Developmental Aspects of Ethylene Biosynthesis during Somatic Embryogenesis in Tissue 4Medicago sativa

Rates of ethylene production were determined in highly embryogenic and virtually non-embryogenic tissue cultures of Medicago sativa ssp. falcata during a 10-d induction period on medium containing 2, 4, -dichlorophenoxyacetic acid and kinetin, and during the first 10 d of somatic embryo formation on growth regulator-free medium. In cultures of both genotypes, ethylene production increased rapidly, peaked after 10 d and then declined again rapidly. This fall in ethylene production rate also occurred when the cultures were kept on the growth regulator-containing medium, but it was more pronounced in cultures which were transferred to growth regulator-free medium, i.e. under conditions favouring somatic embryo formation. There were only minor differences in the rates of ethylene production between the two genotypes, mainly after transfer to growth regulator-free medium. Cobalt and nickel ions strongly inhibited ethylene biosynthesis throughout the culture period under investigation. They did not, however, affect embryo induction, but exerted strongly inhibitory effects on somatic embryo formation. Amino-oxyacetic acid and aminoethoxyvinylglycine had no effect on ethylene production during the inductive period. It is concluded from these experiments that the high rates of ethylene production during embryo induction are not essential for subsequent embryo differentiation.