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-flower-

guide.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.

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(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-and-

flower-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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