4. Thigmotropism a) Stimulus – touch b) Response – the leaves or part of the plant that is touched move or coil away from the touch, or trigger some other action 1) Example: The Venus Fly Trap is a plant that shows thigmotropism. It closes when a bug or some other object touches it.

Example: The Venus Fly Trap is a plant that shows thigmotropism. It closes when a bug or some other object touches it.

An example of thigmotropism is the coiling movement of tendrils in the direction of an object that it touches. On the other hand, the folding movement of the Mimosa pudica leaflets, can be considered as an example of thigmonastism.

Thigmotropism occurs due to actions of the plant hormone auxin. Touched cells produce auxin which then transfers auxin to non-touched cells. These untouched cells then grow faster causing them to bend around the stimulus. The hormone ethylene helps in changing the shape or turgidity of the cell.

If a plant moves towards a stimulus, then it exhibits positive tropism; if a plant moves away from a stimulus, then it exhibits negative tropism. Figure 1: A plant stem showing negative gravitropism and growing upwards away from gravity.

A tropism is a growth toward or away from a stimulus. Common stimuli that influence plant growth include light, gravity, water, and touch. Common tropic responses in plants include phototropism, gravitropism, thigmotropism, hydrotropism, thermotropism, and chemotropism.

Although their procedure confirmed circumnutation, it did not exclude thigmotropism because of the high sensitivity of the roots tips to touch (Massa and Gilroy, 2003). They described that roots of Arabidopsis seedlings grow in a circle when the force of gravity is excluded with clinostats or in true space (Fig. 4).

Plant stems grow up in response to gravity (gravitropism), plant surfaces turn to face the Sun (phototropism), roots grow toward water sources (hydrotropism), and plant tendrils respond to physical touch (thigmotropism).

Typically, thigmotropism is a fairly slow response, but in some plants, it occurs quickly. This is called rapid contact coiling, which occurs due to turgor pressure.

In climbing plants, thigmotropism helps them direct the pattern of growth around an object that is in contact with the plant; the hormones auxin and ethylene are used to facilitate this growth process.

Thigmotropism is a directional growth movement which occurs as a mechanosensory response to a touch stimulus. Thigmotropism is typically found in twining plants and tendrils, however plant biologists have also found thigmotropic responses in flowering plants and fungi.

A thigmonastic response is a touch response independent of the direction of stimulus. In the Venus flytrap, two modified leaves are joined at a hinge and lined with thin fork-like tines along the outer edges. Tiny hairs are located inside the trap.

Thigmonasty differs from thigmotropism in that nastic motion is independent of the direction of the stimulus. For example, tendrils from a climbing plant are thigmotropic because they twine around any support they touch, responding in whichever direction the stimulus came from.

The Venus Flytrap ( Dionaea muscipula) presents a spectacular example of thigmonasty; when an insect lands on a trap formed by two curved lobes of a single leaf, the trap rapidly switches from an open to a closed configuration.

Tropisms are natural responses of organisms to external stimuli. Thigmotropism is a response that’s often seen in plants in response to touch or contact.