Thigmotropism and geotropism are two tropic movements of plants. Tropism is the turning of all or part of a plant or an organism in a particular direction in response to an external stimulus. There are different forms of tropism, such as phototropism (response to light), geotropism (response to gravity), chemotropism (response to chemicals), hydrotropism (response to water), thigmotropism (response to mechanical stimulation), traumatotropism (response to wound lesion), galvanotropism, or electrotropism (response to electric current).
The key difference between thigmotropism and geotropism is their movement. Thigmotropism is the directional growth movement of a plant part in response to the touch of an object, while geotropism is the directional growth movement of a plant part in response to gravity.
CONTENTS
1. Overview and Key Difference
2. What is Thigmotropism
3. What is Geotropism
4. Similarities – Thigmotropism and Geotropism
5. Thigmotropism vs Geotropism in Tabular Form
6. Summary – Thigmotropism and Geotropism
7. FAQ: Thigmotropism and Geotropism
What is Thigmotropism?
Thigmotropism is the growth movement of a plant regulated by a stimulus such as touch. This is usually found in twining plants and tendrils. However, it is also found in flowering plants and fungi. In this mechanism, the growth rate on the side of the stem that is being touched is slower than on the opposite side. Thigmotropism occurs due to unilateral growth inhibition.
Figure 01: Thigmotropism
One common example of thigmotropism is ivy using clinging roots to climb up a tree. Another example is the growth of the tendrils of Cucurbita towards the supportive structure like a wall or a pole.
What is Geotropism?
Geotropism is the movement of plant parts in response to gravity. It is also known as gravitropism. The roots grow towards gravity. Therefore, roots are called positively geotropic. However, the stem grows opposite of the gravity. Hence, the stem is negatively geotropic. Geotropism is a usual feature of all higher and many lower plants as well as other organisms such as fungi.
Figure 02: Types of Geotropism
There is also plenty of evidence to prove that roots bend in response to gravity due to a regulated movement of the plant hormone auxin. This is known as polar auxin transport. The root bending in response to gravity regulated by auxin movement was first described in the 1920s in the Cholodny-Went model.
Similarities Between Thigmotropism and Geotropism
- Thigmotropism and geotropism are two types of tropisms.
- Both mechanisms happen due to a stimulus.
- They can be observed in plants as well as other organisms, such as fungi.
- They are very important for plant growth.
Difference Between Thigmotropism and Geotropism
Definition
- The movement of plant parts in response to the direction of touch stimulus is known as thigmotropism.
- The movement of plant parts in response to the direction of gravity is known as geotropism.
Types
- There are two types as positive thigmotropism and negative thigmotropism.
- There are two types as positive geotropism and negative geotropism.
Found in
- Thigmotropism is found in twining plants, tendrils, and fungi.
- Geotropism is found in all higher and many lower plants as well as other organisms such as fungi.
Examples
- Examples of thigmotropism include ivy climbing using clinging roots to climb up a tree and the growth of the tendrils of Cucurbita towards the supportive structure like a wall or a pole.
- Root bending of all plants towards gravity regulated by auxin transport is an example of geotropism.
The following table summarizes the difference between thigmotropism and geotropism.
Summary – Thigmotropism vs Geotropism
Thigmotropism and geotropism are two types of tropisms. Thigmotropism can be defined as the plant part’s directional growth movement in response to touch stimulus, while geotropism can be defined as the plant part’s directional growth movement in response to gravity. This is the basic difference between thigmotropism and geotropism.
FAQ: Thigmotropism and Geotropism
1. What is thigmotropism and examples?
- Growth movement of plants in response to touch stimulus is known as thigmotropism. For example, tendrils of the Sweet Pea plant coils around support through this mechanism.
2. What is positive and negative thigmotropism?
- Roots depend on touch sensitivity to navigate their way through the soil, when a root feels an object like soil particles, it grows away from it. This is an example of negative thigmotropism. An example of positive thigmotropism is the curling of tendrils around any support.
3. How does thigmotropism help plants?
- Thigmotropism is when plants grow in response to touch stimuli. Plants like vines have small tendrils that curl around walls or trellises. Plants like this don’t usually have strong stems. Therefore, thigmotropism helps these plants to stay upright and keep them growing.
4. What are examples of geotropism?
- The growth movement in response to gravity is called geotropism. Geotropism causes roots to grow downward and stems and leaves to grow up.
5. What are the two types of geotropism?
- The two types of geotropism are positive geotropism and negative geotropism. Positive geotropism is the downward growth of plant structures, such as roots. Negative geotropism is the upward growth of plant structures, such as the shoots.
Reference:
1. “Thigmotropism – An Overview.” ScienceDirect.
2.“Tropism.” Encyclopædia Britannica, Encyclopædia Britannica, inc.
Image Courtesy:
1. “Brunnichia Ovata” By Christopher Meloche, USDA ARS – Agricultural Research Service, the research agency of the United States Department of Agriculture (Public Domain) via Commons Wikimedia
2. “Geotropism” By LauraVitsut – Own work (CC BY-SA 4.0) via Commons Wikimedia
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