Study on the Metabolism of Six Systemic Insecticides in a Newly Established Cell Suspension Culture Derived from Tea (<em>Camellia Sinensis </em>L.) Leaves

Weiting Jiao; Guoqin Ge; Rimao Hua; Jun Sun; Yeyun Li; Ruyan Hou

doi:10.3791/59312

JoVE Journal > Biochemistry

Bioquímica

Study on the Metabolism of Six Systemic Insecticides in a Newly Established Cell Suspension Culture Derived from Tea (Camellia Sinensis L.) Leaves

Published: June 15, 2019

doi:

10.3791/59312

Weiting Jiao*^1,2, Guoqin Ge*¹, Rimao Hua², Jun Sun¹, Yeyun Li¹, Ruyan Hou¹

¹State Key Laboratory of Tea Plant Biology and Utilization, School of Tea and Food Science & Technology,Anhui Province Key Lab of Analysis and Detection for Food Safety, ²School of Resource & Environment, Anhui Agricultural University,Key Laboratory of Agri-food Safety of Anhui Province

Summary

This work presents a protocol for establishing a cell suspension culture derived from tea (Camellia sinensis L.) leaves that can be used to study the metabolism of external compounds that can be taken up by the whole plant, such as insecticides.

Abstract

A platform for studying insecticide metabolism using in vitro tissues of tea plant was developed. Leaves from sterile tea plantlets were induced to form loose callus on Murashige and Skoog (MS) basal media with the plant hormones 2,4-dichlorophenoxyacetic acid (2,4-D, 1.0 mg L^-1) and kinetin (KT, 0.1 mg L^-1). Callus formed after 3 or 4 rounds of subculturing, each lasting 28 days. Loose callus (about 3 g) was then inoculated into B5 liquid media containing the same plant hormones and was cultured in a shaking incubator (120 rpm) in the dark at 25 ± 1 °C. After 3−4 subcultures, a cell suspension derived from tea leaf was established at a subculture ratio ranging between 1:1 and 1:2 (suspension mother liquid: fresh medium). Using this platform, six insecticides (5 µg mL^-1 each thiamethoxam, imidacloprid, acetamiprid, imidaclothiz, dimethoate, and omethoate) were added into the tea leaf-derived cell suspension culture. The metabolism of the insecticides was tracked using liquid chromatography and gas chromatography. To validate the usefulness of the tea cell suspension culture, the metabolites of thiamethoxan and dimethoate present in treated cell cultures and intact plants were compared using mass spectrometry. In treated tea cell cultures, seven metabolites of thiamethoxan and two metabolites of dimethoate were found, while in treated intact plants, only two metabolites of thiamethoxam and one of dimethoate were found. The use of a cell suspension simplified the metabolic analysis compared to the use of intact tea plants, especially for a difficult matrix such as tea.

Introduction

Tea is one of the most widely consumed non-alcoholic beverages in the world¹^,². Tea is produced from the leaves and buds of the woody perennial Camellia sinensis L. Tea plants are grown in vast plantations and are susceptible to numerous insect pests³^,⁴. Organophosphorus and neonicotinoid insecticides are often used as systemic insecticides⁵ to protect tea plants from pests such as whiteflies, leaf hoppers, and some lepidopteran species⁶^,⁷. After application, these insecticides are absorbed or translocated into the plant. Within the plant, these systemic insecticides may be transformed through hydrolysis, oxidation or reduction reactions by plant enzymes. These transformation products can be more polar and less toxic than the parent compounds. However, for some organophosphates, the bioactivities of some products are higher. For example, acephate is metabolized into the more toxic methamidophos⁸^,⁹, and dimethoate into omethoate¹⁰^,¹¹. Plant metabolic studies are thus important for determining the fate of a pesticide within a plant¹².

Plant tissue cultures have been proven to be a useful platform for investigating the pesticide metabolism, with the identified metabolites similar to those found in intact plants¹³^,¹⁴^,¹⁵. The use of tissue cultures, particularly cell suspension cultures, has several advantages. Firstly, experiments can be carried out free of microorganisms, thus avoiding the interference of pesticide transformation or degradation by microbes. Secondly, tissue culture provides consistent materials for use at any time. Thirdly, the metabolites are easier to extract from tissue cultures than from intact plants, and tissue cultures often have fewer interring compounds and lower complexity of compounds. Finally, tissue cultures can more easily be used to compare a series of pesticides metabolism in a single experiment¹⁶.

In this study, a cell suspension derived from the leaves of sterile-grown tea plantlet was successfully established. The tea cell suspension culture was then used to compare the dissipation behaviors of six systemic insecticides.

This detailed protocol is intended to provide some guidance so that researchers can establish a plant tissue culture platform useful for studying the metabolic fate of xenobiotics in tea.

Protocol

1. Tea callus culture

NOTE: Sterile leaves were derived from in vitro-grown plantlet lines first developed in the research group¹⁷. All procedures up to section 5 were carried out in a sterile laminar flow hood, except for the culture time in an incubator.

Adjust the pH of the two media (Murashige and Skoog [MS] basal medium and Gamborg's B5 liquid medium) to 5.8 prior to autoclaving (121 °C, 20 min).
Cut along the middle vein of a sterile leaf using scissors, and then subdivide each half into small pieces of about 0.3 cm x 0.3 cm in a petri dish.
Place the sterile explants (the small leaf pieces) onto MS basal media containing the plant hormones 2,4-D (1.0 mg L^-1) and KT (0.1 mg L^-1). Six explants can be placed in a 300 mL flask containing 100 mL of MS basal media.
Culture the above leaf explants at a constant temperature of 25 °C in the dark. After 28 days, select the first generation of induced callus and transfer to fresh flask (a subculture). Acquire the loose and friable callus after 3−4 subcultures.

2. Tea cell suspension culture

Cut the vigorous, friable and loose calluses from the solid medium into small pieces (range here 0.5−2 mm) using a sterile surgical blade under sterile conditions.
Weigh about 3 g of the small pieces of callus. Place the callus into a 150 mL flask containing 20 mL of B5 liquid media supplemented with 2,4-D (1.0 mg L^-1) and KT (0.1 mg L^-1).
Culture the liquid cell suspension at a constant temperature (25 ± 1 °C) in a shaking incubator at 120 rpm in the dark.
After 7 to 10 days of culturing, remove the culture flasks and let them stand for a few minutes.
Take all the supernatant as seed material for subculture to fresh medium (subculture ratio of suspension mother liquid to fresh medium ranged between 1:1 and 1:2). Remove the precipitated, large calluses.
Obtain the final well-grown cell suspension culture after 3−4 subculture cycles of 28 days each.

3. Triphenyl tetrazolium chloride assay of cell viability

Kill a sample of living cells at 100 °C for 10 min as a control cell before viability staining.
Centrifuge all cell suspension culture for 8 min at 6000 x g. Remove the supernatant before suspending the cells in 2.5 mL of phosphate-buffered saline (PBS) buffer (pH 7.3), and shake it for 1 min by hand.
Add 2.5 mL of the 0.4%triphenyl tetrazolium chloride (TTC) solution and shake by hand again.
Incubate the mixture for 1 h in a standing incubator (30 °C).

4. Treatment and sampling of tea cell suspension cultures with insecticides

Add an aliquot of 400 µL of filter-sterilized stock solution (500 µg mL^-1) of four neonicotinoids (thiamethoxam, acetamiprid, imidacloprid, and imidaclothiz) or two organophosphates (dimethoate and omethoate) into the cell suspension cultures, respectively.
NOTE: If the aim is to compare xenobiotic behaviors, use the same mother batch of cell suspensions to test the different compounds.
Culture the samples of cell suspensions with insecticides at constant temperature (25 ± 1 °C) and shaking incubator speed (120 rpm). Take the samples (see step 4.3 or 4.4) on 0, 3, 5 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70 and 75 days.
To test a sample containing a neonicotinoid, remove a 1 mL aliquot of the homogeneous cell culture, place it into a 1.5 mL plastic centrifuge tube, and centrifuge at 4000 x g for 2 min.
1. Pass the supernatants through a 0.22-µm pore-size filter membrane before analysis by high-performance liquid chromatography-ultraviolet (HPLC-UV) and ultra-high performance liquid chromatography-quadrupole time-of-flight (UPLC-QTOF) mass spectrometry (Table of Materials).
To test a sample containing an organophosphate, remove a 500 µL aliquot of the cell culture and place into a 35 mL centrifuge tube or a 1.5 mL plastic centrifuge tube (prepare the latter sample like that of neonicotinoid).
1. Add 0.1 g of sodium chloride and 5 mL of acetone/ethyl acetate (3:7, v/v) into the 35 mL centrifuge tube of the 500 µL samples.
2. Vortex the mixtures for 1 min, and then allow them to rest for 10 min.
3. Take 2.5 mL of the supernatant into a 10 mL glass tube and evaporate to near-dryness using a nitrogen evaporator at 40 °C.
4. Dissolve the residue with 1 mL acetone, vortex for 1 min, pass it through a 0.22-µm filter membrane before analysis by gas chromatography-flame photometric detector (GC-FPD).

5. Sample preparation of intact tea plant with insecticides

NOTE: The intact tea plant trial was conducted in a hydroponic system using tea seedlings grown in 50 mL of a nutrient solution (30 NH₄+, 10 NO₃-, 3.1 PO₄-, 40 K⁺, 20 Ca²⁺, 25 Mg²⁺, 0.35 Fe²⁺, 0.1 B³⁺, 1.0 Mn²⁺, 0.1 Zn²⁺, 0.025 Cu²⁺, 0.05 Mo⁺, and 10 Al³⁺, in mg L^-1)¹⁸. An experimental greenhouse was under a light-dark cycle (12 h of light and 12 h of darkness) at 20 °C at Anhui Agricultural University.

Put five plants in a 4 L plastic pot for 15 days.
Add 0 ppm (control) or 100 ppm of thiamethoxam or dimethoate into plastic pots, respectively.
Prepare the intact plant sample according to the previous method, except for presoaking¹⁹, and then analyze with mass spectrometry for an accurate mass spectrum.

6. Instrument analysis

HPLC analysis of the metabolic behavior of neonicotinoids
1. Use an HPLC-UV (Table of Materials) to detect the content and metabolic products of thiamethoxam and acetamiprid at a wavelength of 254 nm, and of imidacloprid and imidaclothiz at 270 nm in samples from section 4.3.
  NOTE: The HPLC-UV condition was the same as the previous study¹⁹.
GC analysis of the metabolic behavior of organophosphates
1. Detect the content of dimethoate and omethoate in samples from section 4.4 by a GC-FPD using a chiral column (Table of Materials).
2. Use nitrogen as the carrier gas and set the flow rate at 1.0 mL min^-1.
3. Set the initial temperature to 120 °C, and hold it for 5 min. Increase the temperature to 150 °C at 30 °C min^-1 and hold for 3 min. Increase to 170 °C at 10 °C min^-1 and hold for 7 min. Finally increase to 210 °C at 30 °C min^-1 and then hold for 5 min.
4. Set the injection temperature to 200 °C in splitless mode; Set the detector temperature to 250 °C.
5. Set the injection volume to 1 µL.
UPLC-QTOF analysis of the insecticide metabolites in cell culture
1. Detect the metabolites of the insecticides in cell culture (samples from section 4.3) using UPLC-QTOF with a C18 column (Table of Materials).
2. Set the flow rate to 0.2 mL min^-1. Set the injection volume to 10 µL.
3. For the neonicotinoid-treated samples, set the initial mobile phase to 85% A (5 mM ammonium formate water) and 15% B (acetonitrile). Over 10 min, increase mobile phase B to 38% and return to 15% over 1 min, hold for 9 min.
4. For the organophosphate-treated samples, set the initial mobile phase to 55% A (0.1% formic acid water) and 45% B (acetonitrile). Over 5 min, increase mobile phase B to 70%, then return to 45% of B over 0.5 min, hold for 2.5 min.
5. Set the QTOF operation parameters as follows: gas temperature, 325 °C; drying gas (nitrogen), 10 L min^-1; sheath gas temperature, 350 °C; sheath gas flow, 11 L min^-1; capillary voltage, 4000 V; nozzle voltage, 1000 V; fragmentor voltage, 100 V for neonicotinoid insecticides or 110 V for organophosphorus insecticides; skimmer voltage, 65 V; operating in positive ion mode.
6. Set the instrument to the full scan spectrum and target MS/MS mode.
7. Process the data using accurate mass tools; Infer the metabolites with no standard products from the MS/MS annotation as well as the literature¹²^,¹⁵^,²⁰^,²¹^,²².
UPLC-Orbitrap analysis of the insecticide metabolites in intact plant extract
1. Detect the metabolites of insecticides in intact plant extract using UPLC-Orbitrap mass spectrometry (Table of Materials).
2. Set the mass spectrometry (Table of Materials) operation parameters as follows: sheath gas pressure, 35 arb; gas temperature, 300 °C; nozzle voltage, 3.5 KV; capillary temperature, 350 °C.
3. Set the elution programs as the above (steps 6.3.3 and 6.3.4) for UPLC-QTOF analysis of cell culture.

Representative Results

The induction of callus from leaves harvested from field-grown tea trees and from leaves excised from tea plantlets grown in vitro in a sterile environment was compared by measuring contamination, browning, and induction after 28 days of cultivation on MS media (Figure 1A). Callus growth was recorded at 20, 37, 62 and 90 days of culture (Figure 1B). The callus derived from the in vitro-grown leaves showed more vigorous growth than did the callus derived from the field-grown leaves during the whole 90 days of cultivation. The callus from the sterile leaves was bright yellow, while the callus from the field-grown leaves was brown (Figure 1B).

At a concentration of 1.0 mg L^-1 of 2,4-D²³, the concentration of KT was optimized. At 0.05 mg L^-1 KT, the callus growth rate was slow, the texture was a little compact, and the callus was white in color (Figure 2C); at 0.1 mg L^-1 KT concentration, the callus growth rate was the highest, up to 61.5% (Figure 2A), the texture was loose, and the color was yellowish (Figure 2C); when the KT was increased to 0.5 mg L^-1, the callus was compact and irregular and brown in the center (Figure 2C). After the KT concentration was selected, the concentration of 2,4-D was further studied. At a combination of 1 mg L^-1 2,4-D and 0.1 mg L^-1 KT, the callus growth rate was the highest, reaching 46.9%, and the appearance of the callus was the best (Figure 2B,D).

After the 2^nd subculture on solid media, more than half of the surface of each excised leaf was covered by growing callus (Figure 3A). After the 4^th subculture, the leaf sections were completely covered by the callus. After the 5^th subculture, the callus texture began to become compact with some white and brown spots on the bottom.

When the subculture cycle was 21 days long (Figure 3B), the callus was vigorous, but the greatest amount of growth had not been reached, indicating that frequent subculture would result in less callus amount. When the subculture cycle was 28 days long, the callus had grown vigorously, the color was yellowish color and the texture was loose. After 35 days, the callus began to brown from the center. The callus was in the worst state, with a deep brown color and no longer growing, at 42 days.

Two kinds of liquid media were compared for their effects on the growth of the callus and the color of the cell suspension (Figure 4). Three different ratios of mother liquid to total volume of culture liquid were tested. During the 75 days of cultivation, the cell density gradually increased in cultures started at all three ratios. The ratio of 15 g cells in 40 mL fresh media (v/v) yielded an optical density (OD) value significantly higher than that of 4 g in 40 mL (v/v) and 6 g in 40 mL (v/v) (Figure 5A). After 4 subculture cycles of 28 days each, a tea cell suspension system was successfully established from sterile tea callus in B5 liquid media (Figure 6).

Figure 1: Comparison of callus induction from picked leaves and sterile plantlet leaves. (A) Comparison of callus induction from leaves harvested from plantation-grown tea plants and from leaves excised from sterile, in vitro-grown plantlets. Explants were observed for contamination, browning and induction of callus. (B) Comparison of callus growth of leaves derived from plantation-grown tea plants (set 1) and sterile in vitro-grown plantlets (set 2): Photographs were on different days: 20 (panels a); 37 (b); 62 (c); and 90 (d). This figure has been modified from Jiao et al.²⁴. Please click here to view a larger version of this figure.

Figure 2: The growth rate and growth status of tea-leaf derived callus under different plant hormone concentrations. The growth rate (A) and growth status (C) of tea-leaf derived callus under different KT concentrations and 1 mg L^-12,4-D; The growth rate (B) and growth status (D) of callus under different 2,4-D concentrations and 0.5 mg L^-1 KT. This figure has been modified from Jiao et al.²⁴. Please click here to view a larger version of this figure.

Figure 3: Callus status after different numbers of subculture cycles (A) and different lengths of subculture cycles (B). This figure has been modified from Jiao et al.²⁴. Please click here to view a larger version of this figure.

Figure 4: Influence of different media types on callus growth in liquid suspension culture system. (A) B5 medium. (B) MS medium. This figure has been modified from Jiao et al.²⁴. Please click here to view a larger version of this figure.

Figure 5: The optical density values and TTC staining. (A) The OD₆₈₀value of cell suspension started at different ratios from 0 to 75 days; (B) The TTC staining of living and control cells. This figure has been modified from Jiao et al.²⁴. Please click here to view a larger version of this figure.

Figure 6: The process of establishing a tea cell suspension culture at constant temperature (25 ± 1 °C) in a dark incubator. Sterile culture of tea plantlets as source of leaf explant (a); Tea leaf inoculated onto MS medium with 2,4-D (1.0 mg L^-1) and KT (0.1 mg L^-1) (b); Initial cultured callus after 28 days (c); Callus suitable for cell suspension after 4 subculture cycles of 28 days each (d); The remaining steps were at the same temperature but at a constant speed of 120 rpm in a shaking incubator: Callus inoculated into B5 medium for 7 to 10 days (e); Seeded cell suspension after removing the precipitated and large callus (f); The subculture of cell suspension after 1 cycle of 28 days (g); Mature cell suspension after 3-4 subculture cycles of 28 days each (h). This figure has been modified from Jiao et al.²⁴. Please click here to view a larger version of this figure.

Supplemental Figure 1: The metabolism of 5 µg/mL of 6 insecticides in tea cell suspension culture and in media (CK) incubated at constant temperature (25 ± 1 °C) and shaking incubator speed (120 rpm) over 75 days. Thiamethoxan (A), imidacloprid (B), acetamiprid (C), imidaclothiz (D), dimethoate (E1), and omethoate (F); (E2) Production over time of the metabolite of dimethoate (omethoate) produced in dimethoate-treated cell culture and media. This figure has been modified from Jiao et al.²⁴. Please click here to download this figure.

Supplemental Figure 2: Total ion chromatograms (TICs) of the extracts from untreated control cell culture, thiamethoxam-treated cell culture, thiamethoxam-treated media (cell-free) after 75 days. Peaks 1-5, 7 and 8 were metabolites of thiamethoxam and Peak 6 was thiamethoxam (A); TICs of the extracts from dimethoate-treated cell culture, dimethoate-treated media (cell-free), and untreated control cells after 60 days. Peaks 1 and 2 were metabolites of dimethoate and Peak 3 was dimethoate (B); TICs of the extracts from thiamethoxam-treated (upper) and untreated (lower) intact plants (C); TICs of the extracts from dimethoate-treated (upper) and untreated (lower) intact plants (D); The metabolite of dimethoate at tR 1.86 min in intact plants (D1); No compounds detected at tR 1.86 min in untreated plants (D2). This figure has been modified from Jiao et al.²⁴. Please click here to download this figure.

Supplemental Figure 3: The secondary mass spectrometry using UPLC-QTOF of peaks derived from cultures treated with (A) thiamethoxam and (B) dimethoate. This figure has been modified from Jiao et al.²⁴. Please click here to download this figure.

Supplemental Figure 4: The secondary mass spectrometry using Q-Exactive of peaks derived from intact plant treated with thiamethoxam (A1, A2 and A3) and dimethoate (B1 and B2). This figure has been modified from Jiao et al.²⁴. Please click here to download this figure.

Discussion

This article presents the detailed process of establishing a model of pesticide metabolism in tea plant tissue, including the selection of explants, the determination of cell viability, and the establishment of a tea cell suspension culture with high metabolic activity. Any parts of a plant tissue could be used to initiate callus in a sterilized environment²⁵. Tea leaves were chosen for callus initiation in this study, not only because leaves to tend to be less contaminated than the parts below ground, but also because they are the edible part of the crop and the main target of pesticide application.

In this study, the induction rate and growth status of callus from leaves picked from the field and from leaves excised from a sterile plantlet grown in vitro were compared. The sterile leaves had much lower rates of browning and contamination and a higher rate of induction compared to field-grown leaves. This was likely because leaves from field-grown plants not only underwent surface sterilization using ethanol and mercury but also a change in growth environment, while sterile leaves were cultivated in a sterile environment and could be used directly without additional sterilization. In addition, the callus derived from the in vitro-grown, sterile plantlets showed more vigorous growth than the field-grown leaves during the 90 days of cultivation. Leaves from sterile plantlets were more suitable for induction of tea callus, not only because of their high callus induction and low contamination rates, but also because of the shorter pre-treatment time and independence from seasonal factors.

To culture loose and friable callus, the crucial parameters, primarily plant growth regulator levels and length of and number of subculture cycles, must be optimized²⁵. 2,4-D can effectively promote callus induction and growth and is the most widely used hormone in callus culture²⁶. Subculture times and subculture cycle length are also important for callus culture²⁵. After 2 to 4 subcultures of 28 days of each cycle, the callus had a loose texture with a yellowish color and no browning. The optimization experiments determined that the best callus induction protocol was to place leaf explants from sterile plantlets on MS basal media containing 1 mg L^-12,4-D and 0.1 mg L^-1 KT and to transfer the explant/callus every 28 days for a total of 4 subculture cycles. This protocol initiated loose and friable callus that was suitable for the initiation of a cell suspension.

In plant tissue culture, the solid medium used for callus growth can often be used for cell suspension culture in a liquid form²³. Whereas, tea comes into being large quantities of polyphenols in MS basal medium containing a high concentration of inorganic salts, resulting in the callus browning²⁷^,²⁸. In this study, liquid B5 media and MS media were both tested. The average growth rates were found no significantly difference between the two cultures (16.66% in B5 basal media and 15.77% in MS basal media; Figure 4). However, the calluses were brown in MS basal media. So, B5 basal media was selected in the proposed method.

Oxygen is important to plant cell growth and metabolism. In liquid culture, an excessive volume of liquid will decrease the oxygen concentration and inhibit cell growth, while too little liquid also inhibits cell growth²⁵. Several ratios of liquid to flask volume (mL liquid: mL flask) were tested. Based on the dry weight of the cell growth after 21 d, the liquid: flask ratios ranked as follows: 30:150 > 40:150 > 20:150, 50:150, 60:150 (mL: mL)²³. In this study, 40 mL of culture liquid was placed in a 150 mL flask (40 mL: 150 mL) was selected according to the how the cell suspension looked as observed by the naked eye.

Plant cells cannot grow well when the cell density is too high or too low. Thus, the proportion of mother cell suspension culture to fresh medium at the time of subculture affects the growth potential of the cells²⁹. This study used the OD value of the homogeneous cell suspension culture to represent the amount of cell growth. Inoculation with 15 g of mother liquid into 40 mL of total volume of culture liquid (v/v) was suitable for the cell growth. The subculture ratio was equal to between 1:1 and 1:2 (suspension mother liquid: fresh medium).

Cell viability within the tea cell suspension culture was tested by TTC staining. The colorless TTC compound can be converted to the red colored formazan by dehydrogenases in the mitochondria of living cells, but the color cannot be changed from dead cells (Figure 5B). This method verified the growth status of the cells in liquid culture.

The establishment of a tea cell suspension culture provides an easy in vitro research platform for studying metabolism and metabolites of different pesticides. Independent of season and weather, cell suspension cultures can be treated with different pesticides, different concentrations of active ingredient, and for different lengths of time. The metabolites produced in the tea cell suspension cultures were similar to those extracted from intact plants (Supplemental Figure 1 and Supplemental Figure 2). Interestingly, seven metabolites of thiamethoxam and two metabolites of dimethoate were detected in tea cell suspension culture, but only two metabolites of thiamethoxam and one for dimethoate in treated intact plants (Supplemental Figure 1, Supplemental Figure 2, and Supplemental Figure 3). This may be because of the easier extraction from cells without waxy cuticle, fewer compounds from the tea interfering with the mass spectrometry results (the matrix effect), or the simpler metabolite profile of tea cells compared to the whole plant.

The results showed that thiamethoxam was more readily metabolized by the tea cell compared with the other three neonicotinoids (Supplemental Figure 4). Both of the organophosphates (dimethoate and omethoate) were metabolized faster than the neonicotinoids. These results show the diversity of the metabolic pathways and of metabolic regulation in the tea cell, which need to be further studied.

Using intact plants to study insecticide metabolism and to identify insecticide metabolites presents numerous difficulties, including barriers to absorption and long-distance transport of both initial and breakdown compounds within the plant³⁰. Cell suspension cultures could not only solve this problem, but also reduce matrix interference in sample analysis compared to the extract from fresh leaves²⁴. This research proved that tea cell suspension cultures are an effective platform for studying the metabolism of xenobiotic compounds in the tea plant. It can be served as a mode to study the metabolism of xenobiotics in other plants.

Declarações

The authors have nothing to disclose.

Acknowledgements

This work was supported by the National Key Research & Development Program (2016YFD0200900) of China, the National Natural Scientific Foundation of China (No. 31772076 and No. 31270728), China Postdoctoral Science Foundation (2018M630700), and Open Fund of State Key Laboratory of Tea Plant Biology and Utilization (SKLTOF20180111).

Materials

Acetamiprid (99.8%)	Dr. Ehrenstorfer	46717	CAS No: 135410-20-7
Acetonitrile (CAN, 99.9%)	Tedia	AS1122-801	CAS No: 75-05-8
Agar	Solarbio Science & Technology	A8190	CAS No: 9002-18-0
Clothianidin (99.8%)	Dr. Ehrenstorfer	525	CAS No: 210880-92-5
Dimethoate (98.5%)	Dr. Ehrenstorfer	109217	CAS No: 60-51-5
Imidacloprid (99.8%)	Dr. Ehrenstorfer	91029	CAS No: 138261-41-3
Imidaclothiz (99.5%)	Toronto Research Chemical	I275000	CAS No: 105843-36-5
Kinetin (KT, >98.0%)	Solarbio Science & Technology	K8010	CAS No: 525-79-1
Omethoate (98.5%)	Dr. Ehrenstorfer	105491	CAS No: 1113-02-6
Polyvinylpolypyrrolidone (PVPP)	Solarbio Science & Technology	P8070	CAS No: 25249-54-1
Sucrose	Tocris Bioscience	5511	CAS No: 57-50-1
Thiamethoxam (99.8%)	Dr. Ehrenstorfer	20625	CAS No: 153719-23-4
Triphenyltetrazolium Chloride (TTC, 98.0%)	Solarbio Science & Technology	T8170	CAS No: 298-96-4
2,4-Dichlorophenoxyacetic Acid (2,4-D, >98.0%)	Guangzhou Saiguo Biotech	D8100	CAS No: 94-75-7
chiral column	Agilent CYCLOSIL-B	112-6632	Chromatography column (30 m × 0.25 mm × 0.25 μm)
Gas chromatography (GC)	Shimadu	2010-Plus	Paired with Flame Photometric Detector (FPD)
High-performance liquid chromatography (HPLC)	Agilent	1260	Paired with Ultraviolet detector (UV)
HSS T3 C18 column	Waters	186003539	Chromatography column (100 mm × 2.1 mm × 1.8 μm)
Ultra-high-performance liquid chromatography (UPLC)	Agilent	1290-6545	Tandem quadrupole time-of-flight mass spectrometer (QTOF)
Ultra-high-performance liquid chromatography (UPLC)	Thermo Scientific	Ultimate 3000-Q Exactive Focus	Connected to a Orbitrap mass spectrometer

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Jiao, W., Ge, G., Hua, R., Sun, J., Li, Y., Hou, R. Study on the Metabolism of Six Systemic Insecticides in a Newly Established Cell Suspension Culture Derived from Tea (Camellia Sinensis L.) Leaves. J. Vis. Exp. (148), e59312, doi:10.3791/59312 (2019).