Determination of the Absorption, Translocation, and Distribution of Imidacloprid in Wheat
Summary
Presented here is a protocol for the determination of the absorption, translocation, and distribution of imidacloprid in wheat under hydroponic conditions using liquid chromatography-tandem mass spectrometry (LC-MS-MS). The results showed that imidacloprid can be absorbed by wheat, and imidacloprid was detected in both the wheat roots and leaves.
Abstract
Neonicotinoids, a class of insecticides, are widely used because of their novel modes of action, high insecticidal activity, and strong root uptake. Imidacloprid, the most widely used insecticide worldwide, is a representative first-generation neonicotinoid and is used in pest control for crops, vegetables, and fruit trees. With such a broad application of imidacloprid, its residue in crops has attracted increasing scrutiny. In the present study, 15 wheat seedlings were placed in a culture medium containing 0.5 mg/L or 5 mg/L imidacloprid for hydroculture. The content of imidacloprid in the wheat roots and leaves was determined after 1 day, 2 days, and 3 days of hydroculture to explore the migration and distribution of imidacloprid in wheat. The results showed that imidacloprid was detected both in the roots and leaves of the wheat plant, and the content of imidacloprid in the roots was higher than that in the leaves. Furthermore, the imidacloprid concentration in the wheat increased with increasing exposure time. After 3 days of exposure, the roots and leaves of the wheat in the 0.5 mg/L treatment group contained 4.55 mg/kg ± 1.45 mg/kg and 1.30 mg/kg ± 0.08 mg/kg imidacloprid, respectively, while the roots and leaves of the 5 mg/L treatment group contained 42.5 mg/kg ± 0.62 mg/kg and 8.71 mg/kg ± 0.14 mg/kg imidacloprid, respectively. The results from the present study allow for a better understanding of pesticide residues in crops and provide a data reference for the environmental risk assessment of pesticides.
Introduction
In present day agronomy, the use of pesticides is essential to increase crop yield. Neonicotinoid insecticides alter the membrane potential balance by controlling nicotinic acetylcholine receptors in the insect nervous system, thereby inhibiting the normal conduction of the insect central nervous system, leading to the paralysis and death of the insects1. Compared with traditional insecticides, neonicotinoids have advantages such as novel modes of action, high insecticidal activity, and strong root absorption, making them highly successful in the pesticide market2,3. The sales volume of neonicotinoids was reported to account for 27% of the world pesticide market in 2014. The average annual growth rate of neonicotinoids was 11.4% from 2005 to 2010, of which about 7% was registered in China4,5,6. From the end of 2016 to the first half of 2017, the sales of pesticides in China began to rebound after falling, and the prices of pesticides continued to rise, among which neonicotinoid insecticides showed a significant price increase7. So far, three generations of neonicotinoid insecticides have been developed, each containing pyridine chloride, thiazolyl, and tetrahydrofuran groups of nicotine, respectively8.
Imidacloprid represents the first generation of neonicotinoid insecticides, whose molecular formula is C9H10ClN5O2, and is a colorless crystal. Imidacloprid is used mainly to control pests, such as aphids, planthoppers, mealworms, and thrips9 and can be applied to crops such as rice, wheat, corn, cotton, and vegetables such as potatoes, as well as fruit trees. Due to the long-term, substantial, and continual application of pesticides, both beneficial insects and the natural enemies of pests have been rapidly reduced, and some agricultural pests have become resistant to pesticides, resulting in a vicious circle of applying continual and increasing amounts of pesticides10. In addition, the extensive application of pesticides has led to the deterioration of soil quality, persistent pesticide residues in agricultural products, and other ecological problems, which not only cause significant damage to the agricultural ecological environment11 but also pose a serious threat to human health12. Pesticide spraying severely impacts the growth and quality of soil microbes and soil animals13. The unreasonable or excessive use of pesticides has caused significant security risks to the soil and water environment, animals and plants, and even human life14. In recent years, the problem of excessive pesticide residues in crops has become more severe with the extensive application of pesticides. When imidacloprid was used to increase vegetable yield, the absorption rate of imidacloprid in the vegetables increased with the increase in the amount and residue of imidacloprid15. As a major food crop, both the production and safety of wheat are critical. Therefore, the residue and distribution policies of pesticides used for wheat need to be clarified.
In recent years, many methods have been developed to extract imidacloprid residues from water, soil, and plants. The QuEChERS method (quick, easy, cheap, effective, rugged, and safe) is a new method that combines solid-phase microextraction technology and dispersed solid-phase extraction technology and involves the use of acetonitrile as the extraction solvent and the removal of mixed impurities and water in the sample using NaCl and anhydrous MgSO4, respectively16. The QuEChERS method requires minimal glassware and has simple experimental steps, making it one of the most popular pesticide extraction methods17. For the detection of imidacloprid, a detection limit as low as 1 × 10−9 g18 has been achieved with liquid chromatography (LC), and 1 × 10−11 g19 has been achieved with gas chromatography (GC). Due to their high resolution and sensitivity, LC-MS and GC-MS have shown even lower imidacloprid detection limits of 1 × 10-13 to 1 × 10-14 g20,21; these techniques are, therefore, well suited for the analysis of trace imidacloprid residues.
In the present study, imidacloprid was chosen as the target pollutant, and wheat was selected as the test crop to study the distribution of imidacloprid residues in wheat. This protocol details a method for the comprehensive analysis of the enrichment and transfer of the pesticide imidacloprid in wheat by exploring the absorption and storage of imidacloprid in different parts of wheat plants grown under hydroponic conditions. The present study aims to provide a theoretical basis for the risk assessment of pesticide residues in wheat, guide the rational application of pesticides in agricultural production activities to reduce pesticide residues, and improve the safety of crop production.
Protocol
1. Germination of wheat seeds
- Select 1,000 wheat seeds (Jimai 20) with complete granules, intact embryos, and uniform size (length: 6 mm ± 0.5 mm).
- Transfer 333.3 mL of 30% H2O2 solution to a 1 L volumetric flask and dilute with deionized water to prepare 1 L of 10% H2O2 solution. Immerse the wheat seeds in 10% H2O2 solution for 15 min to disinfect the seed surface (Figure 1).
- Rinse the wheat seeds 5x with running sterile water for 10 s each time.
- Spread the wheat seeds evenly with the embryos pointing up in a glass Petri dish containing moist sterile filter paper (Figure 2). Place the Petri dish in an artificial climate incubator at 30 °C and 80% relative humidity. Culture the wheat seeds in the dark for 3 days until they germinate and take root.
Figure 1: Disinfection of the wheat seeds. The wheat seeds were soaked in 10% H2O2 solution (in a beaker) for 15 min to disinfect the seed surface. Please click here to view a larger version of this figure.
Figure 2: Germinating the wheat seeds. The wheat seeds were spread evenly in a glass Petri dish containing moist sterile filter paper. The Petri dish was placed in an artificial climate incubator to germinate the wheat seeds. Please click here to view a larger version of this figure.
2. Cultivation of wheat seedlings
- Dissolve 551 mg of Hoagland's basal salt mixture in 1 L of deionized water to prepare 1/2 Hoagland nutrient solution (containing 0.75 mmol/L K2SO4, 0.1 mmol/L KCl, 0.6 mmol/L MgSO4, 4.0 × 10−2 mmol/L FeEDTA, 1.0 × 10−3 mmol/L H3BO3, 1.0 × 10−3 mmol/L MnSO4, 1.0 × 10−3 mmol/L ZnSO4, 1.0 × 10−4 mmol/L CuSO4, and 5.0 × 10−6 mmol/L Na2 MoO4).
- After the wheat seeds (step 1.4) have germinated, place 15 wheat seedlings in hydroponic equipment (see Table of Materials) containing 100 mL of 1/2 Hoagland nutrient solution for hydroponics (Figure 3). Place the entire hydroponic apparatus in an artificial climate incubator (see Table of Materials) and incubate for 7 days at 25 °C and 80% relative humidity with a 16 h light/8 h dark photoperiod.
Figure 3: Hydroponic cultivation of the wheat seedlings. The wheat seedlings were hydroponically cultivated for 0 days, 3 days, and 7 days in 100 mL of 1/2 Hoagland nutrient solution. Please click here to view a larger version of this figure.
3. Experiment exposing the wheat plants to imidacloprid solution
- After a 7 day hydroponic period, transplant the wheat plants into 1/2 Hoagland nutrient solution containing 0.5 mg/L or 5 mg/L imidacloprid to conduct the imidacloprid exposure experiments. Grow 15 wheat plants in each hydroponic device. Set up 15 hydroponic devices for each imidacloprid concentration group to ensure that adequate samples are taken during sampling.
- Place the entire hydroponic equipment in an artificial climate incubator for 3 days at 25 °C and 80% relative humidity with a 16 h light/8 h dark photoperiod.
- Throughout the exposure period, collect wheat roots (0.2 g per wheat plant) and leaves (0.5 g per wheat plant) daily. Integrate the wheat samples from every fifth hydroponic device as a parallel group and determine the imidacloprid content of the samples.
4. Procedure for extracting imidacloprid from wheat
- Extraction of imidacloprid from wheat roots
- To avoid experimental errors, wash the wheat roots 4x with running sterile water for 10 s each time to remove any imidacloprid adsorbed on the root surface.
- Shred the wheat roots into approximately 1 cm pieces with scissors (Figure 4). Weigh 10.00 g of the shredded wheat roots and place in a 50 mL centrifuge tube.
- Add 10 mL of acetonitrile to the centrifuge tube and vortex the tube on a vortexer for 1 min. Then, add 4 g of anhydrous MgSO4 and 1.5 g of NaCl to the centrifuge tube and vortex the tube immediately for 30 s. Centrifuge the tube for 5 min at 6,000 x g.
- Aspirate the supernatant with a disposable syringe and pass it through a syringe filter (0.22 µm pore size) to obtain the sample.
- Extraction of imidacloprid from wheat leaves (Figure 5)
- Shred the fresh wheat leaves into approximately 1 cm pieces with scissors (Figure 4). Weigh 10.00 g of the shredded wheat leaves and place in a 50 mL centrifuge tube.
- Add 10 mL acetonitrile to the centrifuge tube and vortex the tube on a vortexer for 1 min.
- Add 4 g of anhydrous MgSO4 and 1.5 g of NaCl to the centrifuge tube and vortex the tube immediately for 30 s.
- Centrifuge the tube for 5 min at 6,000 x g.
- After centrifugation, add 2 mL of the supernatant to a 5 mL centrifuge tube containing 50 mg of graphitized carbon black (GCB) and 150 mg of anhydrous MgSO4 (to remove pigment and moisture from the sample), and vortex the centrifuge tube for 30 s (Figure 6). Centrifuge the tube for 5 min at 6,000 x g.
- Aspirate the supernatant with a disposable syringe and pass it through a syringe filter (0.22 µm pore size) to obtain the sample.
Figure 4: Shredded wheat roots and leaves. Fresh wheat roots and leaves were shredded using scissors into approximately 1 cm pieces. Please click here to view a larger version of this figure.
Figure 5: Extraction of imidacloprid in the wheat leaves. Imidacloprid in the samples was extracted using the QuEChERS method (steps 4.2.1-4.2.4 of the protocol). Please click here to view a larger version of this figure.
Figure 6: Purification of imidacloprid in the wheat leaves. The decontaminant was 50 mg GCB + 150 mg MgSO4. Please click here to view a larger version of this figure.
5. Quantification of imidacloprid
- Quantify the imidacloprid in the sample using liquid chromatography-tandem mass spectrometry (LC-MS-MS),based on a standard curve (y = 696.61x + 56.411, R=1) obtained from 0.2-250 µg/L imidacloprid concentrations. (Figure 7). The mass spectrometer was equipped with a C18 column (100 mm x 2.1 mm, 3 µm) and an electrospray ionization source (ESI+). The elution program and ion source parameters are shown in Table 1.
Figure 7: Chromatogram and mass spectrogram of imidacloprid in the wheat leaves. The upper panel shows a chromatogram of imidacloprid (retention time = 0.93 min). The lower panel shows the mass spectrogram of imidacloprid at 0.93 min, showing the response intensity of the production (m/z = 208.8) of imidacloprid. Please click here to view a larger version of this figure.
| Column temperature | 40 °C |
| Solvent A | 99.9% water/0.1% formic acid (v/v) |
| Solvent B | acetonitrile |
| Elution program | 0–0.5 min, A = 20% |
| 0.5–2 min, A = 20%–50% | |
| 2–3 min, A = 50% | |
| 3–3.1 min, A = 50%–20% | |
| 3.1–5 min, A=20% | |
| Flow rate (mL/min) | 0.3 |
| Injection volume (μL) | 5 |
| Capillary temperature (°C) | 330 |
| Vaporizer temperature (°C) | 350 |
| Sheath gas flow rate (Arb) | 40 |
| Aux gas flow rate (Arb) | 20 |
| Spray voltage (V) | 3900 |
| Collision gas pressure (mTorr) | 1.5 |
| Precursor ion | 256.1 |
| Product ion/Collision energy (eV) | 208.8/16 |
Table 1: Elution program and ion source parameters of the liquid chromatography-mass spectrometry method.
Representative Results
The instrument limit of detection (LOD) of imidacloprid was 5.76 × 10−14 g, and the method's LOD of imidacloprid in the wheat root or leaf was 0.01 µg/kg; no matrix effect was observed. The recovery yields of imidacloprid in wheat are shown in Table 2. The recovery yields of imidacloprid from the wheat roots exposed to imidacloprid concentrations of 0.5 mg/L and 5 mg/L were 94.0%-97.6% and 98.8%-99.2%, respectively; the coefficients of variation were 1.92% and 0.20%, respectively. The recovery yields of imidacloprid from the wheat leaves exposed to imidacloprid concentrations of 0.5 mg/L and 5 mg/L were 88.2%-91.4% and 92.5%-93.4%, respectively; the coefficients of variation were 1.85% and 0.53%, respectively.
The imidacloprid concentrations in the wheat roots and leaves are shown in Table 3. Imidacloprid was detected in both the wheat roots and leaves, with a higher content in the roots than in the leaves. The imidacloprid content increased with a longer exposure time. After 3 days of exposure, the amounts of imidacloprid in the wheat roots and leaves were 4.55 mg/kg ± 1.45 mg/kg and 1.30 mg/kg ± 0.08 mg/kg, respectively, in the 0.5 mg/L treatment group and 42.5 mg/kg ± 0.62 mg/kg and 8.71 mg/kg ± 0.14 mg/kg, respectively, in the 5 mg/L treatment group. When the wheat roots were exposed to imidacloprid for 1 day, imidacloprid was detected in both the roots and leaves of the wheat plants, indicating that the wheat roots could rapidly absorb imidacloprid from the culture medium and conduct it into the wheat plants. The content of imidacloprid in the wheat leaves decreased slightly on day 3 compared with day 2. This was probably caused by the degradation of some imidacloprid, combined with the dilution of the imidacloprid content per unit volume of the wheat leaves with the extension of the hydroponic culture period. The wheat roots and leaves contained different amounts of imidacloprid, indicating that imidacloprid had been absorbed and conducted differently in the wheat plants and did not reach its action sites simultaneously. The differences in imidacloprid residues in different parts of the wheat plant are closely related to the physiological structure of the wheat plant and the physicochemical properties of imidacloprid.
The common enrichment and transfer-related parameters for pesticides absorbed by plants include the root concentration factor (RCF) and translocation factor (TF)22. The RCF is the ratio of the concentration of imidacloprid in the root of the plant to that in the culture medium. An RCF > 1 indicates that imidacloprid is easily enriched by the plant, while an RCF < 1 indicates that the plant does not easily enrich imidacloprid. As can be seen from Table 4, the RCF from the present study was >1, indicating that wheat has an enrichment effect on imidacloprid. The TF represents the ability of the plant (here, wheat) to translocate a substance (here, imidacloprid) between the roots, shoots, and leaves of the plant. A TF > 1 indicates that imidacloprid is easily translocated by the plant, while a TF < 1 indicates that the plant does not easily translocate imidacloprid. The TF is calculated as the ratio of the residual concentration of imidacloprid in different parts of the wheat to the concentration of imidacloprid in the roots: TFleaf = Cleaf/Croot. A TFleaf > 1 indicates that imidacloprid is easily transferred from the plant roots to the leaves, while a TFleaf < 1 indicates the opposite. As can be seen from Table 4, the TFleaf in the present study was <1, indicating that imidacloprid was not easily transferred from the wheat roots to the leaves.
The growth state of wheat plants after exposure to imidacloprid is shown in Figure 8. After 3 days of exposure, neither 0.5 mg/L nor 5 mg/L imidacloprid produced any apparent inhibition of wheat plant growth.
The dataset associated with this study is available at https://doi.org/10.5281/zenodo.7022287.
Figure 8: Wheat plants exposed to imidacloprid for 1 day, 2 days, and 3 days. CK = control group; 0.5 = 0.5 mg/L imidacloprid group; 5 = 5 mg/L imidacloprid group. Please click here to view a larger version of this figure.
| Sample | Imidacloprid concentration (mg/L) | Recovery (%) | RSD (%) | |||
| Treatment 1 | Treatment 2 | Treatment 3 | Average | |||
| Wheat root | 0.5 | 94.00 | 97.60 | 95.20 | 95.60 | 1.92 |
| 5 | 99.00 | 98.80 | 99.20 | 99.00 | 0.20 | |
| Wheat leaf | 0.5 | 88.20 | 91.40 | 90.60 | 90.10 | 1.85 |
| 5 | 93.30 | 93.40 | 92.50 | 93.10 | 0.53 | |
Table 2: Recovery and relative standard deviation (RSD) of imidacloprid in the wheat roots and leaves (n = 3). The imidacloprid concentrations are based on the fresh weight of the wheat roots or leaves.
| Sample | Imidacloprid concentration in solution (mg/L) | Imidacloprid content (mg/kg) | ||
| 1 d | 2 d | 3 d | ||
| Wheat root | 0.5 | 2.11 ± 0.05 | 3.18 ± 0.48 | 4.55 ± 1.45 |
| 5 | 14.83 ± 0.50 | 26.86 ± 1.38 | 42.5 ± 0.62 | |
| Wheat leaf | 0.5 | 0.34 ± 0.03 | 1.43 ± 0.60 | 1.30 ± 0.08 |
| 5 | 2.10 ± 0.18 | 9.81 ± 0.70 | 8.71 ± 0.14 | |
Table 3: Imidacloprid content in the roots and leaves of the wheat after 1 day, 2 days, and 3 days of exposure. Data are expressed as the mean ± SD (n = 2). The imidacloprid concentrations are based on the fresh weight of the wheat roots or leaves.
| Group | RCF | TFleaf | ||||
| 1 day | 2 days | 3 days | 1 day | 2 days | 3 days | |
| 0.5 mg/L imidacloprid group | 4.22 | 6.36 | 9.10 | 0.16 | 0.45 | 0.29 |
| 5 mg/L imidacloprid group | 2.97 | 5.37 | 8.50 | 0.14 | 0.37 | 0.20 |
Table 4: Root concentration factors (RCF) and leaf translocation factors (TFleaf) of wheat to imidacloprid. The RCF is the ratio of the concentration of imidacloprid in the wheat root to that in the hydroponic culture medium. The TFleaf is the ratio of the residual concentration of imidacloprid in the wheat leaf to that in the wheat root.
Discussion
In recent years, methods for the pretreatment and detection of residues of the pesticide imidacloprid have been frequently reported. Badawy et al.23 used high-performance liquid chromatography to determine the content of imidacloprid in tomato fruit grown under greenhouse conditions and reported good linearity for imidacloprid in the range 0.0125-0.15 µg/mL. Zhai et al.24 used LC-MS-MS to study the residue of imidacloprid in Chinese chives. In the present study, the QuEChERS method was used to extract imidacloprid from wheat roots and leaves. As a rapid and efficient method, the QuEChERS method is well suited and widely used for extracting imidacloprid from soil25 and plant20,26 (such as chili, tomato, cabbage, and wheat) samples. The purpose of the current study was to determine whether the recovery of imidacloprid was consistent and met the determination requirements. The recovery rate and coefficient of variation of imidacloprid in wheat met the requirements for residue determination, indicating that this method was feasible for the extraction of imidacloprid from wheat. The imidacloprid content was determined by LC-MS-MS in the present study, and the instrumental detection limit of imidacloprid met the requirements for the quantitative analysis of pesticide residues. However, this method may not be able to detect any imidacloprid when the content in the sample is lower than 0.01 µg/kg. In such cases, the sample should be concentrated, or a higher amount should be injected for LC-MS-MS. The imidacloprid extraction and detection method used in the present study has the characteristics of rapidity, simplicity, reliable reproducibility, convenience, and high accuracy and is suitable for the analysis of pesticide residues. The success of this methodology, as demonstrated in the present study, indicates its potential for use in the food safety evaluation of imidacloprid in wheat. The critical steps in the protocol include the addition of anhydrous MgSO4, NaCl, and GCB. Anhydrous MgSO4 and NaCl are added to remove water from the sample solution, while GCB is added to remove pigment from the sample solution. The extraction method used in this study is limited by the requirement for a sufficiently large (10 g) sample quantity, making it less suitable for evaluating a small sample size.
The presence of imidacloprid in wheat roots and leaves demonstrates that wheat can rapidly absorb and transfer imidacloprid. The enrichment and transport of organic compounds in plants are closely related to their Kow value, which is the ratio of the equilibrium concentration of organic compounds in the N-octanol and water phases under equilibrium27. According to their log Kow value, organic pollutants can be divided into hydrophobic organic pollutants, hydrophilic organic pollutants, and moderately hydrophilic organic pollutants. Hydrophobic organic pollutants (log Kow > 3) can be strongly adsorbed by the root surface and do not easily migrate upward. On the other hand, hydrophilic organic pollutants (log Kow < 0.5) do not get easily absorbed by roots or pass through the cell membrane of plants. Aqueous organic pollutants (log Kow = 0.53) are easily absorbed by plants, enriched, and transferred. The log Kow value (0.57) of imidacloprid indicates it to be a moderately hydrophilic organic matter, which is easily absorbed, enriched, and transferred by plants.
Different tissues of plants have different capacities to absorb and transport different pesticides over time under the same environment28. The present study found that the distribution of imidacloprid varied in different parts of the wheat plant. Specifically, the study detected a large difference in the absorption of imidacloprid between the wheat roots and leaves. Wheat roots have a strong ability to absorb and transfer imidacloprid and can accumulate imidacloprid at concentrations several times greater than the environmental concentration, thereby allowing the transfer of imidacloprid in the environment to the wheat leaves. A study by Yuan et al.20 on the distribution of imidacloprid in wheat after applying controlled release imidacloprid revealed that imidacloprid accumulation in the wheat roots was 5-10 times that in the leaves, which is consistent with the results of the present study.
Although the present study contributes to the overall understanding of pesticide residues of imidacloprid in crops, it has some limitations. For example, only wheat grown under hydroponic conditions was selected as the test plant in the present study. Therefore, future research on the mechanisms of absorption, migration, and distribution of pesticides in vegetables, fruit trees, and other plants grown in soil as well as water is warranted. In further studies, various concentrations of imidacloprid and a variety of plants will be studied to explore in greater detail the absorption, transport, and accumulation of imidacloprid in plants so as to better understand the environmental risk posed by imidacloprid.
Disclosures
The authors have nothing to disclose.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (No. 42277039).
Materials
| Acetonitrile | Sigma-Aldrich (Shanghai) Trading Co. Ltd. | 01-06-1995 | Suitable for HPLC, gradient grade, >99.9% |
| Analytical balance | Sartorius Lab Instruments Co.Ltd. | GL124-1SCN | |
| Artificial climate incubator | Shanghai Badian Instrument Equipment Co. Ltd. | HK320 | |
| Centrifuge | Eppendorf China Co. Ltd. | Centrifuge5804 | |
| Disposable syringe | Sigma-Aldrich (Shanghai) Trading Co. Ltd. | Z116866 | Capacity 5 mL, graduated 0.2 mL, non-sterile |
| Formic acid | Sigma-Aldrich (Shanghai) Trading Co. Ltd. | Y0001970 | European pharmacopoeia reference standard |
| Graphitized carbon black (GCB) | Sigma-Aldrich (Shanghai) Trading Co. Ltd. | V900058 | 45 μm |
| H2O2 | Sigma-Aldrich (Shanghai) Trading Co.Ltd. | 31642 | 30% (w/w) |
| Hoagland’s Basal Salt Mixture | Shanghai Yu Bo Biotech Co. Ltd. | NS1011 | Anhydrous, reagent grade |
| Hydroponic equipment | Jiangsu Rongcheng Agricultural Science and Technology Development Co.Ltd. | SDZ04BD | |
| Hypersil BDS C18 column | Thermo Fisher Scientific (China) Co. Ltd. | 28103-102130 | |
| Imidacloprid | Sigma-Aldrich (Shanghai) Trading Co. Ltd. | Y0002028 | European pharmacopoeia reference standard |
| MgSO4 | Sigma-Aldrich (Shanghai) Trading Co. Ltd. | 208094 | Anhydrous, reagent grade, >97% |
| NaCl | Sigma-Aldrich (Shanghai) Trading Co.Ltd. | S9888 | Reagent grade, 99% |
| pH meter | Shanghai Thunder Magnetic Instrument Factory | PHSJ-3F | |
| Phytotron box | Harbin Donglian Electronic Technology Co. Ltd. | HPG-280B | |
| Pipettes | Eppendorf China Co. Ltd. | Research plus | |
| Syringe filter | Sigma-Aldrich (Shanghai) Trading Co.Ltd. | SLGV033N | Nylon, 0.22 µm pore size, 33 mm, non-sterile |
| Ultra performance liquid chromatography tandem triple quadrupole mass spectrometry | Thermo Fisher Scientific (China) Co. Ltd. | UltiMate 3000 | |
| TSQ Quantum Access MAX | |||
| Vortex mixer | Shanghai Yetuo Technology Co. Ltd. | Vortex-2 | |
| Wheat seed | LuKe seed industry | Jimai 20 |
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