Variation in dynamics of phytochrome A in Arabidopsis ecotypes and mutants

Phytochromes are photoreceptors in plants which can exist in two different conformations: the red light-absorbing form (P-r) and the far-red light-abs orbing form (P-fr), depending on the light quality. The P-fr form is the ph ysiologically active conformation. To attenuate the P-fr signal for phytoch rome A (phyA), at least two different mechanisms exist: destruction of the molecule and dark reversion. Destruction is an active process leading to th e degradation of P-fr. Dark reversion is the light-independent conversion o f physiologically active P-fr into inactive P-r. Here, we show that dark re version is not only an intrinsic property of the phytochrome molecule but i s modulated by cellular components. Furthermore, we demonstrate that dark r eversion of phyA may be observed in Arabidopsis ecotype RLD but not in othe r Arabidopsis ecotypes. For the first time, we have identified mutants with altered dark reversion and destruction in a set of previously isolated los s of function PHYA alleles (Xu et al. Plant Cell 1995, 7, 1433-1443). There fore, the dynamics of the phytochrome molecule itself need to be considered during the characterization of signal transduction mutants.