation potential of these metals in the above ground tissues of Indian mustard plants.
In Holcus lanatus L. phosphate and arsenate are taken up by the same transport system. Short-term uptake kinetics of the high affinity arsenate
transport system were determined in excised roots of arsenate-tolerant and non-tolerant genotypes. In tolerant plants the
Vmax of ion uptake in plants grown in phosphate-free media was decreased compared to non-tolerant plants, and the affinity of
the uptake system was lower than in the non-tolerant plants. Both the reduction in Vmax and the increase in Km led to reduced arsenate influx into tolerant roots. When the two genotypes were grown in nutrient solution containing high
levels of phosphate, there was little change in the uptake kinetics in tolerant plants. In non-tolerant plants, however, there
was a marked decrease in the Vmax to the level of the tolerant plants but with little change in the Km. This suggests that the low rate of arsenate uptake over a wide range of differing root phosphate status is due to loss of
induction of the synthesis of the arsenate (phosphate) carrier.
Present study showed the toxicity caused by Arsenite (As(III)) and its detoxification responses in two varieties (Varuna and Pusa Bold) of Brassica juncea. Comparisons were made in leaves and roots of both the varieties, which showed that the accumulation pattern in both the varieties were dose and duration dependent, being more in roots for two days and in leaves for four days. Increase/decrease of antioxidant enzymes activities (SOD, CAT, GPX) showed not much changes at the given concentrations except that the enzyme activities showed significant increase at the lower concentrations. Semi quantitative RT-PCR analysis of PCS showed more expression of its transcript in P. Bold as compared to Varuna variety due to As(III) stress. The analysis of isoenzyme pattern in leaves of P. Bold showed five and two major bands of SOD and GPX, respectively. As(III) treatment leads to the activation of MAPK activity indicating role of this important cascade in transducing As(III) mediated signals. The data presented indicates the differential responses in both the varieties and also that the increased tolerance in P. Bold may be due to the defensive role of antioxidant enzymes, induction of MAPK and up regulation of PCS transcript which is responsible for the production of metal binding peptides.
The instability of metal and metalloid complexes during analytical processes has always been an issue of an uncertainty regarding their speciation in plant extracts. Two different speciation protocols were compared regarding the analysis of arsenic phytochelatin (AsIIIPC) complexes in fresh plant material. As the final step for separation/detection both methods used RP-HPLC simultaneously coupled to ICP-MS and ES-MS. However, one method was the often used off-line approach using two-dimensional separation, i.e. a pre-cleaning step using size-exclusion chromatography with subsequent fraction collection and freeze-drying prior to the analysis using RP-HPLC–ICP-MS and/or ES-MS. This approach revealed that less than 2% of the total arsenic was bound to peptides such as phytochelatins in the root extract of an arsenate exposed Thunbergia alata, whereas the direct on-line method showed that 83% of arsenic was bound to peptides, mainly as AsIIIPC3 and (GS)AsIIIPC2. Key analytical factors were identified which destabilise the AsIIIPCs. The low pH of the mobile phase (0.1% formic acid) using RP-HPLC–ICP-MS/ES-MS stabilises the arsenic peptide complexes in the plant extract as well as the free peptide concentration, as shown by the kinetic disintegration study of the model compound AsIII(GS)3 at pH 2.2 and 3.8. But only short half-lives of only a few hours were determined for the arsenic glutathione complex. Although AsIIIPC3 showed a ten times higher half-life (23 h) in a plant extract, the pre-cleaning step with subsequent fractionation in a mobile phase of pH 5.6 contributes to the destabilisation of the arsenic peptides in the off-line method. Furthermore, it was found that during a freeze-drying process more than 90% of an AsIIIPC3 complex and smaller free peptides such as PC2 and PC3 can be lost. Although the two-dimensional off-line method has been used successfully for other metal complexes, it is concluded here that the fractionation and the subsequent freeze-drying were responsible for the loss of arsenic phytochelatin complexes during the analysis. Hence, the on-line HPLC–ICP-MS/ES-MS is the preferred method for such unstable peptide complexes. Since freeze-drying has been found to be undesirable for sample storage other methods for sample handling needed to be investigated. Hence, the storage of the fresh plant at low temperature was tested. We can report for the first time a storage method which successfully conserves the integrity of the labile arsenic phytochelatin complexes: quantitative recovery of AsIIIPC3 in a formic acid extract of a Thunbergia alata exposed for 24 h to 1 mg Asv L−1 was found when the fresh plant was stored for 21 days at 193 K.
Figure
On-line HPLC–ICP-MS/ES-MS (bottom) is the preferred method for MS determination of unstable arsenic peptide complexes in plant extracts, since this avoids fractionation and subsequent freeze-drying that are responsible for loss of arsenic phytochelatin complexes in the 2D off-line method (top)
The bioaccumulation of arsenic by plants may provide a means of removing this element from contaminated soils and waters. However, to optimize this process it is important to understand the biological mechanisms involved. Using a combination of techniques, including x-ray absorption spectroscopy, we have established the biochemical fate of arsenic taken up by Indian mustard (Brassica juncea). After arsenate uptake by the roots, possibly via the phosphate transport mechanism, a small fraction is exported to the shoot via the xylem as the oxyanions arsenate and arsenite. Once in the shoot, the arsenic is stored as an As(III)-tris-thiolate complex. The majority of the arsenic remains in the roots as an As(III)-tris-thiolate complex, which is indistinguishable from that found in the shoots and from As(III)-tris-glutathione. The thiolate donors are thus probably either glutathione or phytochelatins. The addition of the dithiol arsenic chelator dimercaptosuccinate to the hydroponic culture medium caused a 5-fold-increased arsenic level in the leaves, although the total arsenic accumulation was only marginally increased. This suggests that the addition of dimercaptosuccinate to arsenic-contaminated soils may provide a way to promote arsenic bioaccumulation in plant shoots, a process that will be essential for the development of an efficient phytoremediation strategy for this element.
Field and greenhouse experiments were performed to assess the performance of phytoremediation of arsenic and lead from contaminated soil at an EPA Superfund site (Barber Orchard). Chinese Brake ferns (Pteris vittata) were used to extract arsenic. On average, fern shoot arsenic concentrations were as high as 20 times the soil arsenic concentrations under field conditions. It was estimated that 8 years would be required to reduce the acid-extractable portion of soil arsenic to safe levels (40 mg/kg). The effect of soil pH on arsenic extraction was also investigated. Results indicate that increasing soil pH may improve arsenic removal. Indian mustard plants (Brassica juncea) were used under greenhouse conditions to phytoextract soil lead. EDTA was applied to soil and was found to improve lead extraction. When the EDTA concentration was 10 mmol EDTA/kg soil in soil containing 338 mg Pb/kg soil, mustard plants extracted approximately 32 mg of lead. In conclusion, phytoremediation would be a suitable alternative to conventional remediation techniques, especially for soils that do not require immediate remediation.
We have developed a method to extract and separate phytochelatins (PCs)-metal(loid) complexes using parallel metal(loid)-specific (inductively coupled plasma-mass spectrometry) and organic-specific (electrospray ionization-mass spectrometry) detection systems-and use it here to ascertain the nature of arsenic (As)-PC complexes in plant extracts. This study is the first unequivocal report, to our knowledge, of PC complex coordination chemistry in plant extracts for any metal or metalloid ion. The As-tolerant grass Holcus lanatus and the As hyperaccumulator Pteris cretica were used as model plants. In an in vitro experiment using a mixture of reduced glutathione (GS), PC(2), and PC(3), As preferred the formation of the arsenite [As((III))]-PC(3) complex over GS-As((III))-PC(2), As((III))-(GS)(3), As((III))-PC(2), or As((III))-(PC(2))(2) (GS: glutathione bound to arsenic via sulphur of cysteine). In H. lanatus, the As((III))-PC(3) complex was the dominant complex, although reduced glutathione, PC(2), and PC(3) were found in the extract. P. cretica only synthesizes PC(2) and forms dominantly the GS-As((III))-PC(2) complex. This is the first evidence, to our knowledge, for the existence of mixed glutathione-PC-metal(loid) complexes in plant tissues or in vitro. In both plant species, As is dominantly in non-bound inorganic forms, with 13% being present in PC complexes for H. lanatus and 1% in P. cretica.
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HPLC-ICP-MS and ESI-Q-TOF analysis of biomolecules induced in Brassica juncea during arsenic accumulation
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