| Herbaceous peony,a herbaceous plant of the genus Paeonia in Paeoniaceae,is a traditional ornamental flower native to China.Herbaceous peony has high ornamental value,and the cut flower production has broad prospects.However,the mismatch between the natural blooming period and the major festivals at home and abroad and the short vase life could not meet the demands for flower appreciation.At the same time,the lack of the basic theory and storage and transportation infrastructure of cut herbaceous peony substantially restrict the ornamental value of this crop,resulting in major economic loss within the floriculture industry.Therefore,it is necessary to study the mechanism in senescence of cut herbaceous peony.In order to comprehensively understand the mechanism of herbaceous peony senescence process,we determined senescence indexes of different cultivars and analyzed their interrelation,verified the function of key transcription factor in senescence of cut herbaceous peony by molecular biological methods,and selected the chemicals and germicides for the cut herbaceous peony to delay flower senescence.The main results are as follow:1.We determined senescence indices of 25 different cultivars and analyzed their interrelation.We found that peony cultivars could be divided into 3 types based on the type of ethylene change:the climacteric type,the nonclimacteric type and the type with a later stage increase.In the climacteric type,the senescence process of flower was accompanied by the large production of abscisic acid（ABA）and ethylene,and the peak of ABA production was earlier than that of ethylene.The content of ethylene was not significantly changed in the nonclimacteric type during flower senescence,but the peak of ABA content appeared,and the peak appeared later than that of the climacteric type.The ethylene content increased gradually during flower senescence in the type with a later stage increase,and the ABA content reached the peak at the early senescence stage.The content of GA in 25 different cultivars of herbaceous peony increased first and then decreased.Combined with the above results,we speculated that ABA is the hormone that initiates flower senescence in the climacteric type and the type with a later stage increase herbaceous peony.The increase of ABA content promotes the release of ethylene,and the large amount of ethylene production accelerates flower senescence.ABA is the key hormone to promote flower senescence in the nonclimacteric type peony varieties,ethylene has no strong effect on flower senescence.High production of ABA or ethylene may inhibit GA synthesis.The contents of MDA and membrane permeability increased during flower senescence.The activities of SOD and CAT kept at a high level before blooming stage,but during senescence stage their activities decreased.The activities of SOD and CAT were negatively correlated with the contents of MDA and membrane permeability,indicating that the cell membrane damage and flower senescence were caused by the imbalance of reactive oxygen production.Correlation analysis results show that the soluble sugar and protein contents were significantly and positively correlated with the ABA content.Thus,we speculated that ABA may influence the accumulation of soluble sugar and protein.2.The previous transcriptome data showed that PlZFP may play an important role in flower senescence.In this study,Pl ZFP-silenced petal discs had longer life while Pl ZFP-overexpressing transgenic tobacco had short flower longevity.On the fourth day after silencing Pl ZFP,GA content in’Hangshao’petals was 1.25 times of that in control petals,while ABA and ethylene content decreased to 0.73 and 0.39 times,respectively.On the fifth day after Pl ZFP overexpression,GA content decreased to 0.71 times of that in wild type tobaccos,while ABA and ethylene content increased to 2.08 times and 1.64 times,respectively.Silencing Pl ZFP in petal discs reduced the transcript abundances of the endogenous hormone biosynthesis-related genes Pl ACO1,Pl ACO3,Pl ACS1,Pl NCED2,and Pl AAO and increased the transcript abundance of Pl GA3ox1.Overexpression of Pl ZFP in tobacco flowers showed the opposite influences on these genes.Furthermore,Pl ZFP directly bound to the Pl NCED2promoter,and silencing Pl NCED2 delayed senescence in discs.Moreover,exogenous ABA,Ethephon and paclobutrazol（PAC,a GA inhibitor）,accelerate senescence in PlZFP-silenced discs.Taken together,the PlZFP-PlNCED2 regulatory checkpoint may positively affect the production of ABA and mediates the combinatorial interactions of ABA with GA and ethylene during flower senescence in cut herbaceous peony.3.The previous transcriptome data also showed that PlMYB308 may play an important role in flower senescence.Silencing Pl MYB308 delayed the longevity of’Hangshao’petal disc.On the fourth day after Pl MYB308 silencing,GA content in petals of’Hangshao’was about1.58 times of that in control petals,while ABA and ethylene content decreased to 0.62 and0.75 times,respectively.The overexpression of Pl MYB308 in tobacco accelerated the senescence of flowers.On the fifth day after Pl MYB308 overexpression,GA content in tobacco flowers decreased to 0.74 times of that in wild type tobaccos,while ABA and ethylene content increased to 1.68 and 2.08 times,respectively.Correspondingly,5 endogenous hormone biosynthetic genes showed variable expression levels in petals after Pl MYB308 silencing or overexpression.A dual-luciferase assay and yeast one-hybrid analysis showed that Pl MYB308specifically binds the Pl ACO1 promoter.Moreover,treatment with ethylene and 1-MCP can accelerate Pl MYB308 silencing-reduced senescence and delay Pl MYB308-overexpression-induced senescence.We also found that PlACO1 silencing delayed senescence in herbaceous peony petals.Taken together,our results suggest that the Pl MYB308-Pl ACO1 regulatory checkpoints positively mediate the production of ethylene,and thus contribute to senescence in herbaceous peony flowers.4.The optimization of VIGS technology and the chemical prescription can delay’Hangshao’flower senescence.In the optimization of VIGS technology,we found that flowers with soft buds and loose petals were the most suitable materials for VIGS infection;Vacuum infection method could silence the senescence related transcription factors Pl ZFP,Pl MYB308without damaging cut flowers.The study of chemical prescription found that sugar,organic acid,inorganic salt and fungicide can be used as the main components to prolong the vase life of cut flower.Single component 4%sucrose,100mg/L citric acid,100mg/L aluminum sulfate（Al2（SO4）3）,200mg/L 8-hydroxyquinoline（8-HQ）had the best effect on prolonging the vase life of’Hang Shao’.4%sucrose+100mg/L citric acid+100mg/L Al2（SO4）3was the most suitable chemical prescription,it could prolong the vase life of’Hangshao’by 23%compared with the control.The optimization of VIGS technology combined with the chemical prescription can prolong the vase life to the maximum.Silencing Pl ZFP combined with 4%sucrose+100mg/L citric acid+100mg/L Al2（SO4）3 chemical prescription treatment can prolong the vase life of 32%. |
