Tree Peony Flowers Research Articles

Anthocyanin biosynthesis and accumulation in developing flowers of tree peony (Paeonia suffruticosa) ‘Luoyang Hong’

Tree peony (Paeonia suffruticosa) ‘Luoyang Hong’, a typical purplish red-flowered cultivar, is particularly appreciated by Chinese among the hundreds of cultivars. However, in-vase ‘Luoyang Hong’ flowers do not exhibit natural flower color as shown by on-tree flowers, since color fading of in-vase flowers is easily observed with the naked eye. This study was carried out to reveal the underlying molecular mechanism of color fading of in-vase P. suffruticosa ‘Luoyang Hong’. Five regulatory genes and six structural genes involved in anthocyanin biosynthesis were isolated based on a transcriptome library from P. suffruticosa ‘Luoyang Hong’ petals. Compared with fully opened on-tree flowers in field conditions, in-vase flowers (vase condition of 21–23°C, 50–60% RH and a 16h photoperiod with an illumination of ∼40μmolm−2s−1) of P. suffruticosa ‘Luoyang Hong’ at full opening stage show significant color fading with 50.20% greater lightness, 37.43% less redness and 36.18% lower chroma in non-blotch parts of the middle petals (the 4th to 6th layer petal). From pre-opening to full opening stage, anthocyanin contents in inner, middle and outer petals of in-vase flowers was 24.49–38.75% lower than those in on-tree developing flowers. With the exception of PsCHI1, another ten anthocyanin biosynthetic genes were preferentially and highly expressed in floral tissues (sepals, petals, stamens or carpels). Temporal expression analysis of anthocyanin biosynthetic genes in on-tree and in-vase developing flowers revealed that only the expression pattern of PsF3′H1 was correlated with anthocyanin content development. On the whole, PsbHLH3, PsWD40-1, PsWD40-2, PsMYB2, PsCHS1, PsF3H1 and PsDFR1 of P. suffruticosa ‘Luoyang Hong’ showed lower transcript abundances in in-vase flowers than in on-tree flowers, suggesting that the low expression of these genes is probably responsible for lower anthocyanin contents, resulting in the color fading in the petals in in-vase flowers.

Overexpression of Ps-CHI1, a homologue of the chalcone isomerase gene from tree peony (Paeonia suffruticosa), reduces the intensity of flower pigmentation in transgenic tobacco

Chalcone isomerase (CHI) is one of the key enzymes in the flavonoid and anthocyanin biosynthesis pathway catalyzing the stereospecific isomerization of chalcones into their corresponding (2S)-flavanones. In this study, to investigate the role of CHI in tree peony flower coloration mechanism, a CHI gene was isolated from Paeonia suffruticosa cv. Guan Shi Mo Yu, and designated as Ps-CHI1. The cDNA sequence of Ps-CHI1 was 924 bp in full length containing an opening reading frame of 654 bp that encoded a peptide of 217 amino acids with a predicted molecular mass of 23.3 kDa and a pI of 5.0. Sequence alignment and phylogenetic analysis revealed that Ps-CHI1 shared high homology with other type I higher plant CHI proteins. Quantitative real-time PCR analysis indicated that Ps-CHI1 showed the highest transcript abundance in petals, moderate levels in sepals, low levels in leaves and carpels and the lowest levels in stamens. Ps-CHI1 was expressed at the highest level in early stage of uncolored flowers and underwent moderate decreases in expression until there was little transcription could be detected when flowers fully opened and deeply pigmented. By inserting Ps-CHI1 into tobacco (Nicotiana tabacum L.) via Agrobacterium-mediated transformation, T1 transgenic plants were obtained. Phenotypes and pigment analysis revealed that they produced up to threefold total flavonols and flavones over wild-type control, and showed a remarkable reduction in anthocyanin content and flower color intensity. These results provide theoretical deduction supporting Ps-CHI1 as an important gene involved in tree peony flower pigmentation.

Transcriptomic analysis of cut tree peony with glucose supply using the RNA-Seq technique

Several unigenes encoding ACS and ERF involved in ethylene biosynthesis and signal transduction were greatly down-regulated in the petal transcriptome of cut tree peony 'Luoyang Hong' with glucose treatment. Glucose also repressed stress-related transcription factor genes DREB, CBF, NAC, WRKY and bHLH. Tree peony (Paeonia suffruticosa Andrews) is a famous traditional flower in China. Glucose supply prolonging vase life of cut tree peony flowers is associated with its role in the suppression of sensitivity to ethylene and ethylene production, but the regulation mechanism of sugar on ethylene biosynthesis and signaling is unclear. In the present work, a normalized cDNA pool was constructed as the reference transcriptome from mixed petals of different developmental cut tree peony 'Luoyang Hong' and sequenced using the Illumina HiSeq™ 2000 platform. We obtained 33,117 unigenes annotated with public protein databases. In addition, the transcriptome change in petals of cut tree peony with glucose supply and the control treatment was investigated. With non-redundant annotation, 173 differentially expressed genes were identified, with 41 up-regulated genes and 132 down-regulated genes. According to RNA-Seq data and real-time quantitative polymerase chain reaction validation, one unigene encoding ACS, a key ethylene synthetic enzyme, and four unigenes encoding ERF, which is involved in ethylene signal transduction was greatly down-regulated with glucose treatment. Furthermore, stress-related transcription factor genes DREB, CBF, NAC, WRKY and bHLH were also repressed with glucose supply, as well as several other stress-responsive and stress-tolerance genes, indicating that glucose supply probably releases the effects induced by various environmental stress. All the results and analysis are valuable resources for better understanding of the beneficial influence of exogenous sugars on cut tree peony.

Molecular Characterization and Expression of Ethylene Biosynthetic Genes During Cut Flower Development in Tree Peony (Paeonia suffruticosa) in Response to Ethylene and Functional Analysis of PsACS1 in Arabidopsis thaliana

Our previous studies have suggested that ethylene is likely to be involved in the regulation of opening and senescence of cut flowers of tree peony. In the present work, to understand the molecular regulation of ethylene biosynthesis in cut tree peony flower development, we isolated two full-length cDNAs encoding ethylene synthetic enzymes, termed PsACS1 and PsACO1, from tree peony flower petals and investigated the effects of exogenous ethylene and 1-methylcyclopropene (1-MCP) on their expressions during vase life. Northern blot analysis revealed that in untreated flowers slight expression of PsACS1 was initiated until flowers half opened and reached the maximum when flowers fully opened, whereas PsACO1 exhibited constitutive levels during flower opening. PsACS1 expression was substantially induced by ethylene and inhibited by 1-MCP during flower development, and no significant alteration was found in the accumulation of PsACO1 transcript in the petals of differently treated flowers. These results suggest that the PsACS1 gene and its resultant protein may be involved in flower opening and senescence, whereas PsACO1 seems constitutively expressed in tree peony. Via Agrobacterium-mediated transformation, PsACS1 was successfully inserted into Arabidopsis and T3 transgenic lines were used for functional analysis of PsACS1. Compared with the wild-type control, PsACS1-overexpressing plants showed a discrepant phenotype, including shorter hypocotyls, fewer leaves, smaller rosette diameter, and later flowering, which were all attributed to the higher ethylene production caused by the ectopic expression of PsACS1 in Arabidopsis. This result provides support of the hypothesis that PsACS1 is an important gene involved in ethylene biosynthesis during cut flower opening and senescence of tree peony.

Identification of floral fragrances in tree peony cultivars by gas chromatography–mass spectrometry

Volatile organic components in petals of thirty tree peony cultivars were analyzed using a headspace solid-phase microextraction technique (HS-SPME) coupled with GC–MS. 146 volatile organic components were detected, in which 81 of them were scent components. The major scent components were terpenes, alcohols, arenes and alkanes. According to major fragrances and the results of sensory evaluation, thirty cultivars were classified into five fragrance patterns: a woody scent, a rose scent, a lily of the valley scent, a phenolic scent and an unidentified scent, in which cis-ocimene, d-citronellol, linalool, 1,3,5-trimethoxybenzene (TMB) and pentadecane were their major floral fragrances, respectively. Seven cultivars were evaluated for their potential in the development and utilization of tree peony flowers: ‘Tian Xiang’, ‘Lan Bao Shi’, ‘Dian Jiang Feng Dan’, ‘Bai He Zhan Chi’, ‘Chun Xue’, ‘Hu Die Bao Chun’ and ‘High Noon’. In particular, ‘High Noon’ has significant high fragrance content for breeding fragrant peonies.

Molecular characterization and expression analysis of chalcone synthase gene during flower development in tree peony ( Paeonia suffruticosa )

Chalcone synthase (CHS, EC: 2.3.1.74) is a key enzyme in the flavonoid and anthocyanin biosynthesis pathway. In order to investigate the role of CHS in tree peony flower coloration mechanism, we isolated and characterized the CHS gene from Paeonia suffruticosa cv. Yu Ji Yan Zhuang and analyzed its spatial and temporal expression patterns during floral development. The cDNA sequence of the CHS gene in P. suffruticosa (Ps-CHS 1, genbank accession no. GQ483511) was 1475 bp in full length containing an opening reading frame (ORF) of 1185 bp that encoded a 394 amino acid polypeptide. Bioinformatic analysis showed that, Ps-CHS1 possessed all the conserved active sites for the CHS function as well as the family signature. Sequence alignment and phylogenetic analysis revealed that Ps-CHS1 shared high homology with CHS from plants in Salicaceae, Malvaceae and Rosaceae. The homology-based structural modeling showed that Ps-CHS1 had the typical structure of CHS. Southern blot analysis indicated that CHS was encoded by a small multigene family in the genome of tree peony. Anthocyanidin content in full-opening flower petals accumulated to the highest level. Real-time polymerase chain reaction amplification (PCR) analysis indicated that, Ps-CHS 1 showed the highest transcript abundance in petals, moderate levels in sepals, low levels in leaves and stamens, and the lowest levels in carpels. Ps-CHS 1 was actively expressed during flower development and increased gradually until reached maximal expression when flower fully opened. These results indicated that PsCHS 1 was involved in the flower pigmentation of tree peony.

Expression of ethylene receptor and transcription factor genes, and ethylene response during flower opening in tree peony (Paeonia suffruticosa)

Tree peony (Paeonia suffruticosa) is a well known traditional ornamental plant in China and cut flowers of tree peony have potential market value. To understand the involvement of ethylene in the cut flowers opening at the transcription level of ethylene signaling, we isolated two partial cDNAs encoding ethylene receptor Ps-ETR1-1 (GenBank accession no. EU526838) and transcription factor Ps-EIN3-1 (GenBank accession no. EU526839) from tree peony flower petals, and studied the effects of exogenous ethylene and 1-methylcyclopropene (1-MCP), an ethylene action inhibitor, on the expression of Ps-ETR1-1 and Ps-EIN3-1 during vase life. Northern blot analysis revealed that Ps-ETR1-1 and Ps-EIN3-1 exhibited constitutive levels during untreated flower opening, and they responded significantly to ethylene and 1-MCP treatments. In contrast with the control, the levels of Ps-ETR1-1 mRNA in petals were substantially inhibited by both ethylene and 1-MCP, and remained at nearly unchangeable level throughout flower development. Expression of Ps-EIN3-1 was strongly inhibited by ethylene and slightly induced by 1-MCP during flower opening and senescence. These results suggest that the Ps-ETR1-1 and Ps-EIN3-1 genes and their resultant protein may be involved in the ethylene sensitivity and responses of tree peony cut flowers.

Flavonoid Composition and Antioxidant Activity of Tree Peony (Paeonia SectionMoutan) Yellow Flowers

Tree peony flowers are edible and traditional Chinese medicine materials. In the present study, 26 flavonoids were identified and quantified in yellow flowers of tree peony by high-performance liquid chromatography with diode array detector (HPLC-DAD) and by HPLC-electrospray ionization-mass spectrometry (HPLC-ESI-MS). Seventeen of them were first reported in flowers of tree peony, and glycosides of kaempferol, luteolin, and apigenin as well as isosalipurposide were the main flavonoids investigated. Furthermore, the petal extracts showed high antioxidant activity according to DPPH*, ABTS*(+), and OH* scavenging assays and ferric reducing antioxidant power assay. There were significant correlations between antioxidant activity and both the total polyphenol content (determined by Folin-Ciocalteu method) and the total content of quercetin, kaempferol, and luteolin glycosides. This work is valuable for elucidation of phenolic composition in tree peony flowers and for further utilization of them as functional food and medicine materials.

Analysis of Petal Anthocyanins to Investigate Flower Coloration of Zhongyuan (Chinese) and Daikon Island (Japanese) Tree Peony Cultivars

; Pn, Cy and Pn, Cy > Pg groups. Each group consequently specified significant features among CIELAB color notation and petal pigmentation, being adequate to characterize tree peony flowers as similar between Zhongyuan and Daikon Island cultivars, thus the cultivars of the two areas are suggested to be related to one another.

Comparative Study of Anthocyanins in Tree Peony Flowers.

Flowers of the tree peony, Paeonia suffruticosa, and its interspecific hybrids with P. lutea, and P. delavayi, which originated in China and which were introduced by American and French breeders, were assayed for anthocyanins to trace their development.Petal hues of all Japanese cultivars (Paeonia suffruticosa) were distributed within the blue-red scope on Commision Internationale de l'Eclairage (CIE) (L*, a*, b*) color coordinate. Red-dish purple cultivars had high values of both blue and red, whereas pink or white cultivars had low values. Dark red or deep red-purple cultivars contained a large amount of anthocyanins in the petals, whereas pink or white cultivars contained a slight amount. Therefore, there was a high negative correlation between petal lightness (Hunter's L value) and petal anthocyanin contents.All dark red or deep red-purple Japanese cultivars contained 6 anthocyanins, peonidin 3, 5-diglucoside (Pn3G5G), peonidin 3-glucoside (Pn3G), cyanidin 3, 5-diglucoside (Cy3G5G), cyanidin 3-glucoside (Cy3G), pelargonidin 3, 5-diglucoside (Pg3G5G) and pelargonidin 3-glucoside (Pg3G). Vivid red cultivars lacked Cy3G/Cy3G5G but contained large amounts of Pg3G/Pg3G5G. Some pink cultivars lacked Pn3G and Pg3G as well as Cy3G/Cy3G5G.Of the 6 anthocyanins present in the Japanese cultivars, the Chinese cvs. of P. suffruticosa and P. suffruticosa var. spontanea generally lack Pg3G, which may account for the absence of the vivid red color.American and French interspecific hybrids between P. suffruticosa and P. lutea and P. delavayi lack Pg3G and Pg3G5G. The lack of pelargonidins gave rise to hybrids with crimson or scarlet flowers; but in the presence of a yellow chalcone, peonidin and cyanidin in some cultivars gave rise to orange or maroon flowers. The yellow pigment is inherited from the P. lutea and P. delavayi.