Effect of sucrose on sensitivity to ethylene and enzyme activities and gene expression involved in ethylene biosynthesis in cut carnations

Application of sugars extends the vase life of many cut flowers. The role of applied sucrose in petal senescence of cut carnations (Dianthus caryophyllus cv. Barbara) was investigated. Petal senescence was significantly delayed by 5% sucrose treatment. Although glucose, fructose, and sucrose concentrations decreased in the petals of control flowers with time, these concentrations increased on sucrose treatment. To investigate the effect of sucrose on sensitivity to ethylene, flowers were pre-treated with aminoethoxyvinyl glycine (AVG) to avoid the effect of ethylene biosynthesis and placed in a sucrose solution for 0 and 5 days. Flowers were then exposed to ethylene at 0.2, 0.6, and 2 μL L⁻¹. Sucrose treatment did not delay petal senescence by ethylene exposure on day 0, suggesting that the effect of sucrose on the sensitivity to ethylene is negligible. Petal wilting was not accelerated by ethylene exposure at 0.2, 0.6, and 2 μL L⁻¹ without sucrose treatment on day 5, but sucrose treatment did not delay petal wilting, implying that sucrose treatment maintains sensitivity to ethylene in the aged flowers. Sucrose treatment delayed climacteric-like increase in the ethylene production of petals and gynoecium. 1-Aminocyclopropane-1-carboxylate (ACC) synthase (ACS) and ACC oxidase (ACO) activity in petals increased during senescence, and sucrose treatment delayed the increase in ACS activity and suppressed the increase in ACO activity. The transcript levels of the ACS gene DcACS1 and the ACO gene DcACO1 in petals increased during flower senescence, and sucrose treatment delayed the increase in the transcript levels of DcACS1 and suppressed the increase in the transcript levels of DcACO1. These results suggest that delay in petal senescence by sucrose treatment is due to maintenance of sugar level in the petals, which delays a climacteric-like increase in ethylene production. The delay in ethylene production is associated with ACS and ACO activities regulated mainly at the transcriptional level.