He proposed that the embryonic development of an individual organism (its ontogeny) followed the same path as the evolutionary history of its species (its phylogeny).

TLS Online TPP Program

#Id: 9810

#Unit 6. System Physiology – Plant

Pfr is the physiologically active forms of Phytochrome

Wild type: short hypocotyl by white light

hy mutant (phytochrome mutant): long hypocotyl by white light

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#Id: 9811

#Unit 6. System Physiology – Plant

A toggle model is for phytochrome interconversion

The structure of the b-hairpin region of Pr is changed to an a helix during the conversion of Pr to Pfr, which initiates other conformational changes in the protein.

TLS Online TPP Program

#Id: 9812

#Unit 6. System Physiology – Plant

There are five phytochrome isoforms in angiosperms

TLS Online TPP Program

#Id: 9813

#Unit 6. System Physiology – Plant

PHYA is the only gene that encodes a Type I phytochrome and predominantly perceives far-red light.

Phytochrome B predominantly perceives red light

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#Id: 9814

#Unit 6. System Physiology – Plant

The PHYA gene is transcriptionally active in dark-grown seedlings, but its expression is strongly inhibited in the light in monocots.

TLS Online TPP Program

#Id: 9815

#Unit 6. System Physiology – Plant

The PRD domain of phyB serve as an NLS. 

Conversion of Pr to Pfr by red light expose the functional NLS of the PRD domain of phyB, facilitating phyB’s import into the nucleus.