Etioplast

They are usually found in stem and leaf tissue of flowering plants (Angiosperms) grown either in complete darkness, or in extremely low-light conditions.

[1] Etioplasts are characterized by the absence of chlorophyll and the presence of a complicated structure called a prolamellar body (PLB).

Due to the higher presence of carotenoids than protochlorophyllide, etiolated leaves appear pale yellow instead of just white.

The structure of PLB itself is almost immediately disrupted, and thylakoid and grana development is started in reaction to light: photosystem I activates within 15 minutes, photosystem II within 2 hours, and after approximately 3 hours an etioplast is completely converted into a functional chloroplast.

[1] The transitional stage between an etioplast and a chloroplast which still contains small PLBs interconnected with developing thylakoids, but already has chlorophyll is sometimes called an "etio-chloroplast".