A detailed analysis of phytochrome decay and dark reversion in mustard cotyledons.

During the first 10 min after a saturating dose of red light, 72 h dark-grown mustard cotyledons show no phytochrome decay. Within the same time interval there exists a transient form of P fr (=P fr (T) ) which is no longer photoconvertible at 0°C, but is at 25°C. This P fr (T) converts in the dark to P fr and P r . These "dark reversions" take about 10 min. After a lag phase of 10 min the P fr decay can be described by a single, first order kinetic curve. The time courses of these reactions are functions of the time of etiolation.