What happens if we continuously stimulate a mimosa plant?

Question

I know there is some mechanism in humans by which we start to ignore a certain stimuli if it persists for a long time (e.g., we don't feel our shoes all the time !).

Can the same thing happen in Mimosa pudica? Can it again get it's original arrangement of leaves if it is stimulated without interruption?

I think it should do this, otherwise it will not be able to grow if it is surrounded by bushes from all the sides as it will be stimulated constantly and so will be unable to photosynthesize properly.

Answer 1

This has actually been experimentally shown by multiple scientists, who all came to the conclusion that Mimosa plants, when constantly stimulated, eventually become insensitive to these stimuli.

This page of the Google Books preview of the book Invertebrate Learning presents a number of primary sources on Mimosa and other plants which react to tactile stimulation. While most of these primary sources could not be immediately found by a Google search, I was able to find the original book by Bose (1906) which describes habituation in the Mimosa plant. (Chapter IX, Page 109)

It will be found, however, that if a Mimosa leaf be continuously stimulated by successive blows or taps, in the manner of Pfeffer's Normal Response experiment, the leaf Will at first fall. But, though the blows be continued, the petiole will, after a time, return to its normal erect position. In this erect posture, however, further blows prove to have no effect upon it, the leaf being now insensitive.

Answer 2

Mimosa leaves have mechanoreceptor cells which sense the mechanical stress through proteins called mechanoreceptors (they are similar to the ones responsible for sense of touch in animals). When stimulated the mechanoreceptors cause ion channels to open leading to depolarization. This generates an action potential (AP; like neurons) which in turn activates the motor cell (Visnovitz et al., 2007). Motor cells cause leaf movements by change in their interior turgor pressure (similar to opening and closing of stomata).

Repolarization (like in neuronal AP) takes time and Mimosa would not respond to stimuli that are too frequent. The time required for the turgor pressure to relax would be an additional factor.

I am no plant biologist but if I compare this situation with that in neurons, I can speculate that long term non-responsiveness similar to LTD may happen because of down-regulation of mechanoreceptors. It has actually been shown that Mimosa does actually become insensitive to a persistent stimulus such as a continual water drop and moreover exhibits a long-term "memory" of this non-responsiveness (Gagliano et al., 2014). However, the exact molecular mechanism has not been elucidated. Again, there would be thresholds (on amplitude and frequency) for the signal to elicit these kind of changes.

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References

• Visnovitz T, Világi I, Varró P, Kristóf Z. Mechanoreceptor Cells on the Tertiary Pulvini of Mimosa pudica L. Plant Signaling & Behavior. 2007;2(6):462-466.

• Gagliano, Monica, et al. "Experience teaches plants to learn faster and forget slower in environments where it matters." Oecologia 175.1 (2014): 63-72.