1998 WWLPT Biology Institute:  Motion

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What Turns Seeds On?

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The Student Lab

Introduction

         In order for a plant to grow, there are a number of factors that come into play.  Plant seeds need both water and an energy source to germinate.  a-amylase is an enzyme produced in seeds which converts starch into simple sugars.  This response is controlled by hormones.  Plants then undergo cellular respiration using these simple sugars to produce energy.

Figure 1: Seed anatomy

(Peter Scott, Sussex University, UK)
 

Figure 2:  Signal transduction pathway

1. Gibberellin binds to the gibberellin receptor site.
2. This signals calcium ions, which act as secondary messengers.
3. These messengers, will then initiate a response from an unknown tertiary messenger which induces a-amylase transcription.

 
 
 
 
 
 
 
 
 

(Peter Scott, Sussex University, UK)

 

There are five major classes of plant hormones.  This exercise will focus specifically on two of the hormones (abscisic acid and gibberellic acid) which are responsible for regulating seed germination.  In general, ABA inhibits the production of a-amylase, while GA₃ stimulates it.  What is significant is the relative concentration of these two plant hormones to each other in eliciting a-amylase production.

Materials & Equipment
The following materials are needed for approximately four to six students, except for the hormones and volumetric flasks, please see the protocol.

Caution:  Please label all containers and solutions ahead of time in order to avoid confusion.

 

120 monocot seeds(e.g. sweet corn Zea mays var. rugosa)	metric ruler
1% bacto-agar solution	100 mg abscisic acid (ABA)
2% soluble potato starch solution	500 mg gibberellic acid (GA3)
600 mL beaker	distilled water
four 500-mL beakers	25 mL Clorox bleach or Lysol disinfectant
10 mL graduated cylinder	95% ethanol
three 100 mL volumetric flasks	aluminum foil
three1-L volumetric flasks	parafilm
500 mL erlenmeyer flask	scalpel or razor blade
two 1-mL disposable pipettes	forceps
forty-eight 8-cm petri dishes	analytical balance
Lugol's iodine (I2KI) solution

 

1. Form a testable question.
2. Create a hypothesis and design an investigation using the following guidelines:
• Describe the roles of GA₃ and ABA in seed germination.
• Any type of seed may be used.
• Determine the control.
• Identify the independent and dependent variables.
• Hint:  Seeds should be soaked overnight and disinfected before using.
• Germination should be allowed to occur for at least 5 days.
• Data collected needs to be organized using a  table or graph.
3. Experimental design should be approved by the instructor.
4. Data should be presented in a format specified by the instructor.