Etioplast Development in Dark-grown Leaves of Zea mays L.

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Abstract
The ultrastructure of etioplasts and the acyl lipid and the fatty acid composition of sequential 2 cm sections cut from the base (youngest) to the top (oldest) of nonilluminated 5 day old etiolated leaves of Z. mays L., and the acyl lipid and fatty acid composition of the etioplasts isolated from them were investigated. There is a 2.5-fold increase in the size of the plastids from the base to the tip of the leaf, and an increase both in the size of the prolamellar body and in the length of lamellae attached to it. The etioplasts in the bundle sheath and mesophyll cells of the older, but not the younger leaf tissue, are morphologically distinct. The monogalactosyl and digalactosyldiglycerides, phosphatidylcholine, phosphatidylglycerol and phosphatidylinositol were the only detectable acyl lipids in the isolated etioplast fractions. Together with phosphatidylethanolamine these were also the major acyl lipids in the whole leaf sections. With increasing age of the leaf tissue, increases occurred in 2 of the major plastid lipids, monogalactosyldiglyceride and phosphatidylglycerol, while the levels of essentially nonplastid lipids remained constant or declined slightly. The monogalactosyldiglyceride to digalactosyldiglyceride ratio increased from 0.4-1.1 in the tissue sections of increasing age and from 0.7-1.2 in the etioplasts isolated from them. Similarly, the galactolipid to phospholipid ratio increased from 0.8-1.4 in the tissue and from 0.5-4.5 in the isolated plastids. In the latter, the proportions of phosphatidylglycerol (as a percent of total phospholipid) increased from 20-41% with increasing age of plastids. Linolenic acid was the major fatty acid in the total lipid of each of the etioplast fractions, but it was only the major fatty acid in the total lipid of the oldest leaf tissue. Its proportion in both total lipid extracts and individual lipids increased with age. The trans .DELTA.3 hexadecenoic acid was absent from all lipids. The protochlorophyllide content of the tissue increased with age. The use of illuminated etiolated leaves for studying chloroplast development is discussed.