DOES ETHYLENE PLAY A ROLE IN THIDIAZURON-REGULATED SOMATIC EMBRYOGENESIS OF GERANIUM (PELARGONIUM X HORTORUM BAILEY) HYPOCOTYL CULTURES

The accumulation of ethylene in headspace of hypocotyl cultures of ger anium (Pelargonium x hortorum Bailey) and its possible role in thidiaz uron-mediated somatic embryogenesis was investigated. The action of et hylene as determined by various ethylene synthesis and action inhibito rs was varied. Silver nitrate (AgNo3), aminoethoxyvinylglycine (AVG), and silver thiosulphate (STS) had no significant influence on the embr yogenic response, while 1-methylcyclopropene (1-MCP) applied during th e initial 3 d of induction or the expression phase, significantly incr eased the number of somatic embryos formed. Thidiazuron-treated tissue s accumulated large quantities of ethylene within 6 h of culture, but the levels decreased after 12 h and reached very low levels after 3 d in culture. In the presence of acetylsalicylic acid (ASA), the levels of ethylene decreased by 20 to 50% during the first 48 h of culture. A nalysis of endogenous auxin, cytokinins, and abscisic acid (ABA) indic ated possible interactions of ethylene with other phytohormones during the induction of somatic embryos on geranium hypocotyl explants. Thid iazuron (10 mu M)) increased, while ASA decreased the levels of endoge nous auxin, cytokinins, and abscisic acid during this period of induct ion.