[Kinetical studies to interpret the effects of succedaneous irradiations with red and far-red on photomorphogenesis (anthocyanin synthesis in mustard seedlings, Sinapis alba L.)].

In a previous paper (BERTSCH and MOHR, 1965) we reported that in light-induced anthocyanin synthesis of the mustard seedling (Sinapis alba L.) a preirradiation with far-red light increases the effectiveness of a following irradiation with red light, whereas a preirradiation with red reduces the effectiveness of a following irradiation with far-red (Table 1). The amount of anthocyanin present 48 hours after the onset of the irradiation programme was taken as a gauge for the effectiveness of the irradiation with succedaneous red and far-red (and vice versa).In the present paper it is shown-using detailed kinetical studies (Fig. 1 and 2) -that a specific potentiating effect of the preceding far-red is not involved. The apparent effect is due to the fact that the preceding far-red eliminates the lag-phase for the following red (Fig. 1). - On the other hand, the depressing effect of red light preceding far-red is very real. This latter effect must be attributed to a loss of phytochrome.We demonstrate in the present paper that the effects of succedaneous red and far-red irradiations can be attributed altogether to phytochrome if several assumptions concerning the stability of phytochrome 730 (HARTMANN, 1966; WAGNER and MOHR, 1966) are made. These assumptions seem to be well justified. - In any case our kinetical studies have revealed no data which indicate that in red or far-red light we have to deal with anything else except phytochrome.