Influence Of Ethylene On Flower Opening And Senescence Process And Expression Of Related Genes In Tree Peony Cut Flower

Ethylene plays a crucial role in the process of tree peony (Paeonia suffruticosa) cut flower postharvest opening and senescence, but the mechanism of its function has been unclear, which results in the lack of the theoretical bases of preservation technology and restricting the development of commercialization and industrialization of tree peony cut flower. So it is of great theoretical value and practial meaning to startup the study of ethylene effect and regulation mechanism in it. In present work, 'Luo Yang Hong' tree peony cut flower, which produced ethylene in a climacteric-like pattern, was taken as material to examine the influence of exogenous ethylene and ethylene action inhibitor 1-MCP on flower opening, and expression of related genes in ethylene biosynthesis and signal transduction. The main experimental results are as follows:10 ppm ethylene treatment for 6 h hastened the process of flower opening, and induced petals abscission seriously after full-open; while 1.0ppm 1-MCP impeded it.Ethylene production of cut flower was promoted by ethylene and inhibited by 1-MCP, which was closely associated with the flower opening process.Changes of ACS activity in petals was related to the endogenous ethylene production, suggesting the main factor of ACS in the influence of tree peony cut flower opening and senescence.Homologic fragments of ethylene synthesis and signal transduction related genes,including ACS, ACO, ETR1 and EIN3, were isolated from petals by RT-PCR, and were named PsACS (GenBank No.DQ337250),PsACO(GenBank No.DQ337251 ),PsETR1 和 PsEIN3.Then full length of PsACS and PsACO cDNA were obtained by RACE-PCR.Sequence analysises showed that PsACS is 1766bp in length and contains a 1479bp open reading frame flanking by a 146bp 5'-non-translation region and a 141bp 3'-non-translation region; PsACO is 1211bp in length and contains a 939bp open reading frame flanking by a 65bp 5'-non-translation region and a 117bp 3'-non-translation region. The analysises of deduced amino acid sequence showed that PsACS shared about 41-73% homology with the accessed ACS in GenBank, such as apple, tomato, geranium, petunia,camellia and so on; PsACO shared more than 80% homology with ACO of tobacco, petunia, camellia, apple, peach and so on. While PsETR1 is 797bp in length, and the homology of nucleotide sequence with Ph-ETR1-3 is 85%; PsEIN3 is 542bp in length and shared homology of 83% with PpEIL2. 3'end of PsETR1 was obtained by RACE, and the final sequence encodes a 587 aa open reading frame, including two of three N-terminal hydrophobic transmembrane regions and all of the five histidine protein kinase domains(H, N, G1 and G2).The results of Northern blot analysis using specific probes indicated that the expression of PsACS was associated with flower opening and senescence process, and abscission of petals as well. With the opening process of flower, PsACS began to express at stage 4 and enhanced obviously at the stage of full-open. Exogenous ethylene promoted the accumulation of PsACS mRNA,while 1-MCP decreased it.Expression of PsACO did not change with the flower opening, and did not affected by ethylene or 1-MCP either.Because the expression of PsACS did not always coincide with the ACS activity and ethylene production, so it was believed that PsACS was involved in the regulation of tree peony cut flower ethylene reaction not only at the transcriptional level but also the post-transcriptional level. While PsACO regulated it mainly at the level of post-transcriptional level. PsETR1 and PsEIN3 showed a constitutive expression in controlled petals, but responded to exogenous ethylene and 1-MCP. It was proposed that the PsETR1 and PsEIN3 genes and their resultant protein may be involved in the ethylene sensitivity and responses of tree peony cut flower.