Ch. 37 - Plant Sensory Systems, Signals, and Responses

Problem 10

Chapter 36, Problem 10

In many species native to tropical wet forests, seeds do not undergo a period of dormancy. Instead, they germinate immediately. Predict the role of ABA in these seeds. How would you test your prediction?

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Step 1: Understand the role of ABA (Abscisic Acid) in seed dormancy. ABA is a plant hormone that plays a crucial role in seed dormancy, which is a period when the seed's metabolic activities slow down significantly. ABA helps to maintain this dormancy by inhibiting growth and preventing germination under unfavorable conditions.

Step 2: Predict the role of ABA in tropical wet forest seeds. Given that these seeds do not undergo a period of dormancy and germinate immediately, it can be predicted that the levels of ABA in these seeds might be lower than in seeds that do undergo dormancy. This is because ABA's role in inhibiting growth and maintaining dormancy might not be as necessary in these seeds.

Step 3: Design an experiment to test your prediction. One way to test this prediction would be to compare the levels of ABA in seeds from tropical wet forests that do not undergo dormancy with the levels of ABA in seeds from other environments that do undergo dormancy. This could be done using techniques such as high-performance liquid chromatography (HPLC) or mass spectrometry.

Step 4: Conduct the experiment and analyze the results. If the levels of ABA are indeed lower in the seeds from tropical wet forests, this would support the prediction. If the levels are similar or higher, this would suggest that ABA might have other roles in these seeds beyond maintaining dormancy.

Step 5: Consider other factors. It's important to remember that seed germination and dormancy are complex processes influenced by many factors, not just ABA. Other hormones, environmental conditions, and genetic factors could also play a role.

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Key Concepts

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

Abscisic Acid (ABA)

Abscisic Acid (ABA) is a plant hormone that plays a crucial role in regulating seed dormancy and germination. It typically promotes seed dormancy by inhibiting germination and is involved in stress responses. In species that do not exhibit dormancy, ABA levels may be lower, allowing for immediate germination in favorable conditions.

Seed Germination

Seed germination is the process by which a seed develops into a new plant. It involves the activation of metabolic processes and the growth of the embryo, leading to the emergence of the seedling. In tropical wet forests, the absence of dormancy allows seeds to germinate quickly in response to suitable environmental conditions, ensuring rapid establishment.

Experimental Design for Testing ABA's Role

To test the role of ABA in the germination of seeds that do not undergo dormancy, an experiment could involve treating seeds with varying concentrations of ABA and observing the effects on germination rates. Comparing germination in treated versus untreated seeds under controlled conditions would provide insights into how ABA influences the timing and success of germination.

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Experimental Design Example 1

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Textbook Question

To explore how hormones function, researchers have begun to transform plants with particular genes. In one experiment, a gene involved in cytokinin synthesis was introduced into tobacco plants. Which one of the following results would be expected? a. Individuals produced more lateral branches. b. Stems grew extremely tall and slender. c. Roots were incapable of responding to gravity. d. Stomata were closed most of the time.

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Textbook Question

Suppose that a mutant plant is unable to make methyl salicylate. Explain why it is not likely to survive in the wild.

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Textbook Question

In general, small seeds that have few food reserves must be exposed to red light before they will germinate. (Lettuce is an example.) In contrast, large seeds that have substantial food reserves typically do not depend on red light as a stimulus to trigger germination. State a hypothesis to explain these observations.

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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 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?

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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