Objective: Tree peony (Paeonia suffruticosa) has a short and concentrated florescence, in order to explore the mechanism of autumn flowering, we studied the effects of gibberellin and DNA methylation during autumn flowering of tree peony. Method: Before natural defoliation in the middle September, all plants of the variety (P. suffruticosa 'Togawakan', a spring and autumn flowering variety of tree peony planted in the open field in Luoyang, Henan Province) were divided into 4 treatment groups: defoliation, defoliation + 650 mg•L-1 gibberellin (GA3), defoliation + 500 mg•L-1 paclobutrazol (PP333) processing, and no treatment. Growth performance of the treatment groups and the control was observed and recorded during autumn bud germination and flowering process, and the physiological and biochemical processes and methylation of genomic DNA of the treatment groups were measured. Result: 1)All of the four treatment groups could naturally flower in the autumn, but applying the treatments could promote 'Togawakan' autumn secondary flowering in advance and increase the effect of the flowering uniformity. Particularly, the treatment group of defoliation + 650 mg•L-1 GA3 had the best effect on promoting 'Togawakan' to sprout and flower, with a sprouting rate of 81.4%, 11 days after the treatment, and initial flowering started 42 days after treatment, 30 days earlier than the control group. 2) The defoliation + 650 mg•L-1 GA3, defoliation and defoliation + 500 mg•L-1 PP333 all contributed to fast and neat sprout and growth of the variety 'Togawakan', and the acceleration of flowering decreased in turn, suggesting that defoliation could promote sprout and growth of the buds, applying GA3 has superposition promoting effect, PP333 could offset the promoting effect of defoliation to a certain degree. Defoliation exerted an inhibitory effect on GA3 and GA4 content for a short time at first, then followed by an increase of GA3 and GA4 contents, and a decrease of ABA content in buds. The application of GA3 enhanced the intensity of increased GA3 and GA4 contents and decreased ABA content, and prolonged the rising period of GA3 and GA4 contents, while the application of PP333 showed the opposite effect. 3) Sprouting and flowering were accompanied by the consumption of a large amount of starch and soluble sugars, and a high concentration of soluble sugar may be beneficial to flowering. 4) MSAP test showed that the variation range of total DNA methylation in 'Togawakan' during the whole experiment period was 57.3%-72.4%, reaching the highest level of total DNA methylation before sprouting, and followed by a gradual decrease. The methylation of the control 1 day after treatments, as the baseline was compared with those of the treatment groups in different treatment periods. It was found that the methylation in treatment groups was more actively changing, and the changes were concentrated in two models, demethylation and hypermethylation. The demethylation rate of each treatment group increased with time and was higher than that of the control group in the same period. It was speculated that the high demethylation rate may be more conducive to the bursting of 'Togawakan' in autumn. Conclusion: P. suffruticosa 'Togawakan' could naturally sprout and flower in autumn, defoliation promoted endogenous GA3 synthesis, combined with the superposition effect of exogenous GA3, increased GA3 and inhibited ABA in vivo, promoted its secondary flowering in autumn, and the flowering period was neat. Exogenous PP333 application to some extents counteract the synthesis of endogenous GA3 caused by defoliation. Sprouting to flowering was accompanied by a large amount of sugar consumption, high concentration of soluble sugar might be conducive to bud sprouting. 'Togawakan' can self-regulate the methylation status at locus CG of relevant DNA sequences, thus inducing flower buds to sprout in autumn, and application of the treatments could trigger this regulation process ahead of time, in which high DNA demethylation rate was more likely to promote autumn germination and flowering. © 2021, Editorial Department of Scientia Silvae Sinicae. All right reserved.
