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1-Aminocyclopropane-1-carboxylate (ACC) oxidase (ACO) catalyzes the final step of ethylene biosynthesis. ACO proteins are also reportedly encoded by a multigene family. Although the presence of several ACO genes is suggested in carnation (Dianthus caryophyllus L.), DcACO1 is the only ACO gene in which full-length cDNA has been isolated. This study aimed to clone another ACO gene in carnation flowers and investigate changes the expression of the two ACO genes in floral organs during flower senescence. We cloned a homolog of the ACO gene from carnation gynoecium and designated it DcACO2. Transcript levels of DcACO2 were higher in the style and ovary than in the petals at harvest, although DcACO2 transcript levels in these organs increased during flower senescence. The ACO activity in the style was very high at harvest, suggesting that this high activity could be attributed to the translation of the DcACO2 transcript. However, DcACO2 transcript was only detected at very low levels in the petals of senesced flowers. Ethylene and ACC treatments accelerated petal wilting and increased ethylene production of the petals, style, and ovary. In the style and ovary, the DcACO1 transcript level was markedly higher than the DcACO2 transcript level as a result of ethylene and ACC treatments, and DcACO1 transcript levels in the petals were also increased by ethylene and ACC treatments. These results indicate that the expression of DcACO1 and DcACO2 are differently regulated among floral organs during senescence in carnation flowers.

Treatment with sucrose promoted petal growth associated with flower opening in cut roses. We investigated the effect of sucrose treatment on cell size and subcellular concentration of soluble carbohydrates in petals of cut rose cv. Sonia flowers. Petals of sucrose-treated flowers, but not control flowers, markedly curved outward, resulting in complete reflection. Petal fresh weight (FW), petal area, and adaxial epidermal cell size in the control flowers increased with time, and treatment with sucrose accelerated this increase, indicating that sucrose promotes petal cell expansion. Glucose, fructose, sucrose, methyl glucoside, and xylose were detected in the petals. In the petals of control flowers, concentration of these carbohydrates, except fructose, decreased. Sucrose treatment markedly increased glucose and fructose concentrations in petals. Estimation of subcellular volumes based on transmission electron micrographs showed that volume of cell walls and vacuoles in the petals of control flowers increased in response to sucrose treatment. Sucrose treatment increased glucose and fructose concentrations in the vacuole and glucose, fructose, and xylose concentrations in the apoplast. We concluded that sucrose treatment increases glucose and fructose concentrations in the vacuole, which may reduce the osmotic potential of the symplast and increase water uptake leading to cell expansion during flower opening.