Study On Phloem Unloading Pathway Of Photosynthates Of Xanthoceras Sorbifolia Bunge

Xanthoceras sorbifolia Bunge is called "northern oil tea".It has wide adaptability,easy reproduction,and high seed oil content.As a bioenergy species with development potential,Xanthoceras sorbifolia Bunge has attracted extensive attention in recent years.The yield deficiency is the main factor limiting the development of the fruit industry.The photosynthate transport and distribution are related to the fruit yield,but the mechanism of the fruit photosynthate phloem unloading is not clear.In this study,the ultrastructural changes of the phloem were observed by transmission electron microscopy.At the same time,fluorescent dye tracing technology and laser confocal scanning electron microscopy technology were used to visualize the phloem unloading path of the photosynthate.The contents of soluble sugar,soluble starch,soluble protein,lipids and the activities of enzymes related to sugar metabolism were measured.Illumina Hi-seqTM2000 high-throughput sequencing platform was used to carry out transcriptome sequencing on the fruits of Xanthoceras sorbifolia Bunge,and a large number of gene sequences were obtained.Semi-quantitative PCR and real-time fluorescence quantitative PCR were used to screen sugar transporter genes involved in fruit homogenate unloading.The results indicated that:1:Observation of the ultrastructure in different development stages showed that there were plasmodesmatas between the sieve element-companion cell(SE-CC)and the peripheral parenchymal cells(PP)at the early and late stages of development,forming a comoplast connection,while there was no plasmodesmatas at the middle stage of development,and there was symplastic isolation.The fluorescence dye tracing results showed that the fluorescence dye carboxyl fluorescein(CF),which was membrane impermeable at the early and late stages of development,could be discharged to the peripheral parenchymal cells,while it was restricted in the vascular bundle at the middle stage of development.In the process of fruit development,the phloem unloading pathway of photosynthate changed from symplastic to apoplastic and then to symplastic.2:Through the study on the changes of organic matter content in the peel and the seed during the development process of Xanthoceras sorbifolia Bunge,the organic matter in the peel,such as protein,starch and soluble sugar,will be transferred to the seed during rapid synthesis of oil,and will be converted into seed oil together with the organic matter in the seed,such as starch,protein and soluble sugar for storage.The change of net activity of glucometabolism-related enzymes verified this process and was also consistent with the change of unloading pathway.3:A total of 68 298 Unigene sequences were obtained by transcriptional sequencing using high-throughput sequencing,including 5 SUT genes and 3 SWEET genes.Two sugar transporter genes,SUT3 and SWEET10,were speculated to be involved in phloem unloading of the fruits by semi-quantitative PCR and real-time quantitative PCR.