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Articles

Lipid Biosynthesis by Isolated Barley Chloroplasts in Relation to Plastid Development ¹

^a Institute of Genetics, University of Copenhagen, Øster Farimagsgade 2A, DK-1353 Copenhagen K., Denmark

The effect of seedling age and of the time of greening on the incorporation of 1-¹⁴C-acetate into lipids by isolated barley (Hordeum vulgare cultivar Svalöf's Bonus) plastids was examined. The fatty acid synthesizing capacity of plastids isolated from 5-day-old seedlings did not increase markedly from zero to 36 hours of greening nor was a light stimulation of fatty acid synthesis observed. However, an increasing capacity for fatty acid synthesis and an increasing light stimulation of this process with greening were attained by the plastids isolated from 7-, 9-, and 11-day-old seedlings.

Plastids of 7-day-old dark-grown plants, which were illuminated at 2 foot-candles showed increasing capacity of ¹⁴C-acetate incorporation with significant flow into phospholipids and sulfolipid, low flow into digalactosyl diglyceride, and considerable flow into 6-methyl salicylic acid. Exposure of these plants to high light intensity for an hour resulted in chloroplasts that after isolation had a 10-fold increased capacity to incorporate ¹⁴C label into digalactosyl diglyceride, while the flow of ¹⁴C label into phospho- and sulfolipids was unaltered, and that into 6-methyl salicylic acid was drastically curtailed.

With plastids from 7-day-old dark-grown plants in early stages of greening, essentially all the ¹⁴C label in the stroma fraction could be accounted for by 6-methyl salicylic acid, while the membrane lipids only contained small amounts of ¹⁴C label. As greening proceeded, the flow of ¹⁴C label into 6-methyl salicylic acid diminished sharply, and the lipids of the lamellar systems became increasingly labeled.

Only palmitic and oleic acids were main sites of ¹⁴C label in the membrane lipids.

The activity of acetyl CoA carboxylase present in plastids of 5- and 7-day-old dark-grown plants fell sharply as the etioplasts differentiated into chloroplasts.

³ Present address: Division of Physiological Chemistry, University of Lund, Sweden.

¹ This investigation was supported by National Institutes of Health Grant GM 10819.