TIME-DEPENDENT FORMATION OF PFR-MEDIATED SIGNALS FOR THE INTERACTION WITH BLUE-LIGHT IN MESOTAENIUM CHLOROPLAST ORIENTATION

Fast chloroplast orientation from edge position to face position in Me sotaenium caldariorum is controlled by an interaction of phytochrome w ith a blue-light photoreceptor; blue amplifies the phytochrome message . The time-dependent formation of phytochrome-mediated signals in the transduction chain and the following decline in their physiological ac tivity were investigated. A single red flash of about 4 ms is sufficie nt to induce the generation of signals, as indicated by the effectiven ess of following B. A strong FR flash applied 5 s after the inducing R flash prevents signal formation by photoreversion of Pfr to Pr and de monstrates clearly the involvement of phytochrome. The time-dependent formation of the Pfr-mediated signals was studied by inserting a varia ble dark period between the R Bash and the FR Bash. Within 1 min the g eneration of signals is saturated at a level, which is determined by t he Pfr-gradient. Half-maximal response can be obtained after about 20 a. The physiological competence of the signals to interact with the ac tivated B-photoreceptor decreases within approximately 5 min, as inves tigated by a variable dark interval between the FR flash and the onset of B. As the memory of a R pulse lasts also for about 5 min in the pr esence of Pfr, it is concluded that a newly formed Pfr-gradient is eff ective in Mesotaenium only for a very short time to generate a distinc t lever of signals in the transduction chain, i.e. for about 1 min.