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. Step 1: Start by understanding the problem. The question is asking about the rate of closing and reopening of leaflets in Mimosa pudica, a plant known for its ability to close its leaflets when touched. The researchers have provided a graph that shows the changes in the distance between opposing leaflets after being touched.
2. Step 2: To find out how long it takes for the leaflets to close, look at the graph and find the point where the leaflets are fully closed. This is where the distance between the leaflets is at its smallest. The time it takes for the leaflets to close is the time from the start of the experiment to this point.
3. Step 3: To find out how long it takes for the leaflets to reopen, look at the graph and find the point where the leaflets are fully open again. This is where the distance between the leaflets is back to its maximum. The time it takes for the leaflets to reopen is the time from when they started closing to this point.
4. Step 4: The mechanism of this movement is due to a process called thigmonasty or seismonasty, where the plant responds to physical stimuli. In the case of Mimosa pudica, when the leaflets are touched, an electrical signal is sent that causes water to move out of the cells at the base of the leaflets, causing them to close.
5. Step 5: The benefit of this unusual response could be to deter herbivores. When the leaflets close, the plant may appear less appetizing or may startle the herbivore, causing it to move on to another plant. Additionally, the movement could help to shake off insects or other small creatures that may be on the leaflets.

Key Concepts

Thigmonasty

Thigmonasty is a type of plant movement that occurs in response to touch or mechanical stimulation. In Mimosa pudica, this rapid movement is a defense mechanism that helps the plant avoid herbivory by making it less appealing to potential grazers. The leaflets close quickly when touched, demonstrating a non-directional response to stimuli, which is crucial for understanding the plant's behavior.

Turgor Pressure

Turgor pressure is the pressure exerted by fluid in the central vacuole of plant cells against the cell wall, providing structural support. In Mimosa pudica, changes in turgor pressure facilitate the rapid closing and reopening of leaflets. When the plant is stimulated, specialized cells called motor cells lose water, causing a decrease in turgor pressure and resulting in leaflet closure.

Adaptive Significance

The adaptive significance of Mimosa pudica's leaf movement lies in its ability to deter herbivores and reduce water loss. By closing its leaflets when touched, the plant minimizes damage from potential threats and conserves moisture during stressful conditions. Understanding this adaptive response is essential for appreciating how such mechanisms enhance survival and reproductive success in plants.