| The chilling injury caused by low temperature has been the key factor that influence the production of crops.Rice's growth and development process are greatly influenced by temperature,especially the rice seedling stage the temperature is not stable,are more likely to suffer from the harm of low temperature,if suffered from the continuous low temperature more than 4 days,the rice will be dysplasia or even death which cause huge losses.A lot studies have shown that chitooligosaccharide(COS)can induce plants,resistance to cold stress,but its resistance mechanism is not yet complete,largely limits the products'applying in agriculture.This study mainly explore the mechanism of COS improving the cold resistance of rice seedlings,and provide the basis for the uses of COS in the field of agriculture as the plant resistance immune inducer.? YOU 1259 seeds was used as the model crop in this paper to explore the mechanism of COS improving rice seedlings' cold resistance at the physiological and transcriptome level.Firstly,choose the optimal soaking concentration of COS according to the growth status and chilling index.Results showed that the chilling index of 0,50,100,200mg/L COS solution treated rice were 3.18,1.83,0.96 and 0.95 after cold stress for 24h.Comprehensive,100mg/L was suitable.Secondly,the difference of physiological and biochemical indexes related to photosynthesis,cell osmotic regulation substances and antioxidant system were compared between the seedlings growing in normal?cold condition and soaking with COS solution.Results showed that:(1)COS solution soaking treatment could promote the chlorophyll accumulation especially the chlorophyll b,the chlorophyll b content of rice increased 164,3%in the COS soaked group compared with the distilled water treated one after cold stress for 24h.(2)COS solution soaking treatment could promote osmotic regulation substances,the soluble sugar?soluble protein and proline content of rice increased 32.6%,35.1%and 13.9%in the COS soaked group compared with the distilled water treated one after cold stress for 24h.(3)COS solution soaking treatment could reduce the oxidation damage,the SOD activity increased 23.9%,the H2O2 and MDA content decreased 43.4%and 36.4%in the COS soaked group compared with the distilled water treated one after cold stress for 24h.Thirdly,cDNA-SCOT technology was used together with the quantitative RT-PCR technology to discover the different expression gene between the COS treatment group and control group under cold stress,and 2 positive differential expressed fragments were found,one of the genes encodes DegQ protein who plays an important role in the degradation of damaged D1 protein,another one encodes the RNA binding protein,researches about its function were less.Finally,Real time quantitative PCR method was used to determine the DegQ protein gene and psbA gene relative expression level.Our data showed that COS solution soaking treatment could increase the expression of psbA and DegQ protein gene under cold stress,the increment of DegQ protein and psbA mRNA transcripts may accelerate the degradation of damaged D1 protein and the synthesis of new D1 protein,our study demonstrated that COS solution has a great effect on the damaged PS ? repairing process,in turn improve the cold resistance of rice seedlings.Results in this paper show that COS could promote the accumulation of protection substances in rice under cold stress,induce the expression of DegQ protein gene and psbA gene,accelerate the repair process of PS ? and the accumulation of chlorophyll b,in turn induce the rice seedlings,cold resistance.Hope this study could provide more adequate theoretical basis for the application of the COS products,and provide a new idea in the cold resistance related genes and plant cold resistance breeding work. |
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