Comparative Study on Physiological Responses and Gene Expression of Bud Endodormancy Release Between Two Herbaceous Peony Cultivars (Paeonia lactiflora Pall.) With Contrasting Chilling Requirements

Abstract

With the global temperature increase, diverse endogenous factors and environmental cues can lead to severe obstacles to bud endodormancy release for important economic plants, such as herbaceous peony (Paeonia lactiflora Pall.). Knowing the underlying mechanism in bud endodormancy release is vital for widely planting herbaceous peony at low latitudes with warm winter climates. A systematic study was carried out between the southern Chinese cultivar ‘Hang Baishao’ with low-chilling requirement (CR) trait and the northern cultivar ‘Zhuguang’ with high-CR trait. Peony buds were sampled at regular intervals under natural cold during the crucial bud endodormancy release stage. Physiology and morphology of the buds were observed, and the roles of reactive oxygen species (ROS) and relevant genes in the regulation of bud endodormancy release were also highlighted, which has been rather rare in previous bud dormancy studies of both herbaceous and tree peonies. The expression of the starch metabolism- and sucrose synthesis-related genes PlAMY PlSPS and PlSUS was lower in the high-CR ‘Zhuguang’ and corresponded to a lower content of soluble sugars. The expression of polyamine oxidase gene PlPAO2 correlated with a higher level of hydrogen peroxide (H2O2) in high-CR ‘Zhuguang’ than in low CR ‘Hang Baishao’ during bud endodormancy. Expression of PlMAPKKK5, an intermediate gene in the abscisic acid (ABA) response to ROS signaling, correlated with ROS levels and ABA content. We present the hypothesis that accumulation of ROS increases ABA content and decreases GA3 content and signal transduction leading to reduced expression of PlSVP and PlSOC1. Reduced cell division and increased cellular damage which probably blocked bud endodormancy release were also observed in high-CR ‘Zhuguang’ through histological observation and related genes expression. This study provides a comparative analysis on physiological responses and gene expression patterns of bud dormancy of geophytes in an increasingly unsuitable environment.

Establishment of a Homologous Silencing System with Intact-Plant Infiltration and Minimized Operation for Studying Gene Function in Herbaceous Peonies

“…The optimal prechilling temperature is 4 • C, which could provide one chill unit (CU), whereas temperatures in other ranges would provide lower or even negative CU values for herbaceous peony. The potted roots of 'Hang Baishao' were treated at 4 • C for at least 4 weeks to obtain a sufficient chilling-to-release bud endodormancy and trim sprouting [37,40].…”

“…If the research topic is bud dormancy and the target gene is relevant to bud dormancy regulation, the prechilling duration could be adjusted to 3-4 weeks; if the research topic is the stress response, resistance, stem strength, and photosynthetic response, among others, the prechilling duration in a 4 • C refrigerator could be adjusted to 4-5 weeks (Figure 5). To be more precise, for bud dormancy regulation research, 3-4 weeks is an applicable chilling duration because the CRs of most herbaceous peony cultivars are unsatisfactory after 3-4 weeks at 4 • C, and these cultivars could not completely break bud endodormancy [40,41]. Bud sprouting and growth performances will show a significant difference between silenced and control plantlets.…”

“…In addition, a series of key processes, such as phenotypic observation, data collection, sampling, and multiple treatments, could be completed in one month, before the decrease or disappearance of the silencing effect. However, most cultivars of herbaceous peony need more than one month to bloom and a much longer cultivation period to obtain fruits, which means that transient verification through root infection is probably inapplicable to blooming-and fruiting-related research [40].…”

“…One-year-old roots were temporarily potted with peat soil and perlite, mixed at a ratio of 1:2, and then continuously treated at 4 • C in darkness and 65% humidity for 3-4 or 4-5 weeks to reach a certain chilling accumulation [40,41]. The prechilling treatment duration depends on the specific research objectives: 3-4 weeks for bud dormancy, budbreak, and growth research, and 4-5 weeks for research on stress resistance, environmental response, stem strength, and photosynthesis, among other processes.…”