[The control by phytochrome of the contents of ascorbic acid and dehydroascorbic acid in the mustard seedling (Sinapis alba L.)].

A dark grown seedling of white seeded mustard (Sinapis alba L.) contains an appreciable amount of ascorbic acid. The content of ascorbic acid, however, will strongly increase under the influence of light. This effect is due to phytochrome. Photosynthesis is not involved under our experimental conditions.The content of dehydroascorbic acid is always very low compared to ascorbic acid (5-8% of total ascorbate). Phytochrome does not influence this relation.The lag-phase of the phytochrome induced increase in ascorbic acid accumulation is remarkably short, about 1 hour after the onset of light compared to about 4 hours for phytochrome induced anthocyanin synthesis under our conditions.This is the shortest lag-phase we have observed hitherto in the case of "positive" photoresponses (MOHR, 1966).If we assume that the function of phytochrome in the case of "positive" photoresponses involves a differential gene activation of "potentially active" genes (MOHR, 1966) the following working hypothesis can be advanced: phytochrome induced accumulation of ascorbic acid will lead to a separation of DNA-histone complexes in the range of "potentially active" genes. This makes possible the DNA-dependent synthesis of m-RNAs at those sites which are lastly responsible for the initiation of "positive" photoresponses. - Arguments are briefly considered which support the view that ascorbic acid exerts a function in connection with the regulation of gene activity.