This study was supported by the National Natural Science Foundation of China (21976160) and Zhejiang Province Public Welfare Technology Application Research Project (LGF21B070006).

1. Differentiation of carrot callus
NOTE: Autoclave all equipment used here and perform all operations in a UV-sterilized ultra-clean workbench.
<ol>
	<li>Vernalize the seeds by immersing the uniform carrot seeds (Daucus carota var. sativus) into deionized water at 4 &#176;C for 16 h.</li>
	<li>Surface-sterilize the vernalized seeds with 75% ethanol for 20 min, and then rinse three times with sterile deionized water under aseptic conditions.</li>
	<li>Further sterilize the seeds with 20% H2O2 for 20 min, and wash them with sterilized deionized water six times under aseptic conditions.</li>
	<li>Aseptically germinate the seeds by sowing them on hormone-free MS medium (pH 5.8, autoclaved at 121 &#176;C for 20 min) containing 1% agar-gel, and incubating at 26 &#176;C with a 16 h photoperiod (350 &#181;mol/m2s) for 15 days.</li>
	<li>Obtain the explants by cutting the hypocotyl and cotyledon of the seedlings into small pieces (0.5 cm).</li>
	<li>Transform the explants to Petri dishes (two to four explants per dish) containing 15-20 mL of aseptic MS medium supplemented with auximone (2,4-dichlorophenoxyacetic acid; 1 mg/L) and phytokinin (6-benzylaminopurine; 0.5 mg/L) under aseptic conditions.</li>
	<li>Incubate the explants in the dark at 26 &#176;C for 3-4 weeks to induce the callus.</li>
	<li>Separate the callus tissues (around 1 cm diameter) formed from the initial explants using a sterile scalpel and forceps. 
	NOTE: The newly formed callus tissues are white to creamy yellow in color and loosely attach to the initial explants.</li>
</ol>
2. 2,4-dibromophenol treatment
<ol>
	<li>Dissolve 1 &#181;g of 2,4-dibromophenol in 10 mL of aseptic liquid MS medium (the final concentration of 2,4-dibromophenol is 100 ppb, pH 5.6-7.0).</li>
	<li>Add 3 g of the fresh carrot callus (step 1.8) into glass flasks containing the prepared 2,4-dibromophenol solution (from step 2.1) under aseptic conditions. Consider this as the 2,4-dibromophenol treatment. 
	NOTE: The glass flasks were autoclaved and sealed using paraffin film.</li>
	<li>Include a medium control containing the 2,4-dibromophenol solution only (prepared in step 2.1) to evaluate the abiotic degradation of 2,4-dibromophenol.</li>
	<li>Include a blank control containing the carrot callus only (no 2,4-dibromophenol solution) to check for any potential contamination.
	<ol>
		<li>Prepare the blank control containing carrot by adding 3 g of fresh collected carrot callus only into 10 mL of sterile MS medium.</li>
	</ol>
	</li>
	<li>Incubate the 2,4-dibromophenol treatment and the medium and blank controls at 130 rpm and 26 &#176;C in the dark in an incubator for 120 h.</li>
	<li>Remove the glass flasks from the incubator to collect the samples from the 2,4-dibromophenol treatment and controls after 120 h of incubation. 
	NOTE: All samples were prepared in triplicate.</li>
</ol>
3. Sample preparation
<ol>
	<li>Separate the callus carefully from the MS medium by filtration with glass fiber filters (0.45 &#181;m) for the 2,4-dibromophenol treatment and the controls. Collect the callus after washing with ultrapure water three times.</li>
	<li>Freeze-dry the collected callus with liquid nitrogen, and subsequently homogenize the collected callus (0.2 g) with a high-throughput tissue grinder at 70 Hz for 3 min.</li>
	<li>Spike the homogenized callus by adding 50 &#181;L of 25 mg/L surrogate 4-n-NP-d4 with a glass microsyringe and subsequently vortexing for 1 min.</li>
	<li>Sonicate the samples with 5 mL of methanol/water (1:1, v/v) in an ultrasonicator (150 W, 40 kHz) filled with ice water for 30 min, to extract 2,4-dibromophenol and the metabolites.</li>
	<li>Centrifuge the suspensions at 8,000 x g at 4 &#176;C for 10 min, and collect the supernatants by pipetting.
	<ol>
		<li>Repeat the extraction processes for the callus sample three times and combine the extracts.</li>
	</ol>
	</li>
	<li>Pass the extracts through hydrophilic lipophilic balanced solid phase extraction (HLB SPE) cartridges with a flow rate of 1 mL/min. 
	NOTE: The HLB SPE cartridges were pretreated sequentially with 6 mL of methanol and 6 mL of water to remove any interferences.</li>
	<li>Elute the analytes by passing 6 mL of methanol through the HLB SPE cartridges. Then, concentrate the obtained eluents to 1 mL under a gentle stream of nitrogen gas for instrumental analysis.</li>
	<li>Inject 10 &#181;L of resultant eluents into the UPLC-Q-TOF-MS for 2,4-dibromophenol and their metabolites analysis15.
	<ol>
		<li>Filter all the samples with a 0.22 &#181;m nylon membrane before instrumental analysis.</li>
	</ol>
	</li>
</ol>
4. Instrumental analysis
NOTE: 2,4-dibromophenol and their metabolites&#39; analyses were performed on an ultra-performance liquid chromatograph (UPLC) in combination with a micrOTOF-QII mass spectrometer equipped with an electrospray ionization (ESI), operating in the positive and negative ion mode.
<ol>
	<li>Open the column heater door and install the UPLC column by connecting the column inlet to the injection valve and column outlet to the mass spectrometer&#39;s inlet. 
	NOTE: A C18 column (50 mm x 2.1 mm; 1.7 &#181;m particle size) was used for the separation of analytes at 40 &#176;C.</li>
	<li>Connect mobile phase A (ultrapure water) and mobile phase B (chromatography-grade methanol) to the instrument by inserting the end of the solvent tubes A and B into the corresponding solvent bottles, respectively.
	<ol>
		<li>Filter all mobile phases (500 mL for each) through a 0.22 &#181;m filter, and sonicate for more than 30 min.</li>
	</ol>
	</li>
	<li>In the software window, click on Instrument | Inlet Method to edit the conditions for the liquid chromatogram.
	<ol>
		<li>Set the gradient conditions of mobile phase B as follows: a flow rate of 1.0 mL/min; 0-0.5 min, 5%; 0.5-3.5 min, 5% to 50%; 3.5-6.5 min, 50% to 100%; 6.5-7 min, 100%; 7-10 min, 100% to 5%.</li>
		<li>Set the injection rate of the samples into the UPLC-Q-TOF-MS as 0.2 mL/min. 
		NOTE: The injection of the sample is programmed using a fully automatic sampler.</li>
	</ol>
	</li>
	<li>In the software window, select MS Method and then set up the parameters of Q-TOF-MS: a drying gas (N2) flow rate of 8 L/min, a temperature of 300-350 &#176;C; a capillary voltage of 4,500 V; a collision energy of 5-45 V; and a full scan range of 40-800 Da.</li>
	<li>Place the sample vials in the corresponding locations of the sample trays by serial number, and re-insert the sample trays into the sample chamber. 
	NOTE: Keep the sample trays flat and make sure that the door of the sample chamber is closed.</li>
	<li>In the software window, select File | New to create a database. Name the database.</li>
	<li>Load the sample program created above by selecting MS File | Inlet file | Inject Volume.</li>
	<li>Save the database in the sample folder of the project by clicking File | Save.</li>
	<li>Select Run | Start in the software main window, and then select Acquire Sample Data and click OK in the window of the start sample list run to collect data. 
	NOTE: The real-time chromatogram can be viewed by clicking Chromatogram | Real-time Update during the data acquisition process.</li>
	<li>Process the data in the software by selecting the target data row and clicking the Chromatogram window to view the MS scan chromatogram.</li>
	<li>In the Chromatogram window, click Display | TIC | ScanWaveDS | Add trace | OK to get the daughter scan mass spectra.</li>
	<li>Identify the metabolites by comparing the chromatograms of the 2,4-dibromophenol treatment and the controls.</li>
	<li>Elucidate the metabolite candidates by the retention time, mass, and fragmentation patterns16,17. 
	NOTE: The error of mass accuracy between the experimental m/z values of the parent ions of the metabolite candidates to their corresponding theoretical m/z should be less than 10 ppm.</li>
</ol>

<ol>
	<li>Chakraborty, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Baseline+investigation+on+plasticizers,+bisphenol+A,+polycyclic+aromatic+hydrocarbons+and+heavy+metals+in+the+surface+soil+of+the+informal+electronic+waste+recycling+workshops+and+nearby+open+dumpsites+in+Indian+metropolitan+cities.">Baseline investigation on plasticizers, bisphenol A, polycyclic aromatic hydrocarbons and heavy metals in the surface soil of the informal electronic waste recycling workshops and nearby open dumpsites in Indian metropolitan cities.</a> Environmental Pollution. 248, 1036-1045 (2019).</li><li>Abril, C., Santos, J. L., Martin, J., Aparicio, I., Alonso, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Occurrence,+fate+and+environmental+risk+of+anionic+surfactants,+bisphenol+A,+perfluorinated+compounds+and+personal+care+products+in+sludge+stabilization+treatments.">Occurrence, fate and environmental risk of anionic surfactants, bisphenol A, perfluorinated compounds and personal care products in sludge stabilization treatments.</a> Science of the Total Environment. 711, 135048 (2020).</li><li>Xu, Y. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+and+occurrence+of+bisphenol+A+and+thirteen+structural+analogs+in+soil.">Determination and occurrence of bisphenol A and thirteen structural analogs in soil.</a> Chemosphere. 277, 130232 (2021).</li><li>Cai, Q. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Occurrence+of+nonylphenol+and+nonylphenol+monoethoxylate+in+soil+and+vegetables+from+vegetable+farms+in+the+Pearl+River+Delta,+South+China.">Occurrence of nonylphenol and nonylphenol monoethoxylate in soil and vegetables from vegetable farms in the Pearl River Delta, South China.</a> Archives of Environmental Contamination and Toxicology. 63 (1), 22-28 (2012).</li><li>Wang, S. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=et+al+Migration+and+health+risks+of+nonylphenol+and+bisphenol+a+in+soil-winter+wheat+systems+with+long-term+reclaimed+water+irrigation.">et al Migration and health risks of nonylphenol and bisphenol a in soil-winter wheat systems with long-term reclaimed water irrigation.</a> Ecotoxicology and Environmental Safety. 158, 28-36 (2018).</li><li>Gunther, K., Racker, T., Bohme, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+isomer-specific+approach+to+endocrine-disrupting+nonylphenol+in+infant+food.">An isomer-specific approach to endocrine-disrupting nonylphenol in infant food.</a> Journal of Agricultural and Food Chemistry. 65 (6), 1247-1254 (2017).</li><li>Van Eerd, L. L., Hoagland, R. E., Zablotowicz, R. M., Hall, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pesticide+metabolism+in+plants+and+microorganisms.">Pesticide metabolism in plants and microorganisms.</a> Weed Science. 51 (4), 472-495 (2003).</li><li>Hillebrands, L., Lamshoeft, M., Lagojda, A., Stork, A., Kayser, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+callus+cultures+to+elucidate+the+metabolism+of+tebuconazole,+flurtamone,+fenhexamid,+and+metalaxyl-M+in+Brassica+napus+L.,+Glycine+max+(L.)+Merr.,+Zea+mays+L.,+and+Triticum+aestivum+L.">Evaluation of callus cultures to elucidate the metabolism of tebuconazole, flurtamone, fenhexamid, and metalaxyl-M in Brassica napus L., Glycine max (L.) Merr., Zea mays L., and Triticum aestivum L.</a> Journal of Agricultural and Food Chemistry. 68 (48), 14123-14134 (2020).</li><li>Macherius, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Metabolization+of+the+bacteriostatic+agent+triclosan+in+edible+plants+and+its+consequences+for+plant+uptake+assessment.">Metabolization of the bacteriostatic agent triclosan in edible plants and its consequences for plant uptake assessment.</a> Environmental Science &amp; Technology. 46 (19), 10797-10804 (2012).</li><li>Sun, J. Q., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Uptake+and+metabolism+of+nonylphenol+in+plants:+Isomer+selectivity+involved+with+direct+conjugation.">Uptake and metabolism of nonylphenol in plants: Isomer selectivity involved with direct conjugation.</a> Environmental Pollution. 270, 116064 (2021).</li><li>Schymanski, E. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identifying+small+molecules+via+high+resolution+mass+spectrometry:+communicating+confidence.">Identifying small molecules via high resolution mass spectrometry: communicating confidence.</a> Environmental Science &amp; Technology. 48 (4), 2097-2098 (2014).</li><li>Moschet, C., Anumol, T., Lew, B. M., Bennett, D. H., Young, T. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Household+dust+as+a+repository+of+chemical+accumulation:+new+insights+from+a+comprehensive+high-resolution+mass+spectrometric+study.">Household dust as a repository of chemical accumulation: new insights from a comprehensive high-resolution mass spectrometric study.</a> Environmental Science &amp; Technology. 52 (5), 2878-2887 (2018).</li><li>Ren, Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydroxylated+PBDEs+and+brominated+phenolic+compounds+in+particulate+matters+emitted+during+recycling+of+waste+printed+circuit+boards+in+a+typical+e-waste+workshop+of+South+China.">Hydroxylated PBDEs and brominated phenolic compounds in particulate matters emitted during recycling of waste printed circuit boards in a typical e-waste workshop of South China.</a> Environmental Pollution. 177, 71-77 (2013).</li><li>de Wit, C. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+overview+of+brominated+flame+retardants+in+the+environment.">An overview of brominated flame retardants in the environment.</a> Chemosphere. 46 (5), 583-624 (2002).</li><li>Sun, J. Q., Chen, Q., Qian, Z. X., Zheng, Y., Yu, S. A., Zhang, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plant+Uptake+and+Metabolism+of+e,4-Dibromophenol+in+Carrot:+In+Vitro+Enzymatic+Direct+Conjugation.">Plant Uptake and Metabolism of e,4-Dibromophenol in Carrot: In Vitro Enzymatic Direct Conjugation.</a> Journal of Agricultural and Food Chemistry. 66 (17), 4328-4335 (2018).</li><li>Chibwe, L., Titaley, I. A., Hoh, E., Simonich, S. L. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Integrated+framework+for+identifying+toxic+transformation+products+in+complex+environmental+mixtures.">Integrated framework for identifying toxic transformation products in complex environmental mixtures.</a> Environmental Science &amp; Technology Letters. 4 (2), 32-43 (2017).</li><li>Hollender, J., Schymanski, E. L., Singer, H. P., Ferguson, P. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nontarget+screening+with+high+resolution+mass+spectrometry+in+the+environment:+ready+to+go.">Nontarget screening with high resolution mass spectrometry in the environment: ready to go.</a> Environmental Science &amp; Technology. 51 (20), 11505-11512 (2017).</li><li>Nafisi, M., Fimognari, L., Sakuragi, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interplays+between+the+cell+wall+and+phytohormones+in+interaction+between+plants+and+necrotrophic+pathogens.">Interplays between the cell wall and phytohormones in interaction between plants and necrotrophic pathogens.</a> Phytochemistry. 112, 63-71 (2015).</li><li>Zhang, Q., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiple+metabolic+pathways+of+2,4,6-tribromophenol+in+rice+plants.">Multiple metabolic pathways of 2,4,6-tribromophenol in rice plants.</a> Environmental Science &amp; Technology. 53 (13), 7473-7482 (2019).</li><li>Hou, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Glycosylation+of+tetrabromobisphenol+A+in+pumpkin.">Glycosylation of tetrabromobisphenol A in pumpkin.</a> Environmental Science &amp; Technology. 53 (15), 8805-8812 (2019).</li></ol>

The authors have nothing to disclose.

This protocol was developed to efficiently identify the biotransformation of xenobiotics in plants. The critical step of this protocol is the culture of the plant callus. The most difficult part is the differentiation and maintenance of the plant callus, because the plant callus is easily infected and developed to plant tissues. Therefore, it is important to make sure that all equipment used is autoclaved, and all operations are performed under aseptic conditions. The differentiation and maintenance of the plant callus s...

An increasing number of organic pollutants have been discarded into the environment due to anthropogenic activities1,2, and soil is considered a major sink for these contaminants3,4. The contaminants in the soil can be taken up by plants and potentially transferred to higher trophic-level organisms along food chains, by directly entering the human body through crop consumption, consequently leading to unintended exposure5,6. Plants utilize different pathways to metabolize xenobiotics for detoxification7; elucidating the metabolism of xenobiotics is important, as it controls the actual fate of contaminants in plants. As the metabolites can be excreted by leaves (to the atmosphere) or the roots, determining the metabolites in the very early phases of exposure hence provides the possibility to test an extended number of metabolites8. However, studies using intact plants require long-term experiments and complex sample preparation protocols that can be affected by various factors.
Plant callus cultures, therefore, are a good alternative for studying the metabolism of xenobiotics in planta, as they can greatly shorten the treatment time. These cultures exclude microbial interference and photochemical degradation, simplify the matrix effect of intact plants, standardize the cultivation conditions, and require less experimental effort. Plant callus cultures have been successfully applied as an alternative approach in metabolic studies of triclosan9, nonylphenol10, and tebuconazole8. These studies showed that the metabolic patterns in callus cultures were similar to those in intact plants. This study proposes a method for the efficient and accurate identification of metabolites of xenobiotics in plants without complex and time-consuming protocols. Here, we use plant callus cultures in combination with high-resolution mass spectrometry for the analysis of metabolites with low-intensity signals11,12.
To this end, carrot (Daucus carota var. sativus) callus suspensions were exposed to 100 &#181;g/L of 2,4-dibromophenol for 120 h in a shaker at 130 rpm and 26 &#176;C. 2,4-dibromophenol was chosen due to its disruptive endocrine activity13 and widespread occurrence in soil14. The metabolites were extracted and analyzed by high-resolution mass spectrometry. The protocol proposed here can investigate the in planta metabolism of other types of organic compounds that can be ionized.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>2,4-dichlorophenoxyacetic acid</td>
			<td>WAKO</td>
			<td>1 mg/L</td>
			<td></td>
		</tr>
		<tr>
			<td>20% H2O2</td>
			<td>Sinopharm Chemical Reagent Co., Ltd.</td>
			<td>10011218-500ML</td>
			<td></td>
		</tr>
		<tr>
			<td>4-n-NP, &#62;99%</td>
			<td>Dr. Ehrenstorfer GmbH</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>4-n-NP-d4</td>
			<td>Pointe-Claire</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>6-benzylaminopurine</td>
			<td>WAKO</td>
			<td>0.5 mg/L</td>
			<td></td>
		</tr>
		<tr>
			<td>75% ethanol</td>
			<td>Sinopharm Chemical Reagent Co., Ltd.</td>
			<td>1269101-500ML</td>
			<td></td>
		</tr>
		<tr>
			<td>7890A-5975&#160;gas chromatography</td>
			<td>Agilent</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>ACQULTY ultra-performance&#160;liquid chromatography</td>
			<td>Waters</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Amber glass vials</td>
			<td>Waters</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Artificial climate incubator</td>
			<td>Ningbo DongNan Lab Equipment Co.,LTD</td>
			<td>RDN-1000A-4</td>
			<td></td>
		</tr>
		<tr>
			<td>Autoclaves</td>
			<td>STIK</td>
			<td>MJ-Series</td>
			<td></td>
		</tr>
		<tr>
			<td>C18 column</td>
			<td>ACQUITY UPLC BEH</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifuge</td>
			<td>Thermo Fisher</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>DB-5MS capillary column</td>
			<td>Agilent</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Dichloromethane</td>
			<td>Sigma-Aldrich</td>
			<td>40071190-4L</td>
			<td></td>
		</tr>
		<tr>
			<td>Freeze dryer</td>
			<td>SCIENTZ&#160;</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>High-throughput tissue grinder</td>
			<td>SCIENTZ&#160;</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Methanol</td>
			<td>Sigma-Aldrich</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>MicrOTOF-QII mass spectrometer</td>
			<td>Bruker Daltonics</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Milli-Q system</td>
			<td>Millipore</td>
			<td>MS1922801-4L</td>
			<td></td>
		</tr>
		<tr>
			<td>Murashige &#38; Skoog medium</td>
			<td>HOPEBIO</td>
			<td>HB8469-7</td>
			<td></td>
		</tr>
		<tr>
			<td>N-hexane</td>
			<td>Sigma-Aldrich</td>
			<td>H109658-4L</td>
			<td></td>
		</tr>
		<tr>
			<td>Nitrogen blowing instrument&#160;</td>
			<td>AOSHENG</td>
			<td>MD200-2</td>
			<td></td>
		</tr>
		<tr>
			<td>NP isomers, &#62;99%</td>
			<td>Dr. Ehrenstorfer GmbH</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Oasis HLB cartridges</td>
			<td>Waters</td>
			<td>60 mg/3 mL</td>
			<td></td>
		</tr>
		<tr>
			<td>Research plus</td>
			<td>Eppendorf</td>
			<td></td>
			<td>100-1000 &#181;L</td>
		</tr>
		<tr>
			<td>Seeds of Little Finger carrot (Daucus carota var. sativus)&#160;</td>
			<td>Shouguang Seed Industry Co., Ltd</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Shaking&#160;Incubators</td>
			<td>Shanghai bluepard instruments Co.,ltd.</td>
			<td>THZ-98AB</td>
			<td></td>
		</tr>
		<tr>
			<td>Solid phase extractor</td>
			<td>AUTO SCIENCE</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Ultrasound machine</td>
			<td>ZKI</td>
			<td>UC-6</td>
			<td></td>
		</tr>
		<tr>
			<td>UV-sterilized ultra-clean workbench</td>
			<td>AIRTECH</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

elucidating the metabolism of 2,4-dibromophenol in plants

Crops can be extensively exposed to organic pollutants, since soil is a major sink for pollutants discarded into the environment. This creates potential human exposure through the consumption of pollutant-accumulated foods. Elucidating the uptake and metabolism of xenobiotics in crops is essential for the assessment of dietary exposure risk in humans. However, for such experiments, the use of intact plants requires long-term experiments and complex sample preparation protocols that can be affected by various factors. Plant callus cultures combined with high-resolution mass spectrometry (HRMS) may provide a solution for the accurate and time-saving identification of metabolites of xenobiotics in plants, as it can avoid interference from the microbial or fungal microenvironment, shorten the treatment duration, and simplify the matrix effect of intact plants. 2,4-dibromophenol, a typical flame retardant and endocrine disrupter, was chosen as the model substance due to its widespread occurrence in soil and its uptake potential by plants. Herein, plant callus was generated from asepsis seeds and exposed to sterile 2,4-dibromophenol-containing culture medium. The results showed that eight metabolites of 2,4-dibromophenol were identified in the plant callus tissues after 120 h of incubation. This indicates that 2,4-dibromophenol was rapidly metabolized in&#160;the plant callus tissues. Thus, the plant callus culture platform is an effective method to evaluate the uptake and metabolism of xenobiotics in plants.

The steps of the protocol are depicted in Figure 1. Following the protocol, we compared the chromatogram of the carrot callus extract from the 2,4-dibromophenol treatment to the controls, and found eight distinct peaks that are present in the 2,4-dibromophenol treatment but absent in the controls (Figure 2). This indicates that a total of eight metabolites of 2,4-dibromophenol (M562, M545, M661, M413, M339, M380, M424, and M187) were successfully detected in the...

Watch this Scientific Journal Video about Elucidating the Metabolism of 2,4-Dibromophenol in Plants at JoVE.com

Elucidating the Metabolism of 2,4-Dibromophenol in Plants

The present protocol describes a simple and efficient method for the identification of 2,4-dibromophenol metabolites in plants.

Crops can be extensively exposed to organic pollutants, since soil is a major sink for pollutants discarded into the environment. This creates potential ...

elucidating-the-metabolism-of-24-dibromophenol-in-plants

Research

JoVE Journal

Environment

746 Views.  Zhejiang University of Technology. The present protocol describes a simple and efficient method for the identification of 2,4-dibromophenol metabolites in plants.

Video: Elucidating the Metabolism of 2,4-Dibromophenol in Plants

Expression of Recombinant Cellulase Cel5A from Trichoderma reesei in Tobacco Plants

Cellulose degrading enzymes, cellulases, are targets of both research and industrial interests. The preponderance of these enzymes in difficult-to-culture organisms, such as hyphae-building fungi and anaerobic bacteria, has hastened the use of recombinant technologies in this field. Plant expression methods are a desirable system for large-scale production of enzymes and other industrially useful proteins. Herein, methods for the transient expression of a fungal endoglucanase, Trichoderma reesei Cel5A, in Nicotiana tabacum are demonstrated. Successful protein expression is shown, monitored by fluorescence using an mCherry-enzyme fusion protein. Additionally, a set of basic tests are used to examine the activity of transiently expressed T. reesei Cel5A, including SDS-PAGE, Western blotting, zymography, as well as&#160;fluorescence and dye-based substrate degradation assays. The system described here can be used to produce an active cellulase in a short time period, so as to assess the potential for further production in plants through constitutive or inducible expression systems.

Expression of Recombinant Cellulase Cel5A from Trichoderma reesei in Tobacco Plants

Tobacco plants were used to produce a fungal cellulase, TrCel5A, via a transient expression system. The expression could be monitored using a fluorescent fusion protein, and the protein activity was characterized post-expression.

Cellulose degrading enzymes, cellulases, are targets of both research and industrial interests. The preponderance of these enzymes in difficult-to-culture ...

Measuring Fluxes of Mineral Nutrients and Toxicants in Plants with Radioactive Tracers

Unidirectional influx and efflux of nutrients and toxicants, and their resultant net fluxes, are central to the nutrition and toxicology of plants. Radioisotope tracing is a major technique used to measure such fluxes, both within plants, and between plants and their environments. Flux data obtained with radiotracer protocols can help elucidate the capacity, mechanism, regulation, and energetics of transport systems for specific mineral nutrients or toxicants, and can provide insight into compartmentation and turnover rates of subcellular mineral and metabolite pools. Here, we describe two major radioisotope protocols used in plant biology: direct influx (DI) and compartmental analysis by tracer efflux (CATE). We focus on flux measurement of potassium (K+) as a nutrient, and ammonia/ammonium (NH3/NH4+) as a toxicant, in intact seedlings of the model species barley (Hordeum vulgare L.). These protocols can be readily adapted to other experimental systems (e.g., different species, excised plant material, and other nutrients/toxicants). Advantages and limitations of these protocols are discussed.

In planta measurement of nutrient and toxicant fluxes is essential to the study of plant nutrition and toxicity. Here, we cover radiotracer protocols for influx and efflux determination in intact plant roots, using potassium (K+) and ammonia/ammonium (NH3/NH4+) fluxes as examples. Advantages and limitations of such techniques are discussed.

Unidirectional influx and efflux of nutrients and toxicants, and their resultant net fluxes, are central to the nutrition and toxicology of plants. ...

The Use of High-resolution Infrared Thermography (HRIT) for the Study of Ice Nucleation and Ice Propagation in Plants

Freezing events that occur when plants are actively growing can be a lethal event, particularly if the plant has no freezing tolerance. Such frost events often have devastating effects on agricultural production and can also play an important role in shaping community structure in natural populations of plants, especially in alpine, sub-arctic, and arctic ecosystems. Therefore, a better understanding of the freezing process in plants can play an important role in the development of methods of frost protection and understanding mechanisms of freeze avoidance. Here, we describe a protocol to visualize the freezing process in plants using high-resolution infrared thermography (HRIT). The use of this technology allows one to determine the primary sites of ice formation in plants, how ice propagates, and the presence of ice barriers. Furthermore, it allows one to examine the role of extrinsic and intrinsic nucleators in determining the temperature at which plants freeze and evaluate the ability of various compounds to either affect the freezing process or increase freezing tolerance. The use of HRIT allows one to visualize the many adaptations that have evolved in plants, which directly or indirectly impact the freezing process and ultimately enables plants to survive frost events.

The Use of High-resolution Infrared Thermography HRIT for the Study of Ice Nucleation and Ice Propagation in Plants

Here we present a protocol that allows one to visualize sites of ice formation and avenues of ice propagation in plants utilizing high resolution infrared thermography (HRIT).

Freezing events that occur when plants are actively growing can be a lethal event, particularly if the plant has no freezing tolerance. Such frost events ...

Measuring Rates of Herbicide Metabolism in Dicot Weeds with an Excised Leaf Assay

In order to isolate and accurately determine rates of herbicide metabolism in an obligate-outcrossing dicot weed, waterhemp (Amaranthus tuberculatus), we developed an excised leaf assay combined with a vegetative cloning strategy to normalize herbicide uptake and remove translocation as contributing factors in herbicide-resistant (R) and &#8211;sensitive (S) waterhemp populations. Biokinetic analyses of organic pesticides in plants typically include the determination of uptake, translocation (delivery to the target site), metabolic fate, and interactions with the target site. Herbicide metabolism is an important parameter to measure in herbicide-resistant weeds and herbicide-tolerant crops, and is typically accomplished with whole-plant tests using radiolabeled herbicides. However, one difficulty with interpreting biokinetic parameters derived from whole-plant methods is that translocation is often affected by rates of herbicide metabolism, since polar metabolites are usually not mobile within the plant following herbicide detoxification reactions. Advantages of the protocol described in this manuscript include reproducible, accurate, and rapid determination of herbicide degradation rates in R and S populations, a substantial decrease in the amount of radiolabeled herbicide consumed, a large reduction in radiolabeled plant materials requiring further handling and disposal, and the ability to perform radiolabeled herbicide experiments in the lab or growth chamber instead of a greenhouse. As herbicide resistance continues to develop and spread in dicot weed populations worldwide, the excised leaf assay method developed and described herein will provide an invaluable technique for investigating non-target site-based resistance due to enhanced rates of herbicide metabolism and detoxification.

This manuscript describes how herbicide metabolism rates can be effectively quantified with excised leaves from a dicot weed, thereby reducing variability and removing any possible confounding effects of herbicide uptake or translocation typically observed in whole-plant assays.

In order to isolate and accurately determine rates of herbicide metabolism in an obligate-outcrossing dicot weed, waterhemp (Amaranthus tuberculatus), we ...

LC-MS Analysis of Human Platelets as a Platform for Studying Mitochondrial Metabolism

Perturbed mitochondrial metabolism has received renewed interest as playing a causative role in a range of diseases. Probing alterations to metabolic pathways requires a model in which external factors can be well controlled, allowing for reproducible and meaningful results. Many studies employ transformed cellular models for these purposes; however, metabolic reprogramming that occurs in many cancer cell lines may introduce confounding variables. For this reason primary cells are desirable, though attaining adequate biomass for metabolic studies can be challenging. Here we show that human platelets can be utilized as a platform to carry out metabolic studies in combination with liquid chromatography-tandem mass spectrometry analysis. This approach is amenable to relative quantification and isotopic labeling to probe the activity of specific metabolic pathways. Availability of platelets from individual donors or from blood banks makes this model system applicable to clinical studies and feasible to scale up. Here we utilize isolated platelets to confirm previously identified compensatory metabolic shifts in response to the complex I inhibitor rotenone. More specifically, a decrease in glycolysis is accompanied by an increase in fatty acid oxidation to maintain acetyl-CoA levels. Our results show that platelets can be used as an easily accessible and medically relevant model to probe the effects of xenobiotics on cellular metabolism.

Here we show isolated human platelets can be used as an accessible ex vivo model to study metabolic adaptations in response to the complex I inhibitor rotenone. This approach employs isotopic tracing and relative quantification by liquid chromatography-mass spectrometry and can be applied to a variety of study designs.

Perturbed mitochondrial metabolism has received renewed interest as playing a causative role in a range of diseases. Probing alterations to metabolic ...

Enhancement of the Initial Growth Rate of Agricultural Plants by Using Static Magnetic Fields

Electronic devices and high-voltage wires induce magnetic fields. A magnetic field of 1,300-2,500 Gauss (0.2 Tesla) was applied to Petri dishes containing seeds of Garden Balsam (Impatiens balsamina), Mizuna (Brassica rapa var. japonica), Komatsuna (Brassica rapa var. perviridis), and Mescluns (Lepidium sativum). We applied magnets under the culture dish. During the 4 days of application, we observed that the stem and root length increased. The group subjected to magnetic field treatment (n = 10) showed a 1.4 times faster rate of growth compared with the control group (n = 11) in a total of 8 days (p &#60;0.0005). This rate is 20% higher than that reported in previous studies. The tubulin complex lines did not have connecting points, but connecting points occur upon the application of magnets. This shows complete difference from the control, which means abnormal arrangements. However, the exact cause remains unclear. These results of growth enhancement of applying magnets suggest that it is possible to enhance the growth rate, increase productivity, or control the speed of germination of plants by applying static magnetic fields. Also, magnetic fields can cause physiological changes in plant cells and can induce growth. Therefore, stimulation with a magnetic field can have possible effects that are similar to those of chemical fertilizers, which means that the use of fertilizers can be avoided.

The goal of this protocol is to demonstrate the acceleration of the initial growth rate of plants by applying static magnetic fields with no external energy.

Electronic devices and high-voltage wires induce magnetic fields. A magnetic field of 1,300-2,500 Gauss (0.2 Tesla) was applied to Petri dishes containing ...

Assessment of Methane and Nitrous Oxide Fluxes from Paddy Field by Means of Static Closed Chambers Maintaining Plants Within Headspace

This protocol describes the measurement of greenhouse gas (GHG) emissions from paddy soils using the static closed chamber technique. This method is based on the diffusion theory. A known volume of air overlaying a defined soil area is enclosed within a parallelepiped cover (named &#34;chamber&#34;), for a defined period of time. During this enclosure period, gases (methane (CH4) and nitrous oxide (N2O)) move from soil pore air near their microbial source (i.e., methanogens, nitrifiers, denitrifiers) to the chamber headspace, following a natural concentration gradient. Fluxes are then estimated from chamber headspace concentration variations sampled at regular intervals throughout the enclosure and then analyzed with gas chromatography. Among the techniques available for GHG measurement, the static closed chamber method is suitable for plot experiments, as it does not require large homogenously treated soil areas. Furthermore, it is manageable with limited resources and can identify relationships among ecosystem properties, processes, and fluxes, especially when combined with GHG driving force measurements. Nevertheless, with respect to the micrometeorological method, it causes a minimal but still unavoidable soil disturbance, and allows a minor temporal resolution. Several phases are key to the method implementation: i) chamber design and deployment, ii) sample handling and analyses, and iii) flux estimation. Technique implementation success in paddy fields demands adjustments for field flooding during much of the cropping cycle, and for rice plant maintenance within the chamber headspace during measurements. Therefore, the additional elements to be considered with respect to the usual application of non-flooded agricultural soils consist of devices for: i) avoiding any unintended water disturbance that could overestimate fluxes, and ii) including rice plants within the chamber headspace to fully consider gases emitted through aerenchyma transportation.

The overall goal of this protocol is to measure greenhouse gas emissions from paddy fields using the static closed chamber technique. The measurement system needs specific adjustments due to the presence of both a permanent water layer in the field and of the plants within the chamber headspace.

This protocol describes the measurement of greenhouse gas (GHG) emissions from paddy soils using the static closed chamber technique. This method is based ...

Protocol for Producing Three-Dimensional Infrared Video of Freezing in Plants

Freezing in plants can be monitored using infrared (IR) thermography, because when water freezes, it gives off heat. However, problems with color contrast make 2-dimensions (2D) infrared images somewhat difficult to interpret. Viewing an IR image or the video of plants freezing in 3 dimensions (3D) would allow a more accurate identification of sites for ice nucleation as well as the progression of freezing. In this paper, we demonstrate a relatively simple means to produce a 3D infrared video of a strawberry plant freezing. Strawberry is an economically important crop that is subjected to unexpected spring freeze events in many areas of the world. An accurate understanding of the freezing in strawberry will provide both breeders and growers with more economical ways to prevent any damage to plants during freezing conditions.
The technique involves a positioning of two IR cameras at slightly different angles to film the strawberry freezing. The two video streams will be precisely synchronized using a screen capture software that records both cameras simultaneously. The recordings will then be imported into the imaging software and processed using an anaglyph technique. Using red-blue glasses, the 3D video will make it easier to determine the precise site of ice nucleation on leaf surfaces.

Here, we present a protocol to image a strawberry plant freezing in 3 dimensions. Two infrared cameras positioned at slightly different angles are used to produce a red-blue anaglyph video to observe the freezing of the plant in 3 dimensions.

Freezing in plants can be monitored using infrared (IR) thermography, because when water freezes, it gives off heat. However, problems with color contrast ...

A Loop-mediated Isothermal Amplification (LAMP) Assay for Rapid Identification of Bemisia tabaci

The whitefly Bemisia tabaci (Gennadius) is an invasive pest of considerable importance, affecting the production of vegetable and ornamental crops in many countries around the world. Severe yield losses are caused by direct feeding, and even more importantly, also by the transmission of more than 100 harmful plant pathogenic viruses. As for other invasive pests, increased international trade facilitates the dispersal of B. tabaci to areas beyond its native range. Inspections of plant import products at points of entry such as seaports and airports are, therefore, seen as an important prevention measure. However, this last line of defense against pest invasions is only effective if rapid identification methods for suspicious insect specimens are readily available. Because the morphological differentiation between the regulated B. tabaci and close relatives without quarantine status is difficult for non-taxonomists, a rapid molecular identification assay based on the loop-mediated isothermal amplification (LAMP) technology has been developed. This publication reports the detailed protocol of the novel assay describing rapid DNA extraction, set-up of the LAMP reaction, as well as interpretation of its read-out, which allows identifying B. tabaci specimens within one hour. Compared to existing protocols for the detection of specific B. tabaci biotypes, the developed method targets the whole B. tabaci species complex in one assay. Moreover the assay is designed to be applied on-site by plant health inspectors with minimal laboratory training directly at points of entry. Thorough validation performed under laboratory and on-site conditions demonstrates that the reported LAMP assay is a rapid and reliable identification tool, improving the management of B. tabaci.

A Loop-mediated Isothermal Amplification LAMP Assay for Rapid Identification of Bemisia tabaci

This paper reports the protocol for a rapid identification assay for Bemisia tabaci based on loop-mediated isothermal amplification (LAMP) technology. The protocol requires minimal laboratory training and can, therefore, be implemented on-site at points of entry for plant imports such as seaports and airports.

The whitefly Bemisia tabaci (Gennadius) is an invasive pest of considerable importance, affecting the production of vegetable and ornamental crops in many ...

Xylem Water Distribution in Woody Plants Visualized with a Cryo-scanning Electron Microscope

A scanning electron microscope installed cryo-unit (cryo-SEM) allows specimen observation at subzero temperatures and has been used for exploring water distribution in plant tissues in combination with freeze fixation techniques using liquid nitrogen (LN2). For woody species, however, preparations for observing the xylem transverse-cut surface involve some difficulties due to the orientation of wood fibers. Additionally, higher tension in the water column in xylem conduits can occasionally cause artifactual changes in water distribution, especially during sample fixation and collection. In this study, we demonstrate an efficient procedure to observe the water distribution within the xylem of woody plants in situ&#160;by using a cryostat and cryo-SEM. At first, during sample collection, measuring the xylem water potential should determine whether high tension is present in the xylem conduits. When the xylem water potential is low (&#60; ca. &#8722;0.5 MPa), a tension relaxation procedure is needed to facilitate better preservation of the water status in xylem conduits during sample freeze fixation. Next, a watertight collar is attached around the tree stem and filled with LN2&#160;for freeze fixation of the water status of xylem. After harvesting, care should be taken to ensure that the sample is preserved frozen while completing the procedures of sample preparation for observation. A cryostat is employed to clearly expose the xylem transverse-cut surface. In cryo-SEM observations, time adjustment for freeze-etching is required to remove frost dust and accentuate the edge of the cell walls on the viewing surface. Our results demonstrate the applicability of cryo-SEM techniques for the observation of water distribution within xylem at cellular and subcellular levels. The combination of cryo-SEM with non-destructive in situ observation techniques will profoundly improve the exploration of woody plant water flow dynamics.

Observing the water distribution within the xylem provides significant information regarding water flow dynamics in woody plants. In this study, we demonstrate the practical approach to observe xylem water distribution in situ&#160;by using a cryostat and cryo-SEM, which eliminates artifactual changes in the water status during sample preparation.

A scanning electron microscope installed cryo-unit (cryo-SEM) allows specimen observation at subzero temperatures and has been used for exploring water ...