Research Article pubs.acs.org/journal/ascecg
Cite This: ACS Sustainable Chem. Eng. 2017, 5, 11034-11041
Alleviating Effect and Mechanism of Flavonols in Arabidopsis Resistance under Pb−HBCD Stress Xu Zhang,† Huanhuan Yang,‡ and Zhaojie Cui*,† †
School of Environmental Science and Engineering, Shandong University, Ji’nan 250100, China School of Life Science, Shandong University, Ji’nan 250100, China
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ABSTRACT: The underlying toxicities of hexabromocyclododecane (HBCD) and lead (Pb) and their toxic effects pose a serious threat to the ecosystem and human beings. As a serious pollutant released from electronic waste, Pb−HBCD has a strong toxic effect on the soil−plant ecosystem. Under Pb−HBCD stress, plant cells produce large amounts of reactive oxygen species (ROS), which cause severe oxidative damage. However, most plants can eliminate active oxygen via active oxygen scavengers (enzymatic and nonenzymatic synthesis). Flavonols are major nonenzymatic active oxygen scavengers that can alleviate ROS accumulation, thereby protecting plants from the damage ROS can cause. The results presented here show that Pb−HBCD stress seriously inhibits plant growth parameters, including germination rate and plant height. However, the exogenous application of flavonols can improve the tolerance of Arabidopsis toward Pb−HBCD by increasing the ROS scavenging ability. 16S rRNA gene sequencing was performed on soil samples to study rhizosphere microbial changes. In the order level, the Pb−HBCD group exhibited variations of richness and diversity compared with the control group. The group with added flavonols showed no obvious changes, indicating that the alleviating effect of exogenous flavonols may mainly depend on the plant system. Our research provides an efficient and clean method to address Pb−HBCD stress in soil. KEYWORDS: E-waste contaminants, Microbial community, ROS, Remediation
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INTRODUCTION With increasing population and arable land reduction, food problems have become more serious than ever.1 As main crops consumed by people, wheat, corn, and rice are extremely sensitive to heavy-metal pollution.2 Lead and hexabromocyclododecane (HBCD) are often present in industrial production and electronic waste. Pb, which is a type of heavy metal, ranks first among industrial pollutants released into soil.3 Pb has been a worldwide concern because of its severe toxicity and extensive distribution. In addition, after being accumulated by plants, Pb is activated and transferred to human beings via the food web4 Meanwhile, HBCD is a brominated cyclic alkane used primarily as an additive flame retardant in polystyrene-based materials, including resins and fabrics. It was listed as a new persistent organic pollutant in Annex A of the Stockholm Convention in 2013. Given its persistence and lipophilicity, HBCD can accumulate in the human body through a combination of diet, dust ingestion, and indoor air inhalation.5 HBCD has been frequently detected in human blood and breast milk. Disrupting effects of HBCD have been obviously detected on rat thyroid hormone metabolism after low-dose exposure (100 μg of HBCD/kg of body weight).6 The subacute subchronic effects of HBCD include liver weight increase, thyroid hyperplasia, nervous system damage, and developmental toxicity.7 Nevertheless, knowledge about the underlying mechanisms of Pb and © 2017 American Chemical Society
HBCD stress is extremely limited. Serious e-waste pollution necessitates thorough research on the physiological function and mechanism of stress tolerance and the improvement of soil environment by exogenous amendments.8 As a secondary metabolite, flavonols play an important role in resistance to adverse environments.9 Exogenous flavonols can effectively accumulate in plants and migrate to the target site. However, different types of flavonols have differential characteristics of uptake and movement systems in root or cotyledon tissues. Quercetin and a quercetin precursor showed stronger uptake ability. Flavonols can generally be used as antioxidants and former oxidants to eliminate the stress caused by reactive oxygen damage.10 Under abiotic stress, plants generate reactive oxygen species (ROS), which cause serious damage to cell structure.11 ROS formation induces the largescale synthesis of flavonols, which can quench ROS and consequently protect cells from oxidative damage.12 Antioxidant and former oxidation of the strongest type of various flavonols were applied in the present study.13 Previous research has mainly focused on the function of flavonols in abiotic adversity but not on the characteristics of different flavonols Received: August 25, 2017 Revised: September 23, 2017 Published: October 4, 2017 11034
DOI: 10.1021/acssuschemeng.7b02971 ACS Sustainable Chem. Eng. 2017, 5, 11034−11041
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ACS Sustainable Chemistry & Engineering under e-waste pollution. The role of flavonols in Pb−HBCD tolerance remains unclear.
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were sheared to an expected average fragment size of 469 base pairs. The sequencing on one lane of Illumina HiSeq 2000 followed the standard protocols.25 Raw reads are available in NCBI BioProjects 33175 and 33117. Data Analysis. Enzyme activity is represented by relative activity (relative activity = (sample group OD/control group OD) × 100%).26 The data were subjected to one-way analysis of variance, and * indicates significant differences between treatments at p < 0.05. Data presented in the figures represent mean ± standard deviation of the three replicates for each treatment.
MATERIALS AND METHODS
Materials. Arabidopsis Columbia ecotype seeds were kept in the laboratory. Seeds of Arabidopsis thaliana were sown on 1/2 MS medium and kept within a controlled temperature range of 22−24 °C. After germination, uniformly germinated seeds were transferred to 1/2 MS medium, given different treatments, and cultured upright for 3−4 days under specific culture conditions (22−24 °C, 60% relative humidity, and photoperiodic light (16 h)/darkness (8 h)).14 The seedlings were grown under controlled conditions. Soil formula and quercetin liquor were independently configured in the laboratory. Superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), and ascorbate peroxidase (APX) kits were purchased from Nanjing Jiancheng Bioengineering Institute. Diaminobenzidine tetrahydrochloride (DAB) and nitro blue tetrazolium (NBT) staining solutions were purchased from Sigma. Phenotypic Analysis of Arabidopsis. Germination Experiment. A. thaliana seeds were sterilized with 70% ethanol for 5 min and then for another 1 min. Quercetin was added in 1/2 MS medium, and then Pb−HBCD was added on the surface of the solidified medium. The seeds were sown on the media and kept in the dark for 2 days at 4 °C for vernalization.15 On the basis of the pre-experiment, the relative median lethal dose of Pb and HBCD was selected for further study. Four different treatments were used (control group, 10 μM quercetin, 5 mM Pb−0.1 mM HBCD, and 5 mM Pb−0.1 mM HBCD + 10 μM quercetin). Each group contained 50 seeds. Germination rates were recorded every 24 h.16 Determination of Fresh Weight and Root Length. The seeds were sown on 1/2 MS medium without any treatment and cultured upright under controlled conditions for 3 days. After the roots reached 2−3 cm, the seedlings were transferred to four different 1/2 MS media (i.e., control group, 10 μM quercetin, 5 mM Pb−0.1 mM HBCD, and 5 mM Pb−0.1 mM HBCD + 10 μM quercetin). Each group contained 12 seedlings, which were cultured under controlled conditions (i.e., temperature = 22 ± 2 °C, relative humidity = 65%−70%, photoperiodic light (16 h)/darkness (8 h)).17 After 10 days, pictures of seedlings were taken. Root lengths were measured from the pictures using ImageJ software. The leaves of each group were cut and weighed to determine the fresh weight.18 The data gathered are averages of three replicates. Analysis of ROS (O2•− and H2O2) Levels. The clipping blade of Arabidopsis was cultivated for approximately 14 days, soaked in water, 10 μM quercetin, 5 mM Pb−0.1 mM HBCD, or 5 mM Pb−0.1 mM HBCD + 10 μM quercetin for approximately 1 h, and then stained.19 O2•− and H2O2 were detected according to the method of Mostofa and Fujita.20 Leaves were stained in 0.1% NBT solution and 1% DAB solution to detect O2•− and H2O2, respectively. After 24 h of incubation, leaves were decolorized by immersing them in boiling ethanol to detect the blue insoluble formazan (for O2•−) or deepbrown polymerization (for H2O2). Extraction and Analysis of Enzymes. To extract enzymes, fresh leaf samples weighing 0.5 g were homogenized separately with a reaction mixture containing 50 mM phosphate buffer (pH 7.0), 100 mM KCl, 1 mM AsA, 5 mM β-mercaptoethanol, and 10% (w/v) glycerol in prechilled mortars. After centrifugation for 15 min, the resultant supernatants were collected to analyze enzyme activities. SOD activity was estimated on the basis of a xanthine−xanthine oxidase system.21 APX activity was determined by monitoring the decrease as AsA was oxidized.22 CAT and GPX were measured using H2O2 as the substrate,23 and optical density (OD) values were measured using a UV spectrophotometer. High-Throughput Sequencing. DNA extracted from each group was used as a template for the amplification of the 16S rRNA gene with the primers 319F (5′-ACTCCTACGGGAGGCAGCAG-3′) and 806R (5′-GGACTACHVGGGTWTCTAAT-3′). For each sample, amplicons from a gradient PCR reaction were pooled and used as input to standard Illumina library preparation24 after the amplicons
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RESULTS AND DISCUSSION Morphological Characteristics. Several plant growth parameters, including germination rate, cotyledon-opening proportion, root length, and fresh weight, were determined in order to evaluate the negative effects of excessive Pb−HBCD on plant growth and the alleviated effects of quercetin on Pb− HBCD-stressed Arabidopsis seedlings. On the germination period, the germination rate and cotyledon-opening proportion were both inhibited by 5 mM Pb−0.1 mM HBCD compared with the control group (Figure 1). However, exogenous addition of 10 μM flavonols obviously
Figure 1. Effect of exogenous flavonols on the germination rate with or without Pb−HBCD stress. * indicates a significant difference.
alleviated the inhibition effects, such as improving the germination rate by 21.7% and increasing the proportion of normal cotyledon (Figure 2). However, compared with the control group, adding flavonols alone did not have obvious effects on the germination rate; by contrast, increasing the cotyledon-opening proportion had evident effects. On the seedling period, leaves turned wilted and yellow when 5 mM Pb−0.1 mM HBCD was added. The root length and fresh weight were decreased by 47.9% and 31.4%,
Figure 2. Effect of exogenous flavonols on cotyledon-opening proportion with or without Pb−HBCD stress. * indicates a significant difference. 11035
DOI: 10.1021/acssuschemeng.7b02971 ACS Sustainable Chem. Eng. 2017, 5, 11034−11041
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ACS Sustainable Chemistry & Engineering respectively, at the 14th day compared with the control group (Figure 3). However, exogenous addition of 10 μM flavonols
Figure 3. Effect of exogenous flavonols on fresh weight and root length with or without Pb−HBCD stress. * indicates a significant difference.
Figure 4. Effect of exogenous flavonols on ROS accumulation in leaves with or without Pb−HBCD stress.
ROS level changes have been regarded as characteristic symptoms of environmental stress.32 Intracellular ROS levels are regulated by numerous enzymes. Highly oxidative O2•− is dismutated by SOD into weakly oxidative H2O2. H2O2 is reduced to H2O through CAT and other enzymes; thus, these enzymes can reflect ROS scavenging.33 Abiotic stress can induce cells to produce considerable ROS, which causes secondary oxidative stress to plants.34 Our results indicated that Pb−HBCD has a toxic effect on the roots and shoots, even on the seedlings, via the ROS pathway. AOX Analysis. As the terminal oxidase of the plant mitochondrial electron transport chain, alternative oxidase (AOX) can relax the highly coupled and tensed electron transport process by maintaining metabolic homeostasis. As the first defense barrier of plant faced with abiotic stress, AOX is an important indicator and functional marker for response of plants to stress, including drought, salinity, cold, and heavy metal.35 AOX acts in the prevention of excessive reduction of the downstream complexes in the case of any dysfunction, thereby finally cutting down the single electron leakage to prevent excessive mitochondrial ROS. As shown in Figure 5, Western blot was used to analyze the AOX level. The thickness
considerably alleviated the effects of Pb−HBCD stress, resulting in significant increases in root length and fresh weight that almost reached above 70% of the control group. Over the experimental period, adding flavonols alone did not significantly affect the root length and fresh weight compared with the control group. These results demonstrated that exogenous flavonol treatment could enhance Pb−HBCD tolerance of Arabidopsis not only in the germination stage but also in the seedling stage. Different physiological indices showed consistent regularity, which indicated that exogenous flavonols could significantly improve the soil environment and achieve normal growth of plants under Pb−HBCD stress. Pb−HBCD is highly toxic and seriously affects plant growth, including the germination and seedling stages, perhaps by combining with proteins and inhibiting the activity of some key enzymes; it then influences a series of physiological and biochemical processes in cells and causes metabolic disorder in plants.27 However, exogenous flavonols can alleviate the adverse effects caused by Pb−HBCD and enhance the growth and biomass of Pb−HBCD-stressed seedlings, which demonstrates the amelioration of flavonols in reducing Pb−HBCD-induced phytotoxicity. A protection role in plants was observed under drought and salinity conditions, which showed the function of flavonols in response to environmental stress.28 ROS (O2•− and H2O2) Levels. ROS is a sensitive indicator of oxidative stress in Pb−HBCD-stressed plants. Plant cells produce large amounts of ROS, which cause severe oxidative damage.29 In the present study, DAB and NBT staining were used to analyze the level of ROS.30 NBT staining showed an increased amount of O2•− as scattered dark blue spots in the Pb−HBCD-stressed Arabidopsis leaves, compared with the nontreated control group (Figure 4a). Similarly, DAB staining confirmed a marked increase in brown polymerization products,31 which indicated the overaccumulation of H2O2 in the leaves of the Pb−HBCD-stressed seedlings31 (Figure 4b). More importantly, the accumulation of O2•− and H2O2 in the leaves of Pb−HBCD-stressed seedlings diminished considerably with the addition of exogenous flavonols compared with those without flavonols. The treatment with exogenous flavonols therefore enhances tolerance in Arabidopsis plants against oxidative stress induced by excessive Pb−HBCD.
Figure 5. Toxic effect of Pb−HBCD and recovery effect of flavonols on AOX. 11036
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Figure 6. Effect of exogenous flavonols on the relative activities of antioxidant enzymes.
Antioxidant Enzyme Activity. As shown in Figure 6, flavonol treatment affected the enzyme activities in a timedependent manner. The SOD activity increased by 25% and 42% at days 7 and 14, respectively, in the Pb−HBCD-stressed treatment compared with the control group. Moreover, the SOD activity increased by 12% and 26% at days 7 and 14, respectively, in the Pb−HBCD-stressed treatment that was subjected to flavonols. The SOD activity did not change in flavonol treatment relative to the control group. The CAT activity decreased by 9% and 30% at days 7 and 14, respectively, in the Pb−HBCD-stressed group. However, the CAT activity in the Pb−HBCD + flavonol group remained at a similar level as for the control group. The GPX activity increased by 39% and 53% at days 7 and 14, respectively, in the Pb−HBCD-stressed group compared with the control group. An increase in GPX activity was also observed in the Pb−HBCD + flavonol group compared with the Pb−HBCD-stressed group. Under nonstressed conditions, the GPX activity in the flavonol-treated group increased relative to the control group. The APX activity increased by 79% and 58% at days 7 and 14, respectively, in the Pb−HBCD-stressed group relative to the control group. The APX activity decreased by 25% at day 7 but increased by 27% at day 14 in the Pb−HBCD + flavonol group compared with the Pb−HBCD-stressed group. The APX activity increased in the flavonol-treated group at day 14 compared with the control group.
of the protein strip represents the content and activity of AOX. AOX significantly increased with the concentration of Pb or HBCD, which showed a good dose−effect relationship. Furthermore, HBCD stress has more severe toxic effects than Pb treatment. By contrast, AOX decreased when Pb−HBCD was added with exogenous flavonols, which indicated that flavonols effectively reduced the toxic effects of Pb−HBCD stress. More importantly, the alleviating effect shows a slight difference with increasing concentration. This result indicates that the recovery ability of flavonols is limited in a certain concentration range. Finally, flavonols play an indirect role in regulating the AOX activity. AOX has important roles to play in countering heavy-metal stress. High expression of AOX induces enhanced tolerance capability in Medicago truncatula through ROS regulation and protection of the photosystem. Saha et al.36 showed that aluminum stress can result in an increase in the amount of AOX protein or in the consumption of electrons by the maximum capacity of the AOX pathway. The AOX analysis in the present study showed consistent regularity with the ROS level, as shown in Figure 4. AOX controls respiration, photosynthesis, and chlorophyll synthesis during stress to maintain homeostasis and enhance plant life span.37 AOX can effectively control ROS synthesis by regulating the ROS signaling pathways in plants. Toxic effects of Pb−HBCD activate AOX in the oxidative phosphorylation process, which is closely related to the ROS pathway. 11037
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ACS Sustainable Chemistry & Engineering SOD, CAT, GPX, and APX constitute the major enzymatic network that detoxifies ROS.38 As a front-line protective enzyme that can convert O2•− into H2O2, SOD is finally removed by CAT and peroxidases.39 The SOD and CAT activities in leaves can be considered as biomarkers for growth and development under heavy-metal stress.40 In the present study, Pb−HBCD induced an increase in SOD activity, which did not correlate with the O2•− level. This result indicates that this level of SOD activity is not sufficient to neutralize the O2•− effect. The decrease in CAT activity in the Pb−HBCD-stressed group accelerated the accumulation of H2O2. However, flavonol treatment resulted in further increases in the SOD and CAT activities, particularly at day 14. This finding indicates that flavonols provide protection against O2•− and H2O2. GPX reduces the peroxide to a nontoxic hydroxyl compound and promotes H2O2 decomposition.41 The previous study on transgenic and hyperaccumulating plants showed that enhanced GPX activity conferred high tolerance to abiotic stresses.42 In the present study, the enhanced GPX activity due to flavonol treatment might scavenge peroxide and reduce oxidative damage. APX is an ascorbate enzyme that acts in H2O2 metabolism and plays a key role in maintaining cellular redox balance.43 APX was stimulated under Pb−HBCD stress; however, the H2O2 level remained significantly high, which indicated that the stimulation effect did not reach the requisite level in lowering excess H2 O2. By contrast, flavonols contributed to regulating the H2O2 level by intensifying the APX activity and enhancing the CAT and GPX activities. Rhizosphere Microbial Community. The microbial community in the test group presented diversity. The relative microbial community abundance at the order level is shown in Figure 7. A total of 130 identified orders were observed, and the dominant orders were Rhizobiales, followed by Ellin329, Sphingobacteriales, and Xanthomonadales. The dominant order of the flavonol group showed similar abundance with the control group. The relative abundance of Acidobacteria
obviously changed under Pb−HBCD stress. Ellin329 and Xanthomonadales obviously decreased, whereas Sphingobacteriales obviously increased. Microbial diversity changed in the Pb−HBCD group compared with the control group: 258ds10, BD7-3, Procamicrobeles, Ohgtaekwangia, Pedosphaerales, Rhodobacterales, AKYG885, and FAC87 disappeared, whereas Campylobacterales, Chromatiales, Roseiflexales, Ellin6067, Fusomicrobeles, Selenomonadales, MSBL9, Syntrophobacterales, and Bryocella appeared. The microbial diversity of the Pb− HBCD + flavonol group was similar to that of the Pb−HBCD group. The dominant order and its proportion slightly changed. Although some species appeared or disappeared between the two test groups, this had a slight influence on the rhizosphere environment because of their low proportions. As shown in Figure 8, the control and the control + flavonol groups were clustered together, which indicates a similar community structure between the two treatments. The Pb− HBCD group had significant differences with the control group because of the highly toxic effect on rhizosphere microbial communities. The control and Pb−HBCD groups were wellseparated from each other, which suggests a clear distinction of microbial community structure. The heat map of order (Figure 8) shows that the proportion of Ellin329, Xanthomonadales, and Sphingobacteriales obviously changed in the Pb−HBCD treatment group compared with the control group. Conversely, the Pb−HBCD + flavonol group showed slight changes in the microbial community. In view of the similarity between the control and control + flavonol groups, flavonols have a minimal influence on rhizosphere microbial communities. As an indirect measurement, soil microbial biomass is sensitive in evaluating the soil quality and can reflect the microbial condition.44 Rhizosphere microbial community structures are closely related to the soil environment and plant growth state.45 Soil properties and environmental quality significantly altered the richness, composition, and structure of microbial species, which may affect the plant system. The microbial biomass activity obviously changed compared with the control group as a result of the stress caused by Pb−HBCD (Figure 7). The high-throughput sequencing indicated that Pb−HBCD could obviously influence the microbial community structure of rhizosphere microorganisms. Pollution stress can affect the microbial community by destroying certain groups and favoring other groups.46 The proportion of dominant species obviously changed under Pb−HBCD stress. The control + flavonol group showed slight changes compared with the control group, similar to the observed changes between the Pb−HBCD and Pb−HBCD + flavonol groups. The analysis of the multiple-sample similarity tree indicated similar community structure between the Pb−HBCD and Pb− HBCD + flavonol groups (Figure 8). Flavonols have a minimal influence on rhizosphere microbial communities, which indicates that flavonols and rhizosphere microorganisms may not work in mutual cooperation.
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CONCLUSIONS As main pollutants in e-waste, Pb and HBCD are highly toxic and are therefore a worldwide concern.47 Pb and HBCD released into soil are finally transferred to the food web, which can harm human beings.48 In this study, we found that Pb− HBCD stress induced high increase in ROS levels, whereas flavonols reduced the ROS levels in Pb−HBCD stress, although they remained higher than for the control group. Flavonols increased the activities of antioxidant enzymes and detoxified
Figure 7. Relative abundance of microbial community structures at the order level. 11038
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Figure 8. Microbial community heat map analysis at the order level.
ROS, which prevented oxidative damage.49 The AOX activity directly evaluated the toxic effect of Pb or HBCD and indirectly assessed the alleviating effect of flavonols. Flavonols may regulate AOX, the first line of defense toward Pb−HBCD stress. Moreover, flavonols can enhance the tolerance to Pb− HBCD stress by improving the antioxidant systems to mitigate ROS toxicity.50 Pb−HBCD has highly toxic effect on the richness and diversity of the rhizosphere microbial community, which affects plant health. However, flavonols have a slight influence on rhizosphere microorganisms and may perform their function directly via the plant system. In short, prolonged exposure to excessive Pb−HBCD causes serious toxic effects on Arabidopsis species by affecting their physiological and biochemical attributes. Exogenous flavonols can improve plant habitats and enhance plant resistance to e-waste pollution.
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(2) Liu, Z.; Zhang, Q.; Han, T.; Ding, Y.; Sun, J.; Wang, F.; Zhu, C. Heavy Metal Pollution in a Soil-Rice System in the Yangtze River Region of China. Int. J. Environ. Res. Public Health 2016, 13 (2), 63. (3) Izquierdo, M.; Tye, A. M.; Chenery, S. R. Sources, lability and solubility of Pb in alluvial soils of the River Trent catchment, U.K. Sci. Total Environ. 2012, 433 (7), 110−22. (4) Younger, P. L.; Wolkersdorfer, C. Mining Impacts on the Fresh Water Environment: Technical and Managerial Guidelines for Catchment Scale Management. Mine Water Environ. 2004, 23 (S1), s2−s80. (5) Mark, F. E.; Vehlow, J.; Dresch, H.; Dima, B.; Grüttner, W.; Horn, J. Destruction of the flame retardant hexabromocyclododecane in a full-scale municipal solid waste incinerator. Waste Manage. Res. 2015, 33 (2), 165−74. (6) Huang, H.; Zhang, S.; Lv, J.; Wen, B.; Wang, S.; Wu, T. Experimental and theoretical evidence for diastereomer- and enantiomer-specific accumulation and biotransformation of HBCD in maize roots. Environ. Sci. Technol. 2016, 50 (22), 12205−12213. (7) Wang, F.; Zhang, H.; Geng, N.; Zhang, B.; Ren, X.; Chen, J. New Insights into the Cytotoxic Mechanism of Hexabromocyclododecane (HBCD) from a Metabolomic Approach. Environ. Sci. Technol. 2016, 50 (6), 3145−3153. (8) Medina, A.; Azcón, R. Effectiveness of the application of arbuscular mycorrhiza fungi and organic amendments to improve soil quality and plant performance under stress conditions. J. Soil Sci. Plant Nut 2010, 10 (10), 354−372. (9) Lois, R.; Buchanan, B. B. Severe sensitivity to ultraviolet radiation in an Arabidopsis mutant deficient in flavonoid accumulation: II. Mechanisms of UV-resistance in Arabidopsis. Planta 1994, 194 (4), 504−509. (10) Aldesuquy, H. S.; Ghanem, H. E. Exogenous Salicylic Acid and Trehalose Ameliorate Short Term Drought Stress in Wheat Cultivars by Up-regulating Membrane Characteristics and Antioxidant Defense System. J. Hortic. 2015, 2 (2), 139. (11) Choudhury, S.; Panda, P.; Sahoo, L.; Panda, S. K. Reactive oxygen species signaling in plants under abiotic stress. Plant Signaling Behav. 2013, 8 (4), e23681. (12) Liu, M.; Li, X.; Liu, Y.; Shi, Y.; Ma, X. Analysis of differentially expressed genes under UV-B radiation in the desert plant Reaumuria soongorica. Gene 2015, 574 (2), 265−272. (13) Ibraheim, Z. Z.; Nafady, A. M.; Mostafa, M. A.; Amin, F. M. Antioxidant Activity and Total Flavonoids Content of Aerial Parts of
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Zhaojie Cui: 0000-0002-7921-046X Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This study was funded by the Ministry of Environmental Protection of China (2011467022): The remediation technologies and demonstration for the combined pollution of oil− heavy metals in saline soil. We especially extend our gratitude to the School of Life Sciences of Shandong University for their suggestions and support in improving our study.
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DOI: 10.1021/acssuschemeng.7b02971 ACS Sustainable Chem. Eng. 2017, 5, 11034−11041
