Corn and mustard seedlings grown either in the light or the dark

Lettuce seed germination is a typical photoreversible response

Absorption spectra of purified phytochrome in the Pr and Pfr forms overlap

Three types of phytochrome responses, based on their sensitivities to fluence

LFR action spectra for photoreversible stimulation / inhibition of seed germination

Structure of the Pr and Pfr forms of the chromophore

Figure 17.7 Several structural domains in phytochrome and cellular changes it mediates

N-terminal portion of a bacterial phytochrome

Figure 17.9 (B) Plant phytochrome

Figure 17.10 Nuclear localization of phy–GFP in epidermal cells of Arabidopsis hypocotyls

Figure 17.11 Phytochrome deficiencies alter growth and development in pea and tomato

Figure 17.12 Differences in phytochrome gene family structure and function

Phytochrome activity is modulated by phosphorylation status

• Phytochrome activation affects membrane potential (~5 sec)

• Phytochrome affects transcription (lag time of less than 5 min)

Transcriptional regulation

• Phytochrome interacting factors (PIFs) act as negative regulators of phytochrome response: PIF mutants exhibit a constituative photomorphogenic response even when plants are grown in the dark.

• Phytochrome initiates degradation of PIFs in the nucleus

Shade avoidance

Figure 25.23 Phytochrome control of flowering by red (R) and far-red (FR) light