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Oil bodies isolated from the mature seeds of rape (Brassica napus L.), mustard (Brassica juncea l.), cotton (Gossypium hirsutum L.), flax (Linus usifafis simum), maize (Zea mays L.), peanut (Arachis hypogaea L.), and sesame (Sesamum indicum L.) had average diameters that were different but within a narrow range (0.6-2.0 fim), as measured from electron micrographs of seria1 sections. Their contents of triacylglycerols (TAC), phospholipids, and proteins (oleosins) were correlated with their sizes. The correlation fits a formula that describes a spherical particle surrounded by a shell of a monolayer of phospholipids embedded with oleosins. Oil bodies from the various species contained substantial amounts of the uncommon negatively charged phosphatidylserine and phosphatidylinositol, as well as small amounts of free fatty acids. These acidic lipids are assumed to interact with the basic amino acid residues of the oleosins on the surface of the phospholipid layer. lsoelectrofocusing revealed that the oil bodies from the various species had an isoelectric point of 5.7 to 6.6 and thus possessed a negatively charged surface at neutra1 pH. We conclude that seed oil bodies from diverse species are very similar in structure. In rapeseed during maturation, TAC and oleosins accumulated concomitantly. TAC-synthesizing acyltransferase activities appeared at an earlier stage and peaked during the active period of TAC accumulation. l h e concomitant accumulation of TAC and oleosins is similar to that reported earlier for maize and soybean, and the finding has an implication for the mode of oil body synthesis during seed maturation.Seeds store TAG as food reserves for germination and postgerminative growth of the seedlings. The TAG are present in small, discrete intracellular organelles called oil bodies (Yatsu and Jacks, 1972; Appelquist, 1975; Stymne and Stobart, 1987; Huang, 1992). Isolated oil bodies have a spherical shape and possess diameters ranging from about 0.5 to 2.0 pm. They contain mostly TAG and small amounts of PL and proteins called oleosins. It is generally agreed that the oil body has a matrix of TAG surrounded by a layer of PL embedded with oleosins. The PL form a monolayer such that the acyl moieties of the molecules face inward to interact with the hydrophobic TAG in the matrix, and the hydrophilic PL head groups are exposed to the cytosol. The embedded oleosin molecule is composed of three structural domains: an N-terminal amphipathic domain, a central hydrophobic domain, and a C-terminal amphipathic a-helical domain (Vance and Huang, 1987; Qu and Huang, 1990; Murphy et al., 1991; Tzen et al., 1992). It is predicted that the hydrophobic portion Supported by U.S. Department of Agriculture grant 91-01430 (A.H.C.H.).* Corresponding author; fax 1-714-787-4437. 267 of the oleosin molecule penetrates the PL layer into the TAG matrix, and its amphipathic portion resides on the PL layer or protrudes to the exterior. The structure of an oil body as described in the preceding paragraph implies that the relative...

Diverse organisms store lipids in subcellular particles as food reserves, which will be mobilized during a forthcoming period of active metabolism. These lipid particles can be found in the seeds, pollens, flowers, roots, and stems of flowering plants, the spores and vegetative organs of nonflowering plants, and algae. They are also present in some animal cells, fungi, and Euglena. Of a11 these subcellular

Abstract. Storage triacylglycerols (TAG) in plant seeds are present in small discrete intracellular organ-

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