Heavy Metal Hyperaccumulation Research Articles

TcOPT3, a member of oligopeptide transporters from the hyperaccumulator Thlaspi caerulescens, is a novel Fe/Zn/Cd/Cu transporter.

Background Thlaspi caerulescens is a natural selected heavy metal hyperaccumulator that can not only tolerate but also accumulate extremely high levels of heavy metals in the shoots. Thus, to identify the transportors involved in metal long-distance transportation is very important for understanding the mechanism of heavy metal accumulation in this hyperaccumulator.Methodology/Principal FindingsWe cloned and characterized a novel gene TcOPT3 of OPT family from T. caerulescens. TcOPT3 was pronouncedly expressed in aerial parts, including stem and leaf. Moreover, in situ hybridization analyses showed that TcOPT3 expressed in the plant vascular systems, especially in the pericycle cells that may be involved in the long-distance transportation. The expression of TcOPT3 was highly induced by iron (Fe) and zinc (Zn) deficiency, especially in the stem and leaf. Sub-cellular localization showed that TcOPT3 was a plasma membrane-localized protein. Furthermore, heterogonous expression of TcOPT3 by mutant yeast (Saccharomyces cerevisiae) complementation experiments demonstrated that TcOPT3 could transport Fe2+ and Zn2+. Moreover, expression of TcOPT3 in yeast increased metal (Fe, Zn, Cu and Cd) accumulation and resulted in an increased sensitivity to cadmium (Cd) and copper (Cu).ConclusionsOur data demonstrated that TcOPT3 might encode an Fe/Zn/Cd/Cu influx transporter with broad-substrate. This is the first report showing that TcOPT3 may be involved in metal long-distance transportation and contribute to the heavy metal hyperaccumulation.

The investigation of the possibility for using some wild and cultivated plants as hyperaccumulators of heavy metals from contaminated soil

The copper production in Bor (East Serbia) during the last 100 years presents an important source of the pollution of environment. Dust, waste waters, tailing, and air pollutants influence the quality of soil, water, and air. Over 2,000 ha of fertile soil have been damaged by the flotation tailing from Bor's facilities. The goal of the present work has been to determine the content of Pb, Cu, and Fe in wild plants (17 species) naturally growing in the damaged soil and in fodder crops (nine species) planted at the same place. The content of Pb, Cu, and Fe has been analyzed in damaged soil as well. This study has also searched for native (wild) and cultivated plants which are able to grow in contaminated soil in the area of the intense industrial activity of copper production in Bor, which means that they can accumulate and tolerate heavy metals in their above-ground tissues. It has been found out that the content of all metals in contaminated soil decreases considerably at the end of the experiment. As it has been expected, all plant species could accumulate investigated metals. All tested plants, both wild-growing and cultivated plants, seem to be quite healthy on the substrate which contained extremely high concentrations of copper.

Comparison of Trace Element Emissions from Thermal Treatments of Heavy Metal Hyperaccumulators

Phytoextraction has become one of the most promising remediation techniques for heavy metal (HM) contaminated soils. However, the technique invariably produces large amounts of HM-enriched hyperaccumulators, which need further safe disposal. In this study, two different thermal treatment methods are investigated as potential options for evaporative separation of HMs from the residues. A horizontal tube furnace and a vertical entrained flow tube furnace were used for testing the disposal of grounded hyperaccumulators. The release characteristics of HMs (Cd, Cu, Pb, and Zn) into flue gas and residues were investigated for thermal treatment of the Cd and Zn hyperaccumulators Sedum plumbizincicola and Sedum alfredii. In a horizontal tube furnace, incineration favors the volatilization of Cu and Cd in contrast to pyrolysis. The percentages of HMs in residues after incineration are lower than those after pyrolysis, especially for Cd, Pb, and Zn. However, in an entrained flow tube furnace, Zn content in flue gas increases with increasing temperature, but Cu and Cd contents are fluctuated. In addition, a higher incineration temperature enhances the Cu content in residues.

Phytoremediation of heavy metal‐contaminated water and sediment by Eleocharis acicularis

AbstractPhytoremediation is an environmental remediation technique that takes advantage of plant physiology and metabolism. The unique property of heavy metal hyperaccumulation by the macrophyte Eleocharis acicularis is of great significance in the phytoremediation of water and sediments contaminated by heavy metals at mine sites. In this study, a field cultivation experiment was performed to examine the applicability of E. acicularis to the remediation of water contaminated by heavy metals. The highest concentrations of heavy metals in the shoots of E. acicularis were 20 200 mg Cu/kg, 14 200 mg Zn/kg, 1740 mg As/kg, 894 mg Pb/kg, and 239 mg Cd/kg. The concentrations of Cu, Zn, As, Cd, and Pb in the shoots correlate with their concentrations in the soil in a log‐linear fashion. The bioconcentration factor for these elements decreases log‐linearly with increasing concentration in the soil. The results indicate the ability of E. acicularis to hyperaccumulate Cu, Zn, As, and Cd under natural conditions, making it a good candidate species for the phytoremediation of water contaminated by heavy metals.

Effect of long-term application of treated sewage water on heavy metal accumulation in vegetables grown in Northern India

Use of industrial and wastewater for irrigation is on the rise in India and other developing countries because of scarcity of good-quality irrigation water. Wastewaters contain plant nutrients that favour crop growth but leave a burden of heavy metals which can enter the food chain and is a cause of great concern. The present study was undertaken on the long-term impact of irrigation with treated sewage water for growing vegetables and the potential health risk associated with consumption of such vegetable. Treated sewage water (TSW), groundwater (GW), soil and plant samples were collected from peri urban vegetable growing areas of Northern India (Varanasi) and analysed to assess the long-term effect of irrigation with TSW on Cd, Cr, Ni and Pb build-up in soils and its subsequent transfer into commonly grown vegetable crops. Results indicate that TSW was richer in essential plant nutrients but contained Cd, Cr and Ni in amounts well above the permissible limits for its use as irrigation water. Long-term application of TSW resulted in significant build-up of total and DTPA extractable Cd, Cr, Ni and Pb over GW irrigated sites. TSW also resulted in slight lowering in pH, increase in organic carbon (1.6 g kg(-1)) and cation exchange capacity (5.2 cmol kg(-1)). The tissue metal concentration and relative efficiency of transfer of heavy metals from soil to plant (transfer factor) for various groups of vegetables were worked out. Radish, turnip and spinach were grouped as hyper accumulator of heavy metals whereas brinjal and cauliflower accumulated less heavy metals. Health risk assessment by consumption of vegetables grown with TSW indicated that all the vegetables were safe for human consumption. However, significant accumulation of these heavy metals in soil and plant needs to be monitored.

Identification of a new potential Cd-hyperaccumulator Solanum photeinocarpum by soil seed bank-metal concentration gradient method

A new method, soil seed bank-metal concentration gradient method was used to screen for heavy metal hyperaccumulators, and Solanum photeinocarpum was found to be a potential Cd-hyperaccumulator. The chlorophyll content and photosynthetic rate of S. photeinocarpum were not affected by Cd pollution, while leaf stomas and transpiration rate were significantly decreased by more than 60 mg kg −1 Cd, and leaf water use efficiency and shoot water content were significantly increased by more than 60 or 100 mg kg −1 Cd, respectively. In the seed bank-Cd concentration gradient experiment, the shoot biomass of S. photeinocarpum showed no significant reduction with soil Cd treatment as high as 100 mg kg −1, but the root biomass was significantly reduced by more than 60 mg kg −1 Cd contamination. Plant tissues accumulated 544, 132 and 158 mg kg −1 Cd in roots, stems and leaves, respectively, and extracted 157 and 195 μg Cd plant −1 in roots and shoots at 100 mg kg −1 Cd in soil, respectively. In the transplanting-Cd concentration gradient experiment, plant shoot biomass and root biomass were unaffected by soil Cd as high as 60 mg kg −1. Plant tissues accumulated 473, 215 and 251 mg kg −1 Cd in roots, stems and leaves, respectively, and extracted 176 and 787 μg Cd plant −1 in roots and shoots at 60 mg kg −1 soil Cd, respectively. Soil seed bank-metal concentration gradient method could be an effective method for the screening of hyperaccumulators.

Accumulation of Pb, Fe, Mn, Cu and Zn in plants and choice of hyperaccumulator plant in the industrial town of Vian, Iran

Various industrial activities contribute heavy metals to the soil environment directly or indirectly through the release of solid wastes, waste gases, and wastewater. Phytoremediation can be potentially used to remedy metal-contaminated sites. A major step towards the development of phytoremediation of heavy metal-impacted soils is the discovery of the heavy metal hyperaccumulation in plants. This study evaluated the potential of 7 species growing on a contaminated site in an industrial area. Several established criteria to define a hyperaccumulator plant were applied. The case study was represented by an industrial town in the Hamedan province in the central-western part of Iran. This study showed that most of the sampled species were able to grow in heavily metal-contaminated soils and were also able to accumulate extraordinarily high concentrations of some metals such as Pb, Fe, Mn, Cu and Zn. Based on the obtained results and using the most common criteria, Camphorosma monospeliacum for Pb and Fe, and Salsola soda and Circium arvense for Pb can be classified as hyperaccumulators and, therefore, they have suitable potential for the phytoremediation of contaminated soils.

Successful Micropropagation of the Cadmium Hyperaccumulator Viola Baoshanensis (Violaceae)

Viola baoshanensis is one of the most rare cadmium (Cd) hyperaccumulators, however, it is hard to propagate. Micropropagation has been applied to solve the problems with propagation of a few heavy metal hyperaccumulators. Therefore there is a high likelihood that micropropagation may offer a suitable method for large-scale propagation of V. baoshanensis. To test this hypothesis, three types of explants were used for shoot regeneration and various combinations of four plant growth regulators were used to improve shoot regeneration efficiency from leaflet of V. baoshanensis. Best shoot regeneration efficiency was obtained by incubating leaflet in a 1/2 MS medium supplemented with 2.5 μM BA + 2.5 μM IBA, therein shoot regeneration rate was 70.9% and the number of shoots formation per explant was 22.4. Rooting was achieved from almost all regenerated shoot growing on 1/2 MS medium without plant growth regulator. Micropropagated seedlings were acclimatized under greenhouse conditions and 95% of them survived and showed no visible morphological variation compared to their donor plant. Furthermore, there were no significant differences between regenerated and seed-germinated V. baoshanensis in Cd tolerance and accumulation. These results suggested that an efficient and rapid micropropogation system was successfully developed for V. baoshanensis.

Determination of Co(II) in plant tissue by microwave digestion and ion chromatography coupled with luminol/perborate or luminol/percarbonate chemiluminescence detection

The cobalt is an essential element for leguminous plants but may be harmful for other species; for that reason determination of Co(II) is very important for the management of polluted areas and for discover plants with capacity for the hyperaccumulation of heavy metals, which has produced a growing necessity of fast, sensitive and selective analytical techniques. To develop an analytical procedure for the determination of cobalt in plant tissue by coupling the ionic chromatography to the luminol-based chemiluminescence detection. The sample was digested in a mixture of concentrated nitric acid and hydrogen peroxide, using an microwave oven to dissolve the Co(II). The solution containing Co(II) ions was injected to an ionic chromatograph using oxalic acid as the eluent. The detection was based on the catalytic effect of Co(II) on the luminol chemiluminescence using perborate or percarbonate as oxidants. Experimental variables, such as concentrations, pH, flow rates and acid digestion conditions were optimised. Well-resolved chromatographic peaks were obtained. The height and area showed linear dependences with the Co(II) concentration, which were used to quantify the heavy metal, with recoveries up to 95%. The microwave irradiation (60 s) was sufficient for the complete mineralisation of 200 mg of sample, employing 2 mL of the acid mixture. The method was free from the interferences, requiring less than 12 minutes to complete the analysis. The method was simple and rapid for the determination of cobalt in plant tissue with detection limits comparable to those obtained with more sophisticated and expensive analytical equipment.

A comprehensive overview of elements in bioremediation

Sustainable development requires the development and promotion of environmental management and a constant search for green technologies to treat a wide range of aquatic and terrestrial habitats contaminated by increasing anthropogenic activities. Bioremediation is an increasingly popular alternative to conventional methods for treating waste compounds and media with the possibility to degrade contaminants using natural microbial activity mediated by different consortia of microbial strains. Many studies about bioremediation have been reported and the scientific literature has revealed the progressive emergence of various bioremediation techniques. In this review, we discuss the various in situ and ex situ bioremediation techniques and elaborate on the anaerobic digestion technology, phytoremediation, hyperaccumulation, composting and biosorption for their effectiveness in the biotreatment, stabilization and eventually overall remediation of contaminated strata and environments. The review ends with a note on the recent advances genetic engineering and nanotechnology have had in improving bioremediation. Case studies have also been extensively revisited to support the discussions on biosorption of heavy metals, gene probes used in molecular diagnostics, bioremediation studies of contaminants in vadose soils, bioremediation of oil contaminated soils, bioremediation of contaminants from mining sites, air sparging, slurry phase bioremediation, phytoremediation studies for pollutants and heavy metal hyperaccumulators, and vermicomposting.

Simultaneous Hyperaccumulation of Multiple Heavy Metals by Helianthus Annuus Grown in a Contaminated Sandy-Loam Soil

Phytoremediation is a promising means for the treatment of contamination arising from heavy metal spills. Although several species have been identified as hyperaccumulators, most of the studies were performed with only one heavy metal. Experiments were conducted with two cultivars of H. annuus exposed to different combinations of metal contamination (30 mg/kg Cd, Cr, Ni, As, and/or Fe). Cultivar efficiency was based on total metal uptake, as well as translocation and selectivity of each metal. The results for each cultivar were also compared after 0.1 g/kg or 0.3 g/kg EDTA was added to enhance metal bioavailability. The key finding was that H. annuus achieved hyperaccumulator status for multiple metals simultaneously: Cd, Cr, and As.

QUALITATIVE ASSESSMENT OF CADMIUM STRESS USING GENOME TEMPLATE STABILITY IN Hordeum vulgare

Cadmium, a non essential heavy metal, does not play any metabolic role and is considered as toxic element even at very low concentration. It is mainly generated through anthropogenic activities, such as mining deposits, aerial fallout from smelters and from industrial, agricultural, energy and municipal sources (McGrath et al., 2001; McBride, 2003; Entezari et al., 2006). Cadmium (Cd) contamination has become a severe global issue and is considered a dangerous environmental pollutant not only for its neurotoxic, mutagenic and carcinogenic effects, but also for the high water solubility and thereby easier entry into human body via food (Koizumi and Yamada, 2003). Phytotoxicity of heavy metals such as Cd, Cu and Zn is long known and well documented (Prasad, 2004; Panda and Choudhury, 2005). Metal ions may directly interfere with the metabolic activities by altering the conformation of proteins, for example enzymes, transporters or regular proteins, owing to their strong affinities as ligands to sulfhydryl and carboxylic groups (Sharma et al., 2004). Genotoxicity of Cd is directly related to its effect on structure and function of DNA, which may be determined using a number of laboratory methods (Angelis et al., 2000; Unyayar et al., 2006). However, there have been few direct experimental demonstrations of the wider relationships between DNA effects and their subsequent consequences at higher levels of biological organization. To address this issue, it is necessary to develop reliable and reproducible genotoxicity assays that can then be used in conjunction with traditional assays for detecting any impairment of population parameters (e.g. growth, reproduction and viability of offspring). Recently, advances in molecular biology have led to the development of new tools for detection of genetic alteration in response to toxic chemicals tolerance at the level of DNA sequence and structure. DNA based techniques (RFLP, QTL, RAPD, AFLP, SSR and VNTR) are used to evaluate the variation at the DNA sequence level (Cenkci et al., 2009). Random amplified polymorphic DNA (RAPD), developed by Williams et al. (1990) and Welsh and McClelland (1990), is a PCR-based technique that amplifies random DNA fragments of genomic DNA with single short primers of arbitrary nucleotide sequence under low annealing conditions. This technique is used extensively for species classification, genetic mapping and phylogeny etc. in addition, their use in surveying genomic DNA for evidence of various types of DNA damage and mutational events (e.g., rearrangements, point mutation, small insert or deletions of DNA changes) in cells of bacteria, plants and animals (Atienzar et al., 2000; Cenkci et al., 2010; Cambier et al., 2010). It is suggested that alterations in RAPD profiles due to genotoxic exposure can be regarded as changes in genomic template stability (GTS, a qualitative measure of genotoxic effects) (Atienzar et al., 1999). It is known that, heavy metal hyperaccumulation potential of some plant species is very high (Ozturk et al., 2010). This feature makes hyperaccumulators highly suitable for phytoremediation, for clean-up of soil and water. On the other hand, an excess of toxic heavy metal ions induces several cellular stress responses and damage to different cellular components such as membranes, proteins and DNA (Patra et al., 1998; Waisberg et al., 2003; Jimi et al., 2004). Therefore, several plant species, such as Allium cepa, Hordeum vulgare, Arabiodopsis thaliana, Vicia faba and Zea mays. etc., have been used as good bioindicators of genetic toxicity of environmental pollutants in recent years. There are many studies on heavy metal uptake and accumulation by crop plants (Chlopecka, 1996; Otabbong et al., 1997; Ali et al., 2004; Al-Qurainy, 2009). On the other hand, tolerant food crops may be dangerous as carriers of toxic metals in the food chain leading to food toxicity. Barley (Hordeum vulgare) has been identified as a plant for efficient uptake and accumulation of Cd with a phytoremediation potential equal to that of mustard plants (Ebbs and Kochain, 1998; Sridhar et al., 2007). To be efficient metal accumulator, plants require efficient detoxification and tolerance mechanisms at both the cellular and plant level. Hence it is important to study how the different plant and cellular characteristics are affected when Cd are accumulated in barley plants. The aims of this study were to investigate the DNA changes induced by Cd using RAPD technique, and to compare changes in RAPD profiles with growth parameters such as root and shoot growth of barley seedlings in order to improve the knowledge about the capacity of Graminae species as phytoextractors. Hordeum vulgare was chosen as test species because of its worldwide economic importance and extensive cultivation.

Influência de temperatura, luz e giberelina na germinação de sementes de Thlaspi caerulescens J. Presl & C. Presl (Brassicaceae)

Thlaspi caerulescens é espécie hiperacumuladora de metais como Cd2+, Ni2+ e Zn2+, considerada como uma plantamodelo para estudar a acumulação e tolerância a metais pesados. No entanto, a baixa produção de sementes em nossas condições climáticas tornam necessária a determinação de condições que possam maximizar a germinação e o vigor de suas sementes. Para identificar as melhores condições para a germinação, sementes de T. caerulescens foram colocadas na presença (15 mmol.m-2.s-1, 8 h luz/16 h escuro) ou ausência de luz nas temperaturas de 10, 15, 20 e 25 ºC, em papel germitest previamente umedecido com solução de ácido giberélico (GA3) a 0,05% ou água destilada. Foram avaliados a porcentagem de germinação (%G) e o índice de velocidade de germinação (IVG). Maior porcentagem de germinação (66%) foi observada nos tratamentos com GA3 e temperaturas de 15 e 20 ºC, na presença de luz. Maiores valores do IVG foram obtidos com a utilização de GA3 nas temperaturas de 15 e 20 ºC, tanto na presença quanto na ausência de luz. Maiores germinação e IVG de T. caerulescens foram observados com uso de GA3 na presença de luz nas temperaturas de 15 e 20 ºC.

Phytoextractive potential among mustard (<i>Brassica juncea</i>) genotypes in Sri Lanka

Heavy metal pollution in soil and water is a global environmental concern. In Sri Lanka, accumulation of heavy metals in soil, water and plant/animal biomass has been widely reported. Phytoremediation, the use of plants and their associated microbes, is an emerging, low-cost, environmental-friendly approach in the cleanup and prevention of environmental pollution. Indian Mustard (Brassica juncea) has been widely used to extract toxic metals from contaminated soils worldwide. Sri Lanka has a genetically diverse mustard collection, but their phytoextarctive potentials are yet to be determined. Present study was conducted to evaluate variation in phytoextractive ability of soil-borne heavy metals by ten different mustard accessions. Heavy metal contents (Mn, Co, Pb and Zn) in 12-week-old mustard plants (whole plant) were estimated during Maha and Yala in 2007-2008 using Atomic Absorption Spectroscopy. Heavy metal content in soils where the plants were grown was also assessed during the two seasons. Soil Mn and Co concentrations were significantly high in Maha than in Yala. Difference in heavy metal concentrations in mustard accessions between the two seasons was not significant. However, significantly high concentrations of Mn were found in accessions 7788, 515 and 8831 (236, 225, 220x102 μg/g). Cobolt (Co) was significantly high in accession 5088 (238x102 μg/g). Lead (Pb) concentrations were significantly high in accessions 8831 (156x102 μg/g) and 5088 (148x102 μg/g) and Zn was significantly high in accession 501 (6413x102 μg/g). The study suggests that screening the entire mustard germplasm in Sri Lanka is worthwhile to identify potential heavy metal accumulators. Key words: heavy metal hyperaccumulation; phytoremediation DOI: 10.4038/cjsbs.v38i2.1862 Cey. J. Sci. (Bio. Sci.) 38 (2): 85-93, 2009

Heavy metal removal and crude bio-oil upgrade from Sedum alfredii Hance harvest using hydrothermal upgrading

In this study, heavy metals were removed and crude bio-oil was yielded from a heavy metal hyperaccumulator harvest, Sedum alfredii Hance, through hydrothermal upgrading process. This paper reports on the optimization of process parameters for the removal of heavy metals (zinc, lead, and copper) and for the upgrading of crude bio-oil from this biomass in an autoclave. Parameters such as granularity, temperature, pressure, and duration were examined for their effect on the removal efficiency of heavy metals and upgrading efficacy of crude bio-oil. Maximum heavy metal removal efficiency of >99% and crude bio-oil upgrading efficiency of >60% were attained with an 18 mesh (1 mm) granularity, and 22.1 MPa at 370 °C in the presence of 10 mg/L additives (K 2CO 3) for 60 s. Under these optimized conditions, an oil phase (mostly composed of phenolic hydrocarbons and derivatives), a water phase raffinate (containing Zn 2+ (0.39 g/L), Pb 2+ (0.10 g/L), Cu 2+ (0.15 g/L)), and a solid phase (the hydrothermal upgrading residue, which completely satisfies the limit set by China legislation related to biosolids disposal) were obtained.

Microcosm Investigation on Phytoremediation of Cr Using Azolla Pinnata

The extent of Chromium (Cr) pollution in Singrauli industrial region, India was assessed and phytoremediation capacity of a small water fern, Azolla pinnata R.BR (Azollaceae) was observed to purify waters polluted by Cr under microcosm condition. Azolla pinnata endemic to India is a potential hyper-accumulator of heavy metals. During 13 days of the experiment the fern was grown in the aqueous medium containing Cr3+ and CrO4 2− ions, each in a concentration 0.5, 1.0, and 3.0 mg L−1. The presence of these ions caused a + 3.1 to −37.5% inhibition of Azolla pinnata growth in comparison to the control. After 13 days of the experiment, metal contents in the solution was decreased up to 70% (CrO4 2− 3.0 mg L−1 treatment) to 88% (CrO4 2− 0.5 mg L−1 treatment). In the Azolla pinnata tissues, the concentration of couple of the ionic forms of Cr under investigation ranged from 415 to 1095 mg kg−1 dry mass (dm); the highest level being found for Cr (III) containing solution.

Identification and functional analysis of two ZIP metal transporters of the hyperaccumulator Thlaspi caerulescens

The heavy metal hyperaccumulator Thlaspi caerulescens expresses several ZIP-like genes at higher levels than their orthologues in non-hyperaccumulator species, but it is not clear why. To elucidate the function of the T. caerulescens orthologues of the Arabidopsis thaliana ZIP5 and ZIP6 genes, full-length cDNAs of TcZNT5-LC and TcZNT6-LC were cloned, their expression was examined and genes were expressed in A. thaliana. Transcript level analysis revealed the constitutively high expression of these two genes in T. caerulescens compared to AtZIP5 and AtZIP6 genes and differential expression of both genes when comparing two accessions of T. caerulescens with different metal accumulation properties. Expression of TcZNT5-LC in A. thaliana did not modify Cd or Zn tolerance, but mildly affected the root and shoot Zn concentrations towards a hyperaccumulator shoot to root concentration ratio. A. thaliana zip5 knock-out mutants showed increased tolerance to Cd and decreased seed mineral concentrations. Expression of TcZNT6-LC enhanced the Cd sensitivity of A. thaliana, but no phenotype was observed for the zip6 mutant. In conclusion, the changes in expression of TcZNT5-LC and TcZNT6-LC upon changes in Zn or Cd exposure indicate both genes act in metal homeostasis, but their CaMV 35S-mediated expression in A. thaliana does not create T. caerulescens hyperaccumulator phenotypes.

Hyperaccumulation and Mobility of Heavy Metals in Vegetable Crops in India

The heavy metals or trace elements play an important role in the metabolic pathways during the growth and development of plants, when available in appreciable concentration. The heavy metal concentration of Cadmium (Cd), Cobalt (Co), Copper (Cu), Iron (Fe), Nickel (Ni), Lead (Pb) and Zinc (Zn) was analyzed using Inductive Coupled Plasma Analyzer (ICPA) (Perkin-Elmer ICP Optima 3300 RL) in 18 vegetable crop plants and their parts along with their soil, collected from various agricultural fields around Anand province, Gujarat, India. The vegetables crop plants were Anthem (Anthum graveolens), Beat (Brassica oleracea), Bitter Gourd (Momordica charantia), Brinjal (Solanum melongena), Cauliflower (Brassica oleracea var. botrytis), Chilli (Capsicum annum), Coriander (Coriandrum sativum), Fenugreek (Trigonella foenum-graceum), Garlic (Alium sativum), Coccinia indica, Lufa (Luffa acutangula), Lady's Finger (Abelmoschus esculentus), Mint (Mentha piperata), Radish (Raphanus sativum), Spinach (Spinacia oleracea), Tomato (Lycopersicum esculentum), Vetches (Cyamopsis soralioides) and White Gourd (Lagernaria vulgaris). The Accumulation Factor (AF) and Mobility Index (MI) were calculated for assessment of mobility of heavy metals from soil to various plant parts: roots, stems and leaves through different levels: Level 1 (Soil-Roots), Level 2 (Roots-Stems) and Level 3 (Stems-Leaves) in studied vegetable crop plants. The results showed concentration dependent variables of heavy metal levels among vegetable crop plants. The lower and higher concentration gradient alongwith their mobility gradient was also determined. A perusal of data reflects that accumulation gradient of each crop plant component vary according to their nature, properties and podsol climate of a particular crop plant. The data on accumulation and mobility of heavy metals such as Cd, Co, Cu, Fe, Ni, Pb and Zn from soil to leaves through roots and stems, suggested that all the metals were highly mobile. Key words: Vegetable crop plants; Heavy metals; Accumulation factor; Mobility index; etc.The Journal of Agriculture and Environment Vol:10, Jun.2009 page: 34-45

Chelation by histidine inhibits the vacuolar sequestration of nickel in roots of the hyperaccumulator Thlaspi caerulescens

* The mechanisms of enhanced root to shoot metal transport in heavy metal hyperaccumulators are incompletely understood. Here, we compared the distribution of nickel (Ni) over root segments and tissues in the hyperaccumulator Thlaspi caerulescens and the nonhyperaccumulator Thlaspi arvense, and investigated the role of free histidine in Ni xylem loading and Ni transport across the tonoplast. * Nickel accumulation in mature cortical root cells was apparent in T. arvense and in a high-Ni-accumulating T. caerulescens accession, but not in a low-accumulating T. caerulescens accession. * Compared with T. arvense, the concentration of free histidine in T. caerulescens was 10-fold enhanced in roots, but was only slightly higher in leaves, regardless of Ni exposure. Nickel uptake in MgATP-energized root- and shoot-derived tonoplast vesicles was almost completely blocked in T. caerulescens when Ni was supplied as a 1 : 1 Ni-histidine complex, but was uninhibited in T. arvense. Exogenous histidine supply enhanced Ni xylem loading in T. caerulescens but not in T. arvense. * The high rate of root to shoot translocation of Ni in T. caerulescens compared with T. arvense seems to depend on the combination of two distinct characters, that is, a greatly enhanced root histidine concentration and a strongly decreased ability to accumulate histidine-bound Ni in root cell vacuoles.

Bidens tripartite L.: A Cd-accumulator confirmed by pot culture and site sampling experiment

Characteristics of accumulation and tolerance of cadmium (Cd) in Bidens tripartite L. were investigated to identify Cd-accumulating properties. In this study, pot culture experiment and site sampling experiments were conducted to assess whether this plant is a heavy metal hyperaccumulator or accumulator. The results indicated that the Cd enrichment factor (concentration in plant/soil) and Cd translocation factor (concentration in shoot/root) of B. tripartite was principally >1 in pot culture and concentration gradient experiments. Shoot biomass was not reduced significantly ( p < 0.05) compared to the controls. However, the Cd concentration in B. tripartite shoots was not higher than 100 mg kg −1, the threshold concentration for a Cd-hyperaccumulator. In the site sampling experiment, B. tripartite also showed Cd-accumulator properties. Based on these results, B. tripartite could be identified as a Cd-accumulator. Thus, B. tripartite should only be considered as a Cd-accumulator.