Kinetics of phytochrome decay in Amaranthus seedlings.

In Amaranthus seedlings the disappearance of the unstable P fr form of phytochrome does not involve dark reversion to P r . The rate constant for the decay of total phytochrome under continuous illumination is directly related to the proportion in the P fr form. This relationship allows calculations to be made of the proportion of P fr under continuous far-red illumination where the amount is too low to be measured directly.