This work was supported by the University of California, Riverside and USDA National Institute of Food and Agriculture, Hatch project 1009710 to J.P.G. This material is based upon work supported by the National Science Foundation under Grant No. 1817363 to J.P.G.

1. Growing A. thaliana Plants
<ol>
	<li>Sow A. thaliana seeds in 5 cm x 5 cm disposable pots filled with standard soil mix. Put 32 of these pots into a plastic tray filled with water (~ 0.5 cm depth) and transfer the plastic tray with the plants into a plant growth chamber.
	<ol>
		<li>Set the growth chamber settings as follows: 200 &#181;mol/ms photosynthetic active radiation (PAR), 24 &#177; 1 &#176;C day and 21 &#177; 1 &#176;C night, 60% humidity, and 14/10 h day/night light regime, respectively.<...

<ol>
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The authors have nothing to disclose.

In this protocol, we describe PNC synthesis, characterization, fluorescent dye labeling, and confocal imaging of the nanoparticles within plant mesophyll cells to exhibit their in vivo ROS scavenging activity. PNC are synthesized from a mixture of cerium nitrate and PAA solution in ammonium hydroxide. PNC are characterized by absorption spectrophotomery and the concentration determined using Beer-Lamberts law. Zeta potential measurements confirmed the negatively charged surface of PNC for enhancing delivery to c...

Cerium oxide nanoparticles (nanoceria) are widely used in living organisms, from basic research to bioengineering, due to their distinct catalytic reactive oxygen species (ROS) scavenging ability1,2,3. Nanoceria have ROS scavenging abilities due to a large number of surface oxygen vacancies that alternate between two oxidation states (Ce3+ and Ce4+) 4,5,6. The Ce3+ dangling bonds effectively scavenge ROS while the lattice strains at the nanoscale promote the regeneration of these defect sites via redox cycling reactions7. Nanoceria have also been recently used for studying and engineering plant function8,9. Plants under abiotic stress experience accumulation of ROS, causing oxidative damage to lipids, proteins, and DNA10. In A. thaliana plants,&#160;nanoceria catalytic scavenging of ROS in vivo leads to improved plant photosynthesis under high light, heat, and chilling stresses8. Applying nanoceria to soil also increases shoot biomass and grain yield of wheat (Triticum aestivum)11; canola (Brassica napus) plants treated with nanoceria have higher plant biomass under salt stress12.
Nanoceria offer&#160;bioengineers and plant biologists a nanotechnology-based tool to understand abiotic stress responses and enhance plant abiotic stress tolerance. Nanoceria&#39;s&#160;in vivo ROS&#160;scavenging capabilities are independent of plant species, and the facile delivery into plant tissues has the potential to enable broad application outside of model organisms. Unlike other genetically-based methods, nanoceria do&#160;not require generating plant lines with the overexpression of antioxidant enzymes for higher ROS scavenging ability13. Leaf lamina infiltration of nanoceria to plants is a&#160;practical approach&#160;for lab-based research.
The overall goal of this protocol is to describe 1) the synthesis and characterization of negatively charged poly (acrylic) acid nanoceria (PNC), 2) the delivery and tracking of PNC throughout leaf cells, and 3) the monitoring of PNC-enabled ROS scavenging in vivo. In this protocol, negatively charged poly (acrylic) acid&#160;nanoceria (PNC) are synthesized and characterized by their absorption spectrum, hydrodynamic diameter, and zeta potential. We describe a simple leaf lamina infiltration method to deliver PNC into plant leaf tissues. For in vivo imaging of nanoparticle distribution within mesophyll cells, a fluorescent dye (DiI) was used to label PNC (DiI-PNC) and observe the nanoparticles via confocal fluorescence microscopy. Finally, we explain how to monitor in vivo PNC ROS scavenging through confocal microscopy.

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			<td height="21" style="height:21px;width:567px;">Cerium (III) nitrate hexahydrate</td>
			<td style="width:228px;">Sigma-Aldrich</td>
			<td style="width:165px;">238538-100G</td>
			<td style="width:265px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Molecular Biology Grade Water, Corning</td>
			<td style="width:228px;">VWR</td>
			<td style="width:165px;">45001-044&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Falcon 50 mL Conical Centrifuge Tubes</td>
			<td style="width:228px;">VWR</td>
			<td style="width:165px;">14-959-49A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Poly (acrylic acid) 1,800 Mw</td>
			<td style="width:228px;">Sigma-Aldrich</td>
			<td style="width:165px;">323667-100G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Fisherbrand Digital Vortex Mixer</td>
			<td style="width:228px;">Fisher Scientific</td>
			<td style="width:165px;">02-215-370</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Fisherbrand Digital Vortex Mixer Accessory, Insert Retainer</td>
			<td style="width:228px;">Fisher Scientific</td>
			<td style="width:165px;">02-215-391</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Fisherbrand Digital Vortex Mixer Accessories: Foam Insert Set</td>
			<td style="width:228px;">Fisher Scientific</td>
			<td style="width:165px;">02-215-395</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Ammonium hydroxide solution</td>
			<td style="width:228px;">Sigma-Aldrich</td>
			<td style="width:165px;">05002-1L</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">PYREX Griffin Beakers, Graduated, Corning</td>
			<td style="width:228px;">VWR</td>
			<td style="width:165px;">13912-149&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">RCT basic</td>
			<td style="width:228px;">IKA</td>
			<td style="width:165px;">3810001</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Eppendorf Microcentrifuge 5424</td>
			<td style="width:228px;">VWR</td>
			<td style="width:165px;">80094-126</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Amicon Ultra-15 Centrifugal Filter Units</td>
			<td style="width:228px;">Millipore-Sigma</td>
			<td style="width:165px;">UFC901024</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Allegra X-30 Series Benchtop Centrifuge</td>
			<td style="width:228px;">Beckman Coulter</td>
			<td style="width:165px;">B06314</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">UV-2600 Sptecrophotometer</td>
			<td style="width:228px;">Shimadzu</td>
			<td style="width:165px;">UV-2600 120V</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Whatman Anotop 10 syringe filter</td>
			<td style="width:228px;">Sigma-Aldrich</td>
			<td style="width:165px;">WHA68091102</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">BD Disposable Syringes with Luer-Lok Tips</td>
			<td style="width:228px;">Fisher Scientific</td>
			<td style="width:165px;">14-829-45</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Zetasizer Nano S</td>
			<td style="width:228px;">Malvern Panalytical</td>
			<td style="width:165px;">Zen 1600</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">1,1&#8242;-Dioctadecyl-3,3,3&#8242;,3&#8242;-tetramethylindocarbocyanine perchlorate</td>
			<td style="width:228px;">Sigma-Aldrich</td>
			<td style="width:165px;">42364-100MG</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Dimethyl Sulfoxide, ACS</td>
			<td style="width:228px;">VWR</td>
			<td style="width:165px;">BDH1115-1LP</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Sunshine Mix #1 LC1</td>
			<td style="width:228px;">Green Island Distributors, Inc</td>
			<td style="width:165px;">5212601.CFL080P</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Adaptis 1000</td>
			<td style="width:228px;">Conviron</td>
			<td style="width:165px;">A1000</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:567px;">TES, &#62;99% (titration</td>
			<td style="width:228px;">Sigma-Aldrich</td>
			<td style="width:165px;">T1375-100G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Magnesium chloride</td>
			<td style="width:228px;">Sigma-Aldrich</td>
			<td style="width:165px;">M8266-1KG</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Air-Tite All-Plastic Norm-Ject Syringe</td>
			<td style="width:228px;">Fisher Scientific</td>
			<td style="width:165px;">14-817-25</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Kimberly-Clark Professional Kimtech Science Kimwipes Delicate Task Wipers</td>
			<td style="width:228px;">Fisher Scientific</td>
			<td style="width:165px;">06-666A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Carolina Observation Gel</td>
			<td style="width:228px;">Carolina</td>
			<td style="width:165px;">132700</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Corning microscope slides, frosted one side, one end</td>
			<td style="width:228px;">Sigma-Aldrich</td>
			<td style="width:165px;">CLS294875X25-72EA</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Cork Borer Sets with Handles</td>
			<td style="width:228px;">Fisher Scientific</td>
			<td style="width:165px;">S50166A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Perfluorodecalin</td>
			<td style="width:228px;">Sigma-Aldrich</td>
			<td style="width:165px;">P9900-25G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Micro Cover Glasses, Square, No. 1</td>
			<td style="width:228px;">VWR</td>
			<td style="width:165px;">48366-045</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Leica Laser Scanning Confocal Microscope TCS SP5</td>
			<td style="width:228px;">Leica Microsystems</td>
			<td style="width:165px;">TCS SP5</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">2&#8242;,7&#8242;-Dichlorofluorescin diacetate</td>
			<td style="width:228px;">Sigma-Aldrich</td>
			<td style="width:165px;">D6883-250MG</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Dihydroethidium</td>
			<td style="width:228px;">Sigma-Aldrich</td>
			<td style="width:165px;">D7008-10MG</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Fisherbrand Premium Microcentrifuge Tubes: 1.5 mL</td>
			<td style="width:228px;">Fisher Scientific</td>
			<td style="width:165px;">05-408-129</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Eppendorf Uvette cuvettes</td>
			<td style="width:228px;">Sigma-Aldrich</td>
			<td style="width:165px;">Z605050-80EA</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:567px;">Chlorophyll meter&#160;</td>
			<td style="width:228px;">Konica Minolta</td>
			<td style="width:165px;">SPAD-502</td>
			<td></td>
		</tr>
	</tbody>
</table>

catalytic scavenging of plant reactive oxygen species in vivo by anionic cerium oxide nanoparticles

Reactive oxygen species (ROS) accumulation is a hallmark of plant abiotic stress response. ROS play&#160;a dual role in plants by acting as signaling molecules at low levels and damaging molecules at high levels. Accumulation of ROS in stressed plants can damage metabolites, enzymes, lipids, and DNA, causing a reduction of plant growth and yield. The ability of cerium oxide nanoparticles (nanoceria) to catalytically scavenge ROS in vivo provides a unique tool to understand and bioengineer plant abiotic stress tolerance. Here, we present a protocol to synthesize and characterize poly (acrylic) acid coated nanoceria (PNC), interface the nanoparticles with plants via leaf lamina infiltration, and monitor their distribution and ROS scavenging in vivo using confocal microscopy. Current molecular tools for manipulating ROS accumulation in plants are limited to model species and require laborious transformation methods. This protocol for in vivo ROS scavenging has the potential to be applied to wild type plants with broad leaves and leaf structure like Arabidopsis thaliana.

PNC synthesis and characterization. 
PNC were synthesized, purified and characterized following the method described in Protocol Section 2. Figure 1A shows the coloration of the solutions of cerium nitrate, PAA, the mixture of cerium nitrate and PAA, and PNC. A color change from white to light yellow is seen after PNC is synthesized. After purification with a 10 kDa filter, PNC were characterize...

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Catalytic Scavenging of Plant Reactive Oxygen Species In Vivo by Anionic Cerium Oxide Nanoparticles

Here, we present a protocol for the synthesis and characterization of cerium oxide nanoparticles (nanoceria) for ROS (reactive oxygen species) scavenging in vivo, nanoceria imaging in plant tissues by confocal microscopy, and in vivo monitoring of nanoceria ROS scavenging by confocal microscopy.

Catalytic Scavenging of Plant Reactive Oxygen Species In Vivo by Anionic Cerium Oxide Nanoparticles

Reactive oxygen species (ROS) accumulation is a hallmark of plant abiotic stress response. ROS play&#160;a dual role in plants by acting as signaling ...

The ability of cerium oxide nanoparticles to catalytically scavenge reactive oxygen species in vivo provides a unique tool to understand and engineer mechanisms of plant signaling and tolerance to stress. Reactive oxygen species play a key role in plants by acting as signal molecules at low levels and damaging molecules at high levels. The main advantage of this technique is the potential to be applied to diverse wild type plant species with broad leaves and leaf structure, like Arabidopsis thaliana.After growing the Arabidopsis thaliana plants, weigh out 1.08 grams of Cerium nitrate and dissolve it in 2.5 milliliters of biology-grade water in a 50-milliliter conical tube. Weigh out 4.5 grams of Poly acid and dissolve it in five milliliters of biology-grade water in a different 50-milliliter conical tube. Combine these two solutions and then use a digital vortex mixer to mix them thoroughly at 2, 000 rpm for 15 minutes.In a fume hood, transfer 15 milliliters of a 7.2-molar ammonium hydroxide solution to a 50-milliliter glass beaker. Begin stirring at 500 rpm and at room temperature. Add the Cerium nitrate and Poly acid mixture drop wise.Cover the beaker with a piece of paper to prevent substantial loss of the solution and let it stir for 24 hours. After this, transfer the resulting solution to a 50-milliliter conical tube. Centrifuge at 3, 900 times g for one hour to remove any debris or large agglomerates.Then, transfer the supernatant into three 50-milliliter, 10-kilodalton filters. Fill the remainder of each filter with molecular-grade water, resulting in a total dilution of 45 milliliters. Centrifuge at 3, 900 times g for 15 minutes.Repeat this process at least six times. Using a UV-vis spectrophotometer, measure the absorbance of each eluent from 220 nanometers to 700 nanometers to ensure that no free polymers or other reagents are present in the final PNC solution. Use a five-milliliter syringe to take up the collected PNC solution.Next, filter the solution against a 20-nanometer pore-sized syringe filter and collect the filtered solution in a 50-milliliter conical tube. Transfer a diluted final PNC solution into a plastic cuvette and measure its absorbance from 220 nanometers to 700 nanometers. Using a particle sizer, measure the hydrodynamic diameter of the synthesized PNC, then store the final PNC solution in a refrigerator at four degrees Celsius until ready to use.After labeling the PNC with DiI fluorescent dye, transfer 0.9 milliliters of a solution containing 0.5 millimolar of either the PNC solution or the DiI-PNC solution to a tube. Add 0.1 milliliter of infiltration buffer and mix by vortexing. Prepare a 10-millimolar TES infiltration buffer as a negative control.Next, transfer 0.2 milliliters of the sample and buffer mixture to a one-milliliter sterile needleless syringe. Tap to remove any possible air bubbles. Just before infiltration, retrieve the plant from the growth chamber.Using a chlorophyll meter, measure the chlorophyll content in the A.thaliana leaves. Measure each leaf with three replicates as outlined in the text protocol. Choose leaves with similar chlorophyll content.Gently press the tip of the needleless syringe against the bottom of the leaf lamina and depress the plunger to infiltrate the leaves. Using a delicate task wiper, gently wipe off any excess solution that remains on the surface of the leaf lamina, then label the plant. Keep the infiltrated plants on the bench to incubate for three hours.First, place a pea-sized amount of observation gel onto a glass slide, roll the gel and spread it out until it is approximately two centimeters in diameter and one millimeter thick. Using a cork borer with a diameter of 0.3 centimeters, cut out a circular section in the center of the gel to create a well. Fill the well completely with PFD, which will provide a deeper and better confocal imaging resolution.Then, use a cork borer with a diameter of 0.2 centimeters to collect leaf disks from the previously-infiltrated A.thaliana plants. Mount each leaf disk in a PFD-filled well with the infiltrated side facing up. After this, place a square cover slip on top of the leaf disk.Press gently and evenly on the cover slip to seal with the well of observation gel and ensure that no air bubbles remain trapped. To begin, prepare 25 micromolar of H2DCFDA dye and 10 micromolar of DHE dye in TES infiltration buffer in separate 1.5-milliliter microcentrifuge tubes. Using a cork borer with a diameter of 0.2 centimeters, collect leaf disks from the adapted PNC-infiltrated A.thaliana plants.Use the sharp tip of forceps to make three to four holes on each leaf disk to accelerate the dye-loading process. Next, load an equal amount of leaf disks into each dye tube. Incubate in darkness for 30 minutes.After this, rinse the leaf disks with double-distilled water three times. Use observation gel to mount each leaf to a glass slide as previously described. Load the slide on a confocal microscope and manually focus to a region of leaf mesophyl cells as outlined in the text protocol, then expose the leaf disks to a UVA laser at 405 nanometers for three minutes to generate ROS.Record the ROS signal intensity change in time series per leaf disk. Image the leaf disk using a 40X water objective and the confocal microscope settings shown here. Use a plant infiltrated with only infiltration buffer solution as the negative control.After purification, the synthesized PNC is characterized using a UV-vis spectrophotometer and is seen to have a peak of absorbance at 271 nanometers. The purification process is confirmed by measuring the final eluent. PNC samples are then labeled with a fluorescent DiI dye to determine the distribution of the nanoparticles in vivo.Three peaks are observed for the DiI-labeled PNC, while a measurement of the final eluent confirms that the non-reacted chemicals are washed out during purification. The distribution of DiI-PNC in leaf mesophyl cells is determined via confocal imaging. While no DiI dye signals are detected in the control samples the DiI-PNC is observed co-localized with chloroplasts in the infiltrated leaves.In vivo ROS scavenging enabled by PNC is monitored in the leaf disk by measuring the fluorescence intensity changes in the DHE and DCF dyes. After three minutes of UV stress, the PNC-infiltrated leaves show significantly less intensity for both dye types when compared to the no-nanoparticle buffer control. A CAT mimetic activity assay reveals a decrease in the resorufin level in the mixture containing PNC.This level is indicative of the hydrogen peroxide level, which therefore is also decreasing, and confirms the CAT mimetic activity of the synthesized PNC. This protocol for synthesizing nanoceria is a simple, stepwise procedure that generates cerium oxide nanoparticles with controlled size, charge, and ROS scavenging abilities. Plant genetic modification methods for ROS manipulation in vivo are currently limited to plant model species.In contrast, nanoceria ROS scavenging has the potential to be applied to diverse wild type plant species both in the laboratory and in the field.

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Bioengineering

8.8K 조회수.  University of California. The ability of cerium oxide nanoparticles to catalytically scavenge reactive oxygen species in vivo provides a unique tool to understand and engineer mechanisms of plant signaling and tolerance to stress. Reactive oxygen species play a key role in plants by acting as signal molecules at low levels and damaging molecules at high levels. The main advantage of this technique is the potential to be applied to diverse wild type plant species with broad leaves and leaf structure, like Arabidopsis t...