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GeoloGy, ecoloGy, and landscapes, 2018 Vol . 2, no . 1, 29– 38 https://doi.org/10.1080/24749508.2018.1438745 INWASCON OPEN ACCESS Comparative study of Zn-phytoextraction potential in guar (Cyamopsis tetragonoloba L.) and sesame (Sesamum indicum L.): tolerance and accumulation a a b c d Hira Amin , Basir Ahmed Arain , Muhammad Sadiq Abbasi , Taj Muhammad Jahangir and Farah Amin a b Institute of plant s ciences, University of sindh, Jamshoro, pakistan; d epartment of Mathematics & s tatistics, Quaid-e-a wam University of engineering, s cience & Technology, nawabshah, pakistan; Institute of a dvanced Research s tudies in chemical s ciences, University of sindh, Jamshoro, pakistan; national c entre of excellence in analytical chemistry, University of sindh, Jamshoro, p akistan ABSTRACT ARTICLE HISTORY Received 4 a ugust 2017 Phytoextraction is a plant-based technique for removing heavy metals from polluted soil. The a ccepted 20 o ctober 2017 experiment reported in this paper was undertaken to study the Zn phytoextraction potential of Cyamopsis tetragonoloba in comparison with Sesamum indicum in the framework of a pot KEYWORDS −1 experiment. Plants were subjected to six Zn concentrations (0, 50, 100, 200, 300, 400 mg kg s oil pollution; zinc; soil) for 90 days to investigate Zn tolerance and accumulation. Results demonstrated that, at phytoextraction; higher Zn levels, root, shoot lengths, biomass and chlorophyll content were all significantly accumulation; translocation reduced (p < 0.05). A steady increase in Zn accumulation with increasing concentration in soil was observed for all treatments. Both plant species had relatively high Zn tolerance and accumulation capacity, with C. tetragonoloba being more tolerant and having higher Zn −1 accumulation than S. indicum. At 400 mg Zn kg kg , accumulation of Zn in C. tetragonoloba −1 −1 −1 was highest in the root (439.33 mg kg ) followed by stem (436.00 mg kg ), leaf (40.67 mg kg ) −1 and pod (11.33 mg kg ). Considering the rapid growth, high biomass, tolerance, accumulation efficiency, bioconcentration factor (BCF), bioaccumulation coefficient (BAC) and translocation factor (TF) (all greater than 1) established C. tetragonoloba as a potential candidate plant for Zn phytoextraction. 1. Introduction pesticides, liming materials, or manures, being added to Zn-deficient agricultural soils to achieve enhanced plant Soil pollution by heavy metals released from anthropo- growth and productivity, has become major factors con- genic activities is a worldwide environmental problem. tributing elevated levels of Zn in world agricultural soils Toxic metals have made their entry into agricultural (Alloway, 2013; Douglas et al., 2017; Kabata-Pendias, soils primarily because of rapid industrialization, inap- 2011). propriate utilization and disposal of toxic metal con- Like other heavy metals, Zn is non-biodegradable taining wastes, excessive use of fertilizers and pesticides contaminant persist in the environment, inevitably accu- (Amel et al., 2016; Dmitry, Alexander, Naser, Ahmad, mulate and eventually get into the food chain (Sveta et & Eduarda, 2015). The most common heavy metal con- al., 2016). e Th toxicological impact of Zn depends on taminants frequently released in the environment are their concentration in the environmental context. At low Cd, Hg, Pb, Cr, Ni, Co, Cu and Zn (Subhashini, Swamy, levels, Zn plays an important role in several metabolic & Hema Krishna, 2013). Their presence in the soil may processes of plant; activate enzymes, involved in pro- leads to harmful effects on both the ecosystem and living tein synthesis and in carbohydrate, nucleic acid and lipid organisms (Demim et al., 2014). metabolism (Demim, Drouiche, Aouabed, & Semsari, Among heavy metals, zinc (Zn) is an essential trace 2013; Fässler, Robinson, Stauffer, & Gupta, 2010) but element belongs to the list of transition metals and stands at high doses Zn adversely aeff cts plants and cause 24th among the most abundant elements on the earth’s alterations in various morphological and physiological crust. In soil, Zn mainly occurs as sulphide (Neha, Hari, processes. Considering known toxic effects of Zn in & Balwinder, 2016; Pratap et al., 2014). Agricultural soil plants such as inhibited plant growth and development, is contaminated with zinc by natural and anthropogenic elevated oxidative stress, and impaired cellular metab- activities including mining and industrial processes and olism, their eventual impact on photosynthesis and agricultural practices. The use of commercial fertilizers, CONTACT Hira amin email@example.com © 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. 30 H. AMIN ET AL. Table 1. plant species selected for pot experiment. biosynthesis of chlorophyll as well as plant productivity (Pratap et al., 2014), root growth and mitotic efficiency, No. Botanical name Vernacular name Family chromosomal aberrations and nutrient accumulation 1 Cyamopsis tetragonolo- Guar Fabaceae ba l. abnormalities (Radha, Srivastava, Solomon, Shrivastava, 2 Sesamum indicum l. s esame pedaliaceae & Chandra, 2010), sustainable minimization of Zn in agricultural soils is imperative. Soil remediation by various physicochemical meth- and antioxidant contents (Saydut, Duz, Kaya, Kafadar, ods has been well documented in literature. However, & Hamamci, 2008). Sesame seed has one of the high- remediation of heavy metal polluted soils by tradi- est oil contents of any seed and is considered to be the tional physical and chemical methods are not suita- oldest oilseed crop known to man, highly resistant to ble for agricultural lands, required large investments drought and has the ability of growing where most crops and technological resources (Oh, Li, Cheng, Xie, & fail (Dawodu, Ayodele, & Bolanle-Ojo, 2014). Sesame Yonemochi, 2013). Thus, a plant-based technology has seeds have been used as an alternative feedstock for the emerged as a cure for the sustainable control of elevated production of a biodiesel fuel. The methyl ester of the levels of various toxic metals in soils and received great sesame plant can successfully be used as petrodiesel attention in recent years. Phytoextraction refers to the (Ahmad et al., 2011). Viscosity and density of methyl efficient use of metal-accumulating plants to transport esters of sesame seed oil are found to be very close to and concentrate metals from soil into the harvesta- that of diesel. The heating value (7.5%), calorific value ble parts of roots and shoot biomass, (i.e. root and (5.4%) of biodiesel is found to be slightly lower than that shoot) and appears to be a promising, cost-effective of diesel (Saydut et al., 2008). technology for the remediation of metal-polluted soils This experiment was set up to identify a plant spe- (Amanullah et al., 2016). cies that could tolerate concentrations of Zn in soil. Literature has reported about 500 vascular plant C. tetragonoloba and S. indicum are plant species with species for metal absorption from contaminated soil. rapid growth and good biomass production. It was The heavy metal uptake, accumulation, mechanism of hypothesized that plant species with high tolerance metal concentration, exclusion and compartmentation could then be tested for their phytoextraction poten- vary among different plant species and also between tial. Thus, the aims of the present investigation are (i) to various plant parts (Sharma, Singh, & Manchanda, study the effect of Zn on plant growth and physiology 2014; Singh & Agrawal, 2010). However, the use of and, (ii) to evaluate the phytoextraction potential of field crop plants for the management of long-term C. tetragonoloba and S. indicum, with respect to Zn pollutant dispersion has been given much emphasis concentrations. in this perspective to crop plants from Brassicaceae followed by Fabaceae, Asteraceae and Poaceae (Zaidi, Wani, & Khan, 2012). 2. Material and methods Guar (Cyamopsis tetragonoloba L.) is one of impor- 2.1. Seed collection and sterilization tant annual legume crops, belonging to the family Fabaceae. The endosperm of guar seeds contains gum, Seeds of the guar variety BR-99 were collected from the which is gaining importance as non-food item (Ashraf, Institute of Fodder Research Program and sesame variety Akhtar, Sarwar, & Ashraf, 2002). Recently, the oil indus- TH-6, from the Institute of Oilseeds Research Program, try has started using guar gum in hydraulic fracturing National Agricultural Research Centre (NARC), in which high pressure is used to crack rock. Guar gum Islamabad (Table 1). In order to avoid any microbial in the fracking fluid increases its viscosity and improves contamination, seeds were surface sterilized with 0.1% the efficiency of natural gas extraction. The increased HgCl for 10 min and washed 7 times with sterilized use of guar gum in oil fracking has boosted the demand water (Pourakbar, Khayami, Khara, & Farbidina, 2007). of guar worldwide (Abidi et al., 2015; Deepak, Sheweta, & Bhupendar, 2014). A key feature of legumes as a 2.2. Soil collection and preparation resource for phytoremediation is their role in providing Soil samples of sandy-loam soil were collected from additional N-compounds to the soil, thus improving its uncontaminated agricultural fields located in Jamshoro, fertility and ability to support biological growth (Xiuli Sindh, Pakistan, at depth of 0–15 cm using hand spade. et al., 2013). Equidistant (2 m) collected samples were homoge- On the other hand, sesame (Sesamum indicum L.) nized to prepare one bulk sample. For the greenhouse is an economically important oil seed crop of family experiment, soil was air dried (at room temperature for Pedaliaceae, planted in arid and semi-arid regions of 15 days) and ground to a final particle size of 2 mm. To the world (Elleuch, Besbes, Roiseux, Blecker, & Attia, enhance soil porosity, sand was mixed in 3:1 ratio with 2007). Sesame is widely used in pharmaceutical indus- sandy loam soil. try in many countries because of its high oil, protein GEOLOGY, ECOLOGY, AND LANDSCAPES 31 2.3. Soil measurements symptoms of metal toxicity exhibited by plants were vis- ually noted during the experimental period. Plants were For soil characterization, the soil samples were air dried harvested 12 weeks aer g ft ermination. Soil samples (in at room temperature, ground in a ceramic mortal to pass triplicate) were also collected for analysis of Zn content through a 2-mm mesh sieve, homogenized, and stored by an Atomic Absorption Spectrophotometer (AAnalyst in polyethylene bags for subsequent analysis (Table 2). 800, Perkin Elmer, USA). Plant growth and biochemical Soil pH was measured with a pH-meter (InoLab-WTB parameters (chlorophyll) were also measured. GmbH; Weilheim, Germany) using glass electrode at the 1:2 (w/v) ratio of soil to water suspension (Rachit, 2.6. Germination percentage Verma, Meena, Yashveer, & Shreya, 2016). The electri- cal conductivity (EC) was measured with an electrical e g Th ermination percentage, expressed as percentage of conductivity meter (WTW – 330i) at the 1:2 (w/v) ratio germinated seeds to the total number of viable seeds, is of soil to water suspension (Rachit et al., 2016). Organic calculated by the following equation: (Talebi, Nabavi, & matter (OM) and organic carbon (%) were measured Sohani, 2014) (1) % G =(Number of germinated seeds∕Total number of planted seeds)× 100 according to Walkley and Black (chromic acid titration) 2.7. Morphological parameters method (Fanrong et al., 2011). Plants were taken from each replicate to measure mor- phological parameters. Root length, shoot length were 2.4. Preliminary screening measured of each replicate with the help of scale. Root and shoot fresh weights were also measured with the In order to select the Zn concentration for treatments, help of analytical balance. Plant samples were air dried various doses of ZnSO .7H O (0, 50, 100, 200, 500, 700, 4 2 −1 for one week. Then, they were oven-dried at 80 °C to a 1000, 1500 and 2000 mg kg ) were tried in the prelim- constant weight and their dry weights recorded inary screening of the C. tetragonoloba and S. indicum for 20 days. Based on the Zn toxicity symptoms and morphological growth of the seedlings, the following 2.8. Estimation of chlorophyll contents −1 doses (0, 50, 100, 200, 300, 400 mg kg ) were finally Photosynthetic pigments, in fully expanded leaves from selected (Table 3). each treatment, were extracted using 0.5 g of fresh mate- rial, ground with 10 mL of 80% aqueous acetone. Aer ft 2.5. Pot experiment filtering, 1 mL of the suspension was diluted with a fur - ther 2 mL of acetone, and optical density were deter- Plastic pots were filled with 5 kg sieved soil, aer w ft hich mined with a UV-Visible spectrophotometer (Biochrom soil was artificially spiked with Zn (aqueous solution) Libra S22), using two wavelengths (663 and 645 nm) using ZnSO .7H O salt to each pot in increasing concen- 4 2 −1 against blank. Chlorophyll a (Chl a), chlorophyll b (Chl trations (50, 100, 200, 300, 400 mg kg ), each with three −1 b) and total chlorophyll contents (mg g f.w) were replicates and kept for 2 weeks to attain equilibrium. The obtained by calculation, following the method of Arnon clean soil without Zn spiking was used as control. Pots (1949). were arranged in a completely randomized design. Aer ft e fift en days of equilibration, 20 surface-sterilized seeds Chlorophyll a = (12.7 × OD 663) − (2.69 × OD 645) were sown per pot. One week aer s ft eed germination, × mg∕g FW plants were thinned to 5 per pot. A plastic tray was kept (2) wt below the treatment pot to collect any leachate, which Chlorophyll b = (29.9 × OD 645) − (4.68 × OD 663) was returned to the pots at next watering. The experi- V 1 ment was conducted in a greenhouse for 90 days. Any × × mg∕g FW 1000 wt (3) Table 2. The properties of soil. Total Chlorophyll = (20.7 × OD 645) − (8.02 × OD 663) Parameter Values obtained × mg∕g FW pH 6.89 ± 0.04 wt (4) −1 a e.c. (μs cm ) 1662 ± 11 organic carbon (%) 2.20 ± 0.04 organic matter (%) 3.79 ± 0.02 Table 3. Treatment levels selected for pot experiment. −1 Zinc (mg kg ) n.d .* total −1 Treatments (mg kg soil) notes: similar letters in same column are statistically non-significant according to d uncan’s Multiple Range Test (p < 0.05), data are means Heavy metal Salt used T1 T2 T3 T4 T5 T6 (n = 3 ± sd ), a in superscript represent significantly highest followed by Zinc (Zn) Znso .7H o 0 50 100 200 300 400 4 2 later alphabets for lower means; *n.d . = not detected. 32 H. AMIN ET AL. 2.9. Determination tolerance index e Z Th n concentration and accumulation in plant root and shoot were calculated by the following formula: Tolerance Index (TI) is expressed as the ratio between (Muhammad et al., 2014) the growth parameters (root/shoot length, root/shoot fresh and dry weight) of the plants in contaminated Zn concentration mg∕kg soil in relation to the growth parameters of plants from = reading × dilution factor∕dry wt.of plant parts non-polluted soil calculated by following equation: (6) according to Chen et al., (2011) Zn accumulation g∕plant = conc.of Zn Growth parameter Zn contaminated soil × dry wt.of plant organ TI = × 100 (5) Growth parameter (7) Control soil 2.12. Soil sample preparation, digestion and Zn 2.10. Quality control and quality assurance determination All the glassware used during the present experimen- Soil samples were air dried at room temperature, tation was of high quality, acid resistant Pyrex glass. ground, homogenized, and stored in polyethylene e a Th nalytical grade reagents with a certified purity of bags for subsequent analysis. Digestions of soil and 99% and stock metal standard solution (1000 ppm) for plant samples were done using aqua regia method AAS analysis were procured from E. Merck (Germany). (Ogunkunle et al., 2017). To quantify the Zn content in Working standards were prepared by appropriate dilu- soil, 1 g soil sample was digested using a wet digestion tions of stock standard solutions with double-distilled method with HNO and HCl (3:1 ratio v/v) and heated water. on a hot plate for 2 h at a temperature of 110 °C until the solution becomes clear. After cooling, the volume 2.11. Plant samples preparation, digestion and Zn was completed to 50 mL by adding distilled water. The determination solution was filtered through Whatman’s filter paper. The filtrate was analysed for Zn content by Atomic To determine Zn accumulation in different plant tissues Absorption Spectrophotometer. (i.e., root, stem, leaf and pod), harvested plants were washed thoroughly with running tap water, and then deionized water to remove adhered soil particles, oven- 2.13. Evaluation of phytoextraction efficiency dried at 80 °C till constant weight. The oven-dried sam- Phytoextraction potential of plants is influenced by the ples were ground thoroughly using a grinder and passed mobility and availability of contaminants in soil and through a 1.0-mm mesh sieve. The ground plant samples plants. To evaluate the phytoextraction potential of (0.5 g) were digested by HNO and HClO mixed at a 3 4 C. tetragonoloba and S. indicum, the following factors ratio of 3:1 (v/v) according to the protocols devised by were calculated based on simple ratios of contaminant Altaf et al., (2017). Aer di-acid dig ft estion, the volume concentration in plant parts and growth matrix (Rohan, was completed to 50 mL by adding distilled water. The Mayank, João, & Paul, 2013). solution was filtered through Whatman’s filter paper. e q Th uantification of zinc (Zn) in respective tissues 2.13.1. Bioconcentration factor (BCF) was carried out using atomic absorption spectrometer e Th bioconcentration factor (BCF) was calculated as the equipped with a zinc cathode lamp, under optimum ana- Zn concentration ratio in plant roots to soil, given in lytical conditions for the estimation of zinc. The opti- equation (8) mum conditions for AAS used throughout these studies [ Zn ] root given in Table 4. The standard calibration method was Bioconcentration Factor [BCF] = (8) [ Zn ] soil adopted for the quantification of results and triplicate samples were run to insure the precision of quantitative 2.13.2. Bioaccumulation coefficient (BAC) results. e b Th ioaccumulation coefficient (BAC) was calculated as a ratio of Zn in shoot to that in soil, given in Equation (9) Table 4. Measurement conditions of F-aas for zinc (Zn) deter - [ Zn ] shoot mination. Bioaccumulation Coeﬃcient [BAC]= [ Zn ] soil Parameters Values (9) Wave length (nm) 213.9 Hollow cathode lamp current (ma ) 5.0 2.13.3. Translocation factor (TF) Flame type air- c H 2 2 Background correction on e t Th ranslocation factor (TF) was determined as a ratio slit-width (nm) 1.0 of heavy metals in plant shoot to that in plant root, given Flame condition o xidizing expansion factor 1 in equation (10) GEOLOGY, ECOLOGY, AND LANDSCAPES 33 [ Zn ] shoot Translocation Factor [TF]= (10) [ Zn ] root 2.14. Statistical analysis All experiments were conducted with three replicates and the data collected were analysed statistically using PASW Statistics 18 (SPSS Inc., Chicago, IL, USA). To compare the means of the treatments, analysis of var- iance (ANOVA) was performed followed by Duncan’s multiple range post hoc tests at significance level of p < 0.05 to observe significance difference among means. Figure 1. eec ff t of Zn stress on germination of C. tertragonoloba and S. indicum seeds after 7 days in soil medium with varying 3. Results and discussion concentrations of Zn. notes: similar letters are statistically non-significant according to d uncan’s 3.1. Soil characterization Multiple Range Test (p<0.05), data are means (n = 3 ± sd ), a in superscript represent significantly highest followed by later alphabets for lower means. e s Th oil was sandy loam with slightly acidic to neutral pH (6.89), organic carbon (2.20%), organic matter contents ae ff cted in terms of root and shoot lengths (Table 5). (3.79%) and electrical conductivity (1662 μS/cm). Among In C. tetragonoloba and S. indicum, the longest roots soil properties, soil pH was found to play the most impor- (16.07 cm and 12.38 cm) and shoots (117.70 cm and tant role in determining metal speciation, solubility from 120.00 cm) were observed in control treatments with mineral surfaces and eventual bioavailability of metals −1 −1 0 mg Zn kg , respectively. At 400 mg Zn kg concen- due to its strong effect on solubility and speciation of met - tration, root length decreased by 12.24 cm and 9.65 cm als both in the soil as a whole and particularly in the soil while shoot length reduced by 90.88 cm and 86.32 cm solution. The mobility and bioavailability of heavy metals in both C. tetragonoloba and S. indicum, respectively. increased with decreased soil pH, whereas organic matter Growth inhibition is a general phenomenon associated supplies organic chemicals to the soil solution that can with most of the heavy metals. Higher level of Zn in serve as chelates and increase metal mobility and avail- the soil directly influences root growth and specific ability to plants (Fanrong et al., 2011). Such factors may superficial area, decreasing the capacity of absorption act individually or in combination with each other and of water and nutrients. Toxic effect of Zn in reduced may alter the soil behaviour of the zinc present, as well seedling height is mainly due to the interference with as the rate of uptake by plants. So, in accordance with metabolic activities of the plant (Mukhopadhyay et al., soil properties, Zn is more mobile and more bioavailable. 2013) ultimately leading to reduction in growth of the plant species, as reported by Luo et al. (2010). 3.2. Zn-induced phytotoxicity Zn contamination showed significant (p < 0.05) negative impacts on both fresh and dry biomass of Gradual increase in Zn concentration significantly C. tetragonoloba and S. indicum (Table 5). Compared (p < 0.05) reduced all tested growth and biochemical −1 to control treatments, Zn stress at 400 mg kg reduced parameter (chlorophyll content) in two plant species. −1 −1 root fresh weight (7.63 g plant and 7.25 g plant ) and In the current investigation, the seed germination of −1 −1 shoot fresh weight (24.17 g plant and 18.00 g plant ) in C. tetragonoloba and S. indicum was not influence sig- C. tetragonoloba and S. indicum, respectively. The dry bio - nificantly (p > 0.05) by Zn concentrations (Figure 1). mass follows the same trend as fresh weight. Compared Zn is an essential micronutrient that promotes seed ger- −1 to control treatments, Zn stress at 400 mg kg reduced mination and growth at optimal concentration but at −1 −1 root dry weight from (3.71 g plant and 2.97 g plant ) higher levels inhibits germination and growth (Kabata- −1 −1 and shoot dry weight (9.67 g plant and 6.33 g plant ) Pendias, 2011). The seeds of guar and sesame were in C. tetragonoloba and S. indicum, respectively. Plant able to germinate in the presence of low to moderate biomass is a good indicator for characterizing the growth concentrations of Zn in soil but germination reduced performance of plants in the presence of heavy metal. −1 at 400 mg Zn kg as compared to control. According Decrease in plant biomass may be associated with dis- to Li, Khan, Yamaguchi, and Kamiya (2005), seed is the turbed metabolic activities due to reduced uptake of only stage in the life cycle of plants well protected against essential nutrients when grown under Zn stress (Li the metal stress. The seed coat acts like a barrier between et al., 2012). Plants produce high aboveground biomass the embryo and the environment; protects the embryo and possess the ability to accumulate heavy metals. This against the heavy metals toxicity. ability is used for phytoextraction purposes including Seedling’s height (root and shoot length) is also removal of heavy metals from polluted soil. Our results among primary determinants of plant growth. Under for Zn phytotoxcity were evident from stunted growth Zn stress the growth was significantly (p < 0.05) 34 H. AMIN ET AL. Table 5. Zn-induced phytotoxic effects on growth parameters of Cyamopsis tetragonoloba l. and Sesamum indicum l. Root fresh Shoot fresh Root dry Shoot dry Zn applied Root length Shoot length weight weight weight weight −1 −1 −1 −1 −1 (mg kg ) (cm) (cm) (g plant ) (g plant ) (g plant ) (g plant ) a a a a a a C. tetragonoloba 0 16.07 ± 0.31 117.70 ± 1.06 13.30 ± 0.84 38.47 ± 0.55 8.07 ± 0.15 21.99 ± 0.99 a a b a a b 50 15.15 ± 0.77 116.28 ± 1.53 11.33 ± 0.94 37.08 ± 8.29 7.61 ± 0.09 17.93 ± 0.12 ab b bc ab a bc 100 14.84 ± 0.15 110.31 ± 2.91 10.22 ± 0.38 31.53 ± 5.54 7.07 ± 0.07 16.63 ± 0.57 bc b c b b bc 200 13.62 ± 0.15 107.10 ± 2.46 9.76 ± 0.34 28.38 ± 0.68 5.51 ± 0.88 14.70 ± 2.49 cd c d b bc c 300 13.16 ± 0.15 91.80 ± 2.22 8.59 ± 0.72 27.07 ± 2.64 4.51 ± 0.88 13.33 ± 3.05 d c d b c d 400 12.24 ± 1.53 90.88 ± 3.06 7.63 ± 0.43 24.17 ± 1.05 3.71 ± 1.22 9.67 ± 2.08 a a a a a a S. indicum 0 12.38 ± 0.43 120.00 ± 1.00 12.07 ± 0.62 37.33 ± 0.58 7.07 ± 0.12 20.00 ± 1.00 ab b ab b b b 50 11.38 ± 0.29 104.83 ± 1.44 10.24 ± 1.95 30.67 ± 0.58 6.03 ± 0.06 14.67 ± 0.58 bc b bc c c c 100 10.94 ± 1.44 104.40 ± 1.44 8.66 ± 2.19 28.37 ± 1.58 5.13 ± 0.23 12.67 ± 0.58 bc c bc d d d 200 10.18 ± 0.65 97.42 ± 1.55 7.84 ± 1.31 23.67 ± 1.53 4.17 ± 0.29 10.67 ± 0.58 c d bc e e e 300 9.94 ± 0.29 87.11 ± 2.59 7.51 ± 0.63 21.00 ± 1.00 3.43 ± 0.40 8.13 ± 0.12 c d c f f f 400 9.65 ± 0.14 86.32 ± 1.51 7.25 ± 1.48 18.00 ± 1.00 2.97 ± 0.06 6.33 ± 1.24 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 ), a in superscript represent significantly highest followed by later alphabets for lower means. and reduced fresh and dry weights that are in conso- nance with the same phenomenon observed in Jatropha seedlings under Zn stress (Luo et al., 2010). Chlorophyll contents decreased significantly (p < 0.05) with gradual increase in Zn concentration −1 from 0 to 400 mg kg (Figure 2). In C. tetragonoloba and S. indicum, the maximum amount of chlorophyll con- −1 tents were measured at 50 mg kg , while the lowest con- −1 −1 centration of chlorophyll a (0.76 mg g and 0.68 mg g ), −1 −1 chlorophyll b (0.25 mg g and 0.21 mg g ) and total −1 −1 chlorophyll (1.01 mg g and 0.89 mg g ) was at 400 mg −1 Zn kg , respectively. Reduction in chlorophyll contents may be due to competition of Zn with iron for binding with protoporphyin, a main precursor of chlorophyll synthesis. Production of reactive oxygen species (ROS) upon Zn exposure inhibits chlorophyll production by damaging the pigment–protein complexes located in thylakoid membranes (Sagardoy et al., 2010; Vassilev, Perez-Sanz, Cuypers, & Vangronsveld, 2007). Tolerance indices (TIs) were also aeff cted by Zn toxicity. Both plant species had different tolerance indices (TIs) under Zn stress (Table 6). In this study, C. tetragonoloba was more tolerant to Zn stress than −1 S. indicum. At 400 mg kg Zn treatment, C. tetragonoloba and S. indicum had the TIs for root lengths (76.09% and 88.00%) and shoot lengths (77.23% and 71.93%), root fresh weights (57.68% and 60.15%) and shoot fresh weights (62.88% and 48.20%), root dry weights (46.11% and 42.00%) and shoot dry weights (43.81% and 31.53%), respectively. Metal tolerance of plant is a prerequisite for studying the plant–metal interactions Figure 2. eec ff t of Zn stress on photosynthetic pigments chlorophyll-a (a) chlorophyll-b (b) and total chlorophyll (a + b) before application for phytoextraction. Plant tolerance (c), on C. tertragonoloba and S. indicum after 90 days growth in to heavy metal stress is estimated based on their root soil medium with varying concentrations of Zn. and/or shoot growth inhibition by the metal present in notes: similar letters are statistically non-significant according to d uncan’s a medium. Growth inhibition is a common response to Multiple Range Test (p < 0.05), data are means (n = 3 ± sd ), a in superscript represent significantly highest followed by later alphabets for lower means. heavy metal stress and is also one of the most important agricultural indices of heavy metal tolerance. According to Audet and Charest (2007), if TI values less than 1, this tolerance with a net increase in biomass (hyper accumu- indicates that the plant sue ff red a stress due to metal pol - lator). If TI values equal to 1, the plant is unae ff cted by lution with a net decrease in biomass. By contrast, if TI metal pollution, indicate no difference relative to control values greater than 1 suggest that plants have developed treatments. GEOLOGY, ECOLOGY, AND LANDSCAPES 35 3.3. Zn concentration in plant tissues in plants (Hanen et al., 2010). A significant rise in Zn accumulation per plant in root and shoot of both the e Th Zn concentration among the different plant tissues plant species varied with respect to Zn concentrations in (root, stem leaf and pod) of both plant species are pre- soil (Figure 3). In this study, both C. tetragonoloba and sented in Table 7. In C. tetragonoloba, the highest con- S. indicum accumulated more Zn contents in shoot than −1 centration of Zn accumulated in the root: 439.33 mg kg root. Root accumulation of Zn in C. tetragonoloba was −1 −1 followed by stem: 436.00 mg kg , leaf: 40.67 mg kg , −1 increased from 50 to 400 mg Zn kg ; however, in S. indi- −1 −1 and pod: 11.33 mg kg at 400 mg Zn kg . However, cum, the accumulation was increased from 50 to 200 mg in S. indicum, Zn accumulated primarily in the leaf: −1 −1 Zn kg , while decreased at 300 and 400 mg Zn kg . The −1 282.33 mg kg , with small amount being transferred highest value of Zn accumulation in C. tetragonoloba −1 −1 to root: 273.67 mg kg , stem: 121.33 mg kg , and pod: −1 −1 root (1615.51 μg plant ) was at 400 mg Zn kg , while −1 −1 12.33 mg kg at 400 mg Zn kg . The high Zn contents in −1 in S. indicum root accumulation (874 μg plant ) at the plant tissues are clearly related to the concentration of −1 300 mg Zn kg . Likewise, shoot accumulation of Zn metal in the growing environment. Studies have shown in C. tetragonoloba was increased from 50 to 300 mg the uptake of metals; their partition and translocation to −1 −1 Zn kg , while decreased at 400 mg Zn kg ; however, different plant parts, as well as the degree of tolerance −1 in S. indicum, increased from 50 to 200 mg Zn kg , to them are dependent on the metal, its availability, the −1 while decreased at 300 and 400 mg Zn kg . The high- plant species, and its metabolism (Rohan et al., 2013). est value of Zn accumulation in C. tetragonoloba shoot e Th Zn accumulation capacity, based on their availabili - −1 −1 (4873.45 μg plant ) was at 300 mg Zn kg , while in ties in the soil, varies greatly among different plants spe - S. indicum the highest shoot accumulation (3155.33 μg cies and cultivars, and is also ae ff cted by various edaphic −1 −1 plant ) was at 200 mg Zn kg . The decrease in root and conditions (Abioye, Ekundayo, & Aransiola, 2015). shoot accumulation is related with high concentration of Zn in soil that ae ff cts the plant biomass production. 3.4. Zn accumulation in root and shoot u Th s, in order to evaluate the accumulation, it is neces- sary to take biomass into consideration. Accumulation Beside concentrations, a total amount of metals accumu- of elements in plant biomass always depends on both lated in the shoots is considered as the most important concentration and biomass (Vymazal, 2016). parameter to evaluate the potential of phytoextraction Table 6. eec ff t of Zn stress on the tolerance indices (TIs) of Cyamopsis tetragonoloba l. and Sesamum indicum l. Tolerance indices Zn applied Root length Shoot length Root fresh Shoot fresh Root dry Shoot dry −1 Plant species (mg kg ) (%) (%) weight (%) weight (%) weight (%) weight (%) a a a a a a C. tetragonoloba 50 94.25 ± 2.96 98.79 ± 0.85 85.35 ± 7.94 96.57 ± 22.70 94.28 ± 1.38 81.67 ± 4.13 ab b ab ab a ab 100 92.39 ± 0.81 93.72 ± 1.92 77.15 ± 6.60 82.08 ± 15.33 87.66 ± 0.80 75.75 ± 4.92 bc b ab ab b ab 200 84.79 ± 2.57 90.99 ± 1.50 73.49 ± 2.50 73.78 ± 0.81 68.41 ± 12.23 67.06 ± 12.99 cd c bc b bc bc 300 81.94 ± 2.51 77.53 ± 3.14 64.99 ± 9.17 70.45 ± 7.76 56.02 ± 12.02 60.57 ± 13.17 d c c b c c 400 76.09 ± 8.08 77.23 ± 3.17 57.68 ± 6.65 62.88 ± 3.57 46.11 ± 16.11 43.81 ± 7.97 a a a a a a S. indicum 50 91.99 ± 5.54 87.37 ± 1.93 84.51 ± 12.78 82.15 ± 1.44 85.40 ± 1.92 73.54 ± 6.27 a a ab b b b 100 88.71 ± 14.73 87.01 ± 1.93 71.44 ± 16.28 76.03 ± 5.16 72.67 ± 3.99 63.52 ± 5.78 a b ab c c c 200 82.36 ± 8.10 81.18 ± 0.62 64.79 ± 8.77 63.37 ± 3.42 58.99 ± 4.65 53.43 ± 4.05 a c ab d d d 300 80.35 ± 5.13 72.61 ± 2.75 62.21 ± 2.06 56.26 ± 2.84 48.58 ± 5.71 40.74 ± 2.15 a c b e d e 400 88.00 ± 3.89 71.93 ± 0.98 60.15 ± 12.04 48.20 ± 2.06 42.00 ± 1.49 31.53 ± 5.01 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 ), a in superscript represent significantly highest followed by later alphabets for lower means. Table 7. Zn concentration, bioconcentration factor (BcF), bioaccumulation factor (Bac ) and translocation factor (TF) of Cyamopsis tetragonoloba l. and Sesamum indicum l. Zn concentration Zn applied Pod −1 −1 −1 −1 −1 Plant species (mg kg ) Root (mg kg ) Stem (mg kg ) Leaf (mg kg ) (mg kg ) BCF BAC TF e de a d a a a C. tetragonolo- 50 55.33 ± 2.52 35.33 ± 4.16 56.00 ± 1.00 3.03 ± 1.95 1.11 ± 0.05 1.89 ± 0.05 1.72 ± 0.07 d d d c a c b ba 100 105.67 ± 0.58 79.33 ± 2.08 20.33 ± 4.04 6.33 ± 1.15 1.06 ± 0.01 1.06 ± 0.03 1.00 ± 0.03 c c c b a c b 200 201.67 ± 15.89 183.33 ± 4.93 30.33 ± 3.22 8.67 ± 0.58 1.01 ± 0.08 1.11 ± 0.02 1.11 ± 0.11 b b c ab a b b 300 325.33 ± 17.89 321.00 ± 0.00 34.33 ± 0.58 10.33 ± 0.58 1.08 ± 0.06 1.22 ± 0.00 1.13 ± 0.06 a a b a a b b 400 439.33 ± 16.50 436.00 ± 6.93 40.67 ± 0.58 11.33 ± 0.58 1.09 ± 0.04 1.22 ± 0.02 1.11 ± 0.06 e d e c b b b S. indicum 50 33.33 ± 4.16 12.33 ± 0.58 39.33 ± 4.36 6.33 ± 1.53 0.67 ± 0.08 1.16 ± 0.02 1.75 ± 0.18 d c d c b a a 100 72.67 ± 10.97 60.33 ± 6.03 72.33 ± 3.22 7.33 ± 0.58 0.73 ± 0.11 1.40 ± 0.07 1.96 ± 0.39 c b c b a a b 200 189.33 ± 3.06 82.33 ± 0.58 203.33 ± 15.28 10.00 ± 1.00 0.95 ± 0.02 1.48 ± 0.08 1.56 ± 0.06 b b b ab a b b 300 254.33 ± 4.04 92.67 ± 4.62 259.33 ± 8.62 10.67 ± 0.58 0.85 ± 0.01 1.21 ± 0.04 1.43 ± 0.04 a a a a b c b 400 273.67 ± 5.51 121.33 ± 10.50 282.33 ± 2.52 12.33 ± 1.53 0.68 ± 0.01 1.04 ± 0.03 1.52 ± 0.06 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 ), a in superscript represent significantly highest followed by later alphabets for lower means. 36 H. AMIN ET AL. and fast-growing crop, C. tetragonoloba can be used as an effective tool to decontaminate Zn polluted soils in quick and successive u fl shes than S. indicum. With application of these plants in the management and remediation of contaminated environment, the great positive character- istics are that the cost is very low in comparison to other physiochemical methods, and can remove pollutants from soil and reduce their movement towards ground- water, sustains the soil properties, and may improve soil quality and productivity. Moreover, these plants can both remediate brownfields and produce valuable biomass, which can bring income for the owners of the contaminated sites. The harvested biomass could then be incinerated and disposed of or the accumulated metal could also be recovered for commercial uses and thus recycled and reused as biofuel. All in all, phytoextrac- tion is a less invasive and cheaper method than stand- ard techniques, as well as more environment-friendly. It would be a reasonable choice to grow these plants and absorb the hazardous materials from the brownfield and the prevention of future browne fi lds emerging in indus - Figure 3. a ccumulation of Zn in root (a) and shoot (b) of C. trial sectors. Further work is needed to understand the tertragonoloba and S. indicum after 90 days growth in soil mechanisms of targeted metal absorption and tolerance medium with varying concentrations of Zn. 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 ), a in superscript represent significantly highest followed by later alphabets for lower means. Disclosure statement 3.5. 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Geology Ecology and Landscapes – Taylor & Francis
Published: Jan 2, 2018
Keywords: Soil pollution; zinc; phytoextraction; accumulation; translocation
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