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Ch. 37 - Plant Sensory Systems, Signals, and Responses
Freeman - Biological Science 8th Edition
Freeman8th EditionBiological ScienceISBN: 9780138276263Not the one you use?Change textbook
All textbooksFreeman 8th EditionCh. 37 - Plant Sensory Systems, Signals, and ResponsesProblem 16f
Chapter 37, Problem 16f

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?
Mimosa leaflets also close on their own at dusk and reopen at dawn (this cycle develops as a circadian rhythm).
What receptor molecule mentioned in this chapter is likely involved in regulating this process?

Verified step by step guidance
1
Understand the mechanism of leaflet closure in Mimosa pudica: The leaflets close due to rapid changes in turgor pressure within the cells at the base of the leaflets, known as pulvini. This is a result of ion movement, primarily potassium ions, which causes water to follow by osmosis, leading to cell shrinkage and leaflet closure.
Explore the speed of leaflet closure: The closure can occur within seconds of stimulation, which is facilitated by the rapid movement of ions and water in response to mechanical stimuli.
Consider the benefits of leaflet closure: This response may protect the plant from herbivory by making it less appealing to predators or may reduce water loss by minimizing the surface area exposed to the environment.
Examine the circadian rhythm of leaflet movement: Mimosa pudica leaflets close at dusk and reopen at dawn, indicating a circadian rhythm that is likely regulated by changes in light and internal biological clocks.
Identify the receptor molecule involved: The receptor molecule likely involved in regulating the circadian rhythm of leaflet movement is phytochrome, which is sensitive to changes in light and helps synchronize plant activities with day-night cycles.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Thigmonasty

Thigmonasty refers to the rapid movement of plant parts in response to touch or physical stimuli. In Mimosa pudica, this 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 against herbivores or environmental stress.

Circadian Rhythms

Circadian rhythms are internal biological clocks that regulate various physiological processes in organisms over a 24-hour cycle. In Mimosa pudica, these rhythms control the opening and closing of leaflets at dawn and dusk, respectively. This rhythmic movement is thought to optimize photosynthesis during daylight and conserve energy at night, enhancing the plant's survival and growth.
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Phytochrome

Phytochrome is a photoreceptor molecule that plants use to detect light and regulate growth and development processes, including circadian rhythms. In Mimosa pudica, phytochrome likely plays a role in signaling the opening and closing of leaflets in response to light changes at dawn and dusk. This helps synchronize the plant's physiological activities with the day-night cycle, ensuring efficient energy use and protection.
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Textbook Question

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?

The mechanism of leaflet closure is similar to what happens during the shrinking of guard cells and closing of stomata (see Figure 37.22). When in the open position, special cells on the upper surface of Mimosa leaflets are filled with water and are under pressure.

Explain how osmosis and flow of ions into and out of these special cells may be involved in leaflet closure and reopening.

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Textbook Question

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?

If just the leaflets located toward the end of a leaf are touched, the adjacent leaflets close in fairly rapid succession until all leaflets on a leaf close up.

Explain how electrical signaling may be involved in this response.

14
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Textbook Question

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 have hypothesized that rapid leaf movements in Mimosa serve as a defense mechanism (e.g., closing leaflets may deter plant-eating insects).

Propose an experiment to test this hypothesis.