Preliminary Study On The Mechanism Of Sucrose Pretreatment Promoting The Preservation Of Cut Flowers Of Chimonanthus Praecox L.

Wintersweet(Chimonanthus praecox L.),which belongs to genus Chimonanthus of Calycanthaceae,is widely used in gardens as a traditional flower in China.It blossoms from December to February of the next year and the fragrance is overflowing.Because of its unique fragrance and flowering time,wintersweet has great ornamental and economic value in the cut flower market,and has formed a considerable cut flower industry in Shanghai,Chengdu and other places.Sucrose is a commonly used preservative for cut flowers.In this experiment,different concentrations of sucrose supplemented with200mg/L 8-hydroxyquinoline sulfate were used as pretreatment solution to pretreat the cut flower of wintersweet ‘Hua Hu Die' for 72 hours.The relevant morphological and physiological indexes were measured to determine the appropriate sucrose concentration and vase time.Furthermore,the samples were sequenced and analyzed by transcriptome,and the results were validated and explored to determine the effect of sucrose pretreatment on the cut flower preservation of wintersweet.The main results of this experiment are as follows:1.The results of morphological measurement during vase life showed that,the10g/L sucrose pretreatment can promote the opening of flowers,increase the maximum flower diameter,extend the time taken to reach the maximum flower diameter,and delay the decline of fresh weight.When the pretreatment concentration of sucrose reached30g/L,it would accelerate the flower wilting,reduce the vase life and shorten the flowering time,thus affecting the cut flower quality.2.The results of several physiological indexes showed that,sucrose pretreatment increased the soluble sugar content in tepals,and the soluble protein content increased first and then decreased,and peaked on the 2nd day of vase time.The proline content in tepals increased with the time,and the MDA content decreased slowly when pretreated with 10 g/L sucrose.The activity of SOD and CAT showed that 10 g/L sucrose pretreatment might contribute to the reduction of superoxide anion and hydrogen peroxide in tepals.3.According to the results of morphological and physiological indexes,10 g/L pretreatment and control samples were selected for transcriptome sequencing.The time points were T0(before pretreatment),D0(after pretreatment),D2(2nd day of vase time)and D5(5th day of vase time).Bioinformatics analysis showed that the highest number of differentially expressed genes appeared on the 2nd day,reaching 1256.The analysis ofGO and KEGG enrichment showed that sucrose pretreatment could cause changes in gene expression in various pathways such as sugar metabolism,secondary metabolism and so on.4.Combining the results of transcriptome sequencing and gene function,it is speculated that the flower opening and the increase of flower diameter may be related to differentially expressed genes CpEXPA4,CpEXPA10 and CpEXPA15.The results of real-time PCR verification were consistent with the transcriptome data.The expression of CpEXPA10 and CpEXPA15 in sucrose pretreatment was higher than that in control,while the expression of CpEXPA4 showed the opposite trend.5.In order to understand the expression patterns of CpEXPA4,CpEXPA10 and CpEXPA15 in different cultivars of wintersweet,the expression levels of CpEXPA4,CpEXPA10 and CpEXPA15 in different flower development stages of ‘H29',‘JDH02',‘Hua Hu Die' and ‘Xiao Mi Xing' were determined.Samples of ‘H29'were also taken to observe the cell changes during flower development.The results showed that the trend of gene expression in the four cultivars was not identical,and there were also differences in different organs and tissues.CpEXPA10 and CpEXPA15 may be more closely related to flower development and opening.6.The protein structures of CpEXPA4,CpEXPA10 and CpEXPA15 were analyzed.All of them contain the DPBB superfamily conserved domain DPBB1 and Pollen allerg1 conserved domain,which are typical of the expansin family,and have high similarity with the expansin sequences in Arabidopsis thaliana,Nelumbo nucifera,Camellia sinensis and other species.In addition,the protein structure and localization were predicted.The results showed that all of them had signal peptides and were localized in extracellular matrix.7.The subcellular localization vectors of CpEXPA4,CpEXPA10 and CpEXPA15 proteins were constructed and found to be mainly localized on the endoplasmic reticulum of the organelle.Therefore,CpEXPA4,CpEXPA10 and CpEXPA15 proteins may be related to the function of the endoplasmic reticulum,which promote the increase of membrane volume,thereby regulating plant cell development.