Die jungen Gametophyten (= Vorkeime) des Wurmfarns Dryopteris filix-mas (L.) Schott, der als Repräsentant der leptosporangiaten Farne

as cellular filaments the protein contents of which are markedly lower than under blue irradiation even under conditions of equal rate of dry matter accumulation in red and blue (Ohlenroth and Mohr, 1963). — It is shown in the present paper that the ENA content of sporelings of the same age is always higher in blue light than in red light (Figs. 1, 3). The blue-dependent increase of RNA occurs faster than the blue-dependent increase of protein (Fig. 2). Furthermore the increase of protein per sporeling is much larger than the increase of RNA (Fig. 4). These facts are in agreement with the hypothesis that in some way or another blue light initiates differential gene activation. The blue light-dependent morphological changes which occur if we put red grown filamentous sporelings under blue light can be measured much faster than the blue light-dependent increase of the bulk protein (Figs. 5, 6). We have to con clude as we did in a previous paper (Kasemir and Mohr, 1965) that the blue light dependent increase in the protein content of the sporelings might be mainly due to an increase of chloroplast protein. — The blue light-dependent increase of the RNA content occurs at least as fast as the morphological changes (Figs. 5, 6). This finding is supplemented by the observation (Fig. 8) that blue light markedly and rapidly stimulates the incorporation of 14C into RNA. The 14C was applied as 14C-uridine (U). — It seems that blue light causes an increase of protein synthesis in the chloro plasts as well as in the cytoplasm. Blue light-dependent RNA synthesis seems to be involved in this response. These data support the view that blue light might exert its morphogenetic control through differential gene activation.