Identification of etioplast membranes in fractions from soybean hypocotyls.

Three independent methods, one cytological and two biochemical, were used to estimate contributions of plastids and plastid fragments to various membrane fractions. In thin sections viewed by electron microscopy, KMnO(4) selectively enhanced the images of plastid membranes in situ as well as in isolated fractions. The amounts of plastid fragments in isolated membrane fractions were determined by electron microscopic morphometry of fractions fixed with KMnO(4) in conjunction with analysis of galactolipids and carotenoids. Monogalactosyl and digalactosyl diglyceride contents were directly correlated with the amount of plastid membranes in the fractions identified by electron microscope morphometry. Amounts of carotenoids also correlated with plastid membranes except at very low levels where estimates based on carotenoids exceeded those based on morphometry.