We thank Jennifer Deke and Urszula Zarzenska for their scientific support. This work was financially supported by a Career Integration Grant (CIG, PCIG14-GA-2013-63 0734) by the European Commission within the 7th framework program, the grant LFF-GK06 &#39;DELIGRAH&#39; (Landesforschungsf&#246;rderung Hamburg), and the DFG grant (DFG KE 856_6-1) awarded to JK.

1. Sampling and preparation of phloem sap from B. napus plants 4,8,20
<ol>
	<li>For phloem sap sampling, use well-watered 8-week-old B. napus plants that show only initial flowering to prevent pollen contaminations.</li>
	<li>Use a hypodermic needle (&#216; 0.8 mm) and punctate the inflorescence stem several times. Repeat at several other inflorescence stems and on other plants to obtain enough phloem sap (Figure 2a). 
	NOTE: For complex analysis, it is recommended to start with at least 600 &#181;L of phloem sap. 4 to 5 plants will yield between 200 and 700 &#181;L of phloem sap.</li>
	<li>Wipe off the first drop from the injured sites with filter paper. These drops mainly contain highly contaminated material from surrounding injured tissue and need to be discarded.</li>
	<li>Collect the following drops by pipetting and store the collected exudate in a pre-chilled conical 1.5 mL reaction tube at -20 &#176;C using an ice-free cooling system.</li>
	<li>Continue collecting until no further drop formation is observable, but no longer than 1 h. This procedure can be repeated after two days without significant loss of collected phloem sap. 
	NOTE: The collected phloem sap can be used immediately or stored at -80 &#176;C for future analysis. For -80 &#176;C storage, shock-freeze the reaction tube in liquid nitrogen.</li>
	<li>Concentrate the phloem sample to approximately 1/6th of the initial volume using centrifugal concentrators with a molecular weight cut off (MWCO) of 10,000 Daltons (Da). Centrifuge the concentrated sample at 4 &#176;C and 20,000 x g for at least 15 min to remove dust particles. 
	NOTE: Phloem sap concentration does not lead to a significant loss of proteins.</li>
	<li>For subsequent complex analysis, proceed with step 3.1.</li>
</ol>
2. Phloem sap purity control using reverse transcriptase PCR (RT-PCR) 4,8,20
<ol>
	<li>Isolate total RNA from phloem sap using a standard RNA extraction method for liquid material (e.g. TRIzol or phenol-chloroform extraction followed by isopropanol precipitation from the aqueous phase and ethanol washing steps according to the manufacturer&#39;s protocol). 
	Caution: Phenol-chloroform is toxic. Work under a hood with appropriate personal protection equipment. The extracted RNA can be stored in ethanol at -80 &#176;C for up to six months.</li>
	<li>Remove contamination of DNA by digestion with DNase I (1 u/&#181;g) for 45 min at 37 &#176;C and inactivate the enzyme by adding EDTA to a final concentration of 5 mM and incubate the sample at 75 &#176;C for 10 min.</li>
	<li>To get pure RNA, purify and concentrate the sample by another purification step (e.g. using RNA Cleanup Kits, according to the manufacturer&#39;s instructions).</li>
	<li>Perform a reverse transcriptase PCR (RT-PCR) for synthesis of cDNA with a cDNA synthesis kit using 150 ng of pure RNA as described by the manufacturer&#39;s protocol. 
	NOTE: The cDNA can be stored at -20 &#176;C until further use.</li>
	<li>Use 5 &#181;L of cDNA as a template for a standard PCR reaction as specified by the manufacturer, to amplify compartment-specific transcripts and check by agarose gel electrophoresis. Confirm the purity of phloem samples by e.g. using primers for rubisco small subunit, thioredoxin h, and the pollen coat protein (Figure 1b, Table 1).</li>
</ol>
3. Blue native PAGE 4,25,26,31
<ol>
	<li>Use either self-poured native gradient gels as described elsewhere27 or commercial Bis-Tris gradient gels.</li>
	<li>Load 20 to 30 &#181;g of the concentrated protein sample per well onto the gel in at least triplicates.</li>
	<li>Run the gel at 4 &#176;C and 150 V using dark blue cathode buffer B and anode buffer (Table 2) until the sample passed 1/3rd of the gel (ca. 20 to 30 min, Figure 3a). 
	NOTE: For northern blotting, a single gel lane is sufficient, while for the analysis of protein composition by 3D PAGE and mass spectrometry it is recommended to combine the same band from up to ten gel lanes to concentrate less abundant proteins.</li>
	<li>Pause the run and exchange dark blue cathode buffer B with light blue cathode buffer B/10 (Table 2) and continue the run. Finish the gel run when the blue front starts to elute out of the gel (ca. 120 to 180 min, Figure 3a). 
	NOTE: The finished blue native gel can be stored at 4 &#176;C for at least one week. Prolonged storage can lead to diffuse bands and should be avoided. Dark blue buffer B can be reused.</li>
</ol>
4. OPTIONAL: Detection of RNA using blue native northern blotting 4
<ol>
	<li>Cut out distinct bands or use the whole gel lane from the Blue native gel and transfer them onto a nylon membrane by semi-dry blotting at 3.5 mA/cm2 for 60 min and mark the upper and lower gel border with a pencil on the membrane (Figure 4a).</li>
	<li>After blotting, wash the membrane with DEPC-treated water and dry between two filter papers.</li>
	<li>Perform UV-crosslinking of the blotted membrane with 120,000 &#181;J/cm2 (85 s if using the Crosslinker in Table of Materials).</li>
	<li>Pre-hybridize the membrane with 6 mL of hybridization buffer (commercial or self-made) for 60 min at 68 &#176;C in a hybridization oven (Figure 4a).</li>
	<li>Add an additional 1 mL of hybridization buffer containing 4 &#181;L of 3&#39;-biotinylated probes (100 nM).</li>
	<li>Incubate the membrane with the probe overnight, while cooling the oven from 68 &#176;C to 37 &#176;C.</li>
	<li>Wash the membrane with buffer containing 2x SSC and 0.1 % SDS, for 5 min at room temperature to remove probes bound unspecifically. 
	Caution: SDS can cause irritations. Wear gloves and lab coat when working with SDS and SDS containing solutions.</li>
	<li>Perform the detection of the 3&#39;-biotinylated probes on the membrane e.g. with a Streptavidin-HRP-conjugate and luminol as a horseradish peroxidase (HRP) substrate, resulting in a sensitive chemiluminescent reaction (Figure 4a).</li>
</ol>
5. Second dimension: Tris-Tricine-urea PAGE 4,28
<ol>
	<li>Excise single bands from the blue native gel. Combine bands from samples run in parallel lanes to achieve a further concentration of complex proteins (Figure 5). 
	NOTE: Excised bands can be stored in single reaction tubes until further use at 4 &#176;C.</li>
	<li>Pour a 12 % Tris-Tricine-urea gel (thickness of 1 mm, 6.8cm x 8.6 cm (width x length)). Prepare 10 mL of gel solution A for the separating gel (Table 2), pour between two glass plates and overlay with isopropanol. Remove the isopropanol after the polymerization is finished and transfer 4 mL of gel solution B (Table 2) for the stacking gel onto the gel and insert a 10 well comb. 
	Caution: Unpolymerized acrylamide can be neurotoxic and TEMED is harmful if inhaled. Always wear personal protection equipment and work under a hood.</li>
	<li>Transfer the excised gel bands into a 1.5 mL reaction tube and add 1 mL of 2x SDS sample buffer for equilibration of the gel pieces (Figure 5, Table 2).
	<ol>
		<li>Incubate the samples for 10 min at room temperature, prior to boiling in a heating block (95 &#176;C) or in a microwave and incubate the samples again at room temperature for a further 15 min.</li>
		<li>Stack several equilibrated gel pieces representing the same complex into one single gel pocket.</li>
		<li>Perform the electrophoresis using anode and cathode running buffers at 150 V for 45 to 60 min and excise the whole gel lane.</li>
	</ol>
	</li>
	<li>Incubate the cut lane for 20 min in acidic buffer (100 mM Tris, 100 mM acetic acid) and equilibrate in 125 mM Tris-HCl, pH 6.8 for another 20 min (Figure 5).</li>
</ol>
6. Third dimension: SDS-PAGE 4,32
<ol>
	<li>Pour a 15 % SDS separating gel according to Laemmli32 (thickness: 1.5 mm, 6.8cm x 8.6 cm (Width x Length)) (Table 2) and add a thin layer of a 4 % stacking gel above. 
	Caution: SDS, acrylamide and TEMED are toxic and harmful. Work under a hood and wear personal protection equipment.</li>
	<li>Transfer the equilibrated gel lane onto the SDS gel and cover the gel with 0.5 % (w/w) agarose in 1x SDS running buffer supplemented with a trace of bromophenol blue (Figure 5).</li>
	<li>Boil the SDS running buffer with agarose in the microwave prior loading onto the gel.</li>
	<li>For running a protein marker to estimate the molecular weights of the single components, insert a piece of filter paper on one end of the gel until the agarose solidified or use a special comb typically used for IPG gels.</li>
	<li>Run the gel at 150 V for 60 min and stain the gel with either colloidal Coomassie, Silver stain or any other staining method suitable for subsequent mass spectrometric analysis.</li>
	<li>Analyze the visible protein spots using mass spectrometric approaches like matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) or LC-MS/MS mass spectrometry. 
	NOTE: We recommend to use the colloidal Coomassie staining as already described33. In our hands, even less abundant proteins can be sufficiently stained and allows a mass spectrometric analysis with reasonable data quality.</li>
</ol>

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Bot. 55 (402), 1473-1481 (2004).</li><li>Walz, C., Giavalisco, P., Schad, M., Juenger, M., Klose, J., Kehr, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Proteomics+of+curcurbit+phloem+exudate+reveals+a+network+of+defence+proteins.">Proteomics of curcurbit phloem exudate reveals a network of defence proteins.</a> Phytochemistry. 65 (12), 1795-1804 (2004).</li><li>Walz, C., Juenger, M., Schad, M., Kehr, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evidence+for+the+presence+and+activity+of+a+complete+antioxidant+defence+system+in+mature+sieve+tubes.">Evidence for the presence and activity of a complete antioxidant defence system in mature sieve tubes.</a> Plant J. 31 (2), 189-197 (2002).</li><li>Kehr, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phloem+sap+proteins:+their+identities+and+potential+roles+in+the+interaction+between+plants+and+phloem-feeding+insects.">Phloem sap proteins: their identities and potential roles in the interaction between plants and phloem-feeding insects.</a> J Exp. Bot. 57 (4), 767-774 (2006).</li><li>Ham, B. -. K., Brandom, J. L., Xoconostle-C&#225;zares, B., Ringgold, V., Lough, T. J., Lucas, W. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+polypyrimidine+tract+binding+protein,+pumpkin+RBP50,+forms+the+basis+of+a+phloem-mobile+ribonucleoprotein+complex.">A polypyrimidine tract binding protein, pumpkin RBP50, forms the basis of a phloem-mobile ribonucleoprotein complex.</a> Plant Cell. 21 (1), 197-215 (2009).</li><li>Schamel, W. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biotinylation+of+protein+complexes+may+lead+to+aggregation+as+well+as+to+loss+of+subunits+as+revealed+by+Blue+Native+PAGE.">Biotinylation of protein complexes may lead to aggregation as well as to loss of subunits as revealed by Blue Native PAGE.</a> J. Immunol. Methods. 252 (1-2), 171-174 (2001).</li><li>Zhang, S., Sun, L., Kragler, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+phloem-delivered+RNA+pool+contains+small+noncoding+RNAs+and+interferes+with+translation.">The phloem-delivered RNA pool contains small noncoding RNAs and interferes with translation.</a> Plant Physiol. 150 (1), 378-387 (2009).</li></ol>

The authors have nothing to disclose.

The phloem is a compartment of high interest, since it constitutes the major transport route for photoassimilates, and is also essential for long-distance signaling between different plant parts9,20,34,35. In addition to small molecules, macromolecules like proteins and RNAs have been implicated with phloem maintenance and signaling4,7,8. The analysis of phloem composition is restricted by the limited accessibility to phloem samples in most plant species. The insect stylet technique is widely applicable, but experimentally demanding and results in very small amounts of phloem samples11. One easy technique used for phloem sampling is EDTA-facilitated exudation12. EDTA chelates divalent ions like Calcium and thus prevents closing of sieve plates by P-proteins and callose. It is easy to use, but is prone to contamination by damaged cells and samples are diluted. Depleting divalent ions by EDTA could also lead to a breakdown of existing complexes. However, it allows sampling from a wide range of species including the model plant A. thaliana15. Spontaneous exudation of phloem sap only occurs in a small number of plant species. It is an invasive method that involves significant injury of plant tissues10. We recently established B. napus as a model species for studying long-distance transport4,8,20. Here, phloem sap can be sampled from small incisions, which reduces wounding effects and sources of contamination.
Using different sampling techniques, the proteome of phloem samples from different plant species has been investigated in recent years7,8,17,36,37,38,39. For these proteome studies, proteins were extracted and precipitated under denaturing conditions and therefore do not allow conclusions about protein:protein and protein:nucleic acid interactions present under native conditions. Co-immunoprecipitation (CoIP) and overlay assays indicated that a major ribonucleoprotein complex might exist in phloem sap from pumpkin40, but it was not demonstrated that any macromolecular complexes exist under native conditions within the phloem system.
Blue native PAGE, introduced by Sch&#228;gger et al.26, in combination with subsequent high-resolution gel electrophoresis steps enable the separation of the individual components of large protein complexes. Using 3D-PAGE analyses of native B. napus phloem exudate, we could recently demonstrate that several high-molecular-weight protein:protein and RNP complexes exist in phloem samples and are enzymatically active4. Alternative methods to isolate protein complexes as well as RNPs like size exclusion chromatography might exist, but fail in terms of resolution when compared to BN-PAGE. Furthermore, for a reasonable quality of complex separation, size exclusion column matrices have to be adapted according to the overall complex molecular weights being investigated. Analyzing complexes of different size will therefore demand different types of columns which is cost intensive and does not allow as high focusing power as a BN-PAGE.
Critical steps to analyze complexes from B. napus include the total amount of phloem sap used as starting material. At least 600 &#181;L of phloem sample are necessary and can be obtained from five well-watered plants. For 3D-PAGE and BN northern blotting it is necessary to start the initial BN gel with a sufficient amount of phloem samples. To achieve this, phloem samples are concentrated until 20 to 30 &#181;g of protein can be loaded into each well and at least triplicates of the same sample are run in parallel. Too low or too high concentrations reduce the detection of complexes (Figure 3). Phloem samples need be collected into reaction tubes on ice and should be stored frozen for later use to avoid protein degradation and turnover. Protease inhibitors have been found in all phloem proteomes analyzed, but also a fully active proteasome was described in the phloem of B. napus4. Furthermore, volume and composition of phloem samples depend on the sampling time-point and environmental conditions10. Therefore care must be taken to collect at the same time of the day under similar conditions. Stress treatments (e.g. drought) can reduce the amount of phloem that can be collected. To identify single proteins by mass spectrometry, it is mandatory to limit possible keratin contaminations by wearing gloves all the time. Keratin leads to additional signals during mass spec analysis and hampers protein identification. Running the BN-PAGE at a higher voltage or at ambient temperature can lead to heating of the gel that might result in disassembly of fragile complexes.
The protocol presented here is suitable for the analysis of protein:protein complexes. We also show that it can be used to detect specific RNAs contained in the complexes in parallel. To achieve this, we recently introduced a protocol for BN northern blotting4. RNAs are prone to degradation by RNAse contaminations. To limit such degradation DEPC-treated, water should be used.
Main limitations of the presented method include the estimation of the molecular weight of protein complexes separated by BN-PAGE, since migration behavior depends on size, shape and even on posttranslational modifications of the complexes31,41. Size estimation of RNP complexes is even more complicated due to the influence of nucleic acids on the migration behavior. It can also not be prevented that complexes of the same size co-migrate in one single band. This can lead to the erroneous prediction of complex compositions. Therefore verifying the observed interactions with complementary techniques, e.g. by functional assays4, might be necessary. Also proteins only weakly or transiently associated to a macromolecular complex might be lost in the BN buffer used. To avoid this, samples could be crosslinked, what can also lead to artifacts or can prevent protein identification, or the buffer conditions can be optimized.
In contrast to classical 2D-PAGE, the combination of urea- and SDS-PAGE allows the separation according to hydrophobicity and molecular weight instead of isoelectric point (pI) and molecular weight 28, and does not limit the separation to proteins of a specific pI range. Similar to classical 2D-PAGE, separated proteins are visible as single spots, but on a diagonal line 4,28 (Figure 5, Figure 6). More hydrophobic proteins appear in spots above this diagonal, whereas more hydrophilic proteins are found below the line28. The polyacrylamide concentrations used in this protocol will separate proteins between 25 to 80 kDa well. To allow a separation of smaller or larger proteins the polyacrylamide concentration can be varied or gradient gels can be used in the third dimension. The components of complex IV (Figure 3) separated by 3D-PAGE (Figure 6) were cut out, trypsin digested, and analyzed by mass spectrometry. This resulted in the identification of several tRNA ligases. The components of the other complexes have been published recently 4. Our 3D-PAGE enabled the separation of different ligases, namely aspartate, asparagine, threonine, lysine and glycine ligases, with similar molecular weights (Table 3). Using a methionine tRNA-specific probe, we were able to detect potentially bound tRNA within complex IV, but if full-length tRNA or tRNA fragments are in the complex cannot be discriminated with the probes used. To check if the nucleic acids are really bound within the complex and not co-migrating, protease digested phloem sap samples might serve as suitable migration controls.
It has been speculated earlier that protein translation can occur within phloem sieve tubes, since almost most components of the entire ribosome as well as elongation factors have been found in phloem samples4,7. Our finding of tRNA and tRNA ligases seems to support this idea. However, tRNA fragments present in phloem samples from pumpkin have been shown to be potent inhibitors of translation42 and functional ribosomes seem to be absent4, suggesting that translation cannot take place.
Taken together, the protocol presented here allows the separation of native protein:protein and even RNP complexes from phloem samples and the separation and identification of their individual components with high resolution. The application of this method enables the discovery of novel protein and RNP complexes in phloem samples and can therefore elucidate new functions in this highly specialized plant compartment.

The long-distance conduits of the phloem are essential for the allocation of organic nutrients in higher plants, but are also involved in regulating many different processes important for growth and development, pathogen defense, and the adaptation to adverse environmental conditions. Besides small effectors like ions, phytohormones, or metabolites themselves, macromolecules like proteins and RNAs have recently emerged as potential signals.
Studies have shown that phloem loading of proteins is size dependent and controlled by the size exclusion limit (SEL) of the pore-plasmodesmal units connecting companion cells (CC) and sieve elements (SE) that are typically in the range of 10 to &#62;67 kDa1,2,3. However, despite these size limitations larger proteins and protein complexes have been found within the phloem system challenging the idea of size exclusion4, and even nonspecific loss of proteins from CC to SE has been suggested5.
Multiprotein as well as large ribonucleoprotein complexes play pivotal roles in biosynthesis and maintaining the structural integrity of the cell6. There is evidence that phloem-mobile protein-protein and ribonucleoprotein complexes exist4,7, but to date little about their function is known. In phloem sieve elements protein:protein and RNP complexes have been implicated with long-distance transport and/ or signaling8,9. To unravel the functions of the translocated complexes, studying their composition under varying environmental or stress conditions is required. To achieve this, native complexes have to be isolated and their components have to be separated with sufficient resolution.
To isolate high-molecular-weight complexes from the phloem, it is first necessary to obtain sap samples in sufficient quality and quantity. The technique that can be used for phloem sampling depends on the plant species of interest. Three main methods to obtain phloem sap exist 10: insect stylectomy11, EDTA-facilitated exudation12, and spontaneous exudation13.
Phloem samples from Arabidopsis thaliana (A. thaliana), the major model plant in laboratories worldwide, can only be obtained by EDTA-facilitated exudation or aphid stylectomy14,15. Both methods lead to either highly diluted phloem sap or very low sample amounts. EDTA-facilitated exudation is also prone to contamination and might not represent the real phloem composition16. Spontaneous phloem exudation is limited to plant species like cucurbits, lupine or yucca, where cutting off plant parts leads to a spontaneous emission of phloem sap that can be easily collected13,17,18,19. We recently established oilseed rape (Brassica napus) as a suitable model system for phloem analysis, since it is a close relative of A. thaliana and several microliters of phloem sap can be obtained from small incisions that has been shown to be of high purity4,8,20. Furthermore, the B. napus genome sequence was released in 201421.
Except for aphid stylectomy, all phloem collection methods described include damaging of surrounding tissue at the site of sampling, and the composition of phloem sap may change in response to injury. Therefore it is essential to check the quality of phloem samples, regardless of the sampling method applied. There are different methods for quality control of collected phloem sap, e.g. by determination of RNase activity22,23, RT-PCR with primers against Rubisco8,24, or the analysis of the sugar composition8.
Different methods to isolate and separate protein complexes can be applied, including size exclusion chromatography, sucrose density ultracentrifugation, or sample filtration through membranes with distinct molecular weight cut offs. However, these approaches do not allow high resolution. The technique called blue native PAGE (BN-PAGE), first described by Sch&#228;gger et al.25, is superior in terms of resolution. It was successfully used to determine the molecular weights of large native protein complexes from various organelles or from cellular lysates and their relative abundances26,27.
To further elucidate the complex composition of protein complexes, it is necessary to separate the individual components under denaturing conditions, leading to complete disassembly of the complex components. This can be achieved by a second dimension of SDS-PAGE 28,29 or, to achieve higher resolution, by a second dimension of isoelectric focusing (IEF) followed by a third dimension of SDS-PAGE30 and subsequent identification of the proteins using mass spectrometry.
In this protocol, we describe sampling of pure phloem sap from B. napus plants and the analysis of protein complexes from such phloem samples using a 3D electrophoretic approach combining BN-PAGE with Tris-Tricine-urea-PAGE and SDS-PAGE. The separated protein complex components are subsequently identified using mass spectrometry. In addition, we introduce blue native northern blotting as a method allowing the detection of RNAs in large RNP complexes4, extending the applicability of the approach.

<table><tbody><tr><td>1.5 mL reaction tubes</td><td>Eppendorf</td><td>30120086</td><td></td></tr><tr><td>10 well comb for SDS PAGE, thickness 1 mm</td><td>BioRad</td><td>1653359</td><td></td></tr><tr><td>2-Propanol</td><td>AppliChem</td><td>131090</td><td></td></tr><tr><td>30 % Acrylamide-bisacrylamide solution (29:1) solution</td><td>BioRad</td><td>1610156</td><td></td></tr><tr><td>30 % Acrylamide-bisacrylamide solution (37.5:1) solution</td><td>BioRad</td><td>1610158</td><td></td></tr><tr><td>96 % Ethanol</td><td>Carl Roth</td><td>P075</td><td></td></tr><tr><td>Acetic acid</td><td>Carl Roth</td><td>6755</td><td></td></tr><tr><td>Agarose</td><td>Lonza</td><td>50004</td><td></td></tr><tr><td>Aluminum sulfate-(14-18)-hydrate</td><td>AppliChem</td><td>141101</td><td></td></tr><tr><td>Ammonium peroxodisulfate (APS)</td><td>Carl Roth</td><td>9592.3</td><td></td></tr><tr><td>Bis-Tris</td><td>AppliChem</td><td>A3992</td><td></td></tr><tr><td>Boric acid</td><td>AppliChem</td><td>A2940</td><td></td></tr><tr><td>Bromophenol blue</td><td>AppliChem</td><td>A2331</td><td></td></tr><tr><td>Centrifugal concentrators &lt;em&gt;e.g.&lt;/em&gt; Vivaspin 500 (Mwco 10 kDa)</td><td>Sartorius</td><td>VS0102</td><td></td></tr><tr><td>Chemiluminescent Nucleic Acid Detection Module Kit</td><td>Thermo Fisher Scientific</td><td>89880</td><td></td></tr><tr><td>Chromatography papers &lt;em&gt;e.g.&lt;/em&gt; 3 mm CHR</td><td>Whatman</td><td>3030-153</td><td></td></tr><tr><td>CoolBox M30 System</td><td>Biocision</td><td>BCS-133</td><td></td></tr><tr><td>Coomassie brilliant Blue G-250</td><td>AppliChem</td><td>A3480</td><td></td></tr><tr><td>Diethyl pyrocarbonate (DEPC)</td><td>AppliChem</td><td>A0881</td><td></td></tr><tr><td>Dithiothreitol (DTT)</td><td>AppliChem</td><td>A1101</td><td></td></tr><tr><td>DNase I</td><td>AppliChem</td><td>A3778</td><td></td></tr><tr><td>Ethanol abs.</td><td>AppliChem</td><td>A3693</td><td></td></tr><tr><td>Ethylenediaminetetraacetic acid (EDTA)</td><td>AppliChem</td><td>A1103</td><td></td></tr><tr><td>Gel Imaging system &lt;em&gt;e.g.&lt;/em&gt; Chemidoc Touch</td><td>BioRad</td><td>1708370</td><td></td></tr><tr><td>GeneRuler 1kb plus</td><td>Thermo Fisher Scientific</td><td>SM1331</td><td></td></tr><tr><td>Glycerol</td><td>AppliChem</td><td>141339</td><td></td></tr><tr><td>Glycine</td><td>AppliChem</td><td>131340</td><td></td></tr><tr><td>Heating block TS1</td><td>Biometra</td><td>846-051-500</td><td></td></tr><tr><td>Hybridization oven &lt;em&gt;e.g.&lt;/em&gt; GFL Hybridization Incubator 7601</td><td>GFL</td><td>7601</td><td></td></tr><tr><td>Hypodermic needle (0.8 mm)</td><td>B Braun</td><td>4658309</td><td></td></tr><tr><td>IPG gel comb, thickness 1 mm</td><td>BioRad</td><td>1653367</td><td></td></tr><tr><td>Labeling of RNA &lt;em&gt;e.g.&lt;/em&gt;Biotin 3&#039;end DNA Labeling Kit</td><td>Thermo Fisher Scientific</td><td>89818</td><td></td></tr><tr><td>Native gradient gel &lt;em&gt;e.g.&lt;/em&gt; Novex NativePAGE 4&amp;ndash;16% Bis-Tris protein gel</td><td>Invitrogen</td><td>BN1002BOX</td><td></td></tr><tr><td>Nylon membrane &lt;em&gt;e.g.&lt;/em&gt; Hybond-N+</td><td>Amersham Pharmacia</td><td>RPN203B</td><td></td></tr><tr><td>Ortho-phosphoric acid</td><td>Carl Roth</td><td>6366.1</td><td></td></tr><tr><td>PageRuler prestained protein ladder</td><td>Thermo Fisher Scientific</td><td>26616</td><td></td></tr><tr><td>Power supply for Gel electrophoresis EPS</td><td>Amersham Pharmacia</td><td>18-1130-01</td><td>available from GE Healthcare</td></tr><tr><td>RNA Cleanup Kit</td><td>Qiagen</td><td>74204</td><td></td></tr><tr><td>Semi dry blot &lt;em&gt;e.g&lt;/em&gt;. Fastblot 43B semi dry Blot</td><td>Biometra</td><td>846-015-100</td><td></td></tr><tr><td>Sodium chloride (NaCl)</td><td>AppliChem</td><td>A1149</td><td></td></tr><tr><td>Sodium dodecyl sulfate (SDS)</td><td>AppliChem</td><td>142363</td><td></td></tr><tr><td>Synthesis of cDNA &lt;em&gt;e.g.&lt;/em&gt; RevertAid First Strand cDNA Synthesis Kit</td><td>Thermo Fisher Scientific</td><td>K1621</td><td></td></tr><tr><td>Tetramethylethylenediamine (TEMED)</td><td>AppliChem</td><td>A1148</td><td></td></tr><tr><td>Tricine</td><td>AppliChem</td><td>A3954</td><td></td></tr><tr><td>Tris</td><td>AppliChem</td><td>A1086</td><td></td></tr><tr><td>Tri-sodium citrate dihydrate</td><td>AppliChem</td><td>A3901</td><td></td></tr><tr><td>TRIzol Reagent</td><td>Thermo Fisher Scientific</td><td>15596026</td><td></td></tr><tr><td>ULTRAhyb Ultrasensitive Hybridization Buffer</td><td>Thermo Fisher Scientific</td><td>AM8670</td><td></td></tr><tr><td>Urea</td><td>AppliChem</td><td>A1360</td><td></td></tr><tr><td>UV Crosslinker &lt;em&gt;e.g.&lt;/em&gt; Stratalinker 2400</td><td>Agilent</td><td>NC0477671</td><td>from Fisher Scientific</td></tr><tr><td>Vertical electrophoresis apparatus &lt;em&gt;e.g.&lt;/em&gt;The XCell SureLock Mini-Cell or Mini-Protean III System</td><td>Thermo Fisher Scientific or BioRad</td><td>EI0001 or 1658004</td><td></td></tr><tr><td>Wipers &lt;em&gt;e.g.&lt;/em&gt; KIMWIPES Delicate Task Wipers</td><td>Kimberly-Clark</td><td>34120</td><td></td></tr></tbody></table>

phloem sap sampling from brassica napus for 3d-page of protein and ribonucleoprotein complexes

Sampling the phloem of higher plants is often laborious and significantly dependent on the plant species. However, proteome studies under denaturing conditions could be achieved in different plant species. Native protein:protein and protein:nucleic acid complexes from phloem samples have as yet scarcely been analyzed, although they might play important roles in maintenance of this specialized compartment or in long-distance signaling. Large molecular assemblies can be isolated using a blue native gel electrophoresis (BN-PAGE). Their protein components can be separated by a subsequent sodium dodecyl sulfate PAGE (SDS-PAGE). However, proteins with similar molecular weights co-migrate, what can hinder protein identification by mass spectrometry. Combining BN-PAGE with two different denaturing gel electrophoresis steps, namely Tris-Tricine-urea and SDS-PAGE, enables the additional separation of proteins according to their hydrophilicity/hydrophobicity and thus increases resolution and the success of protein identification. It even allows distinguishing proteins that only differ in their posttranslational modifications. In addition, blue native northern blotting can be applied to identify the RNA components in macromolecular complexes. We show that our protocol is suitable to unravel the protein and RNA components of native protein:protein and ribonucleoprotein (RNP) complexes occurring in phloem samples. Combining a blue native PAGE with two different denaturing PAGE steps can help to separate different kinds of large protein complexes, and also enables an increased identification rate of their components by mass spectrometry. Furthermore, the protocol is robust enough to simultaneously detect potentially bound nucleic acids within single protein complexes.

Watch this Scientific Journal Video about Phloem Sap Sampling from Brassica napus for 3D-PAGE of Protein and Ribonucleoprotein Complexes at JoVE.com

Phloem Sap Sampling from Brassica napus for 3D-PAGE of Protein and Ribonucleoprotein Complexes | Biology | Video

Phloem Sap Sampling from Brassica napus for 3D-PAGE of Protein and Ribonucleoprotein Complexes

Here we present a protocol to analyze the protein composition of large native protein:protein and protein:nucleic acid complexes from oilseed rape (B. napus) phloem exudate using a 3D polyacrylamide gel electrophoresis (PAGE) approach combining blue native (BN) with two denaturing PAGEs followed by mass spectrometric identification.

Phloem Sap Sampling from Brassica napus for 3D-PAGE of Protein and Ribonucleoprotein Complexes

Sampling the phloem of higher plants is often laborious and significantly dependent on the plant species. However, proteome studies under denaturing ...

phloem-sap-sampling-from-brassica-napus-for-3d-page-protein

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13.7K Views.  Universität Hamburg. Hier presenteren we een protocol voor het analyseren van de samenstelling van de eiwitten van groot eiwit: eiwit en eiwit: nucleïnezuur complexen van koolzaad (B. napus) floëem afgescheiden met behulp van een 3D polyacrylamide-gel elektroforese (pagina) aanpak combineren blauw native (BN) met twee denatureren pagina's, gevolgd door massaspectrometrische identificatie.

Video: Phloem Sap Sampling from Brassica napus for 3D-PAGE of Protein and Ribonucleoprotein Complexes

Transcript and Metabolite Profiling for the Evaluation of Tobacco Tree and Poplar as Feedstock for the Bio-based Industry

The global demand for food, feed, energy, and water poses extraordinary challenges for future generations. It is evident that robust platforms for the exploration of renewable resources are necessary to overcome these challenges. Within the multinational framework MultiBioPro we are developing biorefinery pipelines to maximize the use of plant biomass. More specifically, we use poplar and tobacco tree (Nicotiana glauca) as target crop species for improving saccharification, isoprenoid, long chain hydrocarbon contents, fiber quality, and suberin and lignin contents. The methods used to obtain these outputs include GC-MS, LC-MS and RNA sequencing platforms. The metabolite pipelines are well established tools to generate these types of data, but also have the limitations in that only well characterized metabolites can be used. The deep sequencing will allow us to include all transcripts present during the developmental stages of the tobacco tree leaf, but has to be mapped back to the sequence of Nicotiana tabacum. With these set-ups, we aim at a basic understanding for underlying processes and at establishing an industrial framework to exploit the outcomes. In a more long term perspective, we believe that data generated here will provide means for a sustainable biorefinery process using poplar and tobacco tree as raw material. To date the basal level of metabolites in the samples have been analyzed and the protocols utilized are provided in this article.

Plant biomass offers a renewable resource for multiple products, including fuel, feed, food, and a variety of materials. In this paper we investigate the properties of tobacco tree (Nicotiana glauca) and poplar as suitable sources for a biorefinery pipeline.

The global demand for food, feed, energy, and water poses extraordinary challenges for future generations. It is evident that robust platforms for the ...

Environment

An Efficient Method for the Isolation of Highly Purified RNA from Seeds for Use in Quantitative Transcriptome Analysis

Plant seeds accumulate large amounts of storage reserves comprising biodegradable organic matter. Humans rely on seed storage reserves for food and as industrial materials. Gene expression profiles are powerful tools for investigating metabolic regulation in plant cells. Therefore, detailed, accurate gene expression profiles during seed development are required for crop breeding. Acquiring highly purified RNA is essential for producing these profiles. Efficient methods are needed to isolate highly purified RNA from seeds. Here, we describe a method for isolating RNA from seeds containing large amounts of oils, proteins, and polyphenols, which have inhibitory effects on high-purity RNA isolation. Our method enables highly purified RNA to be obtained from seeds without the use of phenol, chloroform, or additional processes for RNA purification. This method is applicable to Arabidopsis, rapeseed, and soybean seeds. Our method will be useful for monitoring the expression patterns of low level transcripts in developing and mature seeds.

We have succeeded in establishing a method for RNA isolation from plant seeds containing large amounts of oils, proteins, and polyphenols, which have inhibitory effects on high-purity RNA isolation. Our method is suitable for monitoring the expression of genes with low level transcripts in seeds.

Plant seeds accumulate large amounts of storage reserves comprising biodegradable organic matter. Humans rely on seed storage reserves for food and as ...

Biochemistry

mRNA Interactome Capture from Plant Protoplasts

RNA-binding proteins (RBPs) determine the fates of RNAs. They participate in all RNA biogenesis pathways and especially contribute to post-transcriptional gene regulation (PTGR) of messenger RNAs (mRNAs). In the past few years, a number of mRNA-bound proteomes from yeast and mammalian cell lines have been successfully isolated through the use of a novel method called &#34;mRNA interactome capture,&#34; which allows for the identification of mRNA-binding proteins (mRBPs) directly from a physiological environment. The method is composed of in vivo ultraviolet (UV) crosslinking, pull-down and purification of messenger ribonucleoprotein complexes (mRNPs) by oligo(dT) beads, and the subsequent identification of the crosslinked proteins by mass spectrometry (MS). Very recently, by applying the same method, several plant mRNA-bound proteomes have been reported simultaneously from different Arabidopsis tissue sources: etiolated seedlings, leaf tissue, leaf mesophyll protoplasts, and cultured root cells. Here, we present the optimized mRNA interactome capture method for Arabidopsis thaliana leaf mesophyll protoplasts, a cell type that serves as a versatile tool for experiments that include various cellular assays. The conditions for optimal protein yield include the amount of starting tissue and the duration of UV irradiation. In the mRNA-bound proteome obtained from a medium-scale experiment (107 cells), RBPs noted to have RNA-binding capacity were found to be overrepresented, and many novel RBPs were identified. The experiment can be scaled up (109 cells), and the optimized method can be applied to other plant cell types and species to broadly isolate, catalog, and compare mRNA-bound proteomes in plants.

Here, we present an interactome capture protocol applied to Arabidopsis thaliana leaf mesophyll protoplasts. This method critically relies on in vivo UV crosslinking and allows for the isolation and identification of plant mRNA-binding proteins from a physiological environment.

RNA-binding proteins (RBPs) determine the fates of RNAs. They participate in all RNA biogenesis pathways and especially contribute to post-transcriptional ...

Combining X-Ray Crystallography with Small Angle X-Ray Scattering to Model Unstructured Regions of Nsa1 from S. Cerevisiae

Determination of the full-length structure of ribosome assembly factor Nsa1 from Saccharomyces cerevisiae (S. cerevisiae) is challenging because of the disordered and protease labile C-terminus of the protein. This manuscript describes the methods to purify recombinant Nsa1 from S. cerevisiae for structural analysis by both X-ray crystallography and SAXS. X-ray crystallography was utilized to solve the structure of the well-ordered N-terminal WD40 domain of Nsa1, and then SAXS was used to resolve the structure of the C-terminus of Nsa1 in solution. Solution scattering data was collected from full-length Nsa1 in solution. The theoretical scattering amplitudes were calculated from the high-resolution crystal structure of the WD40 domain, and then a combination of rigid body and ab initio modeling revealed the C-terminus of Nsa1. Through this hybrid approach the quaternary structure of the entire protein was reconstructed. The methods presented here should be generally applicable for the hybrid structural determination of other proteins composed of a mix of structured and unstructured domains.

Combining X-Ray Crystallography with Small Angle X-Ray Scattering to Model Unstructured Regions of Nsa1 from S. Cerevisiae

This method describes the cloning, expression, and purification of recombinant Nsa1 for structural determination by X-ray crystallography and small-angle X-ray scattering (SAXS), and is applicable for the hybrid structural analysis of other proteins containing both ordered and disordered domains.

Determination of the full-length structure of ribosome assembly factor Nsa1 from Saccharomyces cerevisiae (S. cerevisiae) is challenging because of the ...

Analysis of N-glycans from Raphanus sativus Cultivars Using PNGase H+

In recent years, the carbohydrate moieties of plants have received considerable attention, as they are a potential source of cross-reactive, allergy-provoking immune responses. In addition, carbohydrate structures also play a critical role in plant metabolism. Here, we present a simple and rapid method for preparing and analyzing N-glycans from different cultivars of radish (Raphanus sativus) using an N-glycanase specific for the release of plant-derived carbohydrate structures. To achieve this, crude trichloroacetic acid precipitates of radish homogenates were treated with PNGase H+, and labeled using 2-aminobenzamide as a fluorescent tag. The labeled N-glycan samples were subsequently analyzed by ultra performance liquid chromatography (UPLC) separation and matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry for a detailed structural evaluation and to quantify relative abundancies of the radish-derived N-glycan structures. This protocol can also be used for the analysis of N-glycans from various other plant species, and may be useful for further investigation of the function and effects of N-glycans on human health.

Analysis of N-glycans from Raphanus sativus Cultivars Using PNGase H+

We describe a simple and rapid method for the preparation and analysis of N-glycans from different cultivars of radish (Raphanus sativus).

In recent years, the carbohydrate moieties of plants have received considerable attention, as they are a potential source of cross-reactive, ...

Preparation of Fungal and Plant Materials for Structural Elucidation Using Dynamic Nuclear Polarization Solid-State NMR

This protocol shows how uniformly 13C, 15N-labeled fungal materials can be produced and how these soft materials should be proceeded for solid-state NMR and sensitivity-enhanced DNP experiments. The sample processing procedure of plant biomass is also detailed. This method allows the measurement of a series of 1D and 2D 13C-13C/15N correlations spectra, which enables high-resolution structural elucidation of complex biomaterials in their native state, with minimal perturbation. The isotope-labeling can be examined by quantifying the intensity in 1D spectra and the polarization transfer efficiency in 2D correlation spectra. The success of dynamic nuclear polarization (DNP) sample preparation can be evaluated by the sensitivity enhancement factor. Further experiments examining the structural aspects of the polysaccharides and proteins will lead to a model of the three-dimensional architecture. These methods can be modified and adapted to investigate a wide range of carbohydrate-rich materials, including the natural cell walls of plants, fungi, algae and bacteria, as well as synthesized or designed carbohydrate polymers and their complex with other molecules.

A protocol for preparing 13C,15N-labeled fungal and plant samples for multidimensional solid-state NMR spectroscopy and dynamic nuclear polarization (DNP) investigations is presented.

This protocol shows how uniformly 13C, 15N-labeled fungal materials can be produced and how these soft materials should be proceeded for solid-state NMR ...

Non-radioactive in situ Hybridization Protocol Applicable for Norway Spruce and a Range of Plant Species

The high-throughput expression analysis technologies available today give scientists an overflow of expression profiles but their resolution in terms of tissue specific expression is limited because of problems in dissecting individual tissues. Expression data needs to be confirmed and complemented with expression patterns using e.g. in situ hybridization, a technique used to localize cell specific mRNA expression. The in situ hybridization method is laborious, time-consuming and often requires extensive optimization depending on species and tissue. In situ experiments are relatively more difficult to perform in woody species such as the conifer Norway spruce (Picea abies). Here we present a modified DIG in situ hybridization protocol, which is fast and applicable on a wide range of plant species including P. abies. With just a few adjustments, including altered RNase treatment and proteinase K concentration, we could use the protocol to study tissue specific expression of homologous genes in male reproductive organs of one gymnosperm and two angiosperm species; P. abies, Arabidopsis thaliana and Brassica napus. The protocol worked equally well for the species and genes studied. AtAP3 and BnAP3 were observed in second and third whorl floral organs in A. thaliana and B. napus and DAL13 in microsporophylls of male cones from P. abies. For P. abies the proteinase K concentration, used to permeablize the tissues, had to be increased to 3 g/ml instead of 1 g/ml, possibly due to more compact tissues and higher levels of phenolics and polysaccharides. For all species the RNase treatment was removed due to reduced signal strength without a corresponding increase in specificity. By comparing tissue specific expression patterns of homologous genes from both flowering plants and a coniferous tree we demonstrate that the DIG in situ protocol presented here, with only minute adjustments, can be applied to a wide range of plant species. Hence, the protocol avoids both extensive species specific optimization and the laborious use of radioactively labeled probes in favor of DIG labeled probes. We have chosen to illustrate the technically demanding steps of the protocol in our film.
Anna Karlgren and Jenny Carlsson contributed equally to this study.
Corresponding authors: Anna Karlgren at Anna.Karlgren@ebc.uu.se and Jens F. Sundstr&#246;m at Jens.Sundstrom@vbsg.slu.se

Non-radioactive in situ Hybridization Protocol Applicable for Norway Spruce and a Range of Plant Species

We describe a modified DIG in situ hybridization protocol, which is fast and applicable on a wide range of plant species including Norway spruce. With just a few adjustments, including altered RNase treatment and proteinase K concentration, the protocol may be used in studies of different tissues and species.

The high-throughput expression analysis technologies available today give scientists an overflow of expression profiles but their resolution in terms of ...

Phosphoproteomic Strategy for Profiling Osmotic Stress Signaling in Arabidopsis

Protein phosphorylation is crucial for the regulation of enzyme activity and gene expression under osmotic condition. Mass spectrometry (MS)-based phosphoproteomics has transformed the way of studying plant signal transduction. However, requirement of lots of starting materials and prolonged MS measurement time to achieve the depth of coverage has been the limiting factor for the high throughput study of global phosphoproteomic changes in plants. To improve the sensitivity and throughput of plant phosphoproteomics, we have developed a stop and go extraction (stage) tip based phosphoproteomics approach coupled with Tandem Mass Tag (TMT) labeling for the rapid and comprehensive analysis of plant phosphorylation perturbation in response to osmotic stress. Leveraging the simplicity and high throughput of stage tip technique, the whole procedure takes approximately one hour using two tips to finish phosphopeptide enrichment, fractionation, and sample cleaning steps, suggesting an easy-to-use and high efficiency of the approach. This approach not only provides an in-depth plant phosphoproteomics analysis (&#62; 11,000 phosphopeptide identification) but also demonstrates the superior separation efficiency (&#60; 5% overlap) between adjacent fractions. Further, multiplexing has been achieved using TMT labeling to quantify the phosphoproteomic changes of wild-type and snrk2 decuple mutant plants. This approach has successfully been used to reveal the phosphorylation events of Raf-like kinases in response to osmotic stress, which sheds light on the understanding of early osmotic signaling in land plants.

Phosphoproteomic Strategy for Profiling Osmotic Stress Signaling in Arabidopsis

Presented here is a phosphoproteomic approach, namely stop and go extraction tip based phosphoproteomic, which provides high-throughput and deep coverage of Arabidopsis phosphoproteome. This approach delineates the overview of osmotic stress signaling in Arabidopsis.

Protein phosphorylation is crucial for the regulation of enzyme activity and gene expression under osmotic condition. Mass spectrometry (MS)-based ...

Identification of Post-translational Modifications of Plant Protein Complexes

Plants adapt quickly to changing environments due to elaborate perception and signaling systems. During pathogen attack, plants rapidly respond to infection via the recruitment and activation of immune complexes. Activation of immune complexes is associated with post-translational modifications (PTMs) of proteins, such as phosphorylation, glycosylation, or ubiquitination. Understanding how these PTMs are choreographed will lead to a better understanding of how resistance is achieved.
Here we describe a protein purification method for nucleotide-binding leucine-rich repeat (NB-LRR)-interacting proteins and the subsequent identification of their post-translational modifications (PTMs). With small modifications, the protocol can be applied for the purification of other plant protein complexes. The method is based on the expression of an epitope-tagged version of the protein of interest, which is subsequently partially purified by immunoprecipitation and subjected to mass spectrometry for identification of interacting proteins and PTMs.
This protocol demonstrates that: i). Dynamic changes in PTMs such as phosphorylation can be detected by mass spectrometry; ii). It is important to have sufficient quantities of the protein of interest, and this can compensate for the lack of purity of the immunoprecipitate; iii). In order to detect PTMs of a protein of interest, this protein has to be immunoprecipitated to get a sufficient quantity of protein.

We describe here a protocol for the purification and characterization of plant protein complexes. We demonstrate that by immunoprecipitating a single protein within a complex, so we can identify its post-translational modifications and its interacting partners.

Plants adapt quickly to changing environments due to elaborate perception and signaling systems. During pathogen attack, plants rapidly respond to ...

Collection and Analysis of Arabidopsis Phloem Exudates Using the EDTA-facilitated Method

The plant phloem is essential for the long-distance transport of (photo-) assimilates as well as of signals conveying biotic or abiotic stress. It contains sugars, amino acids, proteins, RNA, lipids and other metabolites. While there is a large interest in understanding the composition and function of the phloem, the role of many of these molecules and thus, their importance in plant development and stress response has yet to be determined. One barrier to phloem analysis lies in the fact that the phloem seals itself upon wounding. As a result, the number of plants from which phloem sap can be obtained is limited. One method that allows collection of phloem exudates from several plant species without added equipment is the EDTA-facilitated phloem exudate collection described here. While it is easy to use, it does lead to the wounding of cells and care has to be taken to remove contents of damaged cells. In addition, several controls to prove purity of the exudate are necessary. Because it is an exudation rather than a direct collection of the phloem sap (not possible in many species) only relative quantification of its contents can occur. The advantage of this method over others is that it can be used in many herbaceous or woody plant species (Perilla, Arabidopsis, poplar, etc.) and requires minimal equipment and training. It leads to reasonably large amounts of exudates that can be used for subsequent analysis of proteins, sugars, lipids, RNA, viruses and metabolites. It is simple enough that it can be used in both a research as well as in a teaching laboratory.

Collection and Analysis of Arabidopsis Phloem Exudates Using the EDTA-facilitated Method

Knowledge of the composition of the phloem sap as well as the mechanism of its loading and long-distance transport is essential for the understanding of long-distance signaling in plant development and stress/pathogen response and of assimilate transport. This manuscript describes the collection of phloem exudates using the EDTA-facilitated method.

Phloem Sap Sampling from Brassica napus for 3D-PAGE of Protein and Ribonucleoprotein Complexes

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