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GeoloGy, ecoloGy, and landscapes, 2018 Vol . 2, no . 1, 51– 60 https://doi.org/10.1080/24749508.2018.1452464 INWASCON OPEN ACCESS Accumulation and distribution of lead (Pb) in plant tissues of guar (Cyamopsis tetragonoloba L.) and sesame (Sesamum indicum L.): profitable phytoremediation with biofuel crops a a b c d Hira Amin , Basir Ahmed Arain , Taj Muhammad Jahangir , Muhammad Sadiq Abbasi and Farah Amin a b Institute of plant s ciences, University of sindh, Jamshoro, pakistan; national c entre of excellence in analytical chemistry, University of sindh, Jamshoro, pakistan; d epartment of Mathematics & statistics, Quaid-e-a wam University of engineering, science & Technology, nawabshah, pakistan; national c entre of excellence in analytical chemistry, University of sindh, Jamshoro, p akistan ABSTRACT ARTICLE HISTORY Received 21 s eptember 2017 Contamination of lead indicates one of the major threats to soil system. Phytoremediation a ccepted 20 January 2018 technique utilized plants which are able to tolerate and accumulate metals within in their tissues. It has recently been suggested that biofuel plants are more suitable for both utilization KEYWORDS and remediation of metal contaminated soil. This study reported Pb phytoremediation potential s oil pollution; lead; of Cyamopsis tetragonoloba L. in comparison with Sesamum indicum L. in the framework of a accumulation; pot-experiment. Plants were subjected to seven Pb concentrations (0, 100, 200, 400, 600, 800 phytoextraction; -1 and 1000 mg kg soil) for 12 weeks. Our results demonstrated that both C. tetragonoloba and phytostablization -1 S. indicum were able to tolerate Pb concentrations up to 1000 mg kg which confirms the plant ability to grow well in higher Pb levels. Significant metal accumulation was observed in root along with reduced biomass for both plants species. Furthermore, both plant species could possibly be used for phytostabilization, with success in marginally polluted soils where their growth would not be impaired and decontamination of Pb could be maintained at satisfying levels. However, bioconcentration factor (BCF), bioaccumulation coefficient (BAC) and translocation factor (TF) values proposed that C. tetragonoloba was more efficient for phytoremediation than S. indicum at higher Pb levels. 1. Introduction (Punamiya et al., 2010); known to induce a broad range of toxic effects to morphological, physiological, and Soil pollution with toxic trace metals and their accu- biochemical activities of living organisms. Lead impairs mulation in soil is of great concern in agricultural pro- plant growth such as root elongation, seed germination, duction owing to the adverse effects on crop growth seedling development, transpiration, chlorophyll pro- i.e., metal phytotoxicity, and soil micro-organisms duction, lamellar organization in the chloroplast, and (Nagajyoti, Lee, & Sreekanth, 2010). Toxic trace metals cell division (Gupta, Huang, Yang, Razafindrabe, & have entered into agricultural soils primarily because Inouhe, 2010; Maestri, Marmiroli, Visioli, & Marmiroli, of rapid industrialization, inappropriate utilization and 2010). However, the extent of these effects varies and disposal of toxic trace metal containing wastes, exces- depends on the lead concentrations, the duration of sive use of fertilizers and pesticides (Amel et al., 2016; exposure, the intensity of plant stress, and the particu- Bashmakov, Lukatkin, Anjum, Ahmad, & Pereira, 2015), lar organs studied. which become hazardous to human and environmental Lead occurs naturally in the earth’s crust (Arias −1 health. Trace metals, such as lead (Pb), cadmium (Cd), et al., 2010) and its natural levels remain below 50 mg kg nickel (Ni), cobalt (Co), iron (Fe), zinc (Zn), chromium (Pais & Jones, 2000), but anthropogenic activities oen ft (Cr), iron (Fe) (Nagajyoti et al., 2010), are major envi- modify the amount and nature of lead species present ronmental pollutants, particularly in areas with high in soil. Anthropogenic sourced lead (Pb) include lead- anthropogenic activities. based paints, lead arsenate pesticide application, gaso- Among soil pollutant, lead (Pb) is one of the toxic line, coal burning, explosives, lead batteries and from metal pollutants (Shahid, Pinelli, Pourrut, Silvestre, & the disposal of municipal sewage sludge (Tian, Lu, Yang, Dumat, 2011); widely used in many industrial processes et al., 2010; Zheng, Liu, Lütz-Meindl, & Peer, 2011). and occurs as a contaminant in all environmental com- In soils, lead may occur as a free metal ion, complexed − 2− 2− partments including soil, water, and living organisms with inorganic constituents (e.g., HCO , CO , SO , 3 3 4 CONTACT Hira amin firstname.lastname@example.org © 2018 The a uthor(s). published by Informa UK limited, trading as Taylor & Francis Group. This is an open a ccess article distributed under the terms of the creative c ommons a ttribution license (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 52 H. AMIN ET AL. and Cl ), may exist as organic ligands (e.g., amino acids, fertility and ability to support biological growth (Xiuli fulvic acids, and humic acids); or may be adsorbed on et al., 2013; Hao et al., 2014). On the other hand, ses- to particle surfaces (e.g., Fe-oxides, biological mate- ame (Sesamum indicum L.) is an economically important rial, organic matter, and clay particles) (Uzu, Sobanska, oil seed crop of family Pedaliaceae, planted in arid and Aliouane, Pradere, & Dumat, 2009; Vega, Andrade, & semi-arid regions of the world (Elleuch, Besbes, Roiseux, Covelo, 2010). Generally, lead may accumulates on the Blecker, & Attia, 2007) including Pakistan, used as an surface layer of soil (Cecchi et al., 2008) and caused dis- alternative feedstock for the production of a biodiesel turbance of soil system. Thus, in order to reduce the level fuel (Saydut, Duz, Kaya, Kafadar, & Hamamci, 2008). of lead from the natural environment many developed e m Th ethyl ester extracted from sesame seeds can effec - countries has tried to reduce lead emissions using lead- tively be utilized as petrodiesel (Ahmad et al., 2011). free fuels (Adriano, 2001). This study was set up to investigate a plant species that Remediation of lead-polluted soils by traditional could tolerate high toxicity of Pb treatments in soil. Both physical and chemical methods are not suitable for the plant species i.e., C. tetragonoloba and S. indicum agricultural lands (Oh, Li, Cheng, Xie, & Yonemochi, have fast growth and development rate also high above- 2013), required large investments and technological ground biomass. It was estimated that plant species with resources. Phytoremediation is a promising technique high tolerance could then be utilized for phytoreme- to remediate metal-contaminated soils because it oer ff s diation. Considering above facts, the objectives of this in situ advantages, cost effective, and less energy-in- research were: (1) to study the phytotoxicity of lead on tensive than high-cost traditional clean-up methods. plant growth parameters; (2) to determine the accumu- Phytoremediation involves the use of plants to reclaim lation and distribution of lead in plant parts growing high amount of metals from soil into the harvestable on a lead-polluted soil, and (3) to identify a potential parts (i.e., underground roots and aboveground shoots) candidate for effective phytoremediation practice. (Mahmood, 2010). e Th harvested biomass then can be safely processed by drying, ashing, composting, and 2. Material and methods storage at a landfill, anaerobic digestion, pure plant 2.1. Seeds procurement and sterilization oil production, microbial, physical, or other chemical means (Ginneken et al., 2007). Seeds of the guar variety BR-99, from the Institute of e c Th apacities of heavy metal uptake and accumu- Fodder Research Program and sesame variety TH-6, lation, mechanisms of metal concentration, exclusion were collected from the Institute of Oilseeds Research and compartmentation vary among different plant spe- Program, National Agricultural Research Centre cies and also between various parts of plants (Lone, He, (NARC), Islamabad (Table 1). In order to avoid any Stoe ff lla, & Xe, 2008; Sharma, Singh, & Manchanda, microbial contamination, seeds were surface steri- 2014). Various plant species belongs to botanical fami- lized with 0.1% HgCl for 10 min and washed 7 times lies, in particular the Brassicaceae, Asteraceae, Fabaceae, with sterilized water (Pourakbar, Khayami, Khara, & Poaceae, and Chenopodiaceae showing phytoreme- Farbidina, 2007). diation potential, are well documented in the litera- ture (Stanislaw & Gawronski, 2007; Anjum, Umar, & 2.2. Experimental soil collection Iqbal, 2014) but few or less work has been reported on Cyamopsis tetragonoloba L. and Sesamum indicum L. Soil samples were collected from Pb-free agricultural Guar (Cyamopsis tetragonoloba L.) is one of the fields located in Jamshoro, Sindh, Pakistan, at depth of important annual legume crops belongs to family 0–15 cm using hand shovel. Equidistant (2 m) collected Fabaceae. The endosperm of guar seeds contain gum, samples were homogenized to prepare one bulk sam- which is gaining importance as non-food item (Ashraf, ple. For the greenhouse experiment, soil was air dried Akhtar, Sarwar, & Ashraf, 2002). Recently, the oil indus- at room temperature for 15 days and ground to a final try has started using guar gum in hydraulic fracturing in particle size of 2 mm. To enhance soil porosity, sand was which high pressure is used to crack rock. The increased mixed in 3:1 proportion with soil samples soil. use of guar gum in oil fracking has boosted the demand of guar woldwide (Abidi et al., 2015; Deepak, Sheweta, 2.3. Soil samples measurements & Bhupendar, 2014). A key feature of legumes as a resource for phytoremediation is their role in providing Soil pH was measured with a pH-meter (InoLab-WTB additional N-compounds to the soil, thus improving soil GmbH; Weilheim, Germany) using glass electrode at the 1:2 (w/v) ratio of soil to water suspension (Rachit, Verma, Meena, Yashveer, & Shreya, 2016). The electri- Table 1. plant species selected for pot experiment. cal conductivity (EC) was measured with an electrical conductivity meter (WTW – 330i) at the 1:2 (w/v) No. Botanical name Vernacular name Family 1 Cyamopsis tetragonoloba l. Guar Fabaceae ratio of soil to water suspension (Rachit et al., 2016). 2 Sesamum indicum l. s esame pedaliaceae Organic matter (OM) and organic carbon (OC) (%) were GEOLOGY, ECOLOGY, AND LANDSCAPES 53 Table 3. l ead treatment levels given in the experiment. measured according to Walkley and Black (chromic acid titration) method (Fanrong et al., 2011). The properties −1 Treatments (mg kg soil) Heavy of the soil are shown in Table 2. metal Salt used T1 T2 T3 T4 T5 T6 l ead (pb) pb (no ) 100 200 400 600 800 1000 3 2 2.4. Preliminary screening for Pb In order to select the Pb concentrations for treatment, 2.7. Morphological parameters various doses of Pb(NO ) (0, 50, 100, 200, 500, 700, 3 2 Plants were taken from each replicate pot to measure −1 1000, 1500, and 2000 mg kg ) were tried in the prelim- morphological parameters. Root length, shoot length inary screening of the C. tetragonoloba and S. indicum were measured with the help of scale. Root and shoot for 20 days. Based on the Pb toxicity symptoms and mor- fresh weights were also measured with the help of analyt- phological growth of the seedlings, the following doses ical balance. Plant samples were air dried for one week. −1 (0, 100, 200, 400, 600, 800, 1000 mg kg ) were finally en, o Th ven-dried at 80 °C to a constant weight and dry selected (Table 3). weights were recorded. 2.5. Pot experiment 2.8. Estimation of photosynthetic pigments Plastic pots were filled with 5 kg sieved soil, aer w ft hich Photosynthetic pigments, in fully expanded leaves from soil was artificially spiked with Pb (aqueous solution) using each treatment, were extracted using 0.5 g of fresh mate- Pb(NO ) salt to each pot in increasing concentrations 3 2 rial, ground with 10 mL of 80% aqueous acetone. Aer ft −1 (100, 200, 400, 600, 800, 1000 mg kg ), each with three filtering, 1 mL of the suspension was diluted with a fur - replicates and kept for 2 weeks to attain equilibrium. The ther 2 mL of acetone, and optical density were deter- clean soil without Pb spiking was used as control. Pots were mined with a UV–visible spectrophotometer (Biochrom arranged in a completely randomized design. Ae ft r 15 days Libra S22), using two wavelengths (663 and 645 nm) of equilibration, 20 surface-sterilized seeds were sown per against blank. Chlorophyll a (Chl a), chlorophyll b (Chl pot. One week aer s ft eed germination, plants were thinned −1 b) and total chlorophyll contents (mg g f.w) were to 5 per pot. A plastic tray was kept below the treatment obtained by calculation, following the method of Arnon pot to collect any leachate, which was returned to the (1949). pots at next watering. The experiment was conducted Chlorophyll a = (12.7 × OD663) − (2.69 × OD645) in a greenhouse for 3 months. Any symptoms of metal toxicity exhibited by plants were visually noted during V 1 × × mg/g FW (2) the experimental period. Plants were harvested 12 weeks 1000 wt ae ft r germination. Soil samples (in triplicate) were also col - Chlorophyll b = (29.9 × OD645) − (4.68 × OD663) lected for analysis of Pb content by an Atomic Absorption V 1 Spectrophotometer (Perkin-Elmer, AAnalyst 800). Plant × × mg/g FW (3) 1000 wt growth and biochemical parameters were also measured. Total Chlorophyll = (20.7 × OD645) − (8.02 × OD663) 2.6. Germination percentage (%) V 1 × mg/g FW 1000 wt e g Th ermination percentage, expressed as percentage of (4) germinated seeds to the total number of viable seeds, calculated by the following equation: (Talebi, Nabavi, 2.9. Determination of tolerance index & Sohani, 2014) Tolerance Index (TI) is expressed as the ratio between the Total No. of germinated seeds growth parameters (root/shoot length, root/shoot fresh, Germination percentage (%) = × 100 Total No. of seeds sown and dry weight) of the plants in contaminated soil in rela- (1) tion to the growth parameters of plants from non-pol- luted soil calculated according to Chen et al., 2011. Growth parameter Table 2. The properties of experimental soil. Pb contaminated soil Tolerance index (%) = × 100 Growth parameter Parameter Value Control soil b (5) pH 6.89 ± 0.04 -1 a e.c. (μs cm ) 1662 ± 11 organic carbon, % 2.20 ± 0.04 2.10. Quality control and quality assurance organic matter, % 3.79 ± 0.02 −1 pb (total), mg kg nd All the glassware used during the present experimen- notes: similar letters in same column are statistically non-significant tation was of high quality, acid resistant Pyrex glass. according to d uncan’s Multiple Range Test (p < 0.05), data are means e a Th nalytical grade reagents with a certified purity of (n = 3 ±sd ), in superscript represent significantly highest followed by later alphabets for lower means, nd = not detected. 99% and stock metal standard solution (1000 ppm) for 54 H. AMIN ET AL. AAS analysis were procured from E. Merck (Germany). method. To quantify the Pb content in soil, sample of Working standards were prepared by appropriate dilu- 1 g soil was digested by means of wet acid digestion tions of stock standard solutions with double distilled method through HNO along with HCl in proportion water. of 3:1 (v/v) and heated on a hot plate for 2 h until the solution becomes clear. Aer co ft oling, the volume was completed to 50 mL by adding distilled water. e Th solu- 2.11. Plant samples preparation and Pb tion was filtered through Whatman’s filter paper and determination consequently, examine for Pb contents with Atomic To determine Pb accumulation in different plant tissues Absorption Spectrophotometer. (i.e., root, stem, leaf, and pod), harvested plant parts were rinsed thoroughly by means of tap water, and aer ft 2.13. Evaluation of phytoremediation efficiency that with deionized (DI) water to clean adhered compo- nents of soil, then oven-dried at 80 °C till steady weight. To evaluate the phytoextraction/phytostabilization e o Th ven-dried plant tissues were ground carefully using potential of C. tetragonoloba and S. indicum, the fol- an electric grinder and passed through a 1.0 mm mesh lowing factors were calculated: strainer. The ground plant tissue samples (0.5 g) were 2.13.1. Bioconcentration factor (BCF) digested with 12 mL of 3:1 (v/v) HNO /HClO mixtures 3 4 e b Th ioconcentration factor (BCF) was represented as on a hot plate for 2 h. Aer co ft oling, the digested solution the Pb concentration ratio in plant roots to soil, calcu- was filtered through Whatman’s filter paper and finally lated as follow: makes up the volume up to mark 50 mL by adding deionized (DI) water. Pb root e q Th uantification of lead (Pb) in respective tissues (8) Bioconcentration Factor [BCF] = was carried out using atomic absorption spectrometer [ Pb ] soil (Perkin-Elmer, AAnalyst 800) equipped with a lead 2.13.2. Bioaccumulation coefficient (BAC) cathode lamp, under optimum analytical conditions e Th bioaccumulation coec ffi ient (BAC) was expressed as for the estimation of lead. e Th optimum conditions for a ratio of Pb in shoot to that in soil, calculated as follow: AAS used throughout these studies given in Table 4. e s Th tandard calibration method was adopted for the Pb shoot quantification of results and triplicate samples were Bioaccumulation Coeﬃcient [BAC]= [ Pb ] soil run to ensure the precision of quantitative results. e Th (9) Pb concentration and accumulation in plant root and shoot were calculated by the following formula: (Monni, 2.13.3. Translocation factor (TF) Salemaa, & Millar, 2000) e t Th ranslocation factor (TF) was determined as a ratio of heavy metals in plant shoot to that in plant root, cal- AAS interpretation (reading)× dilution factor Pb Conc. mg∕kg = culated as follow: dry wt.of plant tissues (6) Pb shoot (10) Translocation Factor [TF]= [ Pb ] root Pb Acc. μg∕plant = Pb conc. × dry wt.of plant tissues (7) 2.14. Statistical analysis 2.12. Soil sample preparation and Pb All experiments were conducted with three replicates determination and the data collected were analyzed statistically using PASW Statistics 18 (SPSS Inc., Chicago, IL, U.S.A.). To Soil samples were air dried at room temperature, compare the means of the treatments, analysis of variance ground, mixed well, and kept in plastic (polyethylene) (ANOVA) was performed followed by Duncan’s multiple sealed lock bags used for subsequent metal analysis. range Post Hoc tests at significance level of p < 0.05, to Digestions of soil samples were done using aqua regia observe significance difference among means. Table 4. Measurement conditions of aas for lead (p b) determi- 3. Results and discussion nation. 3.1. Soil characterization Parameters Values Wave length (nm) 217.0 e s Th oil was sandy loam with slightly acidic to neutral Hollow cathode lamp current (ma ) 5.0 pH (6.89), organic carbon (2.20%), organic matter con- Flame type air- c H 2 2 -1 Background correction on tents (3.79%), and electrical conductivity (1662 μS cm ). slit width (nm) 1.0 Among soil properties, soil pH has strong effects on Flame condition o xidizing expansion factor 1 solubility and speciation of metals both in the soil and GEOLOGY, ECOLOGY, AND LANDSCAPES 55 particularly in the soil solution (Fanrong et al., 2011), of Pb was significantly (p < 0.05) inhibited growth in whereas, organic matter content has a strong influence terms of root and shoots length in C. tetragonoloba and on cation exchange capacity, buffer capacity as well as S. indicum (Table 5). In C. tetragonoloba and S. indi- on the retention of heavy metals. Thus, metals present cum, the longest roots (17.85 and 13.76 cm) and shoots in organic rich soils contaminated with heavy metals (134.30 cm and 119.04 cm) were observed in control −1 are less mobile and less bioavailable than metals present treatments with 0 mg kg Pb, respectively. Pb is not an in mineral soils (Olaniran, Balgobind, & Pillay, 2013). essential nutrient and at high concentrations inhibits −1 e Th mobility and availability of heavy metals in the soil plant growth. At 1000 mg Pb kg concentration, root are generally low, especially when the soil is high in pH, length decreased by 13.60 cm and 10.67 cm while shoot clay, and organic matter (Rosselli, Keller, & Boschi, 2003). length reduced by 100.47 cm and 85.33 cm in both C. Dede et al. (2012) reported that Pb is an immobile metal tetragonoloba and S. indicum, respectively. Higher con- in soil, since it readily forms a precipitate with a low aque- centration of Pb-induced morphological changes in ous solubility within the soil matrix, and in many cases plants i.e., root and shoot elongation in different plants it is not readily bioavailable. So, in accordance with soil showed a great sensitivity to excessive Pb. Lead exposure properties such factors may act individually or in combi- in plants strongly limits the growth and development nation with each other and may alter the soil behaviour of seedlings (Gopal & Rizvi, 2008). At high concentra- of the lead present, as well as the rate of uptake by plants. tions, lead inhibits the growth of roots which directly influences root growth and decreasing the capacity of water and nutrients absorption, ultimately leading to 3.2. Pb-induced phytotoxic effects reduction in growth of the plant species. Gradual increase in Pb concentration significantly Plant growth is an important parameter used to (p < 0.05) reduced all tested growth and biochemical assess the survival and adaptation of a given species to parameter in two plant species. In the current investiga- environmental factors that decisively control biomass tion, the germination percentage of C. tetragonoloba and production. Addition of Pb-inhibited biomass growth S. indicum seeds were significantly (p < 0.05) ae ff cted at of C. tetragonoloba and S. indicum. Pb contamination −1 1000 mg Pb kg as compared to control (Table 5). The showed significant (p < 0.05) negative impacts on both reduced germination percentages (64.76 and 80.00%) fresh and dry biomass of C. tetragonoloba and S. indicum −1 were recorded at 1000 mg Pb kg in C. tetragonoloba (Table 5). Compared to control treatments, Pb stress at −1 −1 and S. indicum, respectively. It has been well docu- 1000 mg kg reduced root fresh weight (8.15 g plant −1 −1 mented in the literature that germination is an essential and 5.92 g plant ) and shoot fresh weight (21.13 g plant −1 process to determine the effects of Pb toxicity on dif- and 9.15 g plant ) in C. tetragonoloba and S. indicum, ferent plant species. Germination is strongly inhibited respectively. The dry biomass follows the same trend as at very low concentrations of Pb, even at micromolar fresh weight. Compared to control treatments, Pb stress −1 levels (Kopittke, Asher, Kopittke, & Menzies, 2007). In at 1000 mg kg reduced root dry weight from (5.09 g −1 −1 this study, C. tetragonoloba and S. indicum seeds were plant and 3.70 g plant ) and shoot dry weight (10.90 g −1 −1 able to germinate in the presence of low to moderate plant and 5.87 g plant ) in C. tetragonoloba and S. indi- level of Pb concentrations in soil. e Th inhibition of seed cum, respectively. Plant biomass is a signic fi ant indicator germination may also result from the interference of lead for characterizing the growth performance of plants in with protease and amylase enzymes (Sengar et al., 2009). the presence of heavy metal. Under severe lead toxicity Seedling’s height (root and shoot length) is also stress, plants displayed obvious symptoms of growth among primary determinants of plant growth. Addition inhibition. Plant biomass can be restricted by high doses Table 5. phytotoxicity of pb on germination and growth parameters of Cyamopsis tetragonoloba l. and Sesamum indicum l. Root fresh Shoot fresh Root dry Shoot dry Pb applied Germination Root length Shoot length weight weight weight weight −1 −1 Plant species mg kg % cm g plant a a a a a a a C. tetragonolo- 0 88.57 ± 2.86 17.85 ± 0.34 134.30 ± 1.70 14.29 ± 0.18 53.74 ± 5.32 8.93 ± 0.12 20.33 ± 2.08 ab ab b b b b ab ba 100 81.90 ± 1.65 16.83 ± 0.85 129.20 ± 1.70 12.58 ± 1.04 41.19 ± 9.22 7.87 ± 0.65 18.30 ± 1.47 ab ab c c bc c b 200 80.00 ± 17.84 16.49 ± 0.17 122.57 ± 3.23 11.36 ± 0.42 35.03 ± 6.16 7.10 ± 0.26 17.30 ± 1.47 ab bc c c bc c bc 400 80.00 ± 7.56 15.13 ± 0.17 119.00 ± 2.74 10.84 ± 0.37 31.54 ± 0.75 6.77 ± 0.24 15.67 ± 0.57 ab c d d cd d cd 600 76.19 ± 14.09 14.62 ± 0.17 102.00 ± 2.47 9.55 ± 0.81 30.08 ± 2.93 5.97 ± 0.50 14.33 ± 1.52 ab c d e cd e de 800 69.52 ± 10.82 13.60 ± 1.70 100.98 ± 3.40 8.48 ± 0.48 26.86 ± 1.17 5.30 ± 0.30 12.67 ± 1.20 b c d e d e e 1000 64.76 ± 10.82 13.60 ± 1.70 100.47 ± 1.53 8.15 ± 0.28 21.13 ± 6.66 5.09 ± 0.18 10.90 ± 1.40 a a a a a a a S. indicum 0 94.44 ± 5.85 13.76 ± 0.48 119.04 ± 1.60 12.27 ± 0.33 41.33 ± 1.01 8.33 ± 0.12 18.33 ± 1.20 ab ab a ab b ab b 100 90.00 ± 5.00 12.64 ± 0.32 116.48 ± 1.60 10.24 ± 1.95 34.42 ± 6.12 7.33 ± 0.42 16.27 ± 1.10 ab bc a bc ab b c 200 88.33 ± 4.41 12.16 ± 1.60 116.00 ± 1.60 8.66 ± 2.19 36.92 ± 3.31 6.24 ± 0.90 14.03 ± 1.00 ab bcd b bcd bc c d 400 87.22 ± 6.31 11.31 ± 0.72 108.16 ± 1.60 7.84 ± 1.31 31.29 ± 1.49 4.90 ± 0.82 11.56 ± 0.51 ab cd b cd c c e 600 85.56 ± 8.22 11.04 ± 0.32 107.84 ± 1.60 7.51 ± 0.63 25.88 ± 3.59 4.70 ± 0.40 9.67 ± 1.15 ab d b cd d c f 800 83.89 ± 2.55 10.72 ± 0.16 103.04 ± 1.60 7.30 ± 1.48 17.42 ± 1.49 4.53 ± 0.92 7.59 ± 0.72 b d c d e c g 1000 80.00 ± 10.93 10.67 ± 0.56 85.33 ± 9.92 5.92 ± 0.97 9.15 ± 1.18 3.70 ± 0.61 5.87 ± 0.81 notes: similar letters in same column are statistically non-significant according to d uncan’s Multiple Range Test (p < 0.05), data are means (n = 3 ± sd ), in superscript represent significantly highest followed by later alphabets for lower means. 56 H. AMIN ET AL. of lead exposure. Decrease in plant biomass may be asso- ciated with disturbed metabolic activities due to reduced uptake of essential nutrients when grown under Pb stress (Gopal & Rizvi, 2008; Kopittke et al., 2007). Lead, if present at high levels, can interfere with nor- mal enzyme functions in plants and especially photosyn- thesis which is one of the plant processes most drastically ae ff cted by Pb toxicity. It is evident that chlorophyll con - tent in leaves of C. tetragonoloba and S. indicum were influenced by Pb treatments. Chlorophyll contents decreased significantly (p < 0.05) with gradual increase −1 in Pb concentration from 0 to 1000 mg kg (Figure 1). In C. tetragonoloba and S. indicum, the maximum amount of chlorophyll contents were measured at control, while the lowest concentration of chlorophyll a (0.63 and −1 −1 0.51 mg g ), chlorophyll b (0.35 and 0.21 mg g ), and −1 total chlorophyll (0.98 and 0.72 mg g ) was at 1000 mg −1 Pb kg , respectively. A decreased rate of photosynthetic pigment accumulation in association with Pb treatment may be the consequence of peroxidation of chloroplast membranes due to increased level of ROS generation (Srinivasan, Sahi, Paulo, & Venkatachalam, 2014). Lead may inhibit chlorophyll biosynthesis by impairing the uptake of essential photosynthetic pigment elements, such as magnesium, potassium, calcium, and iron (Gopal & Rizvi, 2008) which disturbed photosynthesis with the substitution of divalent cations by lead. Tolerance indices (TIs) were also ae ff cted by Pb tox- icty. Plant tolerance to heavy metal stress is estimated based on their root and/or shoot growth inhibition by the metal present in a medium (Srinivasan et al., 2014). According to Audet and Charest (2007), if TI values less than 1, this indicates that the plant suffered a stress due to metal pollution with a net decrease in biomass. By contrast, if TI values greater than 1, suggest that plants Figure 1. eec ff t of p b stress on photosynthetic pigments have developed tolerance with a net increase in biomass chlorophyll-a (a) chlorophyll-b (b), and total chlorophyll (a + b) (hyper accumulator). If TI values equal to 1, the plant (c), on C. tertragonoloba and S. indicum after 12-week growth in soil medium with varying concentrations of pb. is unae ff cted by metal pollution, indicate no difference notes: similar letters are statistically non-significant according to d uncan’s relative to control treatments. In this study, both the Multiple Range Test (p < 0.05), data are means (n = 3 ± sd ), in superscript plant species (C. tetragonoloba and S. indicum) had represent significantly highest followed by later alphabets for lower means. Table 6. eec ff t of p b stress on the growth tolerance indices (TIs) of Cyamopsis tetragonoloba l. and Sesamum indicum l. Tolerance indices Root fresh Shoot fresh Shoot dry Pb applied Root length Shoot length weight weight Root dry weight weight −1 Plant species mg kg % a a a a a a C. tetragonoloba 100 94.25 ± 2.97 96.20 ± 0.05 88.01 ± 6.32 76.97 ± 18.18 88.01 ± 6.32 91.19 ± 17.30 ab b b ab b a 200 92.39 ± 0.81 91.26 ± 1.25 79.48 ± 2.78 64.89 ± 6.02 79.48 ± 2.78 85.40 ± 7.06 bc b b ab b ab 400 84.79 ± 2.57 88.60 ± 0.93 75.85 ± 1.80 59.13 ± 6.87 75.85 ± 1.80 77.43 ± 5.40 c c c bc c abc 600 81.94 ± 2.51 75.97 ± 2.80 66.84 ± 6.47 56.22 ± 6.54 66.84 ± 6.47 71.54 ± 15.45 c c cd bc cd bc 800 76.09 ± 8.08 75.22 ± 3.48 59.36 ± 4.06 50.18 ± 3.18 59.36 ± 4.06 62.64 ± 7.01 c c d c d c 1000 76.09 ± 8.08 74.81 ± 0.19 57.01 ± 1.74 39.24 ± 11.58 57.01 ± 1.74 53.63 ± 4.13 a a a a a a S. indicum 100 91.99 ± 5.54 97.85 ± 0.029 83.34 ± 14.76 83.13 ± 13.52 88.06 ± 6.23 89.23 ± 11.27 a a ab a a a 200 88.71 ± 14.73 97.45 ± 0.03 70.5 ± 17.63 89.37 ± 8.75 74.83 ± 9.89 76.92 ± 9.40 a ab ab ab b b 400 82.36 ± 8.10 90.88 ± 2.57 63.86 ± 10.19 75.72 ± 3.14 58.72 ± 9.12 63.20 ± 3.68 a ab ab b b bc 600 80.35 ± 5.13 90.59 ± 0.13 61.20 ± 3.59 62.78 ± 10.24 56.33 ± 4.09 52.94 ± 7.72 a b b c b cd 800 77.99 ± 3.89 86.56 ± 0.18 59.22 ± 12.60 42.22 ± 4.52 54.36 ± 10.68 41.38 ± 2.78 a c b d b d 1000 77.49 ± 1.42 71.73 ± 8.94 48.18 ± 7.09 22.13 ± 2.69 44.34 ± 6.74 32.28 ± 6.39 notes: similar letters in same column are statistically non-significant according to d uncan’s Multiple Range Test (p < 0.05), data are means (n = 3 ± sd ), in superscript represent significantly highest followed by later alphabets for lower means. GEOLOGY, ECOLOGY, AND LANDSCAPES 57 different tolerance indices (TIs) under Pb stress (Table 6 ). −1 At 1000 mg kg Pb treatment, C. tetragonoloba and S. indicum had the TIs for root lengths (76.09% and 77.49%) and shoot lengths (74.81% and 71.73%), root fresh weights (57.01% and 48.18%) and shoot fresh weights (39.24% and 22.13%), root dry weights (57.01% and 44.34%) and shoot dry weights (53.63% and 32.28%) respectively. Srinivasan et al. (2014) reported that growth inhibition is a common response to heavy metal stress and is also one of the most important agricultural indices of heavy metal tolerance. 3.3. Pb concentration in plant tissues Concentration trends of Pb uptake among the dif- ferent plant tissues (root, stem leaf, and pod) in both C. tetragonoloba and S. indicum are presented in Table 7. In C. tetragonoloba, the highest concentra- −1 tion of Pb found in the root: 626.67 mg kg followed −1 −1 by stem: 299.67 mg kg , leaf: 89.33 mg kg , and −1 −1 pod: 10.40 mg kg at 1000 mg Pb kg . However, in S. indicum Pb concentration primarily in the root: −1 525.67 mg kg , with small amount being transferred −1 −1 to leaf: 75.33 mg kg followed by stem: 64.89 mg kg −1 −1 and pod: 8.13 mg kg at 1000 mg Pb kg . The high Pb contents in the plant tissues are clearly related to the con- centration of metal in the growing environment. Because of strong Pb binding with organic and/or colloidal mate- rials, it is believed that only small amounts of the lead in soil are soluble, and thereby available for plant uptake (Kopittke, Asher, Kopittke, & Menzies, 2008). The Pb accumulation capacity, based on their availabilities in the soil, varies greatly among different plants species and cultivars, and is also ae ff cted by various soil conditions reviewed by Bertrand, Muhammad, Camille, Peter, and Eric (2011). 3.4. Pb accumulation in root and shoot Beside concentrations, a total amount of metals accumu- lated in the shoots is considered as the most important parameter to evaluate the potential of phytoextraction in plants (Hanen et al., 2010). A significant rise in Pb accumulation per plant in root and shoot of both the plant species varied with respect to Pb treatments are expressed in (Figure 2). The maximum Pb accumulation in root and shoot of both C. tetragonoloba and S. indicum −1 were observed at 600 and 800 mg Pb kg treatment. The mean Pb accumulation in C. tetragonoloba root were −1 ranged from 856.17 to 3585.17 μg plant , while the accumulation of Pb by shoot were ranged from 1749.84 −1 to 4655.07 μg plant . On the other hand, in S. indicum root accumulation was ranged from 747.2 to 2280.53 μg −1 plant while, the accumulation of Pb by shoot ranged −1 from 622.99 to 1177.7 μg plant . Studies have shown the uptake of metals; their partition and translocation to different plant parts, as well as the degree of tolerance Table 7. pb concentration, bioconcentration factor (BcF), bioaccumulation coefficient (Bac ), and translocation factor (TF) of Cyamopsis tetragonoloba l. and Sesamum indicum l. Pb concentration Pb applied Root Stem Leaf Pod −1 −1 Plant species mg kg mg kg BCF BAC TF d d e c ab a a C. tetragonoloba 100 108.67 ± 3.22 54.67 ± 1.53 39.00 ± 3.61 1.70 ± 1.15 1.10 ± 0.03 0.95 ± 0.05 0.88 ± 0.07 c d d bc a b c 200 244.33 ± 41.19 66.33 ± 1.20 50.00 ± 4.00 2.70 ± 1.13 1.22 ± 0.21 0.60 ± 0.02 0.50 ± 0.09 b c cd b ab c c 400 433.00 ± 19.93 128.67 ± 16.30 59.67 ± 5.51 4.43 ± 1.46 1.10 ± 0.10 0.48 ± 0.05 0.45 ± 0.06 a b bc b b c c 600 601.00 ± 7.94 202.33 ± 7.51 69.33 ± 6.03 5.10 ± 0.90 1.00 ± 0.01 0.46 ± 0.02 0.50 ± 0.03 a a b a b c b 800 603.67 ± 16.20 280.33 ± 13.32 78.67 ± 6.11 8.03 ± 0.95 0.75 ± 0.02 0.46 ± 0.03 0.61 ± 0.03 a a a a c d b 1000 626.67 ± 5.51 299.67 ± 20.50 89.33 ± 8.02 10.40 ± 2.03 0.63 ± 0.01 0.40 ± 0.01 0.64 ± 0.02 d e f f a a a S. indicum 100 102.00 ± 3.00 17.17 ± 1.11 20.33 ± 2.31 0.91 ± 0.20 1.02 ± 0.03 0.38 ± 0.03 0.40 ± 0.04 c d e e a b b 200 209.00 ± 11.30 31.13 ± 1.79 34.33 ± 0.58 2.00 ± 0.10 1.05 ± 0.05 0.34 ± 0.01 0.32 ± 0.02 b c d d a c d 400 411.33 ± 9.50 41.67 ± 2.89 43.67 ± 1.53 3.20 ± 0.95 1.03 ± 0.02 0.22 ± 0.01 0.22 ± 0.02 b b c c b c c 600 443.00 ± 38.11 56.07 ± 5.66 61.33 ± 1.53 4.17 ± 0.06 0.74 ± 0.06 0.20 ± 0.01 0.27 ± 0.02 a ab b b c d c 800 500.67 ± 17.62 59.97 ± 4.95 72.67 ± 1.16 7.24 ± 0.16 0.63 ± 0.02 0.17 ± 0.01 0.28 ± 0.02 a a a a d e c 1000 525.67 ± 6.43 64.89 ± 3.37 75.33 ± 0.58 8.13 ± 0.06 0.53 ± 0.01 0.15 ± 0.00 0.28 ± 0.01 notes: similar letters in same column are statistically non-significant according to d uncan’s ple Range Test (p < 0.05), data are means (n = 3 ±sd ), in superscript represent significantly highest followed by later alphabets for lower means. 58 H. AMIN ET AL. indicating that S. indicum can also be categorized as Pb phytostabilizer. 4. Conclusions From this study, it has been concluded that none of the plant species were identified as metal hyperaccumula- tors and not suitable for phytoextraction. Considering the rapid growth, biomass, accumulation efficiency, adaptive properties, tolerance, restoration potential towards Pb, and being leguminous and fast growing crop, C. tetragonoloba can be used as an effective tool to decontaminate Pb-polluted soils in quick and successive u fl shes than S. indicum . Furthermore, the value of BCFs, BACs, and TFs suggests that both the plant species were suitable for Pb phytostabilization but C. tetragonoloba was more potential candidates for phytoremediation than S. indicum. Moreover, both plants species have economic and ecological values. These plants can both remediate metal-contaminated sites and produce valu- able biomass, which can bring income for the owners of the sites. The harvested biomass could then be inciner - ated and disposed off or the accumulated metal could Figure 2. a ccumulation of pb in root (a) and shoot (b) of C. also be recovered for commercial uses and thus reused tertragonoloba and S. indicum after 12-week growth in soil as biofuel. Further work is needed to understand the medium with varying concentrations of pb. mechanisms of metal absorption and tolerance in plants. notes: similar letters are statistically non-significant according to d uncan’s Multiple Range Test (p < 0.05), data are means (n = 3 ± sd ), in superscript represent significantly highest followed by later alphabets for lower means. Disclosure statement No potential conflict of interest was reported by the authors. to them are dependent on the metal, its bioavailability, the plant species and its metabolism (D’Souza, Varun, References Pratas, & Paul, 2013). Abidi, N., Liyanage, S., Auld, D., Imel, R.K., Norman, L., Grover, K., … Trostle, C. (2015). 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Geology Ecology and Landscapes – Taylor & Francis
Published: Jan 2, 2018
Keywords: Soil pollution; lead; accumulation; phytoextraction; phytostablization
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