The Mechanism Of Improving Rice Seedlings’ Cold Resistance By Chitooligosaccharide

Rice,one of the most important crops around the world,and is sensitive to cold stress particularly in the early seedling stages.The unpredictable cold stress can cause significant losses(5-10%)in rice production and negatively affecting agricultural economies.Therefore,enhancing rice tolerance to cold stress is crucial for higher crop yield.Chitooligosaccharides(COS),an environment-friendly biological abiotic-resistant agent,has been used as a plant immune elicitor.But the possible mechanisms of COS induced rice cold tolerance remains unclear.This study mainly explores the mechanism of COS improving the cold resistance of rice seedlings,and provides the basis for the uses of COS in the field of agriculture as the plant resistance immune inducer.Firstly,in this study,the different deacelation degree of two COS in cold resistance was explored under different treatments.The results showed that they had the best effect in the root treatment.After low temperature treatment,When applied the deacetylation degree of 98%COS to rice seedings,100 mg/L COS root supplies had best cold resistance,the fresh weight per plant increased by 7.95%,and the relative electrical conductivity decreased by 34.9%,compared with control plants;for the deacetylation degree of 86%COS,150 mg/L COS root treatments had best cold resistance,the fresh weight per plant increased by 6.25%,and the relative electrical conductivity by 38.0%,compared with control plants.In addition,with the experimental results and considering the economic benefits,the deacetylation degree of 86%COS in root treatment with 150 mg/L was better.Secondly,the effects and relative mechanisms of COS on improving the cold resistance in rice seedlings were further investigated.The difference of physiological and biochemical indexes related to cell osmotic regulation substances,photosynthesis and root vigor were compared between the seedlings treated with and without COS solutions.Results showed that:1)COS treatment could promote osmotic regulation substances,proline content,the soluble sugar of rice increased 13.9%,3.22%in the COS treatment group compared with the distilled water treatment after cold stress for 24 h.2)After low temperature stress for 24 h,the chlorophyll repair capacity of the COS treatment was stronger.The chlorophyll a and chlorophyll b increased by 40.2%and 44.9%,respectively,compared with the control group after recover for 14 days.3)COS could effectively promote the growth of rice seedlings roots and stimulate their vigor.The root vigor of COS treatment increased by 168.5%compared with that of distilled water treatment after cold stress.Moreover,based on the influence of COS on rice seedlings roots,the influence of COS on the absorption of rice roots was further investigated,enzyme activities of glutamate metabolism were determinated,together with the quantitative RT-PCR technology to discover the different expression gene of glutamate metabolism enzymes between the COS treatment group and control group under cold stress.The results showed that COS could enhance the activities of glutamine synthetase and glutamine-oxoglutarate aminotransferase,while decrease the activity of glutamate dehydrogenase,via regulating the corresponding genes with glutamate metabolism,resulting in glutamate accumulation under cold stress,which provided more sources for the synthesis of proline.Finally,the effects of COS on proline metabolism were analyzed,and the expression of proline metabolism related enzyme genes were further analyzed by the quantitative RT-PCR technology.The results showed that the accumulated proline contents in COS supplies,which resulted from the increased activities of△1-pyrroline-5-carboxylate synthetase and ornithine-δ-aminotransferase,were attributed to that COS effectively induced gene expression of△1-pyrroline-5-carboxylate synthetase,△1-pyrroline-5-carboxylate reductase and ornithine-δ-aminotransferase,inhibit proline dehydrogenase gene expression,under cold stress.Results in this paper showed that COS treated rice seedlings has higher resistance to the cold stress possibly by stimulating root vigor,then accelerating the glutamate synthesis pathway and inducing the proline content to adjust osmotic regulation.Hoping this study could provide more adequate theoretical basis for the application of the COS products,a new idea in the cold resistance related genes and plant cold resistance breeding work.