Plant Growth Regulation

• Understand the difference between the broad category, "Plant Growth Regulators" and how "Plant Hormones" include a more specific group of traditional plant growth regulators.
• Identify the five traditional groups of compounds called plant hormones.
• List each of the five plant hormones and explain one major function of each.

This teaching strategy provides a one-hour presentation, with question-and-answer, as well as Internet investigations, to understand plant growth regulation.

1. Pose the question, "what sort of compounds regulate the growth of plants?" Allow participants to provide their own examples, which may include things like fertilizer, herbicides, hormones, and other chemicals that are commonly used to inhibit or promote plant growth.
2. Provide a definition of a plant growth regulator such as "a broad category of organic substances that, in minute amounts, inhibit or promote, otherwise physiological processes." With this definition, point out other terms such as "plant hormone," "phytohormone," and "plant growth substance" that are often used synonymously with the term, "plant growth regulator."
3. Focus on the traditional term, "plant hormone," and list them as follows: auxin, gibberellins, cytokinin, abscisic acid, and ethylene."
4. Provide a brief background of each plant hormone and ask participants if they can come up with a major function of each compound. See the site http://www.merlot.org/merlot/viewMaterial.htm?id=481349 for an overview of the five plant hormones.
5. Explore information about auxin and visit one or more sites on the mode of action of auxin in regulating plant growth. See http://www.merlot.org/merlot/viewMaterial.htm?id=481577
6. Explore information about gibberellins and visit one or more sites on the mode of action of gibberellins in regulating plant growth. See http://www.merlot.org/merlot/viewMaterial.htm?id=420971
7. Explore information about cytokinin and visit one or more sites on the mode of action of cytokinin in regulating plant growth. See http://www.merlot.org/merlot/viewMaterial.htm?id=481737
8. Explore information about abscisic acid and visit one or more sites on the mode of action of abscisic acid in regulating plant growth. See http://www.merlot.org/merlot/viewMaterial.htm?id=481581
9. Explore information about ethylene and visit one or more sites on the mode of action of ethylene in regulating plant growth. See http://www.merlot.org/merlot/viewMaterial.htm?id=481352
10. Discuss how interactions of two or more plant hormones work together to regulate plant growth and development.

Supporting Files:

• Outline - Plant Growth Regulation (Microsoft Word 32kB Aug6 10)
• Questions - Plant Growth Regulation (Microsoft Word 33kB Aug15 10)

This teaching strategy encourages participation to learn about plant growth regulators and the traditional grouping of plant hormones. Interactive learning, through use of the Internet, provides students with an investigative approach to understanding how these plant compounds regulate plant growth and development. Incorporation of some animations, pictures, and investigative information of plant hormone action engages students in the learning process. This type of investigative presentation helps participants get involved in the learning process.

Participants may be tested on their comprehension of this learning material through multiple choice, short-answer, or essay exams. A few example questions are embedded in this Activity Sheet, entitled "Questions – Plant Growth Regulation."

MERLOT description and link to "Plant Hormones," which provides general information on plant hormones. See http://www.merlot.org/merlot/viewMaterial.htm?id=481349

MERLOT description and link to "Auxin as a Plant Hormone," which shows an animation of how auxin stimulates cell elongation. See http://www.merlot.org/merlot/viewMaterial.htm?id=481577

MERLOT description and link to "Gibberellin Mode of Action," which provides an animation of the mode of action of gibberellin. The mechanism shows calcium as a secondary messenger, calmodulin, and the production of protein. See http://www.merlot.org/merlot/viewMaterial.htm?id=420971

MERLOT description and link to "Cytokinin as a Plant Hormone," which provides general information and some detailed explanations about the action of cytokinin. See http://www.merlot.org/merlot/viewMaterial.htm?id=481737

MERLOT description and link to "Abscisic Acid as a Plant Hormone," which provides general information about the action of abscisic acid. See http://www.merlot.org/merlot/viewMaterial.htm?id=481581

MERLOT description and link to "Ethylene as a Plant Hormone," which provides general information and some detailed explanations about the action of ethylene. See http://www.merlot.org/merlot/viewMaterial.htm?id=481352