Events surrounding the early development of Euglena chloroplasts : 17. Light-induced changes in a proplastid remnant in mutant W 3BUL

Abstract

The proplastid remnant found in Euglena gracilis var. bacillaris mutant W 3 BUL is probably composed of nuclear-coded materials. This remnant, in dark-grown resting cells, takes the form of a thin, irregular, circular leaflet of narrow stroma with large intrusions of cytoplasm into the interior, as reconstructed from electron microscopy of serial sections. Microbody-like bodies (0.5–1 μ m in diameter) in the cytoplasm are closely appressed to the plastid membrane. No plastid ribosomes are seen. On illumination for 30 min the stroma expands and the microbodies intrude into it. Numerous small vacuoles appear in the stroma to be replaced by one large one by 48 hr of illumination. By 48 to 72 hr prolamellar bodies are seen in the stroma close to the vacuole. These are of two types (only one type is found in any one cell): one is a loose cluster of tubules and vesicles, the other has the typical lattice structure of higher plants. Both have rudiments of thylakoids radiating from the periphery. The prolamellar bodies are globular, about 1–2 μ m in diameter. It appears that in this mutant of Euglena the lack of plastid DNA-coded materials prevents further development of normal thylakoids and proplastids.