In order to explore the effects of high temperature stress on the physiological characteristics of Paeonia ostii, the Paeonia ostii were subjected to 25 °C, 35 °C, 38 °C, and 40 °C for 7 days. Meanwhile, the physiological indicators of oxidative stress (hydrogen peroxide, H₂O₂; malondialdehyde, MDA; relative electrical conductivity, REC), antioxidant enzyme activity (superoxide dismutase, SOD; ascorbate peroxidase, APX; catalase, CAT; peroxidase, POD), photosynthetic pigment content (chlorophyll a, Chla; chlorophyll b, Chlb), photosynthetic characteristics (net photosynthetic rate, Pn; intercellular CO₂ concentration, Ci; stomatal conductance, Gs; transpiration rate, Tr), and osmoregulatory substances content (soluble protein, SP; soluble sugar, SS) were determined. The results showed that, with the increase in temperature and stress time, the H₂O₂ content, MDA content, REC value, CAT activity, and APX activity increased, while Chla content, Chlb content, SS content, and SP content decreased. With the extension of stress time, the SOD activity, POD activity, and Tr value of each high temperature stress group first increased and then decreased; Ci first decreased, then increased, and then decreased; meanwhile, Pn and Gs showed an overall downward trend. PLS-DA (partial least squares discriminant analysis) was used to analyze the changes in physiological and biochemical indexes of peony leaves under 40 °C stress for different days. SOD was found to be the biggest factor affecting the changes in physiological and biochemical indexes of peony leaves treated with different days of stress.

This study explored the changes in the photosynthetic characteristics of the Fengdan peony under high-temperature stress to provide a reference for understanding the tolerance of peony plants under heat stress. In this study, the effects of high-temperature stress (40 °C) on the photosynthetic characteristics of the Fengdan leaves were studied. At 25 °C, the net photosynthetic rate (Pn), stomatal conductance (Gs), and transpiration rate (Tr) of the leaves decreased gradually with the increase in heat stress time, and intercellular CO₂ concentration (Ci) decreased first and then increased. High-temperature stress reduced the light energy absorption (ABS/RC) and capture (TR_O/RC), light energy for electron transport (ET_O/RC), and heat dissipation (DI_O/RC) per unit leaf area. The maximum photochemical efficiency (F_V/F_M), leaf photochemical performance index (PI_abs), the probability that captured excitons can transfer electrons to other electron acceptors in the electron transport chain beyond Q_A (ψ_O), and the quantum yield for electron transport (φEo), decreased gradually. The results showed that high temperatures damaged the photosynthetic capacity of the peony leaves and destroyed the photosynthetic apparatus of leaves. This study provides a reference for understanding the photosynthetic characteristics and tolerance of peony plants under heat stress.

In order to investigate the causes of the differences in heat tolerance (‘Lu He Hong’ and ‘Zhi Hong’), we studied the physiological changes, photosynthetic properties and regulatory mechanism of the two peony cultivars at high temperature. The results showed that the physiological changed of different peony cultivars varied significantly under high temperature stress. With the extension of high temperature stress time, MDA content of 'Lu He Hong' increased,while 'Zhi Hong' rised first and then decreased, SOD activity of 'Lu He Hong' rised first and then decreased, that of 'Zhi Hong' kept rising, POD activity of 'Lu He Hong' kept decreasing, while 'Zhi Hong' rised. The photosynthetic instrument records the change of peony photosynthesis parameters at high temperature; the chlorophyll A (Chla) fluorescence transient is recorded using the plant efficiency analyzer (PEA), analyzed according to the JIP test (O-J-I-P fluorescence transient analysis), and several parameters were derived to explain the photosynthetic efficiency difference between different peony cultivars. The tested cultivars responded differently to the survey conditions, and the PCA analysis showed that the ‘Zhi Hong’ was more well tolerated and showed better thermal stability of the PSII. The reduced efficiency of the ‘Lu He Hong’ PSII antenna leads to higher heat dissipation values to increase the light energy absorbed by unit reaction center (ABS/RC), the energy captured by unit reaction center (TR₀/RC), and the energy dissipated by unit reaction center (DI₀/RC), which significantly leads to its lower total photosynthetic performance (PI_total). The light capture complex of the variety ‘Zhi Hong’ has high connectivity with its reaction center, less damage to OEC activity, and better stability of the PSII system. The results show that ‘Zhi Hong’ improves heat resistance by stabilizing the cell membrane, a strong antioxidant system, as well as a more stable photosynthetic system. The results of this study provide a theoretical basis for the screening of heat-resistant peonies suitable for cultivation in Jiangnan area and for the selection and breeding of heat-resistant cultivars.

Peony is a traditional Chinese flower with significant ornamental and medicinal value. However, there are still problems, such as serious browning, difficulties in differentiation, and rooting and low regeneration efficiency in the process of the regeneration system established, which have hindered the development of transgenic peony technology. Establishing an efficient regeneration system is considered to be an important goal among peony researchers. Here, we describe a protocol for high-frequency callus induction and establishment of peony plants using flower petals as explants. Murashige and Skoog (MS) medium supplemented with 2.0 mg/L 2,4-dichlorophenoxyacetic acid (2,4-D), 1.5 mg/L N-(phenylmethyl)-9H-purin-6-amine (6-BA), and 0.3 mg/L 1-naphthylacetic acid (NAA) was identified as the best medium for callus induction, achieving an induction rate of up to 98.52%. The highest peony proliferation rate (234%) was achieved on MS supplemented with 0.2 mg/L NAA and 3.0 mg/L 6-BA. The highest callus differentiation rate (34.81%) was achieved on MS supplemented with 2.0 mg/L 6-BA and 0.5 mg/L zeatin (ZT). The highest rooting rate was 23.33% when using 1/2 MS supplemented with 0.1 mg/L NAA and 0.05 mg/L 3-indolebutyric acid (IBA). After acclimation, the plants were transferred to pots, where they showed robust growth. We also observed the surface structures of the calluses using scanning electron microscopy and found that the differentiation characteristics of the calluses were hugely variable and that different surface structures appeared to affect bud differentiation efficiency. The efficient and rapid system for regenerating peonies using petal cultures established here will create new opportunities for the mass reproduction and genetic engineering of peony plants.

An important family of transcription factors (TFs) in plants known as NAC (NAM, ATAF1/2, and CUC2) is crucial for the responses of plants to environmental stressors. In this study, we mined the NAC TF family members of tree peony (Paeonia suffruticosa Andrews) from genome-wide data and analyzed their response to heat and waterlogging stresses in conjunction with transcriptome data. Based on tree peony’s genomic information, a total of 48 PsNAC genes were discovered. Based on how similar their protein sequences were, these PsNAC genes were divided into 14 branches. While the gene structures and conserved protein motifs of the PsNAC genes within each branch were largely the same, the cis-acting elements in the promoter region varied significantly. Transcriptome data revealed the presence of five PsNAC genes (PsNAC06, PsNAC23, PsNAC38, PsNAC41, PsNAC47) and one PsNAC gene (PsNAC37) in response to heat and waterlogging stresses, respectively. qRT-PCR analysis reconfirmed the response of these five PsNAC genes to heat stress and one PsNAC gene to waterlogging stress. This study lays a foundation for the study of the functions and regulatory mechanisms of NAC TFs in tree peony. Meanwhile, the NAC TFs of tree peony in response to heat and waterlogging stress were excavated, which is of great significance for the selection and breeding of new tree peony varieties with strong heat and waterlogging tolerance.

Tree peony (Paeonia suffruticosa Andr.) is a traditional Chinese flower with significant ornamental and medicinal value. Its growth and development process is regulated by some internal and external factors, and the related regulatory mechanism is largely unknown. Myelocytomatosis transcription factors (MYCs) play significant roles in various processes such as plant growth and development, the phytohormone response, and the stress response. As the identification and understanding of the MYC family in tree peony remains limited, this study aimed to address this gap by identifying a total of 15 PsMYCs in tree peony and categorizing them into six subgroups based on bioinformatics methods. Furthermore, the gene structure, conservative domains, cis-elements, and expression patterns of the PsMYCs were thoroughly analyzed to provide a comprehensive overview of their characteristics. An analysis in terms of gene structure and conserved motif composition suggested that each subtribe had similarities in function. An analysis of the promoter sequence revealed the presence of numerous cis-elements associated with plant growth and development, the hormone response, and the stress response. qRT-PCR results and the protein interaction network further demonstrated the potential functions of PsMYCs in the growth and development process. While in comparison to the control, only PsMYC2 exhibited a statistically significant variation in expression levels in response to exogenous hormone treatments and abiotic stress. A promoter activity analysis of PsMYC2 revealed its sensitivity to Flu and high temperatures, but exhibited no discernible difference under exogenous GA treatment. These findings help establish a basis for comprehending the molecular mechanism by which PsMYCs regulate the growth and development of tree peony.