The involvement of sucrose, glucose and other metabolites in the synthesis of triterpenes and dopa in the laticifers of Euphorbia lathyris

Abstract

A quantitative triterpene analysis was made of latex stem tissue of Euphorbia lathyris . Young plants seedlings of E. lathyris were incubated with various labelled precursors. Incorporation into triterpenes was obtained from [2- 14 C]mevalonic acid, [1- 14 C]acetate, [3- 14 C]pyruvate, [U- 14 C]sucrose, [U- 14 C]glucose, [U- 14 C]xylose, [U- 14 C]glyoxylate, [2,3- 14 C]succinic acid, [1- 14 C]glycerol [U- 14 C]serine. Both sugars tyrosine appeared to be effective precursors in DOPA synthesis inside the laticifers. Exogenously supplied mevalonic acid was only involved in triterpene synthesis outside the laticifers. GC-RC of triterpenes synthesized from [U- 14 C]glucose revealed the origin of these compounds in the latex. The labelled triterpenes obtained after incorporation of the other mentioned labelled precursors were only partly synthesized in the laticifers. For quantitative data on latex triterpene synthesis seedlings were incubated with [U- 14 C]sucrose, [U- 14 C]glucose, [U- 14 C]xylose [1- 14 C]acetate in the presence of increasing amounts of unlabelled substrate. From the amount of 14 C incorporated into the triterpenes the amount of substrate directly involved in triterpene synthesis was calculated, as was the absolute triterpene yield. Sucrose showed the highest triterpene yield, equivalent to the daily increase of the triterpene content of growing seedlings. The possible significance of the other precursors in triterpene synthesis in the laticifers is discussed.