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Lesson Outline

Case of the Drought Resistant Genetically Engineered Corn Plant

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This scenario accompanies the online lesson, "Transpiration - Water Movement Through Plants", and is designed to allow you to apply the concepts learned in that lesson to a real-life problem.

Drought

Don Lee
Department of Agronomy and Horticulture at University of Nebraska-Lincoln, USA

This scenario accompanies the online lesson, 'Transpiration - Water Movement Through Plants', and is designed to allow you to apply the concepts learned in that lesson to a real-life problem.

 Lesson Navigation Tips:

  • To answer questions, select the button next to the correct answer and then select ’check it’ to see if you are correct.
  • To review concepts from the Transpiration - Water Movement Through Plants lesson, click on the link below each question.
  • Click once on figures to see enlarged versions.
     

Meet Brandon, a farmer in south-central Nebraska. Brandon raises daughters for fun and corn for profit.

Brandon and family in the field.
Image by Lisa Hunnicutt

Brandon hears about a new type of genetically engineered corn that is being developed to be drought resistant. Brandon is an expert on growing corn in water limiting conditions.

Question: Why would limited water be important in growing corn?
A. the water supports the structure of the plant since that plant does not have bones.
B. the water brings nutrients such as nitrogen and phosphorus into the plant.
C. plants need water in their cells for biochemical processes.
D. All of the above are reasons plants need water to grow. Limiting water will limit how these processes work in the plant.
To review this concept click on the link: Transpiration - What and Why?

Brandon has learned about the crop genetic engineering process and knows that scientists can add a single gene to a plant like corn and change a single trait in the plant. Biotechnology companies are doing this to develop new types of corn for farmers to grow. Companies, however, will not reveal all the details of their new projects until they are finished testing them. Click here Overview of Plant Genetic Engineering: Overview and Objectives. to learn about the plant genetic engineering process.

Crop genetic engineering includes:
1) DNA isolation
2) gene cloning
3) gene design
4) transformation
5) plant breeding

Brandon wonders if adding a single gene to corn can affect a trait like drought resistance. Brandon believes that his success in farming depends on his ability to think ahead about the practical value of different options. Therefore, he contacts his teacher friends in the Agronomy and Horticulture department. He wants to know what they can tell him about this drought resistance trait in corn.

One teacher and researcher in Agronomy and Horticulture is Dr. Jim Specht. Jim is an expert in soybeans and how they use their genes to grow under water limited conditions. He has a pretty good idea what the biotechnology company is doing to produce their drought resistant genetically engineered plants.

IANR Soybean Geneticist Jim Specht examines soybean DNA patterns in his lab.
Image by Research Nebraska, March 2001

The gene the biotechnology company has inserted into corn is probably a version of the DREB1A gene. The DREB1A activates the expression of other genes that govern the plant’s response to cellular dehydration and when these genes are turned on, they produce proteins that allows the plant to better cope with water stress. Jim’s hypothesis is that this work involved some very good molecular genetics research. However, Jim believes that in growing conditions in places like Nebraska, the DREB gene would ultimately influence the function of the cells pictured below.

Leaf surface cells.
Image by Ellen Paparozzi
Question: What are these paired cells called that are found on the surface of leaf cells?
A. stomata
B. phloem
C. guard
D. xylem
Question: What is the open pore called that is formed when the paired cells fill with water?
A. stomata
B. phloem
C. guard
D. xylem
To review this concept click on the link: Side view of stomata.
Question: How are stomates related to the water status of the plant?
A. liquid water enters the plant through open stomates.
B. liquid water leaves the plant through open stomates.
C. water vapor enters the plant through open stomates.
D. water vapor leaves the plant through open stomates.
To review this concept click on the link: Side view of stomata.
Question: What factors influence stomata function?
A. Only water stress, they stay open when the plant has enough water in it’s cells.
B. Water stress and other factors such as time of day, CO2 concentration, temperature and wind speed..
To review this concept click on the link: Side view of stomata.

The biotechnology company shows pictures of plants with the transgene (genetically engineered plants). They do not roll their leaves under the same field conditions that cause the non genetically engineered plants to roll their leaves. Leaf rolling is a common response of plants such as corn to the water conditions.

Stomata cells.
Image courtsey of R.L. Neilsen, Purdue University, 2002
Question: The reason corn plants will roll their leaves is because rolling reduces the surface of the leaf and this?
A. makes the stomates smaller.
B. creates a tube-like leaf within which the air can have a higher humidity and create a thicker boundary layer.
C. decreases the boundary layer.
To review this concept click on the link: Transpiration - Factors Affecting Rates of Transpiration.
Question: The reason the genetically engineered plants are not rolling their leaves is because?
A. they have lost more water than the non genetically engineered plants.
B. they have lost less water than the non genetically engineered plants.

Jim’s concern with the genetic engineering approach is that by making the DREB1A gene more easily turned on when stress occurs, this transgene could have a drag on the yield process because the coping mechanisms are also turned on earlier. In other words, the transgenic plant is now more “sensitive” in its response to water stress. The key question then is how soon does the plant begin “saving” water.

Question: How can a plant save water?
A. close it’s stomates.
B. keep is stomates open.
C. take up more water.
D. None of the above are reasons plants need water to grow. Limiting water will limit how these processes work in the plant.
To review this concept click on the link: Transpiration - What and Why?

Jim Specht has read the research reports that indicate that plants that save water also do not yield as well as those plants that use all of the seasonally available water. He has also observed this with in own studies in soybean. He notes that yield is not improved if stomates close sooner and longer, since corn then cannot obtain the carbon dioxide it needs for photosynthesis to fix carbon it needs for vegetative growth and ultimately for grain. . Simply put, the trend in grain crops is that more transpiration – more seed yield (and unfortunately, vice-versa).

Question: Open stomates are needed for the corn plant to obtain carbon for growth and grain yield because?
A. growth and grain come from carbon in the air that enters the plant through open stomates.
B. carbon in the soil is taken up by the plant when the water is pulled from the soil, through the plant and out the stomates.
C. trick question, the plant can keep it’s stomates closed and still obtain carbon for growth.
To review this concept click on the link: Transpiration - What and Why?

Development of this lesson was supported in part by the Cooperative State Research, Education, & Extension Service, U.S. Dept of Agriculture under Agreement Number PX2003-06237 administered by Cornell University, Virginia Tech and the American Distance Education Consortium (ADEC) and in part by the New Mexico and Nebraska Agricultural Experiment Stations. Any opinions,findings, conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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