Changes in ethylene responsiveness of senescence-related genes during carnation flower development

Changes in ethylene responsiveness of senescence-related (SR) genes in carnation (Dianthus caryophyllus cv. White Sim) petals were investigated during flower development. Dose-response and time-response analysis of SR gene expression indicate that SR genes can be divided into two groups according to their response to ethylene. The ethylene biosynthetic genes, ACC synthase and ACC oxidase represent one group. They show a marked delay of 6 and 9 h in mRNA accumulation in response to ethylene and their apparent dissociation constants of the response (K-r) at open flower stage of development are 17.20 and 1.76 mul l(-1), respectively. The second group of ethylene responsive genes contains SR5, SR8, SR12, and DCCP. These genes show an almost immediate accumulation of their respective mRNAs in response to ethylene and have K(r)s at open flower stage of development of 0.08, 0.46, 0.25, and 0.05 ml l(-1), respectively. All SR genes, including the ethylene biosynthetic genes, show increases in responsiveness to ethylene as measured by the accumulation of their respective transcripts during flower development. A model of ethylene signal transduction in carnation petals and flower senescence is presented taking into account these observations.