Difference Between Thigmotropism and Thigmonasty

The key difference between thigmotropism and thigmonasty is that thigmotropism is a directional response of a plant organ to touch or physically contact a solid object. Meanwhile, thigmonasty is a form of non-directional movement by a plant in response to touch or vibration.

Living organisms respond to different internal and external stimuli. Especially, plants show different movements and growth responses to external stimuli. Tropic and nastic movements are two types among these different movements. Tropic movements are growth movements towards or away from the stimulus. Nastic movements are plant movements that are independent of the direction of the stimulus. Thigmotropism and thigmonasty are two types of tropic and nastic movements, respectively. In both types, the external stimulus is touch or contact.

CONTENTS

1. Overview and Key Difference
2. What is Thigmotropism 
3. What is Thigmonasty
4. Similarities Between Thigmotropism and Thigmonasty
5. Side by Side Comparison – Thigmotropism vs Thigmonasty in Tabular Form
6. Summary

What is Thigmotropism?

Thigmotropism is the directional movement shown by a plant organ to touch or physical contact, especially with a solid object. This response is a result of differential growth. The best example for thigmotropism is the tendrils (thread-like structures) that coil around solid objects. Plant tendrils, when in contact with a solid object, start coiling and climbing around it in order to provide structural support to the climbing plant. Tendrils do not need light to respond to the touch. They only need continuous contact with the surface. Moreover, some plants have clinging roots to climb up and cling to trees. These clinging roots also show thigmotropism when in contact with a solid object.

Several factors affect thigmotropism in plants. Among them, calcium channels and auxin hormone are two of the most important factors. Besides these, thigmotropism can be positive thigmotropism or negative thigmotropism. Tendrils (which grow towards the touch) show positive thigmotropism while roots (which grow away from the touch) show negative thigmotropism. While growing, if touched with a solid object, roots grow away from it by changing the direction and looking for the areas of least resistance.

What is Thigmonasty?

Thigmonasty is a type of nastic movements shown by plants to touch or vibration. But, unlike thigmotropism, thigmonasty is independent of the direction of the stimulus. So it is a non-directional response which is not influenced by the direction of the stimulus.

Moreover, the thigmonastic responses are mainly due to the changes in turgor pressure within the cells rather than the movements caused by plant growth. The closing of the Mimosa pudica leaves in response to touch is the best example for thigmonasty. Another example is the shutting of venus fly-trap.

What are the Similarities Between Thigmotropism and Thigmonasty?

• Thigmotropism and thigmonasty are two different types of plant movements shown by plants in response to the stimulus touch.

What is the Difference Between Thigmotropism and Thigmonasty?

Thigmotropism is a directional movement of plants in response to the stimulus of touch. In contrast, thigmonasty is a non-directional movement of plants in response to the stimulus of touch. So, this is the key difference between thigmotropism and thigmonasty. Moreover, the direction of thigmotropic response depends on the direction of the stimulus, while the direction of thigmonastic movement is independent of the stimulus’s position. Therefore, this is also a difference between thigmotropism and thigmonasty.

Another difference between thigmotropism and thigmonasty is that thigmotropism takes place as the stimulation of growth in particular regions of the plant while thigmonasty is generally associated with changes in turgor pressure within the cells rather than the growth. When considering examples, coiling of plant tendrils around a solid surface and the growth of roots in the soil are two examples for thigmotropism while the closing of Mimosa pudica leaves and shutting of venus fly-trap are two examples for thigmonasty.

Summary – Thigmotropism vs Thigmonasty

Thigmotropism and thigmonasty are two types of responses to the stimulus touch. The key difference between thigmotropism and thigmonasty is that thigmotropism is a directional response to the touch while thigmonasty is independent of the direction of the touch. Moreover, thigmotropism occurs as a result of growth response while thigmonasty occurs due to changes in turgor pressure within the cells rather than the growth.

Reference:

1 “Thigmonasty.” Biology, 12 May 2014, Available here.
2. “Thigmotropism.” Wikipedia, Wikimedia Foundation, 1 Dec. 2019, Available here.

Image Courtesy:

1. “Brunnichia ovata” By Christopher Meloche, USDA ARS – released by the Agricultural Research Service, the research agency of the United States Department of Agriculture (Public Domain) via Commons Wikimedia
2. “Mimosa pudica” By Tauʻolunga – Own work (CC BY-SA 3.0) via Commons Wikimedia