EnvReg213-page9 - Changing ratios of Pr and Pfr also permit...

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Plant Environmental Regulators - 9 The two forms of phytochrome, which have different conformations, are: Pr (for phytochrome red form) is the inactive form Pfr (for phytochrome far-red form) is the active form P r absorbs red light, which converts phytochrome to P fr P r is stable in the absence of light (darkness) P f r absorbs far red light, which converts phytochrome to P r P fr is also converted to P r in the dark in many plants. (Darkness destroys P fr) . Phytochrome Balance In most plants, there is a changing balance between Pr and Pfr during daylight hours that provides data to the plant about light conditions.
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Unformatted text preview: Changing ratios of Pr and Pfr also permit tracking the changing seasons and days, data important to biological clocks and circadian rhythms. For example, trees in shade are exposed to less red light and more far red light, and in response to the far red light, elongate and grow taller. Phytochrome Actions Phytochrome promotes gene transcription. It has roles in the following: • Seeds germinate and seedlings undergo etiolation in the absence of light. Etiolation ceases when the seedling is exposed to red light. Etiolated seedling on left...
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This note was uploaded on 01/08/2012 for the course BIO 213 taught by Professor Makina during the Fall '09 term at SUNY Stony Brook.

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