May the Best Plant Win! Experiment with Genetically Modified Seeds
AbstractFarmers face a variety of challenges in their efforts to grow crops. One of the chief challenges is the presence of unwanted plants (weeds) that compete with the crop plants for water, nutrients, and light. If the weeds are not suppressed, they can reduce or completely eliminate the amount of food derived from the crop at harvest. In this biotechnology and plant science fair project, you will simulate the competition between crop plants and weeds, and determine whether the use of an herbicide, Roundup®, provides a growth advantage to genetically modified plants.
David B. Whyte, PhD, Science Buddies
The objective of this science fair project is to determine the effect of the use of Roundup® on the growth of genetically modified plants that are competing with weeds for food and light.
This science fair project deals with the growth of normal (wild-type) and genetically modified (GM) soybeans. The GM plants have been engineered to so that they are resistant to glyphosate, the active ingredient in Roundup and other commercial herbicides. Glyphosate kills plants by inhibiting an enzyme that performs a function that is critical for the survival of the plant. The GM plants are able to grow in the presence of glyphosate because they carry a modified version of this enzyme.
The modified enzyme is able to carry out the same biochemical steps as the wild-type enzyme, but the modified enzyme has a slightly different 3-dimensional structure that causes it not to bind glyphosate. So when the GM plant is sprayed with Roundup, it is able to keep growing normally.
The GM plants carry a genetically modified gene. The modified gene produces a modified enzyme. This enzyme, called EPSPS (5-enolpyruvylshikimate-3-phosphate synthase), (pronounced EE-nahl-py-ROO-vuhl-SHIH-kih-mate) catalyzes a key step in the synthesis of the amino acids phenylalanine, tyrosine, and tryptophan in plants. Plants need to make these amino acids "from scratch" in order to live; whereas people do not make these amino acids, because we get them from eating the plants. In fact, people do not even have the ability to make these amino acids because we lack the enzymes that are needed for their synthesis. This explains why glyphosate is toxic to plants, but not to people.
Glyphosate is transported from the leaves to the roots of treated plants. This is critical for its effectiveness. Because it is transported to the roots, it is able to actually kill the plant, rather than just damage the weed's leaves. Glyphosate is toxic to nearly all plants, not just weeds. If you are using it in your garden, you need to shield the plants you want to grow from the spray.
Farmers use glyphosate to kill plants that compete with their GM crops for water, nutrients, and light. In this science fair project, you will plant wild-type and GM plants together, so that they are competing for resources. The "weeds" will be represented by the WT plants (soybean or corn) that match the GM plants, as well as other "weed" seeds you will purchase. The procedure calls for planting parsley and radish seeds, since these germinate quickly (about 7–10 days). Feel free to use other seeds as "weeds" if you prefer. The plants will be sprayed with Roundup at various times. You will determine if "killing off the competition" helps the growth of GM plants. Since this science fair project involves growing plants from seeds, keep in mind that it may take over a month to finish. Also keep in mind that because there is no way to predict exactly how the plants will grow and compete with each other, you may need to be flexible with the experimental procedure.
Terms and Concepts
- Genetically modified (GM) crop
- 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS)
- Amino acid
- Based on your research, where did scientists first discover the glyphosate-resistant EPSPS gene?
- What percentage of soybean and corn grown in the United States is genetically modified? How about the world?
- What are some potential environmental risks of using GM crops?
These websites provide more information about some of the key topics related to this science fair project:
- Shaner, D. (2006, December 12). An Overview of Glyphosate Mode of Action: Why Is It Such a Great Herbicide?. Retrieved February 12, 2009.
- Peel, M.D. (2001, October). A Basic Primer on Biotechnology. Retrieved February 12, 2009.
- Wikipedia Contributors. (2009, February 5). Enzyme inhibitors. Wikipedia: The Free Encyclopedia. Retrieved February 12, 2009.
These websites include information about Roundup:
- HowStuffWorks.com. (n.d.). How the herbicide Roundup works. Retrieved April 23, 2009.
- Moran, L. (2007). The Molecular Basis of Roundup Resistance. Retrieved April 23, 2009.
Learn more about soybeans from these websites:
Materials and Equipment
- Plastic cups (2)
- Permanent marker
- Planting pots, 4-inch diameter, with holes to let water drain (15)
- Genetically modified soybean and/or corn seeds; the Genetically Modified Plants Lab Activity kit from Ward's Science contains Roundup-ready genetically modified seeds that can be used for this experiment
- Potting soil, sterile (1 bag)
- Pencil with an eraser
- Plastic wrap (1 roll)
- Radish seeds; available at hardware stores, grocery stores, and plant nurseries
- Basil seeds; available at hardware stores, grocery stores, and plant nurseries
- Roundup® weed and grass killer; available from plant nurseries or online from Amazon.com
- Lab notebook
- Graph paper
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Note: Keep in mind that you will need to perform three trials of this science fair project. To save time, the trials can be run concurrently.
Planting Your Seeds
- Label the two plastic cups with the different seed types: WT soybean or GM soybean.
- WT = wild-type (unmodified) Note: The WT plants are functioning as "weeds" in this procedure, since they compete for resources and are sensitive to Roundup.
- GM = genetically modified
- Add five GM soybean seeds to the GM cup.
- Add 15 WT soybean seeds to the WT cup.
- Add water to both cups and let the seeds soak for 30 minutes.
- Fill five planting pots with potting soil.
- Label five sticks (supplied with the kit) with the numbers 1–5. Also add the date to each stick.
- Place a stick in each of the five plant pots.
- Use the eraser end of the pencil to poke four holes in each pot, about 5 cm deep. Place one hole in the middle, and the other three surrounding the middle hole. Use the same pattern of holes in each pot.
- Plant one GM and three WT seeds in each pot, as follows:
- Plant the GM seed in the middle.
- Plant the three WT seeds in each pot, surrounding the GM seed.
- Cover the seeds with soil.
- Place three radish seeds and three basil seeds on the surface of the soil in each of the previous five pots.
- Note: To increase the competition, add some more "weeds." You may wish to use different competitor plants or more competitor seeds per pot. Just be sure to document your procedure and your observations in your lab notebook.
- Push the radish and basil seeds about 1 cm into the soil.
- Gently cover the seeds with soil.
- Water the plants thoroughly and let them drain completely.
- Cover the pots with plastic wrap to keep them moist while the seeds germinate.
- Water the pots if the soil starts to dry out. Keep the soil moist, but not soggy.
- Remove the plastic wrap when plants start to emerge from the soil.
- Continue to keep the plants well-watered.
- Continue growing the plants outdoors if the temperature is above 13°C (55°F) at night. They can also be grown indoors on a sunny windowsill, in a growth chamber, or in a greenhouse.
Treating Your Plants with Herbicide
- Treat the plants with Roundup, as detailed below.
- Planting pot #1: No Roundup.
- The GM plant will compete with the "weeds" for the duration of the experiment.
- Planting pot #2: Treat with Roundup when the soybean plants are about 2.5 cm tall.
- The GM plant will compete with the weeds early on, but then will have the pot to itself.
- Planting pot #3: Treat with Roundup when the soybean plants are about 5 cm tall.
- Planting pot #4: Treat with Roundup when the soybean plants are about 10 cm tall.
- Planting pot #5: Treat with Roundup when the soybean plants are about 15 cm tall.
- Planting pot #1: No Roundup.
- Follow the directions on the Roundup container.
- Make sure you treat all of the plants with the herbicide. Wear disposable gloves when handling the weed killer and work in a well-ventilated area, such as outdoors, away from any other plants, and at a calm, non-windy time of day.
- Note: You may need to alter the treatment timing for your experiment, depending on how your plants are growing. Feel free to adjust the procedure, as necessary.
- Keep detailed notes of what you do and observe, in your lab notebook. Record the height of the GM plant each day.
- Record the effects of the Roundup on the GM and WT plants. Use a scale from 1–5, with 1 being "very healthy" and 5 being "dead."
- You don't need to record the health of every plant that is growing. You could just note the overall appearance of health for the GM and WT plants in each pot. For example, "Pot # 1: GM plant healthy (score = 1), WT plants healthy (score = 1)," etc.
- Record the dates of your observations.
- Take photographs of the plants for your records.
- Add notes to the photographs, including the sample #, the time and date, and your observations about what is significant about the picture.
- Provide water and sunlight to the plants for the entire duration of the experiment.
- Use your judgment about when to stop the experiment. Stop the experiment when you determine that you have seen clear results, or when you determine that extending the experiment will not yield new valuable data.
- Repeat the entire procedure two more times, with new materials, for a total of three trials. The trials can be run concurrently. The reason for doing three trials is to ensure that your results are consistent and repeatable.
Analyzing Your Data
- Graph the data.
- Put time on the x-axis and the height of the GM plant on the y-axis.
- Use different-colored lines for each treatment (1–5).
- Based on your results, what can you conclude about the benefits vs. drawbacks of Roundup-resistant plants?
Ask an Expert
- Even if the Roundup does not kill the GM plants, does it affect their growth or appearance? Devise an experiment to compare the growth of GM plants with and without treatment. Use WT plants as controls to show that the Roundup is working as an herbicide.
- Repeat the main experimental procedure, using other types of plants as "weeds." You could also vary the number of competing plants.
- Does using GM seeds allow you to successfully grow plants in soil with established weeds? You can test this by planting and watering the "weeds" before planting the GM seeds. For example, plant the weeds 7 days prior to planting the GM seed, and then treat with Roundup at 1 week, 2 weeks, 3 weeks, and 4 weeks.
- Since the plants are competing for limited resources, you might expect the size of the pot to affect the outcome. Devise a way to test this.
- Repeat the procedure above with the GM and WT corn seeds that are in the GM plant kit.
- Repeat the procedure with real weeds. Plant the GM seeds outdoors in an area with lots of weeds. Treat them with Roundup, as described above. Record the height of the GM plants and the effects of the Roundup on the health of the plants.
- In a real farming situation, weeds would be a continuous threat to the GM crops. Model this by adding new "weed" seeds after treatment with Roundup.
- Soybean plants are grown for their beans, and minimizing environmental stress will optimize seed yield. Devise a procedure that uses seed yield as an endpoint, rather than plant height.
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