SUMMARY Tree peony (Paeonia suffruticosa Andr.) ‘Luoyang Red’ cut flowers were placed in separate vases filled with distilled water after pre-treatment with distilled water, 0.01 M H₂O₂, or 0.01 M ascorbic acid (ASA) for 12 h. We measured several morphological indices and physiological changes in the branches of flowers in each vase. H₂O₂ treatment accelerated the flowering and wilting of cut flowers of tree peony. The average vase-life was 3.0 d, which was 1.0 d shorter than that of the untreated control group (4.0 d; P≤ 0.05). The maximum flower diameter was 14.0 cm, which was 0.7 cm larger on average than that of the control group (13.3 cm). Exogenous H₂O₂ also significantly increased superoxide dismutase (SOD) activity, catalase (CAT) activity, and malondialdehyde (MDA) concentrations in petals by 12.2%, 14.4%, and 11.5%, respectively. Exogenous ASA treatment extended the average vase-life of cut flowers of tree peony to 4.8 d, which was 0.8 d longer than that of the control group. This treatment also improved the uptake of water by flower branches and increased the maximum flower diameter (15.0 cm), which was 1.7 cm larger than that of the control group. Exogenous ASA reduced average SOD activities and MDA concentrations in petals by 7.9% and 6.7%, respectively. These findings showed that senescence in cut flowers of tree peony was closely related to membrane lipid peroxidation in the petals, and that exogenous anti-oxidants such as ASA could delay senescence in cut flowers of tree peony and improve their quality.

(1) Tree peony (Paeonia suffruticosa Andrews) is a woody ornamental plant originating from China, and beloved by people worldwide. Non-structural carbohydrates (NSCs) play a crucial role in regulating the flowering quality of tree peonies in both field and potted conditions. However, the effects of NSCs accumulation and allocation in various organs during the vegetative growth stage on the flowering quality of tree peony under forcing culture remains unclear. (2) Two-year-old grafted seedlings of tree peony cv. ‘Luoyanghong’ were subjected to orthogonal treatments to investigate the role of NSCs accumulation in plants’ developmental process. We measured leaf photosynthetic capacity, NSCs accumulation in the organs of seedlings, observed key ornamental characteristics of flowering quality under forcing culture conditions, and evaluated the qualities of seedlings and flowers using the seedling index (SI) and flowering index (FI), respectively. (3) There was a significant positive correlation between leaf photosynthetic capacity and NSCs accumulation in both the whole plant and roots of potted tree peony. Roots were identified as the primary organs for NSCs accumulation in potted tree peonies. Sufficient NSCs accumulation in the plant, particularly in the roots during the defoliation period, was essential not only for enhancing the seedling quality of potted tree peonies but also for improving the flowering quality under forcing culture conditions. Both the seedling index (SI) and flowering index (FI) exhibited a significant dose-response with increasing root NSCs accumulation at defoliation. The T3 group, which involved slight root pruning (by 25%), combined with a high-concentration rooting agent (750 mg·L⁻¹) and Metarhizium anisopliae (20 million U·mL⁻¹), resulted in the highest photosynthetic capacity, SI, FI and NSCs accumulation status (NSCAR), making it the optimal treatment combination. (4) This finding indicates that increasing NSCs accumulation in the roots of potted tree peonies is a crucial biological foundation for producing high-quality potted flowers under forcing culture conditions, which provide new insights into the importance of NSCs in tree peony flowering and may improve the production technology for high-quality potted tree peony flowers under forcing culture conditions.

(1) Background: Tree peonies display extensive cultivar diversity due to widespread hybridization, resulting in a complex genetic architecture. This complexity complicates the selection of universal reference genes across different cultivars for qRT-PCR analyses. Paeonia suffruticosa ‘Doulv’, notable for its unique green blooms in China, exhibits chlorosis post-flowering and features petaloid stamens and pistils. (2) Methods: Based on published literature and RNA-seq data from ‘Doulv’, nine candidate reference genes—ACT (Actin), TUB (β-Tubulin), UBC (Ubiquitin Conjugating Enzyme), UBQ (Ubiquitin), UPL (Ubiquitin Protein Ligase), PP2A (Protein Phosphatase 2A), PP2C (Protein Phosphatase 2C), MBF1A (Multiprotein Bridging Factor 1A), and GAPDH (Glyceraldehyde-3-Phosphate Dehydrogenase)—were selected. Their expression stability was assessed across various tissues and developmental stages of ‘Doulv’ flowers using qRT-PCR, with evaluations conducted via GeNorm_v3.5, NormFinder_v20, and BestKeeper_v1.0. Gene cloning and expression analyses of PsCUC3, including its subcellular localization, were performed. (3) Results: GAPDH and ACT were identified as the most stable reference genes in petaloid stamens across various developmental stages of ‘Doulv’, whereas UBC and MBF1A were optimal across different tissues. Notably, specific conserved amino acids in PsCUC3 from ‘Doulv’ diverged from those in NAM/CUC3 proteins of other species, impacting its protein structure. PsCUC3 expression analysis revealed no correlation with chlorophyll content in petaloid stamens but an association with petaloid organ development. Furthermore, PsCUC3 was predominantly localized in the nucleus. (4) Conclusions: This study comprehensively evaluated suitable reference genes using GeNorm_v3.5, NormFinder_v20, and BestKeeper_v1.0 software, establishing a robust qRT-PCR detection system for ‘Doulv’ peony. These results provide a solid experimental foundation for further research on ‘Doulv’ peony. Building on this experimental foundation, the functional analysis of the PsCUC3 gene was conducted. The findings suggest a potential association between the PsCUC3 gene and floral morphology alterations in ‘Doulv’, identifying PsCUC3 as crucial for understanding the molecular mechanisms influencing floral structure in tree peonies.

Selenium (Se) is an essential micronutrient for human health, yet its deficiency remains prevalent worldwide. Biofortification through foliar Se application is an effective strategy to enhance Se levels in crops. Paeonia ostii ‘Fengdan’ is a multifunctional woody plant with potential for Se enrichment, though its Se uptake and transformation mechanisms remain unclear. This study systematically investigated the effects of foliar-applied Na₂SeO₃ (0–200 mg L⁻¹) on Se uptake, accumulation, speciation, and nutritional quality in tree peony. Results showed that Se uptake increased with higher Na₂SeO₃ concentrations, displaying a clear dose-dependent pattern across all organs. Se accumulation significantly enhanced, with a pronounced shift in distribution towards above-ground organs under experimental conditions. Notably, tree peony exhibited strong biotransformation capacity, converting over 73% of Se in leaves and over 81% in seeds into organic forms, primarily SeCys₂ and SeMet, with minor MeSeCys. Comprehensive evaluation indicated that 100 mg L⁻¹ Na₂SeO₃ yielded optimal results, significantly enhancing leaf and seed biomass, increasing seed nutrient contents (soluble proteins, sugars, phenolics), and improving the unsaturated fatty acid profile of seed oil. These findings highlight tree peony’s potential as an efficient bioreactor for organic Se and provide a theoretical foundation for developing Se-enriched products from tree peony.