Question

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 \(P_{f r}\) form activates the responses to red light. d. It is involved in guard-cell opening.

Short answer

The incorrect statement about phytochrome is c. The \(P_{f r}\) form activates the responses to red light. The correct form should be Pfr, which is the biologically active form produced upon absorption of red light by the Pr form.

Step-by-step solution

Statement a

It is photoreversible: It's true. Phytochrome is photoreversible, meaning it can switch between its two forms: Pr (Red-absorbing phytochrome form) and Pfr (Far-red-absorbing phytochrome form).

Statement b

Its function was understood long before the protein itself was isolated: It's also true. The discovery and understanding of phytochrome's function (as a light sensor and regulator of plant responses) preceded the actual isolation and study of the protein itself.

Statement c

The \(P_{f r}\) form activates the responses to red light: This statement is incorrect. The Pfr (not the \(P_{f r}\) form as written) is the biologically active form and is produced upon absorption of red light by the Pr form. However, it's important to note a small typographical error: \(P_{f r}\) should be written as Pfr.

Statement d

It is involved in guard-cell opening: It's true. Phytochrome (in its Pfr form) has been shown to play a role in the opening of guard cells, which are involved in regulating gas exchange and water loss in plants through the process of transpiration. From our examination of each statement in the context of our knowledge about phytochrome, we can conclude that statement c is incorrect.

Key concepts

Plant Physiology

Plant physiology is the study of how plants function and grow. It encompasses everything from how plants absorb nutrients and water, to how they adapt to their environment. Phytochrome is a part of this field. It's a photoreceptor that lets plants sense light. This ability to detect light is crucial because light affects many aspects of plant growth and development, such as germination, flowering, and circadian rhythms.
Understanding plant physiology helps us comprehend how plants interact with their surroundings. It also informs us about their internal processes. Phytochrome is especially important in these processes due to its role in adjusting plant activities to the light conditions it senses.

• Involves studying plant growth and development
• Explains how plants adapt to environmental changes
• Helps in understanding light-dependent processes in plants

Light Regulation

Light regulation in plants is a fascinating topic. Plants have special receptors that help them perceive light. Phytochromes are one such type of receptor, and they specifically detect red and far-red light. These receptors allow plants to make decisions based on the light quality and quantity they receive.
For example, during early morning or late afternoon, sunlight has a high red to far-red light ratio, signaling specific actions. Phytochromes can switch between their two forms: Pr and Pfr. This switching ability helps them regulate processes like seed germination and flowering.

• Important for optimizing plant growth and productivity
• Helps plants respond appropriately to varying light conditions
• Ensures plants synchronize key developmental events with the external environment

Phytochrome Forms

Phytochromes come in two main forms: Pr and Pfr. The Pr form absorbs red light, which converts it to Pfr. Conversely, Pfr absorbs far-red light and reverts back to Pr. This back-and-forth switching is known as photoreversibility.
Among these forms, the Pfr is generally the active one, triggering various plant responses. This includes processes like seed germination and flowering. Moreover, Pfr can influence guard-cell opening, affecting transpiration rates and gas exchange.
Despite issues in wording, it's key to note that Pfr activation generally follows the conversion of Pr by red light absorption. Understanding these forms and their transitions is essential in plant signaling and response mechanisms.

• Photoreversible with forms Pr and Pfr
• Pfr is typically the biologically active form
• Central to coordinating plant responses to light