Mechanism Of Exogenous ABA Inducing Resistance To Low Temperature In Rice Seedling Stage

Rice is the main grain crop in China,and the low temperature and cold damage at seedling stage is one of the main factors that restrict the safe production of rice.In the middle and lower reaches of the Yangtze River,due to the unstable temperature,it is very easy to have cold wave weather during the seedling stage of early rice.The light ones lead to yellow leaves and slow growth of seedlings,and the heavy ones lead to leaf curling and dead seedlings,which seriously affect the production of early rice.Abscisic acid(ABA),as an important stress hormone in plant growth,plays an important role when plants encounter stress.In this study,the effects of exogenous ABA treatment on live seedling rate of rice seedlings and exogenous ABA root soaking treatment on physiological and biochemical characteristics of rice seedlings roots as well as expression of genes related to ABA synthesis and decomposition under low temperature stress were studied.the main results were as follows:1.A total of 42 materials with the low temperature resistance of grade 1 were screened out by simulating low temperature in an artificial climate box,accounting for 12.21%of the tested materials;14 materials with the low temperature resistance of grade 3,accounting for 4.07%of the test materials;7 materials with the low temperature resistance of grade 5,accounting for 2.03%of the test materials;30 materials with the low temperature resistance of grade 7,accounting for 8.72%of the test materials;239 materials with the low temperature resistance of grade 9,accounting for 72.97%of the test materials.2.The cold-sensitive variety Xiangzaoxian 45 selected from the germplasm resources resistant to low temperature at seedling stage and the cold-resistant variety Sanqishiluo were used as experimental materials.Compared with the control,spraying different concentrations of ABA solution could improve the seedling viability of cold-sensitive rice to different degrees under low temperature stress.For Xiangzaoxian 45,spraying 10 mg/L ABA solution had the most obvious effect,and the seedling survival rate reached 17%.However,there was no significant difference in improving effect on low temperature resistant rice variety Sanqishiluo,but the seedling growth potential was better than that of the control;The treatment with different concentrations and different treatments with 10 mg/LABA solution for root soaking was the best,which could significantly increase the live seedling rate of rice seedlings to 67%under low temperature stress.The root-soaking treatment with 10 mg/LABA was followed by different temperature treatments.With the increase of temperature,the live seedling rate of Xiangzaoxian 45 seedlings increased,while there was no significant difference in the live seedling rate of Sanqishiluo seedlings with that of the control.However,the seedlings grew well,with higher seedlings,thicker stalk base and more hairy roots.This indicated that root soaking treatment with 10 mg/L ABA solution could significantly increase the seedling viability under low temperature,especially for cold sensitive varieties.3.After pretreatment with 10 mg/LABA root soaking and low temperature treatment for 3d,the longest root length,plant height,stem base width,dry weight and fresh weight of Xiangzaoxian 45 rice seedlings were increased,and the increase was greater than that under low temperature stress.Compared with low temperature,exogenous ABA root soaking treatment could improve the activities of SOD,POD,and CAT,and proline content under low temperature stress,and reduce the relative conductivity,MDA content,superoxide anion content,and H2O2 content.The amplitude of variation of Xiangzaoxian 45 was greater than that of Sanqishiluo,which indicated that the growth of rice seedlings was inhibited by low temperature stress at seedling stage.The exogenous ABA root soaking treatment could alleviate the damage of low temperature stress to rice seedlings,and improve the cold tolerance of rice seedlings.The alleviation effect for cold-sensitive varieties was more significant.4.ABA root soaking treatment could increase the expression of root ABA synthesis genes OsNCEDl,OsNCED2,OsNCED3,OsNCED4 and OsNCED5 under low temperature stress.The expression of Sanqishiluo was higher than that of Xiangzaoxian 45;compared with the control,the expression of ABA decomposition genes in the roots of rice seedlings under low temperature stress was induced and increased with the extension of treatment time,while ABA root soaking treatment reduced the expression of ABA decomposition genes in the roots under low temperature stress,and the variation of Xiangzaoxian 45 was greater than that of Sanqishiluo,which indicated that low temperature stress induced the expression of genes related to ABA synthesis and decomposition,and exogenous ABA root soaking treatment could induce the expression of ABA synthesis genes,and inhibit the expression of ABA decomposition gene,so as to enhance the resistance of seedlings to low temperature.