Lipid Composition of Pea and Bean Leaves during Chloroplast Development

Abstract

The changes in composition of the complex lipids were followed during the greening of dark-grown pea (Pisum sativum) and bean (Phaseolus vulgaris) seedlings. No Whole leaves were used in the present work to avoid the possibility of enzymic degradation of glycerolipids during plastid isolation (8,15). Certain glycerolipids (e.g., the galactolipids) are confined mainly to the plastids (6), and therefore particular attention has been paid to changes in the galactolipids during greening. Since the completion of this work, Tremolieres and Lepage (17) have reported on the lipid composition of greening pea seedlings. However, their study was concerned more with long term changes (up to 96 hr), while the present work has concentrated on the early stages of the greening process, during which the dramatic changes in structure of the plastids occur (7). The onset of photosynthetic oxygen evolution is also observed during the first few hours of greening (1 6).The changes in fine structure which occur in higher plant plastids during chloroplast development have been studied extensively (7). The internal membranes of an etioplast of a dark-grown seedling are organized mainly into one or more paracrystalline three-dimensional tubular structures which are termed "prolamellar bodies." On illumination of the etiolated seedlings, the prolamellar bodies are dispersed into sheets of perforated membranes which give rise to the lamellae. Then follows a fusion and elaboration of the lamellae in certain regions to form grana. These electron microscope studies strongly suggest that there is a continuity of membrane structures during chloroplast development, rather than a breakdown of the membranes of the prolamellar bodies of the etioplast followed by a resynthesis of the membranes of the developing chloroplast.In the present study, we have examined the glycerolipid composition of greening pea and bean seedlings. Chloroplast thylakoids contain about 50% by weight of lipid, mainly glycerolipid (6), and therefore it seemed likely that changes in membrane structure and the acquisition of photochemical activity might be reflected in changes in the various chloroplast glycerolipids. On the other hand, a constancy of lipid composition in the early stages of greening would support the view 1Permanent address: Plant Physiology Division, D.S.I.R., Palmerston North, New Zealand. 31MATERIALS AND METHODS Peas (Pisum sativum L. cv. Greenfeast) and beans (Phaseolus vulgaris L. cv. Brown Beauty) were germinated in the dark at 25 C in trays containing vermiculite wetted with Hoagland's nutrient solution. After 10 to 11 days (for peas) and 11 to 14 days (beans), trays were transferred to continuous illumination and maintained at 25 C. White fluorescent tubes provided an average of 400 ft-c at leaf level. At appropriate intervals 1 g fresh weight of leaves was harvested from four trays, wrapped in aluminum foil, and steamed for 10 min (19).The killed leaves were then extracted with 20 ml of chloroform-methanol (2: 1 v/v) in a Tenbroeck tissue gr...

Acyl Lipids, Pigments, and Gramine in Developing Leaves of Barley and Its Virescens Mutant

“…This is in agreement with other reports (20). Although the exact role of this unique fatty acid is not known, it is found specifically in photosynthetic tissue, but it is uncertain whether it is essential for photosynthetic activity and grana stacking (9,13,40).…”

“…7-13). The findings here are in close agreement with those obtained for wheat and barley (5,43) and show a higher level of unsaturation in PG and SL than that found in maize, bean, and pea (29,40,50). Very little change in fatty acid composition except for PG occurred over the period of the study presented here and in other studies on greening etiolated leaves.…”

“…4 and 5) likely reflects an increased chloroplast membrane biosynthesis relative to other cellular membranes. Others have reported similar fmdings with greening etiolated leaves (5,40,43,50). The 4-and 2.5-fold increase in MG and DG, respectively, in the mutant (Figs.…”

“…This may indicate that chloroplast membrane growth is still occurring in the normal between 4 and 6 days. The decline in activities on a (5,40,50) and developing leaf segments (29). Any increases in the PG and SL content are likely masked by the massive changes in the other cellular constituents during chloroplast development inasmuch as PG and SL each contribute only about 5% of the total chloroplast membrane lipids (34).…”

“…The individual lipid classes have been studied extensively and include the pigments and the major acyl lipids which represent approximately 25 and 50%Yo, respectively, of the total chloroplast lipid (34). The acyl lipid fraction is comprised predominately of the galactolipids MG2 and DG, which account for 40 to 45% of the total lipid, and has a restricted phospholipid composition (34). The chloroplast acyl lipids also contain very high levels of polyunsaturated fatty acids, which are concentrated primarily in the major galactolipids, and levulinic acid; DG, digalactosyldiglyceride; LHC a/b, light-harvesting chlorophyll a/b; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PG, phosphatidylglycerol; PI, phosphatidylinositol; SL, sulfolipid; 2D TLC, two-dimensional thin-layer chromatography.…”