Phytochromes have two interconvertible forms that are ‘Pr’ and ‘Pfr’. The red light of about 667 nm is absorbed by Pr and is immediately converted to Pfr. Far-red light of about 730 nm is absorbed by Pfr which results in quick conversion to Pr. The active form of protein is mainly ‘Pfr’ and therefore, exposure to red light increases physiological activity. Exposure to far-red light inhibits chromophore activity and therefore inhibits phytochrome activity. Combining these two forms builds the phytochrome system.
Phytochrome does not mediate plant infection.
The activated Pfr form slower the growth of the plant.
The activated Pr form induces the growth of the plant.