Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892



Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892
Textbook Problem

Summarize the switching mechanism that operates in plant responses to changes in photoperiod.

Summary Introduction

To review:

The summary of the switching mechanism that takes place in plants when they respond to changes in photoperiod.


The plant activities that are repeated after every 24 hours are called circadian rhythms. The circadian rhythms are regulated by biological clocks of plants during which the leaves of plants get folded when they are asleep. The circadian rhythm is regulated independently of the sunset and sunrise in plants. Photoperiodism is the phenomenon in which the lengths of dark and light period regulate the plant’s response to the environment in a 24-hour period.


The seasonal adjustments in development, growth, and reproduction patterns are made by the biological clocks of plants through the change in the photoperiodism. Plants respond to the change in photoperiod through a phytochrome switch. The plants have photoreceptors in the form of blue–green pigments. The blue–green pigments are also called phytochromes and act as photoreceptors. The sensitivity of phytochromes occurs in response to the light wavelengths that lie in the far red and red region of the spectrum.

Most of the studies have been done on Arabidopsis thaliana, which show that phytochromes exist in two conformations that are Pr (inactive phytochrome) and Pfr (active). The Pr conformation absorbs light wavelengths that lie in the red region of the spectrum and the Pfr absorbs light wavelengths that lie in the far-red region of the spectrum...

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