Studies On Petal Anthocyanins Compositions And Coloration Mechanism Of Four Oramental Plants

Flower color is one of the most important ornamental characteristics. The object of a prolonged endeavor for flower breeders is to expand the flower color range and breed cultivars with novel color. However, due to the diversity of flower color, complexity of anthocyanins structures and their intensive relations, it is difficulty to analyze anthocyanins and find out the coloration mechanism of ornamental plants. In order to explore the general law of coloration mechanism, the representative ornamental plants namely Syringa spp., Chaenomeles speciosa, Viola (V. yedoensis, V. prionantha) and Ipomoea purpurea were chosen as the study objects in the present paper, in which Syringa spp. and Chaenomeles speciosa belong to the woody shrub, Viola belongs to the herbaceous cover plant, and Ipomoea purpurea belongs to the herbaceous climber. The identification of anthocyanin constitutions and clarification of petal coloration mechanism of these representative plants were systematically studied. Color were measured by CIEL*a*b* scale and anthocyanins compositions were determined by high-performance liquid chromatography coupled to photodiode array detection and electrospray ionization mass spectrometry (HPLC-DAD/ESI-MS). Multiple linear regression analysis (MLR) was used to explore the relationship of petal color and anthocyanin contents. Based on the clarification of petal coloration mechanism of representative plants, the universal law for the relationship between anthocyanin structures and petal color were summarized. In addition, the biosynthetic pathway of anthocyanins from Syringa was deduced, and the specific methods of breeding rare red Syringa flowers were reported.Main results were as follows:1. Optimization of HPLC separation for anthocyaninsA fast and reliable HPLC method was developed for separation of anthocyanins in V. yedoensis and V. prionantha petals by optimizing solvent system and adjustment of gradient elution, temperature and flow rate. All data from linearity (R = 0.9997) and precision (RSD < 3.67%) experiments revealed that the optimized HPLC method was precise and reliable.2. Complexity of anthocyanin structures29 anthocyanins were characterized in petals of four ornamental plants by HPLC-DAD/ESI-MS, which derivated from various anthocyanidins, glycosylations and acylations. Anthocyanins from Syringa, V. yedoensis and V. prionantha were firstly reported.There were two anthocyanins and two flavonols identified in Syringa spp., which were delphinidin 3-O-rutinoside (Dp3Ru), cyanidin 3-O-rutinoside (Cy3Ru), quercetin 3- O-rutinoside (Rutin) and kaempferol-3-O-rhamnoside-7-O-glucoside (Km3R7G).Six anthocyanins were found in petals of C. speciosa, which were Cy-3-O-galactoside (Cy3Ga), Cy-3-O-glucoside (Cy3G), Pg-3-O-galactoside (Pg3Ga), Pg-3-O-(galactose-glucose) [Pg3 (Ga-G)], Cy-3-O-(galactose-glucose) [Cy3 (Ga-G)] and Cy-3-O-succinylarabinoside (Cy3SucAra). Cy3SucAra was identified firstly in C. speciosa.14 anthocyanins were found in flowers of V. yedoensis and V. prionantha, which were Dp-3-O-rutinoside-5-glucoside (Dp3Ru5G), Cy3Ru5G and Pt3Ru5G; Dp-3-O-(acetyl)-rutinoside-5-glucoside (Dp3acRu5G), Cy3acRu5G and Pt3acRu5G; Dp-3-O-(p-cis-coumaroyl)-rutinoside-5-glucosid (Dp3cispCRu5G), Dp-3-(p-tans- coumaroyl)-rutinoside-5-glucoside (Dp3transpCRu5G), Pt3cispCRu5G, Pt3transpCRu5G, Mv3cispCRu5G, Mv3transpCRu5G, Cy3pCRu5G and Pn3pCRu5G.Seven anthocyanins were analyzed in petals of I. purpurea. They were Pg and Cy derivatives intensively glycosylated and acylated by glucoses and caffeic acids. According to the numbers of glucoses and caffeic acids, they are abbreviated as Cy3C5G, Pg3C5G, Cy2C3G, Cy2C4G, Pg3C4G, Pg2C4G and Pg2C3G.3. Comparison of anthocyanin contentsDp3Ru and Cy3Ru were identified in petals of Syringa. Dp3R is predominant (88.1%). There were no anthocyanins found in white and yellow Syringa flowers.Cy3Ga and Cy3 (Ga-G) are the main anthocyanins in C. speciosa flowers, the average content of which accounts for 94.1%. Other four anthocyanins are trace amounts.There are remarkable differences in anthocyanins between V. yedoensis and V. prionantha. In V. yedoensis, anthocyanins derived from Dp (22.0%), Cy (10.7%), Pt (29.8%), Mv (30.5%) and Pn (7.0%). In V. prionantha, anthocyanins derived from Dp (61.0%), Cy (28.3%) and Pt (10.8%). In V. yedoensis, anthocyanins are mostly of pC3Ru5G type (96.9%), and the rest are ac3Ru5G (3.0%). In contrast, in V. prionantha, predominant anthocyanins belong to ac3Ru5G type (82.1%), and the rest are pC3Ru5G (11.2%) and 3Ru5G (6.8%).Cy2C3G, Cy2C4G and Cy3C5G were characterized in purple-blue I. purpurea flowers. Cy3C5G is major (79.6%). Purple-blue and pink petals of I. purpurea comprise the same anthocyanins, Pg3C4G, Pg3C5G, Pg2C4G and Pg2C3G, but their contents are different. Pg3C5G is the major anthocyanin in purple-blue and pink petals, which account for 68.8% and 86.5%, respectively.4. Clarification of petal coloration mechanismIt was the first time to explore the relationships between petal color and anthocyanin contents in the levels of anthocyanin glycosides of four ornamental plants by multiple linear regression analysis (MLR).Dp3Ru and Rutin determine the Syringa petal color together. Dp3Ru is the main anthocyanin, which gives blue to purple-blue to Syringa petal colors. Increase of Dp3Ru content can shift flower color towards bluer, while in the condition of decrease of Rutin content and increase of Dp3Ru content can enhance the red extent.The different content of Cy3 (Ga-G) and Cy3Ga influences the pink and red color of C. speciosa. MLR showed that Cy3Ga, Pg3 (Ga-G) and Cy3SucAra are important components, high contents of which significantly enhance the red extent of C. speciosa petals.Dp and Pt derivatives are vital anthocyanins impacting on the flower color of V. prionantha and V. yedoensis. Increase of Dp derivatives contents can facilitate flower color bluer, while increase of Pt derivatives contents can shift flower color towards redder.The contents of Pg3C5G, Cy3C5G and TF impact on the flower color of I. purpurea. Increase of Pg3C5G, decrease of Cy3C5G and TF can enhance the red extent, while decrease of Pg3C5G and increase of Cy3C5G can make the flower color shift to bluer.5. Guidance for flower color breedingSelection or creation of red petals is the aim of flower color breeding in Syringa. It is advised to hybrid with the parent of‘5’which comprises high amount of Cy3Ru (78.7%) or to utilize the co-suppression technique. Introduction of F3’5’H can inhibit F3’5’H, interfere or reduce the synthesis of Dp3Ru, and then Cy3Ru amount increases, the petal shift to redder.In brief, we can conclude that Dp derivatives are not the only anthocyanin base in the formation of blue flowers. We should fully consider other key factors such as the co-adjustment of contents of Dp derivatives and TF, the copigmentation effects between anthocyanins and copigments and so on.