Ethylene biosynthetic genes are differentially regulated by ethylene and ACC in carnation styles

Treatment of intact carnation (Dianthus caryophyllus 'White Sim') flowers with ethylene induced increased ethylene production from all flower organs and increased accumulation of transcripts from genes encoding enzymes involved in ethylene biosynthesis. Three members of the 1-aminocyclopropane-1-carboxylate (ACC) synthase gene family (DCACS1, 2 and 3) were differentially regulated by ethylene within the flower. Treatment of isolated flower organs with 10 muL L-1 ethylene for 24 h, enhanced ethylene production in ovaries and petals, but not styles. Transcripts from DCACS2, DCACS3, and DCACO1 (ACC oxidase 1) were increased in isolated treated styles, although not to the levels detected in styles from ethylene-treated flowers. Although ethylene treatment of isolated styles did not induce elevated ethylene biosynthesis, treatment with 100 muM ACC resulted in large increases in ethylene evolution from the style. ACC treatment induced increases in mRNA levels of DCACS1, DCACS2, DCACS3 and DCACO1. When flowers were pretreated with CoCl 2, to prevent the conversion of ACC to ethylene, DCACS1, DCACS2, and DCACO1 transcripts were still induced, although to a lesser degree than following ACC treatment alone. Similar results were seen when flowers were treated with the ethylene action inhibitor, 1-methylcyclopropene (1-MCP), prior to ACC treatment. In styles, DCACS2, DCACS3, and DCACO1 genes were transcriptionally regulated by both ACC and ethylene. In petals, ACC increased transcript abundance of all 4 genes, but these transcripts were not detectable when flowers were pretreated with either CoCl2 or 1-MCP. These results confirm that ethylene is the primary regulator of ACS and ACO gene expression in petals.