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Effect of gibberellic acid on growth, photosynthesis and antioxidant defense system of wheat under zinc oxide nanoparticle stress
Environmental Pollution 254 (2019) 113109
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Effect of gibberellic acid on growth, photosynthesis and antioxidant defense system of wheat under zinc oxide nanoparticle stress* Azka Iftikhar a, Shafaqat Ali a, Tahira Yasmeen a, Muhammad Saleem Arif a, Muhammad Zubair b, Muhammad Rizwan a, *, Haifa Abdulaziz S. Alhaithloul c, Aisha A.M. Alayafi d, Mona H. Soliman e, f a
Department of Environmental Sciences and Engineering, Government College University, Faisalabad, Pakistan Department of Bioinformatics & Biotechnology, Government College University, Faisalabad, Pakistan Biology Department, College of Science, Jouf University, Sakaka, 2014, Saudi Arabia d Biological Sciences Department, Faculty of Science, University of Jeddah, Jeddah, Saudi Arabia e Biology Department, Faculty of Science, Taibah University, Al-Sharm, Yanbu El-Bahr, Yanbu 46429, Saudi Arabia f Department of Botany and Microbiology, Faculty of Science, Cairo University, Giza, 12613, Egypt b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 July 2019 Received in revised form 11 August 2019 Accepted 23 August 2019 Available online 28 August 2019
The production and soil accumulation of nanoparticles (NPs) from the industrial sector has increased concerns about their toxic effects in plants which needs the research to explore the ways of reducing NPs toxicity in pants. The gibberellic acid (GA) has been found to reduce abiotic stresses in plants. However, the effect of GA in reducing zinc oxide (ZnO) NPs-mediated toxicity in plants remains unclear. In this study, foliar application of GA was used to explore the possible role in reducing ZnO NPs toxicity in wheat (Triticum aestivum L.) plants. The plants were grown in pots spiked with ZnO NPs (0, 300, 600, 900, 1200 mg/kg) and GA (0, 100, 200 mg/L) was foliar sprayed at different times during the growth period under ambient environmental conditions. Our results demonstrated that GA inhibited the toxicity of ZnO NPs in wheat especially at higher levels of NPs. The GA application improved the plant biomass, photosynthesis, nutrients, and yield under ZnO NPs stress. The GA reduced the Zn accumulation, and reactive oxygen species generation in plants caused by toxicity of NPs. The protective effect of GA in decreasing ZnO NPs-induced oxidative stress was related to GA-mediated enhancement in antioxidant enzymes in plants. The role of GA in enhancing tolerance of wheat against ZnO NPs was further confirmed by the enhancement in nutrient contents in shoots and roots of wheat. Overall, our study provides the evidence that GA can reduce ZnO NPs-induced toxicity in wheat and probably in other crops which needs further in-depth investigation. © 2019 Elsevier Ltd. All rights reserved.
Keywords: Antioxidant Gibberellic acid Phytotoxicity Wheat Zinc oxide nanoparticles
1. Introduction The production and environmental application of nanomaterials (NPs) has been increasing at an alarming rate worldwide especially during the last decade (Rizwan et al., 2017a). Release of NPs in the different environmental compartments can take place naturally, accidently, and intentionally (De La Torre-Roche et al., 2013; Corsi et al., 2018). The NPs have been employed in different industrial and agricultural sectors (Li et al., 2017; Rafique et al., 2018). The
* €rg Rinklebe. This paper has been recommended for acceptance by Dr. Jo * Corresponding author. E-mail address: [email protected] (M. Rizwan).
https://doi.org/10.1016/j.envpol.2019.113109 0269-7491/© 2019 Elsevier Ltd. All rights reserved.
extensive exposure of NPs may enhance the release of NPs in environmental compartments (Rizwan et al., 2017a). Due to nano size in nature, the NPs have unique attributes including high surface area, reactivity and solubility make them dangerous than their counterparts (Servin et al., 2012; De La Torre-Roche et al., 2013). Once in the environment, NPs may cause positive and negative effects on the living things depending upon their size, dose, duration of exposure etc. All the NPs released into the environment finally end up in the soil which might be through direct soil entrance of NPs or indirect such as through water, and aerial depositions (Pan and Xing, 2012; Ma et al., 2015; Mohamed et al., 2017). Recently, the presence of NPs in the soil has been increasing and is a popular subject of research. The increasing concentrations of NPs in the soil may cause adverse impacts on the
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plants grown in these soils. There is an increasing amount of investigation on the toxic effect of NPs on different plants (Rizwan et al., 2017a; Abdel-Aziz and Rizwan, 2019). First, the removal of positive ions from NPs in the growth medium might be a possible cause of NPs phytotoxicity. Secondly, NPs may directly disrupt the membranes of plants or DNA damage. Furthermore, NPs enhance the production of reactive oxygen species (ROS), such as superoxide radical (O2) and hydrogen peroxide (H2O2) generation. The excess production of ROS can cause lipid membrane peroxidation and damage at cellular level, which has been suggested as one of the primary reasons related to nano-toxicity in general. NPs-mediated toxic effects in plants via ROS have been extensively studied and clarified in the previously published reports (Rizwan et al., 2017a; Abdel-Aziz and Rizwan, 2019; Abbas et al., 2019). These reports deepened our knowledge on the toxicity of NPs in plants. Among NPs, metallic NPs such as zinc oxide (ZnO) NPs are being incorporated into the arable soils continuously due to the wide consideration of ZnO NPs in the agricultural and industrial sectors (Lin and Xing, 2007; Munir et al., 2018; Hussain et al., 2018). The plants may accumulate ZnO NPs via roots and translocate them to the aerial parts (Moghaddasi et al., 2013; Dogaroglu and Koleli, 2017). The numerous studies reported the adverse impacts of ZnO NPs in plants at physiological and biochemical levels (Chen et al., 2015; Dogaroglu and Koleli, 2017; Wang et al., 2018). The ZnO NPs caused oxidative-stress in Vicia faba and tobacco when the plants were exposed to different NPs levels (0.2e0.8 g/L ZnO NPs) (Ghosh et al., 2016). Low levels (1e25 mg/kg) of ZnO NPs showed positive effects on cucumber plants, whereas higher levels of these NPs were toxic to plants under hydroponic conditions (Moghaddasi et al., 2013). The ZnO NPs diminished the root and shoot growth and photosynthesis of tomato (Wang et al., 2018). ZnO NPs are more toxic to plants when compared with their bulk counterparts (Stampoulis et al., 2009; Moghaddasi et al., 2017). It is demonstrated that ZnO NPs were highly toxic to barley plants than TiO2 NPs (Dogaroglu and Koleli, 2017). The above studies highlighted that the negative impacts of ZnO NPs on plants depend upon the concentrations of the NPs along with other factors. However, to date, little knowledge is available regarding the amelioration of NPs-induced toxic effects in plants. Considering the negative impacts of ZnO NPs at elevated concentrations in plants, it is therefore needed to find suitable ways to prevent the ZnO NPs toxicity in plants and their accumulation in the food chain. Gibberellic acid (GA), an important signalling plant hormone, stimulate various plant developmental and physiological processes, that includes seed germination, flowering, cell division and maturity, root formation, etc. GA also enhances the tolerance of plants to environmental stresses including salt, chilling, drought and trace element stress (Saleem et al., 2015; Upreti and Sharma, 2016). GA provide defense for plants in opposition to the environmental stresses by regulating antioxidant enzyme activity as well as reducing the extreme amount of intracellular ROS under stressful conditions (Jaleel et al., 2010; Wen et al., 2010). For instance, it has been depicted that exogenous GA alleviate oxidative stress in wheat due to the salt stress by increasing the nutrient contents which improved the yield of plants (Ashraf et al., 2002). Recent study also found that GA effectively reduced the chromium (Cr) contents and improved the yield of sunflower under Cr stress (Saleem et al., 2015). The GA application improved the growth of Cr-stressed pea plants by improving the antioxidant enzymes, which countered the toxic effects (Gangwar et al., 2011). Therefore, it is logical to hypothesize that GA can be used to ameliorate toxicity due to ZnO NPs in plants. Due to the wide use of ZnO NPs worldwide, the role of GA on ZnO NPs toxicity in wheat have been evaluated in this study. Wheat (Triticum aestivum L.) is one of the major cereal crops which is being
cultivated widespread around the globe. Thus, wheat was chosen as a model crop plant to investigate the impacts of GA on these NPs. The aim of this current study was to explore the response of foliar application of different concentrations of GA on wheat crop to a soil contamination by different concentrations of ZnO NPs. It was hypothesized that GA may alleviate ZnO NPs toxicity in wheat by reducing the oxidative stress caused by NPs and enhancing the photosynthesis and mineral accumulation by plants under NPs stress. 2. Materials and methods 2.1. Soil sampling and analysis The soil was sampled from the agricultural farms located in the research area of University of Agriculture Faisalabad, Pakistan. The soil sampling depth was about 0e20 cm and after sampling all the materials such as plant roots and debris were removed from the samples. The soil was air-dried under shade and sieved and used in the experiment. The standard procedures were used for the characterization of the soil such as soil texture was measured by hydrometric method (Bouyoucos, 1962). The soil pH was recorded by the pH meter and electrical conductivity of the same extract (EC) was determined by EC meter (Jenway Limited Model-4070, England) after calibration. The organic matter level of the soil was determined by using Walkley and Black (1934) method. The cations and anions were determined by standard procedures (US Salinity Laboratory Staff, 1954; Page et al., 1982). The measured properties of the experimental soil have been given in Table 1. 2.2. Soil spiking with NPs and plant growth The soil was spiked with different concentrations of ZnO NPs those were purchased from Alfa Aesar. The ZnO NPs had a purity of 99%, and size of 20e30 nm APS powder, with a density of 5.606. The solutions were prepared with different levels of ZnO NPs and were ultrasonicated and mixed in the soil with final levels of 300, 600, 900, and 1200 mg per kg of air-dried soil. After one weeks of soil spiking, the wheat seeds were sown in the pots amended with NPs containing a control (without NPs treatments) under ambient conditions (approximately 64 ± 5% relative humidity and 32/21 C day night average temperature at the time of sowing). Initially, 10
Table 1 Selected properties of the soil. Parameter
Units
Value
Textural class Sand Silt Clay pH EC CO23 HCO 3 Cl SO24 Ca2þ þ Mg2þ Naþ Kþ SAR CEC CaCO3 OM Total Zn Total Mn Total Fe
e % % % e dS m1 mmolc L1 mmolc L1 mmolc L1 mmolc L1 mmolc L1 mmolc L1 mmolc L1 (mmol L1)1/2 cmolc kg1 % % mg kg1 mg kg1 mg kg1
Sandy clay loam 43 26 31 7.82 1.42 Nil 2.55 3.79 6.23a 7.94 4.84 1.62 2.04 4.86 1.59 0.73 34.57 41.29 125.05
a
- Determined by difference ¼ Total soluble salts - (CO2 3 þ HCO3 þ Cl ).
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seeds were sown in each pot and then thinned to 5 seedlings in each pot after seven days of germination. The GA was applied through foliar spray after thinning the plants, whereas second, third, and fourth foliar sprays were done after fourth, sixth, and eighth week of sowing the seeds. There were three levels (0, 100, and 200 mg/L) of GA used in the study. During GA foliar treatment, replications of each treatment were grouped to ensure homogenous application of GA in each replicate. The control plants were sprayed with d-H2O and total volume used of each treatment was 1.5 litters. There were total five treatments of NPs, three treatments of GA with four replications of each treatment. Recommended rates of NPK fertilizers (120-50-25 kg/ha, respectively) were added in the pots by using salts such as urea, diammonium phosphate and sulfate of potash. The pots were rotated randomly and irrigated with tap water to ensure 70% soil moisture contents twice a week. 2.3. Harvesting and sampling
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A procedure detailed by Dionisio-Sese and Tobita (1998) was employed to estimate EL from leaves. The small pieces of leaves of appropriate size were made and inserted in the tubes already containing 8 ml of d-H2O. The tubes were heated at 32 C for 2 h and then measured the EC1 of the solution just after cooling the solution. Again, the same solution with samples was heated at 121 C for 20 min and recorded the EC2 of the solution after cooling at about room temperature. The below equation was used to calculate EL. EL ¼ (EC1/EC2) 100
(1)
The lipid peroxidation in leaves was estimated in the form of MDA (a product of lipid peroxidation). For this, the thiobabituric acid (TBA) reaction was used as described by Heath and Packer (1968) with little modification thereafter Dhindsa et al., (1981) and Zhang and Kirkham (1994). 2.6. Determination of nutrient elements in plants
The harvesting of the wheat was done at maturity (124 days of seed sowing) and were separated into roots, shoots, and grains. At the time of harvesting, plant height and spike length were recorded by meter scale. The aboveground parts were washed with tap water and then with d-H2O to ensure the removal of any undesired particle on the plant samples. The roots were carefully removed from the soil of each pot and washed with HCl (0.1 M) to ensure the removal of metals adhered to the surface of the roots and then the roots were washed with tap water followed by washing with distilled water. All the plant samples were dried by placing in an oven at about 65 ± 5 C for 72 h. After this, the dry biomasses were recorded and crushed the samples for elemental analysis.
For the measurement of nutrient elements in plants, the samples (0.5 g) ere digested in the mixture of nitric and perchloric acid (3:1, v:v). The mixture was heated at 350 C until a colorless solution and then the specific volume was made and filtered the solutions. The P concentrations were determined by the procedure of Ohno and Zibilske (1991) by taking the readings at 630 nm with a spectrophotometer after the development of green color in the solutions. The concentrations of potassium (K), iron (Fe), zinc (Zn), and manganese (Mn) were determined by Atomic Absorption. Spectrophotometer (Analytik Jena novAA 350).
2.4. Determination of photosynthetic pigments
2.7. Statistical analyses
Plant leaf samples were collected for the measurement of photosynthetic pigments after 75 days of seed sowing when the difference was clear among the treatments. The chlorophyll contents were extracted from the leaves by using acetone solution (85% v/v) under dark environment at 4 C. After this, readings were taken by spectrophotometer at different wavelengths and chlorophyll contents were measured with standard equations (Lichtenthaler, 1987).
SPSS 21.0 software was used for statistical analysis. All parameters were examined using two-way analysis of variance (ANOVA). For means comparison and P value Tukey test was used, considered the significant at 0.05. 3. Results 3.1. Effect of GA on wheat growth and photosynthesis under NPs stress
2.5. Determination of oxidative stress and antioxidant enzymes Electrolyte leakage (EL), hydrogen peroxide (H2O2), malondialdehyde (MDA), and antioxidant enzymes in leaves such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) were measured in leaves of wheat after 75 days of seed sowing. For this, leaf samples were taken, washed and crushed in liquid N2 with mortar and pestle. The crushed samples were treated with 0.05 M phosphate buffer (pH 7.8) for standardization. The samples were filtered and centrifuged in 4 C at 12,000 g for 10 min and this extracted solution was used for the estimation of SOD and POD activities as described by Zhang (1992). For the estimation of CAT activity, the mixture (3 ml) includes enzyme extract (100 ml), H2O2 (100 ml of 300 mM), and 2.8 ml of 50 mM phosphate buffer solution 2 mM CA (pH 7). The decrease in absorbance was recorded at 240 nm which was the result of the H2O2 disappearance (ε ¼ 39.4 mM1 cm1) as described by Aebi (1984). A method described by Nakano and Asada (1981) was employed to estimate APX activity. The mixture comprised of enzyme extract (100 ml), 7.5 mM ascorbate (100 ml), 300 mM H2O2 (100 ml), and 25 mM KH2PO4 buffer with 2 mM citric acid at pH 7 (2.7 ml). A change in wavelength at 290 nm was recorded to estimate the oxidation activity of ascorbate (ε ¼ 2.8 mM1 cm1).
The ZnO NPs affected the growth of wheat as a dose-dependent manner (Figs. 1 and 2). Without GA application, both dry biomass and length of shoots and spikes increased with 300 and 600 mg/kg treatments of ZnO NPs and reduced with higher NPs treatments (900 and 1200 mg/kg) as compared with that of control. At 1200 mg/kg ZnO NPs, the reduction in height of plants, spike length, shoot dry weight, root dry biomass and grain dry biomass was 29, 7, 18, 8, 25%, respectively, as compared to the untreated plants (Fig. 1). The foliar use of GA positively affected the growth attributes and chlorophyll contents of wheat in comparison with the respective NPs treatments without GA application. The highest percentage increase in these parameters was observed in 200 mg/L GA þ 1200 mg/kg ZnO NPs as compared to the same NPs treatment alone. As compared to 200 mg/kg ZnO NPs, the plant height was enhanced by 19% and spike length was enhanced by 17% in 200 mg/ L GA þ 1200 mg/kg ZnO NPs. The 200 mg/L GA application in 0, 300, 600, 900, and 1200 mg/kg ZnO NPs increased shoot dry weight by 9, 12, 11, 13, and 20% in comparison to that of the respective NPs treatments alone. The root and grain dry weight increased by 14 and 29% in 200 GA þ 1200 NPs treatments as compared to the NPs treatment alone. The chlorophyll a, b and carotenoid contents increased or
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Fig. 1. Effect of foliar applied gibberellic acid on growth attributes and yield (g/pot) of wheat at various levels of ZnO NPs applied in the soil. The values reported are means of four replicates and bars sharing similar letters are not significant at p 0.05.
decreased in NPs treated wheat leaves with dose dependent response (Fig. 2). The lower levels of ZnO NPs (300 and 600 mg/kg) enhanced the chlorophyll concentrations by 19 and 40%, chlorophyll b concentrations enhanced by 9 and 29%, and carotenoid concentrations increased by 4 and 18% as compared to the untreated control. The foliar use of GA linearly increased the concentrations of these parameters as compared to ZnO NPs without GA. The effect of higher rate of GA was greater in enhancing the levels of these parameters than the lower GA level.
1200 mg/kg ZnO NPs treatment, the EL, H2O2, and MDA concentrations increased by 62, 28, and 22% as compared with the control. In contrast, combined application of GA (100, and 200 mg/L) and NPs remarkably decreased the EL, H2O2, and MDA concentrations compared to the respective ZnO NPs only treatments. For Instance, 200 mg/L GA with 1200 mg/kg ZnO NPs decreased the EL, H2O2, and MDA concentrations by 22, 17, and 20% compared with respective NPs treatment alone. 3.3. Effect of GA on antioxidant enzymes in leaves under NPs stress
3.2. Effect of GA on EL, H2O2, and MDA concentrations in leaves under NPs stress To understand the efficiency of ZnO NPs induced toxicity in wheat and their amelioration by GA, we examined the EL, H2O2, and MDA concentrations in leaves of wheat as these are often considered one of the reliable parameters of oxidative stress. The NPs caused a significant increase in EL, H2O2, and MDA concentrations in wheat and the response was higher with increasing NPs treatments (Fig. 3). However, lower level of NPs (300 mg/kg) decreased levels of these parameters in comparison with the control. At
The effect of antioxidant enzyme to ZnO NPs alone and combined with GA treatments has been reported in Fig. 4. Among the four tested antioxidant enzymes in leaves such as SOD, POD, CAT and APX, the 300 and 600 mg/kg ZnO NPs alone enhanced the activities of tested enzymes in leaves, whereas the higher NPs (600 and 900 mg/kg) decreased the enzyme activities in comparison with the untreated control. At 600 mg/kg ZnO NPs treatments, the SOD activity increased by 55%, POD activity enhanced by 46%, CAT activity enhanced by 33%, and APX activity enhanced by 32% over control. The activities of SOD, POD, CAT and APX decreased by 26,
A. Iftikhar et al. / Environmental Pollution 254 (2019) 113109
Fig. 2. Effect of foliar applied gibberellic acid on chlorophyll contents of wheat leaves at various levels of ZnO NPs applied in the soil. The values reported are means of four replicates and bars sharing similar letters are not significant at p 0.05.
10, 8, and 24% following the exposure of plants to 1200 mg/kg ZnO NPs in comparison to the control. The combined treatments of GA and NPs remarkably enhanced the activities of the tested four enzymes than the respective ZnO NPs treatments alone. The effect of the higher dose of GA was greater than the lower dose applied as a foliar spray. The highest enzyme activities of four enzyme were detected at 200 mg/L GA þ 600 mg/kg ZnO NPs treatments, whereas the lowest activities of these enzymes were observed at 1200 mg/kg ZnO NPs treatment alone. 3.4. Effect of GA on nutrient elements in wheat under NPs stress To assess whether GA-induced ZnO NPs toxicity in plants is associated with alterations in nutrient element accumulation by wheat, we measured the selected macronutrients such as P and K and micronutrients such as Zn, Fe and Mn contents in shoots and roots of wheat plants following the exposure of plants to different GA and NPs treatments. The results regarding to P and K concentrations in wheat have been reported in Fig. 5. Both P and K concentrations were higher in roots than shoots irrespective of the applied treatments and increased with the lower NPs (300 and 600 mg/kg), whereas decreased with the higher NPs treatments.
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Fig. 3. Effect of foliar applied gibberellic acid on oxidative stress of wheat leaves at various levels of ZnO NPs applied in the soil. The values reported are means of four replicates and bars sharing similar letters are not significant at p 0.05.
The P concentration in shoots and roots increased by 42 and 30% and decreased by 34, and 22% following the exposure of 600 and 1200 mg/kg ZnO NPs treatments, respectively, over control. Similarly, K concentration in roots increased by 26% and decreased by 33% following the exposure of 600 and 1200 mg/kg ZnO NPs treatments, respectively, over control. However, K concentrations were higher in shoots with all NPs treatments compared that of control except in the highest NPs treatment where K concentrations were almost similar to that of control. In addition, P and K accumulation in shoot and root of GA-only treated plants were not significantly different from that of control. The application of GA increased the P and K concentrations in wheat under ZnO NPs treatments than that of respective NPs treatments alone. The highest P and K concentrations were observed in 200 mg/L GA þ 600 mg/kg ZnO NPs. The results related to Zn, Fe and Mn concentrations in wheat plants have been mentioned in Fig. 6. The exposure of plants to all ZnO NPs treatments significantly improved the Zn concentrations in shoot and root compared to that of control (Fig. 6a and b). Interestingly, Zn contents significantly decreased in shoot and roots when GA was applied with ZnO NPs treatments. 200 mg/L GA decreased the Zn concentrations in shoots by 12, 15, 11, and 18% whereas Zn concentrations in roots decreased by 15, 17, 8, and 6%
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Fig. 4. Effect of foliar applied gibberellic acid on antioxidant enzymes of wheat leaves at various levels of ZnO NPs applied in the soil. The values reported are means of four replicates and bars sharing similar letters are not significant at p 0.05.
after exposure to 300, 600, 900, and 1200 mg/kg ZnO NPs, respectively compared with that of NPs treatments alone. The 300 mg/kg of ZnO NPs enhanced the Fe and Mn concentrations in wheat plants, whereas higher NPs treatments consistently decreased Fe and Mn concentrations with increasing NPs levels in the media (Fig. 6cef). Exposure of plants to GA þ NPs treatments improved the Fe and Mn concentrations in wheat than the
respective NPs treatments alone. 4. Discussion The problem of soil contamination with NPs may exists due to larger production and application of NPs in the industries and their toxicity in plants can be reduced to a considerable extent by the
Fig. 5. Effect of foliar applied gibberellic acid on P and K contents of wheat at various levels of ZnO NPs applied in the soil. The values reported are means of four replicates and bars sharing similar letters are not significant at p 0.05.
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Fig. 6. Effect of foliar applied gibberellic acid on zinc (Zn), iron (Fe) and manganese (Mn) concentrations of wheat at various levels of ZnO NPs applied in the soil. The values reported are means of four replicates and bars sharing similar letters are not significant at p 0.05.
application of different strategies. It is not well evident that NPs production and application at large scale is one of the major threats to crop growth and food safety (Li et al., 2017). The plant length and dry biomass are ideal indicators of wheat growth. In the current study, both plant height and dry weights were strongly reduced at high levels of ZnO NPs (Fig. 1). These results are supported by the published studies indicating plant growth and biomass are negatively affected by the exposure of high concentrations of ZnO NPs pez-Moreno et al., 2017). The ZnO (Bandyopadhyay et al., 2015; Lo NPs caused the reduction in tomato root and shoot growth (Wang et al., 2018). The increasing concentrations of ZnO NPs (0e1000 mg/ L) linearly decreased the biomass and root/shoot lengths of rice seedlings (Chen et al., 2015). ZnO NPs decreased the length and weight of tomato in a dose-additive manner (Li et al., 2017). The high concentrations of ZnO NPs caused the root deformation (Moghaddasi et al., 2013). The reduction in weight might be due to ZnO NPs and not from Zn ions as indicated previously (Wang et al., 2018). The lower concentration of ZnO NPs (200 mg/kg) were not toxic to tomato seedlings whereas higher NPs significantly reduced the chlorophyll contents in a dose-additive manner (Wang et al.,
2018). The Zn concentrations increased in the shoots of cucumber with the ZnO NPs application which might be due to the accumulation of ZnO NPs by the roots and also dissolution of NPs in the soil (Moghaddasi et al., 2017). The positive effects of low levels of ZnO NPs (300 and 600 mg/kg) on growth of wheat (Fig. 1) might be due to the moderate concentrations of Zn in plants (Fig. 6a and b). The Zn is a micronutrient for plants which can improve plant growth and improve plant resistance under stressful conditions (Rizwan et al., 2017b, 2019). The GA application enhanced the plant growth under NPs stress (Figs. 1 and 2). The role of GA on the alleviation of abiotic stress has been reported in the literature. The GA is considered a promising hormone in plants which could improve plant growth under numerous abiotic stresses including salinity and metal stresses (Tuna et al., 2008; Saleem et al., 2015; Upreti and Sharma, 2016). The application of GA at 10 mM increased seed germination, length of shoot and root and dry biomass of pea plants under Cr stress whereas higher level of GA (100 mM) showed the negative effects on plants under Cr stress (Gangwar et al., 2011). In conformance with published reports, here we observed that GA application improved
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the wheat growth and yield under various concentrations of ZnO NPs (Figs. 1 and 2). The effect of GA was dose specific as we observed the increased plant growth with increasing GA doses. It is evident that GA response under stressful environment is dose specific that greatly varies with plant species, growth environment and application methods (Tuna et al., 2008; Upreti and Sharma, 2016). The results reported that ZnO NPs caused oxidative stress in leaves of plants (Fig. 3). The increase in oxidative stress in wheat plants may be due to direct entry of ZnO NPs in the roots as was indicated previously that ZnO NPs were detected in root endodermal cells of cucumber (Moghaddasi et al., 2017). The ZnO NPs increased the H2O2 and MDA contents in roots and shoots of rice over control (Chen et al., 2015). The ZnO NPs affected the enzyme activities in leaves (Fig. 4). ZnO NPs affected the antioxidant enzyme activities (CAT, SOD and APX) in barley plants depending upon the concentrations of the NPs applied in the growing media (Dogaroglu and Koleli, 2017). The lower concentrations of ZnO NPs (5 and 10 mg/kg) slightly improved the antioxidant enzyme activities whereas higher concentrations of NPs (20, 40, 80 mg/kg) decreased the enzyme activities in barely plants (Dogaroglu and Koleli, 2017). The GA minimized the oxidative stress in wheat (Figs. 3 and 4). It is reported that GA application in the nutrient solution impacted the antioxidant enzyme activities depending upon the concentrations of GA under Cr stress in pea seedlings (Gangwar et al., 2011). Lower concentration of GA (10 mM) in the nutrient solution improved the antioxidant enzyme activities whereas higher concentration of GA (100 mM) negatively affected the growth, nitrogen assimilation and enzyme activities in pea under Cr stress (Gangwar et al., 2011). However, our results depicted that GA enhanced the enzyme activities in leaves of wheat under ZnO NPs stress (Fig. 4). Our results and published studies demonstrated that the effect of GA on plant under abiotic stress varies with the dose, plant species and application methods along with other factors. The exposure of plants to ZnO NPs improved the Zn concentrations in wheat over control (Fig. 6a and b). These higher concentrations of Zn in treated plants indicated that Zn has been absorbed by the wheat in a dose-additive manner that might be the reason of reduced wheat growth and oxidative stress. These results are also supported by the published reports indicating the exposure of plant to ZnO NPs increased the Zn accumulation by plants (Li et al., 2017; Rizwan et al., 2019). Although, 300 mg/kg ZnO NPs treatment enhanced the Zn concentrations in plants, the growth was positively affected at that NPs treatment (Fig. 1). This positive effect of NPs at this concentration might be due to the fact that lower Zn concentration in plants act as a nutrient especially in Zn deficient soils. Our results reported that GA þ NPs application decreased the Zn and increased the other selected nutrient elements in wheat than NPs treatments alone (Figs. 5 and 6). Li et al. (2017) suggested that reduction of oxidative stress in tomato was attributed to the reduced Zn contents in seedlings by the exposure of brassinosteroid under ZnO NPs stress. Our results indicate that the alleviation of ZnO NPs-induced oxidative stress by GA might be related to GA-mediated reduction in Zn contents in enhancement in P, K, Fe and Mn contents in shoot and roots of wheat under stressful environment. 5. Conclusion The effects of GA on the alleviation of ZnO NPs toxicity in wheat were evaluated. It is clear that higher concentrations of ZnO NPs were toxic to plants which was depicted by the reduced growth, photosynthesis, mineral nutrients uptake (Fe, Mn, P and K) and increase in oxidative stress in plants. Foliar application of GA
enhanced the growth of wheat under ZnO NPs stress. The GA alleviated the NPs toxicity by enhancing the enzyme activities which reduced the ROS production in plants and ultimately sustained the growth, nutrient contents and yield of wheat. More studies should be conducted in various crop species to verify the ameliorative effects of GA on ZnO NPs and other NPs toxicities in plants under various conditions and exposure durations. Acknowledgement The authors gratefully acknowledge Dr Muhammad Adrees (Government College University, Faisalabad) for critically proof reading the manuscript. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.envpol.2019.113109. Conflicts of interest The authors declare no conflict of interest regarding this study. References Abbas, Q., Liu, G., Yousaf, B., Ali, M.U., Ullah, H., Ahmed, R., 2019. Effects of biochar on uptake, acquisition and translocation of silver nanoparticles in rice (Oryza sativa L.) in relation to growth, photosynthetic traits and nutrients displacement. Environ. Pollut. 250, 728e736. Abdel-Aziz, H.M.M., Rizwan, M., 2019. Chemically synthesized silver nanoparticles induced physio-chemical and chloroplast ultrastructural changes in broad bean seedlings. Chemosphere. https://doi.org/10.1016/j.chemosphere.2019.07.035. Aebi, H., 1984. Catalasei n vitro. Methods Enzymol. 105, 121e126. Ashraf, M., Karim, F., Rasul, E., 2002. Interactive effects of gibberellic acid (GA3) and salt stress on growth, ion accumulation and photosynthetic capacity of two spring wheat (Triticum aestivum L.) cultivars differing in salt tolerance. Plant Growth Regul. 36, 49e59. -Yacama n, M., Bandyopadhyay, S., Plascencia-Villa, G., Mukherjee, A., Rico, C.M., Jose Peralta-Videa, J.R., Gardea-Torresdey, J.L., 2015. Comparative phytotoxicity of ZnO NPs, bulk ZnO, and ionic zinc onto the alfalfa plants symbiotically associated with Sinorhizobium meliloti in soil. Sci. Total Environ. 515, 60e69. Bouyoucos, G.J., 1962. Hydrometer method improved for making particle size analyses of soils. Agron. J. 54, 464e465. Chen, J., Liu, X., Wang, C., Yin, S.S., Li, X.L., Hu, W.J., Simon, M., Shen, Z.J., Xiao, Q., Chu, C.C., Peng, X.X., 2015. Nitric oxide ameliorates zinc oxide nanoparticlesinduced phytotoxicity in rice seedlings. J. Hazard Mater. 297, 173e182. Corsi, I., Winther-Nielsen, M., Sethi, R., Punta, C., Della Torre, C., Libralato, G., Lofrano, G., Sabatini, L., Aiello, M., Fiordi, L., Cinuzzi, F., 2018. Ecofriendly nanotechnologies and nanomaterials for environmental applications: key issue and consensus recommendations for sustainable and ecosafe nanoremediation. Ecotoxicol. Environ. Saf. 154, 237e244. De La Torre-Roche, R., Hawthorne, J., Musante, C., Xing, B., Newman, L.A., Ma, X., White, J.C., 2013. Impact of Ag nanoparticle exposure on p,p'-DDE bioaccumulation by Cucurbita pepo (Zucchini) and Glycine max (Soybean). Environ. Sci. Technol. 47, 718e725. Dhindsa, R.S., Plumb-Dhindsa, P., Thorne, T.A., 1981. Leaf senescence correlated with increased levels of membrane permeability and lipid peroxidation and decreased levels of superoxide dismutase and catalase. J. Exp. Bot. 32, 93e101. Dionisio-Sese, M.L., Tobita, S., 1998. Antioxidant responses of rice seedlings to salinity stress. Plant Sci. 135, 1e9. Dogaroglu, Z.G., Koleli, N., 2017. TiO2 and ZnO nanoparticles toxicity in barley (Hordeum vulgare L.). CLEANeSoil. Air, Water 45, 1e8. Gangwar, S., Singh, V.P., Srivastava, P.K., Maurya, J.N., 2011. Modification of chromium (VI) phytotoxicity by exogenous gibberellic acid application in Pisum sativum (L.) seedlings. Acta Physiol. Plant. 33, 1385e1397. Ghosh, M., Jana, A., Sinha, S., Jothiramajayam, M., Nag, A., Chakraborty, A., Mukherjee, A., Mukherjee, A., 2016. Effects of ZnO nanoparticles in plants: cytotoxicity, genotoxicity, deregulation of antioxidant defenses, and cell-cycle arrest. Mut. Res./Gen. Toxicol. Environ. Mut. 807, 25e32. Heath, R.L., Packer, L., 1968. Photoperoxidation in isolated chloroplasts. I. Kinetics and stoichiometry of fatty acid peroxidation. Arch. Biochem. Biophys. 125, 189e198. Hussain, A., Ali, S., Rizwan, M., Rehman, M.Z., Javed, M.R., Imran, M., Chatha, S.A.S., Nazir, R., 2018. Zinc oxide nanoparticles alter the wheat physiological response and reduce the cadmium uptake by plants. Environ. Pollut. 242, 1518e1526. Jaleel, C.A., Salem, M.A., Hasanuzzaman, M., Nahar, K., 2010. Plant growth regulator interactions results enhancement of antioxidant enzymes in Catharanthus
A. Iftikhar et al. / Environmental Pollution 254 (2019) 113109 roseus. J. Plant Interact. 5, 135e145. Li, S., Wang, W., Liang, F., Zhang, W.X., 2017. Heavy metal removal using nanoscale zero-valent iron (nZVI): theory and application. J. Hazard Mater. 322, 163e171. Lichtenthaler, H.K., 1987. Chlorophylls and carotenoids-pigments of photosynthetic biomembranes. In: Colowick, S.P., Kaplan, N.O. (Eds.), Methods in Enzymol, vol. 148. Academic Press, San Diego, pp. 350e382. Lin, D., Xing, B., 2007. Phytotoxicity of nanoparticles: inhibition of seed germination and root growth. Environ. Pollut. 150, 243e250. pez-Moreno, M.L., de la Rosa, G., Cruz-Jime nez, G., Castellano, L., PeraltaLo Videa, J.R., Gardea-Torresdey, J.L., 2017. Effect of ZnO nanoparticles on corn seedlings at different temperatures; X-ray absorption spectroscopy and ICP/OES studies. Microchem. J. 134, 54e61. Ma, C., White, J.C., Dhankher, O.P., Xing, B., 2015. Metal-based nanotoxicity and detoxification pathways in higher plants. Environ. Sci. Technol. 49, 7109e7122. Moghaddasi, S., Fotovat, A., Khoshgoftarmanesh, A.H., Karimzadeh, F., Khazaei, H.R., Khorassani, R., 2017. Bioavailability of coated and uncoated ZnO nanoparticles to cucumber in soil with or without organic matter. Ecotoxicol. Environ. Saf. 144, 543e551. Moghaddasi, S., Khoshgoftarmanesh, A.H., Karimzadeh, F., Chaney, R.L., 2013. Preparation of nano-particles from waste tire rubber and evaluation of their effectiveness as zinc source for cucumber in nutrient solution culture. Sci. Hortic. 160, 398e403. Mohamed, A.K.S.H., Qayyum, M.F., Abdel-Hadi, A.M., Rehman, R.A., Ali, S., Rizwan, M., 2017. Interactive effect of salinity and silver nanoparticles on photosynthetic and biochemical parameters of wheat. Arch. Agron Soil Sci. 63, 1736e1747. Munir, T., Rizwan, M., Kashif, M., Shahzad, A., Ali, S., Amin, N., Zahid, R., Alam, M.F.E., Imran, M., 2018. Effect of zinc oxide nanoparticles on the growth and Zn uptake in wheat (Triticum aestivum L.) by seed priming method. Digest J. Nanomater. Biostruc. 13, 315e323. Nakano, Y., Asada, K., 1981. Hydrogen per oxide scavenged by ascorbate specific peroxidase in spinach chloroplasts. Plant Cell Physiol. 22, 867e880. Ohno, T., Zibilske, L.M., 1991. Determination of low concentrations of phosphorus in soil extracts using malachite green. Soil Sci. Soc. Am. J. 55, 892. https://doi.org/ 10.2136/sssaj1991.03615995005500030046x. Page, A.L., Miller, R.H., Keeny, D.R., 1982. Methods of soil analysis (Part 2). In: Chemical Andmicrobiological Properties. Agron, vol. 9. SSSA, Madison. Pan, B., Xing, B., 2012. Applications and implications of manufactured nanoparticles in soils: a review. Eur. J. Soil Sci. 63, 437e456. Rafique, R., Zahra, Z., Virk, N., Shahid, M., Pinelli, E., Park, T.J., Kallerhoff, J., Arshad, M., 2018. Dose-dependent physiological responses of Triticum aestivum L. to soil applied TiO2 nanoparticles: alterations in chlorophyll content, H2O2 production, and genotoxicity. Agric. Ecosyst. Environ. 255, 95e101. Rizwan, M., Ali, S., Ali, B., Adrees, M., Arshad, M., Hussain, A., Rehman, M.Z.,
9
Waris, A.A., 2019. Zinc and iron oxide nanoparticles improved the plant growth and reduced the oxidative stress and cadmium concentration in wheat. Chemosphere 214, 269e277. Rizwan, M., Ali, S., Hussain, A., Ali, Q., Shakoor, M.B., Rehman, M.Z., Farid, M., Asma, M., 2017b. Effect of zinc-lysine on growth, yield and cadmium uptake in wheat (Triticum aestivum L.) and health risk assessment. Chemosphere 187, 35e42. Rizwan, M., Ali, S., Qayyum, M.F., Ok, Y.S., Adrees, M., Ibrahim, M., Rehman, M.Z., Farid, M., Abbas, F., 2017. Effect of metal and metal oxide nanoparticles on growth and physiology of globally important food crops: a critical review. J. Hazard Mater. 322, 2e16. Saleem, M., Asghar, H.N., Khan, M.Y., Zahir, Z.A., 2015. Gibberellic acid in combination with pressmud enhances the growth of sunflower and stabilizes chromium(VI)-contaminated soil. Environ. Sci. Pollut. Res. 22, 10610e10617. Servin, A.D., Castillo-Michel, H., Hernandez-Viezcas, J.A., Diaz, B.C., PeraltaVidea, J.R., Gardea-Torresdey, J.L., 2012. Synchrotron micro-XRF and microXANES confirmation of the uptake and translocation of TiO2 nanoparticles in cucumber (Cucumis sativus) plants. Environ. Sci. Technol. 46, 7637e7643. Stampoulis, D., Sinha, S.K., White, J.C., 2009. Assay-dependent phytotoxicity of nanoparticles to plants. Environ. Sci. Technol. 43, 9473e9479. Tuna, A.L., Kaya, C., Dikilitas, M., Higgs, D., 2008. The combined effects of gibberellic acid and salinity on some antioxidant enzyme activities, plant growth parameters and nutritional status in maize plants. Environ. Exp. Bot. 62, 1e9. Upreti, K.K., Sharma, M., 2016. Role of plant growth regulators in abiotic stress tolerance. Abiotic Stress Physiol. Hort. Crops 150, 414e418. US Salinity Laboratory Staff, 1954. Diagnosis and Improvement of Saline and Alkali Soils. Agriculture Handbook 60. United States Salinity Laboratory, USDA, Washington DC, p. 160. Walkley, A., Black, I.A., 1934. An examination of the Degtjareff method for determining soil organic matter, and a proposed modification of the chromic soil titration method. Soil Sci. 37, 29e38. Wang, X.P., Li, Q.Q., Pei, Z.M., Wang, S.C., 2018. Effects of zinc oxide nanoparticles on the growth, photosynthetic traits, and antioxidative enzymes in tomato plants. Biol. Plant. 62, 801e808. Wen, F.P., Zhang, Z.H., Bai, T., Xu, Q., Pan, Y.H., 2010. Proteomics reveals the effects of gibberellic acid (GA3) on salt-stressed rice (Oryza sativa L.) shoots. Plant Sci. 178, 170e175. Zhang, J., Kirkham, M.B., 1994. Drought-stress induced changes in activities of superoxide dismutase, catalase and peroxidases in wheat leaves. Plant Cell Physiol. 35, 785e791. Zhang, X.Z., 1992. The measurement and mechanism of lipid peroxidation and SOD, POD and CAT activities in biological system. In: Zhang, X.Z. (Ed.), Research Methodology of Crop Physiology. Agriculture Press, Beijing, pp. 208e211.
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Environmental Pollution journal homepage: www.elsevier.com/locate/envpol
Effect of gibberellic acid on growth, photosynthesis and antioxidant defense system of wheat under zinc oxide nanoparticle stress* Azka Iftikhar a, Shafaqat Ali a, Tahira Yasmeen a, Muhammad Saleem Arif a, Muhammad Zubair b, Muhammad Rizwan a, *, Haifa Abdulaziz S. Alhaithloul c, Aisha A.M. Alayafi d, Mona H. Soliman e, f a
Department of Environmental Sciences and Engineering, Government College University, Faisalabad, Pakistan Department of Bioinformatics & Biotechnology, Government College University, Faisalabad, Pakistan Biology Department, College of Science, Jouf University, Sakaka, 2014, Saudi Arabia d Biological Sciences Department, Faculty of Science, University of Jeddah, Jeddah, Saudi Arabia e Biology Department, Faculty of Science, Taibah University, Al-Sharm, Yanbu El-Bahr, Yanbu 46429, Saudi Arabia f Department of Botany and Microbiology, Faculty of Science, Cairo University, Giza, 12613, Egypt b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 July 2019 Received in revised form 11 August 2019 Accepted 23 August 2019 Available online 28 August 2019
The production and soil accumulation of nanoparticles (NPs) from the industrial sector has increased concerns about their toxic effects in plants which needs the research to explore the ways of reducing NPs toxicity in pants. The gibberellic acid (GA) has been found to reduce abiotic stresses in plants. However, the effect of GA in reducing zinc oxide (ZnO) NPs-mediated toxicity in plants remains unclear. In this study, foliar application of GA was used to explore the possible role in reducing ZnO NPs toxicity in wheat (Triticum aestivum L.) plants. The plants were grown in pots spiked with ZnO NPs (0, 300, 600, 900, 1200 mg/kg) and GA (0, 100, 200 mg/L) was foliar sprayed at different times during the growth period under ambient environmental conditions. Our results demonstrated that GA inhibited the toxicity of ZnO NPs in wheat especially at higher levels of NPs. The GA application improved the plant biomass, photosynthesis, nutrients, and yield under ZnO NPs stress. The GA reduced the Zn accumulation, and reactive oxygen species generation in plants caused by toxicity of NPs. The protective effect of GA in decreasing ZnO NPs-induced oxidative stress was related to GA-mediated enhancement in antioxidant enzymes in plants. The role of GA in enhancing tolerance of wheat against ZnO NPs was further confirmed by the enhancement in nutrient contents in shoots and roots of wheat. Overall, our study provides the evidence that GA can reduce ZnO NPs-induced toxicity in wheat and probably in other crops which needs further in-depth investigation. © 2019 Elsevier Ltd. All rights reserved.
Keywords: Antioxidant Gibberellic acid Phytotoxicity Wheat Zinc oxide nanoparticles
1. Introduction The production and environmental application of nanomaterials (NPs) has been increasing at an alarming rate worldwide especially during the last decade (Rizwan et al., 2017a). Release of NPs in the different environmental compartments can take place naturally, accidently, and intentionally (De La Torre-Roche et al., 2013; Corsi et al., 2018). The NPs have been employed in different industrial and agricultural sectors (Li et al., 2017; Rafique et al., 2018). The
* €rg Rinklebe. This paper has been recommended for acceptance by Dr. Jo * Corresponding author. E-mail address: [email protected] (M. Rizwan).
https://doi.org/10.1016/j.envpol.2019.113109 0269-7491/© 2019 Elsevier Ltd. All rights reserved.
extensive exposure of NPs may enhance the release of NPs in environmental compartments (Rizwan et al., 2017a). Due to nano size in nature, the NPs have unique attributes including high surface area, reactivity and solubility make them dangerous than their counterparts (Servin et al., 2012; De La Torre-Roche et al., 2013). Once in the environment, NPs may cause positive and negative effects on the living things depending upon their size, dose, duration of exposure etc. All the NPs released into the environment finally end up in the soil which might be through direct soil entrance of NPs or indirect such as through water, and aerial depositions (Pan and Xing, 2012; Ma et al., 2015; Mohamed et al., 2017). Recently, the presence of NPs in the soil has been increasing and is a popular subject of research. The increasing concentrations of NPs in the soil may cause adverse impacts on the
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plants grown in these soils. There is an increasing amount of investigation on the toxic effect of NPs on different plants (Rizwan et al., 2017a; Abdel-Aziz and Rizwan, 2019). First, the removal of positive ions from NPs in the growth medium might be a possible cause of NPs phytotoxicity. Secondly, NPs may directly disrupt the membranes of plants or DNA damage. Furthermore, NPs enhance the production of reactive oxygen species (ROS), such as superoxide radical (O2) and hydrogen peroxide (H2O2) generation. The excess production of ROS can cause lipid membrane peroxidation and damage at cellular level, which has been suggested as one of the primary reasons related to nano-toxicity in general. NPs-mediated toxic effects in plants via ROS have been extensively studied and clarified in the previously published reports (Rizwan et al., 2017a; Abdel-Aziz and Rizwan, 2019; Abbas et al., 2019). These reports deepened our knowledge on the toxicity of NPs in plants. Among NPs, metallic NPs such as zinc oxide (ZnO) NPs are being incorporated into the arable soils continuously due to the wide consideration of ZnO NPs in the agricultural and industrial sectors (Lin and Xing, 2007; Munir et al., 2018; Hussain et al., 2018). The plants may accumulate ZnO NPs via roots and translocate them to the aerial parts (Moghaddasi et al., 2013; Dogaroglu and Koleli, 2017). The numerous studies reported the adverse impacts of ZnO NPs in plants at physiological and biochemical levels (Chen et al., 2015; Dogaroglu and Koleli, 2017; Wang et al., 2018). The ZnO NPs caused oxidative-stress in Vicia faba and tobacco when the plants were exposed to different NPs levels (0.2e0.8 g/L ZnO NPs) (Ghosh et al., 2016). Low levels (1e25 mg/kg) of ZnO NPs showed positive effects on cucumber plants, whereas higher levels of these NPs were toxic to plants under hydroponic conditions (Moghaddasi et al., 2013). The ZnO NPs diminished the root and shoot growth and photosynthesis of tomato (Wang et al., 2018). ZnO NPs are more toxic to plants when compared with their bulk counterparts (Stampoulis et al., 2009; Moghaddasi et al., 2017). It is demonstrated that ZnO NPs were highly toxic to barley plants than TiO2 NPs (Dogaroglu and Koleli, 2017). The above studies highlighted that the negative impacts of ZnO NPs on plants depend upon the concentrations of the NPs along with other factors. However, to date, little knowledge is available regarding the amelioration of NPs-induced toxic effects in plants. Considering the negative impacts of ZnO NPs at elevated concentrations in plants, it is therefore needed to find suitable ways to prevent the ZnO NPs toxicity in plants and their accumulation in the food chain. Gibberellic acid (GA), an important signalling plant hormone, stimulate various plant developmental and physiological processes, that includes seed germination, flowering, cell division and maturity, root formation, etc. GA also enhances the tolerance of plants to environmental stresses including salt, chilling, drought and trace element stress (Saleem et al., 2015; Upreti and Sharma, 2016). GA provide defense for plants in opposition to the environmental stresses by regulating antioxidant enzyme activity as well as reducing the extreme amount of intracellular ROS under stressful conditions (Jaleel et al., 2010; Wen et al., 2010). For instance, it has been depicted that exogenous GA alleviate oxidative stress in wheat due to the salt stress by increasing the nutrient contents which improved the yield of plants (Ashraf et al., 2002). Recent study also found that GA effectively reduced the chromium (Cr) contents and improved the yield of sunflower under Cr stress (Saleem et al., 2015). The GA application improved the growth of Cr-stressed pea plants by improving the antioxidant enzymes, which countered the toxic effects (Gangwar et al., 2011). Therefore, it is logical to hypothesize that GA can be used to ameliorate toxicity due to ZnO NPs in plants. Due to the wide use of ZnO NPs worldwide, the role of GA on ZnO NPs toxicity in wheat have been evaluated in this study. Wheat (Triticum aestivum L.) is one of the major cereal crops which is being
cultivated widespread around the globe. Thus, wheat was chosen as a model crop plant to investigate the impacts of GA on these NPs. The aim of this current study was to explore the response of foliar application of different concentrations of GA on wheat crop to a soil contamination by different concentrations of ZnO NPs. It was hypothesized that GA may alleviate ZnO NPs toxicity in wheat by reducing the oxidative stress caused by NPs and enhancing the photosynthesis and mineral accumulation by plants under NPs stress. 2. Materials and methods 2.1. Soil sampling and analysis The soil was sampled from the agricultural farms located in the research area of University of Agriculture Faisalabad, Pakistan. The soil sampling depth was about 0e20 cm and after sampling all the materials such as plant roots and debris were removed from the samples. The soil was air-dried under shade and sieved and used in the experiment. The standard procedures were used for the characterization of the soil such as soil texture was measured by hydrometric method (Bouyoucos, 1962). The soil pH was recorded by the pH meter and electrical conductivity of the same extract (EC) was determined by EC meter (Jenway Limited Model-4070, England) after calibration. The organic matter level of the soil was determined by using Walkley and Black (1934) method. The cations and anions were determined by standard procedures (US Salinity Laboratory Staff, 1954; Page et al., 1982). The measured properties of the experimental soil have been given in Table 1. 2.2. Soil spiking with NPs and plant growth The soil was spiked with different concentrations of ZnO NPs those were purchased from Alfa Aesar. The ZnO NPs had a purity of 99%, and size of 20e30 nm APS powder, with a density of 5.606. The solutions were prepared with different levels of ZnO NPs and were ultrasonicated and mixed in the soil with final levels of 300, 600, 900, and 1200 mg per kg of air-dried soil. After one weeks of soil spiking, the wheat seeds were sown in the pots amended with NPs containing a control (without NPs treatments) under ambient conditions (approximately 64 ± 5% relative humidity and 32/21 C day night average temperature at the time of sowing). Initially, 10
Table 1 Selected properties of the soil. Parameter
Units
Value
Textural class Sand Silt Clay pH EC CO23 HCO 3 Cl SO24 Ca2þ þ Mg2þ Naþ Kþ SAR CEC CaCO3 OM Total Zn Total Mn Total Fe
e % % % e dS m1 mmolc L1 mmolc L1 mmolc L1 mmolc L1 mmolc L1 mmolc L1 mmolc L1 (mmol L1)1/2 cmolc kg1 % % mg kg1 mg kg1 mg kg1
Sandy clay loam 43 26 31 7.82 1.42 Nil 2.55 3.79 6.23a 7.94 4.84 1.62 2.04 4.86 1.59 0.73 34.57 41.29 125.05
a
- Determined by difference ¼ Total soluble salts - (CO2 3 þ HCO3 þ Cl ).
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seeds were sown in each pot and then thinned to 5 seedlings in each pot after seven days of germination. The GA was applied through foliar spray after thinning the plants, whereas second, third, and fourth foliar sprays were done after fourth, sixth, and eighth week of sowing the seeds. There were three levels (0, 100, and 200 mg/L) of GA used in the study. During GA foliar treatment, replications of each treatment were grouped to ensure homogenous application of GA in each replicate. The control plants were sprayed with d-H2O and total volume used of each treatment was 1.5 litters. There were total five treatments of NPs, three treatments of GA with four replications of each treatment. Recommended rates of NPK fertilizers (120-50-25 kg/ha, respectively) were added in the pots by using salts such as urea, diammonium phosphate and sulfate of potash. The pots were rotated randomly and irrigated with tap water to ensure 70% soil moisture contents twice a week. 2.3. Harvesting and sampling
3
A procedure detailed by Dionisio-Sese and Tobita (1998) was employed to estimate EL from leaves. The small pieces of leaves of appropriate size were made and inserted in the tubes already containing 8 ml of d-H2O. The tubes were heated at 32 C for 2 h and then measured the EC1 of the solution just after cooling the solution. Again, the same solution with samples was heated at 121 C for 20 min and recorded the EC2 of the solution after cooling at about room temperature. The below equation was used to calculate EL. EL ¼ (EC1/EC2) 100
(1)
The lipid peroxidation in leaves was estimated in the form of MDA (a product of lipid peroxidation). For this, the thiobabituric acid (TBA) reaction was used as described by Heath and Packer (1968) with little modification thereafter Dhindsa et al., (1981) and Zhang and Kirkham (1994). 2.6. Determination of nutrient elements in plants
The harvesting of the wheat was done at maturity (124 days of seed sowing) and were separated into roots, shoots, and grains. At the time of harvesting, plant height and spike length were recorded by meter scale. The aboveground parts were washed with tap water and then with d-H2O to ensure the removal of any undesired particle on the plant samples. The roots were carefully removed from the soil of each pot and washed with HCl (0.1 M) to ensure the removal of metals adhered to the surface of the roots and then the roots were washed with tap water followed by washing with distilled water. All the plant samples were dried by placing in an oven at about 65 ± 5 C for 72 h. After this, the dry biomasses were recorded and crushed the samples for elemental analysis.
For the measurement of nutrient elements in plants, the samples (0.5 g) ere digested in the mixture of nitric and perchloric acid (3:1, v:v). The mixture was heated at 350 C until a colorless solution and then the specific volume was made and filtered the solutions. The P concentrations were determined by the procedure of Ohno and Zibilske (1991) by taking the readings at 630 nm with a spectrophotometer after the development of green color in the solutions. The concentrations of potassium (K), iron (Fe), zinc (Zn), and manganese (Mn) were determined by Atomic Absorption. Spectrophotometer (Analytik Jena novAA 350).
2.4. Determination of photosynthetic pigments
2.7. Statistical analyses
Plant leaf samples were collected for the measurement of photosynthetic pigments after 75 days of seed sowing when the difference was clear among the treatments. The chlorophyll contents were extracted from the leaves by using acetone solution (85% v/v) under dark environment at 4 C. After this, readings were taken by spectrophotometer at different wavelengths and chlorophyll contents were measured with standard equations (Lichtenthaler, 1987).
SPSS 21.0 software was used for statistical analysis. All parameters were examined using two-way analysis of variance (ANOVA). For means comparison and P value Tukey test was used, considered the significant at 0.05. 3. Results 3.1. Effect of GA on wheat growth and photosynthesis under NPs stress
2.5. Determination of oxidative stress and antioxidant enzymes Electrolyte leakage (EL), hydrogen peroxide (H2O2), malondialdehyde (MDA), and antioxidant enzymes in leaves such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) were measured in leaves of wheat after 75 days of seed sowing. For this, leaf samples were taken, washed and crushed in liquid N2 with mortar and pestle. The crushed samples were treated with 0.05 M phosphate buffer (pH 7.8) for standardization. The samples were filtered and centrifuged in 4 C at 12,000 g for 10 min and this extracted solution was used for the estimation of SOD and POD activities as described by Zhang (1992). For the estimation of CAT activity, the mixture (3 ml) includes enzyme extract (100 ml), H2O2 (100 ml of 300 mM), and 2.8 ml of 50 mM phosphate buffer solution 2 mM CA (pH 7). The decrease in absorbance was recorded at 240 nm which was the result of the H2O2 disappearance (ε ¼ 39.4 mM1 cm1) as described by Aebi (1984). A method described by Nakano and Asada (1981) was employed to estimate APX activity. The mixture comprised of enzyme extract (100 ml), 7.5 mM ascorbate (100 ml), 300 mM H2O2 (100 ml), and 25 mM KH2PO4 buffer with 2 mM citric acid at pH 7 (2.7 ml). A change in wavelength at 290 nm was recorded to estimate the oxidation activity of ascorbate (ε ¼ 2.8 mM1 cm1).
The ZnO NPs affected the growth of wheat as a dose-dependent manner (Figs. 1 and 2). Without GA application, both dry biomass and length of shoots and spikes increased with 300 and 600 mg/kg treatments of ZnO NPs and reduced with higher NPs treatments (900 and 1200 mg/kg) as compared with that of control. At 1200 mg/kg ZnO NPs, the reduction in height of plants, spike length, shoot dry weight, root dry biomass and grain dry biomass was 29, 7, 18, 8, 25%, respectively, as compared to the untreated plants (Fig. 1). The foliar use of GA positively affected the growth attributes and chlorophyll contents of wheat in comparison with the respective NPs treatments without GA application. The highest percentage increase in these parameters was observed in 200 mg/L GA þ 1200 mg/kg ZnO NPs as compared to the same NPs treatment alone. As compared to 200 mg/kg ZnO NPs, the plant height was enhanced by 19% and spike length was enhanced by 17% in 200 mg/ L GA þ 1200 mg/kg ZnO NPs. The 200 mg/L GA application in 0, 300, 600, 900, and 1200 mg/kg ZnO NPs increased shoot dry weight by 9, 12, 11, 13, and 20% in comparison to that of the respective NPs treatments alone. The root and grain dry weight increased by 14 and 29% in 200 GA þ 1200 NPs treatments as compared to the NPs treatment alone. The chlorophyll a, b and carotenoid contents increased or
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Fig. 1. Effect of foliar applied gibberellic acid on growth attributes and yield (g/pot) of wheat at various levels of ZnO NPs applied in the soil. The values reported are means of four replicates and bars sharing similar letters are not significant at p 0.05.
decreased in NPs treated wheat leaves with dose dependent response (Fig. 2). The lower levels of ZnO NPs (300 and 600 mg/kg) enhanced the chlorophyll concentrations by 19 and 40%, chlorophyll b concentrations enhanced by 9 and 29%, and carotenoid concentrations increased by 4 and 18% as compared to the untreated control. The foliar use of GA linearly increased the concentrations of these parameters as compared to ZnO NPs without GA. The effect of higher rate of GA was greater in enhancing the levels of these parameters than the lower GA level.
1200 mg/kg ZnO NPs treatment, the EL, H2O2, and MDA concentrations increased by 62, 28, and 22% as compared with the control. In contrast, combined application of GA (100, and 200 mg/L) and NPs remarkably decreased the EL, H2O2, and MDA concentrations compared to the respective ZnO NPs only treatments. For Instance, 200 mg/L GA with 1200 mg/kg ZnO NPs decreased the EL, H2O2, and MDA concentrations by 22, 17, and 20% compared with respective NPs treatment alone. 3.3. Effect of GA on antioxidant enzymes in leaves under NPs stress
3.2. Effect of GA on EL, H2O2, and MDA concentrations in leaves under NPs stress To understand the efficiency of ZnO NPs induced toxicity in wheat and their amelioration by GA, we examined the EL, H2O2, and MDA concentrations in leaves of wheat as these are often considered one of the reliable parameters of oxidative stress. The NPs caused a significant increase in EL, H2O2, and MDA concentrations in wheat and the response was higher with increasing NPs treatments (Fig. 3). However, lower level of NPs (300 mg/kg) decreased levels of these parameters in comparison with the control. At
The effect of antioxidant enzyme to ZnO NPs alone and combined with GA treatments has been reported in Fig. 4. Among the four tested antioxidant enzymes in leaves such as SOD, POD, CAT and APX, the 300 and 600 mg/kg ZnO NPs alone enhanced the activities of tested enzymes in leaves, whereas the higher NPs (600 and 900 mg/kg) decreased the enzyme activities in comparison with the untreated control. At 600 mg/kg ZnO NPs treatments, the SOD activity increased by 55%, POD activity enhanced by 46%, CAT activity enhanced by 33%, and APX activity enhanced by 32% over control. The activities of SOD, POD, CAT and APX decreased by 26,
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Fig. 2. Effect of foliar applied gibberellic acid on chlorophyll contents of wheat leaves at various levels of ZnO NPs applied in the soil. The values reported are means of four replicates and bars sharing similar letters are not significant at p 0.05.
10, 8, and 24% following the exposure of plants to 1200 mg/kg ZnO NPs in comparison to the control. The combined treatments of GA and NPs remarkably enhanced the activities of the tested four enzymes than the respective ZnO NPs treatments alone. The effect of the higher dose of GA was greater than the lower dose applied as a foliar spray. The highest enzyme activities of four enzyme were detected at 200 mg/L GA þ 600 mg/kg ZnO NPs treatments, whereas the lowest activities of these enzymes were observed at 1200 mg/kg ZnO NPs treatment alone. 3.4. Effect of GA on nutrient elements in wheat under NPs stress To assess whether GA-induced ZnO NPs toxicity in plants is associated with alterations in nutrient element accumulation by wheat, we measured the selected macronutrients such as P and K and micronutrients such as Zn, Fe and Mn contents in shoots and roots of wheat plants following the exposure of plants to different GA and NPs treatments. The results regarding to P and K concentrations in wheat have been reported in Fig. 5. Both P and K concentrations were higher in roots than shoots irrespective of the applied treatments and increased with the lower NPs (300 and 600 mg/kg), whereas decreased with the higher NPs treatments.
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Fig. 3. Effect of foliar applied gibberellic acid on oxidative stress of wheat leaves at various levels of ZnO NPs applied in the soil. The values reported are means of four replicates and bars sharing similar letters are not significant at p 0.05.
The P concentration in shoots and roots increased by 42 and 30% and decreased by 34, and 22% following the exposure of 600 and 1200 mg/kg ZnO NPs treatments, respectively, over control. Similarly, K concentration in roots increased by 26% and decreased by 33% following the exposure of 600 and 1200 mg/kg ZnO NPs treatments, respectively, over control. However, K concentrations were higher in shoots with all NPs treatments compared that of control except in the highest NPs treatment where K concentrations were almost similar to that of control. In addition, P and K accumulation in shoot and root of GA-only treated plants were not significantly different from that of control. The application of GA increased the P and K concentrations in wheat under ZnO NPs treatments than that of respective NPs treatments alone. The highest P and K concentrations were observed in 200 mg/L GA þ 600 mg/kg ZnO NPs. The results related to Zn, Fe and Mn concentrations in wheat plants have been mentioned in Fig. 6. The exposure of plants to all ZnO NPs treatments significantly improved the Zn concentrations in shoot and root compared to that of control (Fig. 6a and b). Interestingly, Zn contents significantly decreased in shoot and roots when GA was applied with ZnO NPs treatments. 200 mg/L GA decreased the Zn concentrations in shoots by 12, 15, 11, and 18% whereas Zn concentrations in roots decreased by 15, 17, 8, and 6%
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Fig. 4. Effect of foliar applied gibberellic acid on antioxidant enzymes of wheat leaves at various levels of ZnO NPs applied in the soil. The values reported are means of four replicates and bars sharing similar letters are not significant at p 0.05.
after exposure to 300, 600, 900, and 1200 mg/kg ZnO NPs, respectively compared with that of NPs treatments alone. The 300 mg/kg of ZnO NPs enhanced the Fe and Mn concentrations in wheat plants, whereas higher NPs treatments consistently decreased Fe and Mn concentrations with increasing NPs levels in the media (Fig. 6cef). Exposure of plants to GA þ NPs treatments improved the Fe and Mn concentrations in wheat than the
respective NPs treatments alone. 4. Discussion The problem of soil contamination with NPs may exists due to larger production and application of NPs in the industries and their toxicity in plants can be reduced to a considerable extent by the
Fig. 5. Effect of foliar applied gibberellic acid on P and K contents of wheat at various levels of ZnO NPs applied in the soil. The values reported are means of four replicates and bars sharing similar letters are not significant at p 0.05.
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Fig. 6. Effect of foliar applied gibberellic acid on zinc (Zn), iron (Fe) and manganese (Mn) concentrations of wheat at various levels of ZnO NPs applied in the soil. The values reported are means of four replicates and bars sharing similar letters are not significant at p 0.05.
application of different strategies. It is not well evident that NPs production and application at large scale is one of the major threats to crop growth and food safety (Li et al., 2017). The plant length and dry biomass are ideal indicators of wheat growth. In the current study, both plant height and dry weights were strongly reduced at high levels of ZnO NPs (Fig. 1). These results are supported by the published studies indicating plant growth and biomass are negatively affected by the exposure of high concentrations of ZnO NPs pez-Moreno et al., 2017). The ZnO (Bandyopadhyay et al., 2015; Lo NPs caused the reduction in tomato root and shoot growth (Wang et al., 2018). The increasing concentrations of ZnO NPs (0e1000 mg/ L) linearly decreased the biomass and root/shoot lengths of rice seedlings (Chen et al., 2015). ZnO NPs decreased the length and weight of tomato in a dose-additive manner (Li et al., 2017). The high concentrations of ZnO NPs caused the root deformation (Moghaddasi et al., 2013). The reduction in weight might be due to ZnO NPs and not from Zn ions as indicated previously (Wang et al., 2018). The lower concentration of ZnO NPs (200 mg/kg) were not toxic to tomato seedlings whereas higher NPs significantly reduced the chlorophyll contents in a dose-additive manner (Wang et al.,
2018). The Zn concentrations increased in the shoots of cucumber with the ZnO NPs application which might be due to the accumulation of ZnO NPs by the roots and also dissolution of NPs in the soil (Moghaddasi et al., 2017). The positive effects of low levels of ZnO NPs (300 and 600 mg/kg) on growth of wheat (Fig. 1) might be due to the moderate concentrations of Zn in plants (Fig. 6a and b). The Zn is a micronutrient for plants which can improve plant growth and improve plant resistance under stressful conditions (Rizwan et al., 2017b, 2019). The GA application enhanced the plant growth under NPs stress (Figs. 1 and 2). The role of GA on the alleviation of abiotic stress has been reported in the literature. The GA is considered a promising hormone in plants which could improve plant growth under numerous abiotic stresses including salinity and metal stresses (Tuna et al., 2008; Saleem et al., 2015; Upreti and Sharma, 2016). The application of GA at 10 mM increased seed germination, length of shoot and root and dry biomass of pea plants under Cr stress whereas higher level of GA (100 mM) showed the negative effects on plants under Cr stress (Gangwar et al., 2011). In conformance with published reports, here we observed that GA application improved
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the wheat growth and yield under various concentrations of ZnO NPs (Figs. 1 and 2). The effect of GA was dose specific as we observed the increased plant growth with increasing GA doses. It is evident that GA response under stressful environment is dose specific that greatly varies with plant species, growth environment and application methods (Tuna et al., 2008; Upreti and Sharma, 2016). The results reported that ZnO NPs caused oxidative stress in leaves of plants (Fig. 3). The increase in oxidative stress in wheat plants may be due to direct entry of ZnO NPs in the roots as was indicated previously that ZnO NPs were detected in root endodermal cells of cucumber (Moghaddasi et al., 2017). The ZnO NPs increased the H2O2 and MDA contents in roots and shoots of rice over control (Chen et al., 2015). The ZnO NPs affected the enzyme activities in leaves (Fig. 4). ZnO NPs affected the antioxidant enzyme activities (CAT, SOD and APX) in barley plants depending upon the concentrations of the NPs applied in the growing media (Dogaroglu and Koleli, 2017). The lower concentrations of ZnO NPs (5 and 10 mg/kg) slightly improved the antioxidant enzyme activities whereas higher concentrations of NPs (20, 40, 80 mg/kg) decreased the enzyme activities in barely plants (Dogaroglu and Koleli, 2017). The GA minimized the oxidative stress in wheat (Figs. 3 and 4). It is reported that GA application in the nutrient solution impacted the antioxidant enzyme activities depending upon the concentrations of GA under Cr stress in pea seedlings (Gangwar et al., 2011). Lower concentration of GA (10 mM) in the nutrient solution improved the antioxidant enzyme activities whereas higher concentration of GA (100 mM) negatively affected the growth, nitrogen assimilation and enzyme activities in pea under Cr stress (Gangwar et al., 2011). However, our results depicted that GA enhanced the enzyme activities in leaves of wheat under ZnO NPs stress (Fig. 4). Our results and published studies demonstrated that the effect of GA on plant under abiotic stress varies with the dose, plant species and application methods along with other factors. The exposure of plants to ZnO NPs improved the Zn concentrations in wheat over control (Fig. 6a and b). These higher concentrations of Zn in treated plants indicated that Zn has been absorbed by the wheat in a dose-additive manner that might be the reason of reduced wheat growth and oxidative stress. These results are also supported by the published reports indicating the exposure of plant to ZnO NPs increased the Zn accumulation by plants (Li et al., 2017; Rizwan et al., 2019). Although, 300 mg/kg ZnO NPs treatment enhanced the Zn concentrations in plants, the growth was positively affected at that NPs treatment (Fig. 1). This positive effect of NPs at this concentration might be due to the fact that lower Zn concentration in plants act as a nutrient especially in Zn deficient soils. Our results reported that GA þ NPs application decreased the Zn and increased the other selected nutrient elements in wheat than NPs treatments alone (Figs. 5 and 6). Li et al. (2017) suggested that reduction of oxidative stress in tomato was attributed to the reduced Zn contents in seedlings by the exposure of brassinosteroid under ZnO NPs stress. Our results indicate that the alleviation of ZnO NPs-induced oxidative stress by GA might be related to GA-mediated reduction in Zn contents in enhancement in P, K, Fe and Mn contents in shoot and roots of wheat under stressful environment. 5. Conclusion The effects of GA on the alleviation of ZnO NPs toxicity in wheat were evaluated. It is clear that higher concentrations of ZnO NPs were toxic to plants which was depicted by the reduced growth, photosynthesis, mineral nutrients uptake (Fe, Mn, P and K) and increase in oxidative stress in plants. Foliar application of GA
enhanced the growth of wheat under ZnO NPs stress. The GA alleviated the NPs toxicity by enhancing the enzyme activities which reduced the ROS production in plants and ultimately sustained the growth, nutrient contents and yield of wheat. More studies should be conducted in various crop species to verify the ameliorative effects of GA on ZnO NPs and other NPs toxicities in plants under various conditions and exposure durations. Acknowledgement The authors gratefully acknowledge Dr Muhammad Adrees (Government College University, Faisalabad) for critically proof reading the manuscript. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.envpol.2019.113109. Conflicts of interest The authors declare no conflict of interest regarding this study. References Abbas, Q., Liu, G., Yousaf, B., Ali, M.U., Ullah, H., Ahmed, R., 2019. Effects of biochar on uptake, acquisition and translocation of silver nanoparticles in rice (Oryza sativa L.) in relation to growth, photosynthetic traits and nutrients displacement. Environ. Pollut. 250, 728e736. Abdel-Aziz, H.M.M., Rizwan, M., 2019. Chemically synthesized silver nanoparticles induced physio-chemical and chloroplast ultrastructural changes in broad bean seedlings. Chemosphere. https://doi.org/10.1016/j.chemosphere.2019.07.035. Aebi, H., 1984. Catalasei n vitro. Methods Enzymol. 105, 121e126. Ashraf, M., Karim, F., Rasul, E., 2002. Interactive effects of gibberellic acid (GA3) and salt stress on growth, ion accumulation and photosynthetic capacity of two spring wheat (Triticum aestivum L.) cultivars differing in salt tolerance. Plant Growth Regul. 36, 49e59. -Yacama n, M., Bandyopadhyay, S., Plascencia-Villa, G., Mukherjee, A., Rico, C.M., Jose Peralta-Videa, J.R., Gardea-Torresdey, J.L., 2015. Comparative phytotoxicity of ZnO NPs, bulk ZnO, and ionic zinc onto the alfalfa plants symbiotically associated with Sinorhizobium meliloti in soil. Sci. Total Environ. 515, 60e69. Bouyoucos, G.J., 1962. Hydrometer method improved for making particle size analyses of soils. Agron. J. 54, 464e465. Chen, J., Liu, X., Wang, C., Yin, S.S., Li, X.L., Hu, W.J., Simon, M., Shen, Z.J., Xiao, Q., Chu, C.C., Peng, X.X., 2015. Nitric oxide ameliorates zinc oxide nanoparticlesinduced phytotoxicity in rice seedlings. J. Hazard Mater. 297, 173e182. Corsi, I., Winther-Nielsen, M., Sethi, R., Punta, C., Della Torre, C., Libralato, G., Lofrano, G., Sabatini, L., Aiello, M., Fiordi, L., Cinuzzi, F., 2018. Ecofriendly nanotechnologies and nanomaterials for environmental applications: key issue and consensus recommendations for sustainable and ecosafe nanoremediation. Ecotoxicol. Environ. Saf. 154, 237e244. De La Torre-Roche, R., Hawthorne, J., Musante, C., Xing, B., Newman, L.A., Ma, X., White, J.C., 2013. Impact of Ag nanoparticle exposure on p,p'-DDE bioaccumulation by Cucurbita pepo (Zucchini) and Glycine max (Soybean). Environ. Sci. Technol. 47, 718e725. Dhindsa, R.S., Plumb-Dhindsa, P., Thorne, T.A., 1981. Leaf senescence correlated with increased levels of membrane permeability and lipid peroxidation and decreased levels of superoxide dismutase and catalase. J. Exp. Bot. 32, 93e101. Dionisio-Sese, M.L., Tobita, S., 1998. Antioxidant responses of rice seedlings to salinity stress. Plant Sci. 135, 1e9. Dogaroglu, Z.G., Koleli, N., 2017. TiO2 and ZnO nanoparticles toxicity in barley (Hordeum vulgare L.). CLEANeSoil. Air, Water 45, 1e8. Gangwar, S., Singh, V.P., Srivastava, P.K., Maurya, J.N., 2011. Modification of chromium (VI) phytotoxicity by exogenous gibberellic acid application in Pisum sativum (L.) seedlings. Acta Physiol. Plant. 33, 1385e1397. Ghosh, M., Jana, A., Sinha, S., Jothiramajayam, M., Nag, A., Chakraborty, A., Mukherjee, A., Mukherjee, A., 2016. Effects of ZnO nanoparticles in plants: cytotoxicity, genotoxicity, deregulation of antioxidant defenses, and cell-cycle arrest. Mut. Res./Gen. Toxicol. Environ. Mut. 807, 25e32. Heath, R.L., Packer, L., 1968. Photoperoxidation in isolated chloroplasts. I. Kinetics and stoichiometry of fatty acid peroxidation. Arch. Biochem. Biophys. 125, 189e198. Hussain, A., Ali, S., Rizwan, M., Rehman, M.Z., Javed, M.R., Imran, M., Chatha, S.A.S., Nazir, R., 2018. Zinc oxide nanoparticles alter the wheat physiological response and reduce the cadmium uptake by plants. Environ. Pollut. 242, 1518e1526. Jaleel, C.A., Salem, M.A., Hasanuzzaman, M., Nahar, K., 2010. Plant growth regulator interactions results enhancement of antioxidant enzymes in Catharanthus
A. Iftikhar et al. / Environmental Pollution 254 (2019) 113109 roseus. J. Plant Interact. 5, 135e145. Li, S., Wang, W., Liang, F., Zhang, W.X., 2017. Heavy metal removal using nanoscale zero-valent iron (nZVI): theory and application. J. Hazard Mater. 322, 163e171. Lichtenthaler, H.K., 1987. Chlorophylls and carotenoids-pigments of photosynthetic biomembranes. In: Colowick, S.P., Kaplan, N.O. (Eds.), Methods in Enzymol, vol. 148. Academic Press, San Diego, pp. 350e382. Lin, D., Xing, B., 2007. Phytotoxicity of nanoparticles: inhibition of seed germination and root growth. Environ. Pollut. 150, 243e250. pez-Moreno, M.L., de la Rosa, G., Cruz-Jime nez, G., Castellano, L., PeraltaLo Videa, J.R., Gardea-Torresdey, J.L., 2017. Effect of ZnO nanoparticles on corn seedlings at different temperatures; X-ray absorption spectroscopy and ICP/OES studies. Microchem. J. 134, 54e61. Ma, C., White, J.C., Dhankher, O.P., Xing, B., 2015. Metal-based nanotoxicity and detoxification pathways in higher plants. Environ. Sci. Technol. 49, 7109e7122. Moghaddasi, S., Fotovat, A., Khoshgoftarmanesh, A.H., Karimzadeh, F., Khazaei, H.R., Khorassani, R., 2017. Bioavailability of coated and uncoated ZnO nanoparticles to cucumber in soil with or without organic matter. Ecotoxicol. Environ. Saf. 144, 543e551. Moghaddasi, S., Khoshgoftarmanesh, A.H., Karimzadeh, F., Chaney, R.L., 2013. Preparation of nano-particles from waste tire rubber and evaluation of their effectiveness as zinc source for cucumber in nutrient solution culture. Sci. Hortic. 160, 398e403. Mohamed, A.K.S.H., Qayyum, M.F., Abdel-Hadi, A.M., Rehman, R.A., Ali, S., Rizwan, M., 2017. Interactive effect of salinity and silver nanoparticles on photosynthetic and biochemical parameters of wheat. Arch. Agron Soil Sci. 63, 1736e1747. Munir, T., Rizwan, M., Kashif, M., Shahzad, A., Ali, S., Amin, N., Zahid, R., Alam, M.F.E., Imran, M., 2018. Effect of zinc oxide nanoparticles on the growth and Zn uptake in wheat (Triticum aestivum L.) by seed priming method. Digest J. Nanomater. Biostruc. 13, 315e323. Nakano, Y., Asada, K., 1981. Hydrogen per oxide scavenged by ascorbate specific peroxidase in spinach chloroplasts. Plant Cell Physiol. 22, 867e880. Ohno, T., Zibilske, L.M., 1991. Determination of low concentrations of phosphorus in soil extracts using malachite green. Soil Sci. Soc. Am. J. 55, 892. https://doi.org/ 10.2136/sssaj1991.03615995005500030046x. Page, A.L., Miller, R.H., Keeny, D.R., 1982. Methods of soil analysis (Part 2). In: Chemical Andmicrobiological Properties. Agron, vol. 9. SSSA, Madison. Pan, B., Xing, B., 2012. Applications and implications of manufactured nanoparticles in soils: a review. Eur. J. Soil Sci. 63, 437e456. Rafique, R., Zahra, Z., Virk, N., Shahid, M., Pinelli, E., Park, T.J., Kallerhoff, J., Arshad, M., 2018. Dose-dependent physiological responses of Triticum aestivum L. to soil applied TiO2 nanoparticles: alterations in chlorophyll content, H2O2 production, and genotoxicity. Agric. Ecosyst. Environ. 255, 95e101. Rizwan, M., Ali, S., Ali, B., Adrees, M., Arshad, M., Hussain, A., Rehman, M.Z.,
9
Waris, A.A., 2019. Zinc and iron oxide nanoparticles improved the plant growth and reduced the oxidative stress and cadmium concentration in wheat. Chemosphere 214, 269e277. Rizwan, M., Ali, S., Hussain, A., Ali, Q., Shakoor, M.B., Rehman, M.Z., Farid, M., Asma, M., 2017b. Effect of zinc-lysine on growth, yield and cadmium uptake in wheat (Triticum aestivum L.) and health risk assessment. Chemosphere 187, 35e42. Rizwan, M., Ali, S., Qayyum, M.F., Ok, Y.S., Adrees, M., Ibrahim, M., Rehman, M.Z., Farid, M., Abbas, F., 2017. Effect of metal and metal oxide nanoparticles on growth and physiology of globally important food crops: a critical review. J. Hazard Mater. 322, 2e16. Saleem, M., Asghar, H.N., Khan, M.Y., Zahir, Z.A., 2015. Gibberellic acid in combination with pressmud enhances the growth of sunflower and stabilizes chromium(VI)-contaminated soil. Environ. Sci. Pollut. Res. 22, 10610e10617. Servin, A.D., Castillo-Michel, H., Hernandez-Viezcas, J.A., Diaz, B.C., PeraltaVidea, J.R., Gardea-Torresdey, J.L., 2012. Synchrotron micro-XRF and microXANES confirmation of the uptake and translocation of TiO2 nanoparticles in cucumber (Cucumis sativus) plants. Environ. Sci. Technol. 46, 7637e7643. Stampoulis, D., Sinha, S.K., White, J.C., 2009. Assay-dependent phytotoxicity of nanoparticles to plants. Environ. Sci. Technol. 43, 9473e9479. Tuna, A.L., Kaya, C., Dikilitas, M., Higgs, D., 2008. The combined effects of gibberellic acid and salinity on some antioxidant enzyme activities, plant growth parameters and nutritional status in maize plants. Environ. Exp. Bot. 62, 1e9. Upreti, K.K., Sharma, M., 2016. Role of plant growth regulators in abiotic stress tolerance. Abiotic Stress Physiol. Hort. Crops 150, 414e418. US Salinity Laboratory Staff, 1954. Diagnosis and Improvement of Saline and Alkali Soils. Agriculture Handbook 60. United States Salinity Laboratory, USDA, Washington DC, p. 160. Walkley, A., Black, I.A., 1934. An examination of the Degtjareff method for determining soil organic matter, and a proposed modification of the chromic soil titration method. Soil Sci. 37, 29e38. Wang, X.P., Li, Q.Q., Pei, Z.M., Wang, S.C., 2018. Effects of zinc oxide nanoparticles on the growth, photosynthetic traits, and antioxidative enzymes in tomato plants. Biol. Plant. 62, 801e808. Wen, F.P., Zhang, Z.H., Bai, T., Xu, Q., Pan, Y.H., 2010. Proteomics reveals the effects of gibberellic acid (GA3) on salt-stressed rice (Oryza sativa L.) shoots. Plant Sci. 178, 170e175. Zhang, J., Kirkham, M.B., 1994. Drought-stress induced changes in activities of superoxide dismutase, catalase and peroxidases in wheat leaves. Plant Cell Physiol. 35, 785e791. Zhang, X.Z., 1992. The measurement and mechanism of lipid peroxidation and SOD, POD and CAT activities in biological system. In: Zhang, X.Z. (Ed.), Research Methodology of Crop Physiology. Agriculture Press, Beijing, pp. 208e211.