Fatty Acids of Spinach Chloroplasts.

The photosynthetic apparatus of higher plants consists of discrete cytoplasmic organelles, the chloroplasts, which contain proteins, lipids, pigments, water. and other substances. Relatively little is known, apparently, concerning the composition of the lipid fraction of the chloroplast. Menke (8), studying chloroplasts of spinach, Spiniacia oleracea, found that essentially all the lipids of the leaf were located in the chloroplasts. The chloroplasts had an average lipid content of 30.9 % of the dry weight, while the cytoplasm had a lipid content of only 0.5 %. For this reason, a number of earlier studies of the lipid content and composition of green leaves as a whole are pertinent to the present problem. Chibnall and Channon (3), studying the fatty acids of leaves of cabbage, Brassica oleracea, found that approximately 10.7 % of the fatty acid fraction consisted of saturated acids, and 89.3 % of unsaturated acids. The saturated fraction was composed of 70 % palmitic acid and 30 % stearic acid. The unsaturated fraction included large quantities of linoleic and linolenic acids. Speer et al. (13) examined the lipids of spinach leaves, finding that 53 % of the fatty acids occurred in the free form, with 47 % as glycerides. The saturated acids consisted chiefly of palmitic and stearic acids. Oleic acid made up 26.3 %, linoleic acid 34.7 %, and linolenic acid 12.7 % of the unsaturated lipid fraction. The fatty acids of the forage grasses Dactylis glomiierata and Lolimn perenne were examined by Smith and Chibnall (12). Saturated acids composed 1 1 % of the total in Dactylis and 12 % in Lolium; the corresponding figures for oleic acid were 16 and 22 %, for linoleic acid 31 and 26 %, and for linolenic acid 42 and 40 %, respectively. According to Chibnall (2), cabbage leaves contain 17.5 % glycerides, 12.3 % waxes, 4.5 % sterols, and 18.4 % phospholipids. Comparable figures for cocksfoot grass, Dactylis gloinerata, were 38.0 % glycerides, 23.5 % waxes, 3.0 % sterols, and 1.5 % phospholipids. Menke (9) isolated chloroplasts from spinach leaves by centrifugation; he found that their lipid content was approximately 37 %. The ether-soluble fraction of the chloroplasts is a complex mixture of pigments, fatty acids, glycerides, phosphatides, and sterols. Bot (1) isolated grana from chloroplasts of