Two non-photosynthetic photoreceptors (phytochrome and a blue light photoreceptor) are involved in light-mediated anthocyanin synthesis in the mesocotyl of Sorghum seedlings. The present study was undertaken to investigate the kind of interaction between phytochrome and the blue light photoreceptor. The data show that phytochrome (Pfr) can only act once a blue light effect has occurred.On the other hand, the blue light effect cannot express itself without PI,. It is concluded that there is an obligatory dependency (or sequential interaction) between the blue light effect and the light effect occurring through phytochrome, although the blue light photoreaction per se is not affected by the presence or absence of phytochrome. The latter statement is based on the results of dichromatic experiments, i.e. simultaneous, high fluence rate irradiation with two kinds of light. Blue light can be replaced by UV light. It is not clarified yet whether the effect of blue and UV light is due to the same photoreceptor.

In contrast to an earlier publication (Drumm et al., Cytobiol. 2, 335, 1970), a definite enhancement by phytochrome of the catalase level in mustard (Sinapis alba L.) cotyledons can be demonstrated. This response can be obtained either with continuous far-red light or with short red pulses, the effect of which is reversible by short far-red pulses. From the comparison of the time courses of catalase activity with the time courses of glyoxysomal (isocitrate lyase) and peroxisomal (glycolate oxidase, glyoxylate reductase) marker enzymes in dark grown and far-red irradiated cotyledons, there appears to be a close relationship between the catalase present in darkness and glyoxysomes and between the phytochrome-stimulated portion of total catalase and peroxisomes, respectively.The isoenzyme pattern of catalase shows 3 strong and several weaker bands in dark grown cotyledons. Irradiation with white or far-red light leads to a more complex pattern with at least 12 detectable bands. The isoenzymes increased by light supplement rather than replace the isoenzymes present in darkness. This is true also in cotyledons and true leaves of white light grown plants which do not possess glyoxysomes. In the hypocotyl of the seedling, catalase formation is depressed by far-red light and no change in the isoenzyme pattern is observed.It is concluded that the development of peroxisomes in the cotyledons is specifically controlled by phytochrome and that this subcellular differentiation also involves the control of catalase, a marker enzyme for both glyoxysomes and peroxisomes. The implications of these results with respect to the developmental origin of peroxisomes in cotyledons of fat-storing, potentially photosynthetically active cotyledons is discussed.

It is demonstrated that phytochrome-mediated anthocyanin synthesis in the epidermal cells of mustard seedling cotyledons takes place only 27 h after sowing onwards (at 25°C). This "starting point" cannot be shifted by light treatments or by nutrients. The late appearance of competence for P fr (P r and P fr, red- and far-red absorbing forms of phytochrome, respectively) with regard to anthocyanin synthesis is not related to the phytochrome system per se (P r⇆P fr) as this is fully functional immediately after sowing of the seed; nor is it related to the primary reaction of phytochrome: P fr+X→P fr X→P fr X' (X, X', two forms of a receptor for P fr) or to the initial action of P fr X':P fr X'+K'→Y' (K', coupling element, leading to the product Y', which is no longer photoreversible). Rather, the "starting point" is determined by internal factors only and is thus not accessible to any specific control by external factors. On the other hand, however, the beginning of the initial action of P fr X' ("coupling point") can be shifted by light via phytochrome under high irradiance conditions. Moreover, it is shown that there is no phytochrome-independent effect of blue light on photomorphogenesis in the young mustard seedling and that there is no "rapid dark reversion of P fr" which can be detected by physiological means, at least during.

Morphogenesis and metabolism of the gametophytes (= sporelings) of the common male fern Dryopteris filix-mas are controlled by visible radiation. Short wavelengths visible radiation (= blue light) leads to an increase in protein synthesis and makes possible the formation of "normal" two-dimensional prothallia. Under long wavelengths visible radiation (= red light) the sporelings grow 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 RNA 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 conclude 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 (14)C into RNA. The (14)C was applied as (14)C-uridine (U). - It seems that blue light causes an increase of protein synthesis in the chloroplasts 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.

Abstract—The dose response curve for light (phytochrome)‐induced anthocyanin synthesis was determined in the mustard seedling. The curve gives the amount of anthocyanin (A) synthesized within 24 h as a function of the amount of Pfr* produced by a brief light pulse. The [Pfr] response curve is composed of two linear parts with very different slopes (a1,2) connected by a relatively narrow transient range (curved segment). The [Pfr] response curve extrapolates precisely through zero [Pfr]. The reciprocity law is valid over the whole range investigated (up to 320 s of irradiation). It is concluded that the initial (or primary) reaction of Pfr (Pfr+ X → PfrX) does not involve any significant cooperativity in the case of phytochrome‐mediated anthocyanin synthesis. It is speculated that the linear parts of the [Pfr] response curve truly reflect the mode of phytochrome action (A=a1,2 [Pfr]; X does not come into play since it is not rate limiting) whereas the curved segment represents a transition of the reaction matrix of Pfr. The large difference between a1 and a2 seems to indicate that the physiological effectiveness of a given amount of Pfr (or PfrX) is determined by [Pfr] through a Pfr‐induced change in the reaction matrix.