Introduction
Can Association Patterns Between Unrelated Stimuli
Classical Conditioning is a type of learning in which an organism
H0: There will be no learned association in the experimental
group, and therefore, no difference from the control groups.
Materials and Methods
General Setup
The pea plants were grown in 6 in. pots in potting soil with
perilite fertilizer. Growing took place in a greenhouse under optimal
growing lights that were set up on a timer to run from 6 a.m. to 9 p.m.
Three groups were established with 18 plants in each group. A
structure was built over each group with hanging wires for the tendrils
of the pea plants to coil around (See Figure 1). The groups were
separated from each other with a thin board that blocked light and
wind between groups. Fans were set up in front of control group 2
and the experimental group to induce winds of approximately 6-7
mph.
The experimental group was subject to the wind from a fan at
night. At 9 p.m. every night the fan turned on and, within two minutes,
the lights in the entire greenhouse turned off. The following morning
at 5 a.m., the fan turned off, and within two minutes, the lights turned
on. Control group 1 grew in the greenhouse at the same time and
was subject to the exact same environment, however, it received no
wind from fans. Control group 2 received wind from a fan for the
same duration of time that the experimental group did. The fan,
however, was not in conjunction with the lights. It turned on at 10
p.m. and off the next morning at 6 a.m. The experiment began 14
days after planting and lasted 16 days.
Fig. 2
There was great individual variance in the photosynthetic
rates of each plant, as well as, great variance in the net change
once the wind was applied. No significant differences were found
between the groups. The photosynthesis results can be found in
Figures 3-5. Morphological results can be found in Table 1.
Table 1. ANOVA Statistical results of morphological
comparisons between each group.
CG1 vs. CG2 CG1 vs. EG CG2 vs. EG
Photosynthetic Study
Fig. 3
Photosynthetic Rate
16
Time 1
Time 2
12
µmol CO2/cm2/s
The eight healthiest plants were chosen from each
group to be tested. An infrared gas analyzer* (IRGA) was
clamped on a leaf that was still attached to the plant. The
photosynthetic rate was allowed four minutes to stabilize
and then a reading was taken. The fan was then turned on
for an additional three minutes and another reading was
taken. The leaf inside the chamber that was being
measured was not subject to the wind. It was hoped that
the plant would have a systemic response to the wind and
photosynthesis across the entire plant would slow.
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Morphological Study
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The small leaves of pea plants did not fill the chamber
of the IRGA. Scion** was used to compute the exact area Fig. 4 Photosynthetic Rate Changes in Control Group 2
of each leaf. This information was then entered back into
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the IRGA so that photosynthetic rate could be accurately
Time 1
determined per cm2.
Stomatal peels were taken from two leaves per plant.
This involved brushing clear nail polish onto the leaves.
Once dry, the nail polish was peeled off the leaf and
mounted onto a microscope slide (Coombs et al. 1985).
The stomata of the leaves were counted to determine
stomatal density on top and bottom of the leaves.
Time 2
12
Biomass of the plants was measured. Dry weights of
roots, stems, and leaves were taken individually. Roots
were washed and patted dry to remove dirt. The leaves,
stems, and roots were dried in a drying oven at 28oC for 4
Fig. 5
days. They were then massed on a balance.
Specific weights of leaves were compared between
groups as well. Two leaves were taken from each plant and
the areas were determined using scion** as mentioned
before. The leaves were then dried in the oven and
weighed. The mass per unit area of the leaves was an
indication of the thickness of the leaves.
Average internode length was determined by dividing
the entire length of the above ground portion of the plant by
the number of internodes present.
Stomatal Ratio (T/B)
* p=0.0264
ns
ns
Stomatal Density- Top
* p=0.0113
ns
ns
Stomatal Density- Bot.
* p<0.05
** p=0.0016
ns
Internode Length
* p<0.05
* p<0.05
ns
Biomass- Leaf
ns
ns
ns
Biomass- Stem
ns
ns
ns
Biomass- Root
ns
ns
ns
Leaf Sp. Weight
ns
* p<0.05
** p<0.01
Photosynthetic Rate Changes in Control Group 1
µmol CO2/cm2/s
H1: It is proposed that by the end of the experiment, when the
fans are turned on, the photosynthetic rate will drop in full
sunlight because the plants anticipate the lights being turned off.
Fig. 1
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Discussion
The photosynthetic rates were too individual to determine
any trends. The plants were in the exact same environment
during the experiment and during the testing. It is difficult to
determine why one plant would photosynthesize at a rate of
under 4 and another at a rate of over 15. There are a myriad of
possible reasons including genetic variability and
equipment/operator error. With this great range of
photosynthesis, it is not surprising that the time 2 results for each
plant were just as scattered. There were no clear results from the
photosynthesis testing. Therefore, we must fail to reject the
null hypothesis. There was no significant difference between
the experimental and control groups.
In conclusion, the plants were not able to associate the two
unrelated stimuli, wind and light. The photosynthetic rates did not
plummet when the fans were turned on. However, the plants did
respond to the wind by altering their morphology. Table 1 shows
that the plants that received wind were morphologically different
than those that did not receive wind. This is evidence that the pea
plants do have the apparatus to perceive and respond to wind.
Literature Cited
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Photosynthetic Rate Changes in the
Experimental Group
Time 1
16
Time 2
12
µmol CO2/cm2/s
The purpose of this research was to determine if an association
pattern between light and the mechanical stimulus wind exists in the
common pea plant Pisum sativum L. Stated simply, the goal is to
entrain the plant to perceive the wind as the cause of the lights going
off. If this is accomplished, by the end of the training period, the
wind should cause a severe drop in the photosynthetic rate due
to anticipation of the lights going off.
Brandon May, and Bruce Smith
Department of Biological Sciences, York College of Pennsylvania
Photosynthetic Rate
Plants and animals share a common cryptochrome, or blue light
receptor, that is responsible for a variety of light responses including
entrainment of circadian rhythms. It is proposed that this cryptochrome
could pre-date the divergence of plants and animals from a common
ancestor (Cashmore et al. 1999). Pea plants are also sensitive to
mechanical stimulations, such as vibrations when the wind blows and
touch (Galston and Jaffee 1966:68). Wind has been shown to increase
pest resistance in the common bean (Cipollini 1997). Therefore, it is
evident that pea plants have the ability to perceive and respond to both
light and wind.
be Instilled in the Plant Pisum sativum L.?
Photosynthetic Rate
is entrained to associate two unrelated external stimuli (Myers 2001).
The classic example is the Pavlovian dog salivating when the dinner
bell rang because it associated the ring with the introduction of food. It
anticipated the presentation of food, when the bell rang. Dr. James
McConnell and associates performed similar studies on the planarian,
Dugesia dorotocephala (Thompson 1955). These flat worms have the
ability to perceive and respond to light and shock stimuli. When the
intensity of the light increased, the animals were shocked. This caused
a longitudinal contraction of the body. At the end of the experiment,
only changing the intensity of the light caused the contraction, as if
shock was anticipated. Cross sections of regenerated planarians
retained the entrained association; the head sections that grew new
tails and the tail sections that grew new heads both responded as
significantly as intact planarians (Jacobson and McConnell 1959). The
fact that the tail sections retained the association leads to a
possible biochemical basis for learning.
Results
Cashmore, A.R., Jarillo J.A., Liu D., and Wu Y.J. 1999. Cryptochromes:
Blue Light Receptors for Plants and Animals. Science 284 760-5.
Cipollini, D.F. 1997, Wind-induced mechanical stimulation increases pest
resistance in common bean: Oecologia. 111 84-90.
Coombs, J., Hall, D.O., Long, S.P. and Scurlock, J.M.O. 1985.
Techniques in Bioproductivity and Photosynthesis. 2nd ed.
Pergamon Press, New York, NY.
Galston A.W. and Jaffe M.J. 1966. Physiological Studies on Pea Tendrils.
I. Growth and Coiling Following Mechanical Stimulation. Plant
Physiology 41 1014-1025.
Galston A.W. and Jaffe M.J. 1968. The Physiology of Tendrils. Annual
Review of Plant Physiology 19 417-434.
Jacobson, A.L. and McConnell, J.V. 1959. The effects of Regeneration
Upon Retention of a Conditioned Response in the Planarian. Journal
of Comparative & Physiological Psychology 52 1-5.
Thompson, R. and McConnell, J.V. 1955. Classical Conditioning in the
Planarian, Dugesia dorotocephala. Journal of Comparative &
Physiological Psychology 48 65-68.
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Acknowledgements
I acknowledge the following people for their contributions to the project:
Dr. Bruce Smith, mentor; Dr. Karl Kleiner; and Dr. Bradley Rehnberg
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*LI-COR Li6400 Infrared gas analyser. LICOR Bioscience, Inc. Lincoln, NE
**Scion Image Grabber Software. Scion Corp. Frederick, MD