Arabidopsis phytochromes C and E have different spectral characteristics from those of phytochromes A and B

The red/far-red light absorbing phytochromes play a major role as sensor pr oteins in photomorphogenesis of plants, In Arabidopsis the phytochromes bel ong to a small gene family of five members, phytochrome A (phyA) to E (phyE ). Knowledge of the dynamic properties of the phytochrome molecules is the basis of phytochrome signal transduction research. Beside photoconversion a nd destruction, dark reversion is a molecular property of some phytochromes . A possible role of dark reversion is the termination of signal transducti on. Since Arabidopsis is a model plant for biological and genetic research, we focussed on spectroscopic characterization of Arabidopsis phytochromes, expressed in yeast. For the first time, we were able to determine the rela tive absorption maxima and minima for a phytochrome C (phyC) as 661/725 nm and for a phyE as 670/724 nm. The spectral characteristics of phyC and E ar e strictly different from those of phyA and B. Furthermore, we show that bo th phyC and phyE apoprotein chromophore adducts undergo a strong dark rever sion. Difference spectra, monitored with phycocyanobilin and phytochromobil in as the apoprotein's chromophore, and in vivo dark reversion of the Arabi dopsis phytochrome apoprotein phycocyanobilin adducts are discussed with re spect to their physiological function. (C) 2000 Federation of European Bioc hemical Societies.