[The inhibitory effect of puromycin and 2-thiouracil on the phytochrome-mediated synthesis of anthocyanin].

The phytochrome-mediated anthocyanin synthesis of the mustard seelding, Sinapis alba L., can be stopped by the application of relatively low concentrations of puromycin and 2-thiouracil. While actinomycin D, which has been investigated in a previous paper (LANGE and MOHR, 1965), will block phytochrome-induced anthocyanin synthesis only if it is applied before or at the onset of light, puromycin and 2-thiouracil will stop anthocyanin synthesis even if they are applied at a later stage, e.g., 12 hours after the onset of light. - The effect of 2-thiouracil can be reversed if the seedlings are transferred to a medium containing uracil or to blank water. The simultaneous application of 2-thiouracil and uracil also leads to at least a partial reversal of the 2-thiouracil effect. - The kinetics of the puromycin inhibition (Fig. 2) indicate that the enzyme with the shortest "life-time" among those enzymes which are involved in anthocyanin production has a "life-time" in the order of 6 hours. One may reasonably conclude on the basis of Fig. 1 and 2 that synthesis of this particular enzyme is controlled by phytochrome 730. - The effect of 2-thiouracil (Fig. 3) cannot - in our case at least - be understood by only assuming that 2-thiouracil will be incorporated into RNA and thus will lead to the formation of "wrong" RNA. Inhibition by 2-thiouracil is much faster than inhibition by puromycin (Fig. 2,3). We have rather to conclude that 2-thiouracil may exert its effect mainly through a direct competitive enzyme inhibition.