The authors would like to thank California Department of Food and Agriculture for funding of the project which led to the development of this protocol. CDFA SCB11019.

1. Planting
<ol>
	<li>Fill plug trays (128 cell; 28 x 54 cm with cells 3 cm square and 5 cm deep) with plug soil mix. To aid in uniform filling of cells compress soil in each tray using an empty plug tray.</li>
	<li>Plant lettuce seed &#188; inch in depth 2-3 seeds per cell. Plant all experimental lines in replicated trays to provide both a drought stressed and control trays for the drought trial.</li>
	<li>Place plug trays into a base tray without holes.</li>
	<li>Water trays and cover with inverted tray or plastic dome. Germination normally occurs in 48-72 hr. After germination remove the cover and move trays into greenhouse. 
	NOTE: This protocol could also be performed in growth chambers.</li>
</ol>
2. Growth and Plant Care
<ol>
	<li>Water trays as needed from 1-4 weeks after germination, normally this is 2-3 times weekly, by filling lower tray and allowing soil to become saturated (~1 hr)&#160;rays to sit for extended periods in water as this may negatively impact plant health and root development and may affect the drought screen.</li>
	<li>Fertilize trays once weekly with a commercial soluble 20-20-20 fertilizer mixed at a rate of 1.5 tsp/gal.</li>
	<li>Thin trays to one plant per cell 1-2 weeks post germination.</li>
</ol>
3. Initiating Drought Stress
<ol>
	<li>When the plants are four weeks old separate trays into 2 groups. Subject one group to severe water stress. Use the other trays as well watered controls. Water the control group as in step 2.1 throughout the experiment. At the initiation of the drought stress suspend fertilizing all trays for the remainder of the experiment.</li>
	<li>The experimental drought period occurs over one week. On the initial day of the drought stress trial (Day 0) fill all lower trays with water and allow the soil in the plug trays to become fully saturated then drain water from trays. Saturating the soil immediately before the initiation of the stress period will help to minimize any variation in soil moisture between individual cells in the plug trays.</li>
</ol>
4. Conducting the Basic Drought Stress Screen with Parameters to be Measured
NOTE: The following steps outline how to collect the three physiological measurements that will be recorded over the course of the drought screen while Table 1 provides a schedule of the measurements taken on each day of the drought-stress trial period.
<ol>
	<li>Measure the Leaf Relative Water Content (RWC) on Days 0, 2, 4 of the trial.
	<ol>
		<li>Clip a lettuce plant from the tray and remove 2 leaves.</li>
		<li>Punch 3 discs from each leaf using a #9 cork borer (~ 1.6 cm diameter). Combine leaf punches as one sample.</li>
		<li>Weigh the leaf discs, this is the fresh weight (FW) value used for the RWC calculation, then place the discs in a petri plate.</li>
		<li>Add just enough Distilled water to the plate to allow all leaf discs to float. This is to fully hydrate the leaf discs to gather turgid weights for RWC analysis. Allow the leaf discs to float for 24 hr at RT.</li>
		<li>Remove the now fully hydrated leaf discs from the plates and gently dry the exterior of the leaf discs with paper towels before weighing the discs. Record these weights as turgid weight (TW) for the RWC calculation.</li>
		<li>Place leaf discs on a paper lab wipe or filter paper disc in an open petri dish and dry in incubator at 55 &#176;C for 24 hr. 
		NOTE: The paper prevents the leaf discs from adhering to the petri dish during drying.</li>
		<li>Weigh dry leaf discs and record as dry weights (DW) for RWC calculation.</li>
		<li>Calculate RWC using Weatherley&#8217;s formula as described by Smart and Bingham11,12. 
		&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; RWC=(FW-DW/TW-DW)*100 
		&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; FW=fresh weight, TW=turgid weight, DW=dry weight</li>
		<li>Repeat step 4.1 for each germplasm and treatment in the trial.</li>
	</ol>
	</li>
	<li>Record the plant wilt once daily beginning on day 1 of the drought stress trial and ending when 100% of plants are wilted, normally day 4 or 5.</li>
	<li>Recovery phase and growth differential
	<ol>
		<li>On day 6, conclude the drought-stress period and the stressed plants enter the recovery phase of the trial. Fill the lower trays with water and allow the drought-stressed trays to soak for 24 hr before resuming the standard watering schedule, step 2.1, as the control trays.</li>
		<li>Allow all plants to recover for 10 days.</li>
		<li>At 10 days post drought-stress harvest the entire above ground portion of each plant and record the fresh weight.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Dijk, A. I. J. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Millennium+Drought+in+southeast+Australia+(2001&#8211;2009):+Natural+and+human+causes+and+implications+for+water+resources,+ecosystems,+economy,+and+society.">The Millennium Drought in southeast Australia (2001&#8211;2009): Natural and human causes and implications for water resources, ecosystems, economy, and society.</a> Water Resour. Res. 49, (2013).</li><li>Aghakouchak, A., Feldman, D., Stewardson, M. J., Saphores, J., Grant, S., Sanders, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Australia&#8217;s+Drought:+Lessons+for+California.">Australia&#8217;s Drought: Lessons for California.</a> Science. 343, 1430 (2014).</li><li>Tolomeo, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=California+Agricultural+Statistics+2012+Crop+Year.">California Agricultural Statistics 2012 Crop Year.</a> USDA National Agricultural Statistics Service Pacific Regional Office-California. , (2013).</li><li>Cavagnaro, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Climate+Change:+Challenges+and+Solutions+for+California+Agricultural+Landscapes.+White+paper+CEC-500-2005-189-SF.">Climate Change: Challenges and Solutions for California Agricultural Landscapes. White paper CEC-500-2005-189-SF.</a> California Climate Change Center. , (2005).</li><li>Lobell, D. B., Gourdji, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Influence+of+Climate+Change+on+Global+Crop+Productivity.">The Influence of Climate Change on Global Crop Productivity.</a> Plant Physiol. 160, 1686-1697 (2012).</li><li>Jackson, L. E., Stivers, L. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Root+distribution+of+lettuce+under+commercial+production:+implications+for+crop+uptake+of+nitrogen.">Root distribution of lettuce under commercial production: implications for crop uptake of nitrogen.</a> Biological Agriculture and Horticulture. 9, 273-293 (1993).</li><li>Jackson, L. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Root+architecture+in+cultivated+and+wild+lettuce+(Lactuca+spp).">Root architecture in cultivated and wild lettuce (Lactuca spp).</a> Plant. Cell and Environment. 18, 885-897 (1995).</li><li>Malcom, S., Marshall, E., Aillery, M., Heisey, P., Livingston, M., Day-Rubenstein, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Agricultural+Adaptation+to+a+Changing+Climate:+Economic+and+Environmental+Implications+Vary+by+U.S+Region.+USDA+Economic+Research+Service.">Agricultural Adaptation to a Changing Climate: Economic and Environmental Implications Vary by U.S Region. USDA Economic Research Service.</a> Economic Research Report Number. 136, (2012).</li><li>Chaves, M. M., Maroco, J. P., Pereira, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Understanding+plant+responses+to+drought-+from+genes+to+the+whole+plant.">Understanding plant responses to drought- from genes to the whole plant.</a> Funct. Plant Biol. 30, 239-264 (2003).</li><li>Ingram, J., Bartels, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Molecular+Basis+of+Dehydration+Tolerance+in+Plants.">The Molecular Basis of Dehydration Tolerance in Plants.</a> Annu. Rev. Plant Physiol. Plant Mol. Biol. 47, 377-403 (1996).</li><li>Weatherley, P. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Studies+in+the+water+relations+of+the+cotton+plant.+I.+The+field+measurement+of+water+deficits+in+leaves.">Studies in the water relations of the cotton plant. I. The field measurement of water deficits in leaves.</a> New Phlytol. 49, 81-97 (1950).</li><li>Smart, R. E., Bingham, G. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+Estimates+of+Relative+Water+Content.">Rapid Estimates of Relative Water Content.</a> Plant Physiol. 53, 258-260 (1974).</li></ol>

The authors declare that they have no competing financial interests.

Considerations of sample number for screen.
The number of samples needed should be based on the desired use of the data from this screen. If publication quality results are desired it is recommended to harvest 3 individual plants (3 biological replicates) from each line and perform a minimum of 2 experimental replicates to give adequate points for quality statistical analysis. If the desired outcome is simply to quickly narrow a large pool of candidate germplasm in order to pe...

Water availability for irrigation has been a concern across much of the United States and globally for decades, but research into the response to drought-stress, along with other abiotic stresses, has lagged behind work in the areas of disease and insect resistance, at the industrial, academic, and governmental levels largely due to a lack of funding. Water availability for agriculture has historically been only an afterthought at the level of policy makers. Recently, due to several severe droughts in important agricultural production regions in both the United States and Australia1,2 fresh water availability has been thrust into the spotlight at both the national and international levels leading to many more resources being directed towards research into developing drought-tolerant cultivars of the major grain crops. While this shifting focus toward the development of drought-tolerant major crops is beneficial, like many areas of plant research specialty crops have largely been left behind. 
A severe drought is currently limiting vegetable production in California, the largest production region for Lettuce (Lactuca sativa L.) in the United States3. These short-term weather patterns coupled with legislative and judicial action along with long-term climate change4,5 have combined to reduce water available for agriculture in many of the most productive regions of California. Lettuce production in California represents a 1.5 billion dollar industry accounting for nearly 80% of lettuce production in the United States3. Leafy vegetables have high leaf water content and lettuce, in particular, has a shallow root system6,7 which leaves the crop vulnerable to water-stress. In lettuce, as in all crops the development of drought-tolerant varieties will become increasingly important as fresh water supplies for irrigation become more constrained8.
This protocol lays out a method by which an initial screen was performed on a large collection of lettuce germplasm in order to identify a pool of potentially drought-tolerant candidate lines for use in physiological, molecular, and genetic studies to identify specific drought-tolerance traits. These candidates can also be used directly as sources of drought-tolerance in breeding programs to improve water use efficiency in commercial cultivars. This protocol was developed specifically to address the challenges that arise during the course of any screen of an extensive germplasm collection, especially issues of space availability and labor. Also, the protocol as presented was developed for use in lettuce, but has been successfully adapted for use in the screening of a germplasm collection of spinach (Spinacia oleracea) for potential drought-tolerance and could be modified simply to screen any leafy vegetable crop. 
An important consideration before initiating a drought-tolerance screen is to understand what this method is and is not. This protocol is meant to represent a rapid method by which a large germplasm pool can be quickly and efficiently narrowed to a manageable number of candidate germplasm for use in more focused and thorough studies to identify individual tolerance traits. This protocol subjects the plants to a rapidly induced severe water-stress in contrast to a more natural slowly-induced moderate continuous drought-stress that would be observed under field conditions. The type of response induced within the plant during these two types of water-stress events (rapid dehydration versus natural drought) is not identical9 which could lead to the exclusion of some materials from future trials. These two stress events are not without overlap though10 and this protocol should serve as an effective way to identify potentially drought-tolerant germplasm contained within a large collection. This protocol alone should not be considered sufficient to identify with a high degree of certainty germplasm that contains durable drought-tolerance under field water-stress conditions, but it represents a significant step forward in the rapid screening of leafy green vegetables for potential drought-tolerance traits.

<table><tbody><tr><td>plug tray 128</td><td>T.O. Plastics&lt;br/&gt; Hummert International</td><td>11-8595-1</td><td>Any brand plug tray will work, but use the same style of trays for all trials.</td></tr><tr><td>lower tray (Display tray)</td><td>T.O. Plastics&lt;br/&gt; Hummert International</td><td>11-3305-1</td><td></td></tr><tr><td>plug/planting mix (Sunshine Mix #5)</td><td>Sunshine&lt;br/&gt; Hummert International</td><td>10-0467-1</td><td>A different mix may need to be substituted if adapting this protocol to a different crop.&amp;nbsp; Sunshine mix #4 was used in spinach trials.</td></tr><tr><td>fertilizer (20-20-20)</td><td>Jack&#039;s: Professional water-soluble fertilizer&lt;br/&gt; Hummert International</td><td>07-5915-1</td><td>Any fertilizer can be used, adjust type as needed for adapting this protocol to specific crop needs.</td></tr></tbody></table>

semi-high throughput screening for potential drought-tolerance in lettuce (lactuca sativa) germplasm collections

This protocol describes a method by which a large collection of the leafy green vegetable lettuce (Lactuca sativa L.) germplasm was screened for likely drought-tolerance traits. Fresh water availability for agricultural use is a growing concern across the United States as well as many regions of the world. Short-term drought events along with regulatory intervention in the regulation of water availability coupled with the looming threat of long-term climate shifts that may lead to reduced precipitation in many important agricultural regions has increased the need to hasten the development of crops adapted for improved water use efficiency in order to maintain or expand production in the coming years. This protocol is not meant as a step-by-step guide to identifying at either the physiological or molecular level drought-tolerance traits in lettuce, but rather is a method developed and refined through the screening of thousands of different lettuce varieties. The nature of this screen is based in part on the streamlined measurements focusing on only three water-stress indicators: leaf relative water content, wilt, and differential plant growth following drought-stress. The purpose of rapidly screening a large germplasm collection is to narrow the candidate pool to a point in which more intensive physiological, molecular, and genetic methods can be applied to identify specific drought-tolerant traits in either the lab or field. Candidates can also be directly incorporated into breeding programs as a source of drought-tolerance traits.

When performing a large screen in order to segregate a population by the desired experimental trait, in the case of this protocol drought-stress response, the data generated will correspondingly be varied from very stress susceptible to likely drought-tolerant and all points in between. Figure 1 contains graphs representing the type of results that can be expected from this protocol. Representative cultivars of three different lettuce types (romaine (cos), crisphead, and butterhead) are included in the d...

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Semi-High Throughput Screening for Potential Drought-tolerance in Lettuce Lactuca sativa Germplasm Collections

This protocol was developed to screen a large germplasm collection of the leafy vegetable lettuce (Lactuca sativa L.) for drought-tolerance, in order to identify a small candidate pool of lettuce for use in physiological, molecular, and genetic studies to identify underlying drought-tolerance traits along with breeding programs.

Semi-High Throughput Screening for Potential Drought-tolerance in Lettuce (Lactuca sativa) Germplasm Collections

This protocol describes a method by which a large collection of the leafy green vegetable lettuce (Lactuca sativa L.) germplasm was screened for likely ...

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9.0K Views.  United States Department of Agriculture. This protocol was developed to screen a large germplasm collection of the leafy vegetable lettuce (Lactuca sativa L.) for drought-tolerance, in order to identify a small candidate pool of lettuce for use in physiological, molecular, and genetic studies to identify underlying drought-tolerance traits along with breeding programs.

Video: Semi-High Throughput Screening for Potential Drought-tolerance in Lettuce Lactuca sativa Germplasm Collections

High and Low Throughput Screens with Root-knot Nematodes Meloidogyne spp.

Root-knot nematodes (genus Meloidogyne) are obligate plant parasites. They are extremely polyphagous and considered one of the most economically important plant parasitic nematodes. The microscopic second-stage juvenile (J2), molted once in the egg, is the infective stage. The J2s hatch from the eggs, move freely in the soil within a film of water, and locate root tips of suitable plant species. After penetrating the plant root, they migrate towards the vascular cylinder where they establish a feeding site and initiate feeding using their stylets. The multicellular feeding site is comprised of several enlarged multinuclear cells called 'giant cells' which are formed from cells that underwent karyokinesis (repeated mitosis) without cytokinesis. Neighboring pericycle cells divide and enlarge in size giving rise to a typical gall or root knot, the characteristic symptom of root-knot nematode infection. Once feeding is initiated, J2s become sedentary and undergo three additional molts to become adults. The adult female lays 150-250 eggs in a gelatinous matrix on or below the surface of the root. From the eggs new infective J2s hatch and start a new cycle. The root-knot nematode life cycle is completed in 4-6 weeks at 26-28&deg;C.
Here we present the traditional protocol to infect plants, grown in pots, with root-knot nematodes and two methods for high-throughput assays. The first high-throughput method is used for plants with small seeds such as tomato while the second is for plants with large seeds such as cowpea and common bean. Large seeds support extended seedling growth with minimal nutrient supplement. The first high throughput assay utilizes seedlings grown in sand in trays while in the second assay plants are grown in pouches in the absence of soil. The seedling growth pouch is made of a 15.5 x 12.5cm paper wick, folded at the top to form a 2-cm-deep trough in which the seed or seedling is placed. The paper wick is contained inside a transparent plastic pouch. These growth pouches allow direct observation of nematode infection symptoms, galling of roots and egg mass production, under the surface of a transparent pouch. Both methods allow the use of the screened plants, after phenotyping, for crossing or seed production. An additional advantage of the use of growth pouches is the small space requirement because pouches are stored in plastic hanging folders arranged in racks.

High and Low Throughput Screens with Root-knot Nematodes Meloidogyne spp.

Two distinct methods to screen plants with root-knot nematodes are described. The described approaches include high-throughput screens with nematodes in a nondestructive manner facilitating the use of these plants in breeding programs.

Root-knot nematodes (genus Meloidogyne) are obligate plant parasites. They are extremely polyphagous and considered one of the most economically important ...

Immunology and Infection

A Flexible Low Cost Hydroponic System for Assessing Plant Responses to Small Molecules in Sterile Conditions

A wide range of studies in plant biology are performed using hydroponic cultures. In this work, an in vitro hydroponic growth system designed for assessing plant responses to chemicals and other substances of interest is presented. This system is highly efficient in obtaining homogeneous and healthy seedlings of the C3 and C4 model species Arabidopsis thaliana and Setaria viridis, respectively. The sterile cultivation avoids algae and microorganism contamination, which are known limiting factors for plant normal growth and development in hydroponics. In addition, this system is scalable, enabling the harvest of plant material on a large scale with minor mechanical damage, as well as the harvest of individual parts of a plant if desired. A detailed protocol demonstrating that this system has an easy and low-cost assembly, as it uses pipette racks as the main platform for growing plants, is provided. The feasibility of this system was validated using Arabidopsis seedlings to assess the effect of the drug AZD-8055, a chemical inhibitor of the target of rapamycin (TOR) kinase. TOR inhibition was efficiently detected as early as 30 min after an AZD-8055 treatment in roots and shoots. Furthermore, AZD-8055-treated plants displayed the expected starch-excess phenotype. We proposed this hydroponic system as an ideal method for plant researchers aiming to monitor the action of plant inducers or inhibitors, as well as to assess metabolic fluxes using isotope-labeling compounds which, in general, requires the use of expensive reagents.

A simple, versatile, and low-cost in vitro hydroponic system was successfully optimized, enabling large-scale experiments under sterile conditions. This system facilitates the application of chemicals in a solution and their efficient absorption by roots for molecular, biochemical, and physiological studies.

A wide range of studies in plant biology are performed using hydroponic cultures. In this work, an in vitro hydroponic growth system designed for ...

Optimizing the Use of a Liquid Handling Robot to Conduct a High Throughput Forward Chemical Genetics Screen of Arabidopsis thaliana

Chemical genetics is increasingly being employed to decode traits in plants that may be recalcitrant to traditional genetics due to gene redundancy or lethality. However, the probability of a synthetic small molecule being bioactive is low; therefore, thousands of molecules must be tested in order to find those of interest. Liquid handling robotics systems are designed to handle large numbers of samples, increasing the speed with which a chemical library can be screened in addition to minimizing/standardizing error. To achieve a high-throughput forward chemical genetics screen of a library of 50,000 small molecules on Arabidopsis thaliana (Arabidopsis), protocols using a bench-top multichannel liquid handling robot were developed that require minimal technician involvement. With these protocols, 3,271 small molecules were discovered that caused visible phenotypic alterations. 1,563 compounds induced short roots, 1,148 compounds altered coloration, 383 compounds caused root hair and other, non-categorized, alterations, and 177 compounds inhibited germination.

Optimizing the Use of a Liquid Handling Robot to Conduct a High Throughput Forward Chemical Genetics Screen of Arabidopsis thaliana

A high throughput screen of synthetic small molecules was conducted on the model plant species, Arabidopsis thaliana. This protocol, developed for a liquid handling robot, increases the speed of forward chemical genetics screens, accelerating the discovery of novel small molecules affecting plant physiology.

Chemical genetics is increasingly being employed to decode traits in plants that may be recalcitrant to traditional genetics due to gene redundancy or ...

Bioengineering

High-Throughput Identification of Resistance to Pseudomonas syringae pv. Tomato in Tomato using Seedling Flood Assay

Tomato is an agronomically important crop that can be infected by Pseudomonas syringae, a Gram-negative bacterium, resulting in bacterial speck disease. The tomato-P. syringae pv. tomato pathosystem is widely used to dissect the genetic basis of plant innate responses and disease resistance. While disease was successfully managed for many decades through the introduction of the Pto/Prf gene cluster from Solanum pimpinellifolium into cultivated tomato, race 1 strains of P. syringae have evolved to overcome resistance conferred by the Pto/Prf gene cluster and occur worldwide.
Wild tomato species are important reservoirs of natural diversity in pathogen recognition, because they evolved in diverse environments with different pathogen pressures. In typical screens for disease resistance in wild tomato, adult plants are used, which can limit the number of plants that can be screened due to their extended growth time and greater growth space requirements. We developed a method to screen 10-day-old tomato seedlings for resistance, which minimizes plant growth time and growth chamber space, allows a rapid turnover of plants, and allows large sample sizes to be tested. Seedling outcomes of survival or death can be treated as discrete phenotypes or on a resistance scale defined by amount of new growth in surviving seedlings after flooding. This method has been optimized to screen 10-day-old tomato seedlings for resistance to two P. syringae strains and can easily be adapted to other P. syringae strains.

High-Throughput Identification of Resistance to Pseudomonas syringae pv. Tomato in Tomato using Seedling Flood Assay

The seedling flood assay facilitates rapid screening of wild tomato accessions for the resistance to the Pseudomonas syringae bacterium. This assay, used in conjunction with the seedling bacterial growth assay, can assist in further characterizing the underlying resistance to the bacterium, and can be used to screen mapping populations to determine the genetic basis of resistance.

Tomato is an agronomically important crop that can be infected by Pseudomonas syringae, a Gram-negative bacterium, resulting in bacterial speck disease. ...

Identification of Novel Regulators of Plant Transpiration by Large-Scale Thermal Imaging Screening in Helianthus Annuus

Plant adaptation to biotic and abiotic stresses is governed by a variety of factors, among which the regulation of stomatal aperture in response to water deficit or pathogens plays a crucial role. Identifying small molecules that regulate stomatal movement can therefore contribute to understanding the physiological basis by which plants adapt to their environment. Large-scale screening approaches that have been used to identify regulators of stomatal movement have potential limitations: some rely heavily on the abscisic acid (ABA) hormone signaling pathway, therefore excluding ABA-independent mechanisms, while others rely on the observation of indirect, long-term physiological effects such as plant growth and development. The screening method presented here allows the large-scale treatment of plants with a library of chemicals coupled with a direct quantification of their transpiration by thermal imaging. Since evaporation of water through transpiration results in leaf surface cooling, thermal imaging provides a non-invasive approach to investigate changes in stomatal conductance over time. In this protocol, Helianthus annuus seedlings are grown hydroponically and then treated by root feeding, in which the primary root is cut and dipped into the chemical being tested. Thermal imaging followed by statistical analysis of cotyledonary temperature changes over time allows for the identification of bioactive molecules modulating stomatal aperture. Our proof-of-concept experiments demonstrate that a chemical can be carried from the cut root to the cotyledon of the sunflower seedling within 10 minutes. In addition, when plants are treated with ABA as a positive control, an increase in leaf surface temperature can be detected within minutes. Our method thus allows the efficient and rapid identification of novel molecules regulating stomatal aperture.

Identification of Novel Regulators of Plant Transpiration by Large-Scale Thermal Imaging Screening in Helianthus Annuus

We provide a method for identifying modulators of foliar transpiration by large-scale screening of a compound library.

Plant adaptation to biotic and abiotic stresses is governed by a variety of factors, among which the regulation of stomatal aperture in response to water ...

Screening of Tobacco Genotypes for Phytophthora nicotianae Resistance

Black shank, caused by the oomycetes Phytophthora nicotianae, is destructive to tobacco, and this pathogen is highly pathogenic to many solanaceous crops. P. nicotianae is well adapted to high temperatures; therefore, research on this pathogen is gaining importance in agriculture worldwide because of global warming. P. nicotianae-resistant varieties of tobacco plants are commonly screened by inoculation with oat grains colonized by P. nicotianae and monitoring for the disease symptoms. However, it is difficult to quantify the inoculation intensity since accurate inoculation is crucial in this case. This study aimed to develop an efficient and reliable method for evaluating the resistance of tobacco to infection with P. nicotianae. This method has been successfully used to identify resistant varieties, and the inoculation efficiency was confirmed by real-time PCR. The resistance evaluation method presented in this study is efficient and practical for precision breeding, as well as molecular mechanism research.

Screening of Tobacco Genotypes for Phytophthora nicotianae Resistance

Here, a protocol is presented for the efficient and accurate screening of tobacco genotypes for Phytophthora nicotianae resistance in seedlings. This is a practical approach for precision breeding, as well as molecular mechanism research.

Black shank, caused by the oomycetes Phytophthora nicotianae, is destructive to tobacco, and this pathogen is highly pathogenic to many solanaceous crops. ...

High-Throughput Analysis of Non-Photochemical Quenching in Crops Using Pulse Amplitude Modulated Chlorophyll Fluorometry

Photosynthesis is not optimized in modern crop varieties, and therefore provides an opportunity for improvement. Speeding up the relaxation of non-photochemical quenching (NPQ) has proven to be an effective strategy to increase photosynthetic performance. However, the potential to breed for improved NPQ and a complete understanding of the genetic basis of NPQ relaxation is lacking due to limitations of oversampling and data collection from field-grown crop plants. Building on previous reports, we present a high-throughput assay for analysis of NPQ relaxation rates in Glycine max (soybean) using pulse amplitude modulated (PAM) chlorophyll fluorometry. Leaf disks are sampled from field-grown soybeans before transportation to a laboratory where NPQ relaxation is measured in a closed PAM-fluorometer. NPQ relaxation parameters are calculated by fitting a bi-exponential function to the measured NPQ values following a transition from high to low light. Using this method, it is possible to test hundreds of genotypes within a day. The procedure has the potential to screen mutant and diversity panels for variation in NPQ relaxation, and can therefore be applied to both fundamental and applied research questions.

The protocol introduces a high-throughput method for measuring the relaxation of non-photochemical quenching by pulse amplitude modulated chlorophyll fluorometry. The method is applied to field-grown Glycine max and can be adapted to other species to screen for genetic diversity or breeding populations.

Photosynthesis is not optimized in modern crop varieties, and therefore provides an opportunity for improvement. Speeding up the relaxation of ...

An Improved Method to Measure Pollen Hydration Profiles in Arabidopsis thaliana

A High-Resolution, Single-Grain, In Vivo Pollen Hydration Bioassay for Arabidopsis thaliana

Sexual reproduction in flowering plants requires initial interaction between the pollen grain and the stigmatic surface, where a molecular dialog is established between the interacting partners. Studies across a range of species have revealed that a series of molecular checkpoints regulate the pollen-stigma interaction to ensure that only compatible, generally intraspecific pollen is successful in effecting fertilization. In species that possess a 'dry stigma', such as the model plant Arabidopsis thaliana, the first post-pollination, prezygotic compatibility checkpoint is the establishment of pollen hydration. 
This phase of pollination is tightly regulated, whereby signals from the pollen grain elicit the release of water from the stigma, thus permitting pollen hydration. The ability to accurately measure and track pollen hydration over time is key to the design of experiments directed at understanding the regulation of this critical step in reproduction. Published protocols frequently utilize flowers that have been excised from the parent plant, maintained on liquid or solid media, and bulk pollinated. 
This paper describes a noninvasive, in vivo pollination bioassay that permits minute-by-minute hydration tracking of individual A. thaliana pollen grains at high resolution. The assay is highly reproducible, able to detect very subtle variations of pollen hydration profiles, and thus is suitable for the analysis of mutants that affect pathways regulating pollination. Although the protocol is lengthier than those described for bulk pollinations, the precision and reproducibility it provides, along with its in vivo nature, make it ideal for the detailed dissection of pollination phenotypes.

Author Spotlight: A High-Resolution, Single-Grain, In Vivo Pollen Hydration Bioassay for Arabidopsis thaliana  

An improved method to measure pollen hydration profiles in Arabidopsis thaliana is described here. The new method offers higher resolution, is noninvasive, and is highly reproducible. The protocol represents a new tool for a finer dissection of the processes that regulate the early stages of pollination.

Sexual reproduction in flowering plants requires initial interaction between the pollen grain and the stigmatic surface, where a molecular dialog is ...

Enabling High-throughput Transgene Expression Studies Using Automated Liquid Handling for Etiolated Maize Leaf Protoplasts

The field of plant biotechnology has witnessed remarkable advancements in recent years, revolutionizing the ability to manipulate and engineer plants for various purposes. However, as research in this field increases in diversity and becomes increasingly sophisticated, the need for early, efficient, dependable, and high-throughput transient screening solutions to narrow down strategies proceeding to stable transformation is more apparent. One method that has re-emerged in recent years is the utilization of plant protoplast, for which methods of isolation and transfection are available in numerous species, tissues, and developmental stages. This work describes a simple automated protocol for the randomized preparation of plasmid within a 96-well plate, a method for the isolation of etiolated maize leaf protoplast, and an automated transfection procedure. The adoption of automated solutions in plant biotechnology, exemplified by these novel liquid handling protocols for plant protoplast transfection, represents a significant advancement over manual methods. By leveraging automation, researchers can easily overcome the limitations of traditional methods, enhance efficiency, and accelerate scientific progress.

This protocol describes the creation of a randomized transfection layout using an automated liquid handler, a protoplast isolation protocol for etiolated maize leaf, and a 96-well transfection procedure using a liquid handler.

The field of plant biotechnology has witnessed remarkable advancements in recent years, revolutionizing the ability to manipulate and engineer plants for ...

Potato Resilience Analysis Under Climate-Related Stresses

High Throughput Image-Based Phenotyping for Determining Morphological and Physiological Responses to Single and Combined Stresses in Potato

High throughput image-based phenotyping is a powerful tool to non-invasively determine the development and performance of plants under specific conditions over time. By using multiple imaging sensors, many traits of interest can be assessed, including plant biomass, photosynthetic efficiency, canopy temperature, and leaf reflectance indices. Plants are frequently exposed to multiple stresses under field conditions where severe heat waves, flooding, and drought events seriously threaten crop productivity. When stresses coincide, resulting effects on plants can be distinct due to synergistic or antagonistic interactions. To elucidate how potato plants respond to single and combined stresses that resemble naturally occurring stress scenarios, five different treatments were imposed on a selected potato cultivar (Solanum tuberosum L., cv. Lady Rosetta) at the onset of tuberization, i.e. control, drought, heat, waterlogging, and combinations of heat, drought, and waterlogging stresses. Our analysis shows that waterlogging stress had the most detrimental effect on plant performance, leading to fast and drastic physiological responses related to stomatal closure, including a reduction in the quantum yield and efficiency of photosystem II and an increase in canopy temperature and water index. Under heat and combined stress treatments, the relative growth rate was reduced in the early phase of stress. Under drought and combined stresses, plant volume and photosynthetic performance dropped with an increased temperature and stomata closure in the late phase of stress. The combination of optimized stress treatment under defined environmental conditions together with selected phenotyping protocols allowed to reveal&#160;the dynamics of morphological and physiological responses to single and combined stresses. Here, a useful tool is presented for plant researchers looking to identify plant traits indicative of resilience to several climate change-related stresses.

Author Spotlight: Unraveling Plant Responses to Abiotic Stresses Using the PlantScreen Robotic Platform

We designed an image-based phenotyping protocol to determine the morphological and physiological responses to single and combined heat, drought, and waterlogging treatments. This approach enabled the identification of early, late, and recovery responses at a whole plant level, particularly above-ground parts, and highlighted the necessity of using multiple imaging sensors.

High throughput image-based phenotyping is a powerful tool to non-invasively determine the development and performance of plants under specific conditions ...

Semi-High Throughput Screening for Potential Drought-tolerance in Lettuce (Lactuca sativa) Germplasm Collections

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A High-Resolution, Single-Grain, In Vivo Pollen Hydration Bioassay for Arabidopsis thaliana

Enabling High-throughput Transgene Expression Studies Using Automated Liquid Handling for Etiolated Maize Leaf Protoplasts

High Throughput Image-Based Phenotyping for Determining Morphological and Physiological Responses to Single and Combined Stresses in Potato