Quantitative aspects of latex lipid synthesis in Euphoribia lathyris L. seedlings

Abstract

Changes in the dry weight of the endosperm of Euphorbia lathyris L. seedlings showed that 2 mg material was taken up by the cotyledons after 10 d germination. A similar amount of sucrose could be taken up by these seedlings after removal of the endosperm. The maximum yield of latex triterpenes synthesized from this exogenously supplied substrate was in the same order of magnitude as the daily latex lipid increase in 19 μg per seedling. Cotyledons and adjacent 1-2 cm segment of the hypocotyl were the most active tissues in latex trieterpene synthesis. Excised cotyledons were able to accumulate 1-1.5 mg sucrose in 48 h from a sugar concentration higher than 0.1 mol l(-1). In this period a maximum amount of 8-10 μg latex triterpenes could be synthesized from this substrate. [(14)C]Mevalonic acid was rapidly taken up by excised cotyledons but not metabolized by the laticifers. This exogenously supplied precursor was rapidly converted to squalene and triterpenes by the adjacent tissue, and after 48 h incubation most of the (14)C in the nonsaponifiable fraction was traced in the phytosterolds.