Preliminary Study On Mechanism Of Floral Coloration During Senescent Process Of Chrysnathemum Moricolium

Chrysanthemum morifolium with aboundant germplasm resources and various cultivars is one of the oldest tranditional flowers in China.Flower color,one of important ornamental traits,has been regarded as a research emphasis all the time.Previous studies about flower color of C.morifolium involved classification of phenotypes,pigment compositions and their metabolic regulation.According to field observation,it was found that C.morifolium turned to redness during the process of aging,which had generality among different cultivars,and was barely reported about its mechanism previously.This study aimed at exploring the relationship between floral coloration and petal senescence,and studying the key mechanism of regulation,as well as providing the theoretical basis for molecular breeding of chrysanthemum flower in the future.Thus,317 chrysanthemum cultivars from "Chinese Chrysanthemum germplasm resources preservation center" in Nanjing Agriculture University were used as the test materials for field investigation and phenotypic measurement.Furthermore,color phenotype of flower,related physiological parameters of petals,and relative expression of anthocyanin metabolism related genes during process of aging were determined on five representative cultivars of three color groups,which were used for preliminary study of petal coloration.The main results are as follows:1.In order to explore the distribution of this phenomenon in different color groups,field investigation and statistics were performed on 317 chrysanthemum cultivars in two consecutive years,using the R.S.H.C.C.for division of color groups.The results showed that chrysanthemum petals gradually turned to be reddish after the blooming period.which was a common phenomenon and appeared in more than half of those cultivars with different degrees of discoloration.Among seven color groups in this research,white group had the lagerst proportion of color change,reaching 89.53%.On the contrary,the color change of red group,only accounting for 10%,was less obvious.2.The flower phenotype of 202 varieties at the full-blooming stages,senescence stage I(10 days after full-blooming stages),and senescence stage II(20 days after full-blooming stages)are measured byCIELab color system.The results indicated that the brightness of petal surface decreased and the red-green value increased from stage one to stage three.Besides,the color phenotypes of each system was dispersed in the stage one and the gradually aggregated in CIELab color system.These results prove that,red degrees of most chrysanthemum cultivars will increase during the senescence of petals.3.The cultivars with outstanding color change including 'White Queen','Mona Lisa White','NA Yukou' of white group,'NA Lvdong' of green group,and 'Ibis-sunny' of yellow group were selected as test materials.Flavonoid content,anthocyanin content and soluble sugar content in petals of different senescence stages were detected.The results showed that the content of flavonoids and anthocyanins and malondialdehyde increased,whereas the content of soluble sugar decreased in three stages.According to these parameters,the color changes of chrysanthemum petals were contributed by the production and accumulation of anthocyanins,and final concentration of anthocyanins could reach tens or even hundred times more than the first stage.In general,'White Queen' is the most obvious variety.4.The relative expression of anthocyanin metabolism related genes in petals of cultivars with color change including 'White Queen','N A Lvdong'and 'Ibis-sunny' during the senescent process were measured by Real-time fluorescence quantitative PCR.The results showed that the expression of CmPAL,CmC4H,CmCHS,CmCH1,CmF3H,CmF3 'H,CmDFR,CmANS and Cm3GT increased,corresponding to the the accumulation of anthocyanins from the first stage to the last stage.The expression of CmCHS and CmCHI were up-regulated in the second stage,while the third stage of expression remained unchanged or slightly down-regulated..The expression change of CmF3H was the most significant different in three cultivars,and were up-regulated to multiple even hundreds times..The expression tendency of transcription factors including CmMYB3,CmMYB6,CmbHLH1 and CmbHLH2 were not the same in different cultivars.Among them,CmMYB3 and CmMYB6 of MYB family changed most significantly,thereby it was speculated that they were involved in the accumulation of anthocynins.On the other hand,the genes of bHLH family had different expression tendency in different cultivars.The expression of CmbHLH1 which changed not very markedly,increased continuously in petals of three cultivars.The expression of CmbHLH2 and CmbHLH24 were up-regulated in all white cultivars.However,the expression change of CmbHLH1 was more obvious,reaching to dozens of times.Therefore CmbHLH2 was suggested to be more related to the accumulation of anthocynins.