Photomorphogenesis, i.e. the control of plant growth and development by light independent of photosynthesis, is mediated mainly through phytoehrome. Recently the hypothesis has been advanced that Pv3o, the active phytochrome, may act through differential gene activation (HOCK and Mom~ 1964) at least in those cases where growth or biosynthetic processes are promoted under the influence of PTao. Phytoehrome-induced anthocyanin synthesis is a typical photoresponse of this type.
In the present paper the hypothesis that P730 acts through the activation of "potentially active genes" has been tested. The phytochrome-induced anthocyanin synthesis of the mustard seedling, Sinapis alba L., has been used as a photoresponse (BERTSCg and MoJ~ 1965). It has been shown that phytochromeinduced anthocyanin synthesis can be blocked by the application of aetinomycin D, which is known to be a highly specific inhibitor of DNA-dependent RNA synthesis. If aetinomycin D at the usual concentrations (e.g. 10 ~g/ml) is applied to the seedlings before or at the onset of light (continuous far-red) the synthesis of anthocyanln is totally blocked. If, however, the actinomycin D is added some time later, e.g. at the end of the lag-phase, 6 hours after the onset of light, anthocyanin synthesis is inhibited only partially (Fig. 2,3). Because a shift in the steady state concentration of P730 influences the rate of anthocyanin synthesis within 4--5 hours (Fig. 4) it cannot be assumed that a m-RNA with a long life-time is involved in light-induced anthoeyanin synthesis. This is supported by the data in Table 2. We therefore conclude that aetinomycin D at a suitable concentration will block the formation of new kinds of m-RNA but will still to a certain extent permit the continued synthesis of m-RNAs already in production at the time the actinomycin is added. --Recently we have reached the same conclusion with respect to phytochrome-indueed expansion of the cotyledons of the mustard seedling (Mogn, SC~rLICKEW~I and LANGE 1965). The conclusions based on the results with aetinomycin D are supported by experiments with pnromycin which is kno~n to be a specific inhibitor of translation, i.e. m-RNA dependent protein synthesis. Puromyein also will selectively inhibit phytochrome-dependent anthocyanin formation in accordance with the hypothesis that PTs0 acts through the activation of potentially active genes (Fig. 5, Table 1).
Einleitung
Die Regulation der pflanzliehen Morphogenese dureh Lieht (,,Photomorphogenese") erfolgt in erster Linie fiber das Phytoehrom (Zu-sammenf~ssung Mo~ 1965). Die morphogenetische Wirkung des 1~ (Berl.), Bd, 67 8