The Arabidopsis thaliana etr1-1 allele, capable of conferring ethylene insensitivity in a heterologous host, was introduced into transgenic carnation plants. This gene was expressed under control of either its own promoter, the constitutive CaMV 35S promoter or the flower-specific petunia FBP1 promoter. In about half of the transgenic plants obtained flower senescence was delayed by at least 6 days relative to control flowers, with a maximum delay of 16 days, a 3-fold increase in vase life. These flowers did not show the petal inrolling phenotype typical of ethylene-dependent carnation flower senescence. Instead, petals remained firm and finally started to rot and decolorize.
In transgenic plants with delayed flower senescence, expression of the Arabidopsis etr1-1 gene was detectable and the expression pattern followed the activity of the upstream promoter. In these flowers expression of the ACO1 gene, encoding the final enzyme in the ethylene biosynthesis pathway, ACC oxidase, was down-regulated. This indicates that the autocatalytic induction of ethylene biosynthesis, required to initiate and regulate the flower senescence process, is absent in etr1-1 transgenic plants due to dominant ethylene insensitivity.
The delay in senescence observed in transgenic etr1-1 flowers was longer than in flowers pretreated with chemicals that inhibit either ethylene biosynthesis (amino-oxyacetic acid) or the ethylene response (silver thiosulfate). This may have important implications for post-harvest management of carnation flowers.