The galactolipid, phospholipid, and fatty acid composition of chloroplast envelope membrane fractions isolated from leaves of Vicia faba L. has been determined. The major lipids in this fraction are: monogalactosyldiglyceride, 29%; digalactosyldiglyceride, 32%; phosphatidylcholine, 30%; and phosphatidylglycerol 9%. The lipid composition of the chloroplast envelope membranes is qualitatively eimilar to that of the lamellar membranes isolated from the same plastids, but the proportion of each lipid present is very different. The total galactolipid to total phospholipid ratio was 1.6 :1 in the envelope and 11.1 : 1 in the lamellae. The monogalactosyldiglyceride-digalactosyldiglyceride ratio was 0.9 : 1 in the envelope and 2.4 : 1 in the lamellae. Both membranes lack phosphatidylethanolamine.Linolenic acid is the major fatty acid in the envelope lipids representing 63 % of the total fatty acid, whereas in the lamellae it represents 83%. The same fatty acids are present in both the envelope and lamellar lipids except the trans-A'-hexadecenoic acid, which is confined to the lamellar lipids, particularly the phospholipid fraction.A quantitative comparison of the lipid and fatty acid compositions of the envelope with those of mitochondrial and microsomal fractions indicates that the chloroplast envelope has a composition intermediate between that of the chloroplast lamellae and these extrachloroplastic membranes.Although the ultrastructure of the chloroplast envelope has been examined in leaf cells (11,19,37), and its permeability properties studied both in the whole leaf (13,14,32) and recently in isolated chloroplasts (5, 15-18, 22, 29, 36, 38), noth-ing is known of its chemical composition. Chemical characterization of the envelope membranes must be carried out on isolated membranes, and methods for the isolation (26) and purification (27) The leaves (30-40 g) were homogenized at full speed for 3 and then 5 sec in an Atomix blender with 180 ml of ice-cold medium A: 53 mm Na2HPO,/KH2PO4 buffer containing 500 mM D(-)sorbitol, 10 mM MgC12 and 10 mm EDTA-Na2, pH 7.3. The resulting homogenate was filtered through four layers of cotton organdy and eight layers of 25 ,um mesh nylon. Chloroplasts and chloroplast envelope membranes (pellet P4) were isolated from this filtrate by a modification of previous methods (26) as shown in Figure 1. Chloroplasts were prepared by sedimentation at 3,000g for 15 sec, and the resuspended pellet was then layered onto a 10-ml (4 cm) band of 400 mm buffered sucrose and centrifuged at 5OOg for 12 sec. This second centrifugation reduced the mitochondrial and bacterial contamination by 60% and removed the majority of broken plastids (25).Isolation of Chloroplast Envelopes. For the isolation of the chloroplast envelopes, the chloroplasts were ruptured osmotically by incubation in buffered 10 mM MgC12. Each washed chloroplast pellet was resuspended in 10 ml of grinding medium from which the sorbitol had been omitted (medium E), and was incubated at 0 C for 10 min. The suspensions were hom...

SUMMARYThe rate of net photosynthesis in each of the foliar organs present on seedlings of Glycine max (L.) Merrill was measured by infrared gas analysis on the fourth day after sowing and every third day thereafter until 5 d after cotyledon abscission. Dark respiration rates for the whole seedling were also measured. Estimates of the daily net carbon assimilation were made using the sum of the net CO2 assimilatory rates for each foliar organ present and the dark respiration rate for the whole seedling. Rates of cotyledon photosynthesis were very low in comparison to the leaves, whether expressed per unit chlorophyll or unit area. Although the cotyledon contribution to seedling assimilation remained small throughout their lifetime, it was enough to balance seedling respiratory losses during days 7 to 10 prior to leaf expansion. Marked increases in the CO2 budget only occurred once primary leaf photosynthesis began on day 10. Net assimilation then increased rapidly as first, second and third trifoliate leaves expanded.

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The ultrastructure of etioplasts and the acyl lipid and the fatty acid composition of sequential 2-centimeter sections cut from the base (youngest) to the top (oldest) of nonilluminated 5-day-old etiolated leaves of Zen mays L., and the acyl lipid and fatty acid composition of the etioplasts isolated from them have been investigated. There is a 2.5-fold increase in the size of the plastids from the base to the tip of the leaf, and an increase both in the size of the prolameliar body and in the length of lameilae attached to it. The etioplasts in the bundle sheath and mesophyli cells of the older, but not the younger leaf tissue, are morphologicaily distinct. The monogalactosyl and digalactosyldiglycerides, phosphatidylcholine, phosphatidylglycerol, and phosphatidylinositol were the only detectable acyl lipids in the isolated etioplast fractions. Together with phosphatidylethanolamine these were also the major acyl lipids in the whole leaf sections.