Comparison of petal senescence between cut and intact carnation flowers using potted plants

Abstract

The phytohormone ethylene is known to play a crucial role in promoting petal senescence in cut carnation flowers. In most previous studies in carnation, petal senescence was analyzed in cut flowers, and knowledge of petal senescence in intact flowers is limited. In this study, we compared changes in sugar level, ethylene production and expression of senescence-associated genes during petal senescence in cut and intact flowers using potted carnations (Dianthus caryophyllus L. cv California Mahalo). Flower longevity was significantly shorter in cut flowers than in intact flowers. Both cut and intact flowers showed inward rolling of petals and an increase in ethylene production at the end of their floral life; however, the timing of increase in ethylene production was clearly accelerated in cut flowers. Glucose and fructose levels in the petals of cut flowers rapidly decreased from the full-opening stage, while these levels remained relatively high in intact flowers. The accelerated induction of genes for 1-aminocyclopropane-1-carboxylate (ACC) synthase (DcACS1) and ACC oxidase (DcACO1) in cut flowers corresponded with ethylene production. The transcript level of DcEIL1/2, a homolog of EIN3, which is a key component in ethylene signaling, rapidly decreased in senescing petals of cut flowers, while it remained relatively high until the end of floral life in intact flowers. We isolated a homolog of autophagy-related gene 8 (DcATG8a), which is an essential gene for autophagy, and a gene for hexokinase (DcHXK1), which is known as a glucose sensor, from carnation flowers. Increasing transcript level of DcATG8a in senescing petals corresponded with ethylene production in both intact and cut flowers. The transcript level of DcHXK1 gradually decreased over time in both cut and intact flowers, but to a lesser extent in intact flowers. These results suggest that petal senescence in cut flowers is hastened by accelerated ethylene production, which is likely due to a rapid decrease in sugar content. Our data on hexokinase may also suggest the involvement of a sugar sensor in the regulation of petal senescence.