Mitochondrial pathway of programmed cell death in Paeonia lactiflora pollen cryopreservation.

Programmed cell death (PCD) is an important factor to reduces the viability of plant germplasm after cryopreservation. However, the pathways by which PCD occurs is not fully understood. To investigate whether there is a mitochondrial pathway for pollen PCD after cryopreservation, the pollen of Paeonia lactiflora two cultivars with different PCD levels after cryopreservation was used as test material and the changes of mitochondrial calcium ions (Ca2+), structure, function and their relationship with PCD were compared. The results showed that compared with fresh pollen, the PCD of 'Feng Huang Nie Pan' was significantly reduced after cryopreservation. Their mitochondrial Ca2+ content decreased by 74.27%, mitochondrial permeability transition pore (MPTP) opening reduced by 25.41%, mitochondrial membrane potential slightly decreased by 5.02%, cardiolipin oxidation decreased by 65.31%, and oxygen consumption remained stable, with a slightly ATP production increase. On the contrary, compared with fresh pollen, 'Zi Feng Chao Yang' showed severe PCD after cryopreservation. The decline in mitochondrial Ca2+-ATPase activity led to an accumulation of excessive Ca2+ within mitochondria, triggering widespread opening of MPTP, significantly affecting mitochondrial respiration and energy synthesis. These results suggest the mitochondrial pathway of PCD exists in pollen cryopreservation.

Unraveling the role of PlARF2 in regulating deed formancy in Paeonia lactiflora.

MAIN CONCLUSION: PlARF2 can positively regulate the seed dormancy in Paeonia lactiflora Pall. and bind the RY cis-element. Auxin, a significant phytohormone influencing seed dormancy, has been demonstrated to be regulated by auxin response factors (ARFs), key transcriptional modulators in the auxin signaling pathway. However, the role of this class of transcription factors (TFs) in perennials with complex seed dormancy mechanisms remains largely unexplored. Here, we cloned and characterized an ARF gene from Paeonia lactiflora, named PlARF2, which exhibited differential expression levels in the seeds during the process of seed dormancy release. The deduced amino acid sequence of PlARF2 had high homology with those of other plants and contained typical conserved Auxin_resp domain of the ARF family. Phylogenetic analysis revealed that PlARF2 was closely related to VvARF3 in Vitis vinifera. The subcellular localization and transcriptional activation assay showed that PlARF2 is a nuclear protein possessing transcriptional activation activity. The expression levels of dormancy-related genes in transgenic callus indicated that PlARF2 was positively correlated with the contents of PlABI3 and PlDOG1. The germination assay showed that PlARF2 promoted seed dormancy. Moreover, TF Centered Yeast one-hybrid assay (TF-Centered Y1H), electrophoretic mobility shift assay (EMSA) and dual-luciferase reporter assay analysis (Dual-Luciferase) provided evidence that PlARF2 can bind to the 'CATGCATG' motif. Collectively, our findings suggest that PlARF2, as TF, could be involved in the regulation of seed dormancy and may act as a repressor of germination.

Exploring the relationship between pollen viability and inclusion in Paeonia lactiflora after cryopreservation.

Pollen, as the male gametophyte, carries half of plant genetic information and is an important source of germplasm. The cryopreservation of pollen can not only preserve germplasm, but also solve the problem of time and space barrier in crossbreeding. So it is of great significance to explore the mechanism of pollen viability maintenance after cryopreservation. In this paper, 10 cultivars of Paeonia lactiflora with different fresh pollen viability that did not change after cryopreservation were taken as objects and the effects of pollen inclusions such as soluble sugar, starch, soluble protein, free amino acids, and proline were explored. The results showed that: (1) The contents of pollen inclusions in the fresh pollen of 10 cultivars were different. After cryopreservation, the contents of starch and free amino acids significantly decreased in 10 cultivars, and the soluble sugar, soluble protein, and proline varied with cultivars. (2) Correlation analysis showed that fresh pollen viability was significantly positively correlated with the soluble sugar (R-values of 0.630) and starch content (R-values of 0.694) in fresh pollen. But after cryopreservation pollen viability was only significantly positively correlated with the starch content (R-values of 0.725). These results suggest that the effects of pollen inclusions on pollen vitality are different before and after cryopreservation. The fresh pollen with higher soluble sugar and starch is more vital. But after cryopreservation, the pollen with high starch content has higher viability. The maintenance of stable pollen viability after cryopreservation appears to be related to starch content or starch metabolism, which requires further to study for a final determination.

Chaetomium globosum D5 confers salinity tolerance on Paeonia lactiflora Pall.

Plants will interact with beneficial endophytic fungi to increase resistance under environmental stress. Among these stresses, salt stress poses one of the major threats to plant growth worldwide. We have studied the response mechanism of Chaetomium globosum D5, a salt-tolerant fungus isolated from the roots of Paeonia lactiflora under salt stress, and its mechanism of action in helping P. lactiflora alleviate salt stress. In our study, high levels of salt inhibit growth, whereas low levels promote the growth of C. globosum D5, which resists salt stress by forming dense hyphae and producing more pigments, soluble proteins, and antioxidants. Under salt stress, growth and photosynthesis of P. lactiflora are inhibited, and they are subjected to osmotic stress, oxidative stress, and ionic stress. C. globosum D5 could help P. lactiflora promote growth and photosynthesis by increasing the uptake of nitrogen and phosphorus and increasing the accumulation of the carbon and photosynthetic pigments, help P. lactiflora alleviate osmotic stress by increasing the accumulation of proline, help P. lactiflora alleviate ion stress by reducing Na+ and increasing K+/Na+, Ca2+/Na+ and Mg2+/Na + ratios in P. lactiflora roots and leaves. In summary, joint action between P. lactiflora and C. globosum D5 is responsible for mitigating damage caused by P. lactiflora under salt stress. We first investigate the interaction between the fungus and P. lactiflora under salt stress, providing a theoretical basis for further investigations into the mechanisms of P. lactiflora's response to salt stress and its promotion in coastal areas.

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

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.

GA3 is superior to GA4 in promoting bud endodormancy release in tree peony (Paeonia suffruticosa) and their potential working mechanism.

BACKGROUND: Sufficient low temperature accumulation is the key strategy to break bud dormancy and promote subsequent flowering in tree peony anti-season culturing production. Exogenous gibberellins (GAs) could partially replace chilling to accelerate dormancy release, and different kinds of GAs showed inconsistent effects in various plants. To understand the effects of exogenous GA3 and GA4 on dormancy release and subsequent growth, the morphological changes were observed after exogenous GAs applications, the differentially expressed genes (DEGs) were identified, and the contents of endogenous phytohormones, starch and sugar were measured, respectively. RESULTS: Morphological observation and photosynthesis measurements indicated that both GA3 and GA4 applications accelerated bud dormancy release, but GA3 feeding induced faster bud burst, higher shoot and more flowers per plant. Full-length transcriptome of dormant bud was used as the reference genome. Totally 124 110 459, 124 015 148 and 126 239 836 reads by illumina transcriptome sequencing were obtained in mock, GA3 and GA4 groups, respectively. Compared with the mock, there were 879 DEGs and 2 595 DEGs in GA3 and GA4 group, 1 179 DEGs in GA3 vs GA4, and 849 DEGs were common in these comparison groups. The significant enrichment KEGG pathways of 849 DEGs highlighted plant hormone signal transduction, starch and sucrose metabolism, cell cycle, DNA replication, etc. Interestingly, the contents of endogenous GA1, GA3, GA4, GA7 and IAA significantly increased, ABA decreased after GA3 and GA4 treatments by LC-MS/MS. Additionally, the soluble glucose, fructose and trehalose increased after exogenous GAs applications. Compared to GA4 treatment, GA3 induced higher GA1, GA3 and IAA level, more starch degradation to generate more monosaccharide for use, and promoted cell cycle and photosynthesis. Higher expression levels of dormancy-related genes, TFL, FT, EBB1, EBB3 and CYCD, and lower of SVP by GA3 treatment implied more efficiency of GA3. CONCLUSIONS: Exogenous GA3 and GA4 significantly accelerated bud dormancy release and subsequent growth by increasing the contents of endogenous bioactive GAs, IAA, and soluble glucose such as fructose and trehalose, and accelerated cell cycle process, accompanied by decreasing ABA contents. GA3 was superior to GA4 in tree peony forcing culture, which might because tree peony was more sensitive to GA3 than GA4, and GA3 had a more effective ability to induce cell division and starch hydrolysis. These results provided the value data for understanding the mechanism of dormancy release in tree peony.

A Paeonia ostii caffeoyl-CoA O-methyltransferase confers drought stress tolerance by promoting lignin synthesis and ROS scavenging.

Paeonia ostii is an emerging woody oil crop, but drought severely inhibits its growth and promotion in arid or semiarid areas, and little is known about the mechanism governing this inhibition. In this study, the full-length cDNA of a caffeoyl-CoA O-methyltransferase gene (CCoAOMT) from P. ostii was isolated, and determined to be comprised of 987 bp. PoCCoAOMT encoded a 247-amino acid protein, which was located in the nucleus and cytosol. Significantly higher PoCCoAOMT transcription was detected in P. ostii treated with drought stress. Subsequently, the constitutive overexpression of PoCCoAOMT in tobacco significantly conferred drought stress tolerance. Under drought stress, transgenic lines exhibited lower reactive oxygen species (ROS) accumulation, and higher antioxidant enzyme activities and photosynthesis. Moreover, the expression levels of senescence-associated genes were significantly downregulated, whereas the expression levels of lignin biosynthetic genes and PoCCoAOMT were significantly upregulated in transgenic lines. Similarly, transgenic lines produced significantly higher lignin, especially guaiacyl-lignin. These results suggest that PoCCoAOMT is a vital gene in promoting lignin synthesis and ROS scavenging to confer drought stress tolerance in P. ostii.

Seed Proteomic Profiles of Three Paeonia Varieties and Evaluation of Peony Seed Protein as a Food Product.

Peony (Paeonia) has high ornamental, edible, and medicinal values. In order to distinguish seeds varieties, describe the proteomic profiles correlated with stress tolerance, and evaluate peony seed protein (PSP) as a functional food product, we characterized the seed protein profiles of these three species and their glucosidase inhibition activities. Results showed that the intensity of protein bands in sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and specific protein ID (especially for specifically expressed proteins (SEPs)) was effective to distinguish these peony seed varieties. Proteomic analysis of the three species showed that P. ostii "Fengdan" has heat and pathogen tolerance-related proteins, while P. rockii has higher content of proteins related to cold resistance, which were all highly consistent with their adaptation of heat or cold habitat. Moreover, stress-related proteins were also accumulated in P. lactiflora Pall "Hangshao" seeds, showing its potential for stress resistance. Further protein analysis showed that the primary composition of PSP was albumin and globulin. And the solubility of PSP was good. Furthermore, PSP also showed high glucosidase inhibition activity, indicating that PSP might have some potential function for the remission of hyperglycemia. And P. ostii "Fengdan" seeds may be a better source for protein production than seeds of the other two species in terms of protein solubility and the content of total protein, albumin, and globulin. In addition, an optimal protocol of microwave-assisted alkali extraction was developed to produce PSP. In conclusion, the evaluated stress-related proteins in three peony seed species by proteomic analysis quite agreed with their adaptation of heat or cold stress; proteomics could also be a very useful tool for distinguishing species in the production; and peony seeds may be a good source for protein production.

Metabolomics analysis reveals Embden Meyerhof Parnas pathway activation and flavonoids accumulation during dormancy transition in tree peony.

BACKGROUND: Bud dormancy is a sophisticated strategy which plants evolve to survive in tough environments. Endodormancy is a key obstacle for anti-season culture of tree peony, and sufficient chilling exposure is an effective method to promote dormancy release in perennial plants including tree peony. However, the mechanism of dormancy release is still poorly understood, and there are few systematic studies on the metabolomics during chilling induced dormancy transition. RESULTS: The tree peony buds were treated with artificial chilling, and the metabolmics analysis was employed at five time points after 0-4 °C treatment for 0, 7, 14, 21 and 28 d, respectively. A total of 535 metabolites were obtained and devided into 11 groups including flavonoids, amino acid and its derivatives, lipids, organic acids and its derivates, nucleotide and its derivates, alkaloids, hydroxycinnamoyl derivatives, carbohydrates and alcohols, phytohormones, coumarins and vitamins. Totally, 118 differential metabolites (VIP ≥ 1, P < 0.05) during chilling treatment process were detected, and their KEGG pathways involved in several metabolic pathways related to dormancy. Sucrose was the most abundant carbohydrate in peony bud. Starch was degradation and Embden Meyerhof Parnas (EMP) activity were increased during the dormancy release process, according to the variations of sugar contents, related enzyme activities and key genes expression. Flavonoids synthesis and accumulation were also promoted by prolonged chilling. Moreover, the variations of phytohormones (salicylic acid, jasmonic acid, abscisic acid, and indole-3-acetic acid) indicated they played different roles in dormancy transition. CONCLUSION: Our study suggested that starch degradation, EMP activation, and flavonoids accumulation were crucial and associated with bud dormancy transition in tree peony.

Molecular characterization and expression analysis of the SQUAMOSA PROMOTER BINDING PROTEIN-LIKE gene family in Paeonia suffruticosa.

KEY MESSAGE: A total of 16 PsSPL genes were identified in tree peony. PsSPLs potentially regulated flowering time, lateral bud and seed development, and the juvenile-to-adult phase transition. SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) transcription factors are important for plant growth and development. Here, we report the identification of 16 full-length PsSPLs in tree peony (Peaonia suffruticosa Andr.) and 9 PsSPLs that have miR156 target sites. Phylogenetic analysis of the relationship of SPLs in P. suffruticosa and Arabidopsis suggested that they can be classified into six groups, and PsSPLs were highly correlated with Arabidopsis SPLs counterparts in the same group. Cis-element of promoter region analysis suggested that PsSPL genes play roles in physiological processes and developmental events. Expression analysis indicated that most PsSPL genes exhibited high expression levels in the tissues and organs examined here. The increasing expression levels of PsSPL1, PsSPL2, PsSPL8, PsSPL9, PsSPL12, and PsSPL16, and decreasing expression levels of PsSPL1A and PsSPL1B in buds over time suggested that they were probably regulated by the juvenile-to-adult phase transition. In addition, the expression profiles of PsSPL genes in different developmental buds and seeds suggested that PsSPL2, PsSPL3, PsSPL9, PsSPL10, PsSPL13, and PsSPL13A were important genes for regulating the flowering time of the tree peony; PsSPL2 and PsSPL8 might play a role in suppressing lateral bud development, and PsSPL2, PsSPL13, and PsSPL14 positively controlled grain size and number, and pod branching. These results provide a foundation for future functional analysis of PsSPL genes in tree peony growth and development.

Herbaceous peony (Paeonia lactiflora Pall.) PlDELLA gene negatively regulates dormancy release and plant growth.

DELLA protein plays a significant role in plant growth and development. In this study, PlDELLA with the open reading frame of 1866 bp in length was isolated from Paeonia lactiflora. Overexpression of PlDELLA in Arabidopsis thaliana showed that seed germination was significantly repressed as it took 144∼192 h for the OEs to reach 100 % germination and it required only 60 h for the WT. The OEs were also inhibited in bolting time and in plant vegetative growth. When PlDELLA was silenced in peony by virus-induced gene silencing method, peony budbreak occurred earlier by 8∼10 d and the vegetative growth was significantly accelerated compared with the control group. These results collectively indicated that PlDELLA negatively regulated dormancy release and plant growth. During chilling process to release peony endodormancy, PlDELLA expression down-regulated, and the content of both endogenous active GAs and ABA decreased, indicating decreasing of PlDELLA expression under chilling was not caused by the known gibberellin signal transduction pathway. Besides, PlDELLA had no interaction with the four screened PlWRKYs, PlWRKY13, PlWRKY18, PlWRKY40 or PlWRKY50. These findings not only enrich the knowledge of DELLA protein family, but also provide insights into understanding the function of PlDELLA protein in endodormancy release in peony.

Defoliation, not gibberellin, induces tree peony autumn reflowering regulated by carbon allocation and metabolism in buds and leaves.

Short and concentrated natural fluorescence hinders tree peony (Paeonia suffruticosa) annual production, and defoliation and gibberellin (GA) application is used to induce its reflowering in autumn. Here, the individual roles of defoliation and GA treatment were determined by monitoring morphological and soluble sugar changes in buds and leaves, and by investigating carbon allocation- and metabolism-related gene expression. Both defoliation and GA treatment induced early bud development, but induction was faster using the GA treatment. Only defoliation, not GA treatment, induced the final reflowering, although their combination accelerated it. Furthermore, defoliation decreased the sucrose content in buds much faster than the GA treatment. This sucrose reduction may play a key role in tree peony reflowering, and the higher carbon metabolism activity in young leaves after defoliation may further help the reflowering process. Defoliation enhanced the expression of sucrose transporters PsSUT4 and PsSWEET12 in buds, and their expression in young leaves was greater than after GA treatment. This indicated that PsSUT4 and PsSWEET12 may help transport carbon into buds after defoliation. In addition, the invertases, PsCIN2 and PsCWIN1 in young leaves were more highly expressed after defoliation, indicating that they may contribute to reflowering after defoliation by accelerating sucrose hydrolysis in young leaves. In addition, the expression levels of PsVIN1 and PsVIN2 in leaves, and PsVIN2 in buds were more highly induced by GA treatment than by defoliation, indicating that PsVINs may mainly respond to GA treatment. These results may help improve the tree peony forcing culture technology and related industrial production.

Effects of drought stress on physiological responses and gene expression changes in herbaceous peony (Paeonia lactiflora Pall.).

Herbaceous peony (Paeonia lactiflora Pall.) is known as the flower phase. This phase is somewhat resistant to drought, but long-term drought and severe water shortage will affect its normal growth and development. In this study, physiological indices and the transcriptome of P. lactiflora were determined to clarify its physiological responses and gene expression changes under drought stress. The results showed that under drought stress, soluble sugar content, peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) activities, and chlorophyll, carotenoid and flavonoid contents were significantly increased, and soluble protein content, superoxide dismutase (SOD), glutathione reductase (GR), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR), ascorbic acid (AsA) and glutathione (GSH) activity first increased and then decreased after day 14. Moreover, drought stress also significantly reduced chlorophyll content, photosynthesis and chlorophyll fluorescence parameters. Transcriptomic analysis revealed that compared with the Control, 10,747 differentially expressed genes (DEGs) were upregulated and 11,835 downregulated under drought stress. These DEGs were classified into three categories and 46 functional groups by GO function classification. The 3,179 DEGs were enriched into 128 pathways by KEGG pathway enrichment. The ROS system, chlorophyll degradation and photosynthetic capacity, as well as secondary pathways of biosynthesis and sugar metabolism were included. Additionally, relevant genes expressed in some metabolic pathways were discovered. These results provide a theoretical basis for understanding the responses of P. lactiflora to drought stress.

The ROS-associated programmed cell death causes the decline of pollen viability recovered from cryopreservation in Paeonia lactiflora.

KEY MESSAGE: After cryopreservation, the occurrence of apoptosis-like programmed cell death events induced by the accumulation of ROS reduces pollen viability. Cryopreservation, as a biotechnological means for long-term preservation of pollen, has been applied to many species. However, after cryopreservation, the viability of pollen significantly decreases via a mechanism that is not completely clear. In this study, the pollen of Paeonia lactiflora 'Zi Feng Chao Yang', which exhibits significantly reduced viability after liquid nitrogen (LN2) storage, was used to study the relationship among pollen viability, programmed cell death (PCD) and reactive oxygen species (ROS). The apoptosis rate was increased significantly in pollen with decreased viability after cryopreservation, and the changes in ROS generation and hydrogen peroxide (H2O2) were consistent with the apoptosis rate. Correlation analysis results showed that the apoptosis rate is positively correlated with ROS generation and H2O2 content. In addition, ascorbic acid (AsA), glutathione (GSH) and ascorbic acid reductase (APX) levels were significantly correlated with ROS and H2O2. After LN2 preservation for 8 months, the exogenous antioxidants AsA and GSH at appropriate concentrations significantly decreased H2O2 content, inhibited PCD indicator levels, and increased cryopreserved pollen viability. These observations suggest that PCD occurred in pollen during LN2 preservation for 1-8 months and was induced by the accumulation of ROS in pollen after cryopreservation, thus explaining the main reasons for the reduction in pollen viability after cryopreservation in LN2.

Evaluating the Comprehensive Performance of Herbaceous Peonies at low latitudes by the Integration of Long-running Quantitative Observation and Multi-Criteria Decision Making Approach.

Enlarging the planting area of economic plants, such as the "Southward Planting of Herbaceous Peony" (Paeonia lactiflora. Pall), is significant for improving people's lives. Peony is globally known as an ornamental because of gorgeous flowers and is mainly cultivated in the temperate regions with relatively cool and dry climates in the Northern Hemisphere. Promoting the landscape application of peony to the lower latitude regions is difficult because of the hot-humid climate. In this study, 29 northern peony cultivars and a unique Chinese southern peony, 'Hang Baishao', were introduced to Hangzhou, located in the central subtropics. Annual growth cycles, resistances and dormancy durations were measured, and crossbreeding between the southern and northern peonies was performed for six years, from 2012 to 2017. Based on data collected from the long-running quantitative observation (LQO), a multi-criteria decision making (MCDM) system was established to evaluate the comprehensive planting performance of these 30 cultivars in the central subtropics. 'Qihua Lushuang', 'Hang Baishao' and 'Meiju' were highly recommended, while 'Zhuguang' and 'Qiaoling' were scarcely recommended for the Hangzhou landscape. This study highlights the dependability and comprehensiveness of integrating the LQO and MCDM approaches for evaluating the introduction performance of ornamental plants.

Integration of Transcriptome, Proteome, and Metabolome Provides Insights into How Calcium Enhances the Mechanical Strength of Herbaceous Peony Inflorescence Stems.

Weak stem mechanical strength severely restrains cut flowers quality and stem weakness can be alleviated by calcium (Ca) treatment, but the mechanisms underlying Ca-mediated enhancement of stem mechanical strength remain largely unknown. In this study, we performed a comparative transcriptomic, proteomic, and metabolomic analysis of herbaceous peony (Paeonia lactiflora Pall.) inflorescence stems treated with nanometer Ca carbonate (Nano-CaCO3). In total, 2643 differentially expressed genes (DEGs) and 892 differentially expressed proteins (DEPs) were detected between the Control and nano-CaCO3 treatment. Among the 892 DEPs, 152 were coregulated at both the proteomic and transcriptomic levels, and 24 DEPs related to the secondary cell wall were involved in signal transduction, energy metabolism, carbohydrate metabolism and lignin biosynthesis, most of which were upregulated after nano-CaCO3 treatment during the development of inflorescence stems. Among these four pathways, numerous differentially expressed metabolites (DEMs) related to lignin biosynthesis were identified. Furthermore, structural observations revealed the thickening of the sclerenchyma cell walls, and the main wall constitutive component lignin accumulated significantly in response to nano-CaCO3 treatment, thereby indicating that Ca can enhance the mechanical strength of the inflorescence stems by increasing the lignin accumulation. These results provided insights into how Ca treatment enhances the mechanical strength of inflorescence stems in P. lactiflora.

Exogenous trehalose confers high temperature stress tolerance to herbaceous peony by enhancing antioxidant systems, activating photosynthesis, and protecting cell structure.

Herbaceous peony (Paeonia lactiflora Pall.) is an excellent ornamental plant, which is usually stressed by summer high temperatures, but little is known about its relevant measures. In this study, the effects of trehalose on alleviating high temperature-induced damage in P. lactiflora were examined. High temperature stress in P. lactiflora increased production of reactive oxygen species (ROS), including superoxide anion free radical (O2·-) and hydrogen peroxide (H2O2), enhanced both malondialdehyde (MDA) content and relative electrical conductivity (REC), decreased superoxide dismutase (SOD) activity, increased catalase (CAT) activity, inhibited photosynthesis, and destroyed cell structure. However, exogenous trehalose effectively alleviated its high temperature-induced damage. Trehalose decreased O2·- and H2O2 accumulation, MDA content, and REC, increased the activities of antioxidant enzymes, enhanced photosynthesis, improved cell structure, and made chloroplasts rounder. Additionally, trehalose induced high temperature-tolerant-related gene expressions to different degrees. These results indicated that trehalose decreased the deleterious effect of high temperature stress on P. lactiflora growth by enhancing antioxidant systems, activating photosynthesis, and protecting cell structure. These findings indicate the potential application of trehalose for managing high temperatures in P. lactiflora cultivation.

A review of the seed biology of Paeonia species (Paeoniaceae), with particular reference to dormancy and germination.

MAIN CONCLUSION: Most Paeonia species have epicotyl dormancy. Germination of peony seeds requires warm stratification for embryo growth and radicle protrusion followed by cold stratification for epicotyl growth. The genus Paeonia (Paeoniaceae) includes many popular ornamentals, has colorful flowers and contains several Chinese medicinal species. The germination protocol for seeds of Paeonia species is complex and impedes the breeding of new cultivars and contributes to the rarity and high cost of the plants. Although numerous reports on seed dormancy/germination in peonies are scattered throughout the literature, most of them are in Chinese. The primary aims of this paper are to provide a general overview of the available information on seed dormancy/germination in peonies and to make some suggestions regarding propagation for the peony industry and breeders. Most Paeonia species have epicotyl dormancy. The embryo is differentiated into organs, but it is underdeveloped (small) and must grow inside the seed before the radicle can emerge. Germination of peony seeds requires warm stratification for embryo growth and radicle protrusion followed by cold stratification for epicotyl growth. In addition, the epicotyl is sensitive to cold stratification only after the root has grown to a certain length. GA3 treatment enhances embryo growth and subsequent germination percentages. Further investigations on the physiology, genetics and proteomics would contribute to a better understanding of seed dormancy in Paeonia.

Defoliation and gibberellin synergistically induce tree peony flowering with non-structural carbohydrates as intermedia.

Although the natural florescence of the tree peony is short, it can be lengthened by forcing culture. In this study, both defoliation or gibberellic acid (GA3) treatment individually induced tree peony (Paeonia suffruticosa 'Luo Yang Hong') flowering under forcing culture, and their combination (D + G) accelerated flowering with a GA3-overdose-like phenomenon, indicating that synergism between defoliation and GA3 treatment may occur. Both defoliation and GA3 treatment induced a GA response, including (i) increased GA3 production, (ii) increased PsCPS and PsGA3ox expression, and (iii) decreased PsGA2ox, PsGID1c, and PsGID2 expression; both treatments also positively influenced non-structural carbohydrate (NSC) accumulation. According to the expression of five PsSWEETs, PsSWEET2 and PsSWEET17 may redundantly exercise the crosstalk of defoliation and GA3 treatment by NSC distribution, whereas PsSWEET12 may act by GA modulation; no synergism resulting from the D + G treatment was detected. Tissue-specific analysis indicated that, in sepals, PsSWEET2 and PsSWET7 are both induced by defoliation and GA3 treatment, whereas PsSWEET2 expression showed synergism with the D + G treatment. In summary, defoliation and GA3 treatment synergistically induce tree peony flowering under forcing culture, and NSCs are suggested as key intermedia. Moreover, sepals may play key roles in their synergism, although more direct evidence is still needed.

Elucidation of the mechanism of reflowering in tree peony (Paeonia suffruticosa) 'Zi Luo Lan' by defoliation and gibberellic acid application.

In this study, the reflowering mechanism of tree peony (Paeonia suffruticosa 'Zi Luo Lan') after defoliation and gibberellic acid (GA) application (autumn-flowering treatment) was investigated by monitoring the morphological changes, measuring the endogenous GA3 and abscisic acid (ABA) contents, and determining the expression patterns of six GA- and two ABA-related genes. The results show that autumn-flowering treatment induced tree peony reflowering in autumn, which was accompanied by nutrient absorption in buds. The application of exogenous GA3 induced a simultaneous increase in GA3 and decrease in ABA levels, suggesting that the high ratios of GA3/ABA may play a key role in inducing tree peony reflowering. RT-qPCR analysis shows that PsCPS and PsGA2ox were significantly induced and inhibited by GA3 application, respectively, which supports the hypothesis that GA3 treatment induces endogenous GA3 production. In addition, GA3 treatment inhibited the expression of the PsGID1c, but its effect on PsGAI1 was limited, whereas the expression of PsGAMYB could be GA- or ABA-related. Furthermore, autumn-flowering treatment significantly inhibited the expression of PsNCED and PsbZIP, which coincides with the observed changes in ABA levels. Therefore, we postulate that autumn-flowering treatment induces tree peony reflowering by inhibiting the function of ABA accumulation and signaling.