The authors thank funding from FAEPEX and FAPESP (2015/26479-6). MPP thanks Capes for his master&#39;s degree scholarship (process 88887.600591/2021-00) and CNPq. JLSM thanks CNPq for productivity grants (303664/2020-7). The authors also thank the access to equipment and assistance provided by LME (Laboratory of Electron Microscopy - IB/Unicamp), INFABiC (National Institute of Science and Technology on Photonics Applied to Cell Biology - Unicamp), and LaBiVasc (Laboratory of Vascular Biology - DBEF/IB/Unicamp); LAMEB (UFSC) and Eliana de Medeiros Oliveira (UFSC) for contributions to cryoprotection protocol; LME for contributions to TEM protocol.

<ol>
	<li>Evert, R. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Esau&#8217;s Plant Anatomy: Meristems, Cells, and Tissues of the Plant Body: Their Structure, Function, and Development. , (2006).</li><li>Yeung, E. C. T., Stasolla, C., Sumner, M. J., Huang, B. Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Plant Microtechniques and Protocols. , (2015).</li><li>Sokoloff, D. D., Jura-Morawiec, J., Zoric, L., Fay, M. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plant+anatomy:+at+the+heart+of+modern+botany.">Plant anatomy: at the heart of modern botany.</a> Botanical Journal of the Linnean Society. 195 (3), 249-253 (2021).</li><li>Leake, J. 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The authors have nothing to disclose.

Image analyses in plant anatomy and morphology have an important potential to fulfil objectives and help understand the relationships between mycoheterotrophic plants and their indispensable fungal endophytes, as demonstrated by studies of subterranean organs6,40, structural analyses of symbiotic germination of seeds39, and aerial and reproductive structures41. Structural botany, despite having lost its prestige and...

Structural research in botany, covering plant morphology and anatomy, is basic in understanding the whole organism1,2, and provides indispensable perspectives to integrate and contribute to knowledge regarding the ecology, physiology, development, and evolution of plants3. Methods in plant morphology and anatomy currently comprise protocols, equipment, and knowledge developed recently as well as more than a century ago2. The continuous execution and adaptation of classical methods (e.g., light microscopy) along with more recent techniques (e.g., confocal microscopy, X-ray microtomography) have the same essential basis: theoretical knowledge enabling the development of a methodology.
The main tool in plant anatomy and morphology is the image. Despite the misconception that such analyses are simple observations, giving space to subjective interpretations2, analyzing and understanding images in this area requires knowledge of the methods applied (the equipment, type of analysis, methodological procedures), cell components, histochemistry, and the plant body (tissue organization and function, ontogeny, morphological adaptations). Interpreting the images obtained via a variety of methods can lead to correlating form and function, deciphering the chemical composition of a structure, corroborating in describing taxa, understanding infections by phytopathogens, and other such assessments.
When researching mycoheterotrophic (MH) plants&#160;(i.e., non-photosynthetic plants that obtain carbon from mycorrhizal fungi4,5),&#160;remarkable aspects of their structural adaptations, the patterns of tissue colonization by fungi, and the morphoanatomy of subterranean organs can enlighten their development strategies and relationships with hyphae, which are the source of nutrients. The subterranean organs of MH plants usually show important adaptations related to their association with soil fungi, hence it is essential to perform these anatomical and morphological investigations6. MH species&#39; aerial organs should not be ignored, as endophytes can be also present in these tissues, even if they are not mycorrhizal fungi (personal observations, not published yet).
Besides the well-established essentiality of mycorrhizal fungi association with MH species during their entire life cycle7, every orchid species, even the autotrophic ones, have an initial obligate mycoheterotrophic stage in natural environments. It occurs because the orchids&#39; embryo is undifferentiated and lacks an endosperm or cotyledons, thus being incapable of developing and establishing itself in natural environments without the nutritional support of fungal partners4,8. Considering that, symbiotic germination protocols can be applied not only to MH species but also to photosynthesizing orchids, aiming to investigate orchid-fungus specificity in germination and protocorm development, a vastly applied methodology in initiatives for the conservation of threatened species9,10,11.
In this methods assembly, we describe important steps involved in collecting, fixing, and storing MH plant samples for anatomical studies (section 1), surface analysis and sample selection (section 2), sectioning methods (freehand: section 3, microtomy: section 4, cryomicrotomy: section 5), staining and mounting (section 6), fluorescence and confocal microscopy of fungal endophytes (section 7), scanning electron microscopy (section 8), and transmission electron microscopy (section 9). Additionally, we describe a symbiotic germination method for orchid seeds (MH and autotrophic, section 10), as the imaging methods previously mentioned can be successfully applied to analyze fungal colonization of seeds, protocorms, and seedlings in the germination process.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/63777/63777fig01.jpg" /> 
Figure 1: Schematic summarization of imaging methods. The schematics provide indications of protocol steps in which they are detailed. Abbreviations: GMA = glycol methacrylate, OCT = optimal cutting temperature compound, SEM = scanning electron microscopy. <a href="https://www.jove.com/files/ftp_upload/63777/63777fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The microscopy techniques described here in detail (Figure 1) are preceded by the following essential steps: collecting, fixing, dehydrating, embedding, and sectioning samples. As the steps are variable (Figure 1) depending on the chosen technique(s), it is important to think ahead, considering the fixatives to be prepared and transported to the collection site, how the samples must be prepared before fixing, the dehydration processes to be used (section 1), and different embedding possibilities and sectioning methods (sections 4, 5, and 9). Figure 1 summarizes sequentially all the steps required for each microscopy technique thoroughly described below.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Acetone</td>
			<td>Sigma-Aldrich</td>
			<td>179124</td>
			<td>(for SEM stubs mounting)</td>
		</tr>
		<tr>
			<td>Agar-agar (AA)</td>
			<td>Sigma-Aldrich</td>
			<td>A1296</td>
			<td>(for seeds germination tests)</td>
		</tr>
		<tr>
			<td>Calcofluor White Stain</td>
			<td>Sigma-Aldrich</td>
			<td>18909</td>
			<td>fluorescent dye (detects cellulose)</td>
		</tr>
		<tr>
			<td>Citrate Buffer Solution, 0.09M pH 4.8</td>
			<td>Sigma-Aldrich</td>
			<td>C2488</td>
			<td>(for toluidine blue O staining)</td>
		</tr>
		<tr>
			<td>Conductive Double-Sided Carbon Tape</td>
			<td>Fisher Scientific</td>
			<td>50-285-81</td>
			<td>(for SEM)</td>
		</tr>
		<tr>
			<td>Confocal Microscope</td>
			<td>Zeiss</td>
			<td></td>
			<td>(any model)</td>
		</tr>
		<tr>
			<td>Copper Grids</td>
			<td>Sigma-Aldrich</td>
			<td>G4776</td>
			<td>(for TEM)</td>
		</tr>
		<tr>
			<td>Critical-point dryer</td>
			<td>Balzers</td>
			<td></td>
			<td>(any model)</td>
		</tr>
		<tr>
			<td>Cryostat</td>
			<td>Leica Biosystems</td>
			<td></td>
			<td>(any model)</td>
		</tr>
		<tr>
			<td>Dissecting microscope</td>
			<td>Leica Biosystems</td>
			<td></td>
			<td>(= stereomicroscope, any model)</td>
		</tr>
		<tr>
			<td>Entellan</td>
			<td>Sigma-Aldrich</td>
			<td>107960</td>
			<td>rapid mounting medium for microscopy</td>
		</tr>
		<tr>
			<td>Ethyl alcohol, pure (&#8805;99.5%)</td>
			<td>Sigma-Aldrich</td>
			<td>459836</td>
			<td>(= ethanol, for dehydration processes)</td>
		</tr>
		<tr>
			<td>Formaldehyde solution, 37%</td>
			<td>Sigma-Aldrich</td>
			<td>252549</td>
			<td>(for NBF solution preparation)</td>
		</tr>
		<tr>
			<td>Formalin solution, neutral buffered, 10%</td>
			<td>Sigma-Aldrich</td>
			<td>HT501128</td>
			<td>histological tissue fixative</td>
		</tr>
		<tr>
			<td>Gelatin capsules for TEM</td>
			<td>Fisher Scientific</td>
			<td>50-248-71</td>
			<td>(for resin polymerisation in TEM)</td>
		</tr>
		<tr>
			<td>Gelatin solution, 2% in H2O</td>
			<td>Sigma-Aldrich</td>
			<td>G1393</td>
			<td>(dilute for slides preparation - OCT adherence)</td>
		</tr>
		<tr>
			<td>Glutaraldehyde solution, 25%</td>
			<td>Sigma-Aldrich</td>
			<td>G6257</td>
			<td>(for Karnovsky&#8217;s solution preparation)</td>
		</tr>
		<tr>
			<td>HistoResin</td>
			<td>Leica Biosystems</td>
			<td>14702231731</td>
			<td>glycol methacrylate (GMA) embedding kit</td>
		</tr>
		<tr>
			<td>Iodine</td>
			<td>Sigma-Aldrich</td>
			<td>207772</td>
			<td>(for Lugol solution preparation)</td>
		</tr>
		<tr>
			<td>Lead(II) nitrate</td>
			<td>Sigma-Aldrich</td>
			<td>228621</td>
			<td>Pb(NO3)2 (for TEM contrast staining)</td>
		</tr>
		<tr>
			<td>Light Microscope</td>
			<td>Olympus</td>
			<td></td>
			<td>(any model)</td>
		</tr>
		<tr>
			<td>LR White acrylic resin</td>
			<td>Sigma-Aldrich</td>
			<td>L9774</td>
			<td>hydrophilic acrylic resin for TEM</td>
		</tr>
		<tr>
			<td>Lugol solution</td>
			<td>Sigma-Aldrich</td>
			<td>62650</td>
			<td>(for staining)</td>
		</tr>
		<tr>
			<td>Metal stubs for specimen mounts</td>
			<td>Rave Scientific</td>
			<td></td>
			<td>(for SEM, different models)</td>
		</tr>
		<tr>
			<td>Microtome</td>
			<td>Leica Biosystems</td>
			<td></td>
			<td>manual rotary microtome or other model</td>
		</tr>
		<tr>
			<td>Oatmeal agar (OMA)</td>
			<td>Millipore</td>
			<td>O3506</td>
			<td>(for seeds germination tests)</td>
		</tr>
		<tr>
			<td>OCT Compound, Tissue-Tek</td>
			<td>Sakura Finetek USA</td>
			<td>4583</td>
			<td>embedding medium for frozen tissues</td>
		</tr>
		<tr>
			<td>Osmium tetroxide</td>
			<td>Sigma-Aldrich</td>
			<td>201030</td>
			<td>OsO4 (for TEM postfixation)</td>
		</tr>
		<tr>
			<td>Parafilm M</td>
			<td>Sigma-Aldrich</td>
			<td>P7793</td>
			<td>sealing thermoplastic film</td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td>Sigma-Aldrich</td>
			<td>158127</td>
			<td>(for Karnovsky&#8217;s solution preparation)</td>
		</tr>
		<tr>
			<td>Poly-L-lysine solution, 0.1% in H2O</td>
			<td>Sigma-Aldrich</td>
			<td>P8920</td>
			<td>(for slides preparation - OCT adherence)</td>
		</tr>
		<tr>
			<td>Poly-Prep Slides</td>
			<td>Sigma-Aldrich</td>
			<td>P0425</td>
			<td>poly-L-lysine coated glass slides</td>
		</tr>
		<tr>
			<td>Polyethylene Molding Cup Trays</td>
			<td>Polysciences</td>
			<td>17177A-3</td>
			<td>(6x8x5 mm, for embbeding samples in GMA resin)</td>
		</tr>
		<tr>
			<td>Polyethylene Molding Cup Trays</td>
			<td>Polysciences</td>
			<td>17177C-3</td>
			<td>(13x19x5 mm, for embbeding samples in GMA resin)</td>
		</tr>
		<tr>
			<td>Potassium iodide</td>
			<td>Sigma-Aldrich</td>
			<td>221945</td>
			<td>(for Lugol solution preparation)</td>
		</tr>
		<tr>
			<td>Potato Dextrose Agar (PDA)</td>
			<td>Millipore</td>
			<td>70139</td>
			<td>(for seeds germination tests)</td>
		</tr>
		<tr>
			<td>Scanning Electron Microscope</td>
			<td>Jeol</td>
			<td></td>
			<td>(any model)</td>
		</tr>
		<tr>
			<td>Silane [(3-Aminopropyl)triethoxysilane]</td>
			<td>Sigma-Aldrich</td>
			<td>A3648</td>
			<td>(for slides preparation - OCT adherence)</td>
		</tr>
		<tr>
			<td>Silane-Prep Slides</td>
			<td>Sigma-Aldrich</td>
			<td>S4651</td>
			<td>glass slides coated with silane</td>
		</tr>
		<tr>
			<td>Silica gel orange, granular</td>
			<td>Supelco</td>
			<td>10087</td>
			<td>(for dessicating processes)</td>
		</tr>
		<tr>
			<td>Sodium cacodylate trihydrate</td>
			<td>Sigma-Aldrich</td>
			<td>C0250</td>
			<td>(for glutaraldehyde-sodium cacodylate buffer)</td>
		</tr>
		<tr>
			<td>Sodium hydroxide</td>
			<td>Sigma-Aldrich</td>
			<td>S5881</td>
			<td>NaOH (for Karnovsky&#8217;s solution preparation and TEM contrast staining)</td>
		</tr>
		<tr>
			<td>Sodium hypochlorite solution</td>
			<td>Sigma-Aldrich</td>
			<td>425044</td>
			<td>NaClO (for seeds surface disinfection)</td>
		</tr>
		<tr>
			<td>Sodium phosphate dibasic, anhydrous</td>
			<td>Sigma-Aldrich</td>
			<td>71640</td>
			<td>Na2HPO4 (for NBF solution and PB preparation)</td>
		</tr>
		<tr>
			<td>Sodium phosphate monobasic monohydrate</td>
			<td>Sigma-Aldrich</td>
			<td>S9638</td>
			<td>NaH2PO4&#183;H2O (for NBF and PB)</td>
		</tr>
		<tr>
			<td>Sputter coater</td>
			<td>Balzers</td>
			<td></td>
			<td>(any model)</td>
		</tr>
		<tr>
			<td>Sucrose</td>
			<td>Sigma-Aldrich</td>
			<td>S0389</td>
			<td>C12H22O11 (for cryoprotection and germination test)</td>
		</tr>
		<tr>
			<td>Sudan III</td>
			<td>Sigma-Aldrich</td>
			<td>S4131</td>
			<td>(for staining)</td>
		</tr>
		<tr>
			<td>Sudan IV</td>
			<td>Sigma-Aldrich</td>
			<td>198102</td>
			<td>(for staining)</td>
		</tr>
		<tr>
			<td>Sudan Black B</td>
			<td>Sigma-Aldrich</td>
			<td>199664</td>
			<td>(for staining)</td>
		</tr>
		<tr>
			<td>Syringe</td>
			<td></td>
			<td></td>
			<td>(3 mL, any brand, for TEM contrast staining)</td>
		</tr>
		<tr>
			<td>Syringe Filter Unit, Millex-GV 0.22 &#181;m</td>
			<td>Millipore</td>
			<td>SLGV033R</td>
			<td>PVDF, 33 mm, gamma sterilized (for TEM contrast staining)</td>
		</tr>
		<tr>
			<td>Tek Bond Super Glue 793</td>
			<td>Tek Bond Saint-Gobain</td>
			<td>78072720018</td>
			<td>liquid cyanoacrylate adhesive, medium viscosity</td>
		</tr>
		<tr>
			<td>Toluidine Blue O</td>
			<td>Sigma-Aldrich</td>
			<td>T3260</td>
			<td>(for staining)</td>
		</tr>
		<tr>
			<td>Transmission Electron Microscope</td>
			<td>Jeol</td>
			<td></td>
			<td>(any model)</td>
		</tr>
		<tr>
			<td>Triphenyltetrazolium chloride</td>
			<td>Sigma-Aldrich</td>
			<td>T8877</td>
			<td>(for the tetrazolium test in seeds germination)</td>
		</tr>
		<tr>
			<td>Trisodium citrate dihydrate</td>
			<td>Sigma-Aldrich</td>
			<td>S1804</td>
			<td>Na3(C6H5O7)&#183;2H2O (for TEM contrast staining)</td>
		</tr>
		<tr>
			<td>Ultramicrotome</td>
			<td>Leica Biosystems</td>
			<td></td>
			<td>(any model)</td>
		</tr>
		<tr>
			<td>Uranyl acetate</td>
			<td>Fisher Scientific</td>
			<td>18-607-645</td>
			<td>UO2(CH3COO)2 (for TEM contrast staining)</td>
		</tr>
		<tr>
			<td>Vacuum pump</td>
			<td></td>
			<td></td>
			<td>(any model)</td>
		</tr>
		<tr>
			<td>Wheat Germ Agglutinin, Alexa Fluor 488 Conjugate</td>
			<td>TermoFisher Scientific</td>
			<td>W11261</td>
			<td>fluorescent dye-conjugated lectin (detects sialic acid and N-acetylglucosaminyl residues)</td>
		</tr>
	</tbody>
</table>

microscopy techniques for interpreting fungal colonization in mycoheterotrophic plants tissues and symbiotic germination of seeds

Structural botany is an indispensable perspective to fully understand the ecology, physiology, development, and evolution of plants. When researching mycoheterotrophic plants (i.e., plants that obtain carbon from fungi), remarkable aspects of their structural adaptations, the patterns of tissue colonization by fungi, and the morphoanatomy of subterranean organs can enlighten their developmental strategies and their relationships with hyphae, the source of nutrients. Another important role of symbiotic fungi is related to the germination of orchid seeds; all Orchidaceae species are mycoheterotrophic during germination and seedling stage (initial mycoheterotrophy), even the ones that photosynthesize in adult stages. Due to the lack of nutritional reserves in orchid seeds, fungal symbionts are essential to provide substrates and enable germination. Analyzing germination stages by structural perspectives can also answer important questions regarding the fungi interaction with the seeds. Different imaging techniques can be applied to unveil fungi endophytes in plant tissues, as are proposed in this article. Freehand and thin sections of plant organs can be stained and then observed using light microscopy. A fluorochrome conjugated to wheat germ agglutinin can be applied to the fungi and co-incubated with Calcofluor White to highlight plant cell walls in confocal microscopy. In addition, the methodologies of scanning and transmission electron microscopy are detailed for mycoheterotrophic orchids, and the possibilities of applying such protocols in related plants is explored. Symbiotic germination of orchid seeds (i.e., in the presence of mycorrhizal fungi) is described in the protocol in detail, along with possibilities of preparing the structures obtained from different stages of germination for analyses with light, confocal, and electron microscopy.

Following the essential stages of fixing plant tissue yields cellular structures as similar as possible to the living state, considering the morphology, volume, and spatial organization of cellular components and tissues16. Observe&#160;such traits in the samples after chemical fixation (Figure 4). Figure 4C-F represents adequately fixed samples under light microscopy. Following the fixation procedures de...

Watch this Scientific Journal Video about Microscopy Techniques for Interpreting Fungal Colonization in Mycoheterotrophic Plants Tissues and Symbiotic Germination of Seeds at JoVE.com

Microscopy Techniques for Interpreting Fungal Colonization in Mycoheterotrophic Plants Tissues and Symbiotic Germination of Seeds

This protocol aims to provide detailed procedures for collecting, fixing, and maintaining mycoheterotrophic plant samples, applying different microscopy techniques such as scanning and transmission electron microscopy, light, confocal, and fluorescence microscopy to study fungal colonization in plants tissues and seeds germinated with mycorrhizal fungi.

Structural botany is an indispensable perspective to fully understand the ecology, physiology, development, and evolution of plants. When researching ...

microscopy-techniques-for-interpreting-fungal-colonization

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Biology

3.6K Views.  University of Campinas (UNICAMP). This protocol aims to provide detailed procedures for collecting, fixing, and maintaining mycoheterotrophic plant samples, applying different microscopy techniques such as scanning and transmission electron microscopy, light, confocal, and fluorescence microscopy to study fungal colonization in plants tissues and seeds germinated with mycorrhizal fungi.

Video: Microscopy Techniques for Interpreting Fungal Colonization in Mycoheterotrophic Plants Tissues and Symbiotic Germination of Seeds

Obtaining Hemocytes from the Hawaiian Bobtail Squid Euprymna scolopes and Observing their Adherence to Symbiotic and Non-Symbiotic Bacteria

Studies concerning the role of the immune system in mediating molecular signaling between beneficial bacteria and their hosts have, in recent years, made significant contributions to our understanding of the co-evolution of eukaryotes with their microbiota. The symbiotic association between the Hawaiian bobtail squid, Euprymna scolopes and the bioluminescent bacterium Vibrio fischeri has been utilized as a model system for understanding the effects of beneficial bacteria on animal development. Recent studies have shown that macrophage-like hemocytes, the sole cellular component of the squid host's innate immune system, likely play an important role in mediating the establishment and maintenance of this association. This protocol will demonstrate how to obtain hemocytes from E. scolopes and then use these cells in bacterial binding assays. Adult squid are first anesthetized before hemolymph is collected by syringe from the main cephalic blood vessel. The host hemocytes, contained in the extracted hemolymph, are adhered to chambered glass coverslips and then exposed to green fluorescent protein-labeled symbiotic Vibrio fischeri and non-symbiotic Vibrio harveyi. The hemocytes are counterstained with a fluorescent dye (Cell Tracker Orange, Invitrogen) and then visualized using fluorescent microscopy.

Obtaining Hemocytes from the Hawaiian Bobtail Squid Euprymna scolopes and Observing their Adherence to Symbiotic and Non-Symbiotic Bacteria

This video will demonstrate how to obtain hemocytes (blood cells) from the Hawaiian bobtail squid, Euprymna scolopes for use in cell biological and bacterial adhesion assays. Hemocytes will be stained with a fluorescent dye and exposed to GFP-labeled bacteria.

Studies concerning the role of the immune system in mediating molecular signaling between beneficial bacteria and their hosts have, in recent years, made ...

Patch Clamp and Perfusion Techniques for Studying Ion Channels Expressed in Xenopus oocytes

The protocol presented here is designed to study the activation of the large conductance, voltage- and Ca2+-activated K+ (BK) channels. The protocol may also be used to study the structure-function relationship for other ion channels and neurotransmitter receptors1. BK channels are widely expressed in different tissues and have been implicated in many physiological functions, including regulation of smooth muscle contraction, frequency tuning of inner hair cells and regulation of neurotransmitter release2-6. BK channels are activated by membrane depolarization and by intracellular Ca2+ and Mg2+ 6-9. Therefore, the protocol is designed to control both the membrane voltage and the intracellular solution. In this protocol, messenger RNA of BK channels is injected into Xenopus laevis oocytes (stage V-VI) followed by 2-5 days of incubation at 18&deg;C10-13. Membrane patches that contain single or multiple BK channels are excised with the inside-out configuration using patch clamp techniques10-13. The intracellular side of the patch is perfused with desired solutions during recording so that the channel activation under different conditions can be examined. To summarize, the mRNA of BK channels is injected into Xenopus laevis oocytes to express channel proteins on the oocyte membrane; patch clamp techniques are used to record currents flowing through the channels under controlled voltage and intracellular solutions.

Patch Clamp and Perfusion Techniques for Studying Ion Channels Expressed in Xenopus oocytes

Ionic current of BK channels is recorded using patch clamp techniques. BK channels are expressed in Xenopus oocytes by injecting messenger RNA. The intracellular solution during patch clamp recordings is controlled by a perfusion system.

The protocol presented here is designed to study the activation of the large conductance, voltage- and Ca2+-activated K+ (BK) channels. The protocol may ...

Tandem High-pressure Freezing and Quick Freeze Substitution of Plant Tissues for Transmission Electron Microscopy

Since the 1940s transmission electron microscopy (TEM) has been providing biologists with ultra-high resolution images of biological materials. Yet, because of laborious and time-consuming protocols that also demand experience in preparation of artifact-free samples, TEM is not considered a user-friendly technique. Traditional sample preparation for TEM used chemical fixatives to preserve cellular structures. High-pressure freezing is the cryofixation of biological samples under high pressures to produce very fast cooling rates, thereby restricting ice formation, which is detrimental to the integrity of cellular ultrastructure. High-pressure freezing and freeze substitution are currently the methods of choice for producing the highest quality morphology in resin sections for TEM. These methods minimize the artifacts normally associated with conventional processing for TEM of thin sections. After cryofixation the frozen water in the sample is replaced with liquid organic solvent at low temperatures, a process called freeze substitution. Freeze substitution is typically carried out over several days in dedicated, costly equipment. A recent innovation allows the process to be completed in three hours, instead of the usual two days. This is typically followed by several more days of sample preparation that includes infiltration and embedding in epoxy resins before sectioning. Here we present a protocol combining high-pressure freezing and quick freeze substitution that enables plant sample fixation to be accomplished within hours. The protocol can readily be adapted for working with other tissues or organisms. Plant tissues are of special concern because of the presence of aerated spaces and water-filled vacuoles that impede ice-free freezing of water. In addition, the process of chemical fixation is especially long in plants due to cell walls impeding the penetration of the chemicals to deep within the tissues. Plant tissues are therefore particularly challenging, but this protocol is reliable and produces samples of the highest quality.

Obtaining high-quality transmission electron microscopy images is challenging, especially in the case of plant cells, which have abundant large water-filled vacuoles and aerated spaces. Tandem high-pressure freezing and quick freeze substitution greatly reduce preparation time of plant samples for TEM while producing samples with excellent ultrastructural preservation.

Since the 1940s transmission electron microscopy (TEM) has been providing biologists with ultra-high resolution images of biological materials. Yet, ...

Measuring Spatial and Temporal Ca2+ Signals in Arabidopsis Plants

Developmental and environmental cues induce Ca2+ fluctuations in plant cells. Stimulus-specific spatial-temporal Ca2+ patterns are sensed by cellular Ca2+ binding proteins that initiate Ca2+ signaling cascades. However, we still know little about how stimulus specific Ca2+ signals are generated. The specificity of a Ca2+ signal may be attributed to the sophisticated regulation of the activities of Ca2+ channels and/or transporters in response to a given stimulus. To identify these cellular components and understand their functions, it is crucial to use systems that allow a sensitive and robust recording of Ca2+ signals at both the tissue and cellular levels. Genetically encoded Ca2+ indicators that are targeted to different cellular compartments have provided a platform for live cell confocal imaging of cellular Ca2+ signals. Here we describe instructions for the use of two Ca2+ detection systems: aequorin based FAS (film adhesive seedlings) luminescence Ca2+ imaging and case12 based live cell confocal fluorescence Ca2+ imaging. Luminescence imaging using the FAS system provides a simple, robust and sensitive detection of spatial and temporal Ca2+ signals at the tissue level, while live cell confocal imaging using Case12 provides simultaneous detection of cytosolic and nuclear Ca2+ signals at a high resolution.

Measuring Spatial and Temporal Ca2+ Signals in Arabidopsis Plants

Ca2+ signaling regulates diverse biological processes in plants. Here we present approaches for monitoring abiotic stress induced spatial and temporal Ca2+ signals in Arabidopsis cells and tissues using the genetically encoded Ca2+ indicators Aequorin or Case12.

Developmental and environmental cues induce Ca2+ fluctuations in plant cells. Stimulus-specific spatial-temporal Ca2+ patterns are sensed by cellular Ca2+ ...

Analysis of Autophagy in Penicillium chrysogenum by Using Starvation Pads in Combination With Fluorescence Microscopy

The study of cellular quality control systems has emerged as a highly dynamic and relevant field of contemporary research. It has become clear that cells possess several lines of defense against damage to biologically relevant molecules like nucleic acids, lipids and proteins. In addition to organelle dynamics (fusion/fission/motility/inheritance) and tightly controlled protease activity, the degradation of surplus, damaged or compromised organelles by autophagy (cellular &#8216;self-eating&#8217;) has received much attention from the scientific community. The regulation of autophagy is quite complex and depends on genetic and environmental factors, many of which have so far not been elucidated. Here a novel method is presented that allows the convenient study of autophagy in the filamentous fungus Penicillium chrysogenum. It is based on growth of the fungus on so-called &#8216;starvation pads&#8217; for stimulation of autophagy in a reproducible manner. Samples are directly assayed by microscopy and evaluated for autophagy induction / progress. The protocol presented here is not limited for use with P. chrysogenum and can be easily adapted for use in other filamentous fungi.

Analysis of Autophagy in Penicillium chrysogenum by Using Starvation Pads in Combination With Fluorescence Microscopy

A convenient and powerful method for studying autophagy in Penicillium chrysogenum by using starvation pads (mixtures of agarose and tap water in a microscope slide containing a central cavity) is presented here.

The study of cellular quality control systems has emerged as a highly dynamic and relevant field of contemporary research. It has become clear that cells ...

Scanning Electron Microscopy (SEM) Protocols for Problematic Plant, Oomycete, and Fungal Samples

Common problems in the processing of biological samples for observations with the scanning electron microscope (SEM) include cell collapse, treatment of samples from wet microenvironments and cell destruction. Using young floral tissues, oomycete cysts, and fungi spores (Agaricales) as examples, specific protocols to process delicate samples are described here that overcome some of the main challenges in sample treatment for image capture under the SEM.
Floral meristems fixed with FAA (Formalin-Acetic-Alcohol) and processed with the Critical Point Dryer (CPD) did not display collapsed cellular walls or distorted organs. These results are crucial for the reconstruction of floral development. A similar CPD-based treatment of samples from wet microenvironments, such as the glutaraldehyde-fixed oomycete cysts, is optimal to test the differential growth of diagnostic characteristics (e.g., the cyst spines) on different types of substrates. Destruction of nurse cells attached to fungi spores was avoided after rehydration, dehydration, and the CPD treatment, an important step for further functional studies of these cells.
The protocols detailed here represent low-cost and rapid alternatives for the acquisition of good-quality images to reconstruct growth processes and to study diagnostic characteristics.

Scanning Electron Microscopy SEM Protocols for Problematic Plant, Oomycete, and Fungal Samples

Problems in the processing of biological samples for scanning electron microscopy observation include cell collapse, treatment of samples from wet microenvironments and cell destruction. Low-cost and relatively rapid protocols suited for preparing challenging samples such as floral meristems, oomycete cysts, and fungi (Agaricales) are compiled and detailed here.

Common problems in the processing of biological samples for observations with the scanning electron microscope (SEM) include cell collapse, treatment of ...

Light Sheet Fluorescence Microscopy of Plant Roots Growing on the Surface of a Gel

One of the key questions in understanding plant development is how single cells behave in a larger context of the tissue. Therefore, it requires the observation of the whole organ with a high spatial- as well as temporal resolution over prolonged periods of time, which may cause photo-toxic effects. This protocol shows a plant sample preparation method for light-sheet microscopy, which is characterized by mounting the plant vertically on the surface of a gel. The plant is mounted in such a way that the roots are submerged in a liquid medium while the leaves remain in the air. In order to ensure photosynthetic activity of the plant, a custom-made lighting system illuminates the leaves. To keep the roots in darkness the water surface is covered with sheets of black plastic foil. This method allows long-term imaging of plant organ development in standardized conditions.

This protocol shows a plant sample preparation method for light-sheet microscopy. The setup is characterized by mounting the plant vertically on the surface of a gel and letting it grow in controlled bright conditions. This allows long-term observation of plant organ development in standardized conditions.

One of the key questions in understanding plant development is how single cells behave in a larger context of the tissue. Therefore, it requires the ...

Characterization of Calcification Events Using Live Optical and Electron Microscopy Techniques in a Marine Tubeworm

Characterizing the first event of biological production of calcium carbonate requires a combination of microscopy approaches. First, intracellular pH distribution and calcium ions can be observed using live microscopy over time. This allows identification of the life stage and the tissue with the feature of interest for further electron microscopy studies. Life stage and tissues of interest are typically higher in pH and Ca signals. 
Here, using H. elegans, we present a protocol to characterize the presence of calcium carbonate structures in a biological specimen on the scanning electron microscope (SEM), using energy-dispersive X-ray spectroscopy (EDS) to visualize elemental composition, using electron backscatter diffraction (EBSD) to determine the presence of crystalline structures, and using transmission electron microscopy (TEM) to analyze the composition and structure of the material. In this protocol, a focused ion beam (FIB) is used to isolate samples with dimension suitable for TEM analysis. As FIB is a site specific technique, we demonstrate how information from the previous techniques can be used to identify the region of interest, where Ca signals are highest.

We demonstrate the use of various microscopy methods that are useful in observing the calcification of a tubeworm, Hydroides elegans, as well as locating and characterizing the first calcified material. Live microscopy and electron microscopy are used together to provide functional and material information that are important in studying biomineralization.

Characterizing the first event of biological production of calcium carbonate requires a combination of microscopy approaches. First, intracellular pH ...

Simple and Effective Administration and Visualization of Microparticles in the Circulatory System of Small Fishes Using Kidney Injection

The systemic administration of micro-size particles into a living organism can be applied for vasculature visualization, drug and vaccine delivery, implantation of transgenic cells and tiny optical sensors. However, intravenous microinjections into small animals, which are mostly used in biological and veterinary laboratories, are very difficult and require trained personnel. Herein, we demonstrate a robust and efficient method for the introduction of microparticles into the circulatory system of adult zebrafish (Danio rerio) by injection into the fish kidney. To visualize the introduced microparticles in the vasculature, we propose a simple intravital imaging technique in fish gills. In vivo monitoring of the zebrafish blood pH was accomplished using an injected microencapsulated fluorescent probe, SNARF-1, to demonstrate one of the possible applications of the described technique. This article provides a detailed description of the encapsulation of pH-sensitive dye and demonstrates the principles of the quick injection and visualization of the obtained microcapsules for in vivo recording of the fluorescent signal. The proposed method of injection is characterized by a low mortality rate (0-20%) and high efficiency (70-90% success), and it is easy to institute using commonly available equipment. All described procedures can be performed on other small fish species, such as guppies and medaka.

This article demonstrates the principles of a quick, minimally invasive injection of fluorescent microparticles into the circulatory system of small fishes and the in vivo visualization of the microparticles in fish blood.

The systemic administration of micro-size particles into a living organism can be applied for vasculature visualization, drug and vaccine delivery, ...

Mycorrhizal Maps as a Tool to Explore Colonization Patterns and Fungal Strategies in the Roots of Festuca rubra and Zea mays

Arbuscular mycorrhizal fungi are symbionts in the roots of plants. Their role is to sustain host development and maintain the nutritional equilibrium in the ecosystems. The colonization process is dependent on several factors like soil ecology, the genetic diversity of the fungi and host, and agronomic practices. Their synchronized action leads to the development of a complex hyphal network and leads to the secondary development of vesicles and arbuscules in the root cells. The aim of this research was to analyze the efficiency of the mycorrhizal patterns (MycoPatt) method for the positioning of fungal structures in the roots of Festuca rubra and Zea mays. Another objective was to explore the fungal colonization strategy as revealed by mycorrhizal maps of each species. The acquisition and assemblage of multiple microscopic images allow mycorrhizal colonization assessment in both corn and red fescue plants to provide information on the realistic position of the developed structures. The observed mycorrhizal patterns highlight the variable efficiency of each plant in terms of developing connections with soil symbiotic fungi, caused by applied treatments and growth stage. Mycorrhizal detailed maps obtained through the MycoPatt method are useful for the early detection of plant efficiency in symbiotic acquisition from the soil.

Mycorrhizal Maps as a Tool to Explore Colonization Patterns and Fungal Strategies in the Roots of Festuca rubra and Zea mays

The protocol here describes the methods for the assessment of the arbuscular mycorrhizal colonization patterns and strategy in roots for two species: Zea mays and Festuca rubra. The use of the MycoPatt method permits the calculation of parameters, the conversion of mycorrhizal structures into digital data, and the mapping of their real position in roots.

Arbuscular mycorrhizal fungi are symbionts in the roots of plants. Their role is to sustain host development and maintain the nutritional equilibrium in ...