[Photometric investigations of the phytochrome system in mustard seedlings (sinapis alba L.)]

The behavior of phytochrome has been investigated in hypocotyl tissue of the mustard seedling (Sinapis alba L.) as a function of destruction, "synthesis" and dark reversion (Pfr→Pr). A method has been developed to separate the 3 processes experimentally. The main results are the following: 1. The kinetics under continuous red light ([P730]/[P]=0.8) (Fig. 2) can be explained on the basis of destruction of Pfr and "synthesis" of Pr alone. 2. The destruction is not intensity dependent (Fig. 6). 3. "Synthesis" of Pr seems to start about 2 hours after the onset of red light (Fig. 3). 4. The difference of the curves b and c in Fig. 4 is exclusively due to Pfr destruction. Dark reversion (Pfr→Pr) cannot be detected. 5. From Fig. 4 the kinetics of the Pfr pool was calculated for the program l.5 hours red light, dark. The result is shown in Fig. 5. Within the experimental error the decay constants of the first order decay of Pfr are the same in red light and in the following dark period τ1/2=45±5 min. From theoretical calculations there should be a difference [Eqs. (7)-(13)]. 6. Continuous far-red light has no influence on the "synthesis" of Pr (Fig. 7). 7. Newly "synthesized" phytochrome shows the same behavior as far as destruction under red light is concerned as the original phytochrome. Furthermore after a secondary red irradiation Pr is also "resynthesized" after a lag of about 1.5 hours after the onset of the secondary light treatment (Fig. 8). 8. Phytochrome in the cotyledons behaves very much like the phytochrome in the hypocotyl. The half-time for Pfr-decay is τ1/2=45±7 min. The extent of "synthesis" of Pr is about double the extent in the hypocotyl (Fig. 9). The data create a basis to correlate the status of Pfr as a function of time with the kinetics of a suitable photoresponse. The approach can be described as [Formula: see text].