Selection Of Cold Tolerance In Rapeseed And Study On Cold Tolerance Mechanism Of Rapeseed(Brassica Napus L.)

Low temperature is one of the most important abiotic factors inhibiting growth,productivity and distribution of rapeseed?Brassica napus L.?.Rapeseed is an important oil crop in China,and it is often subjected to low temperature stress during its growth and development.The most effective solution to cold stress is to genetically improve the resistance of rapeseed varieties,and the primary factor for cold breeding is to obtain useful germplasm resources.The identification method of rapeseed cold tolerancewasbuiltedand the extremely cold tolerant/sensitive resources were selected in the study;the physiological indicators of rapeseed before and after cold stresswereexamined and analyzed;with the Illumina Hi-Seq 4000 high-throughput sequencing platform,the molecular mechanisms of the rapeseed response to cold stress were analyzed at the transcriptome level.The main results are as follows:?1?Built the efficient identification method of rapeseed cold tolerance.Seedling at three or four leaf stage were treated at 4?for 24h as cold acclimation,survival rates?SR?and cold tolerance index?CTI?after-2?1h?-2?1h+-4?1h?-2?1h+-4?1h+-6?1h treatment were calculated.228 rapeseed materials from China and abroad were evaluated.Results indicated the survival rate?SR?after-2?1h,-2?1h+-4?1h and-2?1h+-4?1h+-6?1h treatment were from 0 to 100%,from 0 to 80%,and from 0 to 70%,the cold tolerance index range was from 0 to 52;eight extremely cold tolerant materials were selected and their cold tolerance indexes reached 33-52.?2?Compared with the sensitive material C20,the variety1801 had stronger regulatory effect on hormone levels,antioxidant enzyme activities,osmotic adjustment and gene transcription levels under cold stress.At-2?and-4?conditions,the survival rate of C20 seedlings were 0%and 0%,the survival rate of 1801 seedlings were 100%and 75%,respectively.Under low temperature stress,the accumulation of proline,soluble sugar,soluble protein and antioxidant enzyme activity in 1801 seedlings were greater than C20;the abscisic acid?ABA?and gibberellin 3?GA₃?content of 1801 seedlings increased;the ABA content of C20 seedlings increased,but the GA₃ content of C20 did not change significantly.The results of real-time quantitative PCR?qPCR?showed that the expression levels of cold-resistant marker genes COLD1,CBF4,COR6.6,COR15 and COR25 in 1801 seedlings were much higher compared withC20 under low temperature stress.?3?Under low temperature stress,the1801 had stronger regulatory effect at the transcriptome level compared with C20.Sampled the seedling leaves of C20 and 1801 at2?,0?,-2?and 22?treatment conditions for transcriptome sequencing.Compared with CK?22??,there are 6751,5338 and 6868 differentially expressed genes?DEGs?in1801,and there are 5350,3639 and 3026 DEGs in C20 at 2?,0?,and-2?,respectively.Further bioinformatic analysis showed that inositol metabolism responded to low temperature stress in Brassica napus L..The difference of inositol content between C20and 1801 under low temperature stress may be the cause of the difference in cold resistance between them.Through the determination of endogenous inositol content and the expertment of exogenous inositol application,it was confirmed that inositol could improve the cold resistance of Brassica napus L..