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1. Crambe seeds harvested 6 -30 days after flowering actively incorporated radioactive precursors into lipids. The distribution of label among the different lipid classes depended on the precursor, the age of the seed, and the duration of the incubation.2. Labelled acetate was incorporated preferentially into phospholipids of whole seeds but the proportion of the radioactivity located in triglycerides increased as the age of the seed increased.3. Uniformly labelled glucose was incorporated readily into the glycerol moiety of glycerolipids but not a t all into the fatty acid moiety. The largest proportion was found in the phospholipid fraction and this proportion increased as the age of the seed increased, in contrast to labelled acetate.4. 1:nlformly labelled glycerol was actively incorporated into glycerolipids of whole seeds. Phospholipids were the first fraction to be labelled, and in this fraction labelled phosphatidic acid could be detected at early time periods. Subsequently, diglycerides became labelled and finally triglycerides. Labelled glycerol was quickly converted into a number of water-soluble metabolites, one of the most rapidly labelled of which was glycerol phosphate. Taken together these data are consistent with the presence of the glycerol phosphate pathway for triglyceride synthesis in maturing Crambe seeds.5. A fat fraction has been isolated from mature and maturing Crambe seeds by homogenisation of the seeds followed by flotation in the centrifugc. Electron microscopic examination indicated that the fraction contains the oil bodies that are the storage form of the oil in the seed in vivo.6. The isolated oil bodies contain 75O/, by weight of lipid and 190/, of protein. About 900/, of the lipid is triglyceride, the remainder is mostly phospholipid. No glycolipid is present. .The isolated fat fraction catalysed the conversion of different substrates, malonyl-CoA, long chain acyl-CoA and glycerol 3-phosphate into lipids. Evidence is presented that this is not due to contamination from other cell fractions.The pathways of biosynthesis of triglycerides are well worked out in animal tissues [l]. In plants very little published information exists on the overall pathways by which triglycerides arise, even less on the detailed enzymic steps. Labelled glycerol 3-phosphate is incorporated into phosphatidic acid by spinach-leaf microsomal fractions [2,3] ___-phate first into phosphatidic acid, then into diglycerides and finally into triglycerides, but no similar work has been done with seeds.In a previous paper we have described changes in oil composition as the Crambe seed matures and the complete stereospecific analysis of the seed-oil triglycerides [ 5 ] . Electron microscopy of thin sections of mature Crambe seeds, fixed and stained with osmium tetroxide, revealed cells packed with oil bodies with a mean diameter of about 1 pm. I n this paper we describe the isolation of the oil storage bodies, their chemical composition, and their enzymic activity and present evidence for the existence of the glyce...

Until 10-12 days after %owering the lipid of Crumbk seeds accounts for less than lo/o of the total seen weight. Most of this lipid is phospholipid and glycolipid, the fatty acid composition of which resembles that of green tissue. 2. After 10-12 days the oil content of the seed rises rapidly, due mainly to the synthesis of new triglyceride. Oil synthesis levels off a t about 30 days when the oil comprises 35O/, of the weight of the seed. 3. The fatty acids characteristic of green tissue, C16:0, CIS:^ and C18:3 decrease in proportion to the total fatty acids as the seeds mature. Erucic acid, which is not present before 6 days rises rapidly from 8 days to becomes the major seed oil fatty acid in the mature seeds (53O/,). Oleic acid and C22:1 increase in proportion reaching a maximum a t 12 days. 4. The triglycerides of the mature seed oil are composed of 5 major molecular species, having 2, 3, 3, 4 and 5 double bonds per molecule, respectively. 5. Position two is occupied entirely by C,, fatty acids with A 9 unsaturation, namely CIS:^, C18:2 and C18:3. No erucic acid occurs a t position 2. The acids a t position two are cleaved preferentially by the lipase from Geotrichum candidurn. 6. Position 1 is occupied preferentially by saturated acids or erucic acid. Position 3 is occupied almost entirely by erucic acid.