COMPARISON BETWEEN THE EFFECTS OF 20-HYDROXYECDYSONE AND PHYTOHORMONES ON GROWTH AND DEVELOPMENT IN PLANTS

Insect moulting hormone, 20-hydroxyecdysone or ecdysterone (E), was te sted in a series of bioassays that are commonly used for evaluation of the activity of phytohormones. The assays included: auxin coleoptile bioassay in wheat, gibberellin bioassays in dwarf maize and dwarf rice ; cytokinin bioassay on tobacco callus; brassinolide related ethylene formation assay in dwarf maize, alfalfa and Chenopodium, flowering ass ay on Chenopodium and special assay on somatic embryogenesis in cell c ultures of alfalfa. The 20-hydroxyecdysone has no biological activity in tests used for detecting phytohormone activity, excepting for sligh t gibberellin-like activity in rice. Moreover, E does not have any syn ergistic or antagonistic activity. In tissue cultures of alfalfa, E af fected differentiation of the embryos. It is concluded that, in spite of its widespread occurrence in plants, E has no direct action on grow th and proliferation of plant tissues (which is the main action of E i n arthropods). However, E and other ecdysteroids could provide a sourc e of easily available, slightly polar, polyhydroxylated sterol, requir ed for growth and cell proliferation in plants.