Name: leaf spray mass spectrometry: a rapid ambient ionization technique to directly assess metabolites from plant tissues
Uploaded: 2018-06-21T15:00:00
Description: Watch this Scientific Journal Video about Leaf Spray Mass Spectrometry: A Rapid Ambient Ionization Technique to Directly Assess Metabolites from Plant Tissues at JoVE.com

This work was funded by the NSF Plant Genome Research Program grant IOS-1238812 and the Postdoctoral Fellowship in Biology IOS-1400818. The work was also funded by a Monsanto Graduate Student Fellowship to Katherine A. Sammons. The Fulbright African Researcher Scholars Program (2017-2018) is thanked for funding awarded to Nokwanda P. Makunga. We greatly appreciate the donation of a nanospray source from Jessica Prenni and the Proteomics and Metabolomics facility at Colorado State University.

1. Modifications to Nanospray Source for Leaf Spray MS
<ol>
	<li>Use a modified nanospray source for leaf spray MS. As no fluidic components are necessary for leaf spray MS, modify the source by removing the LC probe from the source.</li>
	<li>Assemble the leaf spray MS wire that will apply the voltage to the plant tissue with the appropriate pin for plugging into the source. Solder the pin to one end of an insulated wire; solder a clamp to the opposite end of the wire. 
	NOTE: The clamp (alligator clip type) may ...

<ol>
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K., Verpoorte, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sample+preparation+for+plant+metabolomics.">Sample preparation for plant metabolomics.</a> Phytochemical Analysis. 21 (1), 4-13 (2010).</li><li>Takats, Z., Wiseman, J. M., Gologan, B., Cooks, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mass+spectrometry+sampling+under+ambient+conditions+with+desorption+electrospray+ionization.">Mass spectrometry sampling under ambient conditions with desorption electrospray ionization.</a> Science. 306 (5695), 471-473 (2004).</li><li>Liu, J., Wang, H., Cooks, R. G., Ouyang, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Leaf+spray:+direct+chemical+analysis+of+plant+material+and+living+plants+by+mass+spectrometry.">Leaf spray: direct chemical analysis of plant material and living plants by mass spectrometry.</a> Analytical Chemistry. 83 (20), 7608-7613 (2011).</li><li>Chan, S. L. -. F., Wong, M. Y. -. M., Tang, H. -. W., Che, C. -. M., Ng, K. -. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tissue-spray+ionization+mass+spectrometry+for+raw+herb+analysis.">Tissue-spray ionization mass spectrometry for raw herb analysis.</a> Rapid Communications in Mass Spectrometry. 25 (19), 2837-2843 (2011).</li><li>Wang, H., Liu, J., Cooks, R. G., Ouyang, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Paper+spray+for+direct+analysis+of+complex+mixtures+using+mass+spectrometry.">Paper spray for direct analysis of complex mixtures using mass spectrometry.</a> Angewandte Chemie International Edition. 49 (5), 877-880 (2010).</li><li>Liu, J., Wang, H., Cooks, R. G., Ouyang, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Leaf+spray:+Direct+chemical+analysis+of+plant+material+and+living+plants+by+mass+spectrometry.">Leaf spray: Direct chemical analysis of plant material and living plants by mass spectrometry.</a> Analytical Chemistry. 83 (20), 7608-7613 (2011).</li><li>Malaj, N., Ouyang, Z., Sindona, G., Cooks, R. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+pesticide+residues+by+leaf+spray+mass+spectrometry.">Analysis of pesticide residues by leaf spray mass spectrometry.</a> Analytical Methods. 4 (7), 1913-1919 (2012).</li><li>Snyder, D. T., Schilling, M. C., Hochwender, G., Kaufman, A. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analytical+methods+profiling+phenolic+glycosides+in+Populus+deltoides+and+Populus+grandidentata+by+leaf+spray+ionization+tandem+mass+spectrometry.">Analytical methods profiling phenolic glycosides in Populus deltoides and Populus grandidentata by leaf spray ionization tandem mass spectrometry.</a> Analytical Methods. 7 (3), 870-876 (2015).</li><li>Falcone, C. E., Cooks, R. 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M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sceletium-a+review+update.">Sceletium-a review update.</a> Journal of Ethnopharmacology. 119 (3), 653-663 (2008).</li><li>Terburg, D., 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=Acute+effects+of+Sceletium+tortuosum+(Zembrin),+a+dual+5-HT+reuptake+and+PDE4+inhibitor,+in+the+human+amygdala+and+its+connection+to+the+hypothalamus.">Acute effects of Sceletium tortuosum (Zembrin), a dual 5-HT reuptake and PDE4 inhibitor, in the human amygdala and its connection to the hypothalamus.</a> Neuropsychopharmacology. 38 (13), 2708-2716 (2013).</li><li>Coetzee, D. D., L&#243;pez, V., Smith, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-mesembrine+Sceletium+extract+(TrimesemineTM)+is+a+monoamine+releasing+agent,+rather+than+only+a+selective+serotonin+reuptake+inhibitor.">High-mesembrine Sceletium extract (TrimesemineTM) is a monoamine releasing agent, rather than only a selective serotonin reuptake inhibitor.</a> Journal of Ethnopharmacology. 177, 111-116 (2016).</li><li>Shikanga, E. 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=In+vitro+permeation+of+mesembrine+alkaloids+from+Sceletium+tortuosum+across+porcine+buccal,+sublingual,+and+intestinal+mucosa.">In vitro permeation of mesembrine alkaloids from Sceletium tortuosum across porcine buccal, sublingual, and intestinal mucosa.</a> Planta Medica. 78 (3), 260-268 (2012).</li><li>Pulliam, C. J., Bain, R. M., Wiley, J. S., Ouyang, Z., Cooks, R. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mass+spectrometry+in+the+home+and+garden.">Mass spectrometry in the home and garden.</a> Journal of The American Society for Mass Spectrometry. 26 (2), 224-230 (2015).</li><li>Lawton, Z. E., 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=Analytical+validation+of+a+portable+mass+spectrometer+featuring+interchangeable,+ambient+ionization+sources.">Analytical validation of a portable mass spectrometer featuring interchangeable, ambient ionization sources.</a> Journal of the American Society for Mass Spectrometry. 28 (6), 1048-1059 (2017).</li><li>. GNPS Available from: <a target="_blank" href="https://gnps.ucsd.edu/">https://gnps.ucsd.edu/</a> (2018)</li><li>Chambers, M. C., 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=A+cross-platform+toolkit+for+mass+spectrometry+and+proteomics.">A cross-platform toolkit for mass spectrometry and proteomics.</a> Nature Biotechnology. 30 (10), 918-920 (2012).</li><li>Pluskal, T., Castillo, S., Villar-Briones, A., Ore, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MZmine2:+modular+framework+for+processing,+visualizing,+and+analyzing+mass+spectrometry-based+molecular+profile+data.">MZmine2: modular framework for processing, visualizing, and analyzing mass spectrometry-based molecular profile data.</a> BMC Bioinformatics. 11, 395 (2010).</li><li>Meyer, G. M. J., Wink, C. S. D., Zapp, J., Maurer, H. 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The successful use of this protocol relies on the optimization of various steps for the plant species, tissue type, and target compound(s) of interest. The parameters described in the protocol provide a good starting point. The following experimental decisions need to be made and tested: whether or not to use (1) cut or uncut tissue and (2) solvent or no solvent, (3) what solvent to use and in what volume, (4) what the distance of tissue from the ion inlet should be, and (5) the voltage amplitude. The goal of optimizatio...

Plants contain a wide range of small molecules with diverse chemical properties. MS is a powerful technique for analyzing plant compounds because it can provide elemental compositions with a high sensitivity and specificity for the detection and identification of metabolites1. Most commonly, MS is performed on solvent-extracted samples, which are separated by chromatography prior to the MS analysis1. However, the use of liquid chromatography (LC) requires lengthy analysis times and is often associated with an extensive sample preparation1. In contrast, direct chemical analysis of intact tissues that circumvents chromatography is a very rapid technique, requiring minimal sample preparation2. Thus, in instances where chromatographic steps can be forgone, a direct chemical analysis can be highly advantageous.
Typical LC-MS for natural products and metabolomics research relies on lengthy bulk extractions of dried or frozen plant materials containing multiple tissues and cell types3. Alternatively, direct chemical analysis, such as the MS detection of metabolites from plant tissue, can isolate cell types and avoid preparation artifacts4. Leaf spray MS, also referred to as tissue-spray5,6, is a direct ambient ionization MS technique, which requires essentially no sample preparation5,7. Leaf spray MS is closely related to paper spray MS, an ambient ionization technique with characteristics of electrospray ionization that allows for the detection of analytes that are deposited onto paper7. In spite of the name, leaf spray MS is applicable to various types of plant tissues, not just leaves, and has been demonstrated on fruit, seeds, roots, floral tissues, and tubers, among others6,8,9,10,11,12. The technique facilitates the ionization of endogenous phytochemicals directly from the plant materials into the mass spectrometer for detection8. Leaf spray MS can also provide information about the spatial distribution of chemicals in different tissue types in plants13. When leaf spray MS is compared with solvent extraction and LC-MS, the results suggest leaf spray MS allows for the rapid detection of surface metabolites from unique cell types such as trichomes13. Figure 1 illustrates the leaf spray MS experimental set-up. Direct electrospray ionization occurs after only minor source modifications. A high voltage is applied to the plant tissue via a metal clamp, producing a spray of highly charged droplets forming a Taylor cone that carries the ions to the ion inlet of the MS. Electrospray ionization occurs from the natural liquid of the plant or from the solvent applied to the plant surface. A pointed tip on the tissue facilitates the electrospray and can be naturally occurring or created by cutting.
Leaf spray MS is a fast method for the qualitative and semi-quantitative analysis of intact plant tissues that have found utility for a wide variety of applications. For example, the technique has been used to detect endogenous compounds to distinguish related species, and even to evaluate changes in the same species grown under different conditions. Previous studies have shown this approach by measuring metabolites in beautyberry (Callicarpa L.)12 and American ginseng (Panax quinquefolium L.)6. In the latter example, ginsenosides, amino acids, and oligosaccharides could be detected after wetting raw ginseng tissue. Wild and cultivated American ginseng were differentiated from tuber slices6. Ginseng tuber integrity was preserved succeeding leaf spray MS, which allowed for a subsequent morphological and microscopic inspection6. Furthermore, exogenous compounds on plant samples can also be detected. A number of pesticides (acetamiprid, diphenylamine, imazalil, linuron, and thiabendazole) have been detected on peel or pulp of fruits and vegetables9. While these studies and many others have shown the utility of leaf spray MS for various specific purposes, a detailed protocol has not been previously reported.
Here, the protocol description will not focus on the optimization of the method for a specific tissue or compound. Rather, the detection of mesembrine alkaloids from Sceletium tortuosum (L.) N.E.Br. (Aizoaceae) is used as an example to discuss the necessary optimization measures that should be taken when setting up a leaf spray MS experiment for a species, tissue, or compound(s) for the first time. S. tortuosum is a succulent endemic to the semi-arid Karroo region of South Africa. A traditional medicine of the San and Khoi Khoi peoples, it was used for appetite and thirst suppression as well as for its psychotropic and analgesic effects14,15. Currently, standardized extracts are used for the treatment of neuropsychiatric and neuropsychological disorders16,17. The primary compounds of interest include the alkaloid mesembrine and its derivatives, many of which are also found in related Sceletium species15. Both wild and cultivated populations of S. tortuosum have variable concentrations of mesembrine alkaloids, thus presenting a quality control challenge18. A method for the rapid detection of mesembrine alkaloids, such as leaf spray MS, may be useful in monitoring Sceletium products. Because previously, there had been no detailed visual experimental protocol for the leaf spray MS technique, we will illustrate the method using the example of S. tortuosum, and the following is described: the modification of a nanospray source, the selection and preparation of the plant tissues, the acquisition of the data, the interpretation of the results, and the optimization of the MS parameters.

<table border="0" cellpadding="0" cellspacing="0" width="880">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Conn Pin</td>
			<td style="width:139px;">Digi-Key elctronics&#160;</td>
			<td style="width:119px;">WM2563CT-ND</td>
			<td style="width:385px;">pin will insert into Thermo Scientific&#160; source to provide voltage&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">small clamp</td>
			<td style="width:139px;">Digi-Key elctronics&#160;</td>
			<td>314-1018-ND</td>
			<td>CLIP MICRO ALLIGATOR COPPER 5A</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">large clamp</td>
			<td style="width:139px;">Digi-Key elctronics&#160;</td>
			<td>290-1951-ND</td>
			<td>ALLIGATOR CLIP NARROW NICKLE 5A</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Heat shrink</td>
			<td style="width:139px;">Digi-Key elctronics&#160;</td>
			<td style="width:119px;">Q2Z1-KIT-ND</td>
			<td>to cover soldering joints&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">NSI source Nanospray Ion Source</td>
			<td style="width:139px;">Thermo scientific</td>
			<td style="width:119px;">NA</td>
			<td>Another brand will work if you are not using a Thermo instrument</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:237px;">Q Exactive- hybrid quadrupole Orbitrap</td>
			<td style="width:139px;">Thermo scientific</td>
			<td style="width:119px;">NA</td>
			<td>Another brand will work if you are not using a Thermo instrument</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Tune Software</td>
			<td style="width:139px;">Thermo scientific</td>
			<td style="width:119px;"></td>
			<td>Another brand will work if you are not using a Thermo instrument</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Xcalibur Software</td>
			<td style="width:139px;">Thermo scientific</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Plant of interest - S. tortousum</td>
			<td style="width:139px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

leaf spray mass spectrometry: a rapid ambient ionization technique to directly assess metabolites from plant tissues

Plants produce thousands of small molecules that are diverse in their chemical properties. Mass spectrometry (MS) is a powerful technique for analyzing plant metabolites because it provides molecular weights with high sensitivity and specificity. Leaf spray MS is an ambient ionization technique where plant tissue is used for direct chemical analysis via electrospray, eliminating chromatography from the process. This approach to sampling metabolites allows for a wide range of chemical classes to be detected simultaneously from intact plant tissues, minimizing the amount of sample preparation needed. When used with a high-resolution, accurate mass MS, leaf spray MS facilitates the rapid detection of metabolites of interest. It is also possible to collect tandem mass fragmentation data with this technique to facilitate a compound identification. The combination of accurate mass measurements and fragmentation is beneficial in confirming compound identities. The leaf spray MS technique requires only minor modifications to a nanospray ionization source and is a useful tool to further expand the capabilities of a mass spectrometer. Here, fresh leaf tissue from Sceletium tortuosum (Aizoaceae), a traditional medicinal plant from South Africa, is analyzed; numerous mesembrine alkaloids are detected with leaf spray MS.

At 10 weeks post-germination, freshly collected greenhouse-grown S. tortuosum leaves were analyzed by leaf spray MS. The experimental workflow for detecting metabolites from S. tortuosum leaves using leaf spray MS is illustrated in Figure 2. A leaf was selected, cut into a thin strip with a tapered end to form a point, and clamped with the leaf spray MS wire clamp apparatus. The plant tissue was positioned ~30 mm from the ion inlet and in li...

Watch this Scientific Journal Video about Leaf Spray Mass Spectrometry: A Rapid Ambient Ionization Technique to Directly Assess Metabolites from Plant Tissues at JoVE.com

Leaf Spray Mass Spectrometry: A Rapid Ambient Ionization Technique to Directly Assess Metabolites from Plant Tissues

Leaf spray mass spectrometry is a direct chemical analysis technique that minimizes the sample preparation and eliminates chromatography, allowing for the rapid detection of small molecules from plant tissues.

Plants produce thousands of small molecules that are diverse in their chemical properties. Mass spectrometry (MS) is a powerful technique for analyzing ...

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