Thigmotropism of a Morning Glory Plant

Thigmotropism
of a Morning
Glory Plant
By Julian Hind
6a
AHS Theodor Kramer Science Expo
Table of Contents
i. Plagiarism pledge:...........................................................................................................................1
ii. Abstract: .......................................................................................................................................... 3
iii. Zusammenfassung:......................................................................................................................... 4
iv. Acknowledgements:.......................................................................................................................4
1. Introduction ........................................................................................................................................ 5
2. Aim: .................................................................................................................................................... 8
3. Hypothesis........................................................................................................................................... 8
4. Method ............................................................................................................................................... 8
5. Results ............................................................................................................................................... 10
6. Discussion of Results ......................................................................................................................... 14
7. Discussion – errors and modifications .............................................................................................. 15
8. Conclusion: ........................................................................................................................................ 16
9. References: ....................................................................................................................................... 17
iv. Acknowledgements:
I would like to thank my mother for driving me to the garden center so I could
buy the equipment required for the experiment. I’d also like to thank the
worker at the garden center, who gave me advice on how to use the soil
efficiently.
ii. Abstract:
Thigmotropism is the response of an organism (in this case plants) to touch.
The vines of a morning glory plant were to be touched and the degree of their
responding curl should have theoretically been measured. However, the plants
died even after the third attempt, meaning that no such results were recorded
whatsoever. One can still for example discuss why the plants would only reach
a certain height before eventually curling up and dying. I have come to the
conclusion that it is nearly impossible to grow plants that need a lot of sunlight
in winter and that the pots of the Morning Glory plants may have been too
small.
1. Introduction
Thigmotropism is the movement of a plant in the direction of touch. “thigmo”
is Greek for touch and “tropism” means moving in a certain direction in
response to a specific factor (e.g. hydrotropism = movement in the direction of
water, phototropism = movement in the direction of light etc…). This can be
observed especially well by the Morning Glory plant and The Sweet Pea plant.
However, it is not the plant’s stem that reacts to touch, but the tendrils of the
plant. This only works with very few plants, since not many have tendrils. The
reason why tendrils actually curl after they are touched is cellular growth. The
side of the tendril that perceives the contact by the touching stimuli
compresses while the opposite side of the tendril expands. The reason why
plants can sense the contact made by touch stimuli so well are the fine hairs on
the surface of its tendrils. So what this contact actually does is stimulate “cell
growth”, because the tendril doesn’t just tend to curl, but also rotates
sometimes even multiple times given enough time. Thigmotropism is often
compared to geotropism, which is a plant’s organ growing in the direction of
gravity, so downwards. This process occurs with a plant’s roots and was
already discovered by Charles Darwin (1880). He even tried to “force” a plant’s
roots to grow upwards by placing touching stimuli in its growing path.
Although he managed to make the roots grow horizontally they would always
end up growing downwards again. This proved that the growth of a plants
roots are based on positive geotropism, while the stem for example is based
on negative geotropism, which basically means that it grows upwards so
against gravity. Actually the principle is very similar with thigmotropism,
because additionally to a root growing in the direction of gravity it also tries to
grow away from objects in the soil or even just the denser soil, so it can have
an easier, smoother growing path. Therefore its growth is based on negative
thigmotropism as well. Tendrils on the other hand grow towards objects and
eventually start to curl around these. An interesting fact is that many plants
are far more sensitive to touch than even the human skin, which can only
detect a thread with a minimum weight of 2-3 mg being drawn across it. A
feeding tentacle of the insectivorous sundew plant can detect a thread
weighing 8-4 mg being drawn across and the tendril of a Sicyos can even
respond to one weighing 2.5 X 10-3. With the constant advance of genetic
engineering it may be possible one day to make the human skin so sensitive
that it could detect germs or bacteria.
iii. Deutsche Zusammenfassung:
Thigmotropismus ist eine Krümungsbewegung des Rankens einer Pflanze, als
Reaktion auf einem Berührungsreiz. Die Ranken einer Trichterwinde hätten
regelmäßig für eine kurze Zeit berührt werden sollen und hätten sich nach
einiger Zeit krümmen sollen. Danach hätte ich bei jeder Pflanze, den Winkel
der Rankenrotation abgemessen. Allerdings ist dies nicht zustande gekommen,
weil die Pflanzen immer einen gewissen Punkt ihres Wachstums erreichen
würden bis sie eventuell abgestorben sind. Man könnte beispielsweise noch
diskutieren was die Ursachen dafür waren, z.B. das die Pflanzen wenig bis
keinen Sonnenlicht bekamen, weil es Winter war, obwohl sie eigentlich viel
gebraucht hätten. Nun kann ich festellen, dass die Töpfe der Pflanzen
möglicherweise zu klein waren und dass es fast unmöglich ist Pflanzen im
Winter anzubauen, die recht viel Sonnenlicht benötigen.
2. Aim:
How do the vines of a plant actually react to touch and how long does it take
to see an actual response? In this experiment, I will test the thigmotropism of a
morning glory plant. One good reason to perform this experiment, is that one
can see how organisms, in this case plants can react to certain touch stimuli.
Most of my research is from http://www.sciencebuddies.org, http://www.plant-and-flowerguide.com and http://www.biology-online.org. The differences between my
experiment and the internet one’s are that I will touch the tendrils with my
hand and/or a pencil for 45 seconds instead of 30 seconds. I will also test if I
can make an already curled tendril uncurl, by touching its outer surface.
3. Hypothesis
If I grow the Morning glory plants until they have tendrils and touch them with
touch stimuli such as a pencil for a short while, they will eventually start to
curl.
4. Method
 First I will plant morning glory seeds in 10 small pots. By watering them
regularly and giving them enough light they will have grown tendrils
after roughly three to four weeks. After these have grown I will insert a
pencil into the soil so that it is touching the tendril. I will repeat this for 2
additional tendrils. Theoretically these should then start to curl around
the pencils, because they see them as a support. I plan to collect data
about the time they started to curl, the angle of the curl and I will take
pictures of these occurrences. Then I will experiment with the stimuli. I
will select 15 different tendrils from various plants and mark the tips of
them with a permanent marker, which is the point where they will be
touched for 45 seconds each day. 3 tendrils will be touched once a day,
3 will be touched 3 times a day and 3 will be touched 6 times a day.
However, 3 will be touched permanently and 3 won’t be touched at all.
 In this experiment the independent variable will be the duration of
touch on the tendrils, since those will be the variables that will be
changed. The dependent variable will be the curling of the tendrils and
rotations they make which will be carefully observed. The controlled
variables will be the same type of touch stimuli used, the same size pot,
same amount of seeds planted and the same type of plant in each pot.
I will record the degree of curl from the tendrils, in my lab notebook, graph the
time it took for each tendril to start curling for the number of times it was
touched and finally as well graph the time it took for each tendril to achieve a
full rotation in response to the number of times it was touched.
5. Results
Since the results that were intended to be gathered, like the angle of the
rotation of the tendrils or the time it took for each tendril to pursue a full
rotation, could not be due to the lack of growth of the plants, I can only display
images that range from the beginning of the Morning Glory’s growth till the
eventual death.
-
(Image a: newly potted plants with fresh soil and water)
(Image b: Newly planted morning glories [horizontal view])
This was still the very first stage of the planting process. There seemed to be
enough light which can be clearly noticed in image a. Also the surface was
steady and the amount of water was more than enough.
(Image c: third day) First signs of growth
(Image d: third day) First signs of growth
(Image e: after roughly 1 week)
(Image f: after roughly 1 week) Phototropism is visible
(Image g: after 2.5 weeks) Plants slowly dying
(Image h: After 3 weeks)
6. Discussion of Results
Although the initial aim for thigmotropism-related results couldn’t be fulfilled, I
could still observe a few attributes in relation to plant growth in general for
instance: in image c the plants first started growing out of the soil. While
observing this I noticed that some plants were growing faster than others and
that the plants had an orange like color, before eventually turning green. In
image d there is also an interesting observation. The plants that were receiving
the least light were growing at the same pace, if not even faster than the ones
who were receiving the most light which were the ones nearest to the window.
It can also clearly be seen that in images f and e the plants are leaning towards
the light coming from the window. This actually demonstrates phototropism
very well. However, soon after this a trend started to develop which was the
each plant would look healthy, but as soon as it reached a certain height (~20
cm) it would start to hang and eventually dry up and die. One might think that
they were dying, because of dehydration, but this couldn’t have been the case
since the soil was often damp.
7. Discussion – errors and modifications
Obviously this experiment just couldn’t work at all, because of the many
errors. First there was the time of year. Even though it is definitely possible to
grow plants indoors in winter it is still a challenge to grow ones that have to be
exposed to a lot of sunlight. I was also missing the equipment to produce
artificial sunlight which might’ve aided their growth. Another modification
would be to use less plants but bigger and better quality pots. I am almost
certain now that the pots were just far too small for the roots to keep growing.
Positive geotropism just wasn’t possible anymore. If I would have had more
time I would have rather done just bought bigger pots and maybe waited till
the winter months had passed.
8. Conclusion:
To conclude, I failed to find out in how far the tendrils of a morning glory plant
curl and rotate. Due to the plants dying, even after three times of trying to
plant them, no valuable results could be collected that would prove my
hypothesis right. Phototropism could be demonstrated for a short period of
time. Positive geotropism may have been a reason for the plants always curling
up and dying.
9. References:
(2002). Abgerufen am 23. October 2012 von Science Buddies: http://www.sciencebuddies.org
(2009). Abgerufen am 23. October 2012 von Plant-and-Flower-Guide.com: http://www.plant-andflower-guide.com
(2001). Abgerufen am 1. October 2012 von Biology online: www.biology-online.org
http://biology.kenyon.edu/edwards/project/steffan/b45sv.htm
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