Effect Of Glucose On Ethylene Biosynthesis And Signal Transduction In Tree Peony Cut Flowers During Postharvest Senescence

Tree peony (Paeonia suffruticosa), a traditional ornamental plant in China, is popular for its attractive flowers around the world. However, the short flower life span and the lack of effective preservation technology restrict the commercialization development of cut tree peony flowers. Ethylene plays a crucial role in flower senescence of tree peony, so it is inhibition of ethylene action that possibly promotes postharvest qualities of this flower. In addition to being carbon and energy sources, sugars have been proved to act as a signaling molecule to interact with plant hormone signals, for example ethylene, in regulating plant growth and development. For cut flowers, the role of sugars on extension of flower longevity is not only due to the supply of respirable substrates, but also due to the influence of ethylene action. Therefore, it is of great practical value to study the effect of sugars on ethylene-mediated cut tree peony flower senescence, which would provide theoretical bases for preservation technology. In the present study,’Luoyang Hong’, an ethylene-sensitive cultivar, was taken as material to examine the influences of glucose on flower opening and senescence, ethylene biosynthesis and signal transduction. The main experimental results are as follows:Treatment with500mM glucose delayed visible senescence of cut tree peony flowers and significantly extended its vase life, whereas the osmolyte mannitol failed to make flowers fully open. N-acetyl-glucosamine (NAG), the hexokinase (HXK) inhibitor, decreased the effect of glucose on postharvest flower development. Glucose directly delayed and inhibited climacteric ethylene production, and also reduced ethylene responsiveness. These results suggest that the extension of flower longevity of cut tree peony by glucose is, at least partially, due to the delay and inhibition of climacteric ethylene production and the decrease in ethylene sensitivity.The results of biochemical analysis and gene expression indicated that glucose delayed and inhibited the increase in ACS activity, which was accompanied by a delay of ACC accumulation, and also lowered ACO activity. ACS was the main factor in the influence of glucose on ethylene biosynthesis. Glucose delayed and inhibited the accumulation of PsACS1mRNA through HXK-dependent pathway. Thus, glucose signal impairs ethylene biosynthetic activities, at least partially through the repression of PsACS1expression, which results in the delay and inhibition of climacteric ethylene production, and therefore delays cut tree peony flower senescence.Full-length cDNAs for transcription factor EIN3homologous genes in ethylene signal transduction were first isolated from tree peony by the combination of RT-PCR and RACE-PCR, named PsEIL1(GenBank No. JQ771469), PsEIL2(GenBank No. JQ771470), and PsEIL3(GenBank No. JQ771471). Real-time PCR analysis revealed that PsEILs are spatiotemporally regulated. PsEIL1is likely associated with petal senescence, and possibly subject to post-transcriptional regulation by ethylene; PsEIL2and PsEIL3are regulated at the transcriptional level, and PsEIL3, which was the most abundant in petals and under positive feedback regulation by ethylene and1-MCP, may play an essential role in ethylene-mediated postharvest development of cut tree peony flowers.Expression analysis of genes involved in ethylene signal transduction showed that glucose interacted with ethylene signaling at many points including PsETR2, PsCTR2～3, PsEIN2, and PsEIL3in cut tree peony flowers. Among these points, changes of PsCTR3and PsEIL3transcript abundance in petals were related to the regulation of ethylene sensitivity by glucose. These data suggest that glucose signal decreases the sensitivity to ethylene at least by inducing the expression of PsCTR3and preventing that of PsEIL3, and therefore delays flower senescence of cut tree peony.