Study On The Physiologyical Mechanism Of Prohexadione-calcium And Daminozide Effects On Flower Colors In Herbaceous Peony(Paeonia Lactiflora Pall.)

Herbaceous peony(Paeonia lactiflora Pall.),a traditional flower originated in China,has now become a kind of popular high-end cut-flowers in the international market,which is mainly used for wedding occasions.According to the investigations into the market of P.lactiflora cut-flowers,the flower colors of red and purple are slightly tacky while the colors of pure white lack the joyness of traditional Chinese.Therefore,the pink or light pink is the most popular flower color in the current market.However,red and purple are the dominant color in traditional P.lactiflora cultivars,and are rich in cultivar resources.In contrast,the varieties and cultivar resources of pink or light pink cultivars for cut-flowers are few,which is hard to meet the demand of the market.Many studies have shown that plant flower color can be regulated by chemical means.For example if flower colors can be turned from purple or red into pink or light pink by the regulation of chemical means,it would provide significant applied values for the development of P.lactiflora cut-flowers industrialization.In this research,we explored the effect of prohexadione-calcium(Pro-Ca)and daminozide application on the flower color in P.lactiflora,analyzed the changes of flavonoid components and contents to chemical treatment,and further explored the effect of chemical treatment on the expression levels of related flavonoid biosynthetic genes.The research yields the following major findings.(1)The flower colors of P.lactiflora cultivar 'Lu Hong' and 'Fenzhu Pan' were turned from purplish red into dark pink and from pink into light pink with application of 1 g·L-1 Pro-Ca 6 times and 5 g·L-1 daminozide 5 times respectively,from the period of leaf extension stage to flower-bud stage.The resulted showed that both the chemical treatment of Pro-Ca and daminozide can bleach the flower color of P.lactiflora,which can be widely applied to the production of P.lactiflora cut-flowers.(2)In 'Lu Hong' petals,five anthocyanins were identified which included cyanidin-3,5-di-O-glucoside(Cy3G5G),peonidin-3,5-di-O-glucoside(Pg3G5G),peonidin-3,5-di-O-glucoside(Pn3G5G),peonidin-3-O-glucoside(Pn3G)and peonidin-3-O-malonylglucoside-5-O-glucoside(Pn3MloG5G),and seven anthoxanthins were detected that included quercetin-3,7-di-O-glucoside(Qu3G7G),quercetin-3-O-galactoglucoside(Qu3GloG),quercetin-3-O-glucoside(Qu3G),kaempferol-3,7-di-O-glucoside(Km3G7G),kaempferol-3-O-malonylglucoside-7-O-glucoside(Km3MloG7G),kaempferol-3-O-galactoglucoside(Km3GloG)and kaempferol-7-O-glucoside(Km7G)were identified using HPLC-ESI-MSn.After Pro-Ca application,the components of both anthocyanins and anthoxanthins were remained the same in three different flower developmental stages when compared to the control group,but the content of each component was significantly decreased.(3)In 'Fenzhu Pan' petals,three anthocyanins and seven anthoxanthins were identified by using HPLC-ESI-MSn.The flavonoids identified in 'Lu Hong' except for anthocyanins Pg3G5G and Pn3G as well as anthoxanthins Km3MloG7G were identified in 'Fenzhu Pan'.Besides,anthoxanthin Km3G was also detected in 'Fenzhu Pan'.After daminozide application,the components of both anthocyanins and anthoxanthins were also remained the same in three different flower developmental stages compared to the control group.The the components and total amount of anthocyanins are significantly reduced,with the decrease in the content of quercetin derivatives and the increase in the content of kaempferol derivatives in anthoxanthins.As a result,the content of total anthoxanthins and total flavonoids were increased after daminozide application.(4)The expression levels of related flavonoid biosynthetic genes P.lactiflora petals were performed by qRT-PCR and the effect of Pro-Ca and daminozide application on the related flavonoid biosynthetic genes was different.Specifically,after Pro-Ca application,the expression of upstream chalcone synthase gene(PlCHS),flavone-3-hydroxylase gene(PIF3H)and flavonoid-3'-hydroxylase gene(PlF3'H)were inhibited,which reduced the level of upstream anthoxanthins.With the lower expression of downstream dihydroflavonol 4-reductase gene(PIDFR),anthocyanidin synthase gene(PlANS)and flavonoid 3-O-glucosyltransferase gene(PlF3GT)after Pro-Ca application the flower colors of 'Lu Hong' would ve bleached as a result.After daminozide application,the expression of upstream PlF3'H and downstream.PIDFR and PIANS were inhibited which decreased the accumulation of anthocyanins and would bleach the flower colors in 'Fenzhu Pan' petals.