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 |
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:
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).
Place
one dish in the light and the other in the dark (wrap with aluminum foil).
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.
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.
Table
1: Stomatal aperture of
Broad bean leaf peels incubated in the dark and light. |
||||||
Rep |
Dark (-ABA) |
Light |
Light (+ABA) |
|||
Stomatal
aperture (omu) |
Stomatal
aperture (μm) |
Stomatal
aperture (omu) |
Stomatal
aperture (μm) |
Stomatal
aperture (omu) |
Stomatal
aperture (μm) |
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Mean +/- std dev |
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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:
What do you conclude about the effect of light and ABA on stomatal aperture?
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Last updated:
01/07/2009 � Copyright by SG
Saupe