Phytochromes

Definition

Phytochromes are a class of photoreceptor proteins in plants that detect light and mediate various physiological responses to it. They play crucial roles in regulating processes such as seed germination, stem elongation, and flowering time.

5 Must Know Facts For Your Next Test

1. Phytochromes exist in two interconvertible forms: Pr (inactive) and Pfr (active).
2. Red light converts Pr to Pfr, while far-red light converts Pfr back to Pr.
3. The ratio of Pr to Pfr helps plants determine the quality of light in their environment.
4. Phytochromes regulate circadian rhythms and photoperiodism, influencing flowering time based on day length.
5. They can also trigger shade avoidance responses, prompting plants to grow taller when under canopy cover.

Review Questions

Related terms

Phototropism:

The growth of a plant toward or away from light due to differential cell elongation.

Photoperiodism:

The physiological reaction of organisms to the length of day or night, affecting processes like flowering.

Circadian Rhythms: Internal biological clocks that cycle roughly every 24 hours, influencing various physiological processes.