Study On The Role And Mechanism Of Sucrose Synthase In Dormancy Release Of Pyrus Calleryana Decne.Seeds

In production,the pears are mainly vegetatively propagated,that is,they are sown with stock seeds,cultivated into seedlings and then grafted into cultivated varieties.Pear seeds need to be stratified before they can germinate,so the seed quality cannot be determined before stratification.However,it takes a long time for the stratification of seeds.If the seed quality is not good,the germination rate is low,or if the moisture or ventilation conditions are not properly controlled during the stratification process,the occurrence of mildew in the seed will seriously affect the seedling production in the current year.At present,there is no effective method to quickly break the dormancy of pear seeds in production.Therefore,the study on the dormancy of pear seed will help to establish a rapid method for releasing seed dormancy.In this dissertation,the seeds of Pyrus calleryana Decne were used as research materials.The contents of sucrose,starch,glucose and fructose as well as the changes of sucrose synthase,sucrose phosphate synthase and alpha amylase activity and gene expression in the dormancy release process of Pyrus calleryana Decne seeds were determined by liquid chromatography,dinitrosalicylic acid colorimetry and ultraviolet spectrophotometry.The antisense oligonucleotide technology was used to reveal the role of sucrose synthase and GA20 oxidase genes in dormancy release of Pyrus calleryana Decne seeds.The specific results are as follows:1.Establish a new method to break the dormancy of pear seeds.The seeds were wrapped with absorbent cotton,placed in a petri dish,stratified at a low temperature of 4 ? and wetted the absorbent cotton 2?3 days once.The seed germination rate was counted every 10 days.After 30 days of treatment,the seeds began to germinate.After 60 days,the seed germination rate was 76.7%,which completely broke the dormancy.It shows that this method can be used to break the dormancy of pear seeds.2.The changes of carbohydrates,related enzyme activities and gene expression levels during the dormancy release of Pyrus calleryana Decne seeds were determined.During the dormancy release of seeds,the content of sucrose and starch decreased gradually but the content of glucose and fructose increased continuously;the sucrose synthase that degrades sucrose and the alpha amylase which degrades starch gradually increased,while the activity of sucrose phosphate synthase that synthesize sucrose decreased;the relative expression levels of sucrose synthase,sucrose phosphate synthase and alpha amylase genes all show a downward trend and then a rapid increase.It showed that sucrose degradation and glucose synthesis were closely related to the dormancy release and germination of seeds.3.It was found that sucrose synthase plays an important role in the process of dormancy release of Pyrus calleryana Decne seeds.After using antisense oligonucleotide technology to inhibit sucrose synthase expression,seed germination was significantly inhibited.Compared with the normal stratification of seeds,the germination rate after antisense treatment was only 20%;the sucrose,glucose and fructose contents were significantly increased;sucrose synthase and alpha amylase activities were significantly decreased;the relative expression levels of sucrose synthase,sucrose phosphate synthase,GAI and ABI-3 et al 8 genes related to sugar metabolism and hormone signal transduction were all significantly reduced.It showed that sucrose synthase played an important role in the dormancy release of Pyrus calleryana Decne seeds.4.It was found that the GA20 oxidase gene regulates the activities of sucrose metabolism and starch degradation-related enzymes.Antisense oligonucleotide technology was used to inhibit the expression of GA20 oxidase,a key enzyme of gibberellin synthesis.After antisense inhibition treatment,the seed could hardly germinate,and the inhibitory effect was more significant than that of sucrose synthase inhibition.The seed germination rate was only 1.1%compared to normal stratification.A large amount of sucrose,glucose and fructose were accumulated in the seeds.The enzyme activities and relative gene expression of sucrose synthase,sucrose phosphate synthase and alpha amylase were all significantly reduced.The expression of ABA signaling factor was significantly higher than GA signal factor.It shows that the GA20 oxidase gene is closely related to the regulation of the activities of enzymes related to glucose metabolism.