The degradation of reserve fat in the cotyledons of Sinapis alba L. under the influence of phytochrome

1. We have used histological and histochemical methods in order to follow the degradation of reserve fat in the cotyledons of the mustard seedling in darkness and under the influence of phytochrome. The results which have recently been obtained by HOCK et al. (1965) with conventional methods of extraction and gravimetric determination of fat could be confirmed. Furthermore the detailed pattern of fat degradation in the cotyledons has been described. 2. In the dormant seed the reserve fat is homogeneously distributed in the cotyledons. After the onset of germination this fat is degraded according to a complicated pattern.-In the dark grow seedling the rate of degradation is higher in the epidermis than in the mesophyll. Within the mesophyll degradation is more intense in the palisade parenchyma than in the spongy parenchyma (fig. 3). -There is still another gradient: the rate of degradation is greater in the centre and in the periphery of the lamina than in between (fig. 2). -In the light grown seedling (continuous far-red) the pattern of fat degradation is not changed compared with that in the dark grown seedling. The rate of degradation, however, is changed in a manner which is characteristic for "complex photoresponses" (MOHR, 1966): at first the rate is lower under the influence of far-red, later on it is higher than in the corresponding dark controls. We conclude: phytochrome does not change the pattern of fat degradation in the cotyledonary tissues; it does, however, exert a strong regulating influence on the rate of degradation. 3. On the basis of the histochemical investigation of the epidermis it was concluded that phytochrome induced anthocyanin synthesis in this tissue is strictly correlated with an intense degradation of reserve fat within this tissue.