Accumulation of protochlorophyll and chlorophyll a as controlled by photomorphogenically effective light

Data are presented which indicate that the rate of synthesis and the pool size of photoconvertible protochlorophyll(ide) in the cotyledons of the mustard seedling are controlled by the active form of phytochrome (Pfr). Inductionreversion experiments show that formation of chlorophyll a through photoconversion of the protochlorophyll(ide) by repeated red pulses (5 min each) has no effect on synthesis of carotenoids and galactolipids. Since the protochlorophyll(ide)-converting activity of the standard far-red light used in this laboratory is very low, chlorophyll-a accumulation is very slow under continuous standard far-red light. It is concluded that photosynthesis (or photosynthetic phosphorylation) does not participate in the "high irradiance reaction" of photomorphogenesis.