Cut flowers of a transgenic carnation (Dianthus caryophyllus L.) line (sACO 1 line), which was transformed with a carnation 1-aminocyclopropane-1-carboxylate (ACC) oxidase cDNA in sense orientation (sACO transgene), had a longer vase life than had flowers of the non transformed plant and produced only a negligible amount of ethylene during natural senescence. The suppressed ethylene production in sACO-1 line was not accompanied with the accumulation of mRNA for ACC oxidase (DC-ACO1) gene in the gynoecium or mRNA for DC ACO1 and ACC synthase (DC-ACS1) genes in the petals. Previously, it was shown that in naturally senescing carnation flowers, ethylene is first produced from the gynoecium the evolved ethylene, acting as a diffusible signal which is perceived by petals, induces the expression of DC- ACO1 and DC-ACS1 genes that results in autocatalytic ethylene production in the petals (Shibuya et al., 2000). The results indicate that sACO transgene inhibits the expression of DC ACO1, probably by cosuppression in the gynoecium, which then suppresses ethylene production in all flowers of sACO-1 line.