ACCUMULATION OF IXERIN-F AND ACTIVITIES OF SOME TERPENOID BIOSYNTHETIC-ENZYMES IN A CELL-SUSPENSION CULTURE OF LACTUCA-VIROSA L

A cell suspension culture of Lactuca virosa L. (Asteraceae, tribe Lact uceae) is capable of synthesizing sesquiterpene lactones of which ixer in F is the main compound. The culture was characterized on growth (by dissimilation rates), on ixerin F accumulation (by RP-HPLC) and on so me enzyme activities involved in early steps of terpenoid biosynthesis . Acetoacetyl-coenzyme A thiolase (AACT, E.C. 2.3.1.9) and 3S-hydroxy- 3-methylglutaryl-coenzyme A synthase (HMGS, E.C. 4.1.3.5) activities o f the cells were assayed spectrophotometrically. HMGS activity increas ed during the culture period and reached a maximum during the stationa ry phase (190 pkat/mg protein), while AACT showed relatively high leve l of activity throughout the growth cycle, with transient decrease at the logarithmic growth phase and the beginning of stationary phase. Ix erin F accumulated inside the cells and the maximum concentration of 0 .08% (on dry weight basis) was found in the early stationary phase of the growth cycle of the culture.