Plant Physiology (Biology 327)  - Dr. Stephen G. Saupe;  College of St. Benedict/ St. John's University;  Biology Department; Collegeville, MN  56321; (320) 363 - 2782; (320) 363 - 3202, fax;    ssaupe@csbsju.edu

Influence of Light & ABA on Stomatal Aperture
 

Background Information:  
    The stomatal aperture is sensitive to a variety of internal and external factors. This is not surprising since plants need to regulate and compromise between the rates of photosynthesis and transpiration.  Thus, we expect the stomata to be more widely open in the light than in dark conditions. The hormone abscisic acid (ABA) is reported to be a potent anti-transpirant.   Increased levels of ABA can be detected soon after water stress and this is related to stomatal closure.  In this exercise we will examine the influence of light and abscisic acid (ABA) on stomatal aperture.

Questions:  Is the stomatal aperture of Broad bean (Vicia faba) more widely open in the light or the dark?  Does ABA cause Broad bean stomata to close?
 

Hypothesis:   Light-treated epidermal strips will have significantly larger stomatal apertures than those in the dark.  ABA-treated epidermal strips will have significantly smaller stomatal apertures than those in the dark.

Protocol:   

1. Float three epidermal peels from Broad bean in each of two petri dishes (15 x 60 mm) containing 50 mM potassium phosphate buffer with 50 mM KCl (pH 6.0).  
   

2. Place one dish in the light and the other in the dark (wrap with aluminum foil).  
   

3. Float three additional peels in a petri dish (15 x 60 mm) containing 10 μM ABA 50 mM potassium phosphate buffer with KCl (pH 6.0).  Place this dish in the light.
   

4. After approximately 1 hour, mount each leaf strip in a drop of oil on a microscope slide.  Determine the aperture, in ocular micrometer units, of 10 randomly-selected stomata per strip with an ocular micrometer.  Record your data in Table 1.  Don't forget to record the magnification (= _________x).

Data: 

1.      Complete Table 1.  Convert aperture data from ocular micrometer units to metric units and calculate the mean and standard deviation of the aperture in both light and dark conditions.  

Perform an unpaired t-test to evaluate your hypothesis concerning the effect of light and dark on stomatal aperture.

• Ho:  Stomatal

• t statistic: 

• p = 

• Conclusion:

 Perform an unpaired t-test to evaluate your hypothesis concerning the effect of ABA on stomatal aperture.

• Ho:  Stomatal

• t statistic: 

• p = 

• Conclusion:

Analysis/Conclusions:

1. What do you conclude about the effect of light and ABA on stomatal aperture?  

Last updated:  01/07/2009     � Copyright  by SG Saupe