Biosynthesis of labdenediol and sclareol in cell-free extracts from trichomes of Nicotiana glutinosa

Biosynthesis of the diterpenes labdenediol and sclareol from all trans-geranylgeranyl pyrophosphate was observed in cell-free extracts prepared from leaf midvein epidermal peels of Nicotiana glutinosa 24A. The bioactivities were shown to be exclusively localized in trichomes, to be conferred by a soluble enzyme(s), and to resemble other plant terpene cyclase activities in basic characteristics. Chromatographic methods for protein purification including gel filtration, anion exchange, hydroxyapatite chromatography, and free-flow isoelectric focusing. Thermal inactivation and end-product inhibition experiments did not afford separation of the biosynthetic activities. Results indicate that these labdane diterpenes are direct products of cyclization reactions catalysed by a soluble cyclase(s). To the best of our knowledge, this report represents the first case for direct biosynthesis of diterpene di-alcohols by cyclization of the acyclic precursor. A unified scheme for formation of labdane mono- and di-alcohols in Nicotiana species is presented.Abbreviations DEAE diethylaminoethyl - GGPP geranyl-geranyl pyrophosphate