Photomodulation by phytochrome of the rate of accumulation of ascorbic acid in mustard seedlings (Sinapis alba L.)

Ascorbic acid accumulation in the mustard seedling is controlled by P fr(active phytochrome). Kinetic studies demonstrate that P frexerts a rapid and fully reversible control over the steady state rate of ascorbic acid accumulation. Following the terminology of Weisz (1967) for this type of metabolic control the term "photomodulation by P fr" is used.-The control by P fris independent of RNA synthesis. Therefore regulation of gene activity is probably not involved in photomodulation of the rate of ascorbic acid accumulation.-There is only a limited period within which P frcan control ascorbic acid accumulation. This period is fixed by the time pattern of "primary" differentiation in the seedling. There is no interaction between photomodulation by P frand control by "primary" differentiation of ascorbic acid accumulation.