[The increase of phytochrome-mediated anthocyanin synthesis in the mustard seedling (Sinapis alba L.) by chloramphenicol]

Chloramphenicol (CAP) within a certain range of concentration (about 20-30μg/ml) increases the rate of far-red mediated anthocyanin accumulation in the mustard seedling (Sinapis alba L.) (Fig. 1). The lag-phase after the onset of far-red and the time of termination of anthocyanin synthesis are not influenced by the presence of the antibiotic (Fig. 2). With and without CAP we observe a constant rate of anthocyanin accumulation over a period of at least 24 hours after the lag-phase at all far-red intensities investigated (Fig. 2). The percentage increase of the rate of anthocyanin accumulation which is due to CAP (20 μg/ml) is independent of the far-red intensity applied and always amounts to about 25% (Table). Formally one can conclude that CAP and far-red seem to act as two independent factors in a multiplicative system. On the "molecular" level the observations can possibly be explained as follows: CAP at a concentration of 20 μg/ml inhibits protein synthesis of the plastids. This inhibition leads to an increase of the pool of phenylalanine in the cotyledons. Because the small concentration of CAP does not interfere with protein synthesis (enzyme synthesis) in the cytoplasm, far-red mediated anthocyanin synthesis can proceed normally. Since phenylalanine acts as a precursor of flavonoids the increased pool of this substance will lead to an increase in the rate of anthocyanin accumulation.

["Primary" and "secondary" differentiation in connection with photomorphogenesis of seedlings (Sinapis alba L.)]

Anthocyanin synthesis of the mustard seedling (Sinapis alba L.), a typical phytochrome-dependent photoresponse has been further investigated. - It has been found that only two types of tissue can synthesize anthocyanin under the influence of active phytochrome (=P730), namely, the epidermis of the votyledons and the subepidermal layer in the hypocotyl (Fig. 2, 3). - Under our standard conditions (25° C; cf. methods) phytochrome-potentiated anthocyanin synthesis is only possible 24 hours after sowing and it ceases about 60 hours after sowing, independent of the amount of anthocyanin which has been accumulated (Fig. 5, 6). On the basis of the whole seedling the highest sensitivity of the anthocyanin producing system to light is around 36 hours after sowing (Fig. 8). Within the tissues which are capable of forming anthocyanin there is a characteristic shift of the ability to respond to P730 as the seedling ages. If we devide the seedling into 4 segments (Fig. 9) it turns out that in the basal and middle part of the hypocotyl the ability to form anthocyanin is rapidly lost whereas in the upper part of the hypocotyl and in the cotyledons this ability even increases at first. The following decrease is slower than in the basal parts (Fig. 10, 11).It is argued that this specific and dynamic cellular pattern of responsiveness to P730 can be regarded as a manifestation of a "primary differentiation" in the course of which the genotype of each individual cell in the dark-grownt seedling is devided into 3 functional types of genes: active, inactive, and potentially active genes (P730) (Fig. 4). - In connection with anthocyanin synthesis P730 is thought to act exclusively at the level of "secondary differentiation", i.e., it is thought to initiate the action of potentially active genes via a signal-chain. The action of P730 is non-specific. The specificity of the photoresponse of an individual cell is determined by the status of its "primary" differentiation (Fig. 4).If the process of differentiation is slowed down (e.g. by the application of low doses of Actiomycin D) anthocaynin synthesis can continue much longer than under our standard conditions where it ceases around 60 hours after sowing (Fig. 12). This fact seems to indicate that the loss of the ability to form anthocyanin is due to an inactivation of pertinent genes by the process of "primary differentiation", which is itself, as one would expect, under the control of genes.

[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.