Galactolipid synthesis in chromoplasts in vitro : Specificities of acyl-and galactosyltransferases

β-Carotene synthesis in isolated chromoplasts from Narcissus pseudonarcissus

A system has been established from isolated intact chromoplasts of Narcissus pseudonarcissus flowers that synthesizes geranylgeraniol, an unknown polyprenoid alcohol, phytoene, and β-carotene from [1-(14)C]isopentenyl pyrophosphate in a good yeild. Long chain pyrophosphates are not accumulated. San 6706 inhibits the dehydrogenation of phytoene, whereas nicotine does not lead to an accumulation of lycopene. Separation and identification of polyprenoid lipids was performed by HPLC. The properties and advantages of the chromoplast system are discussed.

Phosphate translocator and adenylate translocator in chromoplast membranes

It is shown by the criteria of saturation kinetics, specificity, and inhibition experiments that chromoplast membranes from the daffodil flower contain a phosphate translocator for the counter-exchange of phosphate, and 3-phosphoglycerate, as well as phosphoenolpyruvate; they also contain an adenylate translocator. This is the first report on the occurrence of these translocators in non-green plastids. Both translocators exhibit certain dissimilar properties when compared to the corresponding systems of chloroplasts. The transport rates of both translocators are sufficient to allow a prominent fatty acid synthesis in isolated chromoplasts when C3 intermediates of the glycolytic pathway or adenine nucleotides are used as energy sources.

Fatty acid synthesis by isolated chromoplasts from the daffodil. Energy sources and distribution patterns of the acids

1. Fatty acid synthesis in isolated intact chromoplasts from [1-(14)C]acetate was made possible by using ATP, ADP (via adenylate kinase), and, with decreasing efficiency, UTP, CTP, and GTP as energy sources. 2. The glycolytic path from dihydroxyacetone phosphate to acetyl-CoA operates within the chromoplasts. The glycolytic intermediates, especially 2-phosphoglycerate and phosphoenolpyruvate, served as very effective energy donors for fatty acid synthesis by phosphorylating the endogenous adenine nucleotide pool. 3. In the presence of exogenous ATP or ADP, appreciable amounts of in vitro formed fatty acids were found as acyl-CoA and subsequent products, mainly phosphatidylcholine. When other energy sources were used most of the acids formed were in the free form, and to a minor extent, in the phosphatidic acid and diacylglycerol fractions. Similar results have recently been reported for spinach chloroplasts (Kleinig and Liedvogel 1979, FEBS Lett.101, 339-342).

Fatty acid and glycerolipid synthesis in abscised daffodil flowers after acetate feeding

The coronae of Narcissus pseudonarcissus flowers incorporated [1-(14)C]acetate almost exclusively into the fatty acid moieties of glycerolipids. After a 4 h incubation, the newly synthesized acids were: stearate plus palmitate (50%); oleate (17%); linoleate (32%); and linolenate (0.5%). Phosphatidylcholine and diacylglycerol were the principal labelled lipids. In pulse experiments these acids were further desaturated, with time, to an appreciable extent and, concurrently, transferred essentially from phosphatidylcholine to diacylglycerol, diacylgalactosylglycerol, and diacylgalabiosylglycerol. The labelling of diacylgalactosylglycerol and diacylgalabiosylglycerol paralleled the appearance of linolenate. The distribution of labelled acids in phosphatidylcholine, diacylgalactosylglycerol, and diacylgalabiosylglycerol was very different. The results were compared with those obtained in vitro with isolated coronae chromoplasts and discussed in relation to current schemes of fatty acid and glycerolipid synthesis in plant cells.