Regulation in Plants
Introduction
Plants respond to stimuli from their environment just as animals respond. There
is a balance maintained by plants by the interplay of several hormones. This coordination
is not unlike hormonal balancing act of many animals. The following series of labs focus
on learning about the chemical effects of plant hormones and the environment affects
plant growth and development.
I Plant response to Auxin
Background:
Auxins are chemicals that promote the unequal growth of a plant cell due to
enlargement of cells by acting on the unequal growth of the cell wall due to a change in
the cell wall’s composition and an increase in turgor pressure. In this lab you will apply
different concentrations of auxin to young seedlings and measure the curvature effect of
the hormone on the seedling. (Include chemical structure)
Materials for each team
10 – 20 Seedlings (seeds should be germinated in small containers) Oats, Barley are
good choices.
Lanolin paste with one of several concentrations of auxin mixed in.
5000 parts per million (auxin:lanolin paste)
500 Parts per million (auxin:lanolin paste)
Lanolin paste
Dark chamber (shoebox, egg carton)
Toothpicks
Procedure:
Prediction: What do you think will happen when an auxin:lanolin paste is applied to the
seedlings? What affect do you think the two different concentrations will have on the
seedling growth?
Hypothesis: After reading the procedure and relevant text reference, suggest a hypothesis
about the growth of the seedlings under the influence of auxin that you will be able to
test. If …, then…. is a good format to use for your hypothesis.
Examine the tip of the plant using a stereoscope. Identify the coleoptile of the plant.
This colorless covering sits over the green stem of the seedling. These seedlings were
grown with light source directly above so they should be vertical.
Label each seedling on the side of the container with the concentration of auxin that will
be applied.
Using a toothpick, carefully apply a layer of auxin-laced lanolin to only ONE side of the
seedling. Apply the lanolin to the upper 5 mm to 10 mm of each seedling.
Determine what procedure(s) you should include to provide for experimental control(s).
Determine how you should provide for repetition of data collection.
Place a toothpick next to each seedling in a vertical position. This toothpick will be used
to measure the change in curvature from vertical. If a digital camera is available,
photograph each seedling making sure to include seedling label. Your camera should be
placed at a 90 degree angle to the seedling tray. This will make measurements of
curvature easier.
Place your seedlings in a dark chamber in a warm area for 1 – 2 hours or set at room
temperature overnight.
Data collection:
Remove the seedlings from the dark chamber and set them up in the same place where
the initial digital photos were taken.
Take a second photo of each seedling, being sure to include the seedling label with auxin
concentration.
Measure the changes in curvature of each seedling and compare with the seedling before
application of the auxin paste. Include any changes in curvature in all control specimens.
Display your data in a table.
Analysis:
1. Describe the growth of the auxin-treated stems.
2. Does the curvature begin where the auxin:lanolin pste was applied?
3. Describe the growth of your controls.
4. How would you describe the distribution of auxin in your controls?
5. Why were the seedlings placed in the dark for you experiment?
6. What is the suggested relationship between seedling curvature, phototropism and
auxin?
Conclusion:
Do you data support your hypothesis? Indicate the relevant data that either lends
support or does not lend support.
Teacher Information:
1. Best seedlings to use: oats, barley, rye grass (Carolina, Wards, etc)
2. Auxin pastes: Carolina Biological Supply (Joan, provide order numbers)
3. Either shoe boxes could be used as a dark chamber along with small germination trays
for seedlings. Also, useful are plastic egg cartons. These provide individual chambers
that can be darkened easily.
4. Repetition suggestions:
3 seedlings
No Treatment
3 seedlings
Lanolin only treatment
6 seedlings
5000 ppm auxin:lanolin (or 500 ppm auxin:lanolin)
5. With respect to time, it might be best if each team used only ONE of the two
auxin:lanolin concentrations.
6. If a digital camera is not available, then simply using a protractor would provide the
degrees of curvature.
7. Additional experiments to consider
a. Using a powdered source of pure auxin, the teacher could make additional
concentrations of auxin:lanolin pastes. Reference for the production of an auxin:lanolin
paste can be found at the following website:
b. Extend the experiment with similar set-up where the seedlings are subjected to
light coming from one direction by cutting a hole in one side of the egg carton or
shoebox.