Effect Of GA On Autumn Reflowering Of Tree Peony

Tree peony（Paeonia Sect.Moutan）,as a traditional flower of China,has very high ornamental and cultural values.Most tree peony cultivars flower only in spring once a year,but some flower again in autumn.Breeding stable multi-season flowering cultivars and developing corresponding cultivation techniques are two of the ways to solve the problem of short and concentrated tree peony flowering,therefore,it is very important to explore the the mechanism of tree peony multi-season flowering.Previous studies consider that defoliation and gibberellin are closely associated with the peony autumn flowering,but the specific mechanism is not yet clear,therefore.This study in the fall（August or September）through defoliation,defoliation+GA₃,defoliation+Paclobutrazol（a kind of gibberellic acid inhibitor）processing respectively,compare with control in buds bursting rates,the flowers open status,hormone and soluble sugars content and differences in the levels of DNA methylation and transcription,in order to explain the effect of gibberellin on flowering of peony in autumn.The main research results are as follows:（1）The study involved 6 varieties,only‘Hu Chuanhan’could naturally burst and normally flower in autumn,all treatments for the varieties to be involved were promoting effect,could promote buds of‘Chunqiu Hong’‘Fugui Mantang’,‘Hu Chuanhan’and‘Luoyang Hong’to burst and grow（for the promotion of‘Luoyang Hong’only a weak role）,applied GA₃ with superposition effect,and increased the bud to be uniformity,applying PP₃₃₃ could to a certain extent offset defoliation formed by promoting effect,but the influence of applying PP₃₃₃for‘Chunqiu Hong’,‘Fugui Mantang’and‘Luoyang Hong’was weak.Bud formation after bud bursting,but whether the buds could normally flower or not was related to the temperature and bud development after treatment.（2）‘Hu Chuanhan’might accumulate GA_S by exogenous absorption or endogenous synthesis（or both）,thus inhibiting the ultimate secondary flowering of ABA function.However,it remained to be explored whether the change of IAA content was related to the difference of bursting in autumn.High soluble sugar content could be beneficial to bud germination,and the photosynthesis of new leaves after bursting may lead to the accumulation of starch and soluble sugar.Defoliation+GA₃ treatment was the most effective way to promote the bursting of experimental tree peony cultivars in autumn,which may be related to the increase of GAs content,the inhibition of ABA function and the high concentration of soluble sugar.（3）DNA methylation might be involved in the germination and flowering of peony in autumn,and‘Hu Chuanhan’might have some mechanism of its own,which could regulate the methylation or demmethylation of related DNA sequence CG locus to induce its flower buds to germinate and blossom in autumn,and the application of treatment could trigger this mechanism in advance.For the once-a-year flowering tree peony‘Luoyang Hong’,the treatments could alter the degree of DNA methylation to a certain extent,but may not achieve the degree of normal flowering.（4）High quality transcriptome data was obtained by sequencing.Defoliation and application of gibberellin had a stronger effect on the physiological activities of"Hushuan Han".A large number of buds produced more active photosynthesis,more cellulose synthesis and more vigorous growth.Moreover,the treatment increased the content of GA_S and decreased the content of ABA in buds,thus promoting flowering,which may be related to the inhibition of Ps GAI,which plays a negative regulatory role in the gibberellin pathway,and the negative regulatory gene PP2C expression in the aba-activated signaling pathway by high concentration of GA.