Study On The Dehydration Tolerance And Preservation Technology Of Platycodon Grandiflorum Seeds

Platycodon grandiflorum(Jacq.)A.DC.is a perennial dicotyledonous herb belonging to Platycodon of Campanulaceae.It is one of the most commonly used medicinal materials in China with broad application prospects.In order to maintain seed vigor,seeds need to be stored under dehydrated condition during the period from harvest to sowing in next season or long-term preservation of germplasm resources,which demonstrates that the dehydration tolerance of the seeds is closely related to the storage characteristics.In this paper,the seeds of P.grandiflorum(Jacq.)A.DC.and P.grandiflorum(Jacq.)A.DC.var album Hort.were involved as experimental materials to explore the physiological and biochemical mechanism of seed desiccation tolerance,thus obtained seed materials with strong dehydration tolerance.Furthermore,we studied the physiological and biochemical indexes transformation of seeds under diverse conditions of different moisture contents(8.50%,6.50%,4.50% and 2.50%)and different storage conditions(indoor,outdoor,short-term,intermediate and long-term),along with the aging rule and physiological and biochemical mechanism of seeds.This study achieved in providing technical support for conventional storage and medium-long storage of seeds,which made theoretical and practical significance for the production of P.grandiflorum and preservation of germplasm resources.The main results are as follows:1.During the process of P.grandiflorum seeds development,the color of seeds changed from shallow to deep,accompanied with increasing germination rate.The seed color of P.grandiflorum(Jacq.)A.DC.at 61 days after flowers(DAF)and P.grandiflorum(Jacq.)A.DC.var album Hort.at 58 DAF appeared to be black,dark brown and so on.A long strip of grain was found on the surface of the seeds,parallel to the seed axis.With these appearance,the germination rate of seeds reached to highest degree of 72.33% and 93.00% respectively.With the development of the seeds,the moisture content and relative conductivity were decreasing.The changes of POD,CAT and MDA corresponded with single peak curve.The trend of thousand-seed weight was rising-descending.The activity of SOD and the content of soluble protein showed the trend of rising-descending-rising.The content of soluble sugar in seeds showed the trend of rising-descending-rising-descending.2.The dehydration tolerance of P.grandiflorum seeds was obtained during the development process.The seeds of 37 DAF began to acquire desiccation tolerance.After different duration of artificial dehydration on seeds of P.grandiflorum(Jacq.)A.DC.at 61 DAF and those of P.grandiflorum(Jacq.)A.DC.var album Hort.at 58 DAF,following phenomenons were discovered: the germination rate tended to be declining-rising,the content of soluble sugar and protein tended to rise continuously.When the moisture content respectively fell to 2.42% and 2.66%,the rate of germination was highest,rising to 88.67% and 93.00% respectively.It means that the seeds of P.grandiflorum(Jacq.)A.DC.and P.grandiflorum(Jacq.)A.DC.var album Hort.obtained the maximum dehydration tolerance at 61 DAF and 58 DAF respectively,and the latter was more resistant to dehydration than the former.3.After 12 months of storage under the same condition,the germination rate,germination potential and germination index of the seeds increased with the decrease of moisture content,but the difference was not significant.The germination rate of the seeds stored in the germplasm bank remained above 90%.After one year of storage,the emergence rate increased with the decrease of seed moisture content;seeds stored indoor and outdoor with 4.50% and 2.50% moisture content had significantly higher emergence rate than that of other moisture content seeds.The emergence rate of untreated seeds was significantly lower than that of dehydration treatment seeds for 12 months after storage in the germplasm bank.With same moisture content,the emergence rate of P.grandiflorum(Jacq.)A.DC.var album Hort.seeds was greater than that of the seeds of P.grandiflorum(Jacq.)A.DC.,which appeared more obvious in the seeds with high moisture content.It showed that the anti-aging ability of P.grandiflorum(Jacq.)A.DC.var album Hort.seeds was higher than that of P.grandiflorum(Jacq.)A.DC..4.Under the same storage conditions,the SOD activity and MDA content of different moisture content seeds increased with the prolongation of storage time,and the increasing amplitude of MDA content decreased with the decrease of moisture content.The physiological and biochemical indexes of seeds with different moisture content stored indoor and outdoor fluctuated greatly.The CAT and POD activity of seeds stored in germplasm bank decreased slightly at first,then increased obviously,and its activity decreased with the decrease of moisture content.After 6 months of indoor and outdoor storage,the germination rate,germination potential,germination index,soluble sugar content,and the activity of CAT and POD all decreased significantly,while the activity of SOD and the content of MDA increased significantly,which means the condition of high temperature and high moisture accelerated the aging of seeds.At this time,SOD was the main ROS scavenger.In the late storage of the germplasm bank,the aging of the seeds expedited and the activity of CAT and POD increased significantly,mainwhile,CAT and POD were playing the role of the main scavenger of free radicals.After 12 months of storage,the activity of CAT and POD and the content of MDA decreased with the decrease of moisture content,while the content of soluble sugar and soluble protein changed in the opposite way.