Elucidation Of The Mechanism Of Peony Reflowering In Autumn Regulated By Sugar Metabolism Through Defoliation And Hormone Treatment

Tree peony(Paeonia suffruticosa Andr.),the flowers of which are big,colorful and enjoyable,is known as the “King of Flowers” with high ornamental and humanistic value.However,the short and concentrated natural florescence seriously hinders the development of tree peony industry.Autumn-flowering tree peony is a kind of peony with the characteristics of shallow dormancy,which can reflower in autumn.But there are many problems in the process of natural autumn-flowering tree peony development,such as unstable buds germination,lower leaf development,lower reflowering rate,small or abnormal flowers and impacting peony ornamental value.At present,defoliation and hormone treatment are the effective measures to improve the ornamental value of autumn-flowering tree peony.In this study,tree peony ‘Qiu Fa No.1' plants were chosen as the study materials and were subjected to defoliation in different degrees and treated with hormones(GA or ABA).The morphological changes were observed,and the physiological indexs were measured.Furthermore,the gene expression levels of some representative carbohydrate transferring and metabolizing genes were determined by quantitive real time PCR.These results may provide evidence for better understanding the effect of different treatments on the reflowering of autumn-flowering tree peony,and provide a theoretical basis for the regulation of flowering period and technical support for accelerating the development of peony industry.Major conclusion are listed as follows:1.In the experiment of defoliation in different degrees,the flower rate,bud rate and germination rate of defoliation treatment,three leaves treatment and control decreased in turn.And the sucrose content of defoliation treatment decreased in the flower,but glucose and fructose increased.qRT-PCR results showed that the expression of sugar transporter genes PsSUT1,PsSUT4 and PsSWEET12 were up-regulated,PsSWEET1 and PsSWEET7 were down-regulated.The expression of the invertase genes,like PsCIN2,PsCIN3,PsVIN1 and PsVIN2 were up-regulated.Meantime three leaves was up-regulated compared with the control,but lower than the defoliation,which indicated that defoliation regulated the transport and metabolism of sugar,promoted the release of bud dormancy and reflowering.2.The effect of defoliation and GA treatment on the autumn-reflowering showed that defoliation treatment can induce reflowering,while GA treatment just induce bud development and final abortion.Sugar analysis showed that the sucrose content of defoliation treatment was reduced,and it had higher glucose and fructose contents in young leaves,bracts and petals.The expression of PsSUT4 and PsSWEET12 were significantly induced in young leaves and petals.The expressions of PsCIN2,PsCIN3 and PsCWIN1 were up-regulated in petals,and in bracts and leaves,the expressions of PsCIN2 and PsCWIN1 in the defoliation treatment were higher than that in the GA treatment.It is suggested that PsCIN2 and PsCWIN1 play important roles in reflowering of peony.The glucose and fructose contents of different organs treated in GA treatment were higher than control.The expression of PsSUT1 was induced in petals,young leaves and bracts;PsVIN1 and PsVIN2 were induced by defoliation and GA treatment in petals.However,the expressions of PsVIN1 and PsVIN2 in the GA treatment were higher than in the defoliation treatment in bracts and young leaves,indicating that PsVINs responded to GA treatment and regulated sucrose hydrolysis.All of the above results showed that defoliation and GA treatment promote sugar transport,metabolism and flower development.However,only defoliation could induce reflowering by regulating more sucrose transport to flower bud,and promoting sugar metabolism.3.ABA treatment failed to inhibit the autumn-reflowering of D+GA treatment by applying ABA to buds.There were insignificant differences in germination rate,bud rate and flower rate between the two groups,and the sugar content and change trend of each organ were relatively consistent,indicating that the effect of ABA on autumn-reflowering was not inhibited.In the D+GA+ABA treatment,the PsVIN1 was significantly induced in the petals,leaves and bracts at 36 d,indicating the gene promotes sucrose hydrolysis in response to ABA and promote the reflowering.4.Photosynthetic characteristics of different treatments showed that defoliation and GA treatment inhibited the net photosynthetic rate of the leaves;the mature leaves had higher net photosynthetic rate than the young leaves.Probably it is because of the low development of young leaves.This result is consistent with the sugar content,that is,the sucrose content of mature leaves is higher than young leaves.In summary,this study further clarified that the key to reflowering in autumn is defoliation,GA can not induce reflowering of tree peony,only promote dormancy release and bud formation;ABA,which is applied with GA antagonistic,can not inhibit autumn reflowering of peony.Development of flower buds and reflowering were affected by defoliation and hormones,which regulate sugar transport and metabolize.This study provides a scientific and theoretical basis for autumn-reflowering in tree peony and the extension of florescence,and lays the foundation for the better market orientation of tree peony,the supply of National Day,and the promotion of industrial development of tree peony.