BIOSYNTHESIS OF ECDYSTEROIDS IN IN-VITRO PROTHALLI CULTURES OF POLYPODIUM VULGARE

The concentration of ecdysteroids in Polypodium vulgare has been studi ed in different parts of the wild plant as well as in the two in vitro micropropagated tissues. The ecdysteroid composition (abutasterone, p olypodine B, 20-hydroxyecdysone, inokosterone, 24-hydroxyecdysone, pte rosterone and ecdysone) was the same for all the sources investigated, but quantitative differences were found among them, with the exceptio n of spores that did not produce these compounds. In contrast, the in vitro culture of spores originated the formation of haploid (prothalli ) and diploid (sporophytes) tissues with a common feature: a proportio n of 25-deoxyecdysone derivatives higher than that found in the wild p lant. Prothalli micropropagated in vitro, generated from spores collec ted in different European areas, exhibited characteristic phytoecdyste roid contents that were constant over the four-year period studied. On the other hand, results on incorporation of radiolabelled ecdysteroid precursors, such as mevalonate, cholesterol or ecdysone, indicated th at our in vitro system is adequate for biosynthetic studies. Labelled mevalonate and cholesterol were incorporated into all identified ecdys teroids, and labelled ecdysone was biotransformed into other 25-hydrox yecdysteroids present in this plant. Based on the different rates of i ncorporation of these precursors, a biosynthetic pathway for the last steps of ecdysteroid biosynthesis in P. vulgare was proposed. Copyrigh t (C) 1996 Elsevier Science Ltd