Stability of phytochrome concentration in dicotyledonous tissues under continuous far-red light.

The phytochrome concentration in dark-grown seedlings of Pisum sativum, Phaseolus aureus and Sinapis alba remained constant under continuous far-red illumination for periods of up to 6 hours. Similar treatment of Zea mays seedlings reduced the phytochrome concentration by more than 60 percent. The results in the dicotyledonous seedlings may be due to the reversion of Pfr to Pr at a rate sufficient to prevent Pfr destruction; no evidence for reversion has been detected in Zea. Typical photomorphogenic responses were observed in the dicotyledonous seedlings in the absence of Pfr destruction.