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Plant Responses to Mechanical Stimuli

Plant Responses to Mechanical Stimuli
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  • 0:02 Mechanical Stimuli
  • 0:27 Thigmomorphogenesis
  • 1:16 Thigmotropism
  • 1:55 Thigmonasty
  • 3:31 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov
Did you know that animals are not the only living things able to respond to touch? Plants have a sense of touch. Actually, plants respond to all sort of mechanical stimuli, as this lesson explains.

Mechanical Stimuli

All else held equal, children who lift heavy weights as they are growing tend to develop shorter and stockier physiques than those children who do not.

This is partially explained by the mechanical stimulus: the heavy lifting imparts on their forming bones. In essence, the body adapts to its environment.

The forms plants take are also influenced by mechanical changes - the kinds you're about to learn.

Thigmomorphogenesis

For instance, plants that live in very windy environments tend to have shorter and stockier trunks than plants of the same species that grow in less windy environments. Such a trunk has adapted to the mechanical forces the high winds impart on the plant.

The proper term for this is thigmomorphogenesis, the influence generally long-term mechanical stimuli implant on plant growth and development. This long word comes from 'thigma,' which means 'to touch.'

But thickened plant parts in response to lots of wind for a long period of time isn't the only way a plant changes its shape.

This is because plants can change in quite a few spectacular ways when under the influence of all sorts of mechanical stimuli.

Thigmotropism

Remember the last time you were playing on the monkey bars? You extended your hand all the way up, and as soon as you sensed the bar against your hand, you coiled your fingers around the bar?

Plants use a touch-based technique to alter their growth as well. This is clearly evidenced in plants, like vines, which grow basically straight up until they come into contact with something, like a branch, which causes them to quickly coil around the branch.

The technical term for this is thigmotropism, the directional movement and growth of a plant in response to touch.

Thigmonasty

Note how the vine doesn't just move in any direction, it moves in a purposeful direction around the branch, toward the side where it sensed something.

This is different from thigmonasty, the touch- or vibration-induced movement or curvature of a plant in a certain direction or manner that is independent of the direction from which the stimulus appears.

A good example of this is the very famous Venus flytrap. This plant closes its leaves in the same manner regardless of which direction the stimulus, like a fly, is coming from.

Another example is the plant Mimosa pudica, which folds its leaflets when touched. It does so quite quickly.

The question should also be why it does this. Why does the plant bother to expend energy on something like this?

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