Chilling Requirement Validation and Physiological and Molecular Responses of the Bud Endodormancy Release in Paeonia lactiflora 'Meiju'.

Runlong Zhang,Xiaohua Shi,Danqing Li,Jiaping Zhang,Xiaobin Wang,Lingmei Shao,Yiping Xia,Tong Xu

doi:10.3390/ijms22168382

Runlong Zhang, Xiaohua Shi + Show 6 more

Open Access

https://doi.org/10.3390/ijms22168382

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Abstract

The introduction of herbaceous peony (Paeonia lactiflora Pall.) in low-latitude areas is of great significance to expand the landscape application of this world-famous ornamental. With the hazards of climate warming, warm winters occurs frequently, which makes many excellent northern herbaceous peony cultivars unable to meet their chilling requirements (CR) and leads to their poor growth and flowering in southern China. Exploring the endodormancy release mechanism of underground buds is crucial for improving low-CR cultivar screening and breeding. A systematic study was conducted on P. lactiflora ‘Meiju’, a screened cultivar with a typical low-CR trait introduced from northern China, at the morphological, physiological and molecular levels. The CR value of ‘Meiju’ was further verified as 677.5 CUs based on the UT model and morphological observation. As a kind of signal transducer, reactive oxygen species (ROS) released a signal to enter dormancy, which led to corresponding changes in carbohydrate and hormone metabolism in buds, thus promoting underground buds to acquire strong cold resistance and enter endodormancy. The expression of important genes related to ABA metabolism, such as NCED3, PP2C, CBF4 and ABF2, reached peaks at the critical stage of endodormancy release (9 January) and then decreased rapidly; the expression of the GA2ox8 gene related to GA synthesis increased significantly in the early stage of endodormancy release and decreased rapidly after the release of ecodormancy (23 January). Cytological observation showed that the period when the sugar and starch contents decreased and the ABA/GA ratio decreased was when ‘Meiju’ bud endodormancy was released. This study reveals the endodormancy regulation mechanism of ‘Meiju’ buds with the low-CR trait, which lays a theoretical foundation for breeding new herbaceous peony cultivars with the low-CR trait.

Highlights

Bud dormancy has gradually become a popular topic in plant growth and development research fields in recent decades [1,2]
Ecodormancy is the dormancy caused by adverse environmental factors such as low temperature and drought stress [3]
Due to the global warming trend, many plants with winter dormancy traits suffer from hot autumns and warm winters, which disrupt normal endodormancy release because of insufficient chilling accumulation and negatively affect their subsequent growth and development

Summary

Introduction

The complete process of bud dormancy includes three contiguous stages: paradormancy, endodormancy and ecodormancy [3]. As the daylength shortens and the temperature decreases, perennials defoliate, and their buds generally transfer from paradormancy to endodormancy [4]. With a decrease in temperature or day length, buds enter endodormancy, at which stage they are unable to sprout even under favorable conditions until the indispensable chilling accumulation has been completed [5,6]. Due to the global warming trend, many plants with winter dormancy traits suffer from hot autumns and warm winters, which disrupt normal endodormancy release because of insufficient chilling accumulation and negatively affect their subsequent growth and development. Sufficient daylength and low temperature are the two most important environmental factors affecting the bud dormancy process. Short daylength could induce Populus L. and Morus alba L. to enter dormancy, and a low-temperature environment could induce Pyrus spp. and Malus pumila

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