A quantitative comparison has been made of the ultrastructural development taking place in the light and in darkness between plastids in intact etiolated tissue and in suspensions of etioplasts, which have been given various pre-treatments of red, far-red and blue light. Plastid development in situ and in suspensions is enhanced by pre-illumination with red light and this enhancement can be reversed by following red light with far-red light. The reverse is also true; pre-illumination with far-red light inhibits development and this inhibition is abolished and replaced by enhancement by following far-red light with red light. Blue light of short duration has no effect on the early stages of ultrastructural development in plastids.
It is concluded that a phytochrome-mediated mechanism is present either inside the plastid or on the plastid envelopes.