Mevalonate kinase activity in Catharanthus roseus plants and suspension cultured cells

Mevalonate kinase is an early enzyme in plant isoprenoid biosynthesis. Its activity was studied in different parts of Catharanthus roseus (L.) G. Don (Apocynaceae) plants and in C. roseus suspension cultured cells. In the plant specific mevalonate kinase activities were found to be relatively high in the fruits, stem, roots, flowers and buds, and relatively low in young and completely elongated leaves. In suspension cultured cells, the specific mevalonate kinase activity increased during the exponential phase of growth, reaching a maximum of 0.5 nkat/mg protein at 4 days after subculturing. After 6 days, which corresponded to the beginning of the stationary phase, the specific activity decreased. After transferring 14-day-old C. roseus cells to a medium known to induce the production of terpenoid indole alkaloids, an increase in the specific mevalonate kinase activity was observed, reaching a maximum of 1.7 nkat/mg protein at 8 days after transfer. The alkaloid accumulation in the cultures was monitored, and ajmalicine was found to be the major product. Under standard conditions, mevalonate kinase activity showed a diurnal rhythm, with highest activities at 12:00 and 24:00. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.