Materials Included In Kit

Additional Materials Required

Prelab Preparation

Prepare a stock solution of 100 mg/L of gibberellic acid by dissolving 100 mg of gibberellic acid in 5 mL of alcohol. Using a 1-L container, bring the volume of the alcohol/gibberellic acid mixture up to 1 liter with distilled water.

To make a 50 mg/L solution of gibberellic acid combine 500 mL of the stock solution prepared above to 500 mL of distilled water.

To make a 5 mg/L solution of gibberellic acid combine 50 mL of the stock solution to 950 mL of distilled water.

Dispense these solutions into labeled spray bottles. Add tap water to the control bottle.

Safety Precautions

Seeds are routinely treated with mold-inhibiting chemicals to help preserve them. Be sure to wash hands thoroughly upon completion of the laboratory work. Wear appropriate eye protection and follow all laboratory safety rules. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The solutions in this activity may be disposed of according to Flinn Suggested Disposal Method #26b.

Teacher Tips

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. The completion of this laboratory will require at least five class periods.

• Enough gibberellic acid is provided to perform many more experiments, if desired.
• Four spray bottles are included in the kit for spraying the gibberellic acid solutions. Have students spray one of their plant groups and pass the bottle to the next group and so on. If desired, the gibberellic acid solutions may also be placed on the seedlings using disposable dropping pipets (although results may not be as dramatic).
• Be sure that all groups of bean seeds are sprayed in an isolated area to avoid overspray onto the other bean plants.
• Students may experiment with other test factors such as the effect of other concentrations of gibberellic acid solutions, effect of gibberellic acid on different types of seeds, the effect of different methods of applying gibberellic acid, etc.
• Use the prepared gibberellic acid solutions promptly. The shelf life of the prepared solutions is less than two weeks.
• As with any living material, results may vary from class to class.

Sample Data

Answers to Questions

1. Prepare a graph of plant height versus the number of days for each concentration of gibberellic acid solution used.

2. What changes were seen in the plants that were treated with gibberellic acid?

The plants treated with gibberillic acid grew taller and thinner than the control plants.

3. How soon were the changes visible? Did the changes vary based on the concentration of gibberallic acid?

Changes were seen the day after the plants were treated with gibberellic acid. The basic changes were visible at first. However, 5 mg/L and 50 mg/L were near identical until day 3.

4. What concentration of gibberellic acid induced the most growth? Why?

The plants treated with the 50 mg/L solution grew the tallest. Answers will vary.

Introduction

What effects do hormones have on plants? Do various levels of hormones affect plants differently? Find out firsthand by treating seedlings with varying concentrations of a plant hormone known as gibberellic acid.

Concepts

• Plant hormones

• Gibberellic acid
• Plant growth

Background

Gibberellic acid was first isolated from rice seedlings in the early 1900s in Asia (see Figure 1). Sporadically, rice seedlings grew very tall and would topple over. This phenomenon became known as foolish seedling disease. In 1926, Kurosawa discovered that the rapid growth was due to a fungus known as Gibberella that was found in large amounts on some rice seeds. Furthermore, abnormal growth of the seedlings was due to the abundance of the chemical gibberellic acid, which is produced by the gibberella fungus.

Specifically, gibberellic acid is active in promoting the growth of plant stems (internode elongation). It is also used commercially to increase fruit size and speed up the flowering of certain plants. In this experiment, varying concentrations of gibberellic acid solution will be placed on bean seedlings and the visual differences between the seedlings observed.

Materials

Safety Precautions

Seeds are routinely treated with mold-inhibiting chemicals to increase preservation. Be sure to wash hands thoroughly with soap and water upon completion of laboratory work. Wear appropriate eye protection and follow all laboratory safety guidelines.

Procedure

1. Place potting soil into four pots until the soil is within ½" of the top rim.
2. Using a marker, label four plant markers with your group’s initials and as follows:

a. Control
b. GA, 5 mg/L
c. GA, 50 mg/L
d. GA, 100 mg/L

3. Place one marker into the soil of each growing pot.
4. Thoroughly pre-soak the potting soil in each of the pots with water.
5. Place five bean seeds about 1 cm under the surface of the soil in each of the four pots. Allow the bean seeds to have plenty of room to germinate.
6. Cover each of the pots with plastic wrap to help maintain humidity and moisture.
7. Water the seeds from the bottom up by placing the pots in a planting tray. Add sufficient water (~1") to the planting tray. Watering from the bottom up will allow for minimal disturbance of the seeds.
8. Place the tray and pots under a plant growing light or near a window exposed to bright sunlight.
9. Add water to the tray every few days as needed to maintain approximately 1" of water in the bottom of the tray.
10. When the seeds have germinated and the seedlings are visible, remove the plastic wrap.
11. Record the height of each seedling in each pot in the Gibberellic Acid and Plants Worksheet. The first measurement will be recorded under Day 0. Record the average height of the plants in each pot under Day 0 as well. Record any observations in the Gibberellic Acid and Plants Worksheet.
12. Using a spray bottle, spray the appropriate solution on the plants in each pot after the initial measurements for Day 0 are taken. Completely cover the stems and leaves of each seedling with the appropriate treatment solution. Be sure to isolate each pot when spraying the solutions on the plants to avoid contaminating the other bean seedlings with the incorrect solution.
13. Record the height of each plant, the average height for each pot and observations over the next week (or time period determined by the instructor). After measurements have been taken daily, spray the corresponding gibberillic acid solution on each plant.
14. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

10471_Student1.pdf