The plastids of plants germinated in the dark are termed etioplasts and possess quasi-crystalline structures termed prolammelar bodies that contain the phospholipid materials and chlorophyll precursors that are converted to green chloroplasts in response to light. The transmission electron micrograph shows a corn (Zea mays) etioplast fixed after brief exposure to light. The prolamellar body is still largely intact, but thylakoid membranes are starting to form and, in the lower portion, some stacking of thylakoids is seen.
Zea mays seeds were germinated in the dark, briefly exposed to light, and segments of coleoptile, excised, fixed with glutataldehyde, post-fixed with osmuim tetroxide, and embedded in epoxy resin. Thin sections were cut, stained with uranyl acetate and lead citrate, and observed using a Philips 300 transmission EM. Images were recorded on film.
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