Control of Chloroplast Development and Chlorophyll Synthesis by Phytochrome
In higher plants the development of mature chloroplasts takes place only in the light. The developing photosynthetic apparatus is thus a useful model system to investigate the control of development by an exogenous factor, light. We have studied over the years the development of the photosynthetic apparatus in the cotyledons of the mustard seedling (Sinapis alba L.), a representative of the dicotyledonous plants . As long as the seedling develops in complete darkness, the cotyledons function as storage organs. They do not grow or develop significantly. However, when the seedling is illuminated with white light of sufficiently high irradiance, the cotyledons are transformed rapidly into photosynthetic organs, very similar in internal structure and in function to a normal photosynthetically active leaf. The control by phytochrome of plastogenesis has been analyzed on the level of fine structure, with regard to protochlorophyll synthesis, chlorophyll accumulation, and formation of Calvin cycle enzymes. A major problem has been whether the multiple control by phytochrome of the development of the plastid compartment is the consequence of a single initial action of Pfr.
KeywordsPhotosynthetic Apparatus Chloroplast Development Chlorophyll Synthesis Continuous White Light Prolamellar Body
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