BIOL 1
ALLELOPATHY
(Chemical Warfare Among The Plants)
Chaffey College
INTRODUCTION
Plants can be complex chemical factories. They may produce chemical scents and nutrients to
attract pollinators. They may produce and store poisons in their tissues to discourage potential browsers
and parasites. Plants also compete with other plants for sunlight, soil nutrients, and water. Since they do
not have the option of avoiding competition by running away (like animals) they resort to chemical
warefare. To reduce competition they may produce chemicals that inhibit the germination and growth of
neighboring plants. This last phenomenon is termed allelopathy. This chemical warfare can be against
other plants of the same species (intraspecific competition) of "plants of a different species (interspecific
competition).
Plants may release allelopathic substances in a variety of ways:
1. Directly into the soil from their roots.
2. Allelopathic substances may be leached from living or dead shoots into the surrounding soil, or
3. Volatile compounds pass into the air and then are deposited on the soil or the surface of other plants
when dew forms.
In this laboratory exercise, we will test for the presence of allelopathic chemicals in plant shoots from the
chaparral community. Allelopathy appears to be
best developed in perennial and woody species of more humid regions.
MATERIALS & METHODS
Student teams will collect leaves during preceding field exercises or be provided with samples
collected by the instructor. Leaves can be collected in a sandwich-type plastic bag.
1.
In the field, each team will select a plant species to collect from.
2. Pick leaves (no stems) and fill up your team's collecting bag.
3. Upon returning to the lab, label yoar bag and place your bag in the refrigerator.
Extraction of Allelopathic Compounds
For each team
1. Weigh out 10 grams of leaves from your assigned species and place the measured sample in a blender.
2.
Add 100 ml of distilled water to the blender.
3.
Hold the lid of the blender finnly on the blender and blend completely.
4.
Place some folded cheesecloth into a funnel and set into a stock bottle.
5.
Pour the blended mixture through the funnel/cheesecloth to filter the solution.
Testing of Allelopathic Effects
1.
Place 3 pieces of filter paper in each bottom of two petri dishes.
2.
In one petri dish (labeled with the name of the plant you collected), add 10 mI of the filtered solution so
that it soaks the filter paper layers.
3.
In the second petri dish (labeled control ), add 10 mI of distilled water SO that the water soaks the filter
paper layers.
4.
In each petri dish, place 20 radish seeds (Raphanus sativus) on top of the 3 pieces of filter paper
so that they are unifonnly spaced.
5.
Place another piece of filter paper on top of the seeds in both dishes.
6.
Place the lids on the petri dishes to prevent excessive evaporation and store at room temperature.
The seeds will be given a I week germination period and then evaluated.
The seeds will need to be checked periodically to determine the condition of the cultures (you will need
to do this at the end of next lecture). If necessary, small amounts of distilled water will be added to
re-saturate the filter paper and prevent the cultures from drying out. If fungus appears, cultures will be
moved to a cooler incubation environment.
RESULTS & WRITE-UP
+ The results will be gathered after a 1 week growth period.
+ Examine your cultures and fill in the requested information on the lab data sheet.
+ Your write-up should follow the standard report fonnat.
ALLELOPATHY DATA SHEET
Name __________________________________________
Name of plant species tested: ___________________________________________
A. Experimental Group (treated with extract)
1. Total number of seeds tested
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2. Number of seeds that successfully germinated.
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3. Percentage of successful germination
_______
4. Length of each seedling in mm.
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5. Average seedling length.
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B. Control Group (treated with distilled water only)
1. Total number of seeds tested.
__________
2. Number of seeds that successfully germinated.
__________
3. Percentage of successful germination
__________
4. Length of each seedling in mm.
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5. Average seedling length.
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