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

Problem 2

Chapter 36, Problem 2

Which of the following statements about phytochrome is not correct? a. It is photoreversible. b. Its function was understood long before the protein itself was isolated. c. The Pfr form activates the responses to red light. d. It is involved in guard-cell opening.

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Identify the key terms and their roles: Phytochrome is a photoreceptor protein in plants that is sensitive to light, particularly red and far-red light. It exists in two forms: Pr (red light absorbing) and Pfr (far-red light absorbing).

Understand the concept of photoreversibility: Phytochrome is photoreversible, meaning it can switch between Pr and Pfr forms depending on the light it absorbs. This is a reversible transformation triggered by red and far-red light.

Review historical context: The statement that the function of phytochrome was understood before the protein was isolated is correct. Early experiments deduced its role in light detection and plant development before the protein itself was characterized.

Analyze the role of Pfr: The Pfr form of phytochrome is indeed responsible for activating responses to red light, such as seed germination and flowering, which aligns with the statement provided.

Evaluate the involvement in guard-cell opening: Phytochrome primarily regulates processes like flowering and seed germination, not guard-cell opening. Guard cells, which control the opening and closing of stomata, are more directly regulated by blue light receptors and environmental conditions like CO2 concentration and humidity.

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Key Concepts

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

Phytochrome Function

Phytochrome is a photoreceptor protein in plants that detects light and regulates various physiological processes, including seed germination, flowering, and shade avoidance. It exists in two interconvertible forms: Pr (red light-absorbing) and Pfr (far-red light-absorbing), which play crucial roles in signaling pathways that respond to light conditions.

Photoreversibility

Photoreversibility refers to the ability of phytochrome to switch between its Pr and Pfr forms upon exposure to different wavelengths of light. This property allows plants to adapt their growth and development in response to changing light environments, making it essential for processes like phototropism and circadian rhythms.

Guard Cell Function

Guard cells are specialized cells that surround stomata and regulate gas exchange in plants. Phytochrome influences guard cell opening by mediating responses to light, which affects transpiration and photosynthesis. Understanding this relationship is vital for comprehending how plants optimize their water use and gas exchange in varying light conditions.

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