The aim of the present investigation was to find factors critical for the 
co-existence of prolamellar bodies and prothylakoids in etioplasts of wheat 
(Triticum aestivum L. cv Starke II). The lipid composition of the prolamellar 
body and prothylakoid fractions was qualitatively similar. However, the molar 
ratio of monogalactosyl diacylglycerol to digalactosyl diacylglycerol was higher 
in the prolamellar body fraction (1.6 +/- 0.1), as was the lipid content on a 
protein basis. Protochlorophyllide was present in both fractions. The dominating 
protein of the prolamellar body fraction was protochlorophyllide oxidoreductase. 
This protein was present also in prothylakoid fractions. The other major protein 
of the prothylakoid fraction was the coupling factor 1, subunit of the 
chloroplast ATPase. From the lipid and protein data, we conclude that 
prolamellar bodies are formed when monogalactosyl diacylglycerol is present in 
larger amounts than can be stabilized into planar bilayer prothylakoid membranes 
by lamellar lipids or proteins.