The biosynthetic origin of germination stimulants for orobanche ramosa (l.) in tobacco and arabidopsis

Abstract

The germination of root parasites like Orobanche and Striga depends on chemical products exuded from the roots of the host plant, known as germination stimulants (GS). The predominant part of them has structural similarities with sesquiterpene lactones. It is well known that sesquiterpenes are assembled by the cytosol-localized mevalonate pathway in which the key precursor—isopentenyl diphosphate (IDP) is synthesised from mevalonic acid. Our earlier results however suggested that GS originate from plastid- situated 2-C-Methyl-D-Erythritol-4-Phosphate (MEP pathway). Recently Matusova and co-authors al (18) confirmed this and hypothesized that in maize GS originate from carotenoids. In order to better understand the involvement of the two different isoprenoid biosynthetic pathways in GS formation we have used separately and in combination specific chemical inhibitors for each of biosynthetic pathways. Our results indicate that that indeed in Arabidopsis and tobacco the earliest precursors of GS originate from 1-deoxy-D-xylulose 5 phosphate pathway. However application of carotenoid biosynthesis inhibitor—norflurazon did not influences the GS production. Therefore we concluded that in tobacco and Arabodopsis GS are not derived from carotenoids but from an earlier intermediate of MEP biosynthetic pathway, which is later exported from plastids to the cytosol, to be converted to the final product—GS. © 2007 Taylor and Francis Group, LLC.