Die Regulation von Fettabbau und Atmung bei Senfkeimlingen durch Licht (Sinapis alba L.)

1. In the present experiments on control by light of fat degradation and respiration only far-red light has been used because it exerts the strongest effect on morphogenesis without having any photosynthetic activity (Bertsch and Mohr 1965). There is good evidence (Mohr, Wagner and Hartmann 1965) that the effect of far-red is mediated exclusively through phytochrome. 2. The process of fat degradation is restricted mainly to the cotyledons. The contents of fat in hypocotyl and radicle are very small. 3. Light (i.e. continuous far-red) changes the rate of fat degradation characteristically: At first light reduces the rate of degradation as compared with darkness, but after some time the rate is increased much more under the influence of light than in darkness. 4. The rate of respiration (i.e. O₂ uptake) of the cotyledons is correlated with the rate of fat degradation. It is influenced by light in the same way (first, reduction; later on, increase). If dark grown seedlings are irradiated with continuous far-red the rate of respiration is rapidly changed. After 3 hours of far-red, for instance, the rate of respiration of the cotyledons is already drastically reduced. 5. The increase in the "fat free dry weight" of the seedling, i.e. dry weight minus fat weight, can be regarded as a certain gauge of the rate of synthesis of organic material from fat. In this case also light at first causes a reduction and then an increase of the rate compared with the dark control. 6. The regulation of fat degradation and respiration by light has been interpreted as a "secondary photoresponse", i.e. the phytochrome does not cause these phenomena directly in the cotyledons but these responses are the result of correlative signals from other parts of the seedling, possibly from the hypocotyl, where phytochrome is primarily active in this connection.