Screening plants of European North-East Russia for ecdysteroids

A strategy for screening plants for ecdysteroid content based on the ‘positive tribe’ principle is developed and applied, for the first time, to screen the flora of European North-East Russia to identify species which accumulate ecdysteroids; 700 samples representing 411 species from 380 genera of 82 families were investigated. It is established that species with moderate to high ecdysteroid content (detectable with the Drosophila melanogaster BII cell bioassay) are not numerous (4% of all screened species). They are found in 14 families of different kinship level. Within families, ecdysteroid-containing plants form groups of closely cognate species (within certain tribes and/or genera); most ecdysteroid-containing species in this study were present in the tribe Cardueae (within the Asteraceae) and in the tribe Lychnideae (within the Caryophyllaceae). Radioimmunoassay, using an ecdysteroid-specific antiserum, allowed us to detect trace amounts of phytoecdysteroids (0.1–0.5μg ecdysone equivalents/g plant matter) below the threshold detectable by the insect ecdysteroid receptor-based bioassay. It was found that such trace amounts of ecdysteroids are typical of many of the other plant species tested. We propose that a positive response in the bioassay is an appropriate criterion for detecting species with ecdysteroid content sufficient for protecting the plant against non-adapted phytophagous insects. Analysis of the geographical distribution of ecdysteroid-containing species (as detected by the bioassay) reveals that many of them belong to the southern or polyzonal latitudinal groups. This supports the impact of ecological–geographical factors upon ecdysteroid distribution in plants.