Lipid synthesis in the laticifers of Euphorbia lathyris L. seedlings

Various solutions of labeled precursors were absorbed by the cotyledons of etiolated Euphorbia lathyris L. seedlings. Incorporation of ¹⁴C into triterpenes from 2-¹⁴C]mevalonic acid, 1-¹⁴C]acetate, 3-¹⁴C]pyruvate, U-¹⁴C]glyoxylate, U-¹⁴C]glycerol, U-¹⁴C]serine, U-¹⁴C]xylose, U-¹⁴C]glucose, and U-¹⁴C]sucrose was obtained. The ¹⁴] triterpenes synthesized from ¹⁴C] sugars were mainly of latex origin. ¹⁴C]mevalonic acid was only involved in terpenoid synthesis outside the laticifers. Exogenously supplied glyoxylate, serine, and glycerol were hardly involved in lipid synthesis at all. The ¹⁴C-distribution over the various triterpenols was consistent with the mass distribution of these constituents in gas liquid chromatography when ¹⁴C]sugars, ¹⁴C]acetate, and ¹⁴C]pyruvate were used. These precursors were supplied to the seedlings in the presence of increasing amounts of unlabeled substrates. The amount of substrate directly involved in lipid synthesis as well as the absolute triterpenol yield was calculated from the obtained ¹⁴C]triterpenols. The highest yield was obtained in the sucrose incorporated seedlings, being 25% of the daily increase of latex triterpenes in growing seedlings.