| It is very cold in winter and a long period of dry weather in northern China.And negative accumulated temperature and extreme low temperature are the main barrier for winter rapeseed in this area where the temperature begin to drop sharply in mid September.The winter rapeseed?Brassica.rapa L.?stopped growing in late October and leaves gradually turned yellow and dry then only the root alive in the soil in the wintering stage.During this time,the stronger anti-cold resistant cultivars were in the dead leaves stage a little earlier than weak anti-cold resistant cultivars.Many reports showed that plant leaves turned yellow and dry was related to its endogenous ABA content.So this study analyzed the relationship between cold tolerance and endogenous ABA content,and cloned the NCED genes which are the key genes for ABA bio-synthesis.Then applied exogenous ABA on winter rapeseed to get the relationship between the endogenous ABA content and the expression of NCED3.The main results were as follow:1.The results showed,that the rapeseed in northern China can defend the harsh winter environment was related to the endogenous ABA content.There were significant differences in the content of the ABA content of different kinds of cold resistant varieties.The ABA content in strong cold resistant varieties substantial increased earlier,while the weak cold resistant varieties increased late.In the growth and development process,the dead leaves stage of strong resistant varieties were earlier,whereas weak cold resistant varieties were late.The increased time of ABA content was consistent with dead leaves time,and high correlated to the survival rate.So we can get that ABA content increased earlier the survival rate were higher.The high coincidence of the three traits indicated that the endogenous ABA was one of the main regulating substances in winter rapeseed.2.Three NCED genes were cloned from northern Brassica rapa by homology cloning strategy.Sequences analysis showed that three proteins in northern Brassica rapa were both very close to Brassica napus,Arabidopsis,Brassica oleracea,Raphanus sativus.The sequence analysis showed NCED2,NCED3 and NCED5 contained 1746 bp,1794bp and 1770 bp open reading frame?ORF?and coded 581,597 and 589 amino acid,and the calculated molecular mass was 64.31721 KD,65.74438 k D and 65.34794 k D with the theoretical isoelectric point?p I?of 5.32,5.81 and 5.43 respectively.Protein hydrophobicity,transmembrane domains and s ignal peptide analysis indicated that the protein might be transmembrne and hydrophilic,and located on mitochondrial membrane while NCED3 and NCED5 located on mitochondrial membrane.3.Exogenous ABA can enhance the cold resistance of winter rapeseed and up-regulate the NCED3 expression.With the temperature reducing in wintering,the expression quantity increased.The correlation analysis showed that the expression quantity of NCED3 was positive correlate with ABA content.The correlation coefficient of NCED3 expression quantity and endogenous ABA content changed from 0.334 to 0.784 after ABA treatment.At the same time,exogenous ABA induced to increase the SOD,POD,CAT,APX activity and survival rate and to reduce the chlorophyll content.It also induced the ABA content and NCED3 expression and then enhanced the cold resistance.So exogenous ABA treatment is an important way to enhance the cold resistance of winter rapeseed and survival rate.4.The effect of exogenous ABA treatment on cold resistance is related to the ABA concentration and using time.The research showed that exogenous ABA induced to increase the soluble sugar and soluble protein content and the survival rate and improve the agronomic traits.But there was a large difference between different ABA concentration.The best effect on yield when ABA concentration was 15 mg·L-1 to 20 mg·L-1,but not very well when concentration was less was 15 mg·L-1 or greater than 20 mg·L-1.Meantime the processing time influenced the ABA effect.The best processing time was five or six leaf stage from the research results. |
PDF Full Text Request