IN-VITRO INCORPORATION OF RADIOLABELED CHOLESTEROL AND MEVALONIC ACIDINTO ECDYSTEROID BY HAIRY ROOT CULTURES OF A PLANT, SERRATULA-TINCTORIA

After the transformation of stems with Agrobacterium rhizogenes, hairy root cultures have been obtained from Serratula tinctoria (Asteraceae ), a plant containing very high amounts of 20-hydroxyecdysone (20E) an d numerous other phytoecdysteroids. These cultures were found to grow regularly in vitro, either in liquid or solid media, and to maintain a high ecdysteroid production (c.a. 0.1-0.2% dry weight). 20E was the p redominant ecdysteroid, together with the corresponding 3-acetate (20E 3Ac). Ecdysteroids were not secreted in the medium but remained in roo t tissues. Moreover, a concentration gradient was observed in transfor med hairy roots, as in plant roots, characterized by a higher ecdyster oid content in the meristematic zone. In vitro incubations with two ra diolabelled precursors, [H-3]-cholesterol and [C-14]-mevalonic acid, h ave been performed, showing an efficient incorporation of these molecu les into ecdysteroids: with labelled cholesterol, 20E indeed reached 0 .25 to 0.67% of the radioactivity recovered in hairy roots after sever al days of culture and, with labelled mevalonate, 0.4 to 2.7%. Thus, h airy roots of S. tinctoria undoubtedly constitute a very promising too l for the analysis of ecdysteroid biosynthesis and functions in plants .