Regulation of ethylene biosynthesis and interorgan signaling following pollination in Dianthus caryophyllus L. cv 'white sim'

The senescence of carnation (Dianthus caryophyllus L.) flowers is regulated by the phytohormone ethylene and is associated with the increased abundance of certain mRNAs. These transcripts include ACC synthase and ACC oxidase, genes unique to ethylene biosynthesis, and an ethylene responsive cysteine proteinase which is believed to catalyze the mobilization of N from senescing tissues. The carnation ACC synthase gene family includes at least 3 members that are differentially regulated by hormonal, chemical, and developmental stimuli in a floral organ specific manner. The ACC synthase genes show some tissue specificity, with DCACS1 preferentially expressed in petals, DCACS2 and DCACS3 expressed most abundantly in styles, and only low basal levels of DCACS3 detectable in ovaries. Following pollination, increased ethylene biosynthesis in styles and petals correlated well with ACC, ACC synthase activity and the expression of ACC synthase and ACC oxidase genes in these organs. In contrast, ovaries had barely detectable ACC synthase activity and only basal levels of DCACS3 expression following pollination despite the accumulation of ACC and evolution of ethylene. The induction of ACC oxidase in ovaries by pollination suggests that ACC which is translocated from other floral organs is oxidized to ethylene in the ovary. Application of inhibitors of ethylene action to either the pollinated flower or the pollinated style prevented pollination-accelerated corolla senescence, ethylene biosynthesis from ovaries and petals, and the sustained ethylene production from styles. This inhibition of ethylene action in floral organs prevented pollination-induced gene expression in ovaries and petals and the induction of DCACS1 and DCACS2 in styles. The regulation of ethylene within individual floral organs following pollination has led to a model for interorgan signaling in carnation flowers. This model suggests that the primary pollination signal is a pollen-derived factor which induces DCACS3 in styles. Subsequent ethylene production then induces ethylene-responsive ACC synthase genes in styles and ACC oxidase in ovaries. ACC translocated from the styles is oxidized to ethylene in the ovary, and ACC or ethylene from the gynoecium then induces DCACS1 and DCACO1 in petals. This ethylene production by the petals results in the senescence of the corolla.