Leaflets of Mimosa pudica (common names: sensitive plant, touch-me-not) have a remarkable ability to close up in response to being touched or physically moved.
How fast can the leaflets close?
How does this occur?
And more importantly, what benefit could this unusual response provide to the plant?
Researchers studied the rate of closing and reopening of leaflets by measuring changes in the distance between opposing leaflets after being touched. Their results are shown in the accompanying graph (d/dmax is actual leaflet distance relative to maximal leaflet distance).
How long does it take for leaflets to close?
How long to reopen?

Verified step by step guidance

1. Examine the graph provided in the problem, which shows the change in leaflet distance (d/dmax) over time after being touched.
2. Identify the point on the graph where the leaflets begin to close after being touched. This is typically marked by a rapid decrease in d/dmax.
3. Determine the time it takes for the leaflets to reach their minimum distance (fully closed position) by noting the time interval from the initial touch to the point where d/dmax is at its lowest.
4. Observe the graph for the reopening phase, which is indicated by an increase in d/dmax after reaching the minimum distance. Note the time it takes for the leaflets to return to their maximal distance (fully open position).
5. Consider the biological significance of this response. The rapid closing of leaflets may serve as a defense mechanism against herbivores or environmental stress, potentially deterring predators or minimizing damage.

Key Concepts

Thigmonasty

Thigmonasty refers to the non-directional movement of plant parts in response to touch or physical stimuli. In Mimosa pudica, this rapid movement is facilitated by changes in turgor pressure within the pulvini, specialized cells at the base of the leaflets. When touched, these cells lose water, causing the leaflets to close quickly as a defense mechanism.

Turgor Pressure

Turgor pressure is the force exerted by fluid inside the cell against the cell wall, crucial for maintaining plant rigidity and facilitating movement. In Mimosa pudica, changes in turgor pressure within the pulvini cells lead to the rapid closing of leaflets. This pressure change is triggered by ion fluxes that cause water to move out of the cells, resulting in leaflet movement.

Adaptive Significance

The closing of Mimosa pudica leaflets is thought to be an adaptive response to deter herbivores and protect the plant from harm. By closing quickly, the plant may appear less appealing or more difficult to consume, thus reducing the likelihood of being eaten. This response can also minimize water loss and protect against environmental stressors.