Study On Physiological Mechanism Of Anthocyanin Accumulation In Flowers Of Herbaceous Penoy(Paeonia Lactiflora Pall.)

Herbaceous peony (Paeonia lactiflora Pall.) is an important ornamental plant which is widely cultivated in many regions as pot flowers, dry flowers, garden flowers and cutting flowers. On account of the various requirements from different consumer groups and different applications, flower color has been an important research focus for breeding scientists. In this paper, the discrepancy of red color on flowers was studied in two cultivars of P. lactiflora:a red cultivar (’Dafugui’) and a pink cultivar (’Qingwen’) to study physiological mechanism of anthocyanin accumulation in herbaceous penoy flowers. Anthocyanin accumulation and differential expression of its biosynthetic genes were analyzed. Moreover, photosynthetic characteristics and the soluble sugar content of the flower petals were determined. The main results were as follows:(1) The anthocyanins, as well as the flavones and flavonols were extracted from petals and analyzed by HPLC-PDA-MS". The results showed that the two cultivars had the same composition of anthocyanins as well as flavones and flavonols. Two anthocyanins (cyanidin-3,5-di-O-glucoside and peonidin-3,5-di-O-glucoside) and five kinds of flavones and flavonols (quercetin di-hexoside kaempferol di-hexoside, isorhamnetin di-hexoside, quercetin-3-O-rhamnoside and luteolin-7-O-glucoside, respectively) have been identified. The anthocyanin content determined the depth of the red color in P. lactiflora flowers, and the more anthocyanins in petals, the redder the flowers. And the colorless or pale yellow flavones and flavonols can reduce the color of anthocyanins to some extent in the pink’Qingwne’ owing to the copigment effecct.(2) The sequence of PIC4H gene was obtained from P. lactiflora and deposited in GenBank (KC137571). The sequence contained1808base pair (bp) including a1518bp open reading frame that encoded505amino acids. A BLAST analysis showed that this protein shared high identity similarity to C4H from Canarium album, Salvia miltiorrhiza, Platycodon grandiflorus, Malus hybrid and Gossypium arboretum. The amino acid sequence of PIC4H shared conserved domains with other C4H amino acid sequences and it had generally P450-featured motifs, such as the E363-R366-R420triad, the T-containing binding pocket motif A306AIETT311, the heme-iron binding do-main P439FGVGRRSCPG449, the conserved P34PGP37 tetrapeptide, and a proline residue (Pro448) in the central part of the heme-binding loop. In addition, there were5highly conserved substrate recognition sites (SRS) in PIC4H.(3) Expression levels of ten genes involved in the pathway during four developmental stages of flower petals were analyzed. The result suggested that the critical genes in anthocyanin accumulation, which contributed to the discrepancy of red color on ’Dafugui’ and ’Qingwen’, were PlC4H, PlCHS, PlANS and PlUF3GT.’Dafugui’had high accumulation of4-coumarate:CoA due to the high expression level of PIPAL. Then, with low expression of PlC4H,PlCHS, PlCHI and PlF3H, less intermediate products, such as flavanones, dihydroflavonols, flavones, and flavonols were produced. However, with higher expressions ofPlANS and PlUF3GT, the above substances were catalyzed by these enzymes, and resulted in the high accumulation of anthocyanins.(4) We determined the soluble sugar content in flower petal of ’Dafugui’ and ’Qingwen’. Since photosynthesis determines the soluble sugar content in plants, photosynthetic characteristics were measured as well. Higher Pmax, LSP, AQY, and lower LCP gave rise to higher photosynthetic efficiency for ’Dafugui’ than ’Qingwen’. In addition,’Dafugui’ accumulated more photosynthetic products during the daytime than ’Qingwen’. However,’Qingwen’ had higher soluble sugar content. During the development of the flowers, the soluble sugar content showed the opposite trend of anthocyanin content.