[Kinetical studies on phytochrome-induced protein synthesis]

Phytochrome control of protein metabolism has been analyzed in the cotyledons of the mustard seedling (Sinapis alba L.) which can be regarded as being representative of dicotyledonous seedlings. A mustard seedling is a closed system for nitrogen under our experimental conditions. Fig. 2 shows the kinetics of protein content in the cotyledons of the mustard seedling in darkness and under the influence of continuous far-red irradiation, i.e. under the influence of a low but virtually constant concentration of phytochrome 730. -In order to understand these two curves it must be realized that the cotyledons of the mustard seedling contain much storage protein which will be degraded during the development of the seedling. The resulting amino acids are either translocated to other parts of the seedling or used within the cotyledons for the synthesis of enzymes and structural protein. -Histochemical studies have shown (HäCKER, 1966) that under the influence of far-red light the degradation of storage protein in the cotyledons is enhanced; at the same time, however, phytochrome 730 stimulates a strong de novo synthesis of structural and enzyme protein in the cotyledons. -This interpretation of the data on protein content is supported by evidence of the phytochrome-enhanced incorporation of (14)C into the protein fraction after an application of (14)C-Leucine (U) (Figs. 5, 6). - All present findings on phytochrome-controlled protein synthesis agree with the hypothesis that phytochrome 730 exerts its function through a differential gene activation (MOHR, 1966b).